WO2024176635A1

WO2024176635A1 - Ultrasonic inspection device and ultrasonic inspection method

Info

Publication number: WO2024176635A1
Application number: PCT/JP2024/000169
Authority: WO
Inventors: 睦三鈴木; 友輔高麗; 茂大野
Original assignee: 株式会社日立パワーソリューションズ
Priority date: 2023-02-24
Filing date: 2024-01-09
Publication date: 2024-08-29
Also published as: JP2024120595A

Abstract

A scanning measurement device (1) of an ultrasonic inspection device (Z) comprises a transmitting probe (110) and a receiving probe (121) which is installed on the opposite side to the transmitting probe (110) with respect to an object to be inspected, wherein: the transmitting probe (110) emits an ultrasonic beam upon application thereto of a voltage waveform of a repeating wave packet composed of a wave packet having a wave number of two or more, and drives the transmitting probe (110) at an excitation frequency offset from a resonant frequency of the transmitting probe (110); a control device (2) includes a signal processing unit (250); the signal processing unit (250) includes a filter unit (240) that reduces at least a maximum intensity frequency component of a received signal of the receiving probe (121); and the filter unit (240) detects tail components, other than the maximum intensity frequency component, within a fundamental wave band including the maximum intensity frequency component.

Description

Ultrasonic inspection device and ultrasonic inspection method

This disclosure relates to an ultrasonic inspection device and an ultrasonic inspection method.

　A method of inspecting defective parts of an object to be inspected using an ultrasonic beam is known. For example, if there is a defective part (cavity, etc.) with a small acoustic impedance such as air inside the object to be inspected, a gap in acoustic impedance will occur inside the object to be inspected, and the amount of transmission of the ultrasonic beam will be small. Therefore, by measuring the amount of transmission of the ultrasonic beam, it is possible to detect defective parts inside the object to be inspected.

The technology described in Patent Document 1 is known for an ultrasonic inspection device. In the ultrasonic inspection device described in Patent Document 1, a rectangular wave burst signal consisting of a predetermined number of consecutive negative rectangular waves is applied to a transmitting ultrasonic probe arranged opposite the test object through the air. The ultrasonic waves propagated through the test object are converted into a transmitted wave signal by a receiving ultrasonic probe arranged opposite the test object through the air. The presence or absence of a defect in the test object is determined based on the signal level of this transmitted wave signal. In addition, the transmitting ultrasonic probe and receiving ultrasonic probe have a lower acoustic impedance of the transducer and the front panel attached to the ultrasonic transmission and reception side of the transducer compared to a contact type ultrasonic probe that is used by abutting the test object.

JP 2008-128965 A

The ultrasonic inspection device described in Patent Document 1 has a problem in that it is difficult to detect a minute defect in an object to be inspected. In particular, when the size of the defect to be detected is smaller than the ultrasonic beam, it becomes difficult to detect the defect.
The problem to be solved by the present disclosure is to provide an ultrasonic inspection device and an ultrasonic inspection method that have high detection performance for defective parts, for example, a small detectable defect size, making it possible to detect even minute defects.

The ultrasonic inspection device disclosed herein is an ultrasonic inspection device that inspects an object to be inspected by irradiating the object with an ultrasonic beam through a gas, and includes a scanning and measuring device that scans and measures the ultrasonic beam on the object to be inspected, and a control device that controls the driving of the scanning and measuring device. The scanning and measuring device includes a transmitting probe that emits the ultrasonic beam, and a receiving probe that receives the ultrasonic beam and is installed on the opposite side of the transmitting probe with respect to the object to be inspected. The transmitting probe emits an ultrasonic beam by applying a voltage waveform of a repeating wave packet composed of a wave packet with a wave number of two or more, and drives the transmitting probe with an excitation frequency shifted from the resonant frequency of the transmitting probe. The control device includes a signal processing unit, and the signal processing unit includes a filter unit that reduces at least the maximum intensity frequency component of the received signal of the receiving probe, and the filter unit detects the base components other than the maximum intensity frequency component of the fundamental wave band including the maximum intensity frequency component. Other solutions will be described later in the description for implementing the invention.

The present disclosure provides an ultrasonic inspection device and an ultrasonic inspection method that improve the detection performance of defective parts, for example, by making it possible to detect even minute defects with a small detectable size.

1 is a diagram showing the configuration of an ultrasonic inspection apparatus according to a first embodiment; 3 is a schematic cross-sectional view showing a structure of a transmission probe. FIG. FIG. 1 is a diagram showing a propagation path of an ultrasonic beam in a conventional ultrasonic inspection method, showing the time when the ultrasonic beam is incident on a healthy part. FIG. 1 is a diagram showing a propagation path of an ultrasonic beam in a conventional ultrasonic inspection method, showing the time of incidence on a defect portion. FIG. 2 is a diagram showing an interaction between an ultrasonic beam and a defect in an object to be inspected, showing how a direct ultrasonic beam is received. FIG. 2 is a schematic diagram showing a scattered wave, which is an ultrasonic beam that has interacted with a defect. FIG. 2 is a functional block diagram of a control device. FIG. 2 is a diagram illustrating a schematic distribution of frequency components of a received signal. This shows the change in signal strength information depending on the position when the transmitting probe and the receiving probe are scanned so as to straddle the defective portion. This is the result of measuring signal strength information using a control device equipped with a filter section. 1 shows a voltage waveform of a burst wave applied to a transmitting probe. 10 shows a frequency component distribution of a received signal under the conditions shown in FIG. FIG. 1 is a diagram comparing measured data of the frequency component distribution (frequency spectrum) of a received signal between a healthy portion (solid line) and a defective portion (dashed line). 4 shows the frequency spectrum of the transmitted ultrasound when the wave number is changed. These are frequency spectra when the number of waves is 3 (dashed line), 5 (solid line), and 10 (dotted line). FIG. 2 is a diagram illustrating a frequency spectrum of a fundamental wave band. FIG. 1 is a diagram showing the relationship between the full width at half maximum ratio (FWHM ratio) of the fundamental waveband and the wave number. 4 shows the frequency characteristics of the gain in a band-stop filter. FIG. 10 is a diagram illustrating the frequency characteristics of a signal after processing by a band-stop filter. This shows the frequency characteristics of the gain in a low-pass filter. FIG. 2 is a diagram illustrating a frequency characteristic of a signal after processing by a low-pass filter. This shows the frequency characteristics of the gain in a high-pass filter. FIG. 10 is a diagram illustrating a frequency characteristic of a signal after processing by a high-pass filter. FIG. 2 is a block diagram showing a digital filter section; FIG. 13 is a block diagram showing a filter unit according to another embodiment. 1 is a diagram illustrating a schematic diagram of a propagation path of an ultrasonic beam when the focal length of a transmitting probe and the focal length of a receiving probe are set equal to each other. 10 is a diagram illustrating a schematic diagram of a propagation path of an ultrasonic beam when the focal length of a receiving probe is set longer than the focal length of a transmitting probe. 4A and 4B are diagrams illustrating the relationship between a beam incident area in a transmitting probe and a beam incident area in a receiving probe. FIG. 13 is a diagram showing the configuration of an ultrasonic inspection apparatus according to a second embodiment. FIG. 2 is a diagram for explaining the transmission sound axis, the reception sound axis, and the eccentricity distance, in the case where the transmission sound axis and the reception sound axis extend in the vertical direction. 1 is a diagram for explaining a transmission sound axis, a reception sound axis, and an eccentric distance, in which the transmission sound axis and the reception sound axis extend at an angle. FIG. FIG. 13 is a diagram showing the configuration of an ultrasonic inspection apparatus according to a third embodiment. 13A to 13C are diagrams for explaining the reason why the third embodiment has an effect. FIG. 13 is a functional block diagram of a control device 2 in an ultrasonic inspection device according to a fourth embodiment. FIG. 13 is a functional block diagram of a control device 2 in an ultrasonic inspection device according to a fifth embodiment. FIG. 13 is a functional block diagram of a control device 2 in an ultrasonic inspection device according to a sixth embodiment. FIG. 2 is a diagram illustrating a hardware configuration of a control device. 4 is a flowchart showing an ultrasonic inspection method according to each of the above embodiments. FIG. 13 is a diagram showing the configuration of an ultrasonic inspection apparatus according to a seventh embodiment. FIG. 2 is a functional block diagram of a control device. This shows the change in signal strength information depending on the position when the transmitting probe and the receiving probe are scanned so as to straddle the defective portion. The excitation frequency fex of the transmitting probe was set to 0.78 MHz, and the signal strength information was measured using a control device equipped with a filter section. 13 shows a frequency component distribution of a received signal under the conditions shown in the seventh embodiment. FIG. 1 is a diagram comparing measured data of the frequency component distribution (frequency spectrum) of a received signal between a healthy portion (solid line) and a defective portion (dashed line). The wave number of the wave packet and the frequency spectrum of the fundamental wave band of the ultrasound. 36B is a diagram showing how the full width at half maximum of the fundamental wave band of the spectrum shown in FIG. 36A changes with respect to the wave number N0 of the wave packet. FIG. This shows the results of measuring the frequency spectrum of the received signal while changing the excitation frequency fex. FIG. 1 shows the change in instantaneous frequency of a wave packet in the time domain. FIG. 23 is a functional block diagram of a control device in an ultrasonic inspection device Z in the eighth embodiment. FIG. 13 is a functional block diagram of a control device in an ultrasonic inspection device Z in the ninth embodiment. FIG. 23 is a diagram showing the configuration of an ultrasonic inspection apparatus according to an eleventh embodiment. FIG. 23 is a functional block diagram of the control device 2 of the thirteenth embodiment. 1 is an example of a database. FIG. 43B is a three-dimensional view of the database shown in FIG. 43A. FIG. 2 is a diagram illustrating a configuration example of an operation screen of an ultrasonic inspection device according to an example of the present disclosure. A diagram showing steps for obtaining a defect image of an inspection object E in the fourteenth embodiment. The standard inspection object is scanned across the artificial defect, an ultrasonic beam is transmitted, the received signal is measured, and the received signal is subjected to appropriate signal processing to calculate the signal amount and plot the result. A diagram showing steps for obtaining a defect image of an object to be inspected in the fifteenth embodiment. This is a frequency spectrum displayed in steps. FIG. 23 is a functional block diagram of an ultrasonic inspection apparatus according to a sixteenth embodiment. FIG. 2 is a diagram illustrating a hardware configuration of a control device. 4 is a flowchart showing an ultrasonic inspection method according to each of the above embodiments.

Below, a form for implementing the present disclosure (referred to as an embodiment) will be described with reference to the drawings. However, the present disclosure is not limited to the following embodiment, and for example, different embodiments can be combined, or modified as desired without significantly impairing the effects of the present disclosure. In addition, the same components will be given the same reference numerals, and duplicate descriptions will be omitted. Furthermore, components having the same functions will be given the same names. The contents shown are merely schematic, and for convenience of illustration, the actual configuration may be changed without significantly impairing the effects of the present disclosure.

First Embodiment
Fig. 1 is a diagram showing the configuration of an ultrasonic inspection device Z according to a first embodiment. In Fig. 1, a scanning measurement device 1 is shown in a schematic cross-sectional view. Fig. 1 shows a coordinate system of three orthogonal axes including an x-axis as a left-right direction on the paper surface, a y-axis as a direction perpendicular to the paper surface, and a z-axis as a top-bottom direction on the paper surface.

The ultrasonic inspection device Z inspects the object E by irradiating an ultrasonic beam U (described later) onto the object E through a fluid F. In this embodiment, the fluid F is a gas G such as air. The object E is present in the fluid F. In the first embodiment, air (an example of gas G) is used as the fluid F. Therefore, the inside of the housing 101 of the scanning measurement device 1 is a cavity filled with air. As shown in FIG. 1, the ultrasonic inspection device Z includes the scanning measurement device 1, a control device 2, and a display device 3. The display device 3 is connected to the control device 2.

The scanning measurement device 1 scans and measures the object E with an ultrasonic beam U, and is provided with a sample stage 102 fixed to a housing 101, on which the object E is placed. It is more preferable that the object E is fixed to the sample stage 102 with a fixture so as not to move. If the object E is sufficiently heavy and does not move unintentionally, a fixture is not necessary. The object E is made of any material. The object E is, for example, a solid material, and more specifically, is, for example, a metal, glass, a resin material, or a composite material such as CFRP (Carbon-Fiber Reinforced Plastics). In addition, in the example of FIG. 1, the object E has a defect D inside. The defect D is a cavity, etc. Examples of the defect D are a cavity, a foreign material different from the material that should be there, etc. In the specimen E, the portion other than the defective portion D is called the healthy portion N.

The defective area D and the healthy area N are made of different materials, so the acoustic impedance differs between the two, and the propagation characteristics of the ultrasonic beam U change. The ultrasonic inspection device Z observes this change to detect the defective area D.

The scanning measurement device 1 has a transmitting probe 110 that emits an ultrasonic beam U, and a receiving probe 121. The transmitting probe 110 is installed in the housing 101 via the transmitting probe scanning unit 103, and emits an ultrasonic beam U. The receiving probe 121 is installed on the opposite side of the transmitting probe 110 with respect to the subject E, and receives the ultrasonic beam U. The receiving probe 121 is a receiving probe 140 (coaxially arranged receiving probe) that is arranged coaxially with the transmitting probe 110 (the eccentric distance L described below is zero). Therefore, in the first embodiment, the eccentric distance L (distance described below) between the transmitting sound axis AX1 (sound axis) of the transmitting probe 110 and the receiving sound axis AX2 (sound axis) of the receiving probe 140 is zero. This makes it easy to install the transmitting probe 110 and the receiving probe 140.

Here, "the opposite side of the transmitting probe 110" means, of the two spaces separated by the subject E, the space opposite the space in which the transmitting probe 110 is located (the opposite side in the z-axis direction), and does not mean the opposite side with the same x and y coordinates (i.e., a position that is symmetrical with respect to the xy plane).

In this disclosure, the configuration in which the receiving probe 140 is arranged on the opposite side of the transmitting probe 110 with respect to the subject E corresponds to a transmission type arrangement. In addition, a reflection type arrangement is also known in the ultrasound inspection device Z, in which the receiving probe is arranged on the same side as the transmitting probe with respect to the subject E.

The transmission type arrangement is also called the transmission method. In the transmission type arrangement, an ultrasonic beam U that has passed through the object E to be inspected is received. The presence of a defect D in the object E causes a change in the amount of transmission of the ultrasonic beam U, and the defect D is detected. In contrast, the reflection type arrangement is also called the reflection method, and the defect D is detected by detecting the ultrasonic beam U reflected by the defect D.

In the example disclosed herein, the transmitting probe 110 is installed so that the transmission sound axis AX1 of the transmitting probe 110 is perpendicular to the mounting surface 1021 of the sample stage 102. In other words, the transmitting probe 110 is installed so that the transmission sound axis AX1 is normal to the mounting surface 1021 of the sample stage 102 for the object E to be inspected. In this way, for a plate-shaped object E to be inspected, the transmission sound axis AX1 is arranged perpendicular to the surface of the object E to be inspected, which has the effect of making it easier to understand the correspondence between the scanning position and the position of the defect D.

However, the present disclosure is not limited to installing the transmission probe 110 so that the transmission sound axis AX1 is perpendicular to the mounting surface 1021 of the sample stage 102 for the object E to be inspected. The present disclosure is effective even if the transmission sound axis AX1 is not perpendicular to the mounting surface 1021 of the sample stage 102 for the object E to be inspected. In the latter case, to accurately determine the position of the defect D, the path of the transmission sound axis AX1 can be calculated according to the inclination of the transmission sound axis AX1 from the vertical direction.

Here, the positional relationship between the transmitting probe 110 and the receiving probe 121 will be described. The distance between the transmitting sound axis AX1 of the transmitting probe 110 and the receiving sound axis AX2 of the receiving probe 121 is defined as the eccentricity distance L (described below). In the first embodiment, as described above, the eccentricity distance L is set to zero. That is, the receiving probe 121 is positioned so that the transmitting sound axis AX1 and the receiving sound axis AX2 are coaxial. This is called a coaxial arrangement. Note that in this disclosure, the eccentricity distance L is not limited to 0.

In this disclosure, the arrangement of the receiving probe 121 in which the transmission sound axis AX1 and the reception sound axis AX2 are coaxially arranged is called a coaxial arrangement, and the arrangement in which the two sound axes (the transmission sound axis AX1 and the reception sound axis AX2) are shifted (i.e., eccentrically arranged) is called an eccentric arrangement. This disclosure is effective in both cases where the receiving probe 121 is coaxially arranged and where it is eccentrically arranged. Therefore, this disclosure includes both the coaxial arrangement and the eccentric arrangement as the arrangement of the receiving probe 121. Specific illustrations of the eccentric arrangement are provided below.

In this disclosure, particularly when specifying the receiving arrangement position, the coaxially arranged receiving probe 121 will be referred to as receiving probe 140 (coaxially arranged receiving probe), and the eccentrically arranged receiving probe 121 will be referred to as receiving probe 120 (eccentrically arranged receiving probe).

When referring to the receiving probe 121, there is no specific specification as to whether it is arranged coaxially or eccentrically.

The sound axis is defined as the central axis of the ultrasonic beam U. Here, the transmission sound axis AX1 is defined as the sound axis of the propagation path of the ultrasonic beam U emitted by the transmitting probe 110. In other words, the transmission sound axis AX1 is the central axis of the propagation path of the ultrasonic beam U emitted by the transmitting probe 110. The transmission sound axis AX1 includes refraction due to the interface of the object E to be inspected, as described below. In other words, when the ultrasonic beam U emitted from the transmitting probe 110 is refracted at the interface of the object E to be inspected, the center (sound axis) of the propagation path of the ultrasonic beam U becomes the transmission sound axis AX1.

Furthermore, the receiving sound axis AX2 is defined as the sound axis of the propagation path of a virtual ultrasonic beam when it is assumed that the receiving probe 121 emits the ultrasonic beam U. In other words, the receiving sound axis AX2 is the central axis of a virtual ultrasonic beam when it is assumed that the receiving probe 121 emits the ultrasonic beam U.

As a specific example, we will consider the case of a non-converging receiving probe 121 with a planar probe surface 114 (described below). In this case, the direction of the receiving sound axis AX2 is the normal direction of the probe surface 114, and the axis passing through the center point of the probe surface 114 becomes the receiving sound axis AX2. If the probe surface 114 is rectangular, the center point is defined as the intersection of the diagonals of the rectangle.

The control device 2 is connected to the scanning measurement device 1. The control device 2 controls the driving of the scanning measurement device 1, and controls the movement (scanning) of the transmitting probe 110 and the receiving probe 121 by instructing the transmitting probe scanning unit 103 and the receiving probe scanning unit 104. The transmitting probe scanning unit 103 and the receiving probe scanning unit 104 move synchronously in the x-axis and y-axis directions, so that the transmitting probe 110 and the receiving probe 121 scan the subject E in the x-axis and y-axis directions. Furthermore, the control device 2 emits an ultrasonic beam U from the transmitting probe 110, and performs waveform analysis based on the signal acquired from the receiving probe 121. Note that the plane formed by the two axes, the x-axis and y-axis directions, which are the scanning directions of the transmitting probe 110, is called the scanning plane.

In the first embodiment, an example is shown in which the transmitting probe 110 and the receiving probe 121 are scanned in a state in which the test subject E is fixed to the housing 101 via the sample stage 102, that is, in a state in which the test subject E is fixed to the housing 101. Conversely, a configuration in which the transmitting probe 110 and the receiving probe 121 are fixed to the housing 101 and the position of the sample stage 102 is scanned in the x-axis and y-axis directions may also be used. In this configuration, the test subject E placed on the sample stage 102 also moves, so that the relative position with the transmitting probe 110 is scanned in the x-axis and y-axis directions.

In the illustrated example, gas G is interposed between the transmitting probe 110 and the test subject E, and between the receiving probe 121 and the test subject E. Therefore, the transmitting probe 110 and the receiving probe 121 can test the test subject E without contacting it, so it is possible to change the relative positions in the xy plane smoothly and quickly. In other words, by interposing gas G between the transmitting probe 110 and the receiving probe 121 and the test subject E, smooth scanning is possible.

By emitting a localized ultrasonic beam U from the transmitting probe 110, the localized ultrasonic beam U is locally irradiated onto the object to be inspected E. The position to which the localized ultrasonic beam U is irradiated is changed by scanning. As described above, the ultrasonic beam U that reaches the receiving probe 121 changes depending on whether it is a defective part D or a healthy part N of the object to be inspected E, so this configuration makes it possible to detect the defective part D.

In order to generate a localized ultrasonic beam U, in this embodiment, a convergent transmitting probe 110 can be used. The specific configuration of the convergent transmitting probe 110 will be described later. A configuration for generating a localized ultrasonic beam U may be used in which the area of a piezoelectric element (transducer 111 described later; the same applies below) that generates the ultrasonic beam U is reduced to reduce the beam diameter. The convergent transmitting probe 110 is more preferable because it is possible to reduce the beam diameter while increasing the area of the piezoelectric element, thereby generating a localized ultrasonic beam U with high beam intensity and small beam diameter.

The transmitting probe 110 is a convergent type transmitting probe 110. On the other hand, the receiving probe 121 is a probe with looser convergence than the transmitting probe 110. In this embodiment, a non-convergent type probe with a flat probe surface is used for the receiving probe 121. By using such a non-convergent type receiving probe 121, information on the defect portion D can be collected over a wide range.

FIG. 2 is a schematic cross-sectional view showing the structure of the transmitting probe 110. For simplicity, FIG. 2 shows only the outer contour of the emitted ultrasonic beam U, but in reality, a large number of ultrasonic beams U are emitted in the normal vector direction of the probe surface 114 over the entire area of the probe surface 114.

The transmitting probe 110 is configured to focus the ultrasonic beam U. This allows for highly accurate detection of minute defects D in the object E to be inspected. The reason why minute defects D can be detected will be described later. The transmitting probe 110 comprises a transmitting probe housing 115, which comprises a backing 112, a transducer 111, and a matching layer 113 inside the transmitting probe housing 115. An electrode (not shown) is attached to the transducer 111, and the electrode is connected to a connector 116 by a lead wire 118. Furthermore, the connector 116 is connected to a power supply (not shown) and a control device 2 by a lead wire 117.

In this disclosure, the probe surface 114 of the transmitting probe 110 or the receiving probe 121 is defined as the surface of the matching layer 113 if the matching layer 113 is provided, and as the surface of the transducer 111 if the matching layer 113 is not provided. That is, the probe surface 114 is the surface that emits the ultrasonic beam U in the case of the transmitting probe 110, and is the surface that receives the ultrasonic beam U in the case of the receiving probe 121.

Here, we will explain a conventional ultrasonic inspection method as a comparative example.

FIG. 3A is a diagram showing the propagation path of an ultrasonic beam U in a conventional ultrasonic inspection method, showing the beam entering a healthy part N. FIG. 3B is a diagram showing the propagation path of an ultrasonic beam U in a conventional ultrasonic inspection method, showing the beam entering a defective part D. In a conventional ultrasonic inspection method, as described in Patent Document 1, for example, a transmitting probe 110 and a receiving probe 140 serving as a receiving probe 121 are positioned so that a transmitting sound axis AX1 and a receiving sound axis AX2 coincide with each other.

As shown in FIG. 3A, when an ultrasonic beam U is incident on a healthy portion N of an object to be inspected E, the ultrasonic beam U passes through the object to be inspected E and reaches the receiving probe 140. Therefore, the received signal becomes large. On the other hand, as shown in FIG. 3B, when an ultrasonic beam U is incident on a defective portion D, the defective portion D prevents the ultrasonic beam U from passing through, and the received signal decreases. In this way, the defective portion D is detected by the decrease in the received signal. This is as shown in Patent Document 1.

As shown in Figures 3A and 3B, the method of detecting a defect D by blocking the transmission of an ultrasonic beam U at the defect D, thereby reducing the received signal, is referred to here as the "blocking method."

The problem with the conventional technology is that it becomes difficult to detect defects when the size of the defect becomes smaller than the beam size. This point will be explained with reference to Figure 4.

FIG. 4 is a diagram showing the interaction between a defect D and an ultrasonic beam U in an object E to be inspected, and shows how a direct ultrasonic beam U (hereinafter referred to as a "direct wave U3") is received. The direct wave U3 will be described later. Here, we consider the case where the size of the defect D is smaller than the width of the ultrasonic beam U (hereinafter referred to as the beam width BW). The beam width BW here is the width of the ultrasonic beam U when it reaches the defect D.

In addition, since FIG. 4 shows a schematic representation of the shape of the ultrasonic beam U in a minute area near the defect D, the ultrasonic beam U is drawn parallel, but in reality it is a converged ultrasonic beam U. Furthermore, the position of the receiving probe 121 in FIG. 4 is a conceptual position shown for easy understanding, and the position and shape of the receiving probe 121 are not precisely scaled. In other words, when considering the enlarged scale of the shapes of the defect D and the ultrasonic beam U, the receiving probe 121 is located at a position further away in the vertical direction of the drawing than the position shown in FIG. 4.

Figure 4 shows the case of a blocking method in which the transmitting sound axis AX1 and the receiving sound axis AX2 are aligned. If the defect D is smaller than the beam width BW, part of the ultrasonic beam U is blocked, so the received signal decreases, but does not become zero. For example, if the cross-sectional area of the defect D is 5% of the beam cross-sectional area defined by the beam width BW, the received signal decreases by only about 5%, making it difficult to detect the defect D. In other words, in the case shown in Figure 4, where the defect D exists, the received signal decreases by only 5%. In this way, if the defect D is smaller than the beam width BW, many beams pass through without interacting with the defect D, making it difficult to detect the defect.

FIG. 5 is a schematic diagram showing a scattered wave U1, which is an ultrasonic beam U that has interacted with a defect D. In this disclosure, the ultrasonic beam U that has interacted with the defect D is called the scattered wave U1. Therefore, in this disclosure, the "scattered wave U1" refers to an ultrasonic wave that has interacted with the defect D. Some of the scattered waves U1 change direction as shown in FIG. 5. Some of the scattered waves U1 change at least one of the phase or frequency of the wave due to the interaction with the defect D, but the direction of travel does not change. An ultrasonic wave that passes through the defect D without interacting with it is called a direct wave U3. If only the scattered waves U1 can be detected, distinguishing them from the direct waves U3, it will be easier to detect small defects D. In this disclosure, the scattered waves U1 are efficiently detected by focusing on the difference in frequency.

In this embodiment, a gas G such as air is used as the fluid F between the transmitting probe 110 and the test object E. In this case, for the reasons described below, it becomes particularly difficult to detect minute defects D using the conventional blocking method. For this reason, the effect of the present disclosure in detecting the scattered wave U1 is significant.

Compared to liquids, ultrasonic waves are attenuated more in gas G. It is known that the attenuation of ultrasonic waves in gas G is proportional to the square of the frequency. For this reason, the upper limit for ultrasonic waves propagating in gas G is about 1 MHz. In liquids, ultrasonic waves of 5 MHz to several tens of MHz can also propagate, so the frequencies that can be used in gas G are smaller than those in liquids.

In general, as the frequency of the ultrasonic beam U decreases, it becomes more difficult to converge the ultrasonic beam U. Therefore, the 1 MHz ultrasonic beam U propagating through gas G has a larger beam diameter that can be converged compared to the ultrasonic beam U in liquid. On the other hand, as shown in Figure 4 above, in the blocking mode, which is the conventional method, it is difficult to detect a defect D smaller than the beam size. However, according to the present disclosure, as shown in Figure 5 above, the proportion of the scattered wave U1 component is increased for detection, making it possible to detect a defect D smaller than the beam size.

FIG. 6 is a functional block diagram of the control device 2. The control device 2 controls the driving of the scanning measurement device 1. The control device 2 includes a transmission system 210, a reception system 220, a data processing unit 201, a scan controller 204, a driving unit 202, a position measurement unit 203, and a signal processing unit 250. The reception system 220 and the data processing unit 201 are collectively referred to as the signal processing unit 250. The signal processing unit 250 performs signal processing to extract significant information by amplifying and filtering the signal from the receiving probe 121.

The transmission system 210 is a system that generates a voltage to be applied to the transmission probe 110. The transmission system 210 includes a waveform generator 211 and a signal amplifier 212. A burst wave signal is generated by the waveform generator 211. The generated burst wave signal is then amplified by the signal amplifier 212. The voltage output from the signal amplifier 212 is applied to the transmission probe 110.

In this way, the transmission system 210 included in the control device 2 outputs a voltage waveform of a burst wave, and the outputted voltage waveform of the burst wave is applied to the transmission probe 110. In this disclosure, the burst wave is also referred to as a repeating wave packet. The waveform of the burst wave will be described later.

The signal processing unit 250 includes a receiving system 220. The receiving system 220 is a system that detects the received signal output from the receiving probe 121. The signal output from the receiving probe 121 is input to a signal amplifier 222 and amplified. The amplified signal is input to a filter unit 240 (blocking filter). The filter unit 240 reduces (blocks) components of a specific frequency range of the input signal. The filter unit 240 will be described later. The output signal from the filter unit 240 is input to the data processing unit 201.

The data processing unit 201 generates signal strength data from the signal input from the filter unit 240. In this embodiment, the peak-to-peak signal is used as a method for generating signal strength data. This is the difference between the maximum and minimum values of the signal. Another method for generating signal strength data is to use the strength of frequency components in a specific frequency range by performing a Fourier transform.

The data processing unit 201 also receives scanning position information from the scan controller 204. In this way, the signal intensity data value at the current two-dimensional scanning position (x, y) is obtained. By plotting the signal intensity data value against the scanning position, an image (defect image) corresponding to at least one of the position and shape of the defect D is obtained. This defect image is output to the display device 3.

(Filter section 240)
In the present disclosure, the filter unit 240 is defined as a control unit that performs signal processing to reduce the intensity of signal components in a predetermined frequency range. Filter processing is also defined as signal processing to reduce the intensity of signal components in a predetermined frequency range. When a received signal is decomposed into component intensities for each frequency component by Fourier transform or the like, the frequency at which the component intensity is maximum is called the maximum component frequency. The maximum intensity frequency component is a frequency component at the maximum component frequency. In other words, the maximum component frequency is a frequency corresponding to the maximum intensity frequency component. The filter unit 240 of the present disclosure reduces the intensity of the fundamental wave band including the maximum intensity frequency component, that is, the signal components in the frequency range including the maximum component frequency. The distribution of component intensities for each frequency component is called a frequency spectrum.

FIG. 7 is a diagram showing a schematic distribution of frequency components (frequency spectrum) of a received signal. The filter section 240 will be explained in more detail using FIG. 7. In the figure, the horizontal axis shows frequency, and the vertical axis shows component strength (intensity). The vertical axis is shown on a logarithmic scale, and a wide range of strength is shown.

The maximum component frequency at which the component strength is at its maximum is designated as fm. The maximum component frequency fm is approximately equal to the fundamental frequency f0 of the burst wave transmitted from the transmitting probe 110. The frequency components of the signal have a spread before and after the maximum component frequency fm, which is called the fundamental wave band W1.

The component with a frequency (N x fm) that is N times the maximum component frequency fm is a harmonic. The component with a frequency (fm/N) that is 1/N times the maximum component frequency fm is a sub-harmonic. Here, N is an integer N >= 2. Harmonics and sub-harmonics also have a spread. In this disclosure, when it is particularly emphasized that harmonics and sub-harmonics have a frequency spread, they are called harmonic bands and sub-harmonic bands, respectively. Therefore, even when simply written as "harmonic", it has a frequency spread. Harmonic bands and sub-harmonic bands are generated by nonlinear phenomena, and occur when the sound pressure of the ultrasonic beam U input to the test object E is extremely strong.

When gas G is present between the transmitting probe 110 and the test object E as in the first embodiment, it is generally difficult to introduce an ultrasonic beam U with a high sound pressure into the test object E, so at least one of the harmonic bands or sub-harmonic bands is often not observed. Even under the conditions of the first embodiment, the harmonic bands and sub-harmonic bands were below the detection limit.

As shown in Figure 7, the fundamental wave band W1 has a wide frequency range. Within the fundamental wave band W1, the frequency components other than the maximum component frequency fm are referred to as "foot components W3." The foot components W3 also include the side lobes of the fundamental wave.

In the first embodiment, the filter unit 240 reduces the component strength in the cutoff frequency range including the maximum component frequency fm. That is, the filter unit 240 reduces at least the maximum intensity frequency component (the component corresponding to the maximum component frequency fm) of the received signal of the receiving probe 121. The filter unit 240 then detects the skirt component W3 other than the maximum intensity frequency component of the fundamental wave band W1 including the maximum intensity frequency component. Because the filter unit 240 reduces the component strength in the cutoff frequency range, the proportion of the skirt component W3 in the fundamental wave band W1 increases in the signal after passing through the filter unit 240. In this way, the detection performance of the defect portion D can be improved, as described below.

Figure 8A shows the change in signal strength information depending on the position when the transmitting probe 110 and the receiving probe 121 are scanned across the defective area D. Figure 8A shows the results of a measurement using a configuration in which the filter section 240 has been removed from the configuration in Figure 6 above. The signal strength in the healthy area N is v0. On the other hand, at the position (x = 0) corresponding to the defective area D, the signal strength has decreased by Δv, and the defective area D has been detected. However, the rate of change in signal strength (Δv/v0) is small. Here, the rate of change in signal strength is defined as the amount of signal change Δv in the defective area D divided by the signal strength v0 in the healthy area N.

Figure 8B shows the results of measuring signal strength information using a control device 2 (Figure 6) equipped with a filter unit 240. It can be seen that the rate of change in signal strength (Δv/v0) at the location of defect D has increased, improving the detectability of defect D.

The experimental conditions under which the results shown in Figures 8A and 8B were obtained are explained below.

Figure 9 shows the voltage waveform of a burst wave applied to the transmitting probe 110. The horizontal axis is time, and the vertical axis is voltage. In the example of Figure 9, ten sine waves with a fundamental frequency f0 of 0.82 MHz are applied. These ten waves are called a wave packet. The inverse of the fundamental frequency f0 is called the fundamental period T0. As shown in the figure, the fundamental period T0 is the period of the waves that make up one wave packet. The wave packet is applied with a repetition period Tr = 5 ms. Therefore, the transmitting probe 110 emits an ultrasonic beam U when a voltage waveform of a repeating wave packet made up of a wave packet with two or more waves is applied to it.

In this embodiment, each wave packet is a sine wave with a fundamental frequency of f0, but it may be a wave packet other than a sine wave. For example, the wave packet may be a wave packet composed of a rectangular wave with a wave number of N0.

The wave number N0 of a wave packet is the number of waves (number of cycles) of fundamental frequency f0 contained in one wave packet. In the present disclosure, the wave number N0 of a wave packet is 2 or more, and it is preferable that the wave number N0 of a wave packet is 3 or more. Therefore, the transmitting probe 110 emits an ultrasonic beam U by applying a voltage waveform of a repeating wave packet composed of wave packets with a wave number N0 of 2 or more. Under the experimental conditions of this embodiment, the wave number N0 is 10 waves, as described above. A waveform of a repeating wave packet in which wave packets are repeated is called a burst wave.

Figure 10 shows the frequency component distribution of the received signal under the conditions shown in Figure 9. In this figure, the horizontal axis is frequency, and the vertical axis plots the measured data of component strength at each frequency. This graph shows the frequency component distribution of a signal not processed by the filter section 240. 0.82 MHz, where the component strength is at its maximum, is the maximum component frequency fm. The fundamental wave band W1 extends from 0.74 MHz to 0.88 MHz, and the components excluding the maximum component frequency fm are the skirt components W3. In this embodiment, the maximum component frequency fm is equal to the fundamental frequency f0 of the ultrasound transmitted by the transmitting probe 110. Thus, in many cases, the maximum component frequency fm is roughly equal to the fundamental frequency f0 of the ultrasound transmitted.

As described above, the filter section 240 (Fig. 6) excludes the maximum component frequency fm. Specifically, in the illustrated example, the filter section 240 (Fig. 6) transmits the base component W3 below 0.78 MHz and blocks waves above 0.78 MHz, including 0.82 MHz. When such a filter section 240 is used, as shown in Fig. 8B above, the rate of change of the signal intensity at the defective section D increases, and it can be seen that the detectability of the defect is greatly improved.

Figure 11 is a diagram comparing the measured data of the frequency component distribution (frequency spectrum) of the received signal between a healthy part N (solid line) and a defective part D (dashed line). The mechanism by which the filter section 240 improves the detectability of the defective part D is as follows. At the maximum component frequency fm = 0.82 MHz, the difference in component strength (signal magnitude) between the healthy part N and the defective part D is small. On the other hand, for the base component W3 other than the maximum component frequency fm, especially in the low frequency band, the difference between the healthy part N and the defective part D is large.

In this way, the inventors have examined the frequency components of the received signal and found that the difference between the healthy part N and the defective part D is greater for the base component W3 than for the maximum component frequency fm. Based on this knowledge, they have found that the detectability of the defective part D can be improved by using a filter section 240 that reduces the frequency component of the maximum component frequency fm, which is the smallest difference between the healthy part N and the defective part D.

In this way, the present disclosure is based on the new knowledge found by the inventors that in the frequency component distribution of a received signal, the base component W3 of the fundamental wave band W1 has a greater signal change rate at the defect D than the signal component at the maximum component frequency fm. The component at the maximum component frequency fm accounts for a large proportion of the received signal, but the signal change rate at the defect D is small, so by reducing this component, the proportion of the base component W3 increases. In this way, the signal after processing by the filter unit 240 has an increased signal change rate at the defect D, improving the detectability of the defect D. And even when comparing the actual measurement data shown in Figures 8A and 8B, the effect of improving the detectability of the defect D by the filter unit 240 is clear.

(Burst wave effect)
In this disclosure, the effect of applying a burst wave, i.e., a repeating wave packet voltage waveform, to the transmitting probe 110 is described.

As mentioned above, this disclosure is based on the new knowledge that the frequency component (foot component) that is shifted by Δf from the maximum component frequency fm has a large signal change rate at the defect part D. Therefore, by narrowing the bandwidth of the fundamental wave band W1 to an appropriate width, the frequency range of the shifted component (fm±Δf) falls within a specific range, making it easier to detect the defect information contained in the shifted component (foot component W3).

In contrast, when a single pulse or one-cycle voltage waveform is applied, as described below, the frequency band of the transmission wave itself spreads over a wide band, and the shifted component (fm±Δf) also spreads over a wide frequency range. For this reason, it is difficult to extract and detect the frequency component shifted by Δf, as in the present disclosure.

The method of inspecting a defect D inside an object E by applying a single pulse or one cycle of a voltage waveform is known as the pulse-echo method. By measuring the time from when the ultrasonic wave is transmitted to when it is received, the distance to the defect D can be determined.

Next, we will describe the relationship between the wave number N0 of the wave packet applied to the transmitting probe 110 and the frequency band of the transmitted ultrasound.

Figure 12A shows the frequency spectrum of the transmitted ultrasound when the wave number N0 is changed. Here, the frequency spectrum was calculated by Fourier transforming the time waveform of the wave packet composed of wave number N0. The fundamental frequency f0 of the waves that compose wave packet N0 is set to 0.82 MHz. Figure 12A shows the spectrum when wave number N0 is 1 to 3. Note that when there is a wave number of 1, it does not become a wave packet, so it is not a repeating wave packet and is not a burst wave.

When wave number N0=1, as indicated by the dashed line, it can be seen that the frequency components of the fundamental wave band W1 are spread over a frequency range of 0 to 1.6 MHz. This corresponds to 0 to 2 fm. Therefore, as mentioned above, it is difficult to preferentially extract signal components that deviate from the maximum component frequency fm as in this disclosure. The frequency spectrum for wave number N0=1 has a typical spectral shape for the pulse-echo method.

As can be seen from FIG. 12A, when the wave number N0 shown by the solid line is 2, the width (bandwidth) of the fundamental wave band W1 is narrowed to 1/2 of when N0=1. Furthermore, when the wave number N0 shown by the dashed and dotted line is 3, the width (bandwidth) of the fundamental wave band W1 is narrowed to 1/3 of when N0=1. This makes it possible to extract signal components that are shifted from the maximum component frequency fm, as disclosed herein.

Figure 12B shows the frequency spectrum when the wave number N0 is 3 (dashed line), 5 (solid line), and 10 (dotted line). It can be seen that increasing the wave number N0 further narrows the width (bandwidth) of the fundamental wave band.

13 is a diagram showing a schematic diagram of the frequency spectrum of the fundamental wave band W1. Here, the bandwidth of the fundamental wave band W1 is defined as follows. The spectrum intensity at the maximum component frequency fm of the fundamental wave band W1 is set to 1, and the frequency width at half the intensity is set to the full width at half maximum (FWHM). The value obtained by normalizing the full width at half maximum by the maximum component frequency fm is defined as the full width at half maximum ratio (FWHM ratio). That is, the full width at half maximum ratio is expressed by the following formula.
Full width at half maximum ratio = full width at half maximum/fm

FIG. 14 is a diagram showing the relationship between the full width at half maximum ratio (FWHM ratio) of the fundamental wave band W1 and the wave number N0. The full width at half maximum ratio shown on the vertical axis was calculated from the frequency spectrum in FIG. 12A and FIG. 12B. When the wave number N0=1, the full width at half maximum ratio expands to 120%. When the wave number N0=2, the full width at half maximum ratio narrows to 60%. As mentioned above, when N0=1, the frequency spectrum of the transmitted wave expands to the range of 0 to 2 fm. On the other hand, when the wave number N0 is set to 2 or more, the effect of the present disclosure is large.

Incidentally, since the signal components containing information about the defect D appear in the frequency range of fm ±0.25 fm, it is even more preferable that the width of the fundamental wave band W1 of the spectrum of the transmitted wave is narrower than this. In other words, it is preferable that the full width at half maximum of the frequency spectrum of the fundamental wave band W1 is 50% or less of the maximum component frequency fm. This can improve the detection accuracy of the defect D.

As can be seen from FIG. 14, the full width at half maximum ratio (FWHM ratio) of the fundamental waveband W1 can be reduced to 50% or less by setting the wave number N0 of the wave packet to 3 or more. Therefore, as described above, it is even more preferable to set the wave number N0 of the wave packet to 3 or more.

Since defect detectability is improved by detecting the base component W3 of the fundamental wave band W1, it is preferable that the frequencies detected by the filter section 240 include frequencies in the range of (fm±0.25fm) with respect to the maximum component frequency fm. Here, "0.25fm" means 0.25 times (i.e., 25%) the maximum component frequency fm. As an example, when fm=1 MHz, this refers to a range of (1±0.25) MHz, that is, a range of (0.75 to 1.25) MHz. This corresponds to a full width at half maximum ratio of 50% or less.

As can be seen from FIG. 14, when the wave number N0 is set to 5, the full width at half maximum ratio of the fundamental wave band W1 is 30% or less. Correspondingly, it is even more preferable that the frequency detected by the filter section 240 includes a range of (fm±0.15fm) with respect to the maximum component frequency fm.

(Narrowband probe)
As is well known, there are broadband and narrowband probes in the transmitting probe 110. In general, the broadband probe has a full width at half maximum ratio of the fundamental wave band W1 of about 70% or more, and the narrowband probe has a full width at half maximum ratio of about 50% or less.

In the pulse-echo method, a broadband probe is often used to expand the frequency band of the transmitted wave.

On the other hand, narrowband probes are advantageous for detecting frequency components of specific frequencies because the ultrasonic energy is concentrated in a narrow frequency range.

As mentioned above, in this disclosure, it is preferable that the full width at half maximum ratio of the fundamental wave band W1 be 50% or less. From this point of view, it is even more preferable that the transmitting probe 110 is a narrowband probe in this disclosure.

(Specific example of the configuration of the filter unit 240)
Representative examples of frequency characteristics of the filter unit 240 for achieving the effects of the present disclosure are shown below. The filter unit 240 preferably includes at least one of a band-blocking filter, a low-pass filter, or a high-pass filter. By including at least one of these, components in a frequency range including the maximum component frequency fm can be reduced. Among these, by including at least one of a low-pass filter or a high-pass filter, only one of the high frequency or low frequency is blocked, so that the program for blocking can be simplified. Furthermore, when the filter unit 240 is implemented by an electronic circuit, the circuit configuration for blocking can be simplified.

Fig. 15A shows the frequency characteristic of the gain in a band-stop filter. The band-stop filter reduces the components in a frequency range W2 (Fig. 15B) that includes the maximum component frequency fm (maximum intensity frequency component) out of the fundamental wave band W1 (Fig. 15B) that includes the maximum component frequency fm. The reduction rate x is the ratio G1/G0 of the gain G0 in the transmission region to the gain G1 in the blocking region. In the first embodiment, the reduction rate x is set to -20 dB (1/10) to -40 dB (1/100).

FIG. 15B is a diagram showing a schematic of the frequency characteristics of a signal after processing with a band-stop filter. The waveform shown by the solid and dotted lines is the fundamental wave band W1. The dotted lines show the signal components before processing, and the components in the frequency range W2 shown in the dotted line are reduced by the band-stop filter. As a result, the base component W3 of the fundamental wave band W1, shown by the solid line, can be detected.

Fig. 16A shows the frequency characteristics of the gain in a low-pass filter. By setting the cutoff frequency of the low-pass filter to a frequency lower than the maximum component frequency fm, the signal components at the maximum component frequency fm can be reduced. Here, the cutoff frequency of a filter is the frequency at the boundary between the passband that passes the signal and the attenuation band that attenuates the signal. In the first embodiment, the cutoff frequency is set to 0.78 MHz. In other words, it is set to a frequency 40 kHz lower than the maximum component frequency fm (0.82 MHz). The reduction rate at the cutoff section is set to approximately -40 dB.

FIG. 16B is a diagram showing the frequency characteristics of a signal after processing with a low-pass filter. The dotted and solid lines have the same meanings as in FIG. 15B. By using a low-pass filter, it is possible to detect frequency components of the base component W3 that are smaller than the maximum component frequency fm, as shown by the solid line.

Figure 17A shows the frequency characteristics of the gain in a high-pass filter. By setting the cutoff frequency of the high-pass filter to a frequency higher than the maximum component frequency fm, the signal components at the maximum component frequency fm can be reduced.

FIG. 17B is a diagram showing the frequency characteristics of a signal after processing with a high-pass filter. The dotted and solid lines have the same meanings as in FIG. 15B. By using a high-pass filter, it is possible to detect frequency components of the base component W3 that are greater than the maximum component frequency fm, as shown by the solid line.

(Method of mounting filter section 240)
The following describes a typical configuration example of a method for implementing the filter section 240. Methods for implementing the filter section 240 are roughly divided into analog methods and digital methods.

The analog method uses an analog circuit to reduce signal components in a desired frequency range. Typical examples of frequency characteristics of the filter section 240 include a band-blocking filter (Figs. 15A and 15B), a low-pass filter (Figs. 16A and 16B), and a high-pass filter (Figs. 17A and 17B). There are various known methods for realizing analog circuits with such frequency characteristics.

FIG. 18 is a block diagram showing a digital filter section 240. The filter section 240 includes a frequency component conversion section 241, a frequency selection section 242, and a frequency component inverse conversion section 243. The frequency component conversion section 241 converts the received signal of the receiving probe 121 input from the signal amplifier 222 into frequency components. The frequency selection section 242 selects the foot component W3 by removing the frequency band including the maximum component frequency fm (maximum intensity frequency component). The frequency component inverse conversion section 243 converts only the necessary frequency components back into a time domain signal. By including the frequency component conversion section 241 and the frequency selection section 242 among these, in particular, the digital filter section 240 can be configured.

Such a digital filter unit 240 can also reduce components in a frequency range including the maximum component frequency fm. The processing performed by the frequency component conversion unit 241 is processing to convert the signal waveform in the time domain into frequency components, typically using a Fourier transform. The processing performed by the frequency component inverse conversion unit 243 is processing to convert the frequency components (frequency spectrum) into a signal waveform in the time domain, typically using an inverse Fourier transform.

FIG. 19 is a block diagram showing a filter unit 240 according to another embodiment. The filter unit 240 is provided in the signal processing unit 250. The filter unit 240 includes a frequency component conversion unit 241 and a frequency selection unit 242. The output of the frequency selection unit 242 is input to a signal strength calculation unit 231 in the data processing unit 201. The signal strength calculation unit 231 calculates the signal strength based on the information of the frequency components.

As shown in the frequency spectrum of Figure 11 above, the reason why the base component W3 of the fundamental wave band W1 changes sensitively to the defect D is thought to be as follows.

The direct wave U3, which does not interact with the defective part D, does not change in wave propagation direction, phase, frequency, etc. Therefore, the signal component of the maximum component frequency fm is largely dominated by the direct wave U3. Therefore, the change between the defective part D and the healthy part N is small.

As shown in Figure 5 above, the scattered wave U1 that interacts with the defect D has components that change the propagation direction, and components that do not change the propagation direction but at least one of the phase or frequency changes. Furthermore, among the components that change the propagation direction, there are components whose frequency changes. Therefore, the proportion of the scattered wave U1 component, which is the ultrasonic beam U that interacts with the defect D, in the base component W3 of the fundamental wave band W1, which is a component shifted from the maximum frequency fm, increases. As a result, the change between the defect D and the healthy part N becomes greater. In this way, the detection performance of the defect D can be improved by reducing the component of the maximum component frequency fm and detecting the base component W3 of the fundamental wave band W1.

(Focal length of receiving probe)
It is more preferable that the focal length R2 of the receiving probe 121 is longer than the focal length R1 of the transmitting probe 110. This is because, as described below, by doing so, it becomes possible to detect more components of the scattered wave U1. As described above, the scattered wave U1 is an ultrasonic beam U that has interacted with the defect D, so the greater the proportion of the scattered wave U1 components, the easier it becomes to detect the defect D.

The reason why more scattered wave components can be detected by increasing the focal length of the receiving probe 121 will be explained using Figures 20A and 20B.

FIG. 20A is a schematic diagram showing the propagation path of an ultrasonic beam U when the focal length R1 of the transmitting probe 110 and the focal length R2 of the receiving probe 121 are equal. The receiving probe 121 can detect an ultrasonic beam U within the range of a cone (shape) C2 of a virtual beam virtually emitted from the receiving probe 121. In the example shown in FIG. 20A, the convergence point of the ultrasonic beam U transmitted from the transmitting probe 110 and the convergence point of the virtual beam virtually emitted from the receiving probe 121 are the same. Therefore, an ultrasonic beam U whose propagation direction does not change at the defect D can be efficiently received. On the other hand, an ultrasonic beam U whose propagation direction changes at the defect D is difficult to detect.

FIG. 20B is a schematic diagram showing the propagation path of the ultrasonic beam U when the focal length R2 of the receiving probe 121 is longer than the focal length R1 of the transmitting probe 110. The receiving probe 121 can detect the ultrasonic beam U within the range of the cone (shape) C3 of the virtual beam virtually emitted from the receiving probe 121. Therefore, even if the scattered wave U1 has changed its propagation direction slightly at the defect D, it can be detected if it is within the range of the cone C3. In this way, by making the focal length R2 of the receiving probe 121 longer than the focal length R1 of the transmitting probe 110, the detectable scattered wave U1 can be increased. As described above, the scattered wave U1 is a wave that has interacted with the defect D, so this can further improve the detection performance of the defect D.

In Figure 5, the position of the receiving probe 120 is shifted because the scattered wave U1 scattered at a relatively large angle is shown. On the other hand, the scattered wave U1 scattered at a small angle can be detected by increasing the focal length of the receiving probe 121. This improves the detection performance of the defect D.

The magnitude relationship of the convergence is also defined by the magnitude relationship between the beam incident areas T1 and T2 on the surface of the object E to be inspected. The beam incident areas T1 and T2 are explained below.

FIG. 21 is a diagram explaining the relationship between the beam incidence area T1 in the transmitting probe 110 and the beam incidence area T2 in the receiving probe 121. The beam incidence area T1 in the subject E of the transmitting probe 110 is the intersection area of the ultrasonic beam U emitted from the transmitting probe 110 on the surface of the subject E. The beam incidence area T2 in the receiving probe 121 is the intersection area of the virtual ultrasonic beam U2, which is assumed to be emitted from the receiving probe 121, on the surface of the subject E.

In FIG. 21, the path of the ultrasonic beam U is shown when there is no object under test E. When there is an object under test E, the ultrasonic beam U is refracted at the surface of the object under test E, and the ultrasonic beam U propagates along a path different from the path shown by the dashed line. Here, as shown in FIG. 21, the beam incidence area T2 of the receiving probe 121 at the object under test E is larger than the beam incidence area T1 of the transmitting probe 110 at the object under test E. In this way, the convergence of the receiving probe 121 can be made looser than that of the transmitting probe 110.

Furthermore, the focal length R2 of the receiving probe 121 is longer than the focal length R1 of the transmitting probe 110. In this way, the convergence of the receiving probe 121 can be made looser than the convergence of the transmitting probe 110. At this time, the distance from the subject E to the transmitting probe 110 and the receiving probe 121 is, for example, the same for both, but does not have to be the same.

In this manner, in this embodiment, the convergence of the receiving probe 121 is looser than that of the transmitting probe 110. That is, the focal length R2 of the receiving probe 121 is set longer than the focal length R1 of the transmitting probe 110. As a result, the beam incidence area T2 of the receiving probe 121 is wider, so that a wider range of scattered waves U1 can be detected. This makes it possible for the receiving probe 121 to detect the scattered waves U1 even if the propagation path of the scattered waves U1 changes slightly. As a result, a wider range of defective portions D can be detected.

Furthermore, the focus P1 of the receiving probe 121 is located closer to the transmitting probe 110 (above in the illustrated example) than the focus P2 of the transmitting probe 110. By shifting the foci P1 and P2 in this way, it becomes easier for the receiving probe 121 to receive the scattered wave U1, and easier to detect the scattered wave U1.

Note that a non-converging probe (not shown) may be used as the receiving probe 121 in a configuration in which the focal length R2 of the receiving probe 121 is longer than the focal length R1 of the transmitting probe 110. That is, in another embodiment, the receiving probe 121 is a non-converging probe. In a non-converging probe, the focal length R2 is infinite, so it is longer than the focal length R1 of the transmitting probe 110. That is, even with a non-converging receiving probe 121, the convergence of the receiving probe 121 is weaker than the convergence of the transmitting probe 110.

Second Embodiment
22 is a diagram showing the configuration of an ultrasonic inspection device Z in the second embodiment. In the second embodiment, the transmission sound axis AX1 of the transmitting probe 110 and the reception sound axis AX2 of the receiving probe 121 are arranged to be offset from each other. That is, the receiving probe 121 in the second embodiment is a receiving probe 120 (eccentrically arranged receiving probe) having a reception sound axis AX2 arranged at a position different from the transmission sound axis AX1 of the transmitting probe 110. Therefore, the eccentric distance L (distance) between the transmission sound axis AX1 (sound axis) of the transmitting probe 110 and the reception sound axis AX (sound axis) of the receiving probe 120 is greater than zero.

By using such an arrangement, it is possible to detect scattered waves U1 whose spatial direction has changed. By combining the principle of extracting frequency-based scattered waves U1 using the filter unit 240 (Figure 6) with the principle of extracting spatial scattered waves U1 using an eccentric arrangement, it is possible to further improve the detectability of the defect D.

In the second embodiment, the receiving probe 120 is arranged offset by an eccentric distance L in the x-axis direction of FIG. 22 with respect to the transmitting probe 110, but the receiving probe 120 may be arranged offset in the y-axis direction of FIG. 22. Alternatively, the receiving probe 120 may be arranged at L1 in the x-axis direction and L2 in the y-axis direction (i.e., if the position of the transmitting probe 110 on the xy plane is taken as the origin, then the position is (L1, L2)).

FIG. 23A is a diagram explaining the transmission sound axis AX1, reception sound axis AX2, and eccentricity distance L when the transmission sound axis AX1 and reception sound axis AX2 extend vertically. FIG. 23B is a diagram explaining the transmission sound axis AX1, reception sound axis AX2, and eccentricity distance L when the transmission sound axis AX1 and reception sound axis AX2 extend at an angle. For reference, FIGS. 23A and 23B also show the receiving probe 140 (coaxially arranged receiving probe) in dashed lines.

The sound axis is defined as the central axis of the ultrasonic beam U. Here, the transmission sound axis AX1 is defined as the sound axis of the propagation path of the ultrasonic beam U emitted by the transmitting probe 110. In other words, the transmission sound axis AX1 is the central axis of the propagation path of the ultrasonic beam U emitted by the transmitting probe 110. The transmission sound axis AX1 is intended to include refraction due to the interface of the object to be inspected E, as shown in FIG. 23B. In other words, as shown in FIG. 23B, when the ultrasonic beam U emitted from the transmitting probe 110 is refracted at the interface of the object to be inspected E, the center (sound axis) of the propagation path of the ultrasonic beam U becomes the transmission sound axis AX1.

Furthermore, the receiving sound axis AX2 is defined as the sound axis of the propagation path of the virtual ultrasonic beam when it is assumed that the receiving probe 121 emits the ultrasonic beam U. In other words, the receiving sound axis AX2 is the central axis of the virtual ultrasonic beam when it is assumed that the receiving probe 121 emits the ultrasonic beam U.

As a specific example, we will consider a non-focused probe (not shown) with a planar probe surface. In this case, the direction of the receiving sound axis AX2 is the normal direction of the probe surface, and the axis passing through the center point of the probe surface becomes the receiving sound axis AX2. If the probe surface is rectangular, the center point is defined as the intersection of the diagonals of the rectangle.

The reason why the direction of the receiving sound axis AX2 is the normal direction to the probe surface is because the virtual ultrasonic beam U radiated from the receiving probe 121 is emitted in the normal direction to the probe surface. When receiving the ultrasonic beam U, the ultrasonic beam U incident in the normal direction to the probe surface can be received with good sensitivity.

The eccentricity distance L is defined as the deviation between the transmission sound axis AX1 and the reception sound axis AX2. Therefore, as shown in FIG. 23B, when the ultrasonic beam U emitted from the transmission probe 110 is refracted, the eccentricity distance L is defined as the deviation between the refracted transmission sound axis AX1 and the reception sound axis AX2. In the ultrasonic inspection device Z of the second embodiment, the transmission probe 110 and the reception probe 120 are adjusted by the eccentricity distance adjustment unit 105 (FIG. 22) so that the eccentricity distance L defined in this way is greater than zero.

23A shows the case where the transmitting probe 110 is arranged in the normal direction on the surface of the test object E. In Figs. 23A and 23B, the transmitting sound axis AX1 is indicated by a solid arrow. Also, the receiving sound axis AX2 is indicated by a dashed arrow. Note that in Figs. 23A and 23B, the position of the receiving probe 121 indicated by the dashed line is a position where the eccentricity distance L is zero, and the receiving probe 121 where the transmitting sound axis AX1 and the receiving sound axis AX2 coincide is the receiving probe 140 as a coaxially arranged receiving probe. Also, the receiving probe 121 indicated by the solid line is the receiving probe 120 (eccentrically arranged receiving probe) arranged at a position with an eccentricity distance L greater than zero. When the transmitting probe 110 is installed so that the transmitting sound axis AX1 is perpendicular to the horizontal plane (xy plane in Fig. 22), the propagation path of the ultrasonic beam U is not refracted. In other words, the transmitting sound axis AX1 is not refracted. This corresponds to the case where the transmission probe 110 is installed so that the transmission sound axis AX1 of the transmission probe 110 is perpendicular to the mounting surface 1021 of the sample stage 102.

In this embodiment, the transmitting probe 110 is installed so that the transmission sound axis AX1 is normal to the mounting surface 1021 of the test object E on the sample stage 102. As described above, this has the effect of making it easier to understand the correspondence between the scanning position and the position of the defect D, since the transmission sound axis AX1 is arranged perpendicular to the surface of the test object E for a plate-shaped test object E.

23B shows a case where the transmitting probe 110 is arranged at an angle α from the normal direction on the surface of the test object E. In FIG. 23B, as in FIG. 23A, the transmitting sound axis AX1 is indicated by a solid arrow, and the receiving sound axis AX2 is indicated by a dashed arrow. In the example shown in FIG. 23B, as described above, the propagation path of the ultrasonic beam U is refracted at a refraction angle β at the interface between the test object E and the fluid F. Therefore, the transmitting sound axis AX1 is bent (refracted) as shown by the solid arrow in FIG. 23B. In this case, the position of the receiving probe 140 shown by the dashed line is located on the transmitting sound axis AX1, so that the eccentricity distance L is zero. And, as described above, even when the ultrasonic beam U is refracted, the receiving probe 120 is arranged so that the distance between the transmitting sound axis AX1 and the receiving sound axis AX2 is L. In the example shown in FIG. 22, the transmitting probe 110 is installed in the normal direction to the surface of the test object E, so the eccentricity distance L is as shown in FIG. 23A.

It is even more preferable to set the eccentricity distance L at a position where the signal strength at the defective portion D is greater than the signal strength at the healthy portion N of the test object E.

Third Embodiment
24 is a diagram showing the configuration of an ultrasonic inspection device Z in the third embodiment. In the third embodiment, the scanning measurement device 1 includes an installation angle adjustment unit 106 that adjusts the inclination of the receiving probe 120. This makes it possible to increase the strength of the received signal and to increase the signal-to-noise ratio (SNR) of the signal. The installation angle adjustment unit 106 is, for example, configured by an actuator, a motor, etc., neither of which are shown in the figure.

Here, the angle θ between the transmission sound axis AX1 and the reception sound axis AX2 is defined as the receiving probe installation angle. In the case of FIG. 24, the transmitting probe 110 is installed vertically, so the transmission sound axis AX1 is vertical, and the angle θ, which is the receiving probe installation angle, is the angle between the transmission sound axis AX1 (i.e., the vertical direction) and the normal to the probe surface of the receiving probe 120. Then, the installation angle adjustment unit 106 tilts the angle θ toward the side where the transmission sound axis AX1 exists, and sets the angle θ to a value greater than zero. That is, the receiving probe 120 is tilted. Specifically, the receiving probe 120 is tilted so as to satisfy 0°<θ<90°, and the angle θ is, for example, 10°, but is not limited to this.

The eccentricity distance L when the receiving probe 120 is arranged at an angle is defined as follows. An intersection P12 between the receiving sound axis AX2 and the probe surface of the receiving probe 120 is defined. An intersection P11 between the transmitting sound axis AX1 and the probe surface of the transmitting probe 110 is defined. The eccentricity distance L is defined as the distance between the coordinate position (x4, y4) (not shown) obtained by projecting the position of intersection P11 onto the xy plane, and the coordinate position (x5, y5) (not shown) obtained by projecting the position of intersection P12 onto the xy plane.

When the inventor actually tried to detect defect D by positioning the receiving probe 120 at an angle in this way, the signal strength of the received signal increased three times compared to when θ = 0.

FIG. 25 is a diagram explaining why the effect of the third embodiment is produced. The scattered wave U1 propagates in a direction deviating from the transmission sound axis AX1. Therefore, as shown in FIG. 25, when the scattered wave U1 reaches the outside of the test object E, it is incident on the interface between the test object E and the outside at a non-zero angle α2 with the normal vector of the test object E's surface. The angle of the scattered wave U1 emerging from the surface of the test object E has an angle β2, which is a non-zero exit angle with respect to the normal direction of the test object E's surface. The scattered wave U1 can be received most efficiently when the normal vector of the probe surface of the receiving probe 120 is aligned with the traveling direction of the scattered wave U1. In other words, the strength of the received signal can be increased by tilting the receiving probe 120.

The reception effect is highest when the angle β2 of the ultrasonic beam U emitted from the subject E coincides with the angle θ between the transmission sound axis AX1 and the reception sound axis AX2. However, even if the angle β2 and the angle θ do not coincide perfectly, the effect of increasing the reception signal can be obtained, so as shown in Figure 25, the angle β2 and the angle θ do not have to coincide perfectly.

Fourth Embodiment
26 is a functional block diagram of the control device 2 in the ultrasonic inspection device Z in the fourth embodiment. In the fourth embodiment, the filter used in the filter section 240 is determined by irradiating an ultrasonic beam U onto a sample (not shown) having a known position of a defect D before inspection of the object to be inspected E. Then, the inspection of the object to be inspected E is performed using the filter determined before the inspection.

The filter unit 240 includes a detection unit 244 and a determination unit 245. The detection unit 244 detects multiple different foot components W3 of the fundamental wave band W1 in the relationship between frequency and signal strength (component strength). The relationship referred to here is, for example, the relationship shown in FIG. 11, which is obtained by irradiating an ultrasonic beam U to a healthy part N and a defective part D in a sample (not shown) in which the position of the defective part D is known. The determination unit 245 determines which foot component W3 to use by comparing the multiple detected foot components W3. By configuring the filter unit 240 in this way, it is possible to use a foot component W3 that makes it easy to identify signal changes caused by the defective part D, and the detection accuracy of the defective part D can be improved.

The detection unit 244 includes, for example, a filter capable of detecting different foot components W3. The filter here is, for example, at least two of the band-blocking filter (FIG. 15A), low-pass filter (FIG. 16A), and high-pass filter (FIG. 17A). For example, if the detection unit 244 includes these three filters, the detection unit 244 detects the foot components W3 shown in FIG. 15B, FIG. 16B, and FIG. 17B using the three filters in the relationship shown in FIG. 11. The determination unit 245 then compares the three detected foot components W3 with each other, for example by selecting the foot component W3 with the largest difference between the healthy part N and the defective part D, and determines which foot component W3 to use. The filter unit 240 uses the determined foot component W3 to inspect the test object E, thereby improving the detection accuracy of the defective part D.

Fifth Embodiment
27 is a functional block diagram of the control device 2 in the ultrasonic inspection device Z in the fifth embodiment. In the fifth embodiment, before the inspection of the object E to be inspected, the ultrasonic beam U is irradiated onto a sample (not shown) whose position of the defect D is known, and the data obtained is presented to a user, who then decides which base component W3 to use, i.e., which filter to use.

The control device 2 includes a display unit 223 and a reception unit 224. In the illustrated example, the display unit 223 and the reception unit 224 are provided in the data processing unit 201. The display unit 223 displays the relationship between frequency and signal strength (component strength) on the display device 3. The relationship here is, for example, the relationship shown in FIG. 11, which is obtained by irradiating an ultrasonic beam U to a healthy part N and a defective part D in a sample (not shown) whose position of the defective part D is known. The reception unit 224 receives information input by the user based on the relationship between frequency and signal strength, and represents the foot component W3 to be detected. The input is performed through the input device 4, which is, for example, a keyboard, a mouse, a touch panel, etc. Then, the filter unit 240 detects the foot component W3 corresponding to the information based on the information received by the reception unit 224.

By configuring the control device 2 in this way, the base component W3 to be detected can be determined based on the user's subjective opinion. This allows the user to make a determination based on their experience, making it possible to perform an inspection that is suited to the actual inspection.

Sixth Embodiment
28 is a functional block diagram of the control device 2 in the ultrasonic inspection device Z in the sixth embodiment. In the sixth embodiment, the received signal is converted into frequency components by a frequency conversion unit 230 and stored, and after the measurement for the inspection, an image is generated using appropriate frequency components. This constitutes a filter unit 240.

The control device 2 controls the driving of the scanning measurement device 1. The control device 2 includes a transmission system 210, a reception system 220, a data processing unit 201, a scan controller 204, a driving unit 202, a position measurement unit 203, and a signal processing unit 250. The driving unit 202 changes the relative positions of the transmitting probe 110 and the receiving probe 121 with respect to the subject E, for example, by driving the transmitting probe 110 and the receiving probe 121. The position measurement unit 203 measures the scanning position. The scan controller 204 drives the transmitting probe 110 and the receiving probe 121 through the driving unit 202. The scanning positions of the transmitting probe 110 and the receiving probe 121 are input to the scan controller 204 through the position measurement unit 203.

The receiving system 220 and the data processing unit 201 are collectively referred to as the signal processing unit 250. The signal processing unit 250 performs signal processing on the signal from the receiving probe 121, such as amplification processing and frequency selection processing, to extract significant information.

The transmission system 210 is a system that generates a voltage to be applied to the transmission probe 110. The configuration of the transmission system 210 is the same as in the first embodiment.

The voltage waveform applied to the transmitting probe 110 is a repeating wave packet waveform, as shown in FIG. 9 above. The voltage waveform applied is the same as in the first embodiment.

The signal processing unit 250 includes a data processing unit 201 and a receiving system 220. The receiving system 220 is a system that detects the received signal output from the receiving probe 121. The signal output from the receiving probe 121 is input to a signal amplifier 222 and amplified. The amplified signal is input to a frequency conversion unit 230. The frequency conversion unit 230 is included in the signal processing unit 250 and converts the received signal of the receiving probe 121 into frequency components (signal processing). In the example of the present disclosure, the frequency conversion unit 230 converts the received signal, which is a time domain waveform, into frequency components. The frequency components are the magnitude (spectrum) of each frequency component. Examples of frequency components include a method of expressing a combination of a real part and an imaginary part as a complex number, and a method of expressing an amplitude (absolute value) and a phase.

The conversion in the frequency conversion unit 230 can be performed, for example, by a Fourier transform. The conversion may also be performed along with the extraction of only frequency components in a pre-specified frequency range (frequency parameters). The signal converted into frequency components by the frequency conversion unit 230 is input to the data processing unit 201. The frequency conversion unit 230 may be provided inside the data processing unit 201. That is, the conversion into frequency components may be performed within the data processing unit.

(Accumulation of frequency component data)
The data processing unit 201 includes a storage unit 261, a frequency selection unit 242, an imaging unit 262, and a display unit 263. Therefore, the signal processing unit 250 includes a frequency conversion unit 230, an imaging unit 262, a frequency selection unit 242, and a display unit 263.

In the example of the present disclosure, the frequency conversion unit 230 converts the time domain waveform into frequency component data and stores it together with the position information in the storage unit 261. The imaging unit 262 then generates an image 273 (described below) indicating the defect position using a portion of the converted frequency components that is specified by the frequency parameters, as described in detail below. That is, the imaging unit 262 visualizes the signal features based on the input frequency parameters. That is, when the test object E is measured once, the conversion to frequency component data is performed only once, and the extraction of the signal features from the frequency component data is performed multiple times.

This configuration is preferable for the following two reasons.
The first is the time required for calculation. The conversion process to frequency component data in the frequency conversion unit 230 takes time. Typically, a Fourier transform is used as described above, but even if a fast Fourier transform (FFT), known as a high-speed algorithm, is used, the processing time for this conversion is long. On the other hand, the signal feature amount is calculated using equation (1) described later, and the calculation time required for this is short. As a typical example, the process is completed in 0.2 seconds or less even for measurement points of 100 rows x 100 columns.

Thus, according to an example of the present disclosure, as described in detail below, when the frequency parameters are "updated," it is possible to obtain an instantly updated image 273 (described below). In this way, by storing the frequency component data in the memory unit 261, it is possible to quickly select a frequency set suitable for improving defect detectability.

Secondly, the amount of data is reduced. The signal waveform of the receiving probe 140 has about 100,000 points for one measurement position in the time domain waveform, whereas the frequency component data only requires complex numbers for 20 to 100 different frequencies. In other words, the amount of data for the subject E can be reduced to about 1/1000. This has the advantage of significantly reducing the amount of data stored in the memory unit 261.

The data processing unit 201 also receives information on the scanning position from the scan controller 204. In this way, data on the frequency components of the received signal at the current two-dimensional scanning position (x, y) (hereinafter referred to as frequency component data) is obtained. The data processing unit 201 associates the scanning position (x, y) with the frequency component data at that position and stores them in the storage unit 261. Note that an image 273 of the defect D is created by determining the signal feature amount determined from the frequency component data for each scanning position.

The frequency component data is frequency components corresponding to multiple frequencies. In a typical example, the frequency component data is a frequency spectrum obtained by Fourier transform of the received signal. As described above, it is more preferable for the frequency components to include phase information in addition to amplitude (absolute value). This is synonymous with treating the frequency components as complex numbers. As described below, by including phase information, it is possible to calculate signal features with higher performance.

In FIG. 28, the data processing unit 201 includes an imaging unit 262. The imaging unit 262 is included in the signal processing unit 250, and generates an image 273 (described below) indicating the position (defect position) of the defect D using a portion of the converted frequency components that is specified by the frequency parameters. Specifically, the imaging unit 262 creates the image 273 based on the change (amount of change) in the signal caused by the defect D of the test object E in the frequency spectrum of the portion that corresponds to the appropriate frequency parameter out of the frequency spectrum that corresponds to the frequency components converted by the frequency conversion unit 230. In this way, the image 273 can be generated.

The signal change (change in the received signal) referred to here is a signal feature in the example of the present disclosure. Therefore, the imaging unit 262 first calculates the signal feature from the portion of the frequency spectrum corresponding to the converted frequency component that is the input frequency parameter. The signal feature is, for example, a value that represents the signal change as described above, and is a value calculated from the frequency component data so as to appropriately include defect information (for example, the position of the defect D). A specific example of a method for calculating the signal feature will be described later. By plotting the signal feature thus obtained against the scanning position (x, y), a two-dimensional image (defect image) of the defect D present inside the inspected object E is generated.

The above procedure is performed while changing the scanning position (x, y) to scan the desired range. When scanning is completed, frequency component data and signal features corresponding to the scanning position (x, y) are stored in the memory unit 261 in the data processing unit 201. In this disclosure, the signal features are calculated each time a signal is acquired at the scanning position. However, during measurement, the frequency component data may be stored in the memory unit 261, and the signal features may be calculated collectively to generate a defect image after measurement.

(Calculation of signal features)
A method for calculating signal features from frequency component data used in the examples of the present disclosure will be described.
Here, to make the formula easier to understand, the frequency f is expressed as an angular frequency ω. The angular frequency ω is obtained by multiplying the frequency f by 2π. The frequency component expressed as a complex number is represented as H(ω). h(t) is calculated according to the following formula (1).

Here, in equation (1), j is the imaginary unit, and in equation (2), Re[ ] is the process of extracting the real part of a complex number. In equation (1), the subscript ω of the Σ symbol indicates the frequency set of the angular frequency components to be integrated. In equation (1), the angular frequency components to be integrated are calculated for an appropriately set frequency set {ω}, as described below.

In formula (1), the set of frequencies {ω} to be included in the accumulation is called a frequency parameter. The frequency parameter may be specified in the form of a frequency set {ω} or in the form of a frequency range. The frequency parameter may also be set in advance. The frequency parameter may also be input by the user.

The h(t) obtained by equation (2) is a time domain signal waveform synthesized from a frequency set set by the frequency parameters. In the example of this disclosure, the difference between the maximum and minimum values of this h(t) (Peak-to-Peak value) is used as the signal feature. In the example of this disclosure, the difference between the maximum and minimum values (Peak-to-Peak value) is abbreviated as the PP value.

In formula (1), H(ω) and exp(jωt) are both complex numbers, and are calculated as complex numbers. In other words, the signal feature is calculated taking into account the phase information of the frequency component H(ω). This is more preferable because it allows for a signal feature that accurately reflects the position information of the defect D.

The selection of the frequency parameters, i.e., the set of frequencies {ω} to be included in the accumulation in equation (1), is important. The maximum component frequency fm is excluded from the set of frequencies {ω} to be included in the accumulation. In this way, a filter section 240 can be configured that reduces at least the maximum intensity frequency component of the received signal of the receiving probe 120. Furthermore, the frequencies to be included in the accumulation include the frequency of the base component W3 of the fundamental wave band W1. This can improve the detectability of the defective portion D in the inspected object E. Furthermore, it is even more effective to also exclude frequency components near the maximum component frequency fm.

Since angular frequency ω can be converted to frequency f using the relationship ω = 2πf, we will make appropriate conversions and interpretations. For example, if we write "excluding the maximum component frequency fm from the frequency set {ω}," this means "excluding ωm = 2πfm."

The maximum component frequency fm is the frequency at which the spectrum of the fundamental wave band W1 of the received signal is at its maximum, but in this disclosure it is defined as the frequency at which it is approximately at its maximum.

Furthermore, in equation (1), the set of frequencies {ω} to be included in the accumulation may include only frequencies lower than the maximum component frequency fm. This allows the filter section 240 to be configured with low-pass filter characteristics. Similarly, it may include only frequencies lower than the maximum component frequency fm.

The frequency parameters are appropriately set in the frequency selection unit 242 (Figure 28). In this way, the frequency conversion unit 230 and the frequency selection unit 242 form the filter unit 240.

The frequency parameters may be set to appropriate parameters before the test, or may be changed after the measurement. They may also be set by the user.

Note that the signal feature amount is not limited to the above calculation method, as long as it is a value calculated from frequency component data so as to appropriately include the position information of the defect D. In the above example, the PP value of the signal waveform h(t) in the time domain is used as the signal feature amount, but the absolute value of h(t) may be calculated, and the area of h(t) may be calculated as the signal feature amount. Here, the procedure for calculating the area is to sample h(t) at appropriate time intervals and calculate the sum of h(t) at the sampling points. Also, instead of the absolute value of h(t), the squared value of h(t) may be used. Furthermore, instead of using equations (1) and (2), the absolute values of the frequency components H(ω) may be summed for the input frequency set {ω} and used as the signal feature amount.

FIG. 29 is a diagram showing the hardware configuration of the control device 2. The above-mentioned configurations, functions, and each part constituting the block diagram may be realized in hardware by designing some or all of them as an integrated circuit, for example. Also, as shown in FIG. 29, the above-mentioned configurations, functions, etc. may be realized in software by a processor such as a CPU 252 interpreting and executing a program that realizes each function. The control device 2 includes, for example, a memory 251, a CPU 252, a storage device 253 (SSD, HDD, etc.), a communication device 254, and an I/F 255. In addition to being stored in the HDD, information such as programs, tables, and files that realize each function can be stored in a recording device such as a memory or SSD (Solid State Drive), or a recording medium such as an IC (Integrated Circuit) card, an SD (Secure Digital) card, or a DVD (Digital Versatile Disc).

FIG. 30 is a flow chart showing the ultrasonic inspection method of each of the above-mentioned embodiments. The ultrasonic inspection method of the first embodiment can be performed by the above-mentioned ultrasonic inspection device Z, and will be described as an example with reference to FIG. 1 and FIG. 6 as appropriate. The ultrasonic inspection method of the first embodiment inspects the object E (FIG. 1) by irradiating the object E (FIG. 1) with an ultrasonic beam U via a gas G (FIG. 1).

The ultrasonic inspection method disclosed herein includes steps S101 to S105, S111, and S112. First, in response to a command from the control device 2, the transmitting probe 110 performs step S101 (emission step) of emitting an ultrasonic beam U from the transmitting probe 110. In step S101, an ultrasonic beam U of a repeating wave packet composed of a wave packet with a wave number of two or more is emitted from the transmitting probe 110. Next, the receiving probe 121 performs step S102 (reception step) of receiving the ultrasonic beam U.

Thereafter, the filter unit 240 performs step S103 (filter processing step) of reducing a specific frequency range, specifically, a component (maximum intensity frequency component) in a frequency range including the maximum component frequency fm, based on the signal (e.g., waveform signal) of the ultrasonic beam U received by the receiving probe 121. That is, in step S103, the maximum intensity frequency component of the signal of the ultrasonic beam U received in step S102 is reduced. Then, the data processing unit 201 performs step S104 (signal intensity calculation step) of detecting the base component W3 of the fundamental wave band W1 from the signal subjected to the filter processing and generating signal intensity data. That is, in step S104, the base component W3 of the fundamental wave band W1 of the signal of the ultrasonic beam U is detected. In this embodiment, a peak-to-peak signal is used as a method of generating the signal intensity data. This is the difference between the maximum value and the minimum value of the signal.

Next, step S105 (shape display step) is performed. Scanning position information of the transmitting probe 110 and the receiving probe 121 is sent from the position measurement unit 203 to the scan controller 204. The data processing unit 201 plots the signal intensity data at each scanning position against the scanning position information of the transmitting probe 110 obtained from the scan controller 204. In this way, the signal intensity data is visualized. This is step S105.

Note that FIG. 8B shows a case where the scanning position information is one-dimensional (one direction); when the scanning position information is two-dimensional (x, y), the signal intensity data is plotted to show the defect D as a two-dimensional image, which is then displayed on the display device 3.

The data processing unit 201 determines whether the scanning is complete (step S111). If the scanning is complete (Yes), the control device 2 ends the processing. If the scanning is not complete (No), the data processing unit 201 outputs a command to the driving unit 202 to move the transmitting probe 110 and the receiving probe 121 to the next scanning position (step S112), and the processing returns to step S101.

Seventh Embodiment
Fig. 31 is a diagram showing the configuration of an ultrasonic inspection device Z of the seventh embodiment. In Fig. 31, a scanning measurement device 1 is shown in a schematic cross-sectional view. Fig. 31 shows a coordinate system of three orthogonal axes including an x-axis as a left-right direction on the paper, a y-axis as a direction perpendicular to the paper, and a z-axis as a top-bottom direction on the paper.

The ultrasonic inspection device Z inspects the object E by irradiating an ultrasonic beam U (described later) to the object E through a fluid F. The fluid F is a gas G such as air, and the object E is present in the fluid F. In the seventh embodiment, air (an example of gas G) is used as the fluid F. Therefore, the inside of the housing 101 of the scanning measurement device 1 is a cavity filled with air. As shown in FIG. 31, the ultrasonic inspection device Z includes the scanning measurement device 1, a control device 2, and a display device 3. The display device 3 is connected to the control device 2.

The scanning measurement device 1 scans and measures the object E with an ultrasonic beam U, and includes a sample stage 102 fixed to a housing 101, on which the object E is placed. It is more preferable that the object E is fixed to the sample stage 102 with a fixture (not shown) so as not to move. If the object E is heavy enough not to move inadvertently, a fixture is not necessary. The object E is made of any material. The object E is, for example, a solid material, and more specifically, is, for example, a metal, glass, a resin material, or a composite material such as CFRP (Carbon-Fiber Reinforced Plastics). In the example of FIG. 31, the object E has a defect D inside. The defect D (defect) is a cavity, etc. Examples of the defect D are a cavity, a foreign material different from the material that should be there, etc. In the specimen E, the portion other than the defective portion D is called the healthy portion N.

The scanning measurement device 1 has a transmitting probe 110 that emits an ultrasonic beam U and a receiving probe 121 that receives the ultrasonic beam U. The transmitting probe 110 is installed in the housing 101 via the transmitting probe scanning unit 103, and emits an ultrasonic beam U. The receiving probe 121 is a receiving probe 140 (coaxially arranged receiving probe) that is installed on the opposite side of the transmitting probe 110 with respect to the subject E to receive the ultrasonic beam U and is arranged coaxially with the transmitting probe 110 (the eccentric distance L described below is zero). Therefore, in this disclosure, the eccentric distance L (distance, described below) between the transmitting sound axis AX1 (sound axis) of the transmitting probe 110 and the receiving sound axis AX2 (sound axis) of the receiving probe 140 is zero. This makes it possible to easily install the transmitting probe 110 and the receiving probe 140.

Here, "the opposite side of the transmitting probe 110" means, of the two spaces separated by the subject E, the space opposite the space in which the transmitting probe 110 is located (the opposite side in the z-axis direction), and does not mean limited to the opposite side with the same x and y coordinates (i.e., a position that is symmetrical with respect to the xy plane).

The control device 2 is connected to the scanning measurement device 1. The control device 2 controls the driving of the scanning measurement device 1, and controls the movement (scanning) of the transmitting probe 110 and the receiving probe 121 by instructing the transmitting probe scanning unit 103 and the receiving probe scanning unit 104. The transmitting probe scanning unit 103 and the receiving probe scanning unit 104 move in the x-axis and y-axis directions in sync, so that the transmitting probe 110 and the receiving probe 121 scan the subject E in the x-axis and y-axis directions. Furthermore, the control device 2 emits an ultrasonic beam U from the transmitting probe 110, and performs waveform analysis based on the signal acquired from the receiving probe 121. The plane formed by the two axes, the x-axis and y-axis directions, which are the scanning directions of the transmitting probe 110, is called the scanning plane.

In the illustrated example, gas G is interposed between the transmitting probe 110 and the test subject E, and between the receiving probe 121 and the test subject E. Therefore, the transmitting probe 110 and the receiving probe 121 can test the test subject E without contacting it, so that the relative positions in the xy plane can be changed smoothly and quickly. In other words, by interposing a fluid F (gas G) between the transmitting probe 110 and the receiving probe 121 and the test subject E, smooth scanning becomes possible.

When a localized ultrasonic beam U is emitted from the transmitting probe 110, the emitted ultrasonic beam U is locally irradiated onto the object E to be inspected. The position to which the localized ultrasonic beam U is irradiated is changed by scanning. As described above, the ultrasonic beam U that reaches the receiving probe 121 changes depending on whether it is a defective part D or a healthy part N of the object E to be inspected, so this configuration makes it possible to detect the defective part D.

In this embodiment, a focused transmitting probe 110 is used to generate a localized ultrasonic beam U.

The transmitting probe 110 is a convergent type transmitting probe 110. On the other hand, the receiving probe 121 uses a probe with looser convergence than the transmitting probe 110. In this disclosure, a non-convergent type probe with a flat probe surface is used for the receiving probe 121. Therefore, the receiving probe 121 is a non-convergent type receiving probe. By using such a non-convergent type receiving probe 121, information on the defect portion D can be collected over a wide range.

As described in the first embodiment with reference to FIG. 5, in this disclosure, the scattered wave U1 is efficiently detected by focusing on the difference in frequency detected in the received signal. The details are as described with reference to FIG. 5.

FIG. 32 is a functional block diagram of the control device 2. The control device 2 controls the driving of the scanning measurement device 1. The control device 2 includes a transmission system 210, a reception system 220, a data processing unit 201, a scan controller 204, a driving unit 202, a position measurement unit 203, and a signal processing unit 250. The driving unit 202 changes the relative positions of the transmitting probe 110 and the receiving probe 121 with respect to the test subject E, for example, by driving the transmitting probe 110 and the receiving probe 121. The position measurement unit 203 measures the scanning position. The scan controller 204 drives the transmitting probe 110 and the receiving probe 121 through the driving unit 202. The scanning positions of the transmitting probe 110 and the receiving probe 121 are input to the scan controller 204 through the position measurement unit 203.

The receiving system 220 and the data processing unit 201 are collectively referred to as the signal processing unit 250. The signal processing unit 250 performs signal processing on the signal from the receiving probe 121, such as amplification and filtering, to extract significant information.

(The natural frequency of the transmitting probe fres and the excitation frequency fex)
The transmission system 210 is a system that generates a voltage to be applied to the transmission probe 110. The transmission system 210 includes a waveform generator 211, a signal amplifier 212, and a transmission frequency setting unit 213. A burst wave signal is generated by the waveform generator 211. The generated burst wave signal is then amplified by the signal amplifier 212. The voltage output from the signal amplifier 212 is applied to the transmission probe 110.

The waveform of the burst wave signal will be described later, but in brief, the waveform is a repeating wave packet waveform in which a wave packet of wave number N is repeated at fundamental frequency f0. The transmission system 210 includes a transmission frequency setting unit 213. The transmission frequency setting unit 213 can change the fundamental frequency f0. Since one of the features of this disclosure is the method of selecting the fundamental frequency f0, the changed fundamental frequency f0 is called the excitation frequency fex (excitation frequency) in the sense of the frequency that excites the transmission probe 110.

As described below, the performance of the ultrasonic inspection device Z of this embodiment can be improved by setting the excitation frequency fex to an appropriate value.

Generally, when the transmitting probe 110 is operated at a specific frequency determined for each probe, the amplitude intensity (sound pressure) of the generated ultrasound is maximized. This maximum frequency is called the natural frequency fres (resonance frequency) of the transmitting probe 110. The reason that the sound pressure is maximized at the natural frequency is because the vibration of the built-in piezoelectric element resonates at the natural frequency fres. For this reason, the transmitting probe 100 is usually used with the excitation frequency set equal to the natural frequency.

In this embodiment, the excitation frequency fex is set to a frequency that is shifted from the natural frequency fres of the transmitting probe 110. Therefore, the scanning measurement device 1 drives the transmitting probe 110 at the excitation frequency fex that is shifted from the natural frequency fres (synonymous with the resonant frequency) of the transmitting probe 110.

The signal processing unit 250 includes a data processing unit 201 and a receiving system 220. The receiving system 220 is a system that detects the received signal output from the receiving probe 121. The receiving system 220 includes a signal amplifier 222 and a filter unit 240. Thus, the signal processing unit 250 includes a filter unit 240. The signal output from the receiving probe 121 is input to the signal amplifier 222 and amplified. The amplified signal is input to the filter unit 240 (blocking filter). The filter unit 240 reduces (blocks) components of a specific frequency range of the input signal. The filter unit 240 will be described later. The output signal from the filter unit 240 is input to the data processing unit 201.

The configuration of the data processing unit 201 is similar to that used in the first embodiment. The configuration of the filter unit 240 is also similar to that used in the first embodiment.

The data processing unit 201 generates signal strength data from the signal input from the filter unit 240. In this embodiment, the peak-to-peak signal is used as a method for generating signal strength data. The peak-to-peak signal is the difference between the maximum and minimum values of the signal. Another method for generating signal strength data is to use the strength of frequency components in a specific frequency range by performing a Fourier transform.

The data processing unit 201 also receives scanning position information from the scan controller 204. In this way, the signal intensity data value at the current two-dimensional scanning position (x, y) is obtained. By plotting the signal intensity data value (peak-to-peak signal amount) against the scanning position, an image (defect image) corresponding to at least one of the position and shape of the defect D is obtained. This defect image is output to the display device 3.

(Filter section 240)
The configuration of the filter unit 240 used in this embodiment is the same as that of the filter unit 240 in the first embodiment, as described above. The definition of the filter unit 240 is also as described above.

In this disclosure, the filter unit 240 is defined as a control unit that performs signal processing to reduce the intensity of signal components in a specified frequency range. Filter processing is also defined as signal processing that reduces the intensity of signal components in a specified frequency range. When a received signal is decomposed into component intensities for each frequency component using a Fourier transform or the like, the frequency at which the component intensity is maximum is called the maximum component frequency. The maximum intensity frequency component is the frequency component at the maximum component frequency. The filter unit 240 of this disclosure reduces the intensity of the fundamental wave band that includes the maximum intensity frequency component, i.e., the signal components in the frequency range that includes the maximum component frequency. The distribution of component intensities for each frequency component is called the frequency spectrum.

In the seventh embodiment, the filter unit 240 reduces the component strength in the cutoff frequency range including the maximum component frequency fm. That is, the filter unit 240 reduces at least the maximum intensity frequency component (the component corresponding to the maximum component frequency fm) of the received signal of the receiving probe 121. The filter unit 240 then detects the base component W3 other than the maximum intensity frequency component of the fundamental wave band W1 including the maximum intensity frequency component. Because the filter unit 240 reduces the component strength in the cutoff frequency range, the proportion of the base component W3 in the fundamental wave band W1 increases in the signal after passing through the filter unit 240. In this way, the detection performance of the defect portion D can be improved, as described below.

Figure 33A shows the change in signal strength information depending on the position when the transmitting probe 110 and the receiving probe 121 are scanned across the defective portion D. Figure 33A shows the result of measurement using a configuration in which the filter unit 240 is removed from the configuration in Figure 32 above. The excitation frequency fex of the transmitting probe 110 is set equal to the natural frequency fres = 0.82 MHz of the transmitting probe 110. The signal strength in the healthy portion N is v0. On the other hand, at the position (x = 0) corresponding to the defective portion D, the signal strength is reduced by Δv, and the defective portion D can be detected. However, the rate of change in signal strength (Δv/v0) is small. Here, the rate of change in signal strength is defined as the signal change amount Δv at the defective portion D divided by the signal strength v0 at the healthy portion N.

Figure 33B shows the result of measuring signal strength information using a control device 2 (Figure 32) equipped with a filter unit 240, with the excitation frequency fex of the transmitting probe 110 set to 0.78 MHz. It can be seen that the rate of change in signal strength (Δv/v0) at the location of defect D has increased, improving the detectability of defect D.

The experimental conditions under which the results shown in Figures 33A and 33B were obtained are explained below.

As described above, FIG. 9 above shows the voltage waveform of the burst wave applied to the transmitting probe 110. The horizontal axis is time, and the vertical axis is voltage. In this embodiment, ten sine waves with a fundamental frequency f0 of 0.78 MHz are applied in the waveform of FIG. 9. These ten waves are called a wave packet. The inverse of the fundamental frequency f0 is called the fundamental period T0. As shown in the figure, the fundamental period T0 is the period of the waves that make up one wave packet. The wave packet is applied with a repetition period Tr = 5 ms. Therefore, the transmitting probe 110 emits an ultrasonic beam U when a voltage waveform of a repeating wave packet made up of a wave packet with two or more waves is applied to it.

Figure 34 shows the frequency component distribution of the received signal when 10 sine waves with a fundamental frequency f0 of 0.78 MHz are applied to the waveform shown in Figure 9 above. In this figure, the horizontal axis is frequency, and the vertical axis is measured data of component strength at each frequency. This is the frequency component distribution of a signal not processed by the filter unit 240. 0.82 MHz, where the component strength is maximum, is the maximum component frequency fm (Figure 7). The fundamental wave band W1 (Figure 7) extends from 0.72 MHz to 0.86 MHz, and the components excluding the maximum component frequency fm are the skirt components W3 (Figure 7). In this embodiment, the maximum component frequency fm is equal to the fundamental frequency f0 (Figure 9) of the ultrasound transmitted by the transmitting probe 110. In this way, in many cases, the maximum component frequency fm is roughly equal to the fundamental frequency f0 of the ultrasound transmitted.

As described above, the filter section 240 (Fig. 32) excludes the maximum component frequency fm. Specifically, in the illustrated example, the filter section 240 (Fig. 32) transmits the base component W3 below 0.78 MHz and blocks waves above 0.78 MHz, including 0.82 MHz. When such a filter section 240 is used, as shown in Fig. 8B above, the rate of change of the signal intensity at the defective section D increases, and it can be seen that the detectability of the defect is greatly improved.

Figure 35 is a diagram comparing the measured data of the frequency component distribution (frequency spectrum) of the received signal between a healthy part N (solid line) and a defective part D (dashed line). The mechanism by which the filter section 240 improves the detectability of the defective part D is as follows. At the maximum component frequency fm = 0.82 MHz, the difference in component strength (signal magnitude) between the healthy part N and the defective part D is small. On the other hand, for the base component W3 other than the maximum component frequency fm, especially in the low frequency band, the difference between the healthy part N and the defective part D is large.

In this way, the present disclosure is based on the new knowledge found by the inventors that in the frequency component distribution of a received signal, the base component W3 of the fundamental wave band W1 has a greater signal change rate at the defect D than the signal component at the maximum component frequency fm. The component at the maximum component frequency fm accounts for a large proportion of the received signal, but the signal change rate at the defect D is small, so by reducing this component, the proportion of the base component W3 increases. In this way, the signal after processing by the filter unit 240 has an increased signal change rate at the defect D, improving the detectability of the defect D. And even when comparing the actual measurement data shown in Figures 33A and 33B, the effect of improving the detectability of the defect D by the filter unit 240 is clear.

A representative example of the frequency characteristics of the filter section 240 for achieving the effects of the present disclosure is shown below. The filter section 240 preferably includes at least one of a band-blocking filter, a low-pass filter, or a high-pass filter. By including at least one of these, it is possible to reduce components in a frequency range that includes the maximum component frequency fm. A representative configuration of the filter section 240 is similar to that described in the first embodiment.

(Method of Implementing Filter Unit 240)
As described in the first embodiment, the implementation method of the filter unit 240 is roughly divided into an analog type and a digital type. In this embodiment, the effect can be obtained regardless of whether the analog type or the digital type is used. The specific configurations of the analog type and the digital type are described in the first embodiment.

The reason why the base component W3 of the fundamental wave band W1 changes sensitively to the defect D is thought to be as follows.

(Fundamental frequency tail components)
As described above, in the present disclosure, the performance of detecting the defect D is improved by detecting the foot component W3 of the fundamental wave band W1. Therefore, increasing the foot component W3 of the fundamental wave band W1 further contributes to improving the detection performance. Therefore, the inventors have thoroughly studied the relationship of the transmitted ultrasonic waveform to increase the foot component W3 of the fundamental wave band W1.

There are two things that have the effect of increasing the amount of the base component W3 of the fundamental wave band W1: the wave number of each wave packet that makes up the repeating wave packet, and the selection of the excitation frequency.

(Wave number of the wave packet)
First, the relationship between the wave number of a wave packet constituting a repeating wave packet and the tail component will be shown. The wave number of a wave packet is the number of waves of fundamental frequency f0 contained in one wave packet, as shown in FIG.

Figure 36A shows the frequency spectrum of the wave number N0 of the wave packet and the fundamental wave band W1 of the ultrasound. Here, we use an example of ultrasound with a fundamental frequency f0 = 0.82 MHz. The frequency spectra are shown for wave packets of wave numbers N0 = 10 (dashed line) and N0 = 20 (solid line). The spectrum shown by the dashed dotted line is for a continuous wave. In the case of a continuous wave, it only has the component of the fundamental frequency f0, and the skirt component W3 is almost nonexistent. In contrast, as can be seen from the spectra for N0 = 20 and 10, the lower the wave number N0, the wider the width of the fundamental wave band W1 and the larger the skirt component W3.

Figure 36B shows how the full width at half maximum (FWHM) of the fundamental waveband of the spectrum shown in Figure 36A changes with respect to the wave number N0 of the wave packet.

According to the present disclosure, the change due to the defect D is large in the base component W3 of the fundamental wave band W1, so it is preferable that the ultrasonic waves used in the present disclosure are ultrasonic waves composed of repeated wave packets rather than continuous waves. Furthermore, as shown in Figure 36B, the smaller the wave number N0 of each wave packet, the more the base component W3 of the fundamental wave band W1 increases, so the smaller the wave number N0, the more preferable it is. As shown in Figure 36B, when N0≦30, the full width at half maximum spreads to 30 kHz (0.03 MHz) or more, so it is preferable that the wave number N0 of the wave packet is 30 or less.

In addition, it is not preferable that the full width at half maximum (FWHM) of the fundamental wave band is too wide.
In order to set the full width at half maximum of the fundamental waveband W1 to 50% or less of the maximum component frequency fm, the wave number N0 of the wave packet is preferably 2 or more, and more preferably 3 or more. The reasons for this are as described in the first embodiment.

Therefore, it is preferable that the wave number N0 of the wave packet is 2 or more and 30 or less.

As can be seen from FIG. 14 above, in order to make the full width at half maximum of the fundamental wave band W1 50% or less of the maximum component frequency fm, this can be achieved by making the wave number N0 of the wave packet 3 or more. Therefore, as described above, it is even more preferable to make the wave number N0 of the wave packet 3 or more.

Since defect detectability is improved by detecting the base component W3 of the fundamental wave band W1, it is preferable that the frequency detected by the filter section 240 includes frequency components in the range of (fm±0.25fm) with respect to the maximum component frequency fm. Here, "0.25fm" means 0.25 times (i.e., 25%) the maximum component frequency fm. For example, when fm=1 MHz, this refers to the range of (1±0.25) MHz, that is, the range of (0.75 to 1.25) MHz. This corresponds to a full width at half maximum ratio of 50% or less.

As can be seen from FIG. 14 above, when the wave number N0 is set to 5 or more, the full width at half maximum ratio of the fundamental wave band W1 is 30% or less. Accordingly, it is more preferable that the filter section 240 detects frequency components that include the range of (fm±0.15fm) with respect to the maximum component frequency fm.

(excitation frequency)
Next, the relationship between the excitation frequency fex and the base component W3 will be shown. The excitation frequency fex is a frequency corresponding to the fundamental frequency f0 of the wave packet, and is a frequency applied to the transmission probe 110. The excitation frequency fex is set in the frequency range of the fundamental wave band W1.

Generally, the transmitting probe 110 has a natural frequency fres (resonance frequency). The natural frequency fres of the transmitting probe 110 is the frequency at which the piezoelectric element constituting the transmitting probe 110 is most likely to vibrate. When a voltage of the natural frequency fres is applied, the intensity (acoustic energy) of the emitted ultrasonic waves is maximized, so the excitation frequency fex is usually set to be equal to the natural frequency fres of the transmitting probe 110. Note that in this disclosure, the natural frequency fres is synonymous with the resonance frequency fres.

Figure 37 shows the results of measuring the frequency spectrum of the received signal by changing the excitation frequency fex. The natural frequency fres of this transmitting probe 110 is 0.82 MHz. The dashed line in Figure 37 shows the frequency spectrum when the excitation frequency fex is set equal to the natural frequency fres. As mentioned above, this is the normal usage method. This measurement uses a repeating wave packet, and the wave number N0 of each wave packet is 10. For this reason, the fundamental wave band W1 has a certain degree of spread and a skirt component W3. The frequency spectrum shown by the dotted line has a spectral shape that is roughly symmetrical around the natural frequency fres.

In contrast, the solid line in Figure 37 is the frequency spectrum when the excitation frequency fex is set to 0.78 MHz, which is 40 kHz lower than the natural frequency fres. Here, the set value of the excitation frequency fex (0.78 MHz) is within the frequency range of the fundamental wave band W1, and is a value shifted from the natural frequency fres. It can be seen that the amount (component strength) of the base component W3 of the fundamental wave band W1 is increased in the solid line spectrum compared to the dashed line spectrum.

In this way, by setting the excitation frequency fex to a value within the frequency range of the fundamental wave band W1 and shifted from the natural frequency fres, the amount of the base component W3 of the fundamental wave band W1 increases, improving the detection performance of the defect D. Therefore, it is preferable to set the excitation frequency fex within the frequency range of the fundamental wave band W1.

As mentioned above, it is preferable that the full width at half maximum of the fundamental wave band W1 is 50% or less of the maximum component frequency fm. Therefore, it is preferable that the excitation frequency fex is set in the range of (fres ± 0.25 fm), where fres is the natural frequency of the transmitting probe 110. In other words, it is preferable that the absolute value |fex-fres| of the difference between the excitation frequency fex and the natural frequency fres (resonant frequency) is 25% or less of the maximum component frequency fm. Note that in this disclosure, the natural frequency fres is synonymous with the resonant frequency fres.

It is also known that when the transmitting probe 110 is driven at the natural frequency fres, the strongest ultrasonic beam U wave is emitted. The greater the deviation of the excitation frequency fex from the natural frequency fres, the lower the emission efficiency of the ultrasonic beam U. For this reason, it is more preferable that the absolute value |fex-fres| of the difference between the excitation frequency fex and the natural frequency fres (resonance frequency) is 15% or less of the maximum component frequency fm.

(instantaneous frequency)
It has been described that the foot component W3 of the fundamental wave band W1 increases by shifting the excitation frequency fex from the natural frequency fres of the transmission probe 110. The mechanism by which the foot component W3 increases in this manner will be described.

Figure 38 shows the change in instantaneous frequency in the time domain of one wave packet. Here, the amplitude waveform was calculated using a vibrating body model when a piezoelectric element with a natural frequency fres = 0.82 MHz was driven at an excitation frequency fex. The instantaneous frequency was found from the zero crossing points of the amplitude waveform. The zero crossing points indicate the time when the signal crosses the zero point, and the period can be determined from the interval between the zero crossing points, so the instantaneous frequency can be calculated. In the calculations of Figure 38, the wave number N0 of the wave packet was set to 10. The dashed line shows the results when the excitation frequency fex was set to 0.82 MHz, which is equal to the natural frequency fres, and the solid line shows the results when the excitation frequency fex was set to 0.74 MHz.

Looking at the dashed line in Figure 38, when the excitation frequency fex is set equal to the natural frequency fres, the instantaneous frequency becomes constant at the natural frequency fres of 0.82 MHz. This corresponds to the conventional setting conditions. In contrast, looking at the solid line, when the excitation frequency fex is set to 0.74 MHz, the instantaneous frequency changes over time. That is, when the excitation frequency fex is applied at time t = 0 shown on the horizontal axis, vibration begins at a frequency close to the natural frequency fres, and then gradually approaches the excitation frequency fex. Then, when N0 = 10 has passed and the application of the excitation voltage has ended, the instantaneous frequency shown on the vertical axis returns to the natural frequency fres = 0.82 MHz.

In this way, ultrasonic waves are generated over a wide range between the excitation frequency fex and the natural frequency fres, so the amount of the base component W3 of the fundamental wave band W1 increases in the received signal.

(Range of Natural Frequency of Transmitting Probe 110)
A preferred range of the natural frequency fres of the transmitting probe 110 used in this disclosure will now be described.

In this disclosure, a localized ultrasonic beam U is irradiated onto the object E to be inspected, and a defect D at that position is detected. Therefore, the smaller the beam diameter of the localized ultrasonic beam U, the more preferable it is. For this reason, it is preferable to use a convergent probe for the transmitting probe 110.

Because ultrasound is a wave, it is known that it is difficult to converge it to less than the wavelength, even if it is focused using an acoustic lens or the like. This is because of the effect of wave diffraction.

The wavelength λ of an ultrasonic wave with frequency f0 in a medium with sound speed c is expressed as λ = c/f0. If we take acrylic as an example of the test object E, the sound speed c is 2730 (m/s), so the wavelength λ of the ultrasonic wave at frequency f0 = 50 kHz is 54 mm. In other words, even with a focusing probe, ultrasonic waves with frequency f0 = 50 kHz can only be focused to about 50 mm, making it difficult to focus sufficiently.

When the frequency f0 = 200 kHz, the wavelength λ = 14 mm, so a focused ultrasonic beam U can be realized. For this reason, it is preferable that the natural frequency fres of the transmitting probe 110 is 200 kHz or higher. In this embodiment, the natural frequency of the transmitting probe 110 is 0.82 MHz (820 kHz).

In addition, in this disclosure, the scattered wave U1 is detected, so as shown in Figure 5 above, it is possible to detect a defect D that is smaller than the beam diameter.

In this embodiment, each wave packet is a sine wave with a fundamental frequency of f0, but it may be a wave packet other than a sine wave. For example, it may be a wave packet composed of a rectangular wave with a wave number of N0.

Furthermore, the excitation frequency fex may be a wave having multiple excitation frequencies within one wave packet. A chirp wave, whose frequency changes over time, is known as such a wave. Even when using a wave having multiple excitation frequencies, it is preferable that each excitation frequency is set within the frequency range of the fundamental wave band W1.

Eighth embodiment
39 is a functional block diagram of the control device 2 in the ultrasonic inspection device Z in the eighth embodiment. In the eighth embodiment, the filter used in the filter section 240 is determined by irradiating an ultrasonic beam U onto a sample (not shown) having a known position of a defect D before inspection of the object to be inspected E. Then, the inspection of the object to be inspected E is performed using the filter determined before the inspection.

The transmission system 210 is a system that generates a voltage to be applied to the transmission probe 110. The transmission system 210 includes a waveform generator 211, a signal amplifier 212, and a transmission frequency setting unit 213. A burst wave signal is generated by the waveform generator 211. The generated burst wave signal is then amplified by the signal amplifier 212. The voltage output from the signal amplifier 212 is applied to the transmission probe 110.

In this embodiment, as in the seventh embodiment, the transmitting probe 110 is driven by a burst wave. The transmitting system 210 includes a transmitting frequency setting unit 213. The transmitting frequency setting unit 213 can change the fundamental frequency f0 of the burst wave, and can set the fundamental frequency f0 to an appropriate excitation frequency fex.

As in the seventh embodiment, in this embodiment, the excitation frequency fex is set to a frequency shifted from the natural frequency fres of the transmitting probe 110. Therefore, the scanning measurement device 1 drives the transmitting probe 110 at the excitation frequency fex shifted from the natural frequency fres (synonymous with the resonant frequency) of the transmitting probe 110. By setting the excitation frequency fex to an appropriate value, the performance of the ultrasonic inspection device Z of this embodiment can be improved.

The filter unit 240 includes a detection unit 244 and a determination unit 245. The detection unit 244 detects multiple different foot components W3 of the fundamental wave band W1 in the relationship between frequency and signal strength (component strength). The relationship referred to here is, for example, the relationship shown in FIG. 35 above, which is obtained by irradiating an ultrasonic beam U to a healthy part N and a defective part D in a sample (not shown) whose position of the defective part D is known. The determination unit 245 determines which foot component W3 to use by comparing the multiple detected foot components W3. By configuring the filter unit 240 in this way, it is possible to use a foot component W3 that makes it easy to identify signal changes caused by the defective part D, and the detection accuracy of the defective part D can be improved.

The detection unit 244 includes, for example, a filter capable of detecting different foot components W3. The filter here is, for example, at least two of the band-blocking filter (FIG. 15A), low-pass filter (FIG. 16A), and high-pass filter (FIG. 17A). For example, if the detection unit 244 includes these three filters, the detection unit 244 detects the foot components W3 shown in FIG. 15B, FIG. 16B, and FIG. 17B using the three filters, for example, in the relationship shown in FIG. 35. The determination unit 245 then compares the three detected foot components W3 with each other to determine which foot component W3 to use, for example, by selecting the foot component W3 with the largest difference between the healthy part N and the defective part D. The filter unit 240 uses the determined foot component W3 to inspect the test object E, thereby improving the detection accuracy of the defective part D.

Ninth embodiment
40 is a functional block diagram of the control device 2 in the ultrasonic inspection device Z in the ninth embodiment. In the ninth embodiment, before the inspection of the object E to be inspected, data obtained by irradiating an ultrasonic beam U onto a sample (not shown) having a known position of a defect D is presented to a user, and the user decides which base component W3 to use, i.e., which filter to use.

Similar to the seventh embodiment, in this embodiment, the excitation frequency fex is set to a frequency shifted from the natural frequency fres of the transmitting probe 110. Therefore, the scanning measurement device 1 drives the transmitting probe 110 at the excitation frequency fex shifted from the natural frequency fres (synonymous with the resonant frequency) of the transmitting probe 110. By setting the excitation frequency fex to an appropriate value, the performance of the ultrasonic inspection device Z of this embodiment can be improved.

The control device 2 includes a display unit 223 and a reception unit 224. In the illustrated example, the display unit 223 and the reception unit 224 are provided in the data processing unit 201. The display unit 223 displays the relationship between frequency and signal strength (component strength) on the display device 3. The relationship referred to here is, for example, the relationship shown in FIG. 35 above, which is obtained by irradiating an ultrasonic beam U to a healthy part N and a defective part D in a sample (not shown) whose position of the defective part D is known. The reception unit 224 receives information input by the user based on the relationship between frequency and signal strength, and which represents the foot component W3 to be detected. The input is performed through the input device 4, which is, for example, a keyboard, a mouse, a touch panel, etc. Then, the filter unit 240 detects the foot component W3 corresponding to the information based on the information received by the reception unit 224.

(Tenth embodiment. Focal length of the receiving probe 121)
In the tenth embodiment, it is more preferable that the focal length R2 of the receiving probe 121 is longer than the focal length R1 of the transmitting probe 110. This is because, as described above, by doing so, it becomes possible to detect more components of the scattered wave U1. As described above, the scattered wave U1 is an ultrasonic beam U that has interacted with the defect D, so the greater the proportion of the scattered wave U1 components, the easier it becomes to detect the defect D.

The reason why increasing the focal length of the receiving probe 121 allows more scattered wave components to be detected is as described in the first embodiment. That is, by making the focal length R2 of the receiving probe 121 longer than the focal length R1 of the transmitting probe 110, the detectable scattered waves U1 can be increased. As described above, the scattered waves U1 are waves that have interacted with the defect D, and this can further improve the detection performance of the defect D.

In the example disclosed herein, the convergence of the receiving probe 121 is looser than that of the transmitting probe 110. That is, the focal length R2 of the receiving probe 121 is set longer than the focal length R1 of the transmitting probe 110. As a result, the beam incidence area T2 of the receiving probe 121 is wider, so that a wider range of scattered waves U1 can be detected. This makes it possible for the receiving probe 121 to detect the scattered waves U1 even if the propagation path of the scattered waves U1 changes slightly. As a result, a wider range of defective parts D can be detected.

Note that a non-convergent probe (not shown) may be used as the receiving probe 121 in a configuration in which the focal length R2 of the receiving probe 121 is longer than the focal length R1 of the transmitting probe 110. In a non-convergent probe, the focal length R2 is infinite, so it is longer than the focal length R1 of the transmitting probe 110. In other words, even with a non-convergent receiving probe 121, the convergence of the receiving probe 121 is weaker than the convergence of the transmitting probe 110.

Eleventh Embodiment
41 is a diagram showing the configuration of an ultrasonic inspection device Z in the eleventh embodiment. In the eleventh embodiment, the transmission sound axis AX1 of the transmitting probe 110 and the reception sound axis AX2 of the receiving probe 121 are arranged to be shifted from each other. That is, the receiving probe 121 in the eleventh embodiment is a receiving probe 120 (eccentrically arranged receiving probe) having a reception sound axis AX2 arranged at a position different from the transmission sound axis AX1 of the transmitting probe 110. Therefore, the eccentric distance L (distance) between the transmission sound axis AX1 (sound axis) of the transmitting probe 110 and the reception sound axis AX (sound axis) of the receiving probe 120 is greater than zero.

By using this type of arrangement, it is possible to detect scattered waves U1 whose spatial direction has changed. By combining the principle of extracting frequency-wise scattered waves U1 based on the frequency spectrum of the received signal (Figure 7) with the principle of extracting spatially scattered waves U1 using an eccentric arrangement, it is possible to further improve the detectability of the defect D.

In the eleventh embodiment, the receiving probe 120 is arranged offset by an eccentric distance L in the x-axis direction of FIG. 41 with respect to the transmitting probe 110, but the receiving probe 120 may be arranged offset in the y-axis direction of FIG. 41. Alternatively, the receiving probe 120 may be arranged at L1 in the x-axis direction and L2 in the y-axis direction (i.e., if the position of the transmitting probe 110 on the xy plane is taken as the origin, then the position is (L1, L2)).

The definitions and explanations of the transmitting sound axis AX1, the receiving sound axis AX2, and the eccentricity distance L are as described above.

It is even more preferable to set the eccentricity distance L at a position where the signal strength at the defective part D is greater than the signal strength at the healthy part N of the test object E.

Twelfth Embodiment
In the twelfth embodiment, the scanning measurement device 1 includes an installation angle adjustment unit 106 that adjusts the inclination of the receiving probe 120. This makes it possible to increase the strength of the received signal and to increase the signal-to-noise ratio (SNR) of the signal. The configuration of the ultrasonic inspection device Z in this embodiment is as shown in FIG. 24.

Here, the angle θ between the transmission sound axis AX1 and the reception sound axis AX2 is defined as the receiving probe installation angle. In the case of FIG. 24 above, the transmitting probe 110 is installed vertically, so the transmission sound axis AX1 is vertical, and the angle θ, which is the receiving probe installation angle, is the angle between the transmission sound axis AX1 (i.e., the vertical direction) and the normal to the probe surface of the receiving probe 120. Then, the installation angle adjustment unit 106 tilts the angle θ toward the side where the transmission sound axis AX1 exists, and sets the angle θ to a value greater than zero. That is, the receiving probe 120 is tilted. Specifically, the receiving probe 120 is tilted so as to satisfy 0°<θ<90°, and the angle θ is, for example, 10°, but is not limited to this.

Thirteenth Embodiment
42 is a functional block diagram of the control device 2 of the thirteenth embodiment. The control device 2 controls the driving of the scanning measurement device 1. The control device 2 includes a transmission system 210, a reception system 220, a data processing unit 201, a scan controller 204, a driving unit 202, a position measurement unit 203, and a signal processing unit 250. The driving unit 202 changes the relative positions of the transmitting probe 110 and the receiving probe 121 with respect to the test subject E, for example, by driving the transmitting probe 110 and the receiving probe 121. The position measurement unit 203 measures the scanning position. The scan controller 204 drives the transmitting probe 110 and the receiving probe 121 through the driving unit 202. The scanning positions by the transmitting probe 110 and the receiving probe 121 are input to the scan controller 204 through the position measurement unit 203.

The voltage waveform applied to the transmitting probe 110 is a repeating wave packet waveform as shown in FIG. 9 above. Each wave packet is composed of a finite number of wave numbers N0 of sine waves with a fundamental frequency f0. The fundamental frequency f0 corresponds to the excitation frequency fex. In this embodiment, the excitation frequency fex is set to a frequency shifted from the natural frequency fres of the transmitting probe. Specifically, the excitation frequency fex is set to 0.78 MHz for the natural frequency fres of the transmitting probe of 0.82 MHz. The wave number N0 of the wave packet is set to 10.

The signal processing unit 250 includes a data processing unit 201 and a receiving system 220. The receiving system 220 is a system that detects the received signal output from the receiving probe 121. The signal output from the receiving probe 121 is input to a signal amplifier 222 and amplified. The amplified signal is input to a frequency conversion unit 230. The frequency conversion unit 230 is included in the signal processing unit 250 and converts the received signal from the receiving probe 121 into frequency components (signal processing), and in the example of the present disclosure, converts the received signal, which is a time domain waveform, into frequency components. The frequency components are the magnitude (spectrum) of the components at each frequency.

The configuration of the frequency conversion unit 230 is the same as that in the sixth embodiment.

(Accumulation of frequency component data)
The data processing unit 201 includes a storage unit 261, an imaging unit 262, and a display unit 263. The storage unit 261 includes a database 261a. Therefore, the signal processing unit 250 includes a frequency conversion unit 230, an imaging unit 262, the database 261a, and a display unit 263.

As described in the sixth embodiment, this configuration has two favorable points: it requires less time to perform calculations and reduces the amount of data.

As shown in FIG. 42, the control device 2 includes a database 261a in the storage unit 261 constituting the data processing unit 201 in the example of the present disclosure. The database 261a associates information that affects the detection accuracy of the defective part D in the inspected object E (hereinafter referred to as "information about the inspected object E") with frequency parameters. The information here includes, for example, the inspection conditions of the inspected object E. The appropriate frequency parameters may differ depending on the inspection conditions. The appropriate frequency parameters here are frequency parameters for increasing the difference between the frequency spectrum of the healthy part N and the frequency spectrum of the defective part D to a level that makes the defective part D detectable. The frequency parameters indicate a frequency set {ωn} suitable for detecting the defective part D. Therefore, the user can specify the part of the frequency spectrum used to create an image 273 (described later) by inputting the inspection conditions into an input unit 272 (described later).

In this embodiment, it is even more preferable to add the excitation frequency fex used to the frequency parameters and store it in the database 261a. The detection performance of the defect D changes depending on how much the excitation frequency fex is shifted from the natural frequency fres of the transmission probe 110. Therefore, by also registering the excitation frequency fex (amount of shift) in the database 261a, it becomes possible to select an appropriate excitation frequency fex for the next and subsequent measurements.

When registering the used excitation frequency fex as a frequency parameter, since the amount of shift from the natural frequency fres is important, it is preferable to register it in the form of the difference amount Δfex = fex - fres. Furthermore, it is preferable to register the ratio of the difference amount Δfex to the natural frequency fres (Δfex/fres).

The inspection conditions include, for example, at least one of the following: the material of the object E to be inspected, the thickness of the object E to be inspected, the structure of the object E to be inspected (e.g., whether it is a single-layer structure or a multi-layer structure), the position of the object E to be inspected relative to the receiving probe 121 and the transmitting probe 110 (e.g., the position in the z direction), and the type of fluid F. Since these are pieces of information that can affect the appropriate frequency parameters, the appropriate frequency parameters can be determined by the user inputting at least one of these pieces of information.

FIG. 43A is an example of database 261a. In the example disclosed herein, the frequency parameters are a set of ratios f/f0 relative to the transmission frequency f0 (FIG. 9). In the example shown in FIG. 43A, the preferred frequency parameters for information about the subject E are expressed as a certain range. The information here is, for example, the thickness and material of the subject E, as an example for explanation. When measurements are performed with ultrasonic inspection device Z shown in FIG. 31 above and the preferred frequency parameters are repeatedly registered, i.e., updated, information is accumulated in database 261a.

FIG. 43B is a three-dimensional view of the database 261a shown in FIG. 43A. The information about the test object E is multidimensional information having multiple axes. That is, if the information about the test object E is expressed by dividing it into components It[k] (k is an integer equal to or greater than 1), then k=1, 2, ... corresponds to each axis of the multidimensional information. In the example shown in FIG. 43B, as an example for explanation, It[1] is the thickness of the test object E, and It[2] is the material of the test object E.

In Figure 43A, information about the test subject E, which is multidimensional information, is abstracted and shown as one axis. More specifically, as shown in Figure 43B, information about the test subject E is composed of multiple axes. Therefore, in the example of the present disclosure, database 261a is a database that has test subject information, which is multidimensional information, as its axis.

The database 261a may be expressed in a tabular format. That is, a table may be created in which suitable frequency parameters are recorded as one record (row) for each piece of information relating to the multidimensional test subject E. Furthermore, when the database 261a is processed by a computer or the like, it may be expressed as a tabular database, or it may be expressed in a database format in which each piece of information relating to the multidimensional test subject E is a single record.

Returning to FIG. 42, the data processing unit 201 includes an imaging unit 262. The imaging unit 262 is included in the signal processing unit 250, and generates an image 273 (described below) indicating the position (defect position) of the defect D using a portion of the converted frequency components that is specified by the frequency parameters. Specifically, the imaging unit 262 creates the image 273 based on the change (amount of change) in the signal caused by the defect D of the test object E in the frequency spectrum of the portion that corresponds to the input frequency parameters out of the frequency spectrum that corresponds to the frequency components converted by the frequency conversion unit 230. In this way, the image 273 can be generated.

The signal change (change in the received signal) referred to here is a signal feature in the example of the present disclosure. Therefore, the imaging unit 262 first calculates the signal feature from the portion of the frequency spectrum corresponding to the converted frequency component that is the frequency parameter input by the user. The signal feature is, for example, a value that represents the signal change as described above, and is a value calculated from frequency component data so as to appropriately include defect information (for example, the position of the defect D). A specific example of a method for calculating the signal feature will be described later. By plotting the signal feature thus obtained against the scanning position (x, y), a two-dimensional image (defect image) of the defect D present inside the inspected object E is generated.

The data processing unit 201 (signal processing unit 250) includes a display unit 263 that displays on the display device 3. The display unit 263 outputs an image 273 to the display device 3 for display. The display device 3 is, for example, a monitor, a display, or the like. Although details will be described later, the display unit 263 displays, on the display device 3, a frequency spectrum 271 (described later) corresponding to the frequency components converted by the frequency conversion unit 230. In addition, the display unit 263 displays, on the display device 3, an input unit 272 (described later) that accepts input of frequency parameters. The input is performed, for example, by a user of the ultrasound inspection device Z, but may also be input from another device (not shown). In this disclosure, as an example, a case in which the user inputs frequency parameters will be described.

(Calculation of signal features)
The method of calculating signal features from frequency component data used in the examples of the present disclosure is as described in the sixth embodiment above.

In the above formula (1) described in the sixth embodiment, it is important to select the set of frequencies {ω} to be included in the accumulation. The selection is performed, for example, by the user. As can be seen from the above frequency spectrum, by selecting a frequency range in the fundamental wave band W1 (FIG. 7) where the difference between the healthy part N and the defective part D is large, an image of the defective part D can be obtained more clearly. Therefore, it is preferable for the user to input a frequency range (frequency parameter) where the difference between the healthy part N and the defective part D is large. Here, "large" can mean, for example, a difference that allows the user to clearly recognize the difference between the two frequency spectra, or a difference equal to or greater than a predetermined threshold value.

(Frequency Selection)
FIG. 44 is a diagram illustrating a configuration example of the operation screen 270 of the ultrasonic inspection device Z in the example of the present disclosure. The operation screen 270 is displayed on the display device 3 (FIG. 42) by the display unit 263 (FIG. 42). The display unit 263 displays, on the display device 3, a frequency spectrum 271 corresponding to the frequency components converted by the frequency conversion unit 230 (FIG. 42) as described above, and an input unit 272 that accepts input of frequency parameters by the user. In the example of the present disclosure, the display unit 263 displays the operation screen 270 of the ultrasonic inspection device Z on the display device 3, and displays the frequency spectrum 271 and the input unit 272 on the operation screen 270. This allows the user to operate the input unit 272 while checking the operation screen 270 including the frequency spectrum 271.

In the configuration example shown in FIG. 44, an image 273 showing the position of the defective part D of the inspected object E is displayed on the left side. A frequency spectrum 271 is displayed in the upper right side. Here, it is preferable to display the frequency spectrum 271 at multiple locations depending on the inspection position, so that comparison can be made. In particular, the frequency spectrum 271 includes a first frequency spectrum shown by a dashed line and a second frequency spectrum shown by a solid line. The dashed and solid line graphs are the dashed and solid line graphs in FIG. 35 above. This allows the user to compare the frequency spectra with each other, and the user can input the appropriate frequency components. However, the frequency spectrum 271 displayed may be either the first frequency spectrum or the second frequency spectrum. If the user has a certain amount of experience, he or she may be able to determine the appropriate frequency parameters based on only one of the frequency parameters.

The input unit 272 is where the user inputs frequency parameters. In the example of the present disclosure, the input unit 272 is a frequency selection unit configured with a slide bar whose length and position can be adjusted. The user can input a frequency range (frequency set) for extracting signal features by adjusting the length and position of the slide bar using, for example, a mouse, keyboard, etc., to a position corresponding to the frequency position of the frequency spectrum. The frequency range input here is the frequency parameter. After input, the frequency spectrum 271 is updated by pressing the update button 274.

Although it is preferable that the frequency spectrum 271 is displayed, it does not have to be displayed. In the case where it is not displayed, for example, the imaging unit 262 determines, as the initial frequency parameters, frequency parameters corresponding to the information on the object E received through the input unit 275 from the database 261a (FIG. 42). The input unit 275 receives information that affects the detection accuracy of the defect D in the object E (the above-mentioned "information on the object E"). The above-mentioned display unit 263 displays the input unit 275 on the display device 3. If there is no corresponding frequency parameter, the frequency parameters corresponding to the information closest to that information are determined. The determined frequency parameters are displayed on the display device 3. The imaging unit 262 creates an image 273 (FIG. 44) based on the determined frequency parameters. By using the information in the database 261a, the detection accuracy of the defect D can be improved.

Fourteenth Embodiment
The fourteenth embodiment is configured to select an optimal excitation frequency f ex from a plurality of excitation frequencies f ex The fourteenth embodiment uses the ultrasonic inspection device Z of FIG. 31 and the control device 2 of FIG.

FIG. 45 shows the steps for obtaining a defect image of the inspected object E in the 14th embodiment.

Step S100 (image acquisition step) of the 14th embodiment is broadly divided into two steps: step S1 for selecting an appropriate excitation frequency, and step S2 for acquiring a defect image of the object E to be inspected using the selected excitation frequency. Step S1 includes steps S11, S12, and S13. In step S11, an excitation frequency fex[n] is set. In step S12, the signal strength is measured. In step S13, an optimal excitation frequency is selected. Step S2 includes steps S21, S22, and S23. In step S21, the frequency of the ultrasonic beam U transmitted from the transmitting probe 110 is set to the selected excitation frequency. In step S22, measurement is performed by scanning the object E to be inspected. In step S23, an image 273 is displayed.

In the fourteenth embodiment, first, the signal amount of the defect portion D is measured using a standard test object (not shown). The standard test object is an inspection object in which a simulated defect (a defect simulating the defect portion D) with a known shape, location, etc. is formed. It is preferable that the material constituting the standard test object is the same as that of the inspected object E to be inspected, or a material with similar characteristics.

In the standard inspection object used in the 14th embodiment, the shape of the simulated defect can be 10 mm in length and 1 mm in width. It is more preferable to form simulated defects of multiple shapes and positions in terms of width, length, depth position, etc. of the simulated defect.

Figure 46 shows the results of transmitting an ultrasonic beam U while scanning a standard inspection object across a simulated defect, measuring the received signal, and then calculating the signal amount using appropriate signal processing of the received signal, then plotting the results. Curve a in the figure is the result of measurement at excitation frequency fex1, and curve b is the result of measurement at excitation frequency fex2 which is different from excitation frequency fex1. Δv and v0 are the same as in Figures 33A and 33B above. Curve b has a larger Δv than curve a. In this way, a simulated defect with a known position was measured using multiple excitation frequencies. The excitation frequency fex may be changed to around 5 to 10 types, and the signal amount measured as in Figure 46.

The optimum excitation frequency fex can be selected from the results in FIG. 46. In the fourteenth embodiment, as a selection criterion, the excitation frequency fex at which the rate of change of the signal strength Δv/v0 is maximized can be selected. The selection criterion is not limited to this, and the optimum value may be selected from two values, the rate of change of the signal strength Δv/v0 and the signal strength v0.

In the fourteenth embodiment, the control device 2 can automatically select the optimum excitation frequency fex based on the above-mentioned selection criteria. Alternatively, the measurement results in FIG. 46 may be displayed on the operation screen 270, and the user may select the optimum excitation frequency fex.

Then, the excitation frequency fex is set to the optimum frequency selected in this manner, and the test object E is measured, and the defective portion D is measured. According to the fourteenth embodiment, the optimum frequency is used as the excitation frequency fex, which has the effect of further improving the detection accuracy of the defective portion.

Fifteenth embodiment
The fifteenth embodiment is configured to select an optimal excitation frequency fex from a plurality of excitation frequencies fex.

FIG. 47 shows the steps for obtaining a defect image of the inspected object E in the 15th embodiment.

In the fifteenth embodiment, step S14 is further executed between step S12 and step S13 in step S1 of the fourteenth embodiment. Step S100 (image acquisition step) of the fifteenth embodiment is broadly divided into two steps: step S1 for selecting an appropriate excitation frequency, and step S2 for acquiring a defect image of the inspected object E using the selected excitation frequency.

In the fifteenth embodiment, the frequency spectrum is measured at a plurality of excitation frequencies fex using the test object E as the measurement object and displayed on the operation screen 270 (step S14). The position at which the frequency spectrum is measured may be either a healthy part or a defective part D of the test object E.

The excitation frequency of the transmitting probe 110 is set to fex[1] and an ultrasonic beam is irradiated onto the subject E, and the received signal is measured. Next, it is set to another excitation frequency fex[2], and the received signal is measured in the same manner. In this way, the excitation frequency is changed to fex[n] (n = 1, 2, ...) and the received signal is measured.

Figure 48 shows the frequency spectrum displayed in step S14. In step S14, the frequency spectrum is calculated from the measured received signal, and the frequency spectrum corresponding to the excitation frequency fex[n] is displayed on the operation screen 270 as shown in Figure 48. In this way, as shown in Figure 48, each spectrum is displayed corresponding to a different excitation frequency. As described above, Figure 48 shows the result of measuring the frequency spectrum of the received signal by changing the excitation frequency fex. The dashed line in Figure 48 shows the frequency spectrum when the excitation frequency fex is set equal to the natural frequency fres (0.82 MHz). The solid line shows the frequency spectrum when the excitation frequency fex is set to 0.78 MHz, which is 40 kHz lower than the natural frequency fres.

The user looks at these multiple spectra and selects an appropriate excitation frequency fex. In the fifteenth embodiment, the selection criterion for the excitation frequency is that the proportion of the base component W3 in the spectrum is large. The selection criterion for the optimal excitation frequency may be something other than this. For example, the optimal excitation frequency may be selected based on two factors: the proportion of the base component W3 and the magnitude of the signal strength.

Returning to FIG. 47, after the optimum excitation frequency fex is selected in this manner, step S2 is executed to acquire a defect image. In step S2, the selected excitation frequency fex is set, and the inspected object E is scanned to acquire a received signal. Using the acquired received signal, a defect image is displayed on the operation screen 270.

According to the fifteenth embodiment, since an optimal frequency is used as the excitation frequency fex, it is possible to further improve the detection accuracy of the defect portion D. The fifteenth embodiment also has the advantage that it is possible to select the optimal excitation frequency fex without using a standard test piece.

In addition, in the fifteenth embodiment, the frequency range for calculating the signal features can be selected based on the spectrum displayed on the operation screen 270.

Instead of the user selecting the optimal excitation frequency from multiple frequency spectra, the control device 2 may select the optimal excitation frequency. The algorithm for selecting the excitation frequency may calculate the intensity ratio of the tail components for each measured excitation frequency fex[n] based on the component intensity of the center frequency of the spectrum, and select the excitation frequency fex at which this ratio is maximized.

Sixteenth Embodiment
49 is a functional block diagram of an ultrasonic inspection device Z according to the sixteenth embodiment. In this embodiment, the input unit 275 (FIG. 44) does not necessarily have to be provided.

The signal processing unit 250 includes an update unit 291 (frequency parameter update unit). The update unit 291 automatically updates the frequency parameters. An example of a more specific process in the update unit 291 is shown below. The imaging unit 262 calculates the above-mentioned signal feature amount while changing the frequency parameters for the received signals at two points, the defective part D and the healthy part N. The update unit 291 then searches for and determines the frequency parameters that maximize the difference between the signal feature amounts of the defective part D and the healthy part N. Using the frequency parameters thus updated by the update unit 291, the imaging unit 262 creates an image 273. The frequency parameters thus updated are also registered in the database 261a, and the database 261a is updated.

It is more preferable to add the excitation frequency fex used to the frequency parameters and store it in the database 261a. Therefore, it is preferable that the database 261a includes information on the excitation frequency fex. Since the detectability of defects changes depending on how much the excitation frequency fex is shifted from the natural frequency fres of the transmitting probe, by registering this in the database 261a as well, it becomes possible to select the appropriate excitation frequency fex for the next and subsequent measurements.

The determined frequency parameters may be displayed on the display device 3. Also, instead of automatically updating the frequency parameters by the update unit 291, the user may specify the frequency parameters through the input unit 272 while viewing the image 273. This also makes it possible to further improve the detection accuracy of the defective portion D.

FIG. 50 is a diagram showing the hardware configuration of the control device 2. The above-mentioned configurations, functions, and each part constituting the block diagram may be realized in hardware by, for example, designing some or all of them as an integrated circuit. Also, as shown in FIG. 50, the above-mentioned configurations, functions, etc. may be realized in software by a processor such as a CPU 252 interpreting and executing a program that realizes each function. The control device 2 includes, for example, a memory 251, a CPU 252, a storage device 253 (SSD, HDD, etc.), a communication device 254, and an I/F 255. In addition to being stored in the HDD, information such as programs, tables, and files that realize each function can be stored in a recording device such as a memory or SSD (Solid State Drive), or a recording medium such as an IC (Integrated Circuit) card, an SD (Secure Digital) card, or a DVD (Digital Versatile Disc).

FIG. 51 is a flow chart showing the ultrasonic inspection method of each of the above-mentioned embodiments. The ultrasonic inspection method disclosed herein can be executed by the control device 2 of the above-mentioned ultrasonic inspection device Z, and will be described as an example with reference to FIGS. 31 and 32 as appropriate. The ultrasonic inspection method disclosed herein inspects the object E (FIG. 31) by irradiating the object E (FIG. 31) with an ultrasonic beam U via a gas G (FIG. 31).

The ultrasonic inspection method disclosed herein includes steps S101 to S105, S111, and S112. First, in response to a command from the control device 2, the transmitting probe 110 performs step S101 (emission step) of emitting an ultrasonic beam U from the transmitting probe 110.

In step S101, the excitation frequency fex of the transmitting probe 110 is set to a frequency shifted from the natural frequency fres of the transmitting probe 110. Therefore, in step S101, the transmitting probe 110 is excited at the excitation frequency fex shifted from the natural frequency fres (synonymous with the resonant frequency) of the transmitting probe 110 to emit an ultrasonic beam U.

Next, in step S102 (reception step), the receiving probe 121 receives the ultrasound beam U.

Then, the filter unit 240 performs step S103 (filter processing step) to reduce components (maximum intensity frequency components) in a specific frequency range, specifically, a frequency range including the maximum component frequency fm, based on the signal (e.g., waveform signal) of the ultrasound beam U received by the receiving probe 121. That is, in step S103, the maximum intensity frequency component of the signal of the ultrasound beam U received in step S102 is reduced.

Then, the data processing unit 201 performs step S104 (signal intensity calculation step) of detecting the base component W3 of the fundamental wave band W1 from the filtered signal and generating signal intensity data. Therefore, in step S104, the base component W3 of the fundamental wave band W1 in the signal of the ultrasound beam U is detected. In this embodiment, the peak-to-peak signal is used as a method of generating signal intensity data. This is the difference between the maximum and minimum values of the signal.

Note that Figure 33B above shows a case where the scanning position information is one-dimensional (one direction); when the scanning position information is two-dimensional in x and y, the signal intensity data is plotted to show the defect D as a two-dimensional image, which is then displayed on the display device 3.

The ultrasonic inspection device Z and ultrasonic inspection method described above can improve the detection performance of defective areas D, for example the performance of detecting minute defects.

In each of the above embodiments, an example is described in which the defect D is a cavity, but the defect D may also be a foreign object containing a material different from the material of the object E to be inspected. In this case, too, there is a difference (Gap) in acoustic impedance at the interface where the different materials come into contact, so scattered waves U1 are generated, and the configurations of the above embodiments are effective. The ultrasonic inspection device Z according to each of the above embodiments is premised on an ultrasonic defect imaging device, but may also be applied to a non-contact in-line internal defect inspection device.

The present disclosure is not limited to the above-described embodiments, but includes various modified examples. For example, the above-described embodiments have been described in detail to clearly explain the present disclosure, and are not necessarily limited to those having all of the configurations described. In addition, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. In addition, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

In addition, in each embodiment, the control lines and information lines shown are those that are considered necessary for the explanation, and not all control lines and information lines in the product are necessarily shown. In reality, it can be considered that almost all components are interconnected.

1 Scanning measurement device 100 Transmitting probe 101 Housing 102 Sample stage 1021 Mounting surface 103 Transmitting probe scanning section 104 Receiving probe scanning section 105 Eccentricity distance adjustment section 106 Installation angle adjustment section 110 Transmitting probe 111 Transducer 112 Backing 113 Matching layer 114 Probe surface 115 Transmitting probe housing 116 Connector 117 Lead wire 118 Lead wire 120 Receiving probe 121 Receiving probe 140 Receiving probe 2 Control device 201 Data processing section 202 Driving section 203 Position measurement section 204 Scan controller 210 Transmission system 211 Waveform generator 212 Signal amplifier 213 Transmission frequency setting section 220 Receiving system 222 Signal amplifier 223 Display section 224 Reception section 230 Frequency conversion section 231 Signal strength calculation section 240 Filter section 241 Frequency component transform unit 242 Frequency selection unit 243 Frequency component inverse transform unit 244 Detection unit 245 Determination unit 250 Signal processing unit 251 Memory 252 CPU
253 Storage device 254 Communication device 255 I/F
261 Storage unit 261a Database 262 Imaging unit 263 Display unit 270 Operation screen 271 Frequency spectrum 272 Input unit 273 Image 274 Update button 275 Input unit 291 Update unit 3 Display device 4 Input device AX Receiving sound axis AX1 Transmitting sound axis AX2 Receiving sound axis BW Beam width C2 Cone C3 Cone D Defective part E Inspected object F Fluid G Gas L Eccentricity distance N Healthy part P1 Focus P11 Intersection P12 Intersection P2 Focus R1 Focal length R2 Focal length T1 Beam incidence area T2 Beam incidence area U Ultrasonic beam U1 Scattered wave U2 Ultrasonic beam U3 Direct wave W Liquid W1 Fundamental wave band W2 Frequency range W3 Base component Z Ultrasonic inspection device

Claims

1. An ultrasonic inspection apparatus for inspecting an object to be inspected by irradiating an ultrasonic beam onto the object to be inspected through a gas, comprising:
a scanning and measuring device that scans and measures the object to be inspected with the ultrasonic beam; and a control device that controls the driving of the scanning and measuring device,
The scanning measurement device is
a transmitting probe that emits the ultrasonic beam, and a receiving probe that receives the ultrasonic beam and is disposed on the opposite side of the transmitting probe with respect to the object to be inspected,
the transmitting probe emits an ultrasonic beam in response to a voltage waveform of a repeating wave packet having a wave packet with a wave number of two or more;
Driving the transmitting probe at an excitation frequency shifted from a resonant frequency of the transmitting probe;
The control device includes a signal processor.
the signal processing unit includes a filter unit that reduces at least a maximum intensity frequency component of the reception signal of the receiving probe;
The filter unit detects frequency components other than the maximum intensity frequency component in a fundamental wave band that includes the maximum intensity frequency component.
The ultrasonic inspection device according to claim 1, characterized in that the focal length of the receiving probe is longer than the focal length of the transmitting probe.
The ultrasonic inspection device according to claim 1, characterized in that the receiving probe is a non-converged type receiving probe.
The ultrasonic inspection device of claim 1, characterized in that the full width at half maximum of the frequency spectrum of the fundamental wave band is 50% or less of the maximum component frequency, which is the frequency corresponding to the maximum intensity frequency component.
The filter unit includes:
a frequency component converter for converting a received signal of the receiving probe into a frequency component;
a frequency selection unit that selects the base component by removing a frequency band including the maximum intensity frequency component;
2. The ultrasonic inspection apparatus according to claim 1, further comprising:
The ultrasonic inspection device according to claim 1, characterized in that the excitation frequency is set within the frequency range of the fundamental wave band.
The ultrasonic inspection device according to claim 1, characterized in that the wave number of the wave packet is 30 or less.
The ultrasonic inspection device of claim 1, characterized in that the absolute value of the difference between the excitation frequency and the resonant frequency is 25% or less of the maximum component frequency, which is the frequency corresponding to the maximum intensity frequency component.
The ultrasonic inspection device of claim 1, characterized in that the absolute value of the difference between the excitation frequency and the resonant frequency is 15% or less of the maximum component frequency, which is the frequency corresponding to the maximum intensity frequency component.
The ultrasonic inspection device of claim 1, characterized in that the frequencies detected by the filter unit include frequencies in the range of (fm ± 0.25 fm), where fm is the maximum component frequency, which is the frequency corresponding to the maximum intensity frequency component.
1. An ultrasonic inspection apparatus for inspecting an object to be inspected by irradiating an ultrasonic beam onto the object to be inspected through a gas, comprising:
a scanning and measuring device that scans and measures the object to be inspected with the ultrasonic beam; and a control device that controls the driving of the scanning and measuring device,
The scanning measurement device is
a transmitting probe for emitting the ultrasonic beam and a receiving probe for receiving the ultrasonic beam,
Driving the transmitting probe at an excitation frequency shifted from a resonant frequency of the transmitting probe;
The control device includes a signal processor.
The signal processing unit includes:
a frequency conversion unit that converts a received signal of the receiving probe into a frequency component;
an imaging unit that generates an image showing a defect position by using a portion of the converted frequency components that is designated by a frequency parameter;
a database in which information that affects the accuracy of detecting defects in the object to be inspected is associated with the frequency parameters;
A display unit that displays information on a display device;
Equipped with
The display unit displays, on the display device, an input unit that receives information that affects the accuracy of detecting a defect in the object to be inspected.
The ultrasonic inspection device according to claim 11, characterized in that the database includes information on the excitation frequency.
1. An ultrasonic inspection method for inspecting an object to be inspected by irradiating an ultrasonic beam onto the object to be inspected through a gas, comprising:
an emission step of exciting the transmitting probe at an excitation frequency shifted from a resonant frequency of the transmitting probe to emit an ultrasonic beam;
a receiving step of receiving the ultrasonic beam;
a filtering step of reducing a maximum intensity frequency component of the signal of the ultrasonic beam received in the receiving step;
and a signal intensity calculation step of detecting a base component of a fundamental wave band in the signal of the ultrasonic beam.
1. An ultrasonic inspection apparatus for inspecting an object to be inspected by irradiating an ultrasonic beam onto the object to be inspected through a gas, comprising:
a scanning and measuring device that scans and measures the object to be inspected with the ultrasonic beam; and a control device that controls the driving of the scanning and measuring device,
The scanning measurement device is
a transmitting probe that emits the ultrasonic beam, and a receiving probe that receives the ultrasonic beam and is disposed on the opposite side of the transmitting probe with respect to the object to be inspected,
the transmitting probe emits an ultrasonic beam in response to a voltage waveform of a repeating wave packet having a wave packet with a wave number of two or more;
The control device includes a signal processor.
the signal processing unit includes a filter unit that reduces at least a maximum intensity frequency component of the reception signal of the receiving probe;
The filter unit detects frequency components other than the maximum intensity frequency component in a fundamental wave band that includes the maximum intensity frequency component.
The ultrasonic inspection device according to claim 14, characterized in that the focal length of the receiving probe is longer than the focal length of the transmitting probe.
The ultrasonic inspection device according to claim 14, characterized in that the receiving probe is a non-focused probe.
The ultrasonic inspection device according to claim 14, characterized in that the wave number of the wave packet is 3 or more.
The ultrasonic inspection device of claim 14, characterized in that the full width at half maximum of the frequency spectrum of the fundamental wave band is 50% or less of the maximum component frequency, which is the frequency corresponding to the maximum intensity frequency component.
The ultrasonic inspection device according to claim 14, characterized in that the transmitting probe is a narrowband probe.
The ultrasonic inspection device according to claim 14, characterized in that the filter section includes a band-stop filter.
The ultrasonic inspection device according to claim 14, characterized in that the filter section includes a low-pass filter.
The filter unit includes:
a frequency component converter for converting a received signal of the receiving probe into a frequency component;
a frequency selection unit that selects the base component by removing a frequency band including the maximum intensity frequency component;
15. The ultrasonic inspection apparatus according to claim 14, further comprising:
The filter unit includes:
a detection unit that detects a plurality of different base components of the fundamental wave band in a relationship between frequency and signal intensity obtained by irradiating the ultrasonic beam to a healthy portion and a defective portion of a sample having a known position of the defective portion;
15. The ultrasonic inspection device according to claim 14, further comprising a determination unit that determines which of the detected plurality of the footing components is to be used by comparing the detected plurality of footing components with each other.
The ultrasonic inspection device of claim 14, characterized in that the distance between the sound axis of the transmitting probe and the sound axis of the receiving probe is greater than zero.
The ultrasonic inspection device according to claim 14, characterized in that the distance between the sound axis of the transmitting probe and the sound axis of the receiving probe is zero.
1. An ultrasonic inspection method for inspecting an object to be inspected by irradiating an ultrasonic beam onto the object to be inspected through a gas, comprising:
An emission step of emitting an ultrasonic beam of a repetitive wave packet composed of a wave packet having a wave number of two or more from a transmission probe;
a receiving step of receiving the ultrasonic beam;
a filtering step of reducing a maximum intensity frequency component of the signal of the ultrasonic beam received in the receiving step;
and a signal intensity calculation step of detecting a base component of a fundamental wave band of the ultrasonic beam signal.
The ultrasonic inspection device according to claim 14, characterized in that the frequencies detected by the filter unit include frequencies in the range of (fm ± 0.25 fm), where fm is the maximum component frequency, which is the frequency corresponding to the maximum intensity frequency component.
The ultrasonic inspection device according to claim 14, characterized in that the frequencies detected by the filter unit include frequencies in the range of (fm ± 0.15 fm), where fm is the maximum component frequency, which is the frequency corresponding to the maximum intensity frequency component.
The ultrasonic inspection device according to claim 14, characterized in that the transmitting probe is installed so that the transmission sound axis of the transmitting probe is perpendicular to the mounting surface of the sample stage on which the object to be inspected is placed.