JPS60227163A - Electromagnetic ultrasonic transducer for transversal wave using high-frequency magnetic core - Google Patents

Abstract

PURPOSE:To excite a transversal wave having the polarization plane in a specified direction and to avoid provision of signal transmitting and receiving coils near an object to be detected by combining E- or U-shaped magnetic cores, winding an excitation coil for generating bias to a central leg and winding the transmitting and receiving coils to both legs on the outside. CONSTITUTION:A magnetic flux 23 of DC is generated in the E-shaped magnetic core 21 and the magnetic field perpendicular thereto is generated on the surface of the object 24 to be detected if the excitation coil 22 for generating the bias magnetic field is wound to the central leg of the core 21 and if DC current is passed thereto. Induced eddy current 27 flows to the surface of the object 24 if a high-frequency magnetic flux 26 shown by a broken line is generated in the core 21 by passing high-frequency current to the transmitting coils 25 wound on both legs on the outside. Approximately uniformly distributed Lorentz force 28 is generated in parallel with the surface of the object to be detected by the interaction between the bias magnetic field 23 and the induced eddy current 27, by which the transversal wave of the plane wave is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transducer for transverse wave electromagnetic ultrasonic flaw detection useful for flaw detection of intermediate materials.

A conventional electromagnetic ultrasonic transducer for transverse waves has a structure as shown in FIG. Fig. 1 shows a configuration in which an electromagnet is formed by a cylindrical iron core IJ and an excitation coil I2 attached to the cylindrical core, and spiral spiral coils are arranged as a transmitting coil 13 and a receiving coil 14 on the lower end surface of this electromagnet. belongs to. Next, the principle will be explained based on FIG.

When a direct current is passed through the excitation coil 12, a bias magnetic field is applied to the surface 15 of the subject in a perpendicular direction. Next, when a high frequency current is passed through the transmitting coil 13, a high frequency eddy current having a circular distribution approximately the same shape as the spiral coil is induced on the surface J5 of the subject. Due to the interaction between this induced eddy current and the magnetic field perpendicular to the surface of the object, a Lorentz force 16 is generated on the surface 15 of the object, and a transverse ultrasonic wave is excited. However, in the structure shown in FIG. 1, since the transmitting coil 13 is circular, the Lorentz force 16 acting on the object surface 15 is directed in the radial direction, and its distribution is circular, so that the excited ultrasonic waves are radially distributed. It is a transverse wave with a vibrational displacement of .

By the way, conventional piezoelectric transformer. In the ultrasonic flaw detection method using , -sa, transverse waves with uniform polarization plane are used. There's a problem. Furthermore, since the transmitter/receiver coil is provided under the electromagnet, the distance between the electromagnet and the subject increases accordingly, which may lead to a decrease in the bias magnetic field and deteriorate the wave transmitter/receiver sensitivity.

The present invention was made in view of the above points, and excites a transverse wave close to a pure plane wave with a plane of polarization in a certain direction,
Another object of the present invention is to provide a transducer having a structure in which no transmitter/receiver coil is provided near the subject.

The principle of the present invention will be explained below with reference to FIG.

In the figure, when a direct current is passed through the excitation coil 22 for bias magnetic field generation wound around the center leg of the E-shaped high frequency magnetic core 21, a direct current magnetic flux 23 is generated in the magnetic core 21, and this is generated on the surface of the object 24. A magnetic field perpendicular to is applied. Next, the transmitting coil 25 is connected with a polarity such that the magnetic flux generated by the coil current circulates through the outer legs of the magnetic core, and when a high-frequency current is passed through this, high-frequency magnetic flux 26 is generated in the magnetic core 21 as shown by the broken line in the figure. However, this magnetic flux 26 cannot enter the subject 24, and an induced eddy current 27 flows on the surface of the subject so as to satisfy the boundary conditions. As a result, the interaction between the bias magnetic field 23 and the induced eddy current 27 occurs in the portion directly below the central leg of the E-shaped magnetic core 21! A Lorentz force 28 having a substantially uniform distribution in the left direction parallel to the object surface is generated, and a transverse plane wave is excited. However, in the configuration shown in FIG. 2, at the same time as the Lorentz force 28, a Lorentz force 29 is generated that is perpendicular to the surface of the object and has an obliquely symmetrical distribution, which is considered to be the cause of an unnecessary response. Another example of the present invention is shown in FIG. 3 as a method for solving this problem.

In FIG. 3, the principle is almost the same as that in FIG. 2, but the excitation coil 22 in FIG.
An excitation coil 32 similar to the above is wound.

This excitation coil 32 supplies a bias magnetic field 23 perpendicular to the surface 24 of the subject. Furthermore, a transmitting coil 34 is wound around both legs of a U-shaped high-frequency magnetic core 33 arranged to three-dimensionally intersect the E-shaped magnetic core at almost right angles, and a high-frequency current is passed through this to generate an eddy current 27 on the surface of the subject. Induce. Due to the bias magnetic field 23 and the induced eddy current 27, the Lorentz force 28 has a uniform distribution in the direction parallel to the surface of the object to be examined.
occurs, and a transverse plane wave is excited. The structure shown in FIG. 3 is different from the structure shown in FIG. 2 and is thought to be the cause of unnecessary responses during flaw detection. It is considered that the longitudinal wave 29 is hardly excited.

Although the wave transmission operation has been described above, it goes without saying that transverse wave reception is also possible due to the reversibility of the conversion.

In the transverse wave electromagnetic ultrasonic transducer using a high-frequency magnetic core as shown in FIGS. 2 and 3 of the present invention, the high-frequency magnetic flux generated by the transmitting coil circulates through the high-frequency magnetic core. Since the transmitting and receiving coils do not necessarily need to be provided near the surface of the subject as in the conventional method, the distance between the transducer and the subject can be increased accordingly. moreover.

If a U-shaped or E-shaped magnetic core with a large leg spacing is used, a bias magnetic field and a high-frequency magnetic field can be applied over a long distance, so that testing can be performed with a larger distance between the transducer and the subject.

An embodiment of the present invention shown in FIG. 2 will be described below with reference to FIG. 4.

In FIG. 4, an E-shaped magnetic core is formed by bonding a shaped magnetic core 42 to the center of the abdomen of a U-shaped high-frequency magnetic core 41. Both legs of the engineered magnetic core 41, except for surfaces 43a and 43b facing the subject, are covered with insulating layers 44a and 44b, and the outside thereof is covered with shield plates 45a and 45 made of copper plates with a normal thickness of 0.2, for example.
Covered with b.

Further, insulating layers 46a and 46b are applied again to the outside of the shield plates 45a and 45b, and transmitting coils 47a and 46b are applied to the outside of the shield plates 45a and 45b.
47b. Shield plate 45a.

45b is partially cut and insulated so as not to form a short circuit surrounding the shaped magnetic core 41.

The transmitting coils 46a and 46b are connected so that high frequency magnetic flux generated by the coil current circulates through the shaped magnetic core 41. Note that the transmitting coil 47a.

The number of turns of 47b must be, for example, 12 turns each. If necessary, it is wrapped in two or more layers.

After applying an insulating layer 48 to the central shaped magnetic core 42.

An excitation coil 49 for generating a bias magnetic field is wound.

The number of turns of the excitation coil 49 is, for example, 20, and if necessary, the excitation coil 49 may be wound with a larger number of turns or two or more layers.

In Fig. 4, the method of configuring the E-shaped magnetic core is not necessarily limited to the combination of two shaped magnetic cores, but it is also possible to use two shaped magnetic cores to form the E-shaped core, and as a material for the high-frequency magnetic core, it is possible to form an E-shaped core. Any magnetic material may be used as long as it has low eddy current loss in a high frequency band (several tens of kHz or more). In addition, the excitation coil wound around the shaped magnetic core is simply used to generate a magnetic field perpendicular to the surface of the test object, and high-frequency magnetic flux does not pass through this part, so the material of the shaped magnetic core is not necessarily the same. It is not necessary to use a high frequency magnetic core, and two ordinary iron cores may be used. Furthermore, it is also possible to use a permanent magnet instead of the I-shaped magnetic core, thereby omitting the excitation coil and excitation current. By the way, the shield plates 45a and 45b are the transmitting coil 47a,
47b is intended to reduce the leakage of high frequency magnetic flux generated in the U-shaped magnetic core 41, and the shield plate 4
The principle of the explosion of the transformer does not change depending on the presence or absence and shape of 5a and 45b. Furthermore, it is also possible to receive ultrasonic waves with the same structure as shown in FIG.
Although 47b can also be used as a receiving coil, a structure in which a transmitting coil and a receiving coil are provided separately is also conceivable. Therefore, changes to the above items do not go beyond the scope of the present invention. These things are the same when implementing FIG. 3.

Next, a block diagram of an experimental apparatus for measuring the characteristics of the electromagnetic ultrasonic transducer for transverse waves as described above is shown in FIG. 5, and will be explained. An aluminum block or an iron block was used as the test object 51 in this case.

As the transmitting transducer 52, the one shown in FIG. 4 was used, and the high-frequency magnetic core of the transducer 52 was made by cutting a 50 μm thick silicon steel plate wound core. As the receiving transducer 53, an electromagnetic ultrasonic transducer for transverse waves using a conventional periodic structure magnet shown in FIG. 6 was used.

In FIG. 5, 54 indicates the trigger iJ? rus generator.

Reference numeral 55 is a pulse delay circuit, and reference numeral 56 is an instantaneous large current generating circuit for bias having a configuration as shown in FIG.

The circuit 56 is charged by the DC power supply 61 and triggers the electric charge of the PC capacitor and triggers the pulse generator 54.
When the SCR is turned on at 9 pulses, a resonance discharge is caused and a low frequency large current is supplied to the excitation coil 49.

57 is a transmitting circuit having a configuration as shown in FIG.
The circuit 57 causes the charge of the capacitor charged by the high-voltage DC power supply 81 to be resonantly discharged by turning on the discharging switch with a pulse of the delay generator.
A high frequency large current is supplied to the transmitting coils 47a and 47b. The transmission transducer 52 is driven after the pulse is delayed by the pulse delay circuit 55 so as to generate ultrasonic waves when the discharge current to the excitation coil 49 is almost at its maximum. added to the circuit.

On the other hand, the ultrasonic waves propagated inside the subject are received by the receiving transducer 53, and the output of the receiving transducer 53 is obtained by using a wideband amplifier with an input impedance of, for example, 50Ω and a gain of 40 dB, and the waveform thereof is, for example, Observe and measure with an oscilloscope. Further, 58 is a spacer having a thickness of, for example, 0.85 mm1 between the receiving transuser and the subject.

Characteristic diagrams obtained based on the experimental block diagram as described above are shown in FIGS. 9 and 10. First, the 9th
The figure is a characteristic diagram showing the relationship between the transmission sensitivity and the magnitude of the current of the excitation coil 49 for generating a bias magnetic field. However, in this experimental example, the air gap length 59 of the transmitting transducer was set to 40
μm, and the voltage of the high-voltage DC power source 81 for transmission was 16 kV. Examining the characteristic diagram, we can see that when using an iron block as the test object, a higher transmission sensitivity is obtained than when using an aluminum block. This is thought to be due to the large magnetic permeability, which reduces the magnetic resistance of the magnetic circuit that supplies the bias magnetic field, increasing the bias magnetic field.

Next, FIG. 10 is a diagram showing the relationship between the transmission sensitivity and the gap length 59 of the transmission transducer. In this example experiment,
The magnitude of the current of the excitation coil 49 for bias magnetic field generation is set to 5.
00A, and the voltage of the high-voltage DC power source 81 for transmission was set to 16 kV. Similar to FIG. 8, when the iron block is used as the object, a greater transmission sensitivity is obtained than when the aluminum block is used, but when the gap length 59 is gradually increased.

The rate of decrease in transmission sensitivity is smaller in the case of aluminum blocks than in the case of iron blocks. However, it can be seen that even when the distance between the transducer and the subject is 5 or more, ultrasonic waves are transmitted with sufficient sensitivity both when the subject is an iron block or aluminum.

Since this application uses a low roller that acts on induced eddy currents, it can be used as a non-contact transducer.As in the case of piezoelectric transducers, the coupling medium between the transducer and the test object is Not necessary. As a result, it can be used as a sensor to inspect 1) materials with uneven surfaces, 9) materials whose surfaces are coated with paint, high-temperature objects, or objects that move at high speed, especially for checking for cracks and internal defects in these objects. be.

Since the present application uses transverse electromagnetic ultrasound, it is possible to measure even if the object to be examined is a magnetic material without losing its sensitivity.

[Brief explanation of drawings]

Fig. 1 is a principle diagram of an electromagnetic ultrasonic transducer for transverse waves constructed using a conventional spiral coil, and Fig. 2 is a diagram of the principle of an electromagnetic ultrasonic transducer for transverse waves using the E-shaped high frequency magnetic core of the present invention. Figure 3 is a diagram of the principle of an electromagnetic ultrasonic transducer for transverse waves that has a structure in which E-shaped and U-shaped high-frequency magnetic cores are orthogonal to each other. The figure which shows the Example of the electromagnetic ultrasonic transducer for transverse waves. Figure 5 is a block diagram of the experiment for measuring characteristics, Figures 6 and 7 are the instantaneous large current generation circuit and transmission circuit for generating bias magnetic field, respectively, and Figure 8 is the relationship between transmission sensitivity and excitation current. FIG. 9 is a characteristic diagram showing the relationship between the transmission sensitivity and the distance between the transducer and the subject. Child 3 Figure 6 Figure 7 Figure 8 Section Excitation current (A)

Claims (1)

[Claims] 1) Applying a bias magnetic field almost perpendicularly to the surface of a metal object using an electromagnet or a permanent magnet, and generating a high-frequency magnetic field whose main component is parallel to the surface of the object in the biased region. For detection, a high-frequency magnetic core with an open magnetic path is placed, and a transmitter/receiver coil is wound around it.
An electromagnetic ultrasonic transducer for transverse waves, characterized in that it generates and detects transverse ultrasonic waves having vibrational displacement in the direction of the high-frequency magnetic field. 2) Using a high-frequency magnetic core having an E-shape, or a U-shape (or C-shape, U-shape, etc.) high-frequency magnetic core with an I-shaped iron core attached to the center to make an E-shape, An excitation coil for generating a bias magnetic field is wound around the central leg of the magnetic core, and transmitting/receiving coils are wound around the outer legs. The electromagnetic ultrasonic transducer for transverse waves according to item 1 above, characterized in that it is constructed by connecting a receiving coil. 3) An E-shaped magnetic core wrapped with an excitation coil PV to generate a perpendicular bias magnetic field just below the central leg. The electromagnetic ultrasonic wave for transverse waves according to item 1 above, characterized in that a U-shaped (or C-shaped, U-shaped, etc.) high-frequency magnetic core around which transmitting/receiving coils are wound is arranged so as to intersect three-dimensionally. Transnosa. 4) In the transformer of items 2) and 3) above,
An electromagnetic ultrasonic transformer for transverse waves, characterized in that a part of the E-shaped magnetic core is made into a permanent magnet, thereby eliminating the need for an excitation coil and excitation current.