JPS6333440Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an electromagnetic acoustic transducer used for ultrasonic flaw detection of a specimen.

As an electromagnetic acoustic transducer (hereinafter abbreviated as EMAT) for performing ultrasonic flaw detection on a test object such as a steel plate, a structure shown in FIGS. 1 and 2 is conventionally known. That is, 1 in the figure is a disk-shaped core, and this core 1 has a ring-shaped groove 2 formed therein. An excitation coil 3 is loaded into the groove 2 of the core 1 . A ring-shaped transmitting coil 4 is disposed close to the circular bottom surface surrounded by the groove 2, and the coil 4 is disposed close to the bottom surface.
There is a ring-shaped receiving coil 5 on the outer circular bottom of the
is close to the bottom surface and arranged in a circular shape with respect to the transmitting coil 4.

Next, the operation of the above-mentioned EMAT will be explained with reference to FIG.

First, EMAT is placed on a subject (conductor) 6 so that its transmitting coil 4 and receiving coil 5 face the subject 6, and when a high-frequency current is passed through the transmitting coil 4, the transmitting coil 4 An eddy current J is generated on the surface of the nearby subject 6. When the excitation coil 3 is energized in this state, a magnetic field B is applied from the core 1 to the surface of the subject 6, and their interaction generates a Lorentzka F, which causes the surface to vibrate and generate ultrasonic waves. .

Defect detection is performed by detecting ultrasonic waves by the receiving coil 5 using a mechanism opposite to that described above.

However, in the conventional EMAT described above, ultrasonic waves are generated not only in the subject 6 but also in the core 1 near the transmitting coil 4, and as shown in FIG. 3, the ultrasonic waves 7 are generated near the receiving coil 5. Since it returns as a noise component, it becomes impossible to distinguish it from the defect detection signal. As a result, there was an inconvenience that defect detection could not be performed reliably.

The present invention aims to provide an electromagnetic acoustic transducer that can easily detect only defective signals by preventing the generation of ultrasonic waves to the core and the like.

Hereinafter, the present invention will be explained in detail based on the embodiment shown in FIG. Note that members similar to those in FIG. 1 are given the same reference numerals and their explanations are omitted.

As shown in FIG. 4, the EMAT of the present invention has a structure in which a plate 8 made of a highly electrically conductive material such as copper is interposed between the core 1 and the transmitting coil 4.

Therefore, when the EMAT of the present invention is placed on a subject (not shown) so that the transmitting coil 4 and the receiving coil 5 face the subject, and when a high-frequency current is passed through the transmitting coil 4, the transmitting coil Eddy currents are generated in the object near 4. At this time, since the copper plate 8 is arranged on the core 1 side of the transmitting coil 4, an eddy current is only generated in the plate 8, and almost no eddy current is generated on the surface of the core 1. As a result, ultrasonic waves are generated in the plate 8 by the mechanism described above, but not in the core 1. Moreover, since the ultrasonic waves generated in the plate 8 do not propagate to the core 1, no ultrasonic waves enter the core 1. In addition, a receiving coil 5 disposed close to the core 1
Since it is separated from the plate 8, it is not affected by this plate 8. Therefore,
When a high-frequency current is passed through the transmitting coil 4 to generate an ultrasonic wave in the subject, and this ultrasonic wave is detected by the receiving coil 5, the ultrasonic wave that becomes a noise component is returned to the receiving coil 5 by the plate 8. Therefore, only the defective signal can be detected by the receiving coil 5,
As a result, defect detection can be performed reliably.

In the above embodiment, a core loaded with an excitation coil was used as a member for arranging the transmitting coil, etc., but the same effect can be achieved by using a permanent magnet instead.

As described in detail above, according to the present invention, it is possible to provide an electromagnetic acoustic transducer that can easily detect only a defect signal and, in turn, can reliably perform defect detection.

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing a conventional EMAT, Figure 2 is a plan view of the EMAT in Figure 1 seen from below, and Figure 3 is a schematic diagram showing a conventional EMAT.
The figure is a principle explanatory diagram showing the operation of EMAT in Figure 1.
FIG. 4 is a schematic diagram of EMAT showing an embodiment of the present invention. 1... Core, 3... Excitation coil, 4... Transmission coil, 5... Receiving coil, 6... Subject, 8
...A plate with high electrical conductivity.

Claims (1)

[Scope of utility model registration request] An electromagnetic acoustic transducer characterized in that a transmitting coil is disposed in the core of an electromagnet or a permanent magnet, and a plate with high electrical conductivity is interposed between the core or permanent magnet and the coil.