JPH0538562U - Electromagnetic ultrasonic probe - Google Patents

Abstract

(57) [Summary] [Purpose] To prevent the saturation of the receiving amplifier due to the excitation pulse current during transmission, and to enable inspection from one direction of the object with a single miniaturized probe. [Structure] Excitation pulse current I input during transmission
Is supplied to the cylindrical coil 12 and the spiral coil 14 to excite each coil in parallel. The excitation pulse current I that excites the cylindrical coil 12 and the vortex coil 14 is the clamp circuit 1
5 and then to ground (GND). Since the output terminals of the clamp circuit 15 are kept at the same potential, no potential difference occurs between the input terminals of the isolation amplifier. Further, upon reception, the coils are in series and voltages are generated in opposite directions. However, due to the difference in the receiving ability of the coils, almost only the received signal from the spiral coil 14 is obtained, this is amplified by the insulating amplifier 16 and output as a received signal.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 This invention relates to an electromagnetic ultrasonic probe applied to nondestructive inspection of structures (plants).

[0002]

[Prior Art]

 BACKGROUND ART Conventionally, an electromagnetic ultrasonic probe (hereinafter referred to as EMAT) is one of ultrasonic probes used for nondestructive inspection of a conductive object. The operating principle of this EMAT is shown in FIG.

The magnetic flux B generated from the magnet body 1 made of a permanent magnet or an electromagnet is made conductive by passing a pulsed high frequency current I through a coil 3 provided between the magnet body 1 and the subject 2. An eddy current J is generated on the surface of the subject 2. The Lorentz force F is generated by the interaction between the eddy current J and the magnetic flux B. Further, ultrasonic waves S are generated by using the Lorentz force F as a vibration source. Further, when receiving the ultrasonic wave S, the ultrasonic signal is converted into an electric signal in the reverse process of the above-described ultrasonic wave generation. An example of EMAT using the above principle is shown in FIG.

A magnet 4 a is provided on one side of the subject 2, and transmission coils 5 a and 5 b are arranged in parallel between the magnet 4 a and the subject 2. Here, the transmission coil 5a is used as a comparison coil, and the transmission coil 5b is used as a measurement coil. The excitation pulse current I is supplied to the transmission coils 5a and 5b.

A magnet 4b is provided on the opposite side of the subject 2, and receiving coils 6a and 6b are juxtaposed between the magnet 4b and the subject 2, and the receiving coil 6a is used as a comparison coil and a receiving coil 6b. Is the measuring coil. The receiving coils 6a and 6b are connected to the amplifiers 7a and 7b, respectively, so that the received signals can be amplified. Further, since the amplifiers 7a and 7b are connected to the differential amplifier 8, the difference between the two amplifiers can be taken out.

The transmitter coils 5a and 5b generate ultrasonic waves when supplied with the excitation pulse current I. Here, when the defect 9 exists in the subject 2, the receiving coil 6a which is the comparison coil and the receiving coil 6b which is the measurement coil receive different signals. The two different received signals are amplified by the amplifiers 7a and 7b, and then the differential amplifier 8 extracts the difference between the two received signals. As a result, it is possible to eliminate the equal effect of the transmitted wave or the like on the receiving coils 6a and 6b, and only the signal caused by the presence or absence of the defect 9 is output as the received signal.

[0007]

[Problems to be solved by the device]

 However, in the above-mentioned conventional method, the electroacoustic conversion efficiency in EMAT is generally low, so that a large current flows on the transmitting side and a weak current (signal) is detected on the receiving side. Therefore, when inspecting from one side of the subject, when the transmitter coil and the receiver coil are placed close to each other, the pulse current at the time of excitation causes a very large current (voltage) compared to the signal from the defect in the receiver coil. ) Is induced. This current (voltage) causes saturation of the receiving amplifier, etc., resulting in an unmeasurable state (dead zone). This dead zone makes it impossible to detect signals from defects near the surface.

Further, as shown in the above-mentioned conventional example, when the differential signal by the two sets of coils is taken out, the level difference between the transmission signal (excitation pulse current) and the received signal is large, so that the two sets of coils are Even if the arrangement, shape and characteristics are slightly different, the dead zone is generated as described above. It is very difficult to match the arrangement, shape, and characteristics of these two sets of coils so as not to generate a dead zone. Further, in the above-mentioned conventional example, the transmission signal is not removed and the differential signal is extracted. Adding a structure will make the probe larger.

The present invention has been made in view of the above circumstances, and it is possible to perform inspection from one side of a subject and prevent saturation of a reception amplifier due to an excitation pulse current at the time of transmission. It is an object of the present invention to provide an electromagnetic ultrasonic probe.

[0010]

[Means for Solving the Problems]

 The electromagnetic ultrasonic probe according to the present invention is composed of a tubular coil and a vortex coil. The above coils are arranged in parallel during transmission and the coils are arranged in series during reception. And a means for amplifying an electric signal generated in the clamp circuit.

[0011]

[Action]

 During transmission, the input excitation pulse current is supplied to the cylindrical coil and the spiral coil to excite each coil. At this time, by exciting the two coils in parallel, the transmission capability for generating ultrasonic waves is doubled. The excitation pulse current that excites the cylindrical coil and the vortex coil is input to the clamp circuit and further to the ground (GND). At this time, since the output terminals of the clamp circuit are kept at the same potential, no potential difference occurs between the input terminals of the isolation amplifier.

At the time of reception, the above-mentioned coils are in series and voltages are generated in opposite directions. However, due to the difference in the receiving ability of the coils, it is possible to obtain only the received signal from the spiral coil.

[0013]

【Example】

 An embodiment of the present invention will be described below with reference to the drawings. The overall structure of the electromagnetic ultrasonic probe (EMAT) according to the present invention is shown in FIG. 1, and a development view of the probe portion of this EMAT is shown in FIG.

A cylindrical coil 12 is arranged inside a columnar magnet 11 vertically divided into a plurality of parts in the SN direction, and the spiral coil 1 is provided between the magnet 11 and the cylindrical coil 12 and a subject 13. 4 are provided. The spiral coil 14 has better conversion efficiency between ultrasonic waves and electric signals in transmission and reception than the cylindrical coil 12. For this reason, the cylindrical coil 12 is set so as to generate ultrasonic waves in the subject 13 at the same level as the spiral coil 14 by using the magnet 11 and further increasing the number of coil turns during transmission. To be done.

An excitation pulse current I is supplied to the cylindrical coil 12 and the vortex coil 14 to generate ultrasonic waves in the subject. The cylindrical coil 12 and the spiral coil 14 are connected to a clamp circuit 15, and the clamp circuit 15 is connected to an insulating amplifier 16. The characteristics of the elements (diodes) applied to this clamp circuit are all the same. Next, the operation of the above embodiment will be described with reference to FIG. 3 showing the electrical connection of the electromagnetic ultrasonic probe.

During transmission, the input excitation pulse current I is supplied to the cylindrical coil 12 via the terminals c and d, further via the terminal b, and to the spiral coil 14 via the terminal e. Excite. At this time, by exciting the two coils in parallel, it is possible to double the transmission capability for generating ultrasonic waves. The excitation pulse current that excites the cylindrical coil 12 is input to the clamp circuit 15 via terminals a and g, and the excitation pulse current that excites the vortex coil 14 is input to the clamp circuit 15 via terminals f and h. Input to the ground (GND) respectively. At this time, the terminals g and h are kept at the same potential by the clamp circuit 15, so that no potential difference occurs between the input terminals of the isolation amplifier 16. Next, the operation at the time of reception will be described.

The signal received by the tubular coil 12 is Vab, and the signal received by the spiral coil 14 is Vef. At this time, since voltages are generated in the respective coils in opposite directions, the received signal (Vgh) received by the probe is Vgh = Vaf = Vef to Vab (1)

Is represented by At this time, the cylindrical coil 12 has a much lower reception capacity than the spiral coil 14, and therefore the voltage generated in each coil has a relationship of Vef >> Vab. Therefore, the above equation (1) becomes

[0019]

[Equation 1] The received signal represented by the equation (2) is amplified by the isolation amplifier 16 and output as a received signal. In the above-mentioned probe portion, the cylindrical coil 12 may have a shape surrounding the outer circumference of the columnar magnet 11.

[0020]

[Effect of the device]

 As described above in detail, according to the present invention, the probe is formed by using the cylindrical coil and the vortex coil, and the clamp circuit is further provided, so that the saturation of the receiving amplifier due to the excitation pulse current at the time of transmission is caused. It is possible to perform inspection from one direction of the subject with a single probe.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an electromagnetic ultrasonic probe according to an embodiment of the present invention.

FIG. 2 is a development view of a probe unit of the electromagnetic ultrasonic probe in the example.

FIG. 3 is a circuit configuration diagram of the electromagnetic ultrasonic probe according to the embodiment.

FIG. 4 is a principle diagram of an electromagnetic ultrasonic probe.

FIG. 5 is an overall view of a conventional electromagnetic ultrasonic probe.

[Explanation of symbols]

11 ... Magnet, 12 ... Cylindrical coil, 13 ... Subject, 14 ...
Vortex coil, 15 ... Clamp circuit, 16 ... Isolation amplifier.

Claims (1)

[Scope of utility model registration request] 1. An electromagnetic ultrasonic probe comprising a cylindrical coil and a vortex coil, wherein each coil transmits a current by exciting in parallel the current for exciting the coil. Of the electromagnetic transducer, which includes a probe for receiving the signal in series, a clamp circuit provided on the signal output side of the probe, and means for amplifying an electric signal generated in the clamp circuit. Sonic probe.