JPS63139250A - Electromagnetic-ultrasonic transducer apparatus - Google Patents

Abstract

PURPOSE:To generate ultrasonic waves having a plurality of frequencies by one electromagnetic-ultrasonic transducer (EMAT), by providing EMAT, a transmission coil and a receiving coil. CONSTITUTION:EMAT consisting of a magnet generating a magnetic field in the direction parallel or vertical to a surface to be inspected and three coils arranged to the surface of the magnet in a zigzag pattern so as to be shifted by a 1/3 pitch to each other is provided. Further, transmission coils 3a-3c supplying currents same in frequency to three coils with respect to a plurality of frequencies so as to shift the same by a definite phase and receiving coils 3a'-3c' receiving the receiving signals of three coils so as to delay the same by delay circuits 7a-7c corresponding to respective transmission phase shifts with respect to each of the frequencies are provided. By this method, ultrasonic waves having a plurality of frequencies can be generated by one EMAT.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electromagnetic ultrasonic transducer device used for ultrasonic detection of structures and the like.

[Conventional technology]

Conventional longitudinal wave oblique electromagnetic ultrasound transducer (hereinafter referred to as E)
MAT5) is, for example, shown in Fig. 6 (A) front view, (B)
As shown in the bottom view, the magnetic field generating portion that generates a magnetic field in a direction parallel to the test surface, such as the magnet 1 and the deflector 2, and the pitch T
When a current of frequency f is passed through coil B, as shown in the explanatory diagram in Fig. 7,
An eddy current J is generated in a direction perpendicular to the plane of the paper, and the direction of this eddy current is reversed at a pitch T. On the other hand, the magnet 1 generates a horizontal magnetic field B, which interacts with the eddy current J to generate a magnetic field F, which excites each part of the coil B.

At this time, the direction of the force F is reversed by the pitch T, and the phases of the ultrasonic waves generated by the excitation differ by 180°.

Therefore, the wavefronts of the ultrasonic waves from each point match when the following equation (1) is satisfied, and the composite wavefront W propagates through the subject 10 in the direction of the refraction angle θ.

Tssin O=V/(2f) s・*・
o fl) The velocity V is the sound velocity of the ultrasound in the subject 1o.

Note that image reception is performed using the reverse mechanism described above.

However, in such a device, as is clear from equation (1), the refraction angle θ and coil pitch T are fixed, so the frequency is constant), and the necessary ultrasonic waves cannot be obtained at other frequencies. I can't.

Therefore, one EMAT can efficiently generate only one frequency, and if it is desired to change to a different frequency when investigating the characteristics of a defect, it is necessary to replace two or more EMATs with different coil pitches.

[Problem that the invention seeks to solve]

The present invention was proposed in view of these circumstances, and
An EMA device that can generate ultrasonic waves of multiple frequencies with one EMAT, and therefore does not require replacing the EMAT depending on the characteristics of the defect.

[a stone whose purpose is to provide [Failure to solve the problem]

To this end, the present invention provides an electromagnetic ultrasonic transducer comprising a magnet that generates a magnetic field in a direction parallel or perpendicular to the surface to be inspected, and three coils arranged meanderingly on the surface of the magnet, shifted by h pitches from each other; A transmission circuit that sends currents of the same frequency to multiple frequencies with a certain phase shift to the three coils, and a transmission circuit that delays the received signals of the three coils according to the transmission phase shift for each frequency. and a receiving circuit for receiving signals.

[For production]

With the above configuration, one EMAT can generate ultrasonic waves of multiple frequencies, and therefore the EMAT can generate ultrasonic waves of multiple frequencies depending on the characteristics of the defect.
It is possible to obtain an EMAT without the need to replace the MAT.

〔Example〕

An embodiment of the present invention will be explained with reference to the drawings. Fig. 1 shows the longitudinal wave oblique angle E MAT main body, Fig. 1 (A) is a front view, Fig. 2 (B) is a bottom view, and Fig. 2 is E A system diagram of the entire MAT device, FIG. 3 is a waveform diagram of the current flowing through the coil, FIG. 4 is an explanatory diagram of the oblique incidence mechanism, and FIG. 5 is a bottom view of the EMAT for transverse waves.

First, in FIG. 1 showing the main body of the longitudinal wave oblique angle E MAT, a magnetic field Q generating portion is constituted by a magnet 1 and a pair of commutated poles 2, and three coils 3a and 3b.

3C meander like a rectangular wave with a pitch T, and are arranged to be shifted from each other by a pitch of T/3.

In FIG. 2 showing the device configuration when transmitting and receiving using this EMAT, each transmitting coil 5a, 3b
, 3c are connected to transmitters 4a, 4b, 4c, respectively. The transmission controller 5 controls the generation of repeated pulses for performing comb-back transmission and the oscillation frequency and phase to each transmitter 4a to 4C.

In addition, each receiving coil 3a, 3b having the same configuration as the transmitting coil,
3c are connected to amplifiers 6a, 6bs6C, respectively, and the outputs of each amplifier are connected to delay circuits 7a, 7b, 7, respectively.
The signals are added by the adder circuit 8 via the signal line c and displayed on the display 9.

In such a device, an ultrasonic wave with a frequency f is refracted at a refraction angle θ
We will explain the operation when it is incident.

As shown in FIG. 3, the transmitters 4a to 4C generate transmission currents having a frequency f and phases different from each other by 60°. At this time, as shown in FIG. 4, eddy currents are generated at points d, e, and f, and ultrasonic waves are generated from these points. dg, eh
, fi are calculated as follows using equation (1):
(It will look like formula 41.

dg = T-sin θ=2, ・,, +
,b;5=S'I"5sinθ=mu
Conflict... (3) λ = = j - T - sin θ = - (43) where λ is the wavelength of the ultrasonic wave (= V/f) The above lengths are:
Compared to the adjacent one, it is 2/6 (60 in terms of phase)
This matches the phase of the transmission current shown in FIG. Therefore, the phases of the wavefronts of the ultrasonic waves match in the direction of the refraction angle θ, forming a composite wavefront, and generating an ultrasonic wave with the refraction angle θ.

Next, one example will be described in which the frequency is increased six times, currents of 3f are applied to the coils 3a, 3b, and 3c with a phase change of 180, and the generated ultrasonic waves are incident at a refraction angle θ.

In this case, the frequency is tripled in the above formulas (2), (31, and (43), so the relationship between the wavelength λ1 and the wavelength λ at this time is as shown in the following formula.

λ: 3λ, e, 5es (51 Substituting this into (2), (3), (4) gives the following (6
) to (8) are obtained.

−3−−−−−f6) dg=,λ1 eh−λseems(7)Wealth=1λ
...(8) The difference between these is iλ
1 (or 180 in terms of phase), which matches the phase of the transmission current, so that an ultrasonic wave is generated in the direction of the refraction angle θ.

Next, reception will be explained. Ultrasonic signals having a phase shift as described above are detected in contrast to the transmission, so these are amplified by amplifiers 6ae6b and 6c, respectively, and the phase shift is corrected by delay circuits 7a and 7b. 7c, these are combined by an adder circuit 8 and displayed on a display 9.

Also, the refraction angle θ is set to 90 degrees, and the sound velocity is changed to a surface wave (approximately 290 degrees).
0 m/s), the same thing can be implemented as a surface wave EMAT.

Furthermore, if the magnet structure is changed as shown in FIG. 5 so that a magnetic field is generated in a direction perpendicular to the surface to be measured, a transverse wave EMAT can be constructed and a similar effect can be produced.

〔Effect of the invention〕

In short, according to the present invention, an electromagnetic ultrasonic transducer includes a magnet that generates a magnetic field in a direction parallel or perpendicular to the surface to be inspected, and six coils arranged meanderingly on the surface of the magnet, shifted by 73 pitches from each other. , a transmission circuit that sends currents of the same frequency to multiple frequencies with a certain phase shift to the six coils, and a transmission circuit that delays the received signals of the six coils at each frequency according to the transmission phase shift. Because it is equipped with a receiving circuit for receiving data over and over
The present invention is extremely useful industrially because it provides an EMAT that can generate ultrasonic waves of multiple frequencies with one EMAT and therefore does not require replacing the EMAT depending on the characteristics of the defect.

[Brief explanation of the drawing]

Figures 1 to 4 show the electromagnetic ultrasonic transducer of the present invention.
This shows an example in which the device is applied to a longitudinal wave oblique EMAT. Figure 1 shows the main body of the EMAT, Figure (A) is a front view, Figure (B) is a bottom view, and Figure 2 is the EMAT. A system diagram of the entire device, Figure 3 is a waveform diagram of the current flowing through the same coil as above, and Figure 4 is a diagram of the current flowing through the same coil.
The figure is an explanatory diagram of the oblique incidence mechanism same as above, and FIG. 5 is a bottom view of the EMAT for transverse waves. Fig. 6 shows the conventional longitudinal wave oblique angle E M A T, and the same figure (
A) is a front view, CB) is a bottom view, and FIG. 7 is an explanatory diagram of the same operation. 1...Magnet, 2...Capture, 3a, 3b, 3c...
Transmitting coils, 3a, 3b', 3c'...Receiving coil 4
a, 4b, 4c...transmitter, 5...transmission controller, 6a, 6b, 6C...amplifier,
7a. 7b, 7c...delay circuit, 8...addition circuit, 9...
·display. Sub-Agent Patent Attorney Masa Tsukamoto Figure 1 (A) CB) Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Scope of Claims] An electromagnetic ultrasonic transducer consisting of a magnet that generates a magnetic field in a direction parallel or perpendicular to a surface to be inspected, and three coils arranged in a meandering manner on the surface of the magnet, shifted by 1/3 pitch from each other; A transmission circuit that sends currents of the same frequency to multiple frequencies with a certain phase shift to the three coils, and a transmission circuit that delays the received signals of the three coils according to the transmission phase shift for each frequency. An electromagnetic ultrasonic transducer device comprising: a receiving circuit for receiving signals.