JPH11125622A - Sh wave electromagnetic ultrasonic transducer and measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To transmit and receive SH ultrasonic waves of a wide band in a short pulse waveform with high sensitivity, by disposing a plurality of alternately reversed permanent magnets with N, S poles arranged in a staggered manner with different distances. SOLUTION: A probe main body 3 of this SH wave electromagnetic ultrasonic transducer 1 has rectangular permanent magnets 2 alternately reversed with having N, S poles arranged in a staggered manner. Moreover, spacers 5 of different thicknesses are interposed between adjacent permanent magnets 2, and a rectangular flat coil 4 in plane is set below the probe main body 3. At this time, a distance between the permanent magnets 2 varies by the thickness of the spacer 5. SH waves generated when an alternating current is sent to the coil 4 have a chirp waveform corresponding to the distance of the permanent magnets 2. Since the distance between the permanent magnets varies from narrow to wide, SH waves can be oscillated in a wide band with high sensitivity from a short wavelength to a long wavelength.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a permanent magnet and an oscillator.
The present invention relates to an SH wave electromagnetic ultrasonic transducer having a receiving probe coil and a measurement method using the transducer.

[0002]

2. Description of the Related Art One of ultrasonic waves propagating through a plate material is an SH wave (horizontally polarized transverse wave). Since the SH wave propagates without being affected by the surface roughness or the like of the plate, it is suitable for flaw detection of internal defects of the plate material and measurement of physical properties. In addition, electromagnetic ultrasonic waves can be generated and detected in a non-contact manner with respect to a subject, and thus are often used where an acoustic coupling medium cannot be used. The flaw detection and the measurement of physical properties of a cold-rolled thin steel sheet are indispensable for the above two features. Therefore, Japanese Patent Laid-Open No. 1-23
SH waves are generated as described in
An electromagnetic ultrasonic transducer that can be detected has been invented.
FIG. 6 is a configuration diagram of a conventional SH-wave electromagnetic ultrasonic transducer. In this SH-wave electromagnetic ultrasonic transducer, a rectangular parallelepiped permanent magnet 2 is arranged with its magnetic pole surfaces on the front and back.
Further, it comprises a probe main body 3 arranged in a plate shape so that the N pole and the S pole are staggered, and a flat coil 4 having a rectangular shape in plan view.

FIG. 7 is an explanatory view showing the principle of generation and detection of SH waves (plate waves). As shown in FIG.
Is disposed immediately above the test object 7, and the permanent magnet 2 is disposed thereabove. The permanent magnet 2 generates a magnetic field B perpendicular to the surface of the test object 7 and acting alternately in the opposite direction corresponding to the direction of the magnetic pole of each permanent magnet 2, while passing an alternating current through the coil 4. As a result, eddy current I
Generate. Due to the interaction of the magnetic field B and the eddy current I,
A Lorentz force F parallel to the surface of the test object 7 and perpendicular to both the magnetic field B and the eddy current I is generated. The direction of the Lorentz force F is determined by the pitch of the width D of the permanent magnet 2. Invert 180 °. Such a Lorentz force F causes the metal grid of the test object 7 to vibrate in parallel to the surface, and forms an angle θ with respect to a direction perpendicular to the vibration direction, that is, the thickness direction of the test object 7. An SH wave (shown as H in the drawing) that propagates obliquely downward in the interior is generated.
Here, the wavelength of the SH wave is represented by the following equation (1). λ = v / f = 2D · sin θ (1) where λ: wavelength of SH wave v: sound velocity f: frequency of SH wave D: distance between centers of adjacent permanent magnets

[0004]

In the SH wave electromagnetic ultrasonic transducer according to the prior art, that is, the SH wave electromagnetic ultrasonic probe, permanent magnets are arranged at equal intervals, so that the SH wave generated on the object to be inspected is low. It becomes a burst wave shape,
There is a problem that the frequency band becomes narrow. Such ultrasonic waves are unsuitable for physical property measurement such as flaw detection and sound velocity measurement because of their low temporal resolution. In order to widen the frequency band, there is a method of reducing the number of permanent magnets. However, if the number of magnets is reduced, the sound pressure of the generated SH wave will be reduced.
There is a problem that S / N deteriorates during measurement.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an SH-wave electromagnetic ultrasonic transducer capable of transmitting and receiving a wide-band SH-wave ultrasonic wave with high sensitivity and a short pulse waveform, and a measuring method thereof. The purpose is to provide.

[0006]

The SH wave electromagnetic ultrasonic transducer according to the present invention has a magnetic pole alternately oriented front and back.
And a plurality of permanent magnets in which N and S poles are arranged in a staggered manner,
An SH wave electromagnetic ultrasonic transducer comprising the permanent magnet and a flat coil disposed between the test object,
The permanent magnets are arranged so as to be different from each other. Specifically, each permanent magnet is arranged via a nonmagnetic spacer having a different thickness.

[0007] With this configuration, the distance between the permanent magnets that determines the oscillation wavelength of the SH wave ranges from a narrow one to a wide one, so that it is possible to oscillate from a short-wave SH wave to a long-wave SH wave. is there. Further, since the probe can be broadened without reducing the number of magnets, the sound pressure of the oscillating SH wave does not decrease. Therefore, according to the present invention, a high-sensitivity, wide-band SH-wave electromagnetic ultrasonic transducer can be realized.

Further, the SH wave electromagnetic ultrasonic measuring method according to the present invention is a method in which the above SH wave electromagnetic ultrasonic transducer is flaw-detected by a two-probe flaw detection method using two transmitting and receiving transducers. It is.

Since the SH wave electromagnetic ultrasonic transducer of the present invention changes the interval between the permanent magnets arbitrarily, it generates a chirped SH wave corresponding to the spatial change. In fact, when the SH wave propagates, the SH wave propagates through the device under test in a form having a temporally changed frequency. When the SH wave is received using the SH-wave electromagnetic ultrasonic probe having the same permanent magnets as the SH-wave electromagnetic ultrasonic probe used for transmission, the SH-wave electromagnetic ultrasonic probe has a spatial change in the interval between the permanent magnets. A received signal can be obtained only when resonating in phase. this is,
This is equivalent to performing pulse compression by performing interphase processing on the transmission modulation signal and the reference modulation signal. As described above, the measuring method of the present invention enables flaw detection and measurement using pulsed SH waves.

[0010]

FIG. 1 is a block diagram showing an example of an SH-wave electromagnetic ultrasonic transducer according to the present invention. The probe main body 3 has rectangular parallelepiped permanent magnets 2 arranged so that the directions of magnetic poles are alternately turned upside down, and N poles and S poles are staggered. Are arranged by arranging spacers 5 having different characteristics. Then, a flat coil 4 having a rectangular shape in a plan view is arranged below the probe main body 3 configured as described above, and the SH-wave electromagnetic ultrasonic transducer 1 is configured.

The interval between the permanent magnets 2 is determined by the spacers 5 interposed between the permanent magnets 2. In the present embodiment, the thickness of the spacers 5 is 0.3 to 5.5 m in order from the left side of the drawing.
m. For this reason, the SH wave 9 generated by passing an alternating current through the coil 4
The chirp waveform as shown in FIG. The Fourier transform of this oscillation waveform is as shown in FIG. 4B, and the relative bandwidth of the full width at half maximum is 42%.

In this embodiment, an acrylic plate is used as the spacer 5, but any spacer may be used as long as it is a non-magnetic material. In order to make the frequency band wider than in this embodiment,
The minimum value and the maximum value of the thickness of the spacer 5 may be smaller or larger than those of the present embodiment. Furthermore, S / N
In order to improve the number of permanent magnets 2, it is preferable to change the thickness of the spacer 5 in smaller steps than in this embodiment.

FIG. 2 is a diagram showing a method for detecting a flaw by the two-probe flaw detection method using two SH-wave electromagnetic ultrasonic transducers of the present invention. In FIG. 2, reference numerals 6a and 6b denote a transmission SH-wave electromagnetic ultrasonic probe and a reception SH-wave electromagnetic ultrasonic probe configured as described above. in this case,
The transmitting and receiving probes 6a and 6b are arranged so that the interval between the permanent magnets 2 changes in opposite directions. 7 is the test object,
8 is an ultrasonic flaw detector.

When a pulse-like alternating current is passed from the ultrasonic flaw detector 8 to the SH wave electromagnetic ultrasonic probe 6a for transmission, the chirped SH wave 9 as shown in FIG.
a can be generated in the test object 7. The generated SH wave 9a propagates in both directions of the transmission SH wave electromagnetic ultrasonic probe 6a, and is a reflector (edge or defect) of the inspection object 7.
The SH wave 9b reflected by the is received by the receiving SH wave electromagnetic ultrasonic probe 6b. At this time, if the receiving SH wave electromagnetic ultrasonic transducer 6b is arranged in the direction of the chirp wave of the reflected SH wave 9b, the receiving current 10 having a short pulse width as shown in FIG. 8 obtained.
The SH wave reception waveform 10 shown in FIG.
In μs (FIG. 4A), the center frequency is 310 kHz (FIG. 4B).

For comparison, SH waves were generated and detected using a conventional SH wave electromagnetic ultrasonic probe, and the results were as follows. 3.5mm thick permanent magnet on one side
The SH wave electromagnetic ultrasonic transducer as shown in FIG. 6 is constituted by using two of the two, and when a pulse current of 470 kHz and one wave is passed through the coil 4, an SH wave having a center frequency of 470 kHz is generated in the test object. I was able to make it. However, the frequency band of the generated SH wave is as narrow as 13% in the relative bandwidth of the full width at half maximum as shown in FIG.
Was very long with a burst waveform of about 24 μs as shown in FIG. 5B. As described above, the use of the SH-wave electromagnetic ultrasonic transducer according to the present invention improves the temporal resolution because the pulse width is reduced despite the center frequency being lower than in the conventional method.

[0016]

As described above, according to the present invention,
Since the permanent magnets are arranged so that the intervals between the permanent magnets in the SH wave electromagnetic ultrasonic transducer are different, the frequency band of the SH wave electromagnetic ultrasonic wave that can be transmitted and received can be widened, and the pulse width can be shortened, so that the time resolution can be improved. It has excellent effects such as improved and reduced dead zone in flaw detection.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an SH-wave electromagnetic ultrasonic transducer according to the present invention.

FIG. 2 is an explanatory diagram showing an SH-wave electromagnetic ultrasonic measurement method of the present invention.

FIG. 3 is a conceptual diagram of an SH wave generated by the SH wave electromagnetic ultrasonic transducer of the present invention.

FIG. 4 (a) shows a flaw detection waveform obtained by transmitting and receiving SH waves in the embodiment, and FIG. 4 (b) shows a spectrum of the received signal of FIG. 4 (a).

FIG. 5 (a) shows a flaw detection waveform obtained by transmitting and receiving SH waves in a conventional example, and FIG. 5 (b) shows the spectrum of the received signal in FIG. 5 (a).

FIG. 6 is a configuration diagram of a conventional SH-wave electromagnetic ultrasonic transducer.

FIG. 7 is a diagram showing the principle of generation of SH waves by a conventional SH wave electromagnetic ultrasonic transducer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 SH-wave electromagnetic ultrasonic transducer 2 Permanent magnet 3 Probe body 4 Coil 5 Spacer 6a SH-wave electromagnetic ultrasonic probe for transmission 6b SH-wave electromagnetic ultrasonic probe for reception 7 Inspection object 8 Ultrasonic flaw detector 9 SH waves

Claims (3)

[Claims] 1. The magnetic pole direction is alternately changed between front and back, and N pole and S
SH comprising a plurality of permanent magnets in which the poles are arranged in a staggered manner, and a flat coil disposed between the permanent magnets and the test object
A wave electromagnetic ultrasonic transducer, wherein the permanent magnets are arranged so as to be different from each other. 2. The SH wave electromagnetic ultrasonic transducer according to claim 1, wherein said permanent magnets are arranged via non-magnetic spacers having different thicknesses. 3. An SH wave electromagnetic ultrasonic measurement method, comprising using two SH wave electromagnetic ultrasonic transducers according to claim 1 and performing flaw detection by a two probe flaw detection method.