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JPH01239453

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DESCRIPTION JPH01239453
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
method of generating SH waves by an electromagnetic method and a transducer used for the
implementation thereof. [Prior Art] Conventionally, when flaws are performed on a material with
high attenuation of ultrasonic energy, such as welds of austenitic stainless steel, SH waves
(horizontal deflection transverse waves) are generated by an electromagnetic ultrasonic
transducer. Is used. FIG. 6 is a schematic view of a conventional electromagnetic ultrasonic
transducer, in which rectangular solid permanent magnet pieces 20a, 20a,... Are arranged with
their pole faces on the front and back, and N and S poles are staggered. It consists of the
permanent magnet 20 arranged in plate shape so that it may become, and the flat coil 21 of a
planar view rectangle. FIG. 7 is an explanatory view of the principle of SH wave generation by
this electromagnetic ultrasonic transducer. As shown in the figure, the coil 21 is disposed
immediately above the object 22 to be inspected, and the permanent magnet 20 is disposed
above it. The permanent magnet 20 generates a magnetic field B which is perpendicular to the
surface of the inspection object 22 and works alternately in the opposite direction corresponding
to the direction of the magnetic pole of each permanent magnet piece 20a, while passing an
alternating current through the coil 21. As a result, an eddy current (4) is generated in the
vicinity of the surface of the inspection object 22. The interaction of the magnetic field B and the
eddy current 4 generates a Lorentz force F in a direction parallel to the surface of the inspection
object 22 and perpendicular to both the magnetic field B and the eddy current 4, and the
direction of the Lorentz force F Are inverted by 180.degree. At the pitch of the width of the
permanent magnet piece 20a. Such Lorentz force F vibrates the metal grid of the inspection
object 22 parallel to the surface, and forms an angle θ with the direction perpendicular to the
vibration direction, that is, the thickness direction of the inspection object 22. An SH wave (H in
FIG. 9) is generated that propagates in the lower part of the inside. Here, the wavelength of the
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SH wave is expressed by the following equation (11). λ = υ / f = 2D-sin θ (1) where λ:
wavelength of SH wave 音速: speed of sound f: frequency D of SH wave: width of one permanent
magnet piece [problem to be solved by the invention] as mentioned above In such a conventional
electromagnetic method of generating SH waves, since a permanent magnet is used to generate
an external magnetic field, the strength of the magnetic field in the vicinity of the surface of the
inspection object is as low as about 3 to 5 KOe, It can not generate the SH wave that it has. On
the other hand, there are also cases where it is required to generate high frequency SH waves for
the purpose of enhancing the resolution of flaw detection. (11, the incident angle of the SH wave
is made constant and the width of one permanent magnet piece is made small (If it is, the sound
speed υ is constant, the frequency f of the SH wave can be increased, but the magnetic field
strength decreases. There is a problem that the output S / N ratio of the electromagnetic
ultrasonic transducer also decreases.
The present invention has been made in view of such circumstances, and the object of the
present invention is to use an SH wave generating method and an SH wave generating method
for generating high frequency SH waves by means of electromagnetic ultrasonic transducers. To
provide a transducer. [Means for Solving the Problems] The method of generating SH waves by
the electromagnetic method according to the present invention generates a magnetic field in a
direction crossing the surface of the object to be inspected by the magnet positioned above the
object to be inspected. In the method of generating an eddy current in the vicinity of the surface
of the object by passing an alternating current through the coil, and generating an SH wave in
the object by the interaction of the eddy current and the magnetic field, as the magnet It is
characterized in that an electromagnet is used, and direct current or alternating current is passed
through the coil. Further, the transducer according to the present invention is provided with a
conductor which is disposed on the plate so as to be sewn in the thickness direction and in which
the portions through which current flows in the reverse direction are alternately positioned in
the current flow direction. It is characterized by [Function] In the method of the present
invention, high energy, high frequency SH waves are generated in the subject by the external
magnetic field generated by the electromagnet and the eddy current generated by the coil. The
method of the present invention will be specifically described below with reference to the
drawings. FIG. 1 is a block diagram of an apparatus used to implement the method of the present
invention. In the figure, reference numeral 1 denotes a DC power supply, which applies a DC
current to the coil 2 a of the electromagnet 2. The electromagnet 2 has a shape in which one side
of a rectangular ring is cut out in a side view, and the magnetic pole surface 2c is made to face
the upper surface of the rectangular parallelepiped test object 10 and the other magnetic pole
surface 2b is made to face the side surface ing. A coil 3 shown in FIG. 2 is disposed between the
pole face 2c and the upper surface of the test object 10. The coil 3 is a rectangular plate 30 in
which a large number of elongated holes 3a, 3a, ... parallel to one side are drilled at an equal
pitch D, and a conductor 3b is passed through the elongated holes 3a, 3a, ... It consists of The
conductor 3b is inserted so as to sew the long holes 3a, 3a, ... and extends in a direction
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perpendicular to the longitudinal direction of the long holes 3a, 3a, ... The longitudinal direction
of the long holes 3a, 3a, ... Is wound multiple times. The output current of the burst pulser 4 for
intermittently outputting a high frequency current is applied to the coil 3 through the matching
circuit 5. According to such a configuration, current flows in the reverse direction for each pitch
D of the long holes 3a, 3a,. Therefore, when this is placed in the direct current magnetic field, a
parallel force is generated on the surface of the object to be inspected which is opposite in
direction every pitch D, as in the prior art.
Since this force reverses the direction in synchronization with the applied alternating current, an
SH wave of a wavelength represented by (1) is generated as in the prior art. FIG. 3 is a drawing
showing the principle of generation, in which ▪ indicates an eddy current, B indicates a
magnetic field, F indicates a Lorentz force, and H indicates an SH wave. A coil 3 'having the same
structure as the coil 3 is for detection, is juxtaposed to the coil 3, and is connected to the
preamplifier 6 via a matching circuit 5' for detection of a received wave of SR waves, The
detection signal is amplified here and input to the synchronous amplifier 8 through the band
pass filter 7 for noise removal. The signal amplified by the synchronous amplifier 8 is manually
input to the oscilloscope 9 and synchronized with a signal synchronized with the output timing of
the burst pulser 4 to display the received signal. FIG. 5 is a graph showing the S / N ratio of the
received wave for the method of the present invention (.smallcircle.) And the conventional
method (.DELTA.). In the present invention, as the electromagnet 2, one having an input of 3 kW
and a magnetic flux density of 1.2 T just below the pole surface was used. Further, the pitch D of
the long holes 3a is 3, 4 * 鳳, and the same length as the width of the magnet piece in the
conventional method to be compared. The conduction current to the transmitter coil 3 is 0 to
300 (peak to peak), and in the case of the conventional method, the number of magnet pieces is
10, the transmitter coil current frequency is 475 kHz, and the test object is 400 × 5Q mm. It is a
steel block. The current supplied to the coil 3 of the method of the present invention is 475 kHz,
and in this case, SH waves propagating in parallel to the block surface are generated, and the S /
N ratio of the amplitude of the reflected wave from the block end face to the backround noise.
The ratio was determined. As apparent from the figure (in accordance with the present invention,
the S / N ratio is significantly improved. FIG. 4 shows another embodiment of the coil 3, 3 ', in
which the conductor 3b is formed on a printed circuit board, in which conductors of length D are
aligned and formed on both front and back surfaces, The connection is made by the penetrating
conductor, and the same connection as shown in FIG. 2 is made. Although direct current is
passed through the coil 2a of the electromagnet 2 in the above-described embodiment, it goes
without saying that the same effect can be obtained by energizing the coil 3 while being at one
polarity through alternating current. In the case of the present invention as described above,
since the electromagnet is used, the magnetic field strength can be increased to obtain a high S /
N ratio. In the case of the present invention, since the value of D is determined by the coil,
reducing it has nothing to do with the reduction of the magnetic field strength, and it becomes
possible to make f high frequency accordingly. Play an effective
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[0002]
Brief description of the drawings
[0003]
FIG. 1 is a schematic block diagram showing an embodiment of the method of the present
invention, and FIGS. 2 and 4 are schematic structural views of coils of the transducer according
to the present invention, and FIG. 3 is SH in the case of the present invention. FIG. 5 is a graph
showing the effect of the present invention, FIG. 6 is a schematic structural diagram of a
conventional transducer, and FIG. 7 is an explanatory view of the principle of SH wave generation
thereby.
2 · · · · · electromagnet 3 3, 3 · · · coil 3a · · · long hole 3b · · · · Patent applicants Sumitomo Metal
Industries, Ltd. Attorney Attorney Attorney Kono No. 3rd division No. 6 body 7 mouth
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