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a, Industrial application The present invention relates to an electromagnetic acoustic transducer
(converter) corresponding to the generic concept described in line 44 of the 8th column of the
German unexamined patent application (DE-PS) 2655804. . The invention according to claim 1
relates generally to plane wave and surface wave transducers, in particular to cylindrical wave
transducers, in addition to the Lamb wave transducers described in the above section. The
electromagnetic acoustic transducer includes means for generating a magnetic field in the
subject by the magnetic field generating means, and a coil for generating an induced current in
the subject, and the interaction between the magnetic field and the Lorentz force of the induced
current Is an apparatus for generating an ultrasonic wave in the test object and detecting the
ultrasonic wave in the test object. b. Prior art technology This type of transducer according to the
prior art has the advantage that a large ultrasonic amplitude is generated in the direction of
ultrasonic wave propagation, since a high frequency signal which has caused one phase shift is
simultaneously transmitted to the winding. Have. However, in the case of applying a high
frequency signal in this manner, an acoustic wave is first generated in the rear winding, and this
acoustic wave does not cause cancellation interference with an acoustic wave of the front
winding. This wave, which travels in the opposite direction to the direction of propagation of the
ultrasound, causes unwanted reverberation. C1 Problem to be Solved by the Invention The object
of the present invention is to provide a transducer (electromagnetic acoustic transducer) that
completely eliminates from the beginning the acoustic wave traveling in the direction opposite to
the propagation direction of the ultrasonic wave. It is in. d, Means for Solving the Problem The
above problem is solved by a converter having the features described in the first claim 1). In the
above transducer, an acoustic signal is generated only in the direction of the winding where the
high frequency signal is initially applied. An acoustic signal generated in the front winding and
traveling in the direction opposite to the ultrasonic wave propagation direction is canceled by the
delayed high frequency signal generated in the rear winding. In that case, an ultrasonic wave
having the same maximum amplitude as the ultrasonic wave produced by the transducer
described in line 44 of column 8 of DE-A 2 65 5804 and below is generated in the propagation
direction of the ultrasonic wave. In the claim (1), the wavelength of the ultrasonic vibration is
indicated by ? and the period is indicated by T. The same principle of the features as claimed in
claim 1 applies to any of the above converters. The present invention will be described in detail
based on the following drawings. e, the embodiment The tube 1 to be examined is surrounded by
an electromagnetic acoustic transducer. Magnetic field generating means are not shown. The
transducer consists of a transducer body in which the winding recesses a3, 4 and 5.6 are
engraved at a spacing of ? / 2.
Two windings 7 and 8 are wound in these winding grooves 3, 4, and 5.6. The winding 8 at the
front as viewed in the direction of ultrasound propagation travels within the recess 4 and travels
back to the recess 6 through the bridge 10 provided behind the transducer. The winding 7 at the
rear as viewed in the direction of ultrasound propagation travels in the recess 3 and returns to
the recess 5 through a bridge 1) provided behind the transducer. At the same time, in this
example, the winding directions of both windings are reversed. Although not shown, high
frequency generators for supplying high frequency current to the windings are connected to
these windings. First, at 1 = 0, a high frequency current is supplied to the winding 8 disposed in
the ultrasonic wave propagation direction 9. Thus, as shown in FIG. 2, two ultrasounds 12 and 13
are generated in the tube 1, these ultrasounds having the same intensity, in the ultrasound
propagation direction 9 and in the opposite direction respectively. To propagate. At t = T / 4,
these waves in tube 1 have forms 14 and 15, respectively. At this time, a high frequency current
is applied to the winding 7 with a delay of T / 4. In the tube 1 there are then generated two new
ultrasound waves 16 and 17 which propagate in opposite directions. However, these waves are
not independent of each other (as they interfere with each other, complete signal cancellation
occurs in the direction opposite to the direction of ultrasound propagation 9). Therefore, no
ultrasound reflection occurs, which results in a false signal in the inspection at the defect
position of the tube cross-section between the transducer 2 and the conduit end 19, ie in the
direction opposite to the propagation direction of the ultrasound. On the other hand, in the
ultrasonic wave propagation direction 9, an ultrasonic wave of which signal form at T / 20 time
point is shown in FIG. The transducer 2 is provided on the tube 1 in FIG. The ultrasound
propagation direction is again indicated at 9 here. Of the transformer windings 7 and 8, the
winding indicated by 8 is energized by the high frequency impulse generated by the transmission
amplifier 21. The transmitted signal may be a sine wave as indicated by reference numeral 22 or
other waveforms. The winding indicated by 7 is activated by the transmission amplifier 23 with a
delay of t = T / 4. This delayed high frequency electrical signal is indicated by 24. The same is
true for signal 22 as for signal 22, but both signals must have the same waveform. The
transmitter 21 is started via the impulse generator 25 and the transmitter 23 receives the same
impulse delayed by a fixed time. This delay corresponds to one-fourth of the ultrasonic wave
propagation time T described in FIG.
Brief description of the drawings
FIG. 1 is a schematic view of the cross section of the structure of the transducer, and FIG. 2 is
related to FIG. t = T / 4. FIG. 3 is a configuration diagram of an ultrasonic signal generated in a
pipe at three time points of t = T / 2, and FIG. 3 is a configuration diagram of an electrical
installation for power transmission to a transducer.
DESCRIPTION OF SYMBOLS 1 ... Tube 2, 2 ... Transducer main body, 3.4, 5.6 ... Winding, 7.8 ...
Winding, 9 ... Direction of ultrasonic wave propagation, 10 ... Bridge 1)
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transmission amplifier 22 signal 23 transmission amplifier 24 high frequency signal 25 impulse
generator 26 delay time. Patent application applicant Mannesmann Akchen Gesellschaft toe ?-l-j
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