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Magnetoacoustic l · Regarding the transducer. An electromagnetic transducer / stater
(hereinafter abbreviated as EMAT) 2 is inserted into a capillary tube to perform ultrasonic flaw
detection, and the structure shown in FIG. 1 is known. ている。 That is, 1 ··· in the figure is a
permanent magnet arranged so that the polarities of −LT are mutually V (oppositely, for
example, 5 permanent stones are 1 uni, 1 uni, 1 l The coil 2 is wound so that the B2 MAT 3 is
configured. In addition, 4 in the figure is a thin tube into which 112 MAT 3 is inserted. The
operation of the EMAT will be described with reference to FIG. I! : When a high frequency current
is applied to the coil 2 of M AT 3, an eddy current (I) is generated in the capillary 4 in contact
with the coil 2. On the other hand, the magnetic flux (B), which changes periodically from the
permanent magnets 1 to the blood in the capillary 4, is obtained with the force 11 and the
mutual f'l with the eddy current (I); 111 VC J:! : J Lorentzka (F) occurs. These CJ-L to Zdza (F)
change in the same cycle as the magnetic flux cycle, and this capillary force (F) causes the
capillary tube 4 to generate an ultrasonic wave e. (Plate wave) is generated. In addition, the
detection of an ultrasonic wave is converted into an electrical signal and detected in the reverse
process to that described. However, in the EMAT described above, ultrasonic waves are
generated only on a part of the surface where the coil 2.. Needs to rotate either the capillary tube
or the EMAT, which makes the flaw detection operation troublesome. A part of the surface of the
coil 2... And the inner surface of the thin tube 4 inevitably occurs from the shape of the
permanent magnet 1 ..-from the shape of the permanent magnet 1. The present invention u: '-two ffd was made to eliminate the defect, by generating SH waves simultaneously on the entire
peripheral wall of the capillary, ultrasonic waves are efficiently generated on the entire
peripheral wall of the capillary without rotating the capillary etc. It is an object of the present
invention to provide a capable electromagnetic acoustic transducer / sensor. That is, according to
the present invention, a disk-shaped permanent magnet or electromagnet is sequentially
arranged between the disk-shaped cores so that the polarities thereof face each other, and a
cylinder of a cylindrical high conductivity conductor is covered thereon, and the cylinder An
electromagnetic acoustic transducer is characterized in that the coil is wound like a toroidal coil.
One embodiment of the transducer of the present invention will be described with reference to
FIGS. In FIG. 3 to FIG. 8 Vc, 11 in the figure is an electromagnetic acoustic transducer (JT 2 + tll A
T l, and in this EMAT II-FIG. 0 / a plurality of disks having high magnetic permeability). And the
core 12... And the disc-like permanent magnet 13... Inserted between the cores 12.
Until the alignment period (TO) of the core 12.12 and the permanent magnet 13.13 is equal to
the wavelength λ of the generated ultrasonic wave 4, the magnetic circuit of these magnetic
circuits can be made of a high conductivity material such as copper. Cover the cylinder 15. The
toroidal coil 14 '(1. -It is rolled up. Outside the cylinder 9, the coil 14 passes axially in the axial
direction, and inside the cylinder, the coil [4] passes axially in the opposite direction of the
outskirts of the Mit. The operation of the EMATll of the above-described structure will be
described. First, as shown in FIG. 7 (EMAT II is placed in a predetermined region in the thin tube
4 by either inserting the EMAT 11 into the thin tube 4 as the subject or fitting the thin tube 4
with EMA THVC. When 16 frequency current J'f is supplied to the coil 14 in such a state, an eddy
current (I) parallel to the axial direction is generated in the thin tube 4σ! Wall portion adjacent
to the coil outside the cylinder as shown in FIG. On the other hand, the current r "flowing through
the coil through the inner shell S of the cylinder 15 is a highly conductive object, and the surface
V thereof generates an eddy current in the opposite direction to the eddy current generated in
the capillary. The effect on the capillary of the coil passing inside is eliminated. On the other
hand, a magnetic flux (B) parallel to the direction of the thin tube 40 whose direction changes
with its period (T,) is emitted to the wall of the thin tube 4 It will occur. Due to the interaction
between the eddy current (I) and the magnetic flux (B), a low level sensor (F) is generated. The
direction of this Lorefuka (F) is reversed at tll simultaneously with the period (To) of the
magnetic field distribution. As a result, an SR wave which propagates in the direction II1111 of
the wall of the capillary 4 is generated by the Lorefuka (F), and a whole peripheral wall v 'csH
wave (ultrasonic wave) of the capillary 4 in which the matrix is disposed is generated. This
supersonic 'e. Propagates through the thin tube 4 and is reflected back at the defect point of the
thin tube 4 or the like. Therefore, it is possible to detect the thin tube 4 by converting the 7'L into
the electric signal in the reverse process of the above. Therefore, according to the present
invention, the following effects can be obtained. (1)-When flaw detection is performed on a
capillary tube using KMAT as described above, the core and the permanent magnet are discshaped so that the cylinder can be broken so that the clearance between the KMAT and the inner
surface of the capillary tube is small. Thus, ultrasonic waves can be generated over the entire
inner surface of the capillary adjacent to the EMAT, and as a result, defects in the capillary can be
easily detected without the complicated operation of rotating the transducer or the capillary.
(2) The coil passing inside the cylinder has a current flowing in the opposite direction to the
external coil, but the eddy current is absorbed in the cylinder, and the coil outside the cylinder
cancels the eddy current generated in the capillary wall. You can prevent that. (3) Since the coil
cross-section of the l-rJ idal coil is fairly small, the innoidance of the coil can be lowered, and the
current can be reduced easily. It should be noted that the electromagnetic acoustic transformer
according to the present invention is not limited to the one having permanent magnets
interposed between the cores so that the polarities face each other as in the embodiment 11-,
using electromagnets instead of permanent magnets. It is also good.
Brief description of the drawings
FIG. 1 is a schematic perspective view of F2 MAT, FIG. 2 is an explanatory view of the motion
principle of the conventional F2 MAT, and FIGS. 3 to 8 are one embodiment of EMA T of the
present invention 3 is a front view of E1φAT, 4 is a right side view of FIG. 3, FIG. 5 is a V-V
cross-sectional view of FIG. 3, and FIG. FIG. 7 is a front view, FIG. 7 is a perspective view showing
i1j EMAT and a capillary tube, and FIG. 3 is an explanatory view of the operation principle of
4: subject thin tube, 11: rcMAT, 12: co 'γ, 13: permanent magnet, 14: coil, 15: cylinder 3
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