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JPS61107154

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JPS61107154
[0001]
TECHNICAL FIELD OF THE INVENTION The present invention relates to a noncontact
electromagnetic ultrasonic transducer for use in ultrasonic flaw testing (UT). [Technical
background of the invention and its problems] As a conventional noncontact electromagnetic
ultrasonic transducer, EMAT (E 1ectr as shown in FIG. 3).
MagneticACOIIStiCTranSdllCerンがある。 In the figure, reference
numerals 31 (31a to 31e) denote permanent magnets, which are magnetized in opposite
directions. Reference numerals 32 (32 a to 32 d) denote high magnetic permeability yokes,
which are respectively disposed between the permanent magnets 31. Reference numerals 33
(33a to 33d) denote zigzag line conductors (the shape of which is shown in FIG. 4) referred to as
meander lines, and are adhered onto the insulating layer 34. Reference numeral 35 is a material
to be inspected. In this EMAT, the magnetic field lines 36 (36a,..., 36e) from the permanent
magnet 31 pass through the high permeability yoke 32 to reach the surface of the test material
35, and the magnetic field 37 (37a,. . 37d) is obtained. Next, when a high frequency current is
applied to the meander line 33, 38 (38a) in the figure. Since the current flows in the direction
shown in ~, 38d), high frequency eddy currents 39 (39a, ~, 39d) are induced on the surface of the
test material 35 opposite to it. The interaction between the induced eddy current 39 and the bias
magnetic field 37 generates a Lorentz force 40 (40a,..., 40d) in a direction parallel to the surface
of the material 35 to be examined. It becomes a sound source of (41a, 41b). The Lorentz force 40
is parallel to the surface of the test material 35 and in opposite phase with each other. As a
result, the ultrasonic wave 41 to be excited is a transverse wave and an obliquely propagating
mode. In this case, assuming that the propagation direction of the ultrasonic wave 41 is θ (dea),
θ is given by the following 0 formula. θ-5in ′ ′ (Vs / Pf) ..... where Vs [m / S] is the shear
wave velocity of the material to be inspected, P [m] is the distance between the meander lines 33,
f [)-121 Is the frequency of the transmission current. As understood from the equation (0), the
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propagation direction θ of the ultrasonic wave 41 can be easily controlled by changing the
frequency. Here, as the number of meander lines 33 increases and the number of sound sources
generated on the surface of the inspection material 35 increases, the ultrasonic beams interfere
with each other to obtain an oblique beam which is generally well-aligned. The Lorentz force 40
generated in the test material 35 under the meander line 33 is proportional to the product of the
DC magnetic field in the test material 35 and the high frequency current flowing through the
meander line 33.
Therefore, the smaller the gap between the material 35 to be inspected and the high magnetic
permeability yoke 32 is, the stronger the magnetic field strength can be obtained. Also, it is
necessary that the Lorentz force 40 under the meander line 33 be constant in order to obtain a
well-aligned beveled beam. Therefore, the gap between the high magnetic permeability yoke 32
and the material 35 to be inspected also needs to be constant. However, in actual ultrasonic flaw
detection, as a material to be inspected, there are more pipes than flat plates. FIG. 5 is a
conceptual view in which a 2 W long transducer is disposed in a diameter pipe. In this case, the
difference X between the center and edge of the transducer is given by: From these equations, it
can be seen that the gap difference X increases as the diameter decreases. For this reason,
although the gap at the center of the transducer is small, the gap between the pipe to be
inspected and the transducer becomes uniform (the gap between the inspection pipe and the
transducer becomes uniform) because the gap in the green increases. In particular, in small
diameter pipes, the uniformity of the gap is significantly reduced. As described above, the
problems that arise when the gap is not uniform will be described below. In FIG. 3, the strength
of the Lorentz force 40 generated in the test material 35 is the same as that of the test material
when the magnetic field B produced by the magnet 31 in the test material 35 and the current
flowing through the meander line 33 shown in FIG. It is proportional to the product with the
induced eddy current i created in 35. Here, B is approximately in inverse proportion to the
distance between the high magnetic permeability yoke 32 and the material 35 to be inspected.
The induced eddy current i is also inversely proportional to the distance between the meander
line 33 and the material 35 to be inspected. Therefore, the Lorentz force 4 o generated is small
where the gap between the transducer and the material to be inspected 35 is large. In an oblique
angle transducer that generates a beam at an originally windowed angle, the number of pitches
of the meander lines 33 is large, and the Lorentz force 40 under each meander line 33 is
uniformly distributed. In the case, an ideal oblique ultrasound beam is obtained. As described
above, when the Lorentz force is not uniform, the beams are not combined into one, and the
angles at which the beams are directed are also offset. In particular, if the beam is not combined
into one beam, the reflection surface of the ultrasonic beam will not be a constant spot point, so
that the position of the defect can not be accurately determined at the time of flaw detection
work. SUMMARY OF THE INVENTION The present invention has been made in consideration of
the above circumstances, and the object of the present invention is to keep the gap between the
pipe and the transducer constant even in the case of probe in the pipe, which is ideal. It is an
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object of the present invention to provide an ultrasonic transducer capable of obtaining an
oblique angle ultrasonic beam.
SUMMARY OF THE INVENTION According to the present invention, in order to make the gap
between the pipe and the transducer uniform, the transducer is divided into small pieces and
joined together so that the surface of the transducer is in close contact with the pipe surface. It
was made to turn. That is, the present invention comprises a plurality of flat plate permanent
magnets of the same shape magnetized in the thickness direction and a plurality of magnetic
materials having the same surface shape as the magnets, and the same poles of adjacent magnets
are aligned in the thickness direction. And an excitation portion formed by laminating alternately
so as to face each other, and an electric conductor piece having a zigzag shape having the same
pitch as the magnet and attached to one side surface of the excitation portion via an electric
insulating layer. In the N release ultrasonic transducer, a plurality of magnetic members at
arbitrary locations are divided to divide the excitation part into a plurality of parts, and the
divided excitation parts are deformable connecting members in the surface of the insulating
layer. Connection. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present
invention will be described in detail by way of the illustrated embodiments. FIG. 1 is a schematic
view showing an ultrasonic transducer according to an embodiment of the present invention. In
the figure, 11 (11a to 11f) are permanent magnets magnetized in the thickness direction, and
these magnets 11 are alternately stacked with high permeability yokes 12 (12 to 12e), and The
same poles of adjacent ones are opposed to each other. On the lower surface of the excitation
portion composed of the magnet 11 and the high magnetic permeability yoke 12, a meander line
13 (13a,...) With an electrical insulating layer 14 interposed therebetween. 13e) is attached. The
basic configuration up to this point is the same as that of the prior art, and the present
embodiment is different from this in that a part of the plurality of yokes 12 is divided and the
excitation part is divided. That is, among the high magnetic permeability yokes 12, the yokes 12b
and 12 (j is divided into two, whereby the excitation part is also divided into a plurality of smallpiece elements. The small-piece element is connected on the lower surface side by a connecting
member 25 (25a, 25b) made of cloth, soft vinyl or the like. The small piece element of the
exciting unit is rotatable by the deformation of the connecting member 25. The portions 13b and
13d of the meander line 13 corresponding to the yokes 12a and 12b are divided into two as
shown in FIG. Furthermore, the meander lines 13 are connected in series by connecting wires. In
FIG. 1, reference numerals 26 (26a to 26f) denote rollers attached to the lower surface of the
insulating layer 13, and these O-rollers 26 are in contact with the material to be inspected.
With such a configuration, it is possible to bend the excitation portion consisting of the
permanent magnet 11 and the high magnetic permeability yoke 12 for each small piece element,
and in particular, the opposing face for each small piece element has the same polarity as a
magnet. The power to emanate arises. This force causes the exciter to bend naturally as a whole.
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In this state, when this is placed on a pipe such as carbon steel, in particular, the exciting portion
surface and the pipe surface are attracted because there is a magnetic flux passing through the
yoke 12, and repulsion between the small piece elements takes place. Naturally adheres to the
pipe surface. In this case, the roller 26 abuts on the surface of the pipe, the gap between the
excitation portion and the surface of the pipe is kept constant, and the excitation portion can
slide on the surface of the pipe. Thus, according to the present embodiment, even if the diameter
of the pipe changes, the gap between the pipe and the excitation unit does not change. For this
reason, even if the diameter of the pipe changes, the gap is kept constant, so the magnetic field
strength on the surface of the pipe becomes uniform, and the Lorentz force generated under the
meander line also becomes uniform. As a result, it is possible to generate an ideal oblique
ultrasonic beam also in piping. Therefore, the accuracy of flaw detection in ultrasonic flaw
detection can be improved. The present invention is not limited to the embodiments described
above. For example, the connection member is not limited to cloth, vinyl, etc., as long as it is a
flexible insulating material. Further, conditions such as the size and the number of the permanent
magnet and the magnetic material may be appropriately determined according to use.
Furthermore, as a matter of course, the number of divisions of the excitation unit can be changed
as appropriate. In addition, various modifications can be made without departing from the scope
of the present invention. [Effects of the Invention] As described above, according to the present
invention, since the excitation portion composed of the permanent magnet and the magnetic
material is divided into a plurality of parts, the piping and the excitation portion can be separated
also in ultrasonic flaw detection such as piping. The gap can be kept constant. For this reason, an
ideal oblique beam can be obtained, and a significant improvement in flaw detection accuracy
can be achieved.
[0002]
Brief description of the drawings
[0003]
FIG. 1 is a schematic block diagram showing an ultrasonic transducer according to an
embodiment of the present invention, FIG. 2 is a schematic view showing a main part
configuration of the above-mentioned transducer, and FIGS. For the purpose of explanation, FIG.
3 is a schematic diagram showing a conventional ultrasonic transducer, FIG. 4 is a schematic
diagram showing the main part configuration thereof, and FIG. 5 is a schematic diagram showing
the relationship between the piping and the gap of the transducer. It is.
11 (11a ~ ~ 11f)-permanent magnet, 12 (12a ~ ~ 12e) ... high permeability yoke, 13 (13a ~ ~ 13e)
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... meander line (N air conductor piece), 14 ... Insulating layer, 25 (25a, 25b) ... connecting
member, 26 (26a to 26f) ... roller. Applicant agent Patent attorney Takehiko Suzue Figure 1
Figure 2 Figure 3
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