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JPH01127950

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DESCRIPTION JPH01127950
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
focusing electromagnetic ultrasonic probe used, for example, for nondestructive inspection of a
structure. [Prior Art] FIG. 6 shows an electromagnetic ultrasonic probe (hereinafter referred to as
EMAT) used for conventional ultrasonic flaw detection. The EMAT shown in FIG. 6 is composed
of a magnet 4 consisting of a permanent magnet or an electromagnet, and a coil 5 provided on
the lower surface of the magnet 4. In the above, EMAT, when an electric current flows through
the coil 5, the interaction force between the eddy current J generated on the surface of the
conductive object A by the current current and the magnetic field line B of the magnet body 4, K
It produces a low-Lorentz nose F and acts as an oscillator to become the same Lorentz φ
vibration source and generate an ultrasonic wave S. When an ultrasonic wave is transmitted to
the surface of the subject A, the vibration by the ultrasonic wave and the magnet 4 In order to
generate a conductive flow in the coil 5 by the interaction with the magnetic lines of force B, the
EMAT also functions as a geophone. When flaws in a subject A are to be detected by the abovedescribed KMAT, it is necessary to focus on the ultrasonic waves generated in the subject A in
order to enhance the resolution. As KMAT to focus on the ultrasonic waves generated in the
subject A, there is a play kite using an EMAT divided in several ways, and as shown in FIG. 7 and
FIG. There is a focal point EMAT for focusing the focal point P in the width direction W by tilting
the wavefront of the generated ultrasonic wave S using one magnet 4. [Problems to be Solved by
the Invention] Generally, EMAT has a drawback in that it has a low time resolution. Although it is
necessary to converge the depth direction of the ultrasonic wave generated by the EMAT in the
subject A, it is impossible to do this with the conventional focal point EMAT. Also, the
conventional focus EMAT can focus the width direction W of ultrasonic waves, but the
conventional focus KMAT is not effective because the same purpose can be achieved by reducing
the width of the EMAT magnet. The The present invention is intended to solve the above
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problems. [Means for Solving the Problems] In the present invention, a plurality of magnets are
arranged in a row sequentially from thick to thin, and adjacent magnets have different polarities
and different polarities. And a coil formed by winding an electric wire so as to spring the magnet
through a face having the polarity of the magnet array. [Operation] In the above, n is numbered
sequentially from the thick one, and the angle θ n between the wave front of the ultrasonic wave
generated by the n th magnet and the surface of the object and the n−1 th magnet The distance
between the centers of the n-th magnets is dn, the speed of sound of ultrasonic waves is Sv, the
frequency of ultrasonic waves is f, the wavelength of ultrasonic waves is λ, and the distance
from the magnet center to the focal point of n-th magnets is 1n , In-1n--λ / 2 When the distance
an of the magnet centers of the mutually adjacent magnets is set so that the above two
expressions stand, the components in the depth direction of the ultrasonic waves focus.
As described above, since the component of the ultrasonic wave in the depth direction in the
subject can be converged K, the temporal resolution can be improved and detection of the
damage in the subject becomes easy. . (’ii! EXAMPLE One embodiment of the present
invention is shown in FIGS. 1 and 2. FIG. In this embodiment shown in FIG. 1 and FIG. 2, magnets
are arranged in a row from thick to thin ones in a row, and adjacent magnets are arranged to
have different polarities to form one surface. The magnet array 1 and a coil 2 formed by winding
an electric wire so as to spring the surface having the polarity of the magnet array 1 with an
under-magnet. In the above, an eddy current J is generated on the surface of the subject A when
an electric current flows through the coil 2. The magnetic lines of force of the magnets of the
magnet array 1 act on the eddy current J to generate Lorentz 4 F forces F with 180 ° different
phases on the surface of the subject A, and the Lorentz 4 I ′ ′ becomes a vibration source and
Generate a sound wave. As shown in FIG. 5, ultrasonic waves generated by arranging the
magnets 3 in a line so that adjacent magnets 3 having different 9 mutually different polarities
have 1800 phases different, and ultrasonic waves formed by the above-mentioned magnet array
The wave front H has an angle of θ with the surface of the subject A. The above-mentioned
angle θ is expressed by the following equation, where d is the distance between the magnets
and λ of the wavelength of the ultrasonic wave. Assuming that the speed of sound is Sv and the
frequency is f, the above-mentioned .lambda. Can be expressed by .lambda.-S / f so that the above
equation (1) can be converted into the following equation. In the present invention, as shown in
FIG. 1, since the thin magnets of thickness are arranged at points 5 away from focal point P as
shown in FIG. 1, the respective angles .theta. The distance between the centers of the magnets
adjacent to each other is adjusted so that the line connecting the centers of the respective
magnets is at an angle of 90 '-. About.00 with the surface to the subject. Then, the wave front of
the ultrasonic wave generated by each magnet can be directed to the focal direction. The abovementioned angle θ n is expressed by the following equation, assuming that the distance between
the centers of the magnets adjacent to each other is in (nwl, 2.3.4). Furthermore, since the
ultrasonic waves generated by the magnets adjacent to each other are 180 ° out of phase, the
distances 1n and fin-t (n-1, z, a, 4) to the respective focal points of the magnets adjacent to each
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other are different. If the relationship of fin-jln-t-λ / 2 (4) is established between them, the
phases of the ultrasonic waves by the respective magnets will coincide at the focal point P. When
the thickness of each magnet of the magnet array 1 is set so as to satisfy the equations (3) and
(4), the ultrasonic waves generated by each magnet converge the component in the depth
direction in the subject A at the focal point P When the focal point P is damaged or the ultrasonic
wave is reflected at the point P, the reverse operation is performed to generate the conductive
flow in the coil 2 and detection of the damage or the like of the subject A is performed. It
becomes possible.
By setting the thicknesses of the respective magnets so as to satisfy the above-mentioned
conditions (3) and (4), the component of the ultrasonic wave in the depth direction in the subject
A can be converged at the focal point P. Since it became possible to improve the temporal
resolution, it became easy to detect the damage in the subject. In the present embodiment shown
in FIGS. 3 and 4 in which the other essential embodiment of this essential example is shown in
FIGS. 3 and 4, the magnets of the component in the above one embodiment are thick and small.
In this embodiment, the wave front of the ultrasonic wave converges at the focal point P in
addition to the depth direction, so that the resolution is further improved as compared with the
above embodiment. did. [Effects of the Invention] According to the present invention, the
magnets are arranged in a row sequentially from thick to thin, and magnets adjacent to each
other have different polarities. Since the wavefront is focused to K, the temporal resolution is
improved, and the detection of the damage in the object is facilitated.
[0002]
Brief description of the drawings
[0003]
FIG. 1 is an explanatory view of an embodiment of the present invention, FIG. 2 is a view taken
along the line-of FIG. 1, FIG. 3 is an explanatory view of another embodiment of the present
invention, and FIG. FIG. 5 is a detailed explanatory view of the present invention, FIG. 6 is an
explanatory view of the conventional apparatus, and FIG. 7 is an explanatory view of another
example of the conventional apparatus, FIG. FIG. 7 is a view taken in the direction of arrows of
FIG.
1 ・ ・ ・ Magnet row, 2,5.6 ... coil. 3.4 between ... magnet Attorney Attorney hill Xiao outside
Two Figure 6 Figure 7 Figure 8
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