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Description 1, title of the invention
Ultrasonic transducer user
3. Detailed Description of the Invention The present invention relates to a transducer for
generating ultrasonic waves used for ultrasonic equipment in non-destructive EA, and more
particularly to a transducer for generating ultrasonic waves in a liquid. Even in an optically
opaque medium, as long as it is acoustic (C transparent and 10, it is possible to observe a
fluoroscopic image by a sound wave as in X-ray fluoroscopy. Optical imaging of transparencies of
optical old year can be applied to the fields of medical diagnosis, microscopy, nondestructive
inspection, observation of seafloor patterns, and earthquake research. As ultrasonic transducers
of 15 U.S.A., those using an acoustic phase plate and those using an annular array. Those using
an acoustic lens, those using a light-acoustic transducer, and the like have been proposed.
However, the fact is that there is still room for improvement at point 20EndPage: 1, which is the
convergence of the sound wave necessary for the supersonic V imaging. Therefore, a noninventor previously proposed Japanese Patent Application No. 52-31.507 as a remedy for the
above-mentioned drawbacks of the prior art. In this technique, an interdigital transducer is
provided on the surface of a piezoelectric body, and an ultrasonic voltage is emitted from the
interdigital transducer by applying an alternating voltage 7JD to the electrode while the
electrode is in contact with a liquid. The thickness of the piezoelectric body is sufficient to excite
surface waves (Rayleigh waves). However, in the above-mentioned technology, since the delicate
serpentine electrode vibrates in contact with the liquid, there arises a problem that mechanical
and chemical protection must be provided. Therefore, the non-invention aims to ameliorate the
disadvantages of the prior art and its characteristics are the thickness of the piezoelectric body.
Instead of a Rayleigh wave which is as thin as or less than the wavelength of the sound wave in
the piezoelectric body, it is to excite a Lamb wave. An embodiment will be described below with
reference to the drawings. FIG. 1 shows a structural example of an ultrasonic transducer
according to the present invention, wherein 1 is a piezoelectric substrate, and its thickness is
about the same as or less than the wavelength (λ) of the acoustic wave in the substrate. As
shown in FIG. 2 with two interdigital transducers. The comb-like electrode fingers are alternately
arranged in an interdigitated manner. Reference numeral 3 denotes a flat electrode provided on
the back surface of the substrate 1, and reference numeral 4 denotes a liquid material 5 in
contact with the flat electrode. In this structure, when a three-phase AC voltage is applied to each
of the electrode terminals (al, (bl, (C)) 7IO, longitudinal wave acoustic radiation satisfying the
following equation of surface force on the liquid side of the piezoelectric body is generated. It is
emitted into the liquid. Where θ is the direction of the emitted sound wave, the velocity of the
sound wave in the VWn liquid, and v L is the velocity of the Lamb wave propagating on the
piezoelectric body.
Unlike the Rayleigh wave, Lamb waves have displacements on both the front and back sides of
the medium through which one wave propagates, and in the case of symmetrical mode, the
custom order of the displacements is the same. Therefore, in consideration of this characteristic,
the situation of displacement is the same between the side having the clover electrode and the
opposite side, and the side including the interdigital electrode is not in contact with the surface
night body. By contacting the surface (surface that shoulders the flat electrode 20) with the
liquid, efficient radiation of acoustic waves into the liquid can be realized. Furthermore, it is also
possible to efficiently convert the sound wave that has reached this type of transducer part into
an electrical signal, and also in that case the sensitivity to the sound wave from the direction
satisfying the above-mentioned equation (1) is maximum. Become. Parallel to the direction
satisfying the seventh-order equation in the relation with the equation (1) in the sound wave
radiated from each section to the lamp and the interdigital when the period of the interdigital
electrode provided on the piezoelectric plate is equal interval It is emitted as a sound beam. Here,
f is the carrier frequency of the electrical signal to be detected by the transducer, and d1 ′ ′ j
is the electrode period of the interdigital transducer. In the above description, even when the
planar electrode is removed and a single-phase AC voltage is applied to the interdigital
transducer, the function as a transducer can be similarly maintained. When the AC voltage to be
applied is single phase. The uni 2 acoustic beam is emitted 2 waves in the 10 direction of + θ
force direction. Also, in the case where the AC voltage to be applied is three phases (only one
wave in either the 100 direction or the -θ direction is emitted. It should be noted that even when
a three-phase AC voltage is applied, it is to be noted that the five interdigitated electrodes shown
in FIG. 2 are sufficient for the non-invention interdigital transducer, as described in FIG. It is not
necessary to provide a three-phase electrode (in this case, a special structure is required to
prevent a short circuit at the intersection of electrode leads) on one side of the piezoelectric
body. Therefore, according to the present invention, the electrode structure is greatly simplified
to 1) as an example of an interdigitated electrode as an interdigitated electrode which is
simplified as O. However, a single arc-shaped interdigital electrode can also hold the same
function. Needless to say. Next, the distance between the electrodes will be described with
reference to FIG. The relationship between the wavelength λ in a liquid with a sound wave of 15
frequencies f and the direction (angle θ) of the maximum output of the beam is determined by
the following equation. Match S stone θ = λ f / 2 d (3120 EndPage: 2-,-where d is the electrode
distance. Therefore, in FIG. 3, in order for the sound waves generated from the respective
electrodes to converge to the point P (conditions in which the sound waves generated at each
point pass through the point P and are in phase), the following condition must be satisfied. It
does not.
X, = (R: sl, 2θ. + N λ t Ro +) n 2 λ 7) V 2 (4 J n-0, ± 1. ±2. ..., 10 N where λ, is the
wavelength in the liquid of the sound wave of frequency f. Ro is the distance from the zeroth
electrode to the convergence point of the beam, and 4 is the horizontal distance between the
origin (0) and the electrode. In the above description, for example, a combination of Cr and Au is
preferable as the material of the electrode, in which the strength is strong. The electrodes are
formed on the piezoelectric surface by known techniques such as vapor deposition and
sputtering. As a piezoelectric material, LiNbO3 crystal + 7? Z12 GeO 20 t PZT-based porcelain
(for example, Tokyo N Gas Chemical Industry Co., Ltd. [91 A material) or the like is possible.
Experimental Example (11 ", Piezoelectric Piezoelectric Porcelain 9 made by TDK, Interdigital
electrodes equally spaced in one crucible of A material (electrode period: 1.4 m + n). Electric #! In
a device provided with a planar electrode with the same overlapping width IQym, electrode
finger width and electrode spacing, high frequency pulse electric signals were applied to two
electrode terminals of interdigital * electrode, and the carrier frequency was changed In case. The
direction 5 (θ) of the sound beam emitted from the back side in contact with the liquid changes
with frequency as shown in Fig. 4 0 In this case 1 polarization axis is perpendicular to the weir
including the piezoelectric ceramic interdigital transducer , Piezoelectric porcelain is 70 cylinders
long. Width 2 Qrun, thickness 0.1! 11111である。 In addition, a combination of one of the
two interdigital 10-electrode terminals with a planar electrode on another surface (for stool as a
ground electrode) and a planar electrode are not provided. Similar characteristics were obtained.
In the latter case, 15 sound waves are emitted in both directions of ten and ten. The sound waves
in two directions can be used positively, but depending on the situation, one may be eliminated
by a sound absorption procedure. Experimental Example (2): In a piezoelectric ceramic having
the same characteristics as in Experimental Example 1, an experimental result of an apparatus
designed to converge a sound wave of 2.3 MH 2 from a transducer to 20 fields of 30α is shown.
It is FIG. The graph is centered on energy! l) A 3 dB reduction in beam width is shown. From this
result, it can be seen that the beam width at the converging portion is 7.5 barrels, and the
distance of the sound beam at the converging point l is also close to the design value. The result
is that a flat electrode in contact with the liquid is used as the ground electrode. As a result of
applying a three-phase electrical signal to a total of three sets of electrode terminals with the two
terminals of the interdigital transducer, the emission of the acoustic beam is confirmed in only
one direction. Similar beam focusing of the acoustic wave was also confirmed when applying a
single-phase electrical signal using two of the three electrode terminals.
As described in detail above, by applying an alternating voltage to the interdigital electrode that
can be received on a thin piezoelectric substrate! (ii) A well focused ultrasonic beam can be
emitted into the liquid in contact with the substrate. Non-inventive application lamps, which are
not limited to simple imaging stages, but are generally applicable to applications where it is
necessary to focus the acoustic beam, eg 1 to focus the beam at the interface of liquid and air,
The liquid can be atomized.
4. Brief description of the drawings. FIG. 1 shows an example of the structure of the ultrasonic
transducer 5 according to the non-invention, FIG. 2 shows an example of the structure of the
interdigital transducer 2, FIG. 3 shows the operation of the present invention. FIG. 5 and FIG. 5
show an example of the experimental results. 1; piezoelectric substrate, 2; 3; Flat electrode, 4;
liquid, 10 patent applicants Koji Toda Tokyo Electric Chemical Industry Co., Ltd. Patent
application agent 15 Megumi Yamamoto-"20EndPage: 3 Procedure correction (Spontaneous)
October, 1959 q Patent Office Mr. Yoshiya Kumagaya ■ Indication of the case Patent application
No. 100929 No. 2 title of the invention 2 name of the invention ultrasonic transducer 3 person
who makes correction Related patent applicant name (306) Tokyo Electric Chemical Industry Ltd.
(1 other person) 4 agent address 〒 116 Tokyo Arakawa-ku Nishinippori 3-chome 6-14-407
Telephone 823-8373, -4 name patent attorney (7493) Yamamoto Megumi-
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