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JPS5478688

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DESCRIPTION JPS5478688
Description 1, title of the invention
Ultrasonic conversion method
3. Detailed Description of the Invention The present invention relates to an ultrasound
conversion method for use in an ultrasound system, and in particular to a method for the
generation or detection of focused ultrasound. Even in an optically opaque medium, as long as it
is acoustically transparent, observation of a fluoroscopic image by acoustic waves is possible as
in X-ray fluoroscopy. Ultrasound imaging of optically opaque materials can be used for medical
diagnostics, microscopy, nondestructive testing, observation of seafloor patterns, and response to
the field of seismic research, EndPage: 1. As a conventional ultrasonic transducer, one using an
acoustic phase plate and one using an annular array. 'The one using an acoustic lens, the one
using a light-acoustic transducer, etc. have been proposed. However, there is still room for
improvement in terms of the convergence of the sound waves necessary for ultrasonic imaging.
In order to improve the above points, the applicants have previously proposed an ultrasonic
transducer that generates an ultrasonic beam with excellent convergence according to Japanese
Patent Application No. 52-31507 and others. This transducer generates an ultrasonic wave beam
by applying an alternating current signal to the interdigital transducer which is received by the
surface of the piezoelectric substance and in contact with the liquid. Although the abovementioned conventional transducer can generate focused ultrasound, the focused ultrasound
converges on a straight line. That is, one-dimensional convergence. Accordingly, it is an object of
the present invention to provide a method for generating an ultrasonic wave which converges to
a point in a two-dimensional plane which is a further improvement of the conventional ultrasonic
transducer and converges on the point. It is in. The characteristics of the i sound wave generation
method according to the present invention to achieve this purpose. A plurality of interdigital
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electrodes are arranged on the surface of the piezoelectric material in the longitudinal direction
of the electrode fingers, and the spacing between the interdigital electrodes of each interdigital
electrode is determined according to a predetermined rule. The transducer is used by contacting
interdigital electrodes with an appropriate liquid, and the interdigital electrodes are applied with
electric signals of the same frequency and different in phase. An embodiment will be described
below with reference to the drawings. FIG. 1 is a structural example of a convergent ultrasonic
transducer according to the present invention, wherein a liquid 2 is produced in a container 1
and a piezoelectric substance 3 having an interdigital electrode 4 on one surface is produced in
the liquid. . As a liquid. Water, ether, acetone, glycerin and the like are possible. As shown in FIG.
2 (A), the electrode 4 is a single-phase electrode in which tooth-like electrodes of a brush are
alternately interdigitally arranged and an alternating current signal is applied to the terminals (,)
and (b). And, as shown in Fig. 2 (B), the electrodes configured in interdigital are connected to
every third wood, and three-phase AC signal is applied from terminals (α input (3), (b) and (1)
electrode.
Or similarly, it is possible to connect multi-phase electrodes by connecting electrodes of every -n
(where n is a natural number greater than or equal to 4 and-n) woods to apply an n-phase
alternating current signal. In the case of a single-phase electrode, two ultrasonic beams are
generated, whereas in the case of a three-phase electrode, a single ultrasonic beam is obtained.
For example, 0? Water resistance is strong and good by combining Au and Au. As the
piezoelectric substance, LLNb 03. crystal. BL12Ge02o, PZT-based porcelain (for example, 91A
material manufactured by Tokyo Electric Chemical Industry Co., Ltd.) can be used. Next, the
distance between the electrodes will be described with reference to FIG. The relationship between
the wavelength λf in a liquid having a sound wave of frequency f and the direction (angle θ) of
the maximum output of the beam is determined by the following equation, which agrees well
with the experimental results by the inventor. sin θ 2 λ r / li − (1) where d is the electrode
period. 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 the
respective points pass through the point P and are in phase) (4) r ", = R2 o- L2 == k, nλtL + k2s2
coin +++ (2) needs to be established. Here, rn is the distance between the nth electrode and the
point Q, Rn is the distance between the nth electrode and the point P, 1 is a constant, and 2 is a
constant. The value of (k □, 2) is (−i−9). The distance between the electrodes can be obtained
by calculating the equations (1) and (2) by a computer. Next, the experimental results of the
beam radiation angle θ with respect to the combination layer of each piezoelectric substance
and liquid are shown in the following table. EndPage: 2 From the above table, it can be
understood that in order to reduce the value of θ, it is sufficient to combine a liquid with a slow
sound velocity and a piezoelectric material with a high surface acoustic wave transmission
velocity. It is clear from the 9 or more explanations that the convergence condition of the sound
wave changes depending on the frequency of the sound wave, and the experimental results are
shown in FIGS. 4 and 5 (the piezoelectric material is 91A and the liquid is water). . FIG. 4 shows
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the results of observing the directivity characteristics at each frequency and determining the
shape of the sound beam from the directivity characteristic curve, where the horizontal axis
indicates the distance from the sound source and the vertical axis indicates the beam width. If the
focal length for each frequency is determined from FIG. 4, it becomes as shown in FIG. When the
characteristics were examined by scaling the electrode pattern of the transducer to 1, it showed a
focal length of 16 cm and a beam width of 3.8- at a center frequency of 5 MHz. Also, the focal
length with respect to the change of frequency changed as well. Thus, it can be seen that the
transducers according to the invention satisfy the similarity relation. By the above structure, the
ultrasonic beam can be converged in one direction (X direction).
Next, the convergence of the beam in the V direction will be described. FIG. 6 is a structural
example of an ultrasonic transducer according to the present invention, in which a plurality of
interdigital electrodes 1α + 4b * 4 ('+... 4i are formed on the piezoelectric substance 3 and these
interdigital electrodes are used. An electrode group 10 is configured. Regarding the electrode
period of each interdigital electrode, the conditions described earlier in FIG. 3 and FIG. 2 are
assumed to hold. The interdigital electrodes 1α, 4b, 4c,... Are arranged in the longitudinal
direction of the electrode fingers as illustrated. Although each interdigital transducer in FIG. 6 is
actually used in contact with the liquid as shown in FIG. 1, the liquid is omitted in FIG. In the
configuration of FIG. 6, the electrode configuration satisfies the relationship described earlier
with reference to FIGS. 3 and 2. Due to this relationship, the ultrasound beam converges in the π
direction. A number of X-directionally converging beams corresponding to the number of
interdigital electrodes are obtained. On the other hand, with regard to the characteristics in the yaxis direction, the plurality of interdigital electrodes 4α, 4b, 4c,... Have the same function as the
diffraction grating in optics. Therefore, the phase of the ultrasonic wave generated by setting the
electric signal applied to each interdigital electrode as a signal (φ1.φ2.φ3.φ4...) With the same
frequency and phase difference (7) Differently, the beam can be converged on a line parallel to
two axes as a whole (convergence in the V-axis direction). As a result, by combining the
convergence in the π axis direction and the convergence in the V axis direction, it is possible to
obtain a two-dimensional convergent ultrasound which converges to the point F. Now, V is the
position of the n-th interdigital transducer in the V-axis direction. , Ω angular frequency of the
signal. , In front of the transducer of the acoustic wave emitted when a signal of a phase shift
Δφ (uo ") from the reference value is applied ('. Assuming that the phase of the sound wave φ n
(y * g) when it reaches the line located at g), φ n ('+ g) is given by the following equation, where t
is the speed of sound in the liquid, and the rear 9 is t. The sound beams are all in phase and thus
converge on the in-phase line □. In addition, 2 is the distance of the focus direction from an
electrode, and distance. (8) where m is an integer, and when the distance between the interdigital
electrodes is L, 'IIn = nt. Therefore, an ultrasonic beam focused on a single line can be obtained
by applying an electrical signal of a phase satisfying the above equation to each interdigital
transducer in FIG. An electrical signal having a phase difference can be obtained by a surface
wave delay line having a tap, or can be obtained by combining known circuit techniques.
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As an experimental example of convergence in the 1 · v axis direction, a piezoelectric substance
(C Tokyo Electric Chemical Industry Co., Ltd. exfoliated piezoelectric ceramic 91A material is
used. When a signal with a phase satisfying the above equation is applied at 9 frequencies 5.0
MH, using 10 equally spaced interdigital electrodes (interdigital electrodes) with an electrode
period of 428 μm, the distance from the transducer is 20 crIL It was possible to obtain one
linear beam in the plane in FIG. 7 is another structural example of the ultrasonic transducer
according to the present invention on a single piezoelectric substrate 3. EndPage: 3 A plurality of
electrode groups 10 shown in FIG. 6 are provided as 10a and 10b. The electrode group 10α has
interdigital electrodes 4α, 4b,..., And the other electrode group 10b has interdigital electrodes
4a, 4b,. The electrode period (d) in each electrode group and the position of the interdigital
transducer in the V-axis direction are different from each other. Since the focusing position of the
ultrasonic beam of each electrode group depends on the applied frequency and the structure of
the electrode group, the focal length can be varied by switching the electric signal using the
transducer of the structure of FIG. Sound waves can be obtained. Of course, three or more
electrode groups can be placed on a single piezoelectric material. As described above in detail,
there is provided a transducer reducer in which a plurality of interdigital electrodes arranged at
appropriate intervals on the piezoelectric material are formed in the longitudinal direction of the
electrode fingers. By arranging the electrodes so as to be in contact with the liquid and applying
AC signals of the same frequency and different phases to the electrodes, an ultrasonic beam
converging to 91 points can be obtained. The electrode surface can be protected from
deterioration of the electrode by covering the surface with a protective film such as silicon
rubber. In the above embodiment, generation of ultrasonic waves is mainly described as an
example, but the transducer according to the present invention can also detect ultrasonic waves
and convert them into electric energy. At this time, a strong electrical signal is generated with
respect to the ultrasonic wave generated from the focal point. The application of the invention is
not limited solely to imaging, but is generally applicable to applications where it is necessary to
focus the acoustic beam, for example by focusing the beam at the liquid-air interface to make it It
can be atomized.
4. Brief description of the drawings. FIG. 1 shows an example of the structure of an ultrasonic
transducer according to the present invention, FIGS. 4 and 5 show an example of experimental
results, FIG. 6 shows another structural example of the ultrasonic transducer according to the
present invention, and FIG. 7 further shows the ultrasonic transducer according to the present
invention. It is another structural example. 1; container, 2; liquid. (11) 3; Piezoelectric substance.
4.4α, 4b, 4α, 4b; Patent applicant Tokyo Electric Chemical Industry Co., Ltd. To 1) Koji patent
application agent Patent attorney Attorney Yamamoto Megumi-(12) EndPage: 4 4 M 'J 45 Figure
C ~ X X End Page: 5
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