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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasound transducer for delivering ultrasound into a liquid. (Conventional art) Conventional
submerged ultrasonic transducers have been known in which interdigital electrodes are formed
on a substrate on a hard piezoelectric material such as ceramic. However, such configurations are
difficult to match with the acoustic impedance of the liquid, eg water, and have required
complicated procedures to obtain high resolution. Recently, polyvinylidene fluoride (PVDF) has
attracted attention as a flexible, high-flexibility piezoelectric polymer film that has characteristics
such as acoustic impedance close to water and living bodies, and an efficient ultrasonic
transformer using this It is being considered to create a drug. (Problems to be Solved by the
Invention) The present invention has been made to address these problems and to eliminate the
above-mentioned conventional drawbacks, and provides a high-resolution submerged ultrasonic
transducer. The purpose is (Means for Solving the Problems) The in-liquid ultrasonic transducer
according to the present invention is disposed at the interface between gas and liquid, and the
direction in which the ultrasonic wave is radiated to the liquid is concave. A substrate of a
polymer film curved with a radius of curvature, an interdigital electrode formed on one surface of
the substrate, and a counter electrode formed on the other surface of the substrate. It is a thing.
According to the present invention, the ultrasonic transducer in liquid is excited by applying a
high frequency voltage between the interdigital electrode and the counter electrode to emit
ultrasonic waves of longitudinal waves in the liquid. At the same time, the resolution is improved
by focusing the Y-axis direction on the X-axis direction while keeping the electrode finger length
of the interdigital electrode constant. (Embodiment) FIG. 1a is a perspective view showing the
structure of an ultrasonic transducer in water according to an embodiment of the present
invention. Substrate l is XI! It consists of a piezoelectric polymer film (LAZ material made by
Mitsubishi Yuka Chemical Co., Ltd.) having a focal distance fiF-15 mm (7) radius of curvature r in
the direction of lb, and on the convex side (left side in the figure) electrode index N-20, electrode
A sheet-like charge I 42 is formed which is excited with a finger spacing p-100 μm, electrode
cross length t + -611 Im, f-12 Mllz, and the opposite electrode 3 is formed on the concave side
(right side in the figure) as shown by the dotted line. And is grounded. When the focal length is F
= 15 mm, the resolution (: ldB beam width) is approximately 1 mm in the X-axis direction and
approximately 0. 0 in the Y-axis direction. : 1 mm. The surface of the substrate 1 on the side on
which the counter electrode 3 is formed (right side in the drawing) is backed by a backing
material 4 made of an acrylic resin (cc 1-0.321) whose acoustic impedance is liquid, ie, 2 mm in
thickness close to water. It is placed in contact with the water via it, as will be explained by
means of FIG. 2 below.
For adhesion between the substrate 1 and the backing material 4, methylene dichloride (not
shown) as an acrylic adhesive is used. The characteristics of the backing material 4 greatly affect
its acoustic characteristics. However, since the backing material 4 in this case is made of a thin
flexible acrylic resin, it gives rigidity to this and the substrate! The backing material 4 is used
because there is a need to protect the formation surface of the upper counter electrode 3. FIG. 2
shows an ultrasound transmitting and receiving system using the ultrasound transducer shown
in FIG. In FIG. 2, a function generator 5 generates an output signal 5a of frequency f-12 MHz to
drive the submerged ultrasonic transducer 6 of the present invention. The submerged ultrasonic
transducer 6 is disposed rotatably around the Y axis in the water 8 filled with water ffI 7. In the
water 8, the hydrophone 9 is disposed to receive the longitudinal ultrasonic wave 6 a emitted
from the submerged ultrasonic transducer 6 through the water 8. A normal detection device 1o
is connected to the hydrophone 9, and the detection output 9a is input as an electrical signal
obtained by delaying the output signal 5a, and this is displayed in synchronization with the
output signal 5a of the function generator 5・ Has a function. In operation, the function
generator 5 excites the submerged ultrasonic transducer 6 by the output signal 5a consisting of
RF (12Mllz) pulses, and when this causes the longitudinal ultrasonic wave 6a to be emitted into
the water 8, the water M7 is generated. Sound pressure waves of ultrasonic waves are generated.
The hydrophone 9 responds to such a sound pressure wave to generate a detection output 9a
having an amplitude proportional to that, and makes the detection device 10 be manual.
Accordingly, the detection device 10 displays the characteristic diagrams as shown in FIGS. 3 to
6 described below. The acoustic field formed in water is shown in FIG. 1 when the submerged
ultrasonic transducer is vibrated at a velocity of ξeJ1m / j in a direction perpendicular to the
plane, assuming that it has an infinite plane. As described above, it can be obtained by regarding
the micro surface Md5 (x, y, z) of the vibration surface of the in-liquid ultrasonic transducer as a
point sound source. The velocity potential dφ on the observation point P (X, Y, Z) located at a
distance 1 @ R from this point sound source is given by the following equation. For this reason,
the velocity potential formed over the entire vibration plane can be obtained by the following
equation by dividing the equation (1) into areas. When the sound source composed of the
interdigital transducer 2 is represented by the superposition of linear sound sources as shown in
FIG. 1, the velocity potential can be calculated as follows: (a) in the case of a planar sound source;
The case is represented by R =.
Where N is an electrode finger, k is a wave number (2π / λ), λ 9 is a wavelength of a
longitudinal wave in water, b is an electrode finger length, r is a curvature radius, p is an
electrode finger distance, θ is ds and F It is an angle which a connecting line forms between two
axes. FIG. 3 is a characteristic diagram showing the sound field distribution on the Z axis, and
shows the case where the structure of the interdigital electrode 2 is N-20, p-100 μI, b = 6 mm)
and the excitation frequency is 12 MHz. In FIG. 3, the X axis represents the distance (mm) from a
planar sound source (ultrasonic transducer in liquid), and the Y axis represents the relative
amplitude (dll) of the sound field (ultrasound 6a). As is apparent from the figure, when the
aperture surface of the ultrasonic transducer in liquid is rectangular, the maximum relative
amplitude is obtained in the distance 111Z (aperture length / 22 / λ) depending on the aperture
length in the X and Y axis directions. There is a value, and the emitted ultrasonic wave
propagates in the form of plane wave independently in the X and Y axis directions to the vicinity
of the maximum value, converges at the vicinity of the maximum value, and propagates as a
cylindrical wave again. I understand that. FIG. 4 is a characteristic diagram showing the
dependence of the vertical distance of the width of the ultrasonic beam emitted from the
ultrasonic transducer in the liquid regarded as a planar sound source, and the vertical distance of
the beam width along the X axis ( mm) and the width (mm) of the ultrasonic beam emitted from
the interdigital transducer 2 on the Y axis. Also, the solid line in the figure indicates the case of 1
3 dB, and the dotted line indicates the case of 1 6 dB. FIG. 5 is a characteristic diagram showing
the sound field distribution with respect to the distance from the sound source when the
excitation frequency of the concave sound source (the ultrasonic transducer in liquid) is 12 MHz,
and the X axis represents the distance Il from the sound source ! (11111) is shown, and the
relative amplitude (dB) of the ultrasonic wave 6a is shown on the Y axis. The bold lines in the
figure are the measured values, and the dotted lines are the calculated values. FIGS. 6a and 6b
show that when the excitation frequency of the sound source (the ultrasonic transducer in liquid)
is 12 MHz, the distance from the concave sound source to the X axis is 1! It is a characteristic
view showing (Olffl) and beam width (mm) to a Y-axis. A thick line in the figure is a characteristic
diagram showing a case of 13 dB and a thin line a case of 16 dB. As apparent from the
characteristic diagrams shown in FIGS. 3 to 6, the submerged ultrasonic transducer according to
the present invention gives an actual measurement result close to the theoretical value, and the
sound source is regarded as a superposition of linear sound sources. It can be confirmed that it
matches well with the sound field analysis of time. As described above, according to the in-liquid
ultrasonic transducer of the present invention, since the interdigital electrodes are arranged on
one surface of the piezoelectric polymer film, (a) in the X and Y axial directions It is possible to
independently control the sound field distribution, and (b) the ultrasonic wave propagates like a
plane wave to the vicinity of the maximum value of the sound field and the ultrasound converges
in the vicinity of the maximum value. By keeping the finger length constant and focusing the Y-
axis focus on the X-axis focus, the resolution can be improved, and (C) a compact ultrasound
device can thus be easily created. Become.
Such a submerged ultrasonic transducer can (a) scan each interdigital electrode electronically
and (b) divide the interdigital electrode into a plurality of groups without using a circulator. It is
possible to transmit and receive signals with the same aperture area, and (C) control of beam
convergence and radiation direction and suppression of side ropes by applying signals of
different phases or amplitudes to each of the electrode fingers. Is possible.
Brief description of the drawings
FIG. 1 is a perspective view showing a submerged ultrasonic transducer structure according to
the present invention, and FIG. 2 is an ultrasonic wave transmitting / receiving system using the
submerged ultrasonic transducer shown in FIG. 1, FIGS. 3 to 6 FIG. 2 is a characteristic diagram
of the in-liquid ultrasonic transducer shown in FIG.
1 ... substrate 2 ... interdigital transducer 3 ... counter electrode 4 ... backing material.