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DESCRIPTION JPS5739699

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DESCRIPTION JPS5739699
Description 1, title of the invention
Ultrasound transducer
3. Detailed Description of the Invention The present invention relates to an ultrasonic transducer
having a piezoelectric element configured to have a variable curvature, and in particular, from
the back side of the transmission / reception wavefront of the piezoelectric element when
transmitting / receiving an ultrasonic wave. It is intended to prevent the generation of the noise-e
due to the reflected wave of. When a voltage is applied to the piezoelectric layer of a laminate
having at least two layers of a piezoelectric layer and a non-piezoelectric layer to stretch or
contract only the piezoelectric layer, the laminate bends in one direction. Japanese Patent
Application No. 54-1129iS proposes an ultrasonic transmitter-receiver that changes the
curvature of the ultrasonic transmission / reception surface by utilizing this bending action. Also,
if the arched primary curved sheet is supported on both sides of the dome and the width of this
support is changed, the curvature of the dome changes or the hemispherical sheet is tightened
from the periphery It is well known that the curvature of this spherical surface changes to a
certain extent. The arched or hemispherical sheet may be used as a piezoelectric body, and the
concave surface of the curved sheet may be used as an ultrasonic transducer or a wave receiving
surface, to provide an ultrasonic transducer with variable curvature. When such a variablecurvature ultrasonic transducer emits a sound wave parallel to one direction, the curvature of the
radiation surface is changed according to the condition of the medium along the way, which
makes the radiation wave always preferable. In the case where the sound waves are concentrated
at one point, the focal point can be freely changed, which is useful as an ultrasonic underwater
transmitter-receiver or an ultrasonic imaging apparatus. Furthermore, Japanese Patent
Application No. 54-9415 proposes an acousto-optic device in which an ultrasonic medium layer
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is provided in contact with a curved piezoelectric element surface. This optical device d generates
a compressional wave of the curved surface in the medium by the ultrasonic wave radiated from
the curved pressure EndPage: 1 collector element, the angle of the incident light causing the
Bragg reflection is a plane The gist of the present invention is that it can be taken in a wide range
as compared with the compression wave of If the curvature of the curved piezoelectric element is
made variable, it is possible to arbitrarily Bragg-reflect incident light in a wider range of angles.
In addition, it is often preferable that the curvature of the curved surface can be changed in an
ultrasonic device that is used by bending the transmission / reception surface of the ultrasonic
device. On the other hand, in transmitting and receiving sound waves by the piezoelectric
element, when the back surface of the transmitting and receiving surface of the piezoelectric
element is in contact with a gas phase such as air, the piezoelectric material such as ceramic or
polyvinylidene fluoride constituting the piezoelectric element and the air Because of the large
difference in acoustic impedance between the two, sound waves may be reflected on the back
surface, and these reflected waves may be superimposed on normal radiation waves and received
waves to become noise.
In order to remove noise due to reflection from the back side of such a pressure 'clt body
element, the difference in acoustic impedance between the piezoelectric element and the back
side of the piezoelectric element is small, and the sound absorption It is practiced to provide
good material layers (e.g., rubber mixed with metal powder in an appropriate ratio). However, if a
sound absorbing material layer such as thick rubber is provided on the back side of the abovedescribed piezoelectric element with variable curvature, the deformation is naturally greatly
restricted, even if it is deformed locally Large distortion may occur to make the transmitted and
received sound waves uneven. According to the present invention, in an ultrasonic transducer
having a piezoelectric element configured to have a variable curvature, a sound absorbing means
made of a liquid such as liquid, slurry or paste is provided in contact with the back side of the
piezoelectric element. Thus, the deformation of the piezoelectric element is not impeded, and the
reflected wave noise from the back side of the piezoelectric element is eliminated. In the present
invention, as a sound absorbing means comprising a liquid, the liquid such as a liquid, a slurry or
a paste may be sealed in an elastic body such as a relatively thin rubber, and such a sealing
means may be used. You may use it. Generally, the back electrode of the piezoelectric element to
be used is, for example, plastic or rubber v to avoid corrosion and leakage. In this case, as the
covering layer, one having an acoustic impedance intermediate to the liquid having a small
acoustic impedance of the piezoelectric element constituting the piezoelectric element is selected,
and the thickness is also selected. It is preferable that the reflection wavelength from the back
side can be further reduced by setting it to t or more of the normal frequency t of this transducer.
Furthermore, the dielectric layer can be configured as a bag-like container for sealing the liquid.
Also, it is possible to use two or more layers of liquid sound absorption means separated by a bag
or hm, and it is also possible to provide a solid sound absorption means such as a comb behind
the liquid sound absorption means. . The invention will now be described by way of example with
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reference to the drawings. In FIG. 1, (1) is a piezoelectric element, for example, an aluminum
vapor deposited electrode (3) (3) 'is formed on both sides of a piezoelectric polyfluoride
(redidentate) (2) having a thickness of 200μ, respectively. Further, thin silicone rubber coating
layers (41 (4) 'A (each are provided on the surfaces of the both electrodes (6), (3)'). Also, the
electrodes (3), (3), '75, etc. lead to the wiring connected to the transmitting circuit and the
receiving circuit. The piezoelectric element (1) is curved in an arched primary curved surface,
and the two classes are supported by flexible side plates (eg, rubber plate, thin metal plate, etc.)
(5), (5) ' .
Further, although not shown, the front and rear side surfaces of the piezoelectric element 1 are
joined to a side plate capable of elastic deformation, such as a rubber plate, for example, so as
not to prevent the deformation thereof. A sound absorbing material layer (6) of a liquid such as
an aqueous dispersion of iron hydroxide is provided on the back surface (upper surface in the
figure) of this piezoelectric element (1), that is, the surface opposite to the wave transmitting /
receiving surface Accordingly, a solid sound absorbing material layer (a force is provided on the
upper portion of the liquid layer (6) such as rubber mixed with metal powder. Furthermore, in
the position just opposite to the two class parts of the piezoelectric element (1) outside the side
plate (5) (5) ', the direction perpendicular to the figure over the length of the piezoelectric
element (1) The push rods (8) (8) 'are respectively provided, and these push rods (8) (8)' may be
provided, for example, by side plates (5 bars 5) by means of plungers EndPage: 2 bars (9) (9) '. )
Is pressed. Then, when the plunger rod (9) (9) 'is pushed out by the front wheel f (10) (10) / and
the push rod (8 bar 8)' is pushed harder, the side plates (5) (5) Since the 'is deformed to press
both edge portions of the piezoelectric element (1) in the direction of the arrow in the figure, the
piezoelectric element (1) is further curved and its curvature is increased. Conversely, when the
plunger rod (9) (9) 'is retracted, the piezoelectric element (1) is restored by its elasticity and the
curvature is reduced. At this time, since the back side of the piezoelectric element (1) is a liquid,
the piezoelectric element (1) is not prevented from being deformed, and the sound absorbing
layer (6) (from the back side due to the presence of force Reflected wave noise is greatly reduced.
FIG. 2 shows an example using a hemispherical piezoelectric element (1) '(the constitution of the
layer may be the same as that of the piezoelectric element (1) in FIG. 1). A rubber ring (12)
having a notch groove (11) 'f is fitted to the inner peripheral portion around the piezoelectric
element (1)', and the ring (12) further has a periphery Is supported by a plurality of diaphragm
plates (14) of the diaphragm mechanism (13). The diaphragm mechanism (13), as shown in FIG.
3, is such that the central hole is opened and closed by the relative movement of a large number
of diaphragm plates (14) sliding relative to each other, and is generally used as a camera
diaphragm mechanism. It may have the same configuration as that of When the diaphragm plate
(14) is squeezed, the piezoelectric element (1y is clamped from the periphery, and within the
elastically deformable range of the material constituting the piezoelectric element (1) ', the
piezoelectric element (outside of 1y) As the diameter decreases, the curvature increases, and
when the diaphragm plate (14) is opened, the curvature decreases due to the elastic restoring
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force of the piezoelectric element (1) '.
The diaphragm p mechanism (13) is attached to the lower part of the cylindrical outer wall (15).
In addition, a sound absorbing means filled with a sound absorbing liquid (17) obtained by
emulsifying fraction of clay and water in heavy oil is superimposed in a piezoelectric element (1
in the upper part in a rubber or plastic bag (16) . At this time, if air is left between the bag (16)
and the back surface of the piezoelectric element (1) ', this becomes an anti-reflection layer of
sound waves, so when overlapping the bag (16), for example, liquid surface activity It is
preferable that an agent or the like be applied between the bag (16) and the piezoelectric
element (1y back surface so as not to leave an air layer). Another cylindrical outer wall (25) is
further superimposed on top of the cylindrical outer wall (15). On the lower part of this
cylindrical outer wall (25), a stone gap M (26) made of a flexible film such as rubber is disposed,
and iron powder is dispersed in the outer wall The paste-like sound-absorbing material (27) is
filled. As described above, in the ultrasonic transducer according to the present invention, since
the sound absorbing means made of liquid is provided on the back side of the piezoelectric
element configured to have a variable curvature, the deformation of the piezoelectric element is
prevented. It can eliminate the reflected wave noise from the back side.
4. Brief Description of the Drawings Fig. 1 is a cross-sectional view of an essential part of an
ultrasonic transducer according to a first embodiment of the present invention, and Fig. 2 is an
ultrasonic transducer according to a second embodiment of the present invention. FIG. 3 is a
schematic plan view showing the throttling mechanism in the transducer of FIG. In addition, in
the reference numerals used in the drawings, (1) (1) '... Liquid layer (16)... Agent Katsuya
Katsuhiro Saka Matsumura EndPage: 3
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