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JPH01166697

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DESCRIPTION JPH01166697
[0001]
<Industrial field of application> The present invention radiates a sound wave or an ultrasonic
wave toward a detected object into water, or reflects it back from the detected object, such as a
seafloor seismic surveyor or a fish finder. (The present invention relates to an underwater
piezoelectric transducer sheet for receiving reflected waves. <Prior Art> Piezoelectric organic
matter such as polyvinylidene fluoride, polyvinylidene fluoride, polyvinylidene chloride, polyvinyl
chloride, nylon, etc. or organic matter of synthetic rubber or synthetic resin, such as lead
zirconate titanate, lead titanate, etc. A piezoelectric flexible sheet such as a piezoelectric organic
ceramic composite formed by mixing dielectric ceramic particles has a characteristic that
acoustic impedance approximates to acoustic impedance of water, and therefore, propagates in
water as a piezoelectric transducer. Used to receive acoustic waves. Other than this, there are
piezoelectric ceramic plates that are used as piezoelectric transducers. Furthermore, a
piezoelectric flexible sheet or a piezoelectric ceramic plate is also used as a transmitter for
emitting a sound wave or an ultrasonic wave toward a detected object. This is a piezoelectric
transducer sheet for water using a piezoelectric plate consisting of this piezoelectric flexible
sheet, piezoelectric Mi plate, etc., and as shown in FIG. 4, electrodes are formed on the upper and
lower sides and polarized in the thickness direction The outer periphery of a piezoelectric plate a
formed by laminating two piezoelectric plate layers b and b in such a manner that their
polarization directions face each other is covered with a metal coating d having a substantially
rectangular cross section, and the periphery of the piezoelectric plate a and metal coating It has
been proposed to form voids e, e between it and the inner surface of d, and to contact the metal
coated inner surface with the front and back surfaces. The piezoelectric plate a can be formed of
only one piezoelectric plate layer. The piezoelectric wave-receiving sheet of this configuration
immerses this in water and applies an alternating voltage to the electrodes of each piezoelectric
plate layer, b to oscillate sound waves or ultrasonic waves from the main surface of the
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metallized, or A reflected wave is captured from the main surface of the metallized ld, and an
output signal is extracted from between the electrodes to receive an acoustic wave propagating
in water. <Problems to be Solved by the Invention> In the case where the piezoelectric plate a
according to the above configuration is used as a delivery device, it detects acoustic waves under
hydrostatic pressure, and its sensitivity is different from that of each piezoelectric plate layer. It
is determined by the piezoelectric constant gh. The piezoelectric constant gh is given by the
following equation. g h: g 3 s + 2 g sr Here a constant g. Represents the sensitivity to pressure pl
in the thickness direction (polarization direction), and the constant gm + represents the
sensitivity to pressure p2 in the surface direction (direction perpendicular to the polarization
axis). By the way. Since l g 3+ is a negative value, g n <g 3 s, and when the influence of the
pressure p 2 is strong, only low sensitivity can be obtained.
This is the same as in the case of being used as a transmitter, and the water pressure from the
surface direction causes a decrease in the piezoelectric constant d7. Therefore, in the abovedescribed conventional configuration, the air gaps e, e are formed between both side surfaces of
the piezoelectric plate a and the inner surface of the metal cover lWd, and the pressure p2 from
the outer surface direction is the air gap e. Buffering is performed by the deflection of the metal
coating d around e, and this pressure component is relieved. However, this force causes the
upper and lower surfaces of the metal coating d to bulge because the corner edges of the metal
cover ld are curved, and as shown in FIG. 4, the outward pressure in the thickness direction
(polarization direction) Produces p3. Since this pressure acts in the opposite direction to the
effective pressure p +, it eventually reduces the pressure in the thickness direction (polarization
direction). For this reason, even in the above-described conventional configuration, the apparent
underwater reception sensitivity is reduced due to the influence of the pressure p2. The present
invention provides an underwater piezoelectric transducer sheet capable of removing outward
bulging of the upper and lower surfaces of the metal covered rMd due to the pressure p2 in the
surface direction (direction perpendicular to the polarization axis) to improve the receiving
sensitivity. It is the purpose. <Means for Solving the Problems> The present invention is
characterized in that an outward bulging portion is formed at the corner edge of the metal
coating. In the above configuration, when the pressure p2 acts in the surface direction (direction
perpendicular to the polarization axis) from the peripheral edge of the piezoelectric plate, the
upper and lower surfaces are inward due to the bulges formed on each corner of the metal
coating Try to swell. Therefore, the pressure p2 is in the thickness direction to generate an
inward component force p4. Therefore, since this pressure p4 is in the same direction as the
pressure p due to one reflected wave, it works in the direction to improve the delivery sensitivity.
EXAMPLE With reference to FIGS. 1 to 3, reference numeral 1 denotes a piezoelectric plate, and
lead zirconate titanate (Pb (Ti-ZrlO-), lead titanate (Pt) in an organic base material such as
synthetic rubber or synthetic resin. A piezoelectric flexible sheet or a piezoelectric ceramic
sintered body made of a composite material in which a piezoelectric ceramic powder such as
PbTi03) is mixed. Two rectangular piezoelectric plate layers 2a and 2b which are polarized in the
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thickness direction are laminated on each other so that the polarization directions thereof are
opposite to each other. Electrodes 3.4 are respectively formed on the front and back of the
piezoelectric plate layers 2a and 2b. A substantially rectangular metal coating 10 is coated on the
outer periphery of the piezoelectric plate l with an air gap 11 at the periphery of the piezoelectric
plate l. The upper and lower inner surfaces of the metal cover 7110 are in contact with the front
and back surfaces of the piezoelectric plate l. In the upper and lower corners of the air gap 11, an
acute-angled enlarged portion 12.12 in the figure according to the main part of the present
invention is formed.
When a pressure p2 is applied from the peripheral edge of the piezoelectric transducer sheet
having such a configuration, the force is in the thickness direction, and the upper and lower
portions of the metal coating 10 are inside by the swelling portion 12.12. Produces a component
that expands towards you. The pressure P4 (see FIG. 3) due to this component force is the
pressure p4 at which the metal film 10 is in pressure contact with the front and back surfaces of
the piezoelectric plate l, and it is in the same direction as the pressure pl by the acoustic wave to
be received. Reinforce. Therefore, delivery sensitivity will be improved. Then, an output signal
due to the pressure wave in the thickness direction is generated between the electrodes 3.4 in
each of the piezoelectric plate layers 2a and 2b, and the sum of the outputs is taken out by a
connection unit (not shown). As shown in the following table, the improvement in improvement
of 3.6 dB was recognized when the underwater wave receiving sensitivity was compared with the
conventional one in the above example. In the embodiment, the shape of the bulging portion
12.12 may be variously applied such as an arc shape and may be bulging from around the corner
edge of the metal cover 11i10. Further, although the piezoelectric plate l is configured by
laminating two piezoelectric plate layers 2a and 2b, it can be configured by a negative plate or a
large number of piezoelectric plate layers. <Effects of the Invention> As the present invention
clarified in the above description, since the bulge 1111m12.12 is formed at the corner edge of
the metal coating 10 covering the piezoelectric plate 1, the bulge 12 ° 12 is viewed from the
surface direction The component force in the thickness direction due to the force is converted
into a force that causes the upper and lower portions of the metal coating 10 to bulge inward,
and the component force does not lower the receiving sensitivity as in the prior art. On the
contrary, there is an excellent effect that the sensitivity can be improved.
[0002]
Brief description of the drawings
[0003]
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1 is a partially cutaway perspective view of a piezoelectric wave receiving sheet according to an
embodiment of the present invention, FIG. 2 is a cutaway plan view of the same portion, FIG. 3 is
a side view of the same layer, and FIG. It is a side view.
1: Piezoelectric plate 10: Metal coating ll: Air gap 12.12; bulged portion [2 塘 2 (2 FIG. 4)
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