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JPH05183994

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JPH05183994
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention radiates a
sound wave or 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 that receives an incoming reflected wave.
[0002]
A piezoelectric rubber plate formed by mixing ferroelectric ceramic particles such as lead
zirconate titanate and lead titanate in synthetic rubber has a characteristic that acoustic
impedance approximates to acoustic impedance of water, Therefore, it is used as a transducer
that receives an acoustic wave propagating in water as a piezoelectric transducer, or radiates an
ultrasonic wave toward a detected object.
[0003]
As shown in FIG. 5, in the conventional configuration of a piezoelectric transducer sheet for
water using this piezoelectric rubber plate, electrodes b and c are formed on the front and back
surfaces of the piezoelectric rubber plate a, and a predetermined distance between the electrodes
b and c is provided. DC voltage is applied to polarize the piezoelectric rubber plate a in the
thickness direction, and the piezoelectric rubber plate a is covered with a molding material d
made of urethane resin or the like to form a rectangular plate, which is immersed in water Then,
an alternating voltage is applied to the electrodes b and c to oscillate sound waves or ultrasonic
waves, or an output signal is extracted from between the electrodes b and c to receive an
acoustic wave propagating in water.
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[0004]
By the way, when the piezoelectric rubber plate according to the above configuration is used as a
receiver, it detects acoustic waves under hydrostatic pressure, and its sensitivity is the
piezoelectric constant gh Determined by
This gh is given by the following equation.
Here, the constant g33 indicates the sensitivity to the pressure p1 in the thickness direction
(polarization direction), and the constant g31 indicates the sensitivity to the pressure p2 in the
surface direction (direction perpendicular to the polarization axis). By the way, since g31 is a
negative value, gh <g33, and in the above-mentioned conventional configuration, the value of gh
is only 1/2 to 1/3 of g33, and only low sensitivity can be obtained because of the pressure p2. I
could not This is the same as when used as a transmitter, and the hydraulic pressure from the
surface direction causes a decrease in the piezoelectric constant dh. The present invention
reduces the constant g 31 as much as possible by removing the influence of the pressure p 2 in
the surface direction (direction perpendicular to the polarization axis) as much as possible, and
makes the constant gh approximate to g 33 and receive sensitivity. It is an object of the present
invention to provide a piezoelectric wave transmitting / receiving sheet for water which can
improve the wave transmission performance by increasing the constant dh.
[0005]
In the piezoelectric transducer sheet for water of the present invention, a tensile force in the
surface direction is applied to a piezoelectric rubber plate having electrodes formed on the front
and back surfaces and polarized in the thickness direction. It is characterized by
[0006]
As a means for applying this tensile force, the outer peripheral edge of the piezoelectric rubber
plate having electrodes formed on the front and back surfaces and polarized in the thickness
direction is surrounded by a rigid frame at intervals, and heat is at least within the interval. It
may be proposed that a mold material made of a curable resin be filled, heat cured, and further
cooled and integrally bonded.
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[0007]
Further, in the case of using such tension means, the flexible carrier plate is stretched in the
surface direction in the rigid frame in order to make it easy to arrange the piezoelectric rubber
plate at intervals in the rigid frame. It may be proposed that a polarized piezoelectric rubber
plate be attached to at least one side of the plate.
[0008]
When a piezoelectric rubber plate x formed by mixing ferroelectric ceramic particles z such as
lead zirconate titanate and lead titanate in synthetic rubber y as shown in FIG. From the state of
(a), as shown in (b) of FIG.
While maintaining such a state, when pressure p2 acts from the circumference of piezoelectric
rubber plate x from the circumferential direction by hydrostatic pressure etc., pressure p2 is
relieved by gap s and acts on ferroelectric ceramic particles z. Therefore, apparently, the
piezoelectric constant d31 and the piezoelectric constant g31 decrease.
[0009]
As a means for applying this tensile force, as described above, the outer peripheral edge of the
piezoelectric rubber plate is surrounded by a rigid frame at intervals, the molding material is
filled in the interval, the temperature is raised for thermal expansion, When the temperature is
reduced to cause thermal contraction, the mold material between the inner peripheral surface of
the rigid frame and the outer peripheral surface of the piezoelectric rubber plate is tensioned in
the contraction direction by this contraction step, and hence the contraction force is piezoelectric
rubber As a force for pulling the outer periphery of the plate outward, it acts as a tensile force in
the surface direction on the piezoelectric rubber plate.
[0010]
BRIEF DESCRIPTION OF THE DRAWINGS An embodiment of the invention will be described with
reference to the accompanying drawings, in which: FIG.
Referring to FIGS. 2 and 3, 2 is a rectangular piezoelectric rubber plate obtained by mixing
piezoelectric ceramic powder such as lead zirconate titanate (Pb (Ti.Zr) O3) and lead titanate
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(PbTiO3) into synthetic rubber. It is polarized in the thickness direction, the electrodes 3 are
formed on the front and back surfaces, and signals can be taken out from between the electrodes
3 by the lead wires 4.
[0011]
A rectangular rigid frame 10 thicker than the piezoelectric rubber plate 1 is loosely fitted to the
outer peripheral edge of the piezoelectric rubber plate 1 at rectangular intervals 11.
The rectangular rigid frame 10 uses a rigid (large spring constant) material such as metal or
plastic.
[0012]
Next, a mold material 12 made of a thermosetting resin such as an epoxy resin or a urethane
resin is provided on the inner side of the rigid frame 10 so as to surround the piezoelectric
rubber plate 2 and to have a thickness substantially equal to that of the rigid frame 10 Fill in as
shown in Fig. 3a.
Then, the molding material 12 is heated and cured in a thermally expanded state as shown in
FIG. Further, temperature curing is carried out at normal temperature to shrink the mold material
12 as shown in FIG. As a result of this contraction process, the mold material 12 in the space 11
between the inner peripheral surface of the rigid frame 10 and the peripheral surface of the
piezoelectric rubber plate 2 is tensioned in the contraction direction as shown by the arrow and
thus the contraction force is As a force for pulling the outer periphery of the piezoelectric rubber
plate 2 outward, it acts on the piezoelectric rubber plate 2 as a tensile force in the surface
direction. For this reason, as shown in FIG. 1, a gap s is generated between the synthetic rubber y
and the synthetic rubber y around the surface direction of the ferroelectric ceramic particles z in
the synthetic rubber y, apparently the piezoelectric constant d31 and the piezoelectric The
constant g31 becomes smaller. The molding material 12 is filled only in the space 11 to bridge
the inner peripheral surface of the rigid frame 10 with the peripheral portion of the piezoelectric
rubber plate 2 and expose the main front and back surfaces of the piezoelectric rubber plate 1.
You may do so.
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[0013]
Thus, in the case where the underwater piezoelectric transducer sheet 1 is configured and the
pressure p2 is present in the water from the periphery, the piezoelectric constant d31 and the
piezoelectric constant g31 due to the gap s approximate zero. By the pressure resistance action
of the rigid frame 10, the influence of the pressure p2 can be removed, the sensitivity
(piezoelectric constant d33 or g33) to the pressure p1 in the thickness direction (polarization
direction) is relatively increased, and the constant gh is improved. In addition to high sensitivity,
in the case of transmission, the constant dh is increased to improve transmission performance.
[0014]
According to the experiment, the noise due to the pressure p2 from the circumferential direction
was reduced by the hydrostatic pressure etc., and the fluctuation of the output was reduced to
1.5 dB as compared to 3.1 dB in the conventional configuration.
Also, the receiving sensitivity has been improved by 4 to 7 dB.
[0015]
FIG. 4 makes it easy to arrange the piezoelectric rubber plate 2 at intervals 11 in the rigid frame
10 as described above, and the peripheral edge of the rigid rubber frame 10 is rigid in the inside
thereof. The flexible carrier plate 20 made of glass fiber, carbon fiber, aramid fiber or the like is
stretched in the surface direction, fixed to the inner peripheral surface of the frame 10, polarized
in the thickness direction on the front and back surfaces, and the front and back surfaces The
piezoelectric rubber plates 2a and 2b on which the electrodes 3 and 3 are formed are attached
thereto. Then, the piezoelectric rubber plates 2a and 2b are held by the flexible carrier plate 20,
and the molding material 12 is filled in the rigid frame 10 as in FIG. 3, heated and cured, and
cooled at normal temperature. As a result, the underwater piezoelectric transmitting and
receiving sheet 1 is configured, and the same effects as those described above can be obtained. A
piezoelectric rubber plate may be disposed only on one side of the flexible carrier plate 20.
[0016]
According to the present invention, as clarified by the above description, the piezoelectric rubber
plate x is pulled in the surface direction to form a gap s in the surface direction of the
ferroelectric ceramic particles z in the synthetic rubber y. Since the piezoelectric wave
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transmitting / receiving sheet for water is generated to generate the underwater pressure
transmitting / receiving sheet, even if pressure in the surface direction is applied to the
peripheral edge of the water transmitting / receiving sheet, the piezoelectric constants d31 and
g31 are apparently reduced. The piezoelectric constant gh is improved to provide high
sensitivity, and in the case of transmission, the constant dh is increased to improve transmission
performance.
[0017]
Brief description of the drawings
[0018]
1 is a longitudinal side view showing the action of the piezoelectric rubber plate x in the surface
direction by tension.
[0019]
2 is an exploded perspective view of the piezoelectric transmitting and receiving sheet 1 for
water.
[0020]
3 is a longitudinal side view showing the process of filling the mold material 12 of the
piezoelectric wave sheet 1 for water, and heating and cooling steps.
[0021]
4 is a longitudinal side view showing the underwater piezoelectric transmitting and receiving
sheet 1 in which the flexible carrier plate 20 is stretched inside the rigid frame 10. FIG.
[0022]
5 is a longitudinal side view of the conventional configuration.
[0023]
Explanation of sign
[0024]
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DESCRIPTION OF SYMBOLS 1 Piezoelectric wave sheet for underwater 2 Piezoelectric rubber
plate 10 Rigid frame 11 Interval 12 Mold material 20 Flexible support plate x Piezoelectric
rubber plate y Synthetic rubber z Ferroelectric ceramic particle s Gap
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