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JPH03114399

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DESCRIPTION JPH03114399
[0001]
FIELD OF THE INVENTION The present invention relates to acoustoelectric transducers, and
more particularly to a hydrophone used for detecting underwater acoustic waves. [Prior Art]
Conventionally, a piezoelectric ceramic (for example, lead zirconate titanate) is often used as a
hydrophone for detecting acoustic waves in water. In recent years, new materials such as
polyvinylidene fluoride (hereinafter referred to as PVDF) and piezoelectric rubber are used. In
particular, a transducer using PVDF is flexible, and has an advantage that it can be manufactured
even with a small specific gravity and a large area. As shown in FIG. 3, the general structure of a
converter using PVDF is as follows: a metal electrode 32 is deposited on both surfaces of a
stretched PVDF plate 31 or a PVDF electrode 310 obtained by copolymerizing a metal foil
electrode on both surfaces It has a structure with 32 attached. [Problems to be Solved by the
Invention] The above-mentioned conventional converter has a structure in which a metal is used
as an electrode material and a PVDF plate is sandwiched. In such a PVDF converter, in the case of
using the volume reception mode (a mode in which an underwater sound wave is converted to an
electric signal using the piezoelectric distortion constant gh = g33 + g31 + g32 as a conversion
parameter), the larger the piezoelectric constant gh of the piezoelectric converter, the same The
thickness of the PVDF plate can provide a highly sensitive transducer. As is well known, g33 and
g31. G32 has an opposite sign to each other. Therefore, in order to increase gh, g31. It suffices to
realize g32 to a small value. For this purpose, it is sufficient to suppress the stress generated in
the direction along the surface of the PVDF plate when a sound wave is applied. Conventionally,
the stress in the direction along the surface of the PVDF plate has been reduced by increasing the
thickness of the metal electrode. However, in this method, g31. The amount of reduction of g32
is limited by the modulus and thickness of the metal material, but increasing the thickness of the
electrode to increase the amount of reduction increases the acoustic impedance (square root of
product of density and modulus) of PVDF and electrode material Because of the difference, there
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is an acoustic mismatch in the opening of the water and the converter, which causes a problem
that the receiving sensitivity can not be increased. In addition, since metal has a large specific
gravity, it acts as a load mass when vibration is applied to the PVDF plate, and acceleration
sensitivity (sensitivity when noise output is produced by acceleration generated by vibration etc.
transmitted from the periphery outside the volume) is high. It has the drawback of becoming The
present invention has been made in view of the above-described conventional circumstances, and
an object of the present invention is to provide an acoustoelectric transducer having a high
delivery sensitivity without causing the above-mentioned drawbacks.
[Means for Solving the Problems] In the acoustoelectric converter of the present invention,
electrodes are provided on both surfaces of a polyvinylidene fluoride plate having
piezoelectricity, and the surface of a polyvinylidene fluoride plate is provided outside of at least
one of the electrodes. A fiber reinforced plastic layer reinforced with fibers arranged in parallel
to each other is provided. That is, the stress in the direction along the surface of polyvinylidene
fluoride (PVDF) plate is reduced by the transition reinforced plastic layer, and the piezoelectric
constant Frgh does not decrease g33. Keep g32 small. Next, the present invention will be
described with reference to the drawings. FIG. 1 is a perspective view showing the structure of an
embodiment of the present invention. In the present embodiment, the electrodes 2 are provided
on both surfaces of the PVDF plate 1, and the fiber reinforced plastic N3 is provided on the outer
side thereof. FIG. 2 is an explanatory view showing the operation of the acoustoelectric converter
of the above-mentioned construction. The fiber-reinforced plastic layer 3 weaves reinforcing
fibers 4 (for example, carbon fibers etc.) in at least one direction or more in a direction along the
surface of the PVDF plate 1 (that is, any direction included in the xy plane). The rate is high. Now,
the sound thickness P is applied not only from the upper and lower surfaces of the PVDF plate 1
but also from the side surfaces. However, the elasticity in the thickness direction of the fiber
reinforced plastic layer 3 is rather close to the elastic modulus of the plastic material alone of the
base material because there is almost no effect of the reinforced fiber 4. Here, since the density
of the plastic material, the elastic modulus in the Z-axis direction, and the density and elastic
modulus of PVDF are respectively approximately equal, the acoustic impedance (the square root
of the product of density and elastic modulus) is also approximately equal to cause a mismatch.
Sound pressure is applied to the PVDF plate 1. Therefore, g33 hardly changes even if the fiber
reinforced plastic layer is provided. On the other hand, in the xy plane direction, the elastic
modulus is high due to the reinforcing fiber 4 (for example, the epoxy resin of plastic material
has a tensile elastic modulus of about 6 GPa, while the epoxy resin reinforced with carbon fiber
has a tensile of about 190 GPa Has an elastic modulus), suppresses the stress generated in the xy
plane direction (direction along the surface) of the PVDF plate 1, and the acoustic impedance
ratio with water increases by the amount of the elastic modulus, and the sound pressure It
becomes difficult to add to PVDF board 1. That is, if the reinforced plastic layer 3 is provided,
g31 and g32 can be reduced without changing g33. For example, g33 is 0. If constant at 2 vm /
N, before applying the fiber reinforced plastic layer g31. The g 32 of 0 ░ 02 vm / m can be
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reduced to 0.002 vm by providing the fiber reinforced plastic layer, and the gh constant can be
improved by 22%.
Although the fiber reinforced plastic layers are provided on both surface sides of the PVDF plate
in the above embodiment, sufficient effects can be obtained by providing the fiber reinforced
plastic layers on only one of them. Also, if the fiber orientation of the fiber reinforced plastic
layer is parallel to the surface of the PVDF plate, the stress in this direction can be suppressed, so
there is no particular limitation on the other, but as shown in FIG. A mode in which the direction
of force crosses and is oriented is preferable in view of the stress suppressing effect. Further, the
electrode material is not limited to metal, and may be conductive plastic or the like. [Effects of
the Invention] As described above, according to the present invention, by providing electrodes on
both surfaces of a PVDF plate having piezoelectricity and further providing a fiber reinforced
plastic layer on at least one of the outer side, sound pressure in the thickness direction can be
reduced. The stress in the direction along the surface of the PVDF plate can be suppressed
without inhibiting the transmission. For this reason, since the volume reception mode gh
constant can be increased as compared with the conventional case, there is an effect of
increasing the acousto-electrical conversion efficiency. In addition, fiber reinforced plastic has
lighter specific gravity (for example, 8.9 for copper vs. 1.6 to 2.0 for reinforced plastic), but even
if fiber reinforced plastic is provided to increase the gh constant There is little deterioration in
acceleration sensitivity observed when the metal layer is thickened, and it is difficult to receive
the influence of vibration transmitted from the surroundings.
[0002]
Brief description of the drawings
[0003]
1 is a perspective view showing an embodiment of the present invention, FIG. 2 is an explanatory
view showing the operation of the embodiment of the present invention, and FIG. 3 is a
perspective view of a converter using a conventional PVDF plate. .
1.31 ииииииииииииииии Polyvinylidene fluoride (PVDF) board, 2 и 23 и 4 и P и electrode, metal electrode, fiber
reinforced plastic, reinforced fiber, sound pressure.
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