JPH01138893

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DESCRIPTION JPH01138893
[0001]
<Industrial field of application> The present invention is intended to receive an acoustic wave
generated in the water while being supported by the stern of a marine research vessel or the like
at one end and being towed like a wind in the sea, The present invention relates to a towing
piezoelectric cable suitably used for seismic survey and fish school detection. <Prior Art> The
towing piezoelectric cable X used for seafloor seismic survey, fish school detection, etc. is caught
by being connected to the winch 2 disposed at the stern of the ship y, as shown in FIG. It is towed
freely. The piezoelectric cable X is classified into one using sinter material pressure 'wt Ti 1
material and one using a piezoelectric composite material. In the piezoelectric cap pull X using
the former sinter piezoelectric ceramic material, as shown in FIG. 10, the piezoelectric wave
receiving units b are disposed at appropriate intervals in the flexible tube a, and The piezoelectric
wave receiving unit b is connected by a conducting wire C, and the flexible tube a is filled with an
oil d having an acoustic characteristic close to the acoustic impedance of water. The structure of
the piezoelectric wave receiving member b) is such that two piezoelectric ceramic plates e, e
made of a ferroelectric such as lead titanate zirconate or lead titanate having the polarization
direction reversed are brought into contact with each other. Two piezoelectric element plate
pairs f are disposed in the direction orthogonal to the axial direction, and the respective opposing
electrodes are short-circuited by the conductive paths g. At this time, for example, in the upper
piezoelectric element plate pair f, the opposing electrodes are negative, and in the lower frame
piezoelectric element plate pair f, the polarization directions are opposite in the upper and lower
directions, for example, positive. (The arrows in the figure indicate the polarization direction.)
Then, connect the inner electrodes of each piezoelectric element plate pair f, f to each other,
connect each outer electrode to the conductor C side, and send the signal from the conductor C It
is designed to be removable. In such a configuration, in addition to the acoustic wave, for
example, tensile stress during blowing, bending stress due to oscillation, etc. acts on the
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piezoelectric cable X, but these mechanical stresses cause the pressure Wt porcelain plates e, e to
be distorted. Charge or voltage, which add to the acoustic wave as a noise signal and reduce the S
/ N ratio. Therefore, in the above configuration, the removal of noise is performed according to
the following principle. That is, when a force is applied in a direction perpendicular to the axis, as
shown in FIG. 12, the same upper and lower bending strain is generated in the upper and lower
piezoelectric element plate pair f, and at this time the piezoelectric element of the upper frame
The electric charges generated between the facing electrodes of the plate pair f and the charges
generated between the electrodes facing the piezoelectric element plate pair f in the lower frame
are equal to each other in absolute value and different in polarity, so that they cancel each other.
It does not occur as an output from C.
Also, the strain caused by the tensile force in the axial direction is eliminated by the same
principle. On the other hand, when receiving an acoustic wave, since the acoustic wave is
received from the entire circumference of the piezoelectric wave receiving unit b), as shown in
FIG. 11, the distortion directions of the upper and lower piezoelectric element plate pair f, f are
reversed As a result, charges of the same polarity are generated in the opposite electrodes, and
they do not erase each other. Therefore, an output signal can be effectively extracted from the
conductor C. By the way, when towing the piezoelectric cable X, an unnecessary signal called
flow noise is generated due to cavitation dione and turbulence generated around the cable, but in
such a conventional configuration, each piezoelectric wave receiving unit b is compared Because
they are arranged at extremely large intervals, the flow noise can not be sufficiently suppressed.
Next, a conventional configuration using a piezoelectric composite material will be described.
Ferroelectric ceramic particles such as lead zirconate titanate and lead titanate in organic
substances such as polyvinylidene fluoride, polyvinylidene fluoride, polyvinylidene chloride,
polyvinyl chloride, nylon, etc. or organic substances of synthetic rubber or synthetic resin The
piezoelectric composite material formed by mixing has a characteristic that the acoustic
impedance approximates to the acoustic impedance of water, and therefore, when this is used as
the piezoelectric cable X, acoustic waves propagating in water are efficiently received and the
sensitivity is Create benefits that can increase Therefore, as shown in FIG. 13, a piezoelectric
layer made of the piezoelectric material is disposed around the electrode core i, and a conductive
material j such as a conductive paint is disposed on the outer periphery of the piezoelectric layer,
and the electrode core i is disposed. Between the electrode core i and the conductive material 1
by applying a predetermined DC voltage between the electrode 1 and the conductive material 1
to form a coaxial piezoelectric cable X in which the piezoelectric layer is polarized in the radial
direction, and immersing it in water. There is a device for taking out an output signal from to
receive an acoustic wave propagating in the water. In such a configuration, for bending force, the
areas of the extension part and the contraction part are almost equal, and charges of different
polarities are generated in each domain and erased, but the force acts in the direction
perpendicular to the axis. Then, since the areas of the depression and the bulge are different, the
generation of noise from this direction is observed. Further, even in the case of the tensile force
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in the axial direction, the noises are generated because they are not erased together. <Problems
to be Solved by the Invention> As described above, none of the conventional piezoelectric cables
X can erase all of the effects of various forces in water, and noise is generated. A high S / N ratio
could not be obtained. An object of the present invention is to provide a tow piezoelectric cable X
capable of blocking effects other than acoustic waves and eliminating the drawbacks of the
conventional configuration.
In the present invention, as shown in FIG. 1, the piezoelectric element layers 5a and 5b polarized
in the thickness direction are made conductive so that their polarization directions are
unidirectionally arranged. By arranging on the front and back surfaces of the connecting plate 4,
the inner electrodes 7 a and 6 b of both piezoelectric element layers 5 a and 5 b are shortcircuited with each other to constitute the wave receiving element 3. By means of the flexible
flexible shaft 2, a large number of the wave receiving elements 3 can be fixed via the buffer area
9, and the potential difference generated between the outer electrodes 6a and 7b of both
piezoelectric element layers 5a and 5b can be taken out. A wire connection (8a, 8b) is applied to
each wave receiving element, which is covered with a flexible tube l, and the inside thereof is
filled with an insulating oil 10. The piezoelectric element layers 5a and 5b may be formed of a
piezoelectric composite material or a sintered ceramic material. Operation> The operation of the
wave receiving element 3 in the above construction will be described with reference to FIGS. In
each of the wave receiving elements 3, as shown in FIG. 3, the acoustic wave acts evenly on the
outer peripheral surfaces of the piezoelectric element layers 5a and 5b. Therefore, as shown in
FIG. 3, the sum of voltages generated from the two piezoelectric element layers 5a and 5b is
taken out from the lead wires 8a and 8b connected to the outer surface side electrodes 6a and
7b. Become. Next, the noise cancellation principle in such a configuration is as follows. Now, as
shown in FIG. 4, when a tensile force is applied from the shaft core 2 in the axial direction, if the
rigidity of the conductive connecting plate 4 is strong, as shown in the dynamic model diagram
of FIG. The piezoelectric element layer 5a on the left side in the figure is pressed against the
conductive connecting plate 4 by the inertial force and contracted in the thickness direction, and
the piezoelectric element layer 5b on the right side in the figure forms the left inner surface to
the conductive connecting plate 4 It is pulled and expands in the thickness direction. For this
reason, since the polarity of the generated charges in the piezoelectric element layers 5a and 5b
is in the opposite direction, the external electrodes 6a and 7b have the same polarity as in the
opening of FIG. When the plate has flexibility, each piezoelectric element layer 5a, 5b is curved
according to the conductive connecting plate by inertia, but the piezoelectric element layer 5a
disposed in the inside of the curve is contracted in the radial direction The piezoelectric element
layer 5b disposed outward in the curved direction expands in the radial direction, and similarly
the polarity of the generated charge is reversed, so that no potential difference is generated
between the outer surface side electrodes 6a and 7b. Further, as shown in FIG. 5A, when acting in
the direction orthogonal to the axial direction (upward direction in the figure), as shown by a
dynamic model diagram to FIG. 5, the piezoelectric element layers 5a and 5b are made by inertia
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force. The upper half in the figure contracts in the radial direction, and the lower half in the
figure expands in the radial direction by pulling the inner surface thereof.
For this reason, since the polarity of the generated charge is different in the upper and lower
portions, the piezoelectric element layers 5a and 5b themselves are short-circuited as shown in
FIG. Next, when a force in the bending direction is applied, as shown in FIG. 6, since the buffer
area 9 is disposed between each of the wave receiving elements 3, even if it is relatively inclined,
it is mechanically dynamic. There is no effect, no distortion occurs in each piezoelectric element
layer 5a, 5b, and thus no noise is generated. The present invention is canceled based on the noise
cancellation principle, and does not generate noise even when the piezoelectric cable is subjected
to pulling or bending due to rippling, towing, etc., while it is effective for acoustic waves. Output
signal can be generated. EXAMPLE FIG. 7 shows a piezoelectric cable X according to an example
of the present invention. The shaft core 2 is inserted into the flexible tube 1 serving as the outer
shell of the piezoelectric cable X, and the end of the shaft core 2 is connected to a winch 2
disposed at the stern of the ship y and towed. Ru. The plate-like piezoelectric element layers 15a
and 15b polarized in the thickness direction are attached to the shaft core 2 on the front and
back surfaces of the conductive connecting plate 14 made of a metal plate so that the
polarization directions become the same. A large number of the wave receiving elements 3
configured as described above are held concentrically by inserting the shaft core 2 at the center
of the conductive connecting plate 4 and fixing the center. The piezoelectric element layers 15a
and 15b are made of a piezoelectric composite material and formed by punching the material. A
flexible annular cushioning material 19 such as foam rubber is interposed between the respective
wave receiving elements 3 described above, and it is closely continuous in the axial direction. The
buffer material 19 has a role of maintaining the distance between the wave receiving elements 3
while allowing relative tilt of the wave receiving elements 3, but excluding this, the space
between the wave receiving elements 3 and 3 is eliminated. The oil 10 itself may constitute a
buffer zone. And each piezoelectric element layer 15 a of the wave receiving element 3. Lead
wires 8a and 8b are connected to the outer surface side electrodes of 15b, respectively, and
output voltages generated in the piezoelectric element layers 15a and 15b are connected to a
control circuit provided on the ship y. Furthermore, in the flexible tube l, an insulating oil 10
such as silicon oil is filled so that the electrodes of the lead wires 8a and 8b and the piezoelectric
element layers 15a and 15b do not short. In the above configuration, when an acoustic wave
propagates from the periphery of the flexible tube 1, as shown in FIG. 3, a signal voltage is
generated in the piezoelectric elements R15a and 15b of each wave receiving element 3, and the
lead wire 8a , Ab between. On the other hand, when a force is generated in the axial direction or
in a direction orthogonal to the axial direction, as shown in FIGS. 4 and 5, the force is canceled by
the noise cancellation principle already described.
When a bending stress is applied, as already described with reference to FIG. 6, although the
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shaft core 2 is bent, the wave receiving element 3 fixed to the shaft core 2 is made of the buffer
material 19. Since the relative tilting is freed by the contraction action, respectively, no distortion
occurs and no charge is generated. Furthermore, since a large number of piezoelectric element
plates are continuously arranged in the length direction at short intervals, at the time of towing.
Flow noise can be sufficiently suppressed. Thus, the piezoelectric cable X does not output from
the lead wires 8a and 8b due to various forces other than the acoustic wave. FIG. 8 shows
another embodiment of the wave receiving element 3. In the synthetic rubber, piezoelectric
powder is applied to the front and back surfaces of a conductive connecting plate 24 made of a
conductive composite material in which metal powder is dispersed in synthetic rubber.
Piezoelectric element layers 25a and 25b made of dispersed piezoelectric rubber are formed. In
order to explain the manufacturing process of the wave receiving element 3, first, the conductive
composite material constituting the conductive connecting plate 24 is formed in an annular
shape (FIG. 9A). 0 Next, on both sides of the conductive composite material, By toluene becoming
solvent. A material obtained by dissolving synthetic rubber and FT powder is applied by printing
technology or the like to form piezoelectric element layers 25a, 25b (Fig. 9 port), which are semicross-cured and then in toluene, synthetic rubber A material obtained by mixing metal powder
such as silver and silver is applied to the surface of the piezoelectric element layers 25a and 25b
to form outer side electrodes 26a and 27b, and then it is vulcanized and further polarized (9th
Figure c). The respective components described above can be simultaneously vulcanized as
described above because they are made of synthetic rubber as the base material, and therefore,
they are integrally formed and the adhesion step is not necessary. In this configuration, the
connecting plate 24 also serves as the inner surface side electrode of the piezoelectric element
layers 25a and 25b. Further, in such a configuration, one sheet having a material layer
corresponding to each of the above-described components is formed by crosslinking in advance,
and this is punched to obtain a shape as shown in FIG. May be In the previous embodiment, the
conductive connecting plate 24. The base material of the piezoelectric element layers 25a and
25b and the electrodes 26a and 27b can be changed from synthetic rubber to a synthetic resin
material. Also in this case, it can be integrally formed by heat molding or the like. <Effects of the
Invention> As clarified by the above description, the present invention can eliminate the
influence as much as possible even if various forces act by waving, towing, etc. There are
excellent effects such as being able to significantly improve the S / N ratio of the output.
[0002]
Brief description of the drawings
[0003]
1 is a longitudinal sectional view showing the wave receiving element 3 of the present invention,
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FIG. 2 is a front view thereof, and FIGS. 3 to 6 are explanatory views showing the operation of the
present invention. 5 and 6 are side views of the wave receiving element 3 showing the action of
pressure, the ports in FIGS. 3 to 5 are equivalent circuit diagrams, and c in FIGS. 4 to 5 are
dynamic model diagrams, FIG. 7 is a longitudinal sectional side view of the piezoelectric cable X
according to an embodiment, FIG. 8 is a longitudinal sectional side view showing the
configuration of another wave receiving element 3, and FIG. It is.
10 is a longitudinal sectional side view of a part of a conventional piezoelectric cable X, and FIGS.
11 to 12 are side views of a piezoelectric wave receiving unit b showing the action of pressure,
and FIG. The mouth of FIG. 12 is its equivalent circuit diagram, and FIG. 13 is a perspective view
of part of another conventional configuration. Furthermore, FIG. 14 is an explanatory view
showing a use mode of the piezoelectric cable X. 1; flexible tube 2; axial core 3; wave receiving
element 4.14, 24; conductive connecting plate 5a, 5b. 15a, 15b, 25a, 25b; piezoelectric element
layers 6a, 7b, 26a, 27b; outer surface side electrodes 6b, 7a; inner surface side electrodes 9;
buffer layer 8a. 8b: Reed @ 10: Insulating oil 19: Buffer material FIG. 1 R FIG. 3 FIG. 4 FIG. 4 (o)
(c) FIG. 5 (c) FIG. 6 FIG. 10 FIG. 110 T FIG.
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