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JPH04179398

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DESCRIPTION JPH04179398
[0001]
FIELD OF THE INVENTION The present invention relates to a hydrophone for underwater
acoustic sensors such as fish finders and the like and a method of manufacturing the same.
(Conventional art) Conventionally, as a material of hydrophone for underwater acoustic sensor,
lead zirconate titanate ceramics (referred to as PZT ceramics), composite of PZT ceramics and
plastics such as epoxy resin, or Piezoelectric materials such as composites of PZT ceramics and
air (ie, porous PZT ceramics) have been used. The manufacturing method of the hydrophone
processed these piezoelectric materials to a designated shape, formed electrodes by silver baking
etc. on the surface, and made it the water-resistant structure by resin sealing etc. With regard to
the application of such a PZT ceramic and a composite of PZT ceramic to a hydrophone, it has
been described, for example, in "Application of Piezoelectric Ceramics" (Gakudensha, P-199-203).
However, since the hydrophone manufactured from the PZT itself has a density of about 7.5 g /
ci of the PZT ceramic, which is larger than the density of water, the acoustic impedance (density
× sound velocity) is also extremely higher than that of water. There was a problem that the
sound was easily reflected. As a technology for solving the problem of sound reflection, there is
the technology of the above-mentioned porous piezoelectric ceramic and composite piezoelectric
material. This porous piezoelectric ceramic is a piezoelectric ceramic formed by increasing the
number of pores in order to introduce air into the ceramic, and in this way it is possible to reduce
the density, so that the reflection of sound can be suppressed. . The latter composite piezoelectric
material is a composite of a high molecular organic substance such as rubber and a piezoelectric
ceramic, and the density is reduced as a whole to suppress the reflection of sound. (Problems to
be Solved by the Invention or Problems) However, in order to reduce the density of hydrophones,
when the number of pores in the porous piezoelectric ceramic is increased or the organic matter
content of the composite piezoelectric body is 50% or more, those piezoelectrics Because the
dielectric constant of the body is reduced, the capacitance of hydrophones made from those
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piezoelectrics is also reduced. Then, since the capacitance of the hydrophone and the capacitance
of the cable led from the hydrophone become close values, if the cable is long, the loss due to the
voltage drop is large, and as a result, the sensitivity obtained for the hydrophone And was
susceptible to noise. The object of the present invention is to provide a method for producing a
hydrophone which has a good matching with the acoustic impedance of water and which does
not reduce the capacitance in order to eliminate the above-mentioned drawbacks.
(Means for Solving the Problems) In order to achieve the above object, the present invention is a
hydrophone using a piezoelectric ceramic having a slope in porosity. Further, according to the
present invention, in a method of producing a hydrophone from a piezoelectric ceramic obtained
by molding and firing a ceramic material, a pore forming material is formed on a green sheet
containing no pore forming material. A plurality of sheets having different contents of V are
gradually laminated so as to increase the content of the pore-forming material, and a laminate is
formed. (Operation) According to the present invention, as described above, since the
piezoelectric ceramic of the hydrophone is a pore-inclined piezoelectric ceramic in which the
porosity is inclined, the porosity of the hydrophone receiving surface is large. Therefore, the
density is low and no sound reflection occurs. In addition, the density is increased as it gradually
enters the interior from the receiving surface, and the density of the PZT ceramic itself is set at a
position farther than the receiving surface, so the dielectric constant of the hydrophone as a
whole does not become small and the sensitivity is excellent. It becomes a thing. (Examples) Five
types of calcined PZTs of the following (1) to (5) were prepared. (1) High purity lead monoxide
(PbO, purity 99.9%), titanium dioxide (Ti02. The same), zirconium oxide (Zr 02. The same amount
of each of the above additives and other additives was weighed and mixed with pure water for
about 20 hours using a bot mill. The mixture was dehydrated, dried and calcined at 800 ° C. to
900 ° C. for 2 to 10 hours, and the calcined material was pulverized to obtain a calcined powder
of lead zirconate titanate (ie, PZT). Next, 100 g of the above-mentioned PZT calcined powder, 50
g of water, 8 g of Ceramo D-134 (trade name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.)
as a peptizer, and a particle diameter of 0.2 to 0.411 II11 as a pore forming material 40 g of
carbon particles were mixed in a ball mill for 4 to 5 hours. Thereafter, 100 g of Ceramo TB-13
(trade name, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) as a binder, 12 g of Ceramo P-17
(trade name, manufactured by Dai-ichi Kogyo Seiyaku Pharmaceutical Co., Ltd.) as a plasticizer,
and antifloss F-102 as an antifoaming agent 1 g (trade name, manufactured by Shoichi Kogyo
Seiyaku Co., Ltd.) was added and mixed in a ball mill for 20 hours to prepare a first slurry. It
shape | molded by a doctor blade method using this 1st slurry, and obtained the 1st green sheet.
The thickness of this green sheet was about 0.6-. (2) 100 g of PZT calcined powder of the same
type as in the above (1), 45 g of water, 8 g of a reducing agent and 30 g of carbon particles as a
pore forming material were mixed in a ball mill for 4 to 5 hours.
Thereafter, 90 g of a binder of the same type as in (1), 11 g of a plasticizer and 1 g of an
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antifoaming agent were added, and mixed in a ball mill for 20 hours to prepare a second slurry.
The second slurry was molded by a doctor blade method to obtain a second green sheet. (3) 100
g of PZT calcined powder of the same type as in (1), 40 g of water, 7 g of a peptizer and 20 g of
carbon particles as a pore forming material were mixed in a ball mill for 4 to 5 hours. Thereafter,
80 g of a binder of the same type as in (1), 10 g of a plasticizer, and 1 g of an antifoaming agent
were added, and mixed in a ball mill for 20 hours to prepare a third slurry. It shape | molded by
doctor blade method using this 3rd slurry, and obtained the 3rd green sheet. (4) 100 g of PZT
calcined powder of the same type as in (11), 35 g of water, 6 g of a peptizer, and 10 g of carbon
particles as a pore forming material were mixed in a ball mill for 4 to 5 hours. Thereafter, 70 g of
a binder of the same type as that of the above (1), 9 g of a plasticizer and 1 g of an antifoaming
agent were added and mixed in a ball mill for 20 hours to prepare a fourth slurry. It shape |
molded by the doctor blade method using this 4th slurry, and obtained the 4th green sheet. (5)
100 g of PZT calcined powder of the same type as in the above (1), 34 g of water and 6 g of a
disintegrant were mixed in a ball mill for 4 to 5 hours. Thereafter, 60 g of the same type of
binder as that of the above (1), 8 g of a plasticizer and 1 g of an antifoaming agent were added
and mixed in a ball mill for 20 hours to prepare a fifth slurry. The fifth slurry was molded by a
doctor blade method to obtain a fifth green sheet. As mentioned above, five types of said 1st-5th
green sheets which changed the compounding quantity of the carphone particle were used for
shaping | molding of a laminated body. First, five fifth green sheets containing no pore-forming
material are stacked, and then two sheets of first to fourth green sheets having different content
of the pore-forming material are stacked one on another. It laminated so that content of a hole
formation material might increase gradually, and it heated and pressurized, and obtained the
laminated body. The laminate was fired in air at a temperature rising rate of 100 ° C./hour, at a
temperature of 1200 ° C. to 1300 ° C. for 2 hours to produce a hole-graded piezoelectric
ceramic. The figure shows the outline of preparation of porous piezoelectric ceramics. FIG. A
shows the distribution of carphone particles in the green sheet before firing. The figure shows
the distribution of the pores of the porous piezoelectric ceramic after firing.
Thus, the carbon particles 12 form the pores 22 in the PZT piezoelectric ceramic by firing the
laminate formed from the green sheet. In the obtained piezoelectric ceramic, a piezoelectric
ceramic is obtained in which the pore distribution ratio gradually decreases from the surface to
the surface, that is, the pores are inclined. This hole graded piezoelectric ceramic is processed to
30φ x 6t (-), silver is baked on both sides to produce an electrode, and a voltage of 2 to 3 kV /
mm is applied in heated silicon oil at 100 ° C to 130 ° C. And polarized to produce
piezoelectric electrons. The piezoelectric electrons were molded with a urethane resin to produce
a hydrophone, and the capacitance was measured. Next, a transmitter and a hydrophone were
placed in water, and sound was received on the surface of the hydrophone with many holes, and
the wave receiving sensitivity was measured. The receiving sensitivity of the hydrophone
according to the present invention is -105 dB, which is an improvement of about 10 dB as
compared to the receiving sensitivity -116 dB of the hydrophone made from PZT itself. In
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addition, the capacitance of the hydrophone according to the present invention is 1500 pF, and
the capacitance of the conventional hydrophone manufactured with the porous piezoelectric
material or the composite collector is 500 to 7009 F, which is the whole hydrophone or uniform
density. It is about three times larger than. The present invention is not limited to the
embodiments described above, and various modifications are possible based on the spirit of the
present invention, and these are not excluded from the scope of the present invention. For
example, in the present embodiment, carphone particles are used as the pore forming material,
but the material is not limited to carbon particles, and it is possible to uniformly disperse in the
slurry with the PZT powder and disappear if it is fired. It may be plastic or anything. (Effects of
the Invention) As described above, according to the present invention, since the piezoelectric
ceramic of the hydrophone is a pore-inclined piezoelectric ceramic in which the porosity is
inclined, the porosity of the hydrophone receiving surface is the porosity. It's big, it's like it's low
in density and it doesn't reflect sound. Also, as the density gradually increases toward the inside
from the wave receiving surface (and the density of the PZT ceramic itself at a position farther
than the wave receiving surface, the dielectric constant of the hydrophone as a whole does not
decrease, so the cable It is an excellent hydrophone with low sensitivity to voltage drop.
[0002]
Brief description of the drawings
[0003]
The figure is a diagram showing an outline of the preparation of the porous piezoelectric
ceramic.
1]-Green sheet, 12-carbon particles, 21-· PZT piezoelectric ceramics, 22-holes. Patent Assignee
Oki Electric Industry Co., Ltd. Attorney General Attorneys for Light Yoshihiko (For two others) a
(before firing) b (after firing) Preparation of Piezoelectric Ceramics diagram Procedure
amendment (for February 15, 1991 Day
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