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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
underwater transducer using an electro-acoustic transducer such as a fish finder for detecting an
underwater target, and in particular, suppresses the sub-pole level to improve directivity. The
present invention relates to an underwater transducer. [Prior Art] In recent years, a piezoelectric
composite has come to be used as an electro-acoustic transducer of an underwater transducer.
This piezoelectric composite is formed, for example, by firing a PZ'l'-based ceramic plate and
polishing it to a required thickness, then baking electrodes on both surfaces, etc., and subjecting
it to one polarization treatment. Thereafter, the substrate is placed on an appropriate substrate,
and cut into vertical and horizontal directions like a base using a diamond cutter to form small
prisms. Then, the space between the small prisms is filled with a substance having a lower elastic
modulus than that of the PZT ceramic such as urethane rubber resin or epoxy resin, and the
small prisms are elastically connected and then separated from the substrate. . When the
underwater transducer is configured using the piezoelectric composite obtained in this manner,
there is a problem that the directivity is not very good. Incidentally, as related to the piezoelectric
composite, Ferroelectrics 1985, Vol, 00 (Ferroeleotrics. 1985, vol, OO), Takeuchi Hiroshi,
Nakabayashi published rP Z T / polymer composite for medical ultrasonic probe (pz and φ
OLYMER C0 MPO 31 'FES F' O J 'i MEDICAL ULTRONIC PROBBS) J In addition, as a prior art
technique for improving the directivity of the electro / acoustic transducer, the technique of area
shading technology decreases as the array area of the transducers goes as the peripheral button
goes, published by Corona Co. Pp. 291-294. [Problems to be Solved by the Invention] It is
impossible to realize the area shudding method according to the above-mentioned prior art as it
is for the piezoelectric composite at a low cost in the manufacturing process of the piezoelectric
composite. When the above-described piezoelectric composite is used for an underwater
transducer, it is necessary to develop a new technology different from the conventional one in
order to reduce the level of the sub-electrode and improve the directivity. An object of the
present invention is to provide an underwater transducer which uses a piezoelectric composite
and is excellent in directivity. [Means for Solving the Problems] The above-mentioned problems
are a planar piezoelectric composite formed by elastic coupling of a plurality of small
piezoelectric elements regularly, and an electrode formed on at least one of the upper surface or
the lower surface of the piezoelectric composite. Is achieved by narrowing the area of the central
portion toward the peripheral portion.
[Operation] The vibrator (small piezoelectric element) in the piezoelectric composite only moves
under the electrode and performs piston movement at the time of driving to perform electric /
acoustic conversion, that is, in the above-mentioned piezoelectric composite, the piston moves
vibration The number of children is large in the central part and decreases as going to the
peripheral part. As a result, the sub-pole level is suppressed and directivity is improved. An
embodiment of the present invention will be described below with reference to the drawings. FIG.
1 is a perspective view of a piezoelectric composite to which an embodiment of the present
invention is applied. The piezoelectric composite 1 is manufactured as follows. For example, a
PZT-based ceramic plate is fired and polished to a required thickness (the plate thickness is
generally adjusted to the half wavelength resonance of the PZT material), and then an electrode
material such as silver is formed on one surface. And polarization treatment. Thereafter, the
substrate is placed on an appropriate substrate, and cut with a diamond cutter vertically and
horizontally like a base of a base, and diced to form small prism groups composed of small
piezoelectric elements. Then, a material having a lower modulus of elasticity than that of PZTbased ceramic such as urethane rubber resin or epoxy resin is filled in the groove between the
small prisms, and the small prisms are elastically connected and separated from the substrate.
The piezoelectric composite 1 produced in this manner also includes the small prisms 2 of the
diced PZT-based ceramic and the filled resin 6 which elastically connects the small prisms 2.
Next, an electrode is formed by applying, for example, silver paste or the like to the surface
(upper surface) and the back surface (lower surface) of the piezoelectric composite 1. At this
time, an area shoeing is applied in the following manner to form a planar shape of the electrode.
First, silver paste is applied to one surface, for example, the entire surface on the back surface.
On the other hand, the shape of the electrode on the surface is as shown in FIG. That is, the
electrode surface 5a at the central portion is wide, the intermediate electrode surfaces 3b and 5o
on both sides thereof are narrower, and the electrodes [3d and 3e at one end] are the narrowest.
FIG. 3 is a graph showing directivity when a drive voltage is supplied between the front and back
electrodes of the piezoelectric composite 1 formed as described above. The number of image
pickup actuators (piezoelectric elements) 2 which perform piston movement by the supply of
drive voltage is the largest under the electrode surface sa, and then the electrode surface 3b. The
number below 30 is large, and the number below 3d and 3θ is the smallest. Therefore, in the
directivity graph, the sub pole 4 is suppressed more than the main pole 5, and in the example
shown in FIG. 3, it is suppressed by 28 dB. FIG. 4 is a diagram in which transducers are arranged
in 12 rows. As compared with the case where the same drive voltage is supplied to the
transducers of this-row, when the drive voltage is weighted, it is possible to suppress the sub
pole level as well.
For example, the weight of the drive voltage given to the fourth to ninth vibrators is 1.0, and the
weight of the drive voltage given to the third and tenth vibrators (L875, given to the second and
eleventh vibrators) The weight of the drive voltage is (L75. The weight of the drive voltage given
to the first and twelfth vibrators is Cl3. When such voltage shudding is applied, the sub-pole level
in the directivity characteristic is suppressed as shown by a solid line B, as compared with the
broken line AK in the case where no voltage shoeing is applied, as shown in FIG. As described
above, by applying voltage thinning, the sub pole level is suppressed. Therefore, the sub-pole
level can be further reduced by using the area shading described in FIG. 2 in combination with
voltage shading. For example, electrodes 5m, 5b, 5o. Instead of forming 5 d and 3 e continuously,
they are electrically separated, and the weight of the electrode 3 a is 1.0, and the electrode 5 b.
When weighting of the drive voltage is carried out by setting the weight of the 3C as α75 and
the weight of the electrodes 3d, 3a as 15, etc., the sub pole level of the piezoelectric composite
10 directivity characteristic is suppressed by the sub pole 4 of FIG. Ru. In the above-described
embodiment, the back electrode of the piezoelectric composite is applied to the entire surface,
but this is because the area coating by electrode coating should be applied to the surface (it is
easy to manufacture. However, it is technically made the same shape as the surface electrode,
and the front and back electrodes match. It is needless to say that the arrangement of the area
shoeing, the ratio and the value of the weighting of the voltage shading are not limited to the
present embodiment, as long as they can be arranged opposite to each other. . According to the
present invention, when an underwater transducer is manufactured using a piezoelectric
composite, the sub-pole level can be suppressed, and the suppression of the sub-pole level can be
achieved only by changing the planar shape of the electrode. It has the effect of being able to
Brief description of the drawings
FIG. 1 is a perspective view of a piezoelectric composite according to an embodiment of the
present invention, FIG. 2 is a top view obtained by applying area shading to the surface of the
piezoelectric composite, and the like, and FIG. FIG. 4 is a configuration diagram of the
transducers arranged in a line, and FIG. 5 is a directivity characteristic graph when the
transducers in FIG. 4 are subjected to voltage shading.
1 ... Piezoelectric composite, 2 ... Small square prism (piezoelectric element) 3a, 5b, 3c, 3d, 5eelectrode. 4 ... subpolar level. 5 ... Main pole level. 6 ・ ・ ・ filling material. Fig. 1 Fig. 20 Fig. 3
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