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JPH07312794

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DESCRIPTION JPH07312794
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention transmits and
receives cylindrical waves and the like using a piezoelectric vibrator such as a piezoelectric
ceramic having an annular shape or a cylindrical shape and a small coupling of resonance modes
other than in the thickness direction. The present invention relates to an underwater transducer.
[0002]
2. Description of the Related Art Heretofore, as a technique in such a field, there have been
described, for example, the following documents. Literature 1: Japanese Utility Model Publication
No. 56-10077 Publication: Document 2 Technical Report, US 80-33 (1980) Telecommunications
Society, Yamashita, Yokoyama, Okuma, Well "PbTiO3-based piezoelectric ceramic material" P.I.
47-54 Reference 3: Journal of Applied Physics (Japanese Journal of Applied Physics), 22 (1983)
Supplement 22-2, Yamashita, Yoshida, Takahashi "Effects of MnO Additive on Piezoelectric
Properties in Modified (Pb, Ca) TiO3 Ferroelectric Ceramics "P. 40-42 Document 4: Yanagida and
Nagai, "Science of Ceramics", 2nd Edition (1993-2-5), Gikenbo Publishing, P., et al. FIG. 2 is a
perspective view of a one-channel transducer element constituting the conventional underwater
transducer described in the above-mentioned document 1. As shown in FIG. The transducer
element includes a piezoelectric vibrator 1 made of an annular piezoelectric ceramic having a
height H for one channel. The height H of the piezoelectric vibrator 1 for one channel is smaller
than 1/3 of the thickness D thereof. The inner surface electrode 2 is vapor deposited on the inner
peripheral surface of the piezoelectric vibrator 1, and the outer surface electrode 3 is vapor
deposited on the outer peripheral surface of the piezoelectric vibrator 1. On the outer peripheral
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surface of the piezoelectric vibrator 1, a plurality of longitudinal grooves 4 are machined at a
pitch P equal to or less than D / 3 at a depth of 3⁄4 or more of the thickness D in the thickness D
direction. A lead wire (not shown) is connected to the inner surface electrode 2 and a plurality of
divided outer surface electrodes 3 are commonly connected by a lead wire (not shown), and the
whole of them is waterproofed by resin molding etc. A transducer is configured. Note that y in
FIG. 2 indicates the directivity (vertical directivity) in the longitudinal direction of the
piezoelectric vibrator 1.
[0003]
In the above configuration, for example, when transmitting a cylindrical wave in water, a high
voltage is applied between the inner surface electrode 2 and the plurality of outer surface
electrodes 3. Then, residual polarization and residual strain occur in the piezoelectric vibrator 1
to vibrate. Thereby, a cylindrical wave is radiated (sent) from the underwater transducer. When
receiving a cylindrical wave in water, the cylindrical wave is converted into an electric signal by
the piezoelectric vibrator 1, and the electric signal is output from the inner surface electrode 2
and the plurality of outer surface electrodes 3. The annular piezoelectric vibrator 1 that transmits
and receives this type of cylindrical wave determines the circumferential diameter separately
from the resonance frequency, unlike the piezoelectric vibrator used in respiratory vibration
mode, assuming that the fundamental resonance is thickness resonance. There is an advantage
that can be. However, a piezoelectric element (hereinafter referred to as PZT ), which is a
piezoelectric ceramic generally used for underwater acoustics and medical ultrasonic waves, also
generates vibrations other than in the thickness D direction. Therefore, in order to transmit and
receive a cylindrical wave with the piezoelectric vibrator 1 formed of PZT, a depth at a depth of
3/4 or more of the thickness D and a pitch smaller than D / 3 in the thickness D direction. It is
necessary to form the vertical groove 4 by P.
[0004]
FIG. 3 is a perspective view of a multi-channel transducer element constituting another
conventional underwater transducer described in the above-mentioned document 1. As shown in
FIG. This transducer element is an element that can control both horizontal directivity and
vertical directivity, can scan the sound beam two-dimensionally, and has a cylindrical
piezoelectric vibrator 11 made of piezoelectric ceramic. The inner electrode 12 is deposited on
the inner peripheral surface of the piezoelectric vibrator 11 and the outer electrode 13 is
deposited on the outer peripheral surface thereof. On the outer peripheral surface of the
piezoelectric vibrator 11, a plurality of longitudinal grooves 14 are machined in the longitudinal
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direction at a depth of 3/4 or more of the thickness D, and in the lateral direction to form a
plurality of channels. A plurality of annular lateral grooves 15 are machined. The inner electrode
12 is connected to a lead wire not shown. Since the outer surface electrode 13 divided into each
channel by the lateral groove 15 is divided into a plurality of electrodes by the longitudinal
groove 14 in the channel, lead wires (not shown) are commonly connected to the divided
electrodes. ing. The entire transducer element is waterproofed with resin mold or the like to form
an underwater transducer. In this underwater transducer, the piezoelectric vibrator 11 for each
channel divided by the lateral groove 15 performs the same operation as the piezoelectric
vibrator 1 of FIG.
[0005]
However, the conventional underwater transducer for transmitting and receiving cylindrical
waves in water has the following problems. When the piezoelectric vibrators 1 and 11 using
annular or cylindrical piezoelectric ceramics are used in a thickness resonance mode in which
basic resonance is thickness resonance, vibrations other than thickness vibration are also
generated in the piezoelectric ceramics. Therefore, in the outer peripheral surface of the
piezoelectric vibrators 1 and 11, the longitudinal grooves 4 and 14 having a depth of 3⁄4 or
more of the thickness D or the annular horizontal grooves 15 are machined in the thickness D
direction. The coupling of resonances other than D is reduced. That is, in the piezoelectric
vibrator 1 of FIG. 2, there is a relationship such as P <D / 3 and H <D / 3. The number of
longitudinal grooves 4 needs to be set such that P <D / 3. There is no problem if the height is H
<D / 3, but if it is desired to make the vertical directivity y sharp, then it may also be the case
that H / 3D / 3. In this case, it is necessary to insert the lateral groove 15 as shown in FIG.
Naturally, the depth of this lateral groove needs to be D / 3/4 or more and the pitch is less than
D / 3. Also in this case, the lateral groove is in the channel of FIG. That is, apart from the channel
size, it is necessary to insert the vertical groove and the horizontal groove so that P <D / 3 and H
<D / 3. No matter how small the piezoelectric vibrators 1 and 11 are made, the length of the
outer periphery of the annular ring or the cylinder can not be smaller than D / 3. With regard to
the lateral groove, it is unnecessary if H <D / 3 as shown in FIG. As described above, in the
conventional underwater transducer, since the piezoelectric vibrators 1 and 11 are grooved, the
piezoelectric vibrators 1 and 11 are easily broken, the production yield is low, and the cost
increases due to the groove processing There is a problem of In addition, since the vertical
grooves 4 and 14 are machined in the channel, the divided outer electrodes 3 and 13 need to be
connected in common by the lead wires, which causes a problem that the wiring structure
becomes complicated. The present invention solves the problems of these conventional
techniques, and does not require groove processing using a piezoelectric material with small
coupling of resonant modes other than in the thickness direction, and transmits / receives water
for transmitting / receiving cylindrical waves etc. Provide the
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[0006]
According to a first aspect of the present invention, there is provided an underwater transducer
for transmitting and receiving cylindrical waves and the like, wherein the inner and outer
peripheral surfaces of the uniform curved surface are provided. An outer surface formed on the
outer peripheral surface of the piezoelectric vibrator so as to face the inner surface electrode,
and an inner surface electrode formed on the inner peripheral surface of the piezoelectric
vibrator. And an electrode. And, the piezoelectric vibration constant is −2d31 / d33 <0.2, or the
piezoelectric output constant is −2g31 / g33 <0.2, and the piezoelectric vibration is polarized in
the thickness direction by the inner surface electrode and the outer surface electrode. The
thickness vibration mode of the child is used. In a second aspect of the invention, in the
underwater transducer according to the first aspect of the invention, the inner surface electrode
or the outer surface electrode has a divided structure. According to a third aspect of the present
invention, in the underwater transducer according to the first or second aspect, the piezoelectric
vibrator is formed of a piezoelectric material of PbTiO3 based piezoelectric ceramics, bismuth
layer structured particle oriented piezoelectric ceramics, or PbNb2O6 based piezoelectric
ceramics. It is done. In a fourth invention, in the underwater transducer according to the third
invention, the PbTiO3-based piezoelectric ceramic is (Pb1-x, Mex) ((Co1 / 2W1 / 2) y, Ti1-y) O3,
or (Pb1- (3/2) x, Lnx) (Ti1-y, Mny) O3-based piezoelectric material (where Me; alkaline earth
metal, Ln; rare earth element, 0 <x <1, 0 <y <1 Is formed by Furthermore, the bismuth layered
structure particle-oriented piezoelectric ceramic is formed of a (Na1 / 2, Bi1 / 2) 1-x Cax Bi4 Ti4
O15) piezoelectric material (where 0 <x <1).
[0007]
According to the first, third and fourth inventions, since the underwater transducer is configured
as described above, the piezoelectric vibrator has a small coupling of resonant modes other than
in the thickness direction, The thickness is oscillated in an annular shape or a cylindrical shape
polarized in the longitudinal direction. This enables transmission and reception of cylindrical
waves and the like to the entire space and the like. According to the second invention, the divided
inner surface electrode (or outer surface electrode) and the outer surface electrode portion (or
inner surface electrode portion) opposed thereto effectively act, and a cylindrical wave or the like
with respect to a specific direction Transmission and reception can be performed. Therefore, the
problem can be solved.
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[0008]
FIG. 1 shows a first embodiment of the present invention, and is a perspective view of a onechannel transducer element constituting an underwater transducer for transmitting and receiving
cylindrical waves. This transducer element has an annular piezoelectric vibrator 21 of thickness
E, the inner surface electrode 22 is formed by vapor deposition or the like on the inner
peripheral surface of the uniform curved surface, and the outer peripheral surface of the uniform
curved surface. The outer electrode 23 is formed by vapor deposition or the like. Although not
shown, lead wires are connected to the inner surface electrode 22 and the outer surface
electrode 23. The whole of such a transducer element is waterproofed by resin molding or the
like to form an underwater transducer. The annular piezoelectric vibrator 21 is formed of a
piezoelectric material having a piezoelectric strain constant of −2d31 / d33 <0.2 or a
piezoelectric output constant of −2g31 / g33 <0.2. One such piezoelectric material is PbTiO3
based piezoelectric ceramics. For example, (Pb1-x, Mex) ((Co1 / 2W1 / 2) y, Ti1-y) O3 system or
(Pb1- (3/2) x, Lnx) (Ti1-) is used as a PbTiO3-based piezoelectric ceramic. There are piezoelectric
ceramics such as y, Mny) O3. Here, Me is an alkaline earth metal, and barium Ba, strontium Sr,
calcium Ca or the like is used. Ln is a rare earth element, and lanthanum La, samarium Sm,
neodymium Nd, gadolinium Gd, etc. are used. x and y are required to satisfy 0 <x <1 and 0 <y <1.
The case where the piezoelectric vibrator 21 is formed of, for example, a (Pb1-xCax) ((Co1 / 2W1
/ 2) 0.04Ti0.96) O3 system piezoelectric ceramic will be described by way of example.
[0009]
Piezoelectric ceramics of the (Pb1-xCax) ((Co1 / 2W1 / 2) 0.04Ti0.96) O3 system, as described in
the documents 2 and 3 above, satisfy the condition 0.1.ltoreq.x.ltoreq.0.4. The piezoelectric strain
constant is −2d31 / d33 <0.2, or the piezoelectric output constant is −2g31 / g33 <0.2.
Therefore, the coupling of the resonance modes other than the thickness E direction of the
piezoelectric vibrator 21 is small, and it can be considered that thickness oscillation is performed
in an annular shape polarized in the thickness E direction. When transmitting the cylindrical
wave A using the underwater transducer having such a configuration, a high voltage is applied
between the inner surface electrode 22 and the outer surface electrode 23 through a lead wire
(not shown). Then, residual polarization and residual strain occur in the piezoelectric vibrator 21.
The (Pb1-xCax) ((Co1 / 2W1 / 2) 0.04Ti0.96) O3 based piezoelectric ceramic has a small
coupling of resonant modes other than in the thickness direction, so a piezoelectric vibrator 21
to which a high voltage is applied is used. In this case, a thickness vibration is performed in an
annular shape polarized in the thickness E direction, and a cylindrical wave A is emitted. When
receiving a cylindrical wave A from the outside, the cylindrical wave A is converted into an
electric signal by the piezoelectric vibrator 21, and the electric signal is output from the inner
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surface electrode 22 and the outer surface electrode 23 through a lead wire not shown. Be done.
[0010]
In addition, the annular piezoelectric vibrator 21 is a (Pb1-x, Mex) ((Co1 / 2W1 / 2) other than
the (Pb1-xCax) ((Co1 / 2W1 / 2) 0.04Ti0.96) O3 system. The same operation can be performed
even if it is formed of other PbTiO3 based piezoelectric ceramics such as y, Ti1-y) O3 system or
(Pb1- (3/2) x, Lnx) (Ti1-y, Mny) O3 system. Is possible. As described above, in the first
embodiment, since the annular piezoelectric vibrator 21 is formed of PbTiO3 based piezoelectric
ceramics having a small coupling of resonance modes other than in the thickness direction, the
following advantages (a) There is ˜ (c). (A) A cylindrical wave can be transmitted and received by
the annular piezoelectric vibrator 21 without the conventional groove processing. Therefore,
while being able to prevent the crack of the piezoelectric vibrator 21 by groove processing like
before, the crack of the piezoelectric vibrator 21 by water pressure can also be prevented, and
the mechanical strength is improved. (B) Since the piezoelectric vibrator 21 does not require the
groove processing, it is possible to reduce the reduction in the effective sound wave transmission
/ reception area due to the groove processing as in the prior art. (C) Since it is not necessary to
machine the longitudinal groove in the channel of the annular piezoelectric vibrator 21 as in the
prior art, it is not necessary to mutually connect the outer electrodes 23 divided by the
longitudinal groove. Therefore, the wiring structure is simplified.
[0011]
Second Embodiment FIG. 4 is a perspective view of a multi-channel transducer element
constituting an underwater transducer for transmitting and receiving cylindrical waves according
to a second embodiment of the present invention. is there. This transducer element is an element
that can control both horizontal directivity and vertical directivity, enables scanning of the
acoustic beam in two dimensions, and has a cylindrical piezoelectric vibrator 31 of thickness E
There is. Similar to the first embodiment, the cylindrical piezoelectric vibrator 31 is formed of
PbTiO3 based piezoelectric ceramic, and the inner surface electrode 32 is formed on the entire
inner peripheral surface of the uniform curved surface by vapor deposition or the like. On the
entire outer peripheral surface of the uniform curved surface of the piezoelectric vibrator 31, a
plurality of annular outer electrodes 331 to 33n divided for each channel are formed. That is, the
plurality of outer surface electrodes 331 to 33 n are divided for each channel by the annular
lateral groove 34. For example, after forming an electrode film on the outer peripheral surface of
the piezoelectric vibrator 31 by screen printing or the like, the annular outer groove portion of
the electrode film is photolithographically etched etc. It can manufacture by removing with.
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Although not shown, lead wires are connected to the inner surface electrode 32 and the plurality
of outer surface electrodes 331 to 33n, and the whole of them is waterproofed with a resin mold
or the like to constitute an underwater transducer. In this type of underwater transducer, since
the piezoelectric vibrator 31 is formed of PbTiO3 based piezoelectric ceramic, the coupling of
resonant modes other than in the thickness E direction is small. Therefore, when a high voltage is
applied between the inner surface electrode 32 and each of the outer surface electrodes 331 to
33n, the piezoelectric vibrator 31 vibrates in thickness in an annular shape polarized in the
thickness E direction. Due to this thickness vibration, cylindrical waves for each channel are
sequentially emitted. Also, cylindrical waves from the outside are converted into electrical signals
in the piezoelectric vibrator portion for each channel between the facing inner surface electrodes
32 and the respective outer surface electrodes 331 to 33 n, and the electrical signals are
transmitted through unshown lead wires. It will be output sequentially.
[0012]
As described above, in the second embodiment, since the piezoelectric vibrator 31 is formed of
PbTiO 3 -based piezoelectric ceramic in which coupling of resonant modes other than in the
thickness E direction is small, the advantages of the first embodiment ((1) Besides having the
same advantages as a) to c), it has the following advantage (d). (D) Since the cylindrical
piezoelectric vibrator 31 is formed of PbTiO3 based piezoelectric ceramics, the coupling of
resonant modes other than in the thickness E direction is small, and the thickness vibration is an
annular shape polarized in the thickness E direction. do. Therefore, even if it does not machine an
annular lateral groove having a depth of 3⁄4 or more of the thickness as in the prior art, it is
simply divided into a plurality of outer surface electrodes 331 to 33 n by the annular lateral
groove 34. The acoustic beam can be scanned two-dimensionally with high accuracy without
affecting the channels. In addition, the divided external electrodes 331 to 33 n can be easily
formed by, for example, screen printing at the time of forming the electrodes, and
photolithography etching after the formation of the electrodes. Therefore, the mechanical
strength of the cylindrical piezoelectric vibrator 31 is large, the manufacturing yield is high, and
the effect of reducing the manufacturing cost can be expected.
[0013]
Third Embodiment FIG. 5 shows a third embodiment of the present invention, and is a
perspective view of a one-channel transducer element constituting the underwater transducer. In
the first embodiment shown in FIG. 1, a cylindrical wave is transmitted / received to the entire
space. On the other hand, in the third embodiment, a cylindrical wave in a specific direction is
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transmitted and received. That is, the transducer element of the third embodiment has the
piezoelectric vibrator 21a formed of a part of the annular piezoelectric vibrator 21 shown in FIG.
1, and the uniform curved surface of the piezoelectric vibrator 21a is obtained. An inner surface
electrode 22a is formed on the circumferential surface by vapor deposition or the like. Further,
an outer surface electrode 23a is formed by vapor deposition or the like on the outer peripheral
surface of the uniform curved surface of the piezoelectric vibrator 21a. The piezoelectric vibrator
21a is formed of PbTiO3 based piezoelectric ceramic, as in the first embodiment. A lead wire (not
shown) is connected to the inner surface electrode 22a and the outer surface electrode 23a
formed on the inner and outer peripheral surfaces of the piezoelectric vibrator 21a, and the
whole of them is waterproofed with resin mold or the like to be an underwater transducer. Is
configured. The underwater transducer functions to transmit and receive cylindrical waves in a
specific direction. Therefore, in addition to the advantages similar to the advantages (a) to (c) of
the first embodiment, since the piezoelectric vibrator 21a is constituted by a part of the annular
shape, the number of piezoelectric materials can be reduced.
[0014]
Fourth Embodiment FIG. 6 shows a fourth embodiment of the present invention, and is a
perspective view of a multi-channel transducer element constituting an underwater transducer.
This transducer element is constituted by a part of the transducer element of the second
embodiment shown in FIG. 4, and a piezoelectric transducer 31a comprising a part of the
cylindrical piezoelectric transducer 31 of FIG. have. The piezoelectric vibrator 31a is formed of
PbTiO3 based piezoelectric ceramic as in the second embodiment, and an inner surface electrode
32a is formed on the inner peripheral surface of the uniform curved surface by vapor deposition
or the like. Further, on the outer peripheral surface of the uniform curved surface of the
piezoelectric vibrator 31a, a plurality of outer surface electrodes 33a1 to 33an divided for each
channel by the lateral groove 34a are formed. Lead wires (not shown) are connected to the inner
surface electrode 32a and the plurality of outer surface electrodes 33a1 to 33an, and the whole
of them is waterproofed with a resin mold or the like to form an underwater transducer. The
underwater transducer according to the second embodiment shown in FIG. 4 has the function of
transmitting and receiving cylindrical waves to the entire space. On the other hand, in the
underwater transducer according to this embodiment, there is a function of transmitting and
receiving cylindrical waves in a specific direction. Therefore, in addition to having the advantages
(a) to (c) of the first embodiment, there is also an advantage that the piezoelectric material can be
reduced and the electrode can be easily formed from the structural viewpoint.
[0015]
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Fifth Embodiment FIG. 7 shows a fifth embodiment of the present invention, and is a perspective
view of a one-channel transducer element constituting the underwater transducer. This
transducer element is an element for transmitting and receiving a cylindrical wave in a specific
direction, and, as in the first embodiment shown in FIG. 1, an annular piezoelectric vibrator 21
made of PbTiO3 based piezoelectric ceramic is used. Have. An inner surface electrode 22a similar
to that of the third embodiment shown in FIG. 5 is formed on a part of the inner peripheral
surface of the piezoelectric vibrator 21 by vapor deposition or the like. Furthermore, an outer
surface electrode 23a similar to that of the third embodiment is formed on part of the outer
peripheral surface of the piezoelectric vibrator 21. A lead wire (not shown) is connected to the
inner surface electrode 22a and the outer surface electrode 23a, and the whole of them is
waterproofed with a resin mold or the like to form an underwater transducer. In this underwater
transducer, since the inner surface electrode 22a and the outer surface electrode 23a are
respectively formed only on a part of the inner peripheral surface and the outer peripheral
surface of the annular piezoelectric vibrator 21, the direction in which these electrodes are
formed The cylindrical wave can be transmitted and received (that is, in any direction only by
electrode division). Therefore, it has the same advantages (a) to (c) as the first embodiment. In
order to divide the electrode, for example, as in the second embodiment shown in FIG. 4, it can be
easily performed by screen printing at the time of electrode formation, photolithography after
electrode formation, or the like.
[0016]
Sixth Embodiment FIG. 8 shows a sixth embodiment of the present invention, and is a perspective
view of a multi-channel transducer element constituting an underwater transducer. This
transducer element is an element for transmitting and receiving cylindrical waves in a specific
direction, and has a cylindrical piezoelectric vibrator 31 made of PbTiO3 based piezoelectric
ceramics similar to the second embodiment shown in FIG. ing. On a part of the opposing inner
peripheral surface and a part of the outer peripheral surface of the piezoelectric vibrator 31, an
inner surface electrode 32 a similar to that of the fourth embodiment shown in FIG. 6 and a
plurality of outer surface electrodes 33 a 1 divided by the lateral groove 34 a .About.33 an are
formed by vapor deposition or the like. Lead wires (not shown) are connected to the inner
surface electrode 32a and the plurality of outer surface electrodes 33a1 to 33an, and the whole
of them is waterproofed with a resin mold or the like to form an underwater transducer. In this
underwater transducer, as in the fourth embodiment shown in FIG. 6, the facing inner electrode
32a and the plurality of outer electrodes 33a1 to 33an are formed only in a certain direction, so
Transmission and reception of cylindrical waves can be performed only in a specific direction. As
described above, since cylindrical waves can be transmitted and received in an arbitrary direction
only by electrode division, it has almost the same advantages as the advantages (a) to (d) of the
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first and second embodiments. ing. The division of the electrode can be easily performed by, for
example, screen printing at the time of electrode formation, and photolithography etching after
electrode formation.
[0017]
The present invention is not limited to the illustrated embodiment, and various modifications are
possible. As another embodiment, for example, there is the following. (1) In the fifth embodiment
of FIG. 7, an annular outer electrode 23 similar to that of the first embodiment shown in FIG. 1
may be formed on the entire outer peripheral surface of the annular piezoelectric vibrator 21. .
With such a configuration, the inner surface electrode 22a formed on a part of the inner
peripheral surface of the piezoelectric vibrator 21 and the outer surface electrode portion
opposed thereto act effectively. Therefore, as in the fifth embodiment, cylindrical waves can be
transmitted and received in an arbitrary direction only by dividing the inner surface electrode
22a. Similarly, instead of the ring-shaped outer surface electrode 23 of the first embodiment
shown in FIG. 1, an outer surface electrode 23a of the fifth embodiment shown in FIG. It may be
formed on an annular piezoelectric vibrator 21. With such a configuration, the outer surface
electrode 23a and the inner surface electrode portion opposed thereto effectively operate.
Therefore, as in the fifth embodiment, it is possible to transmit and receive cylindrical waves in
any direction, just by dividing the outer surface electrode. (2) In the sixth embodiment shown in
FIG. 8, the surface electrodes 331 to 33n of the fourth embodiment shown in FIG. 4 are formed
instead of the partial outer surface electrodes 33a1 to 33an, or Instead of the inner electrode
32a, the inner electrode 32 of FIG. 4 may be formed. With such a configuration, the inner surface
electrode 32a and the outer surface electrode portion opposed thereto, or the outer surface
electrodes 33a1 to 33an and the inner surface electrode portion opposed thereto, function
effectively. Therefore, as in the sixth embodiment, a cylindrical wave can be transmitted and
received in an arbitrary direction only by electrode division.
[0018]
(3) In the above embodiment, the piezoelectric vibrators 21, 21a, 31, 31a are formed of PbTiO3
based piezoelectric ceramics, but the piezoelectric strain constant is -2d31 / d33 <0.2, or the
piezoelectric output constant is- It is also possible to replace with other piezoelectric ceramics
such that 2g31 / g33 <0.2. As other piezoelectric ceramics, for example, bismuth layered
structures such as (Na1 / 2, Bi1 / 2) 1-x Cax Bi4 Ti4 O15 system (where 0 <x <1) as described in
the above-mentioned document 4 There are particle-oriented piezoelectric ceramics or PbNb 2 O
6 -based piezoelectric ceramics. Even when the piezoelectric vibrators 21, 21a, 31, 31a are
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formed of such other piezoelectric ceramics, the coupling of resonance modes other than in the
thickness direction is small, and thickness vibration is generated in an annular shape polarized in
the thickness direction. Since it can be considered, the same operation and effect as the above
embodiment can be obtained. (4) As the piezoelectric material, if the piezoelectric strain constant
is −2d31 / d33 <0.2 or the piezoelectric output constant is −2g31 / g33 <0.2, the abovementioned piezoelectric material other than the piezoelectric ceramic is used. Even if the
piezoelectric vibrators 21, 21a, 31, 31a of the embodiment are formed, substantially the same
operation and effect as those of the above embodiment can be obtained. As piezoelectric
materials other than piezoelectric ceramics, for example, piezoelectric polymer materials such as
P (VDF-TrFE) composed of polyvinylidene fluoride (PVDF) and trifluoride ethylene (TrFE), or
composite piezoelectric materials (piezoelectric ceramics · Composite) etc.
[0019]
As described above in detail, according to the first aspect of the present invention, there is
provided a piezoelectric vibrator comprising a whole or a part of a cylindrical shape, an inner
surface electrode formed on the inner peripheral surface and the outer peripheral surface, and
An external electrode, and having a piezoelectric strain constant of −2d31 / d33 <0.2, or a
piezoelectric output constant of −2g31 / g33 <0.2, and being polarized in the thickness
direction by the inner electrode and the outer electrode Since the thickness vibration mode of the
piezoelectric vibrator is used, the following effects can be obtained. (A) It is not necessary to
groove the piezoelectric vibrator as in the prior art, and cylindrical waves can be transmitted and
received. Therefore, it is possible to prevent cracking of the piezoelectric vibrator due to groove
processing as in the prior art and cracking of the piezoelectric vibrator due to water pressure,
and improve mechanical strength. (B) Since it is not necessary to groove the piezoelectric
vibrator as in the prior art, it is possible to reduce the reduction in the effective sound wave
transmission / reception area due to the groove processing. (C) Since there is no groove
processing of the conventional vertical groove or horizontal groove in the channel, there is no
need to connect the electrodes divided by the vertical groove or horizontal groove, and the wiring
structure is simplified. (D) Even if the electrode is divided for each channel without performing
the groove processing as in the prior art, thickness oscillation is performed in an annular shape
polarized in the thickness direction, which affects adjacent channels. The two-dimensional
scanning of the sound beam can be performed accurately. According to the second aspect of the
invention, since the inner surface electrode or the outer surface electrode has a divided structure,
the divided inner surface electrode (or outer surface electrode) and the outer surface electrode
portion (or inner surface electrode portion) opposite thereto work effectively. Therefore, the
cylindrical wave can be transmitted and received in an arbitrary direction only by dividing the
electrode. According to the third and fourth inventions, since the piezoelectric vibrator is formed
of the piezoelectric ceramic, the coupling of the resonance modes other than in the thickness
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direction is small, and the thickness vibration is generated in an annular shape polarized in the
thickness direction. It can transmit and receive cylindrical waves well.
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