JPH0937379

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DESCRIPTION JPH0937379
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasonic transducer for transmitting and receiving cylindrical waves and the like, which is used
for underwater acoustics and medical treatment and is formed of a piezoelectric ceramic material
having an annular shape or a cylindrical shape. It is about
[0002]
2. Description of the Related Art Heretofore, as a technique in such a field, for example, there are
those described in the following documents. Document 1: Japanese Utility Model Publication No.
56-10077 Publication document 2: Ferroelectric (Ferroelectrics), 49 (1983) Gorgon and Breach,
Science Publichers (US) HIKITA et al. "PIEZOELECTRIC PROPERTIES" OF THE POROUS PZT AND
THE POROUS PZT COMPOSITE WITH SILICONE RUBBER " p. 265-272 Document 3: Proceedings
of the Conferences on Ferroelectrics Application 27-A-3 (1992) Miyata et al. Study on
application of porous piezoelectric ceramics to high frequency transducers . 5-6 Document 1
describes the technology of an ultrasonic transducer using a piezoelectric transducer. Document
2 describes various techniques of piezoelectric ceramic materials. Further, Document 3 describes
the technology of a high frequency transducer using porous piezoelectric ceramics.
[0003]
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FIG. 2 is a perspective view of the conventional one-channel ultrasonic transducer described in
the document 1. The ultrasonic transducer includes a piezoelectric transducer 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. An inner
surface electrode 2 is formed on the inner peripheral surface of the piezoelectric vibrator 1, and
an outer surface electrode 3 is formed on the outer peripheral surface of the piezoelectric
vibrator 1. On the outer peripheral surface of the piezoelectric vibrator 1, a plurality of
longitudinal grooves 4 are machined at a distance (pitch) P of D / 3 or less to a depth of 3/4 or
more of the thickness D in the thickness D direction. ing. 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 the lead wire (not shown), and the whole of them is waterproofed by resin molding
or the like. Note that y in FIG. 2 indicates the directivity (vertical directivity) in the longitudinal
direction of the ultrasonic transducer. 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. Thus, a cylindrical wave is emitted (transmitted) from the
ultrasonic 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 has high
transmission sensitivity and low input / output impedance, unlike the piezoelectric vibrator used
in respiratory vibration mode, assuming that the thickness resonance is fundamental resonance.
Therefore, there is an advantage that the circumferential diameter can be increased. However,
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 of 3/4 or more of the thickness D and a pitch of 3/3 or less in the thickness D direction.
It is necessary to form the vertical groove 4 by P.
[0004]
FIG. 3 is a perspective view of another conventional multi-channel ultrasonic transducer
described in the above-mentioned document 1. As shown in FIG. The ultrasonic transducer is an
element that can control both horizontal directivity and vertical directivity, can scan the sound
beam in one dimension, and has a cylindrical piezoelectric transducer 11 made of piezoelectric
ceramic. An inner surface electrode 12 is formed on the inner peripheral surface of the
piezoelectric vibrator 11, and an outer surface electrode 13 is also formed on the outer
peripheral surface. On the outer peripheral surface of the piezoelectric vibrator 11, a plurality of
longitudinal grooves 14 are machined in the longitudinal direction at a depth of 3/4 or more of
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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. Then, the entire ultrasonic transducer is
waterproofed with a resin mold or the like. In this ultrasonic transducer, the piezoelectric
transducer 11 for each channel divided by the lateral groove 15 performs the same operation as
the piezoelectric transducer 1 of FIG.
[0005]
However, the conventional ultrasonic transducer 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 the lateral groove needs to be D / 3/4 or more, and the pitch is D / 3
or less. 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 ultrasonic transducer, since the piezoelectric transducers 1 and 11 are grooved, the
piezoelectric transducers 1 and 11 are easily broken, the production yield is low, and the cost
increase due to the groove processing. There's a problem. 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 the prior art, and provides an
ultrasonic transducer for transmitting and receiving a cylindrical wave or the like which does not
require groove processing, and a method of manufacturing the same.
[0006]
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According to a first aspect of the present invention, there is provided an ultrasonic transducer for
transmitting and receiving cylindrical waves and the like, which has an inner peripheral surface
and an outer peripheral surface which have a uniform curved surface. A piezoelectric vibrator
consisting of a whole or a part of a cylindrical shape, an inner surface electrode formed on the
inner circumferential surface of the piezoelectric vibrator, and an outer surface electrode formed
on the outer circumferential surface of the piezoelectric vibrator facing the inner surface
electrode And have. The piezoelectric vibrator is formed of a piezoelectric ceramic material in
which a group of holes is distributed and formed in a plane which is perpendicular to the
direction of the cylindrical axis and in the direction of the cylindrical axis. In a second aspect of
the invention, in the ultrasonic transducer of the first aspect, the surface on which the group of
holes is formed is a pitch that is 1/3 or less of the thickness dimension in the surface of the
cylinder diameter of the piezoelectric transducer. It is formed in multiple places. In a third aspect
of the present invention, in the method of manufacturing an ultrasonic transducer for
transmitting and receiving cylindrical waves and the like, a piezoelectric transducer forming step,
a firing step and an electrode forming step are sequentially performed.
[0007]
Here, in the piezoelectric vibrator forming step, a second green sheet made of a first green sheet
material in which particles burnt away by heating are mixed in a piezoelectric ceramic material at
a predetermined mixing ratio, and a piezoelectric ceramic material in which the particles are not
mixed And the first green sheet material is located in a plane perpendicular to the axial direction
of the cylinder using the material, and the first green sheet material is 1/3 or less of the
thickness dimension in the plane of the cylinder diameter A piezoelectric vibrator is formed of
the whole or a part of a cylindrical shape having a uniformly curved inner peripheral surface and
an outer peripheral surface such that the first green sheet material is disposed at intervals. Next,
in the firing step, the piezoelectric vibrator is temporarily fired at a predetermined temperature
to burn out the particles to form pores, and then the piezoelectric vibrator is subjected to main
firing at a temperature higher than the predetermined temperature. Thereafter, in the electrode
forming step, an inner surface electrode is formed on the inner circumferential surface of the
fired piezoelectric vibrator, and an outer surface electrode is formed on the outer circumferential
surface of the piezoelectric vibrator opposite to the inner surface electrode.
[0008]
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According to the first and second aspects of the invention, since the ultrasonic transducer is
configured as described above, the group of holes distributed and formed at a predetermined
location in the piezoelectric transducer is the Young of the piezoelectric transducer. It has a
function to reduce the coupling of resonant modes other than in the thickness direction by
reducing the rate or the like. Therefore, since the piezoelectric vibrator vibrates in thickness in an
annular shape or a cylindrical shape polarized in the thickness direction, transmission and
reception of cylindrical waves and the like to the entire space can be performed. According to the
third aspect of the present invention, the first green sheet material and the second green sheet
material are used to form a piezoelectric vibrator consisting of the whole or a part of a cylindrical
shape, and then, if it is temporarily fired, the first The large number of particles in the green
sheet material are burned off and a large number of pores are formed. The holes have the
function of reducing the Young's modulus or the like of the piezoelectric vibrator to reduce the
coupling of resonant modes other than in the thickness direction. After the pores are formed by
pre-firing, if the main firing is performed at a high temperature, a piezoelectric vibrator made of
a piezoelectric ceramic material having high mechanical strength is formed. Therefore, the
problem can be solved.
[0009]
1 (a) and 1 (b) are block diagrams of a one-channel ultrasonic transducer showing a first
embodiment of the present invention, wherein FIG. 1 (a) is a perspective view, and FIG. 1 (b) is
the same. It is a perspective view of the A1-A2 line longitudinal cross section of a figure (a). This
ultrasonic transducer is used for underwater acoustics and medical treatment, etc., and has an
annular piezoelectric transducer 21 with a thickness E, and the inner surface electrode 22 is
deposited on the inner peripheral surface of the uniform curved surface, etc. The outer surface
electrode 23 is formed by vapor deposition or the like on the outer peripheral surface of the
uniform curved surface. The annular piezoelectric vibrator 21 is formed of, for example, a PZTbased piezoelectric ceramic material, and includes a hole group consisting of a large number of
holes 24 a in a plane which is in the cylinder radial direction and perpendicular to the cylinder
axis direction. 24 are distributed. The surface on which the holes 24 are distributed is formed at
a plurality of positions at a pitch P which is 1/3 or less of the thickness E in the surface of the
cylindrical diameter of the piezoelectric vibrator 21. The average sphere diameter of each of the
holes 24 a in the hole group 24 is, for example, about 200 μm. The porosity of the piezoelectric
material portion where the void group 24 is not formed is 0%. In addition, Z in (a) of FIG. 1 is a
cylindrical wave. Although not shown, lead wires are connected to the inner surface electrode 22
and the outer surface electrode 23, and the entire ultrasonic transducer is waterproofed by resin
molding or the like. FIG. 4 is a diagram for explaining a method of manufacturing the ultrasonic
transducer of FIG. Hereinafter, an example of a method of manufacturing the ultrasonic
transducer of FIG. 1 will be described with reference to FIG. The ultrasonic transducer of FIG. 1 is
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manufactured, for example, through the following steps (1) to (3).
[0010]
(1) Step of Forming Piezoelectric Vibrator As shown in FIG. 4, a raw material powder of PZTbased piezoelectric ceramic in which particles (for example, carbon particles having an average
sphere diameter of about 200 μm) to be burned off by heating are mixed at a predetermined
mixing ratio. The first green sheet material 21 a mixed with water or a suitable solvent (for
example, an organic solvent or the like) is annularly arranged at a predetermined pitch P. A
second green sheet material 21b in which raw material powder of PZT-based piezoelectric
ceramics not mixed with the particles 24b is mixed with water or a suitable solvent (for example,
an organic solvent etc.) is annularly formed between the respective first green sheet materials
21a. A plurality of green sheets 21c which are arranged in a thin annular film (or plate) and dried
are manufactured. The plurality of green sheets 21c are stacked. Under the present
circumstances, each green sheet 21c is piled up so that the 1st green sheet material 21a in each
green sheet 21c may mutually overlap. Then, the stacked plurality of green sheets 21c are
pressed by a press or the like to form an annular piezoelectric vibrator 21 made of a ceramic
mass.
[0011]
(2) Firing step The piezoelectric vibrator 21 is temporarily fired under a predetermined condition
(for example, a heating temperature of about 700 to 800 ° C.) such that the particles 24b are
burned off, and the particles 24b are burned off to form a large number of pores 24a. The void
group 24 is formed. Thereafter, the piezoelectric vibrator 21 is main-baked at, for example, 1000
° C. or more. Such a green sheet method in which a plurality of green sheets 21c are stacked,
pressed by a press or the like, and then fired to produce the piezoelectric vibrator 21 does not
particularly require a die for firing, and ceramic It is a general manufacturing method.
[0012]
(3) Electrode Forming Step, etc. The inner electrode 22 is formed on the inner peripheral surface
of the annular piezoelectric vibrator 21 by evaporation or the like, and the outer electrode 23 is
formed on the outer peripheral surface thereof by evaporation or the like. Thereafter, lead wires
are connected to the inner surface electrode 22 and the outer surface electrode 23, and the
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entire ultrasonic transducer is waterproofed by resin molding or the like, whereby the production
of the ultrasonic transducer of FIG. 1 is completed. For example, when transmitting the
cylindrical wave Z in water using the ultrasonic transducer manufactured in this manner, 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. As described in the document 3, when comparing a porous
piezoelectric ceramic in which a large number of pores are formed with a piezoelectric ceramic
having a porosity of 0%, the density, the relative dielectric constant, the Young's modulus, the
piezoelectric constant, The electromechanical coupling coefficient of the porous piezoelectric
ceramic is smaller than that of the piezoelectric ceramic having a porosity of 0%, and the
resonance sensitivity is lowered at the time of transmission and reception. Because of this, in the
first embodiment, a cavity group 24 is provided at a position corresponding to the longitudinal
groove 4 of the conventional FIG. 2, and coupling of resonant modes other than the thickness E
direction of the vibrator 21 is obtained. It's smaller. Therefore, the piezoelectric vibrator 21 to
which the high voltage is applied vibrates in thickness in an annular shape polarized in the
thickness E direction, and radiates a cylindrical wave Z. Further, when receiving a cylindrical
wave Z from the outside, the cylindrical wave Z is converted into an electric signal by the
piezoelectric vibrator 21, and the converted electric signal is not shown from the inner surface
electrode 22 and the outer surface electrode 23. Is output via As described above, in the first
embodiment, the thickness E of the piezoelectric vibrator 21 is in the plane perpendicular to the
cylinder axis direction of the piezoelectric vibrator 21 and in the plane of the cylinder diameter.
Since the vacancy groups 24 are distributed and formed at a plurality of locations at the
following pitch P, coupling of resonant modes other than in the thickness E direction of the
piezoelectric vibrator 21 is reduced, and an annular shape polarized in the thickness E direction
Thickness vibration can be performed. Therefore, the following effects (a) to (d) are obtained.
[0013]
(A) The cylindrical wave Z can be transmitted / 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 the past, the crack of this piezoelectric
vibrator 21 by water pressure can also be prevented, and mechanical strength can be improved.
(B) Since the groove processing is unnecessary for the piezoelectric vibrator 21, it is possible to
prevent a decrease in manufacturing yield and an increase in cost due to the groove processing
as in the related 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 external electrodes 23 divided by the longitudinal groove. Therefore, the wiring
structure is simplified. (D) In the method of manufacturing the ultrasonic transducer shown in
FIG. 4, the plurality of green sheets 21 c are stacked and then pressurized by a press or the like,
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and the particles 24 b are burned off by temporary firing it. The vacancy group 24 can be easily
and accurately formed at a predetermined location. Thereafter, since the piezoelectric vibrator 21
is subjected to firing, an ultrasonic vibrator with high mechanical strength can be manufactured.
[0014]
Second Embodiment FIG. 5 shows a second embodiment of the present invention, and is an
illustration of another method of manufacturing the ultrasonic transducer of FIG. In this method
of manufacturing an ultrasonic transducer, a raw material powder of PZT-based piezoelectric
ceramic in which particles 24b such as carbon particles are mixed at a predetermined mixing
ratio is mixed with water or a suitable solvent (for example, an organic solvent etc.) A plurality of
first green sheet members 21D made into a film (or plate) shape and dried are produced. Further,
a raw material powder of PZT-based piezoelectric ceramic free of particles 24b is mixed with
water or a suitable solvent, and a plurality of second green sheet materials 21e made into a fanshaped film (or plate) and dried are manufactured. The plurality of first green sheet members 21
d and the second green sheet members 21 e are used, and the first green sheet members 21 d
and the first green sheet members 21 d have a predetermined pitch P. The green sheet material
21e of No. 2 is stacked in a cylindrical shape, and pressed by a press or the like to form a
piezoelectric vibrator 21 made of ceramic solid. Next, as in the manufacturing method of FIG. 4,
the piezoelectric vibrator 21 is temporarily fired to burn off the particles 24 b to form the void
group 24 composed of a large number of voids 24 a at a predetermined position, and then the
main firing is performed. Thereafter, when the same electrode forming process and the like as
the manufacturing method of FIG. 4 are performed, the manufacturing process of the ultrasonic
transducer is completed. The second embodiment has the following effects (i) and (ii).
[0015]
(I) In the method of manufacturing the ultrasonic transducer according to the second
embodiment, the first green sheet 21d mixed with the particles 24b and the second green sheet
21e not mixed with the particles 24b are used. Since the piezoelectric vibrator 21 is formed by
superimposing them, the void group 24 can be easily and accurately formed at a predetermined
position, as in the manufacturing method of FIG. (Ii) In the manufacturing method of FIG. 4, the
piezoelectric vibrator 21 is formed by laminating a plurality of green sheets 21c composed of the
first green sheet material 21a and the second green sheet material 21b. Therefore, the
production of the green sheet 21c may be somewhat complicated. On the other hand, in the
second embodiment, since the first green sheet material 21d and the second green sheet material
21e are overlapped in an annular shape to form the piezoelectric vibrator 21, as shown in FIG. It
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is easier than the manufacturing process.
[0016]
Third Embodiment FIGS. 6 (a) to 6 (c) are block diagrams of a multi-channel ultrasonic
transducer showing the second embodiment of the present invention, and FIG. 6 (a) is a
perspective view, FIG. (B) is a perspective view of the B1-B2 line longitudinal cross section of the
same figure (a), and the same figure (c) is a perspective view of the C1-C2 line cross section of
the same figure (a). This ultrasonic transducer is an element that can control both horizontal
directivity and vertical directivity, can scan an acoustic beam one-dimensionally, and has a
cylindrical piezoelectric transducer 31 with a thickness E. . The cylindrical piezoelectric vibrator
31 is formed of PZT-based piezoelectric ceramic as in the first embodiment, 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 surface electrodes 331 to 33n
divided for each channel are formed by vapor deposition or the like. That is, the plurality of outer
surface electrodes 331 to 33 n are divided for each channel by the annular lateral groove 34. In
the cylindrical piezoelectric vibrator 31, as in the first embodiment, a hole group 35 composed of
a large number of holes 35a is formed. The group of holes 35 is disposed in a plane which is in
the cylinder diameter direction and perpendicular to the cylinder axis direction, and is arranged
and formed at a pitch P of 1/3 or less of the thickness E in the surface of the cylinder diameter. .
[0017]
FIG.6 (c) is a figure which shows the cross section in the position of the lateral groove 34 which
does not have the exterior electrodes 331-33n of Fig.6 (a). As shown in FIG. 6C, on the surface of
the cylindrical diameter at the location of each lateral groove 34, a vacancy group 35 composed
of a large number of holes 35a is formed. Although not shown, lead wires are connected to the
inner surface electrode 32 and the plurality of outer surface electrodes 331 to 33 n, and the
whole of them is waterproofed by resin molding or the like. The ultrasonic transducer of such a
configuration is manufactured, for example, as follows. The cylindrical piezoelectric vibrator 31
is formed by the manufacturing method as shown in FIG. 4 or 5. An inner surface electrode 32 is
formed on the entire inner circumferential surface of the uniform curved surface of the
cylindrical piezoelectric vibrator 31 by vapor deposition or the like. Furthermore, after an
electrode film is deposited on the outer peripheral surface of the piezoelectric vibrator 31 by
screen printing or the like, the annular lateral groove 34 of the electrode film is removed by
photolithography and the like, and the outer surface electrode 331 divided into a plurality Form ˜
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33n. Thereafter, lead wires are connected to the inner surface electrode 32 and the plurality of
outer surface electrodes 331 to 33 n, and the whole of them is waterproofed with a resin mold or
the like, whereby the production of the ultrasonic transducer is completed. In the ultrasonic
transducer manufactured in this manner, since the group of holes 35 is formed in the portion
corresponding to the vertical groove 14 and the horizontal groove 15 of FIG. 3 in the prior art,
the resonance mode other than the thickness E direction is Bonding is small. Therefore, when a
high voltage is applied between the inner surface electrode 32 and each of the outer surface
electrodes 331 to 33 n, the thickness of the piezoelectric vibrator 31 vibrates in an annular
shape polarized in the thickness E direction. Due to this thickness vibration, cylindrical waves for
each channel are sequentially emitted. In addition, cylindrical waves from the outside are
converted into electrical signals by 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. Output sequentially. As
described above, in the third embodiment, the thickness of the cylindrical piezoelectric vibrator
31 is in the plane perpendicular to the cylindrical axis direction of the cylindrical piezoelectric
vibrator 31 and in the plane of the cylindrical diameter Since the vacancy groups 35 are
arranged and formed at a pitch P that is 1/3 or less of E, coupling of resonant modes other than
in the thickness E direction is reduced. Therefore, in addition to the effects substantially similar
to the effects (a) to (d) of the first embodiment, there is also the following effect (e).
[0018]
(E) Since the group of holes 35 is formed on the surface of the cylindrical diameter of each of the
34 horizontal grooves, the coupling of resonance modes other than in the thickness E direction is
small, and the ring shape is polarized in the thickness E direction Vibration in thickness.
Therefore, even if the annular lateral groove 15 having a depth of 3⁄4 or more of the thickness D
is not machined as in the conventional FIG. The sound beam can be scanned one-dimensionally
with high accuracy without affecting adjacent channels only by dividing into 〜 33 n and forming
the void group 35 in each of the lateral grooves 34. In addition, the divided external electrodes
331 to 33 n can be easily formed by, for example, screen printing at the time of electrode
formation, and photolithography etching after electrode formation. Therefore, the mechanical
strength of the cylindrical piezoelectric vibrator 31 is large, the manufacturing yield is high, the
manufacturing is easy, and the manufacturing cost can be reduced. The present invention is not
limited to the above embodiment, and various modifications are possible. As a modification, there
are, for example, the following (1) to (4).
[0019]
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(1) The structure of the annular ultrasonic transducer in FIG. 1 and the structure of the
cylindrical ultrasonic transducer in FIG. 6 have been described, but the present invention is not
limited to these shapes. For example, in the annular ultrasonic transducer shown in FIG. 1, a part
of the ultrasonic transducer may be shaped like an arc. Such an arc-shaped ultrasonic transducer
functions to transmit and receive cylindrical waves in a specific direction. Such a shape can
reduce the number of piezoelectric materials. Similarly, in the cylindrical ultrasonic transducer
shown in FIG. 6, the same action and effect as described above can be obtained even if the
ultrasonic transducer has a shape in which a part thereof is cut longitudinally in an arc shape. (2)
In FIG. 6, the outer surface electrodes 331 to 33n are divided by the lateral grooves 34, but even
if the outer electrodes 331 to 33n are divided by the lateral grooves without dividing the outer
electrodes 331 to 33n, FIG. Similar actions and effects can be obtained. Further, an inner
electrode and an outer electrode are respectively formed on a part of the inner peripheral surface
and outer peripheral surface of the annular piezoelectric vibrator 21 of FIG. 1 to transmit and
receive a cylindrical wave in a specific direction. It is also good. Similarly, inner and outer
electrodes are formed on a part of the inner and outer peripheral surfaces of the cylindrical
piezoelectric vibrator 31 shown in FIG. 6 so that cylindrical waves are transmitted and received
in a specific direction. It is also good.
[0020]
(3) The annular piezoelectric vibrator 21 or the cylindrical piezoelectric vibrator 31 may be
manufactured by a method other than FIG. 4 or 5. For example, in FIG. 4, a plurality of annular
green sheets 31 c are prepared, and after laminating them, the piezoelectric vibrator 21 is
manufactured by pressing with a press or the like. After laminating the green sheets, a circular
hole may be made in the center of the sheet. Similarly, in FIG. 5, the fan-shaped first green sheet
material 21d and the fan-shaped second green sheet material 21e are stacked in a cylindrical
shape and pressed by a press or the like to form the piezoelectric vibrator 31. However, after a
plurality of green sheet materials are stacked in a cylindrical shape, circular holes may be made
in their central portions. (4) In the above embodiment, the piezoelectric vibrators 21 and 31 are
formed of a PZT-based piezoelectric ceramic material. It is possible to use various piezoelectric
ceramic materials such as PbTiO3-based, Pb2NbO6-based, and BaTiO3-based.
[0021]
As described above in detail, according to the first and second inventions, a piezoelectric vibrator
consisting of the whole or a part of a cylindrical shape, and an inner peripheral surface and an
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outer peripheral surface thereof are respectively formed. Since the piezoelectric vibrator is
provided with an inner surface electrode and an outer surface electrode, and the piezoelectric
vibrator is formed of a piezoelectric ceramic material in which a group of holes is distributed and
formed at a predetermined location, coupling of resonant modes other than in the thickness
direction is small by the group of holes. The thickness oscillation can be performed in an annular
shape which is polarized in the thickness direction by the inner surface electrode and the outer
surface electrode. Therefore, the following effects (a) to (d) are obtained.
[0022]
(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 the cracking of the
piezoelectric vibrator due to groove processing as in the prior art and the cracking of the
piezoelectric vibrator due to water pressure or the like, and to improve the mechanical strength.
(B) Since it is not necessary to groove the piezoelectric vibrator as in the prior art, it is possible to
prevent a decrease in manufacturing yield and an increase in cost due to the groove processing.
(C) Since there is no groove processing of the conventional vertical grooves or horizontal grooves
in the channel, it is not necessary to connect the electrodes divided by the vertical grooves or
horizontal grooves, and the wiring structure is simplified. (D) An annular ring polarized in the
thickness direction can be obtained by dividing the electrode for each channel and forming a
group of holes on the surface of the cylindrical diameter of the divided portion without
performing the groove processing of the horizontal groove as in the prior art. Since the thickness
is vibrated by the shape, the sound beam can be scanned one-dimensionally with high accuracy
without affecting adjacent channels. According to the third aspect of the invention, after the
piezoelectric vibrator consisting of the whole or a part of the cylindrical shape is formed using
the first and second green sheet materials, it is temporarily fired to form the inside of the first
green sheet material. After firing the particles to form pores, the main firing is performed, so that
a pore group consisting of a large number of pores can be easily and accurately formed at a
predetermined position in the piezoelectric vibrator. Therefore, the manufacturing process of the
ultrasonic transducer can be simplified and the manufacturing cost can be reduced accordingly.
[0023]
Brief description of the drawings
[0024]
1 is a block diagram of a one-channel ultrasonic transducer showing a first embodiment of the
present invention.
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[0025]
2 is a perspective view of a conventional one-channel ultrasonic transducer.
[0026]
3 is a perspective view of another conventional multi-channel ultrasonic transducer.
[0027]
4 is an explanatory view of a method of manufacturing the ultrasonic transducer of FIG.
[0028]
5 is an explanatory view of a method of manufacturing an ultrasonic transducer showing a
second embodiment of the present invention.
[0029]
6 is a block diagram of a multi-channel ultrasonic transducer showing a third embodiment of the
present invention.
[0030]
Explanation of sign
[0031]
21 and 31 Piezoelectric vibrators 21a and 21d First green sheet 21c Green sheet 21b and 21e
Second green sheet 22 and 32 inner surface electrodes 23, 331 to 33 n outer surface electrodes
24 and 35 hole groups 24a and 35a holes 34 horizontal groove
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