JPH0923499

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DESCRIPTION JPH0923499
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
piezoelectric vibrator, and more particularly to a piezoelectric vibrator used as a high frequency
transducer in water and using a vibration mode in a thickness direction of a cylindrical
piezoelectric material. In addition, although the above-mentioned transducer usually means a
transducer, a high frequency transducer here means an electroacoustic transducer, for example,
a transducer of an ultrasonic wave.
[0002]
2. Description of the Related Art Japanese Patent Application No. 06-104229 entitled
"Transmitter for water" filed by the patent applicant of the present invention and the same patent
applicant as the above-mentioned prior art. In the above-mentioned document, in a piezoelectric
vibrator having a cylindrical shape and using a vibration mode in the thickness direction,
vibration coupling in a direction perpendicular to the thickness direction is small (in other words,
a resonant mode other than the thickness direction) It is taught that in order to form a multichannel array with one piezoelectric vibrator using a piezoelectric material such as a
piezoelectric ceramic having a small coupling), it is possible by dividing only the electrodes
between the channels. There is.
[0003]
However, in the case of the conventional high frequency transducer for water, the thickness
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(distance) between the positive and negative electrodes is originally about 1/10 or more thicker
than the width of the electrodes (10). When it becomes larger than one-half), the spread (leakage)
of the electric field to other channels becomes large, which makes non-negligible coupling of
capacitances between the channels, and one piezoelectric oscillator makes multi-channel array It
was a problem when forming.
[0004]
And although the above-mentioned conventional underwater transducer provides a solution to
the above-mentioned problems, as shown in the prior art of the above-mentioned document, the
interchannels along the circumference Grooves can reduce the capacitive coupling between the
channels.
However, in the actual working frequency band of several hundreds kHz, the thickness is 2 to 3
mm, and to cut the cylindrical piezoelectric vibrator into three quarters or more of the thickness,
the remaining thickness is 0. It is very thin, 5 to 0.6 mm. Therefore, in the prior art of the abovementioned document, the piezoelectric vibrator has been pointed out to be a defect that becomes
very fragile. Furthermore, in the manufacture, since the technique of cutting a groove is required,
making it rotate along a periphery, there existed a problem that processing was difficult.
[0005]
In a piezoelectric vibrator according to the present invention, positive and negative electrodes
are provided on the inner surface and the outer surface of a cylindrical piezoelectric body
consisting of a whole or a part of a cylindrical shape, It has a basic configuration that uses
vibration in the thickness direction of the piezoelectric body, and at least one of the positive and
negative electrodes is divided along a plane perpendicular to the cylinder central axis of the
piezoelectric body to form a channel to form a cylinder center A piezoelectric vibrator
constituted of a vibrator array along an axis, wherein a part of a cylindrical shape of the
piezoelectric body is left, the inside of the piezoelectric body is reached from the outer surface of
the cylindrical shape, and at least one of positive and negative electrodes is It is separated by a
dividing groove formed by grooving which separates completely at predetermined intervals. The
piezoelectric body is preferably formed of a piezoelectric material having a piezoelectric
characteristic with small vibrational coupling in the direction perpendicular to the thickness
direction. For example, it is preferable to use lead titanate-based ceramics as the piezoelectric
material. . The other piezoelectric material may be a polymeric piezoelectric material such as
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polyvinylidene fluoride or a trifluorinated ethylene-fluorinated ethylene copolymer, or a
composite piezoelectric material such as a piezoelectric ceramic / rubber composite.
[0006]
In the present invention, for example, a part of a cylindrical shape of a piezoelectric body having
small piezoelectric characteristics with small vibrational coupling in a direction perpendicular to
the thickness direction such as lead titanate-based ceramics is left Since the electric field reaches
the inside and is separated by a dividing groove formed by grooving that completely separates at
least one of the positive and negative electrodes by a predetermined distance, the spread of the
electric field to the other channels is slight, Capacitance coupling is greatly reduced.
[0007]
DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic explanatory view
showing an embodiment of a piezoelectric vibrator according to the present invention.
In the drawings, the left side is a side view, and the right side is a front view. FIG. 1 shows a semicylindrical vibrator in which an array of five channels is formed as an example of an array of
other channels. In FIG. 1, 11 is a semi-cylindrical piezoelectric ceramic, 12 and 13 are film-like
electrodes provided on the outer surface and the inner surface of the piezoelectric ceramic 11,
12 is a positive electrode of the piezoelectric vibrator, and 13 is a piezoelectric vibration Child's
negative electrode. Denoted at 14 are a plurality of (four in this embodiment) split grooves for
forming channels formed by grooving in a direction perpendicular to the height (length of the
cylinder) direction of the piezoelectric ceramic 11. In the above configuration, the positive
electrode 12 and the negative electrode 13 are provided on the outer surface and the inner
surface of the piezoelectric ceramic 11, respectively. However, depending on the usage form, the
opposite arrangement may be employed. An array-type piezoelectric vibrator configured as
described above is used as a multi-channel underwater transducer.
[0008]
In general, in a submersible transducer, for waterproofing, the piezoelectric vibrator is placed in
a rubber boot filled with silicone oil, or rubber is molded around the piezoelectric vibrator.
Therefore, the dividing groove 14 is filled with silicone oil or rubber. As seen in the front view of
FIG. 1, left and right ends of the semicircular piezoelectric ceramic 11 are left, and as seen in the
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side view of FIG. ing.
[0009]
The positive electrode 12 is divided by grooving, and each positive electrode 12 can apply a
voltage separately (in time). The positive electrode 12 is formed in a portion not including the
base portions 17 and 17a at the left and right ends of the piezoelectric ceramic 11, while the
negative electrode 13 is the same as the positive electrode 12 at the right end side of the
semicircular piezoelectric ceramic 11. Further, it is formed on the entire inner surface other than
the base portion 17, for example, the inner side surface of the base portion 17a at the left end,
and constitutes a common electrode of each channel. Therefore, each one of the parts divided by
grooving serves as a channel. And 15 and 16 are a positive lead wire and a negative lead wire,
respectively. One positive lead 15 is connected to each channel. One negative lead wire 16 is
connected to the inside of the base portion 17 a at the left end of the piezoelectric ceramic 11. In
addition, although the connection position of these lead wires is not limited to the abovementioned position, in general, it is desirable that the lead wires do not disturb (shield or disturb)
transmission and reception of ultrasonic waves (cylindrical waves, etc.) Alternatively, since it is
necessary not to disturb, it is preferable to be the end of each electrode as in this embodiment.
[0010]
The piezoelectric ceramic 11 is formed using a PbTiO3 (lead titanate) -based ceramic material. As
the PbTiO 3 -based piezoelectric ceramics, as described in detail in the literature indicated in the
description of the prior art described above, several materials having different compositions and
composition ratios are currently usable. However, in the present embodiment, the specific one is
not limited. That is, the PbTiO3-based piezoelectric ceramic has a feature that the piezoelectric
constant in the direction perpendicular to the polarization direction is very small, and is suitable
as a material for forming the piezoelectric ceramic 11 for a piezoelectric vibrator according to
the present invention. .
[0011]
That is, among piezoelectric ceramics, particularly, PbTiO3 based piezoelectric ceramics have an
electromechanical coupling coefficient smaller by about an order of magnitude than piezoelectric
ceramics materials such as PZT (lead zirconate titanate) which are generally used, but the
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coupling coefficient It is characterized in that the anisotropy of is large and the dielectric
constant is small. For example, while the piezoelectric strain constant -2d31 / d33 of the PZTbased piezoelectric ceramic is approximately 1, that of the PbTiO3 -based piezoelectric ceramic
used in this example is 0.2 or less. Therefore, vibrations in the circumferential direction of the
cylinder and in the axial direction of the cylinder can be ignored, and only thickness vibrations in
the radial direction can be obtained.
[0012]
Hereinafter, the operation of the present piezoelectric vibrator will be described. First, when a
signal is applied to a channel to which a voltage is applied to the positive electrode 12 connected
thereto via an arbitrary positive lead wire 15, vibration in the thickness direction of the
piezoelectric ceramic 11 occurs on the entire surface of the positive electrode 12 of that channel.
To be done. Then, a partial cylindrical wave along the channel from the vibrating portion radiates
to the outside of the piezoelectric ceramic 11.
[0013]
In this case, as described above, the dividing groove 14 is filled with silicone oil or rubber. Here,
with regard to the relative dielectric constant, that of the PbTiO3 based piezoelectric ceramic
material is about 200, while it is 2 to 3 for silicone oil and 4 to 5 for rubber material. Therefore,
compared to the conventional type without the dividing groove 14, in the case of the present
embodiment, the spread (leakage) to the other channel of the electric field is small, and the
coupling of the capacitance between the channels has been a problem in the above-mentioned
documents. Will be greatly reduced. This configuration makes it possible to emit cylindrical
waves excellent in array independence for each channel.
[0014]
As described above, according to the present embodiment, since the grooves are cut leaving the
left and right ends of the piezoelectric ceramic 11 thick (in the circumferential direction) as the
base portions 17 and 17a, the channels are divided. Is structurally formed firmly, and has the
effect of solving the problem of the prior art being fragile. Here, in the cylindrical shape, the
channels are completely separated by this grooving in the part where both the positive and
negative electrodes face, but in this grooving by lathing, it suffices to move the grooving cutter
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linearly. Therefore, it is possible to solve the problems of the prior art that it is technically easy
and difficult to process.
[0015]
In the above embodiment, although the case where PbTiO3 (lead titanate) -based piezoelectric
ceramic is used as the piezoelectric material is described, a material having a characteristic
similar to this material in that the vibration coupling in the direction perpendicular to the
thickness direction is small As PVDF, there are polymer piezoelectric materials such as PVDF:
polyvinylidene fluoride and P (VDF · TrFE): trifluorinated ethylene / fluorinated ethylene
copolymer, or composite piezoelectric materials (composite of piezoelectric ceramic / rubber).
The same effect can be obtained even if a piezoelectric vibrator is configured using these
piezoelectric materials.
[0016]
As described above in detail, according to the present invention, positive and negative electrodes
are provided on the inner surface and the outer surface of the cylindrical piezoelectric body, and
the vibration in the thickness direction of the piezoelectric body is used. It has a basic
configuration, and at least one of the positive and negative electrodes is divided along a plane
perpendicular to the cylinder center axis of the piezoelectric body to form a channel, and a
transducer array is formed along the cylinder center axis. A divided groove which is formed by
grooving that completely leaves at least one of the positive and negative electrodes from the
outer surface of the cylindrical shape, leaving a part of the cylindrical shape of the piezoelectric
body of the piezoelectric vibrator. Since the whole piezoelectric vibrator is structurally rigidly
formed because of the separated structure, it has the advantage of facilitating grooving
processing, and the spread of the electric field to the other channels is small, and the
interchannels Capacitance coupling is greatly reduced Te, excellent cylindrical wave array
independent for each channel is obtained effect of radiation.
[0017]
Brief description of the drawings
[0018]
1 is a schematic explanatory view showing an embodiment of a piezoelectric vibrator according
to the present invention.
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[0019]
Explanation of sign
[0020]
Reference Signs List 11 piezoelectric ceramic 12 positive electrode 13 negative electrode 14
dividing groove 15 positive lead wire 16 negative lead wire 17, 17 a base portion
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