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DESCRIPTION JPH05284600

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DESCRIPTION JPH05284600
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
piezoelectric ceramic element used for various elements such as pressure sensors, ultrasonic
transducers, ultrasonic sensor elements, sensor elements for high temperature, and actuator
elements.
[0002]
2. Description of the Related Art Conventionally, as piezoelectric ceramics used for pressure
sensors and ultrasonic transducers, those obtained by firing a piezoelectric ceramic component
such as lead titanate alone are used.
[0003]
SUMMARY OF THE INVENTION The dielectric constant and piezoelectricity of this piezoelectric
ceramic show a maximum near the transformation point or Curie point.
Therefore, when a piezoelectric ceramic is used for a pressure sensor or an ultrasonic transducer,
the temperature dependence of the characteristics of these elements becomes large under the
influence of the material characteristics. Therefore, the problem is how to reduce the
temperature dependency of the piezoelectric constant.
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[0004]
As a countermeasure therefor, conventionally, it has been dealt with by using a piezoelectric
ceramic having a high Curie point such as the above-mentioned lead titanate, but it can not be
said that the temperature dependency is sufficiently improved. Furthermore, the development of
piezoelectric ceramics having a high Curie point and good piezoelectricity is currently difficult.
[0005]
An object of the present invention is to provide a piezoelectric ceramic device having improved
temperature dependency.
[0006]
According to the present invention, a pressure sensor, an ultrasonic transducer, and an ultrasonic
sensor having improved temperature dependency by connecting a temperature compensating
capacitor to a piezoelectric ceramic in parallel or in series. It is a piezoelectric ceramic element
such as an element or an actuator element.
[0007]
The invention according to claim 2 is a piezoelectric ceramic element in which the piezoelectric
ceramic and the temperature compensating capacitor are laminated.
[0008]
The invention of claim 3 is an integrated composite piezoelectric ceramic element in which a
piezoelectric ceramic component and a temperature compensating capacitor component are
mixed and sintered to a desired component ratio.
[0009]
[Operation] In order to solve the above-mentioned problems, theoretical considerations were
added and further experiments were made to prove it.
Since the piezoelectric vibrator is replaced by an electrical equivalent circuit, the relationship
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2
between the circuit constant and the piezoelectric constant is clarified, and as a result of
examining how each circuit constant changes with temperature, circuit elements are added for
temperature compensation. It is clarified that the method can improve the temperature
dependence.
As an additional method, the invention of claim 1 electrically connects the piezoelectric ceramic
and the compensation element, the invention of claim 2 makes the piezoelectric ceramic and the
compensation element have a laminated structure, and the claim 3 The invention is to make the
piezoelectric ceramic and the compensating element into a composite structure.
[0010]
DESCRIPTION OF THE PREFERRED EMBODIMENTS (1) Theoretical Consideration The equivalent
circuit of a piezoelectric vibrator is shown in FIG. 1 (B).
When a piezoelectric element is used for a vibrator or a sensor element, the piezoelectric g
constant measures the applied pressure by voltage, and the piezoelectric d constant measures a
sensor followed by a circuit such as a charge amplifier. Corresponding to the sensor sensitivity of
Here, when the relationship between the piezoelectric constant and the circuit constant is
derived, the following relationship is obtained.
[0011]
Here, if the coupling coefficient K33 <0.4, it can be handled as C0 >> C1 and the thermal
expansion coefficient of a general piezoelectric ceramic is small, so the above equation can be
approximated as follows.
[0012]
That is, the temperature change of C0 and C1 causes the temperature dependency of the
piezoelectric d constant and the piezoelectric g constant.
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The temperature dependence of C0 and C1 is an unavoidable problem as long as piezoelectric
ceramics are used.
[0013]
On the other hand, as shown in FIG. 1A, the composite equivalent in the case where the
temperature compensating capacitor (Cs) is connected in series or the temperature compensating
capacitor (Cp) is connected in parallel to the piezoelectric ceramic (C0, C1, L1, R1) The circuit
constants of the circuit have the following relationship.
[0014]
Parallel: C0 '= (C0 + Cp) C1' = C1 L1 '= L1 R1' = R1 series; C0 '= C0 · Cs / (C0 + Cs) C1' = C1 · Cs 2
/ (C0 + C1 + Cs) (C0 + Cs) L1 '= L1 · (1 + C0 / Cs) 2R1' = R1 · (1 + C0 / Cs) 2 (2) Temperature
dependence of piezoelectric constant Curie point is high, and piezoelectric element using lead
titanate with small temperature dependence such as C0 The temperature dependence of the
piezoelectric g constant was calculated from the temperature change of the combined circuit
constant when the piezoelectric element alone and the capacitor were connected.
According to this result, in the temperature range of 0 ° C. to 150 ° C., the piezoelectric g
constant shows a change of about 29% in the case of a single piezoelectric element, but
suppresses the change to about 7% in the case where capacitors are connected in parallel. be
able to.
[0015]
Here, the temperature coefficient of the capacitor is the reverse of that of the piezoelectric
element.
[0016]
(3) Operating characteristics of pressure sensor A pressure sensor was fabricated using the
above-described piezoelectric element, and the temperature dependency of the output voltage
when a certain amount of pressure was applied to the pressure sensor was actually measured.
While the change in output voltage for a pressure sensor alone was about 16% in the
temperature range of C, the change in output voltage could be suppressed to about 7% by
connecting capacitors in parallel.
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[0017]
(4) When a lead oxide ceramic capacitor is used as a capacitor for compensating the temperature
of the laminated and composite piezoelectric elements, capacitors having various dielectric
constants and temperature coefficients can be manufactured.
In addition, lamination with lead zirconate titanate or lead titanate piezoelectric ceramics is
possible.
[0018]
FIG. 2 is a schematic view showing the structure of a laminated element, in which a piezoelectric
ceramic 31 and a ceramic capacitor 32 for temperature compensation are laminated in series via
an internal electrode 33, and an external electrode 34 is provided. It is an element and is
electrically connected in series.
Therefore, the temperature characteristics of the piezoelectric d constant can be improved. When
this element is used for a pressure sensor, it is necessary to measure through a charge amplifier
that measures charge.
[0019]
FIG. 3 is a schematic view of the bolted piezoelectric element, in which the piezoelectric ceramic
41 and the temperature compensating capacitor 42 are stacked together by tightening them with
a bolt 43 and a nut 44. 45,46Are electrodes respectively attached to the piezoelectric ceramic
41 and the capacitor 42. The case of this bolting element is basically the same structure as the
element shown in FIG. 2, and the improvement effect of the temperature characteristic is also the
same.
[0020]
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FIG. 4 is a schematic view of a composite type element, which is a ceramic element obtained by
mixing and forming a piezoelectric ceramic particle 51 as a piezoelectric ceramic component and
a temperature compensating ceramic capacitor particle 52 as a temperature compensating
capacitor component. The electrode 53 is provided on the In this composite type, first, solid
solutions of a piezoelectric ceramic and a capacitor are separately prepared, and these are mixed
and formed with a composition exhibiting desired characteristics, and then sintered to produce a
composite piezoelectric ceramic element as shown in FIG. Do. Here, the piezoelectric ceramic
exhibits a large piezoelectricity, and a composition having a small temperature dependency is
selected. The capacitor is selected to have a composition that changes inversely with the
temperature change of the capacitance of the piezoelectric ceramic.
[0021]
The mixing ratio between the piezoelectric ceramic and the capacitor material is the ratio
necessary for temperature compensation of the capacitor to cancel the temperature dependency
of the piezoelectric ceramic, and this element is a solid solution mixed randomly, so the ratio
calculated by the logarithmic mixing law Make it
[0022]
According to the invention of claim 1, by electrically connecting a temperature compensating
capacitor to the piezoelectric ceramic, it is possible to use a piezoelectric ceramic element such as
a pressure sensor or an ultrasonic transducer using the piezoelectric ceramic. The temperature
dependency can be greatly improved, and the reliability of the device can be greatly improved.
[0023]
According to the second aspect of the invention, it is possible to provide a compact piezoelectric
ceramic element with improved temperature dependency by the laminated structure of the
piezoelectric ceramic and the temperature compensating capacitor.
[0024]
According to the third aspect of the present invention, by mixing and sintering the piezoelectric
ceramic component and the temperature compensating capacitor component, it is possible to
provide a piezoelectric ceramic element having an integrated composite structure with improved
temperature dependency.
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