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JPH01160200

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DESCRIPTION JPH01160200
[0001]
The piezoelectric sensor of the present invention will be described according to the following
items. A, Industrial Application Field B1 Outline of the Invention C0 Prior Art [FIG. 5] Problems to
be Solved by the Invention [FIG. 5] E Means for Solving the Problems E1, Example [FIG. 1] To 4]
a, base ring, piezoelectric plate, electrode plate, resonance plate, etc. C0 Coupling 61 of each
member e, usage example G0 effect of the invention (A, industrial field of application) The
present invention is a novel piezoelectric It relates to a sensor. More specifically, the present
invention relates to an apparatus for measuring a pressure change of a vibration source or a
body in which the vibration source is built by contacting a piezoelectric element with the
vibration source or a body in which the vibration source is contained. By improving the contact
structure of the piezoelectric element with respect to the vibration source and the like, it is
possible to accurately measure the pressure change without causing distortion in the
piezoelectric element other than the strain caused by the vibration transmitted from the vibration
source and the like. It is an object of the present invention to provide a novel piezoelectric sensor
capable of reliably measuring even pressure changes and in which the characteristics of the
piezoelectric element do not change due to the temperature of a vibration source or the like. (B,
Summary of the Invention) The piezoelectric sensor of the present invention measures the
vibration transmitted from the vibration source or the like as a voltage change by bringing the
piezoelectric element into contact with the vibration source or the body in which the vibration
source is contained. In a piezoelectric sensor that measures pressure change of a source or the
like, distortion of the piezoelectric element due to a contact with a vibration source or the like
may occur as the contact of the piezoelectric element against the vibration source or the like is
made through the enclosed space and the resonator. The temperature of the vibration source and
the like is not transmitted to the piezoelectric element and the vibration of the vibration source is
amplified and transmitted to the piezoelectric element, whereby the pressure change of the
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vibration source can be accurately and weakly. Also, it is intended to be able to measure reliably.
(C, prior art) [Fig. 5] Today, a piezoelectric element, that is, a piezoelectric sensor using an
element that exerts a so-called piezoelectric effect in which an electric charge is generated when
stress is applied is a medical measuring instrument such as a pulse measuring instrument or It is
used for various applications such as a piezoelectric buzzer or a piezoelectric micro-bon. FIG. 5
shows, for example, m pieces a of the conventional piezoelectric sensors disclosed in Japanese
Utility Model Application Publication No. 55-74198. In the figure, b is a circuit board provided
with a center electrode C and an outer peripheral electrode C ', d is a piezoelectric element fixed
to the upper surface of the circuit board in contact with the center electrode C, and e is a circuit
board A base cover provided so as to cover the lower surface, an electrode cover f provided in
contact with the piezoelectric element d and the outer peripheral type FJc ', terminals not shown
being fixed to the center electrode C and the outer peripheral electrode C' There is.
Therefore, for example, when the outer surface of the electrode cover f is brought into contact
with a vibration source or a body in which the vibration source is contained, the vibration from
the vibration source is transmitted to the piezoelectric element d through the electrode cover f.
Periodic distortion corresponding to the frequency of the vibration occurs, and a voltage
changing according to the distortion is generated, and the pressure change of the vibration
source is measured by detecting this voltage change. Become. (D, Problems to be Solved by the
Invention) [FIG. 5] By the way, when such a piezoelectric sensor is used for pulse measurement,
for example, in order to improve sensitivity to vibrations due to the heartbeat and blood flow.
Usually, it will be pressed against the skin of the living body with a certain degree of strength.
However, when the above-described conventional piezoelectric sensor a is used in such a
manner, the piezoelectric sensor d causes distortion or deformation in the piezoelectric element d
when the piezoelectric sensor is pressed against the living body. Each time the force pressing the
living body changes, the strain changes, so that an electric charge is generated. That is, during
measurement, the piezoelectric element is charged by elements other than the vibration from the
vibration source such as the heart, and such a charge naturally becomes noise in the pulse
measurement. Therefore, there is a problem that it is impossible to accurately measure the pulse
in a state where such noise occurs. Further, since the heartbeat or the like is extremely weak
vibration, there is a problem that it becomes difficult to reliably measure the pulse unless a
sensor with high vibration sensitivity is used as much as the electrode cover f or the piezoelectric
element d. . Furthermore, since the piezoelectric element usually has the property that its
characteristics change significantly when the temperature exceeds a certain range, the electrode
cover f with which the piezoelectric element d is in contact like the piezoelectric sensor a. If the
vibration source is in direct contact with the vibration source etc., the heat of the vibration
source etc. will be transmitted to the piezoelectric element d, so the temperature of the
piezoelectric element d changes and its characteristics change. There's a problem. (E, Means for
Solving the Problems) Therefore, in the piezoelectric sensor of the present invention, in order to
solve the above-mentioned problems, the resonator in contact with the vibration source is
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disposed opposite to the piezoelectric element across the sealed space. It is a thing. Therefore,
according to the piezoelectric sensor of the present invention, since the piezoelectric element is
opposed to the vibration source through the enclosed space and the resonator, the piezoelectric
element does not generate distortion due to contact with the vibration source and the vibration
source does not The temperature from the vibration source is not transmitted, and furthermore,
the vibration from the vibration source is amplified by the resonator and the enclosed space and
transmitted to the piezoelectric element, whereby the distortion generated in the piezoelectric
element is a distortion due to the vibration from the vibration source Therefore, the pressure
change of the vibration source can be measured very accurately, the characteristics of the
piezoelectric element are not affected by the temperature of the vibration source, and also the
weak vibration from the vibration source can be surely ensured. It can be measured.
(F, Example) [FIG. 1 to FIG. 4] Hereinafter, the details of the piezoelectric sensor of the present
invention will be described according to Example 1 illustrated. (A, base ring, piezoelectric plate) 2
is a base ring of the piezoelectric sensor 1, and the base ring 2 is formed of a synthetic resin so
as to form a relatively thick and substantially annular shape, and the thickness of the inner
peripheral surface 2a An annularly extending groove 3 is formed in a portion excluding both end
portions in the direction, and the groove 3 has a half value depth of the width of the base ring 2.
4 is a piezoelectric plate, which is a piezoelectric material that generates polarized charges when
strained, for example, a hybrid ternary ternary PZT, or so-called piezoplastics or piezoceramics
piezoelectric material such as polyacetal or rubber of the same system, etc. It is formed in a
substantially disc shape. (B, electrode plate, resonant plate, etc.) 5 and 6 are electrode plates, and
these electrode plates have an annular shape whose outer diameter is substantially the same as
the outer diameter of the piezoelectric plate 4 and terminals 7 from the outer edge .7 'are
projected to the side. The lower electrode plate 6 is formed thicker than the upper electrode plate
5. A pressure lead-out pipe 8 having a substantially U-shape is provided, and most of the lower
electrode plate 6 except for the lower end 8a, that is, both ends of the portion extending along
the direction orthogonal to the thickness direction of the piezoelectric sensor 1 It is fixed to the
electrode plate 6 in a state in which a portion located on the substantially opposite side to the
terminal 7 'is penetrated in a direction orthogonal to the thickness direction of the electrode
plate 6, and the upper portion 8b, that is, the thickness direction of the piezoelectric sensor 1 A
portion extending along the groove is located outside the electrode plate 6. 9 is a resonant plate.
The resonance plate 9 is made of a material having a high vibration transmission rate and a high
thermal conductivity, such as copper or aluminum, and has a ring-shaped fixing portion 9a
having substantially the same size as the electrode plate 5.6, An intermediate portion 9b which
protrudes downward from the inner peripheral edge of the fixed portion 9a and which gradually
decreases in diameter toward the lower end, and a contact portion 9C having a substantially disc
shape closing the lower end surface of the intermediate portion 9b are integrated. It is formed.
Reference numeral 10 denotes, for example, a heat sensing element such as a film thermistor,
which has a substantially disc shape and is fixed to the upper surface of the contact portion 9C of
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the resonance plate 9. (C, connection of each member) And, as for the piezoelectric plate 4, the
electrode plate 5.6 and the resonance plate 9 described above, the electrode plates 5 and 6 are
positioned across the outer peripheral edge of the piezoelectric plate 4 in the thickness direction,
The fixing portion 9a of the resonance plate 9 is superimposed on the lower surface of the lower
electrode plate 6, and the outer peripheral portions of the respective members 4.5.6 and 9 are
fitted in the groove 3 formed in the base ring 2 It is supported, and the upper end of the pressure
lead-out pipe 8 is open to the upper surface of the base ring 2.
The piezoelectric sensor 1 having such a structure may be formed, for example, by insert
molding, that is, in the cavity of a molding die for molding the base ring 2, the piezoelectric plate
4, the electrode plate 5.6 and the resonance plate 9. As described above, they are formed by
injecting a molten resin into the above-mentioned mold in a state in which these outer peripheral
portions are arranged. Thus, a sealed space 11 is defined between the piezoelectric plate 4 and
the resonant plate 9, and the piezoelectric plate 4 faces the resonant plate 9 with the sealed
space 11 interposed therebetween, and a terminal provided on the electrode 5.6 The tip end of
the flange 7 'is positioned so as to protrude from the outer peripheral surface 2b of the base ring
2, and one end of the pressure lead-out pipe 8 opens into the sealed space 11. Reference numeral
12 denotes a connecting pipe whose one end is connected to the pressure lead-out pipe 8 and
the other end is connected to a pressure sensor 13 such as a semiconductor pressure sensor. The
terminal sensor 7 ', the pressure sensor 13 and the heat sensing element 10 are connected to a
processing circuit (not shown) for processing the terminal voltage of the terminal sensor 7', the
pressure sensor 13 and the heat sensing element 10. (D, action) Then, when the contact portion
9C of the resonance plate 9 is pressed against the vibration source or the body containing the
vibration source, the vibration from the vibration source is transmitted to the contact portion 9C
and the contact portion 9C vibrates. At the same time, the air in the enclosed space 11 vibrates
due to the vibration. Therefore, stress is applied to the piezoelectric plate 4 by this vibration to
cause distortion, so that a voltage is generated in the piezoelectric plate 4 and the voltage
changes according to the vibration frequency of the vibration source, and the change of this
voltage Are output through the electrode plate 5.6 and the terminals 7 '. That is, a voltage which
changes in accordance with the vibration frequency of the vibration source is taken out from the
terminal 7 '. Thus, the pressure change of the vibration source can be measured by detecting the
change of the terminal voltage. And the measurement of the pressure change in this case
becomes a very accurate measurement without noise. That is, as described above, in order to
measure vibration or the like in this type of piezoelectric sensor, it is necessary to press the
sensor against a vibration source or the like with a certain degree of pressure. The resonator
plate 9 is in direct contact with the source and the like, and the piezoelectric plate 4 is indirectly
opposed to the vibration source and the like via the sealed space 11 and the resonator plate 9.
Therefore, when the piezoelectric sensor is pressed against a vibration source or the like, a
certain amount of distortion or deformation occurs in the resonance plate 9, but such a distortion
does not occur in the piezoelectric plate 4, so the piezoelectric The distortion generated in the
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plate 4 is only distortion due to the vibration from the vibration source.
Moreover, since the vibration from the vibration source transmitted to the resonance plate 9 is
amplified while being propagated through the enclosed space 11 and is transmitted to the
piezoelectric plate 4, the change in the vibration of the vibration source even if the vibration is
weak Can be detected reliably. Further, since the heat of the vibration source or the body in
which the vibration source is contained is transmitted to the heat sensing element 10 via the
contact portion 9C of the resonance plate 9, the vibration is detected by detecting the terminal
voltage of the heat sensing element 10. The temperature of the source or the body can be
measured. Since the heat transmitted to the resonance plate 9 is not transmitted to the
piezoelectric plate 4, the characteristics of the piezoelectric plate 4 are not changed.
Furthermore, since the pressure in the enclosed space 11 is detected by the pressure sensor 13
via the pressure lead-out pipe 8 and the connection pipe 12, the pressure in the enclosed space
11 changed by the vibration of the contact portion 9C of the resonance plate 9 is a pressure
sensor 13 will be detected. (E, Use Example) The piezoelectric sensor 1 having such a structure
can be used, for example, as a medical measuring instrument for measuring pulse, body
temperature, blood pressure and the like. That is, when the contact portion 9C of the resonance
plate 9 is pressed to a position close to the heart or a position close to the artery in the human
body skin, for example, vibration due to heartbeat or blood flow of the heart is transmitted
through the resonance plate 9 and the enclosed space 11 The voltage is amplified and
transmitted to the piezoelectric plate 4, thereby causing distortion in the piezoelectric plate 4 and
generating a voltage, which is generated according to the frequency of the heartbeat and the like.
Therefore, the pulse is measured by detecting this changing voltage. In this case, although the
resonance plate 9 is distorted to some extent by being pressed against the outer skin of the
human body, distortion due to such a cause does not occur in the piezoelectric plate 4. Further,
since the heat of the human body is transmitted to the heat sensing element 10 through the
contact portion 9c of the resonance plate 9, it becomes possible to measure the body
temperature. Further, the pressure of the enclosed space 11 which is changed by the
transmission of the heartbeat or the like is detected by the pressure sensor 13, and the data of
the detected pressure and the data of the pulse detected by the piezoelectric plate 4 are
processed Blood pressure can be measured. (G, Effect of the Invention) As is apparent from the
above description, in the piezoelectric sensor of the present invention, the piezoelectric element
and the resonator in contact with the vibration source are disposed opposite to each other with
the sealed space therebetween, A terminal for taking out the generated voltage is provided.
Therefore, according to the present invention, since the piezoelectric element is opposed to the
vibration source through the enclosed space and the resonator, the piezoelectric element does
not generate distortion due to contact with the vibration source and the temperature of the
vibration source has The vibration from the vibration source is amplified by the resonator and
the enclosed space and transmitted to the piezoelectric element.
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Therefore, according to the piezoelectric sensor of the present invention, the strain generated in
the piezoelectric element is only the strain due to the vibration from the vibration source, so that
the pressure change of the vibration source can be measured extremely accurately It is not
affected by the temperature of the sensor, and weak vibrations from the vibration source can be
reliably measured. In the above embodiment, a pressure sensor for fixing the heat sensitive
element to the inner surface of the resonator and measuring the pressure in the enclosed space is
provided. By doing this, a vibration source or a body incorporating the vibration source is
provided. The pressure of the vibration source and the temperature of the vibration source can
also be measured. In the above-described embodiment, two substantially ring-shaped electrodes
are disposed to face each other in the thickness direction of the piezoelectric element with the
outer peripheral portion of the piezoelectric element interposed therebetween, and the terminals
are protruded from these electrodes. For example, the means for taking out the voltage generated
in the piezoelectric element can also function as a spacer between the piezoelectric element and
the resonator. However, in the practice of the present invention, a special spacer may be
provided to form an enclosed space between the piezoelectric element and the resonator, or a
terminal may be provided directly to the piezoelectric element. Furthermore, a circuit for
processing the voltage generated in the piezoelectric element may be provided in the enclosed
space. The piezoelectric sensor of the present invention is not limited to the piezoelectric sensor
for measuring the pulse described in the paragraph of the application example, but may be used
as various piezoelectric sensors for measuring the pressure change of the vibration source by
bringing the piezoelectric element into contact with the vibration source. can do.
[0002]
Brief description of the drawings
[0003]
1 to 4 show an embodiment of the piezoelectric sensor according to the present invention, FIG. 1
is a vertical sectional view, FIG. 2 is a perspective view showing the whole, and FIG. 3 is a
diagram III-- FIG. 4 is an exploded perspective view of the main part, and FIG. 5 is a crosssectional view showing an example of a conventional piezoelectric sensor.
DESCRIPTION OF NUMERALS 1 ... piezoelectric sensor, 4 ... piezoelectric element, 7.7 '... terminal,
9 ... resonator, 11 ... applicant for enclosed space Japan Byuren Co., Ltd. same new electronics
industry Ltd. 1-,-rLll t hi in L * fr4. '+-Year L [321 (I [-[k) Figure 3 broken? 1ii O 圓 (4 points 11)
Fig. 5
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