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JP2007142540

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JP2007142540
An object of the present invention is to provide an acoustic element capable of measuring a
minute acoustic wave. An acoustic element according to the present invention includes two
piezoelectric elements that output equal electrical signals to equal acoustic waves and
electromagnetic waves, and differentially outputs electrical signals from the piezoelectric
elements to generate acoustic noise and electromagnetic waves. It is characterized in that noise
can be offset. Specifically, the acoustic element according to the present invention comprises two
piezoelectric elements 11 and 12, a common terminal 13 for electrically connecting one of two
electrodes 21 a and 22 a of the same polarity, and two common terminals 13. It is characterized
by including two sensor output terminals 14 and 15 electrically connected to the other
electrodes 21 b and 22 b. [Selected figure] Figure 1
Acoustic element
[0001]
The present invention relates to an acoustic element capable of measuring a minute acoustic
wave using a piezoelectric element.
[0002]
In order to continuously measure blood pressure values, pulse wave detection methods have
been proposed for the fingers and the outer ear.
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1
As a pulse wave detection method, there are Korotkoff sound and pressure pulse wave detection
(see, for example, Patent Document 1). However, since the pulsation of the artery transmitted to
the epidermis was detected, only the pulsation of the thick artery where the pulsation was
transmitted to the epidermis could be detected.
[0003]
On the other hand, piezoelectric elements are used as acoustic elements for converting acoustic
waves into electrical signals. The piezoelectric element is an element that generates a voltage
when pressure is applied. An acoustic element using a piezoelectric element has high sensitivity
and can detect a minute acoustic wave, but since an acoustic wave is always generated when
there is a medium and some pressure, some kind of pressure from the periphery of the acoustic
element is large and acoustic noise It had become.
[0004]
Also, the piezoelectric element is a high impedance element. If the element has high impedance,
external electromagnetic waves are likely to be added as electromagnetic noise. Since the
electrical signal changes due to the added electromagnetic noise, the SN ratio of the electrical
signal output from the piezoelectric element tends to deteriorate.
[0005]
As a method of preventing acoustic noise and electromagnetic noise, there is a method of
providing a sound absorbing material that absorbs acoustic waves, or an electromagnetic wave
shield that reflects electromagnetic waves. However, when the acoustic wave to be measured is
minute, even if the sound absorbing material and the electromagnetic wave shield are provided,
the acoustic wave to be measured can not be measured. Japanese Patent Laid-Open No. 6-14888
[0006]
As described above, in the conventional acoustic element, measurement of a minute acoustic
wave is difficult because ambient acoustic waves and electromagnetic waves become large
acoustic noise and electromagnetic noise.
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[0007]
An object of the present invention is to provide an acoustic element capable of measuring a
minute acoustic wave.
[0008]
The present invention achieves the above object, and comprises two piezoelectric elements that
output equal electrical signals to equal acoustic waves and electromagnetic waves, and
differentially outputting the electrical signals from the piezoelectric elements to generate
acoustic noise and It is characterized in that electromagnetic noise can be canceled out.
[0009]
Since the two piezoelectric elements having substantially the same characteristics are
differentially operated, noise applied in common to the two piezoelectric elements and acoustic
noise and electromagnetic noise generated by electromagnetic waves can be canceled out.
On the other hand, since only one piezoelectric element measures an acoustic wave to be
measured, acoustic noise and electromagnetic noise can be removed from the electrical signal of
the acoustic wave detected with high sensitivity.
Therefore, the acoustic element which can measure a minute acoustic wave can be provided.
[0010]
Specifically, in the acoustic element according to the present invention, the two piezoelectric
elements having the same material characteristics that generate a voltage between the two
electrodes according to the applied sound pressure, and the two electrodes having the same
polarity. And one of the two sensor output terminals electrically connected to the other of the
two electrodes.
[0011]
Since two piezoelectric elements having the same material properties are provided, equal
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voltages can be generated for equal acoustic waves and electromagnetic waves.
Furthermore, among the electrodes of the same polarity of the two piezoelectric elements, since
one of the electrodes is electrically connected, it is possible to output the same electrical signal to
the same acoustic wave and electromagnetic wave.
Accordingly, if electrical signals from the other electrodes of the two electrodes of the same
polarity are differentially detected, the acoustic noise and the electromagnetic noise generated in
the two piezoelectric elements can be canceled out. it can. Here, since only one piezoelectric
element measures the acoustic wave to be measured, acoustic noise and electromagnetic noise
can be removed from the electrical signal of the acoustic wave detected with high sensitivity.
Therefore, the acoustic element which can measure a minute acoustic wave can be provided.
[0012]
It is preferable to further comprise a balanced line for balanced transmission of the output of the
sensor output terminal.
[0013]
The electrical signals output from the two piezoelectric elements can be balanced and
transmitted.
Therefore, if the balanced line is differentially terminated, the in-phase component of the external
noise applied during balanced transmission can be removed at the termination point of the
balanced line.
[0014]
It is preferable to further comprise a differential amplifier circuit that terminates the balanced
line and differentially amplifies the output of the balanced line.
[0015]
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Since the outputs of the sensor output terminals are differentially detected, acoustic noise and
electromagnetic noise applied to the two piezoelectric elements can be offset.
Furthermore, since the balanced line is differentially terminated, it is possible to remove the inphase component of the extraneous noise applied during balanced transmission, and to
efficiently detect the difference between the voltages generated in the two piezoelectric elements.
[0016]
It is preferable to further comprise a differential amplifier circuit that differentially amplifies the
outputs of the two sensor output terminals.
[0017]
Since the electric signal output from the sensor output terminal is differentially detected, the
acoustic noise and the electromagnetic noise generated in the two piezoelectric elements are
canceled out, and the acoustic noise and the electromagnetic noise superimposed on the acoustic
wave to be measured are removed. can do.
Furthermore, since differential amplification is performed, it is possible to efficiently detect the
difference between the voltages generated in the two piezoelectric elements.
[0018]
It is preferable that the differential amplification circuit further includes a balanced line that
differentially outputs and balancedly transmits differential outputs of the differential
amplification circuit.
[0019]
Differentially amplified electrical signals can be balancedly transmitted.
Therefore, if the balanced line is differentially terminated, the in-phase component of the
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extraneous noise can be removed at the termination point of the balanced line.
[0020]
The specific acoustic impedance of the surface layer of the element facing surface, which is
disposed on the other surface of the two electrodes provided to one of the two piezoelectric
elements, substantially corresponds to the specific acoustic impedance of the piezoelectric
element Preferably, the device further comprises an acoustic matching layer whose surface has a
specific acoustic impedance substantially equal to that of water.
[0021]
The other surface of the two electrodes provided on one of the two piezoelectric elements is a
sound receiving surface to which the sound pressure of the acoustic wave to be measured is
applied.
Since the specific acoustic impedance of the outer surface of the sound receiving surface is
substantially equal to that of water, and the specific acoustic impedance on the piezoelectric
element side is substantially equal to the specific acoustic impedance of the piezoelectric
element, The reflection of sound pressure on the sound receiving surface can be reduced.
[0022]
It is preferable that the acoustic matching layer contains metal powder.
[0023]
Since the acoustic matching layer contains metal powder, the acoustic matching layer can reflect
electromagnetic waves.
Thereby, the electromagnetic noise generated by the electromagnetic wave incident from the
acoustic matching layer can be reduced.
[0024]
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Preferably, at least a portion of the piezoelectric element is covered with a sound absorbing
material that absorbs an acoustic wave, except for the other surface of the two electrodes
provided on one of the two piezoelectric elements.
[0025]
The surface of the piezoelectric element is covered with a sound absorbing material except for
the sound receiving surface to which the acoustic wave to be measured is applied.
As a result, noise from the outside can be absorbed, and acoustic noise generated by acoustic
waves from the outside can be reduced. Furthermore, the oscillation or vibration of the
piezoelectric element itself can be absorbed. As a result, it is possible to reduce the acoustic noise
generated by the vibration or oscillation of the piezoelectric element due to the vibration or
oscillation of the acoustic element itself or the piezoelectric change.
[0026]
The two piezoelectric elements are preferably adjacent to each other with the sound absorbing
material interposed therebetween.
[0027]
Since the piezoelectric elements are adjacent to each other, the difference between acoustic noise
and electromagnetic noise generated in the two piezoelectric elements can be reduced.
Furthermore, since the sound absorbing material is sandwiched between the piezoelectric
elements, acoustic noise generated between the piezoelectric elements can be reduced.
[0028]
The piezoelectric element is an electromagnetic wave reflecting material that reflects an
electromagnetic wave or an electromagnetic wave absorbing material that absorbs an
electromagnetic wave, except for the other surface of the two electrodes provided on one of the
two piezoelectric elements. It is preferable to be covered.
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[0029]
Since the portion other than the sound receiving surface is covered with the electromagnetic
wave reflecting material or the electromagnetic wave absorbing material, the electromagnetic
noise generated in the two piezoelectric elements can be reduced.
[0030]
According to the present invention, two piezoelectric elements that output equal electrical signals
to equal acoustic waves and electromagnetic waves are provided, and acoustic noise and
electromagnetic noise can be canceled by differentially outputting the electrical signals from the
piezoelectric elements. Therefore, an acoustic element capable of measuring a minute acoustic
wave can be provided.
[0031]
Embodiments of the present invention will be described with reference to the accompanying
drawings.
The embodiments described below are examples of the configuration of the present invention,
and the present invention is not limited to the following embodiments.
[0032]
Embodiment 1 FIG. 1 is a schematic view of an acoustic element according to the present
embodiment.
An acoustic element 91 shown in FIG. 1 includes two piezoelectric elements 11 and 12, a
common terminal 13 electrically connecting one of two electrodes 21 a and 22 a of the same
polarity, and the other 21 b of the two electrodes. , 22b and two sensor output terminals 14 and
15 electrically connected to each other.
In FIG. 1, the external surface of the other 21b of the electrodes of the piezoelectric element 11 is
a sound receiving surface 31 to which the sound pressure of the acoustic wave 1 to be measured
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is applied. Note that, in FIG. 1, the piezoelectric element 11 and the piezoelectric element 12 are
disposed in a housing constituted by the sound receiving surface 31, the bottom surface 33 and
the side surface 34.
[0033]
The acoustic element 91 performs balanced transmission of the outputs of the sensor output
terminal 14 and the sensor output terminal 15, the differential amplification circuit 17 which
terminates the balanced transmission line 16 and differentially amplifies the output of the
balanced transmission line 16, and It is preferable to further include an acoustic matching layer
18 disposed on the sound receiving surface 31 to which the acoustic wave 1 to be applied is
applied, and a soundproof plate 19 for preventing transmission of the acoustic wave between the
piezoelectric element 11 and the piezoelectric element 12 .
[0034]
The piezoelectric elements 11 and 12 are piezoelectric elements of the same material
characteristics that generate a voltage according to the sound pressure to be applied.
That is, the piezoelectric element 11 generates a voltage between the electrode 21a and the
electrode 21b in accordance with the sound pressure to be applied. The piezoelectric element 12
also generates a voltage between the electrode 22 a and the electrode 22 b according to the
sound pressure to be applied. The piezoelectric elements 11 and 12 may be of a monomorph
type, a bimorph type, or a laminated type.
[0035]
The piezoelectric element 11 and the piezoelectric element 12 have the same material
characteristics. The material property is, for example, a constant of the piezoelectric equation. If
the constant of the piezoelectric equation is d type, it becomes an elastic stiffness matrix, a
piezoelectric strain constant matrix, and a dielectric constant matrix at a constant stress. In
addition, if the constant of the piezoelectric equation is e type, it becomes a dielectric constant
matrix at a constant stress, a piezoelectric stress constant matrix, and a dielectric constant matrix
at a constant strain. In addition, as piezoelectric elements having the same material properties,
piezoelectric elements having the same composition, resonance frequency, sensitivity or band
may be used. Furthermore, as a material property, an antiresonance frequency, a mechanical
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quality factor, an electromechanical coupling factor, a relative permittivity or a capacitance may
be used. Since the material characteristics of the piezoelectric element 11 and the piezoelectric
element 12 are equal, a voltage generated between the electrode 21a and the electrode 21b
when equal sound pressure or an electromagnetic wave is applied to the piezoelectric element 11
and the piezoelectric element 12; And the voltage generated between the electrode 22b and the
electrode 22b can be equalized.
[0036]
It is preferable that a soundproof plate 19 for preventing transmission of the acoustic wave be
provided at the boundary between the piezoelectric element 11 and the piezoelectric element 12.
As the soundproof plate 19, for example, a sound absorbing material that absorbs an acoustic
wave, and a sound insulating material that blocks an acoustic wave can be used. As a sound
absorbing material, a sponge can be used, for example. Examples of the sponge include
polyurethane foam which is a polyurethane foam, rubber sponge, acrylic foam and polyolefin
foam. As a sound insulation material, a gypsum board, a plywood, and an iron plate can be used,
for example. If the soundproof plate 19 is sandwiched between the piezoelectric element 11 and
the piezoelectric element 12, the sound pressure of the acoustic wave 1 applied to the
piezoelectric element 11 is transmitted from the piezoelectric element 11 to the piezoelectric
element 12, and the piezoelectric element 12 is Can be prevented from being applied. As a result,
since the acoustic wave 1 to be measured applied to the piezoelectric element 11 is detected by
only one of the piezoelectric elements, the minute acoustic wave 1 can be measured.
[0037]
As the soundproof board 19, it is preferable to use a sound absorbing material. Since the sound
absorbing material is lighter than the sound insulating material, the load on the subject can be
reduced when the biological information measuring device such as a sphygmomanometer
equipped with the acoustic element 91 is mounted. As described above, if the soundproof plate
19 is sandwiched between the piezoelectric element 11 and the piezoelectric element 12,
acoustic noise generated between the piezoelectric element 11 and the piezoelectric element 12
can be reduced.
[0038]
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Furthermore, it is preferable that the piezoelectric element 11 and the piezoelectric element 12
be adjacent to each other with the sound absorbing material interposed therebetween. For
example, it is preferable that a sound absorbing material be used for the soundproof plate 19 and
the piezoelectric element 11 and the piezoelectric element 12 be mounted as close as possible. If
the piezoelectric element 11 and the piezoelectric element 12 are mounted close to each other,
the phase difference between acoustic noise and electromagnetic noise added to the two
piezoelectric elements can be reduced. Furthermore, the difference between the acoustic noise
and the electromagnetic noise itself can be reduced.
[0039]
It is preferable that at least a part of the piezoelectric element 11 or the piezoelectric element 12
is covered with a sound absorbing material that absorbs an acoustic wave except for the sound
receiving surface 31. For example, the bottom surface 33 is preferably covered with a sound
absorbing material. Further, it is preferable that the side surface 34 be covered with a sound
absorbing material. As the sound absorbing material, those described for the above-described
soundproofing plate 19 can be used.
[0040]
Furthermore, the sound absorbing material preferably has an antibacterial action. For example,
one in which a photocatalyst such as TiO 2 is coated on the surface can be used. Moreover, what
uses resin containing a photocatalyst as a raw material can be used. Examples of this resin
include fluorine resins such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl
fluoride, ethylene-tetrafluoroethylene copolymer, etc .; polyamides such as polyamide 6,
polyamide 66, polyamide 12; polyethylene, polypropylene, polymethylpentene Polyolefins such
as: aromatic vinyl resins such as polystyrene and poly α-methylstyrene; polyesters such as
polyethylene terephthalate and polybutylene terephthalate; vinyl resins such as vinyl chloride
resin and polyvinylidene chloride; acrylic resins, ABS resins, ethylene-acetic acid Vinyl
copolymers, norbornene resins, polyacetals, polyether imides, polycarbonates, polyvinyl acetates,
polyvinyl alcohols and the like can be mentioned. The photocatalyst may be photocatalyst
apatite. TiO2 has three crystal structures, anatase type, rutile type and brookite type, but those
having photocatalytic activity are those of anatase type and brookite type. Also, a resin blended
with a natural antibacterial component can be used. For example, there is a polyolefin foam
blended with an antibacterial component of bamboo. If the sound absorbing material disposed on
the surface of the housing has an antimicrobial property, it can be kept clean even when sweat or
the like adheres when the acoustic element 91 is attached to the epidermis of the human body.
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11
[0041]
Thus, if it is covered with a sound absorbing material that absorbs acoustic waves, noise 2 from
the outside can be absorbed. Thereby, since the noise 2 reaching the piezoelectric elements 11
and 12 can be reduced, acoustic noise generated by an acoustic wave from the outside can be
reduced. Furthermore, the oscillation or vibration of the piezoelectric elements 11 and 12 can be
absorbed. As a result, it is possible to reduce acoustic noise generated by an impact or vibration
applied to the acoustic element 91 from the outside. In addition, it is possible to reduce acoustic
noise generated when the piezoelectric elements 11 and 12 vibrate or swing due to a change in
voltage applied to the piezoelectric elements 11 and 12. Furthermore, if the sound absorbing
material disposed on the surface of the housing has an antimicrobial property, when the acoustic
element 91 is attached to the skin of the human body, it can be kept clean even if sweat adheres.
It is preferable that the piezoelectric element 11 or the piezoelectric element 12 be covered with
a sound absorbing material, but the noise 2 may be blocked by a sound insulating material
instead of the sound absorbing material. Furthermore, both a sound absorbing material and a
sound insulating material may be used.
[0042]
It is preferable that at least a part of the piezoelectric element is covered with an electromagnetic
wave reflecting material that reflects an electromagnetic wave or an electromagnetic wave
absorbing material that absorbs an electromagnetic wave, except for the sound receiving surface
31. For example, it is preferable that a housing other than the sound receiving surface 31 be
covered with an electromagnetic wave reflecting material or an electromagnetic wave absorbing
material. The housing other than the sound receiving surface 31 is, for example, the bottom
surface 33 or the side surface 34 or a part of these. Also, the bottom surface 33 and the side
surface 34 may be used. Examples of the electromagnetic wave reflecting material include a
conductor. The conductor may be metal or carbon fiber fabric. As the electromagnetic wave
absorbing material, for example, there is one obtained by solidifying ferrite particles alone. As
described above, if the portion other than the sound receiving surface 31 is covered with the
electromagnetic wave reflecting material or the electromagnetic wave absorbing material, the
application of the electromagnetic wave 3 to the piezoelectric element 11, the piezoelectric
element 12 and the wiring accommodated in the housing is suppressed. be able to. If the
differential amplifier circuit 17 is disposed in the housing, the electromagnetic noise generated in
the differential amplifier circuit 17 can be suppressed by the application of the electromagnetic
wave 3. Furthermore, as for the piezoelectric elements 11 and 12, it is preferable to provide a
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soundproof layer in the outer wall of a housing. As the soundproof layer, for example, the sound
absorbing material described in the above-described soundproofing plate 19 can be used. In this
case, the sound absorbing material preferably has an antibacterial action.
[0043]
In the acoustic matching layer 18, the specific acoustic impedance of the surface of the element
facing surface 32 facing the piezoelectric element 11 is substantially equal to the specific
acoustic impedance of the piezoelectric element 11, and the specific acoustic impedance of the
surface of the sound receiving surface 31 is substantially equal to water It is. The intrinsic
acoustic impedance when the sound pressure and the particle velocity are in phase is called
intrinsic acoustic resistance, and the intrinsic acoustic resistance of water is 1.48 × 10 <6> N · s ·
m <−3>. The sound receiving surface 31 is a surface of the other of the two electrodes 21 a and
21 b of the piezoelectric element 11 which is one of the two piezoelectric elements 11 and 12.
The element facing surface 32 is a surface in contact with the piezoelectric element 11. As the
acoustic matching layer 18, for example, ceramics or a polymer can be used. Since the specific
acoustic impedance of the outer surface of the sound receiving surface 31 is substantially equal
to water, and the specific acoustic impedance on the piezoelectric element 11 side is
substantially equal to the specific acoustic impedance of the piezoelectric element 11, the sound
receiving surface 31 is in contact with human skin. When this is done, the reflection of the sound
pressure at the sound receiving surface 31 can be reduced. Although in FIG. 1 there is a gap
between the acoustic matching layer 18 and the piezoelectric element 11, the acoustic matching
layer 18 and the piezoelectric element 11 may be in close contact with each other.
[0044]
The acoustic matching layer 18 preferably contains a metal powder. For example, tungsten
powder can be used as the metal powder. In this case, the acoustic matching layer 18 can be
formed, for example, using a material in which a polymer is mixed with a metal powder such as
tungsten powder. If the acoustic matching layer 18 contains metal powder, the acoustic matching
layer 18 can reflect an electromagnetic wave. Thereby, the electromagnetic noise generated in
the piezoelectric element 11 can be reduced.
[0045]
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13
The common terminal 13 is a terminal for electrically connecting one of the electrodes 21a and
one of the electrodes 22a. One of the electrodes 21a and one of the electrodes 22a are electrodes
of the same polarity. For example, low voltage sides or high voltage sides. Furthermore, the
common terminal 13 is preferably grounded. Since one of the electrodes 21a and one of the
electrodes 22a are electrically connected, the potential difference between the one of the
electrodes 21a and the one of the electrodes 22a can be eliminated.
[0046]
The sensor output terminal 14 is a terminal electrically connected to the other electrode 21 b.
The sensor output terminal 14 outputs an electrical signal 5 of a signal level proportional to the
voltage generated between the electrode 21a and the electrode 21b. The sensor output terminal
15 is a terminal electrically connected to the other electrode 22 b. The sensor output terminal 15
outputs an electrical signal 6 having a signal level proportional to the voltage generated between
the electrode 22a and the electrode 22b.
[0047]
Here, since one side 21a of the electrode and one side 22a of the electrode are connected to the
common terminal 13, a potential difference between the other side 21b of the electrode and the
other side 22b of the electrode is generated in the voltage generated in the piezoelectric element
11 and the piezoelectric element 12 It becomes a potential difference with the voltage. For this
reason, if the potential difference of the differential output outputted from the other 21b of the
electrode and the other 22b of the electrode is measured, the sound pressure applied to only one
of the electrodes can be measured.
[0048]
The balanced line 16 is a line for balanced transmission of the outputs of the sensor output
terminal 14 and the sensor output terminal 15. If the balanced line 16 is differentially
terminated, it is possible to remove the in-phase component of the extraneous noise applied from
the sensor output terminal 14 and the sensor output terminal 15 to the differential termination
at the termination point of the balanced line. Thereby, noise generated outside the piezoelectric
elements 11 and 12 can be reduced.
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[0049]
The differential amplifier circuit 17 is a circuit that terminates the balanced line 16 and
differentially amplifies the output of the balanced line 16. As the differential amplifier circuit 17,
for example, an operational amplifier or a transformer can be used. Since the outputs of the
sensor output terminals 14 and 15 are differentially detected, common mode noise of acoustic
waves generated in the two piezoelectric elements 11 and 12 and common mode noise of
electromagnetic waves can be canceled out.
[0050]
An example of the operation of the acoustic element 91 shown in FIG. 1 will be described. The
sound pressure of the acoustic wave 1 to be measured is applied to the sound receiving surface
31 of the piezoelectric element 11. The piezoelectric element 11 generates a voltage proportional
to the sound pressure of the acoustic wave 1, and the sensor output terminal 14 outputs an
electrical signal 5 of a signal level proportional to the voltage generated by the piezoelectric
element 11. At this time, since noise 2 and electromagnetic wave 3 are applied to the
piezoelectric element 11 and the piezoelectric element 12, acoustic noise and electromagnetic
noise of signal levels according to the noise 2 and the electromagnetic wave 3 are superimposed
on the electric signal 5 .
[0051]
On the other hand, the piezoelectric element 12 generates a voltage according to the noise 2 and
the electromagnetic wave 3, and the sensor output terminal 15 outputs an electrical signal 6 of a
signal level proportional to the voltage generated by the piezoelectric element 12. Here, if the
piezoelectric element 12 is disposed adjacent to the piezoelectric element 11 and the soundproof
plate 19 and the bottom surface 33 are formed or covered with a sound absorbing material, the
voltage generated by the acoustic wave 1 is removed. The voltage generated by the piezoelectric
element 12 can be made close to the voltage generated by the piezoelectric element 11. As a
result, the sensor output terminal 15 can output the electric signal 6 substantially equal to the
electric signal corresponding to the acoustic noise and the electromagnetic noise generated by
the piezoelectric element 11 by the noise 2 and the electromagnetic wave 3.
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[0052]
The balanced line 16 balancedly transmits the outputs of the sensor output terminal 14 and the
sensor output terminal 15. The differential amplifier circuit 17 terminates the balanced line 16.
Since the balanced line 16 is differentially terminated, the in-phase component of the external
noise applied from the sensor output terminal 14 and the sensor output terminal 15 to
differentially terminating can be removed at the termination point of the balanced line 16.
Furthermore, since the differential amplification circuit 17 performs differential amplification,
the electrical signal 5 and the electrical signal 6 can be differentially detected. Since the electrical
signal 6 is substantially equal to the electrical signal corresponding to the acoustic noise and the
electromagnetic noise, the differential amplifier circuit 17 can output the electrical signal from
which the acoustic noise and the electromagnetic noise are removed. Therefore, the acoustic
element 91 can extract an electrical signal generated by the application of the sound pressure of
the acoustic wave 1.
[0053]
As described above, the acoustic element 91 according to the present embodiment detects the
minute acoustic wave 1 using the piezoelectric element 11, and the acoustic noise and the
electromagnetic noise superimposed on the output signal 5 from the piezoelectric element 11 are
detected. It can be removed. Thereby, the acoustic element which can measure a minute acoustic
wave can be provided. Furthermore, if the balanced transmission path 16 and the differential
amplifier circuit 17 are provided, the electric signal generated by the application of the sound
pressure of the minute acoustic wave 1 can be extracted and amplified, so the efficiency of the
minute acoustic wave 1 is increased. It can be measured well. As described above, since the
acoustic element 91 can measure the minute acoustic wave 1, it is possible to detect pulsation
even in a region without a thick artery such as a finger or an outer ear.
[0054]
Second Embodiment FIG. 2 is a schematic view showing a first example of an acoustic element
according to the present embodiment. In the acoustic element 92 shown in FIG. 2, the differential
amplifier circuit 17 of the acoustic element 91 shown in FIG. 1 differentially amplifies the
outputs of the two sensor output terminals 14 and 15. The functions and operations of the
piezoelectric elements 11, 12, common terminal 13 and sensor output terminals 14, 15, etc.
included in the other acoustic elements 92 except for the operational amplifier circuit 17 and the
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balanced line 16 are the same as those of the first embodiment. It is.
[0055]
The operation amplification circuit 17 can be the same as that of the first embodiment described
above. However, in the present embodiment, the differential amplifier circuit 17 directly
compares the electrical signal 5 output from the sensor output terminal 14 with the electrical
signal 6 output from the sensor output terminal 15 without passing through the balanced line
16. Dynamically amplify. In FIG. 2, the differential amplifier circuit 17 is disposed outside the
housing in which the piezoelectric elements 11 and 12 are disposed. In this case, the differential
amplifier circuit 17 is preferably disposed near the piezoelectric element 11 and the piezoelectric
element 12. Further, it is preferable that the line from the sensor output terminals 14 and 15 to
the differential amplifier circuit 17 be short. If the line from the piezoelectric element 11 and the
piezoelectric element 12 to the differential amplifier circuit 17 is short, electromagnetic noise
generated in the line can be suppressed.
[0056]
FIG. 3 is a schematic view showing a second example of the acoustic element according to the
present embodiment. The acoustic element 93 shown in FIG. 3 is disposed inside the housing in
which the differential amplifier circuit 17 shown in FIG. 2 is housed. The inside of the housing
can be, for example, between the piezoelectric element 11 and the piezoelectric element 12. In
this case, as shown in FIG. 3, the differential amplifier circuit 17 is preferably sandwiched
between the soundproof plates 19. As described above, when the differential amplifier circuit 17
is disposed inside the housing, the lines from the piezoelectric element 11 and the piezoelectric
element 12 to the differential amplifier circuit 17 can be shortened, so electromagnetic noise
generated in the lines can be generated. Can be further suppressed.
[0057]
Third Embodiment FIG. 4 is a schematic view showing a first example of an acoustic element
according to the present embodiment. The acoustic element 94 shown in FIG. 4 further includes
a balanced line 20 which the differential amplifier circuit 17 of the acoustic element 92 shown in
FIG. . The acoustic element 94 can have the same configuration as the acoustic element 91
except for the operation amplification circuit 17 and the balanced line 16. For example, the
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17
piezoelectric elements 11 and 12, the common terminal 13 and the sensor output terminals 14
and 15 are the same as those in the first embodiment described above.
[0058]
The operation amplification circuit 17 can be the same as that of the first embodiment described
above. However, in the present embodiment, the differential amplifier circuit 17 does not include
the balanced line 16 shown in FIG. 1, and the electric signal 5 output from the sensor output
terminal 14 and the electric signal 6 output from the sensor output terminal 15 , Differential
amplification directly, and differential output. In FIG. 4, the differential amplifier circuit 17 is
disposed outside the housing in which the piezoelectric elements 11 and 12 are disposed.
[0059]
FIG. 5 is a schematic view showing a second example of the acoustic element according to the
present embodiment. In the acoustic element 95 shown in FIG. 5, the differential amplifier circuit
17 shown in FIG. 4 is disposed inside a housing in which the piezoelectric elements 11 and 12
are disposed. The inside of the housing can be, for example, between the piezoelectric element
11 and the piezoelectric element 12. In this case, the differential amplifier circuit 17 is preferably
sandwiched between the soundproof plates 19 as shown in FIG.
[0060]
As described above, the acoustic elements 91, 92, 93, 94, and 95 described in the first, second,
and third embodiments include two piezoelectric elements that output equal electrical signals to
equal acoustic waves and electromagnetic waves, Since the acoustic noise and the
electromagnetic noise can be canceled by differentially outputting the electric signals from the
piezoelectric elements 11 and 12, an acoustic element capable of measuring the minute acoustic
wave 1 using the piezoelectric element 11 is provided. can do.
[0061]
INDUSTRIAL APPLICABILITY The present invention can measure minute acoustic waves, and
thus can be used for a biological information measurement device capable of easily measuring
blood pressure and pulse rate with a fingertip or an outer ear of a human body.
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18
[0062]
FIG. 1 is a schematic view of an acoustic element according to Embodiment 1.
FIG. 6 is a schematic view showing a first example of an acoustic element according to
Embodiment 2.
FIG. 7 is a schematic view showing a second example of the acoustic element according to the
second embodiment. FIG. 7 is a schematic view showing a first example of an acoustic element
according to Embodiment 3. FIG. 14 is a schematic view showing a second example of the
acoustic element according to the third embodiment.
Explanation of sign
[0063]
Reference Signs List 1 acoustic wave 2 noise 3 electromagnetic wave 5, 6 electric signal 8a, 8b
differential output 11, 12 piezoelectric element 13 common terminal 14, 15 sensor output
terminal 16, 20 balanced line 17 differential amplifier circuit 18 acoustic matching layer 19
soundproof plate 21a , 21b Electrodes 22a and 22b of the piezoelectric element 11 Electrodes
31 of the piezoelectric element 12 Sound receiving surface of the acoustic element 32 Element
facing surface of the acoustic matching layer 33 Element bottom surface of the acoustic element
34 Bottom surface of the body of the acoustic element 91, 92, 93, 94, 95 sound element
04-05-2019
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