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JP2012127759

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DESCRIPTION JP2012127759
An impact and acoustic sensor capable of detecting both impact and sound is provided.
SOLUTION: First and second piezoelectric elements 16 and 20 are accommodated in a package 2,
and the first and second piezoelectric elements 16 and 20 are deformed in the opposite phase to
the acoustic input, and vibration is caused. An impact and acoustic sensor 1 comprising a wiring
structure arranged to deform in phase with respect to an input and configured such that output
signals of the first and second piezoelectric elements are extracted individually. [Selected figure]
Figure 1
Impact and acoustic sensor
[0001]
The present invention relates to an impact and acoustic sensor capable of detecting an impact
and sound pressure, and more particularly to an impact and acoustic sensor using a plurality of
piezoelectric plates.
[0002]
Conventionally, various kinds of acoustic sensors, acceleration sensors, and the like using a
piezoelectric element have been proposed.
Patent Document 1 below discloses a mechanical vibration canceling piezoelectric ceramic
microphone.
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1
[0003]
As shown in FIG. 16, in the microphone 1001, piezoelectric elements 1003 and 1004 are
disposed to face each other in a housing 1002. The piezoelectric elements 1003 and 1004 are
respectively attached to diaphragms 1005 and 1006 which divide the inside of the housing
1002. Thereby, the inside of the housing 1002 is divided into the spaces A1 to A3. The space A3
is a portion where the diaphragms 1005 and 1006 face each other. A through hole 1002 a is
formed in the housing 1002 so as to face the space A3. Further, through holes 1002 b and 1002
c are formed to be continuous with the spaces A 1 and A 2 respectively.
[0004]
The piezoelectric elements 1003 and 1004 are connected in series. That is, the wiring 1007 is
connected to one end of the piezoelectric element 1003, and the other electrode of the
piezoelectric element 1003 is connected to the wiring 1008. In addition, one electrode of the
piezoelectric element 1004 is in contact with the wiring 1008, and the other electrode is in
contact with the wiring 1009.
[0005]
In the microphone 1001, when the sound wave reaches the space A3 from the through hole
1002a, the piezoelectric elements 1003 and 1004 are displaced in reverse phase. That is, the
diaphragms 1005 and 1006 are bent to protrude to the spaces A1 and A2, respectively, and the
piezoelectric elements 1003 and 1004 are bent to protrude to the spaces A1 and A2 accordingly.
In this case, since the piezoelectric elements 1003 and 1004 are connected in series, based on
the signal from the piezoelectric element 1003 and the signal from the piezoelectric element
1004, an output to the sound pressure input in the output device 1010 can be taken out. it can.
That is, it functions as a microphone.
[0006]
On the other hand, as shown in FIG. 17, when an impact is applied in the direction indicated by
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arrow F, the piezoelectric elements 1003 and 1004 are displaced in phase. However, in the
arrow F direction, the polarization direction of the piezoelectric element 1003 and the
polarization direction of the piezoelectric element 1004 are opposite to each other. Therefore,
the polarity of the signal extracted by the piezoelectric element 1003 and the polarity of the
signal extracted by the piezoelectric element 1004 are reversed. Therefore, no signal is output
from the output device 1010.
[0007]
Therefore, the microphone 1001 does not output a sound when an impact or the like is applied,
and only an electrical signal based on the sound pressure that has reached the inside of the
housing 1002 from the through hole 1002 a is extracted.
[0008]
Japanese Patent Publication No. 6-508498
[0009]
In the microphone 1001 described in Patent Document 1, as described above, the electric signal
due to the impact force can be erased.
However, such a microphone 1001 can detect a signal due to sound pressure, but can not detect
the impact force itself.
That is, in the case where the microphone 1001 is used as an acoustic sensor and it is desired to
further detect an impact, an impact sensor has to be separately prepared.
[0010]
An object of the present invention is to provide an impact and acoustic sensor that is configured
using a plurality of piezoelectric elements and can detect not only acoustics but also impacts.
[0011]
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An impact and acoustic sensor according to the present invention comprises a package and first
and second piezoelectric elements housed in the package.
In the package, the space on one side of each of the plate-like first and second piezoelectric
elements is an acoustically closed space.
[0012]
The first and second piezoelectric elements are disposed in the package so as to deform in
opposite phase with respect to the acoustic input and in phase with respect to the vibration
input. Further, in the present invention, a wiring structure is provided which individually takes
out the output of the first piezoelectric element and the output of the second piezoelectric
element.
[0013]
In a specific aspect of the shock and acoustic sensor according to the present invention, the
shock and acoustic sensor further includes a signal processing circuit connected to the first and
second piezoelectric elements, and the output signal of the first piezoelectric element is x, second
When the output signal of the piezoelectric element is y, the signal processing circuit is
configured to output ax + by (where a and b are complex numbers) as an acoustic output and
output ax−by as a signal output. In this case, the sound processing output of ax + by and the
impact detection output of ax−by can be taken out from the signal processing circuit.
[0014]
The first and second piezoelectric elements may be bimorph type piezoelectric elements or
unimorph type piezoelectric elements.
[0015]
In a further specific aspect of the impact and acoustic sensor according to the present invention,
the first piezoelectric element and the second piezoelectric element are disposed to face each
other in the package.
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In this case, the dimension in the direction orthogonal to the facing direction of the first and
second piezoelectric elements can be reduced.
[0016]
Further, in still another specific aspect of the impact and acoustic sensor according to the present
invention, in the package, a space sandwiched between the first piezoelectric element and the
second piezoelectric element is acoustically closed. The sound is guided to the side opposite to
the space between the first piezoelectric element and the second piezoelectric element. In this
case, since the rear air chamber is common to the acoustic input, the degree of decrease in the
acoustic detection sensitivity is equal between the first and second piezoelectric elements.
Therefore, when detecting a vibration, the removal performance of the signal by a sound is
improved and S / N can be raised. Furthermore, the volume of the space sandwiched between the
first and second piezoelectric elements does not change with respect to the vibration input.
Therefore, it is hard to produce the fall of the acceleration sensitivity by air. Therefore, at the
time of sound detection, since the signal removal performance by vibration is enhanced, the S / N
at the time of sound detection can be increased.
[0017]
In still another specific aspect of the impact and acoustic sensor according to the present
invention, a sound is guided in a space between the first piezoelectric element and the second
piezoelectric element in the package, and The opposite side of the space of the second
piezoelectric element and the space of the second piezoelectric element is an acoustically closed
space. In this case, it is guided to the space sandwiched between the first and second
piezoelectric elements, and the sound pressure by the sound is equally applied to the first and
second piezoelectric elements. Therefore, as a function of the impact sensor, noise signals due to
sound can be removed in a wide frequency band.
[0018]
In still another specific aspect of the impact and acoustic sensor according to the present
invention, the first plate-like piezoelectric element and the second plate-like piezoelectric element
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are juxtaposed in the package so as not to face each other. In each of the first and second
piezoelectric elements, a rear air chamber, which is a space acoustically closed, is provided on the
surface opposite to the pressure receiving surface that receives the acoustic signal, and the first
piezoelectric The pressure receiving surface of the element and the rear air chamber, and the
pressure receiving surface of the second piezoelectric element and the rear air chamber are
opposite to the first and second piezoelectric elements. In this case, the dimensions of the impact
and acoustic sensor along the thickness direction of the first and second piezoelectric elements
can be reduced. That is, a low-profile impact and acoustic sensor can be provided.
[0019]
In still another specific aspect of the impact and acoustic sensor according to the present
invention, the surface density σ of the first and second piezoelectric elements is in the range of
0.01 to 1 kg / m <2>. In this case, it is possible to provide a compact and highly sensitive impact
and acoustic sensor.
[0020]
The impact and acoustic sensor according to the present invention is arranged such that the first
piezoelectric element and the second piezoelectric element deform in the opposite phase with
respect to the acoustic input and in the same phase with respect to the vibration input. Since the
wiring structure is formed so as to separately take out the outputs of the first and second
piezoelectric elements, it is possible to detect both the sound and the impact. Thus, a single
sensor makes it possible to detect shock and sound.
[0021]
(A) and (b) are front sectional views of the impact and acoustic sensor according to the first
embodiment of the present invention, and the connection relationship between the first and
second piezoelectric elements of the impact and acoustic sensor and the signal processing circuit.
Is a block diagram showing FIG. (A) is a disassembled perspective view for demonstrating the
laminated structure of the 1st, 2nd piezoelectric element in 1st Embodiment, (b) and (c) is a 1st,
2nd piezoelectric element It is each typical top view which shows the electrode shape of the
lower surface of. It is a circuit diagram showing the 1st and 2nd piezoelectric element of a shock
and sound sensor of a 1st embodiment, and a signal processing circuit. (A) and (b) are schematic
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diagrams showing displacement states of the first and second piezoelectric elements when
vibration input is added and when acoustic input is added in the impact and acoustic sensor of
the first embodiment. FIG. It is a figure which shows the sensitivity characteristic as an acoustic
sensor of the impact and acoustic sensor of 1st Embodiment. It is a figure which shows the
sensitivity characteristic as an impact sensor of the impact and acoustic sensor of 1st
Embodiment. It is a schematic diagram which shows the example with a good balance of the
sound pressure sensitivity and acceleration sensitivity in an impact and an acoustic sensor. It is a
schematic diagram which shows the example in which the balance of the sound pressure
sensitivity and acceleration sensitivity in an impact and acoustic sensor is not good. It is a block
diagram which shows the connection relation of an impact and acoustic sensor, and a signal
processing circuit in the modification of the impact and acoustic sensor of this invention. It is
front sectional drawing of the impact and acoustic sensor of 2nd Embodiment of this invention. It
is front sectional drawing of the impact and acoustic sensor which concerns on the 3rd
Embodiment of this invention. It is a disassembled perspective view of the impact and acoustic
sensor of 3rd Embodiment of this invention. It is a typical front sectional view of an impact and
sound sensor concerning a 4th embodiment of the present invention. It is a perspective view of
an impact and acoustic sensor of a 4th embodiment of the present invention. It is a typical front
sectional view of an impact and sound sensor concerning a 5th embodiment of the present
invention. It is a typical sectional view showing an example of the conventional microphone. FIG.
17 is a schematic front cross-sectional view for explaining the displacement state of the
piezoelectric element when acceleration is applied to the microphone shown in FIG. 16;
[0022]
Hereinafter, the present invention will be clarified by describing specific embodiments of the
present invention with reference to the drawings.
[0023]
Fig.1 (a) is front sectional drawing which shows the impact and acoustic sensor which concern on
the 1st Embodiment of this invention.
[0024]
The impact and acoustic sensor 1 comprises a package 2.
The package 2 includes a substrate 3 and a lid 4 fixed to the upper surface of the substrate 3.
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The substrate 3 is made of an insulating material. Electrode lands 5 to 7 are formed on the upper
surface of the substrate 3. Further, external electrodes 8 and 9 are formed on the lower surface
of the substrate 3. A via hole electrode 11 is formed on the substrate 3 so as to electrically
connect the electrode land 6 and the external electrode 9. Although not shown in FIG. 1A, the
electrode land 5 and the FET 12 are electrically connected, and the electrode land 7 and the
external electrode 8 are connected via holes. An FET 12 (not shown) is mounted on the substrate
3 so as to be electrically connected to the electrode lands 6 and 7.
[0025]
The FET 12 and the FET 12A function to amplify the outputs of the first and second piezoelectric
elements 16 and 20. The FET 12 and the FET 12A constitute a part of a signal processing circuit
described later.
[0026]
The lid 4 has an opening opened downward. The lower opening edge is bonded to the upper
surface of the substrate 3. Thus, a space surrounded by the upper surface of the substrate 3 and
the lid 4 is formed. A through hole 4 a is formed on the top surface of the lid 4. The through hole
4 a is a sound through hole for introducing a sound into the space in the package 2 as described
later. The lid 4 is made of metal in the present embodiment. Thereby, it is possible to
electromagnetically shield the internal space. However, the lid 4 may be formed of a conductive
material other than metal, or a material having a conductive layer on the surface or in the inside.
Furthermore, the lid 4 may be formed of an insulating material having no electromagnetic
shielding function.
[0027]
In the space in the package 2, rectangular frame-like spacers 14 are joined via the conductive
adhesive layer 13. The rectangular frame shaped spacer 14 is made of insulating ceramic in the
present embodiment. However, other insulating materials may be used.
[0028]
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The plate-like first piezoelectric element 16 is bonded onto the spacer 14 via the adhesive layer
15. In addition, a rectangular frame-shaped holding member 18 is bonded on the first
piezoelectric element 16 via the adhesive layer 17. The plate-like second piezoelectric element
20 is bonded onto the rectangular frame-like holding member 18 via the adhesive layer 19.
[0029]
FIG. 2A is an exploded perspective view of a structure in which the first piezoelectric element 16,
the holding member 18, and the second piezoelectric element 20 are stacked. As shown to Fig.2
(a), the 1st piezoelectric element 16 has the rectangular-plate-shaped piezoelectric plate 16a in
which the main surfaces mutually oppose. The piezoelectric plate 16a is made of two layers of
piezoelectric ceramics and polarized in opposite directions in the thickness direction. A first
electrode 16b is formed on the upper surface which is one of the main surfaces of the
piezoelectric plate 16a. As shown in FIG. 2B, the second electrode 16c is formed on the lower
surface which is the other main surface of the piezoelectric plate 16a. The first electrode 16b is
drawn to one end of the piezoelectric plate 16a, and the second electrode 16c is drawn to the
other end. In this embodiment, although lead zirconate titanate ceramics are used as the material
of the piezoelectric body, it is possible to appropriately use piezoelectric materials such as leadfree piezoelectric ceramics such as potassium sodium niobate series and alkali niobate series
ceramics. it can.
[0030]
In the present embodiment, the first and second piezoelectric elements 16 and 20 are bimorph
piezoelectric elements in which piezoelectric layers having electrodes formed on the upper
surface and the lower surface of the elastic plate are disposed. The piezoelectric layers on the
upper and lower surfaces are electrically connected in series. Furthermore, in the present
invention, the first and second piezoelectric elements may have a bimorph structure, and may
have a configuration in which the upper and lower piezoelectric layers are electrically connected
in parallel, or have a unimorph structure. It may be one. Further, the number of piezoelectric
layers is not particularly limited, and in the case of the bimorph piezoelectric element, more
piezoelectric layers may be stacked. Moreover, when using a unimorph type piezoelectric
material element, a plurality of piezoelectric material layers may be laminated to constitute one
piezoelectric material. In addition, you may have an internal electrode in the inside of a
piezoelectric material layer.
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[0031]
Similarly, as shown in FIGS. 2A and 2C, the second piezoelectric element 20 also has a
rectangular plate-shaped piezoelectric plate 20a and first and second electrodes 20b and 20c.
The first electrode 20b is drawn out to one end of the piezoelectric plate 20a, and the second
electrode 20c is drawn out to the other end.
[0032]
As shown in FIG. 2A, in the stacked structure, first and second side electrodes 21 and 22 are
formed on one end side in the length direction. The first side electrode 21 is electrically
connected to the first electrode 16 b of the first piezoelectric element 16, and the second side
electrode 22 is connected to the first electrode 20 b of the second piezoelectric element 20. It is
connected. That is, on the side surface of the laminate, the first and second side electrodes 21
and 22 are formed at different positions in the width direction of the laminate structure.
[0033]
Similarly, a third side electrode 23 is formed on the other end side of the laminated structure,
and the third side electrode 23 is a second electrode 16 c of the first piezoelectric element 16
and a second piezoelectric element. It is connected to the second electrode 20 c of the element
20.
[0034]
As shown in FIGS. 2A and 2B, the first electrode 16b and the second electrode 16c are partially
formed on the upper surface and the lower surface of the piezoelectric plate 16a.
The first electrode 16b and the second electrode 16c have the same shape except for the leadout portion, and are opposed to each other via the piezoelectric plate 16a. In the present
embodiment, the shape of the facing portion excluding the lead portions of the first electrode 16
b and the second electrode 16 c is rectangular. However, the planar shape of this opposing part
is not limited to a rectangle.
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[0035]
The above-described FET 12 and the FET 12A not shown in FIG. 1A constitute part of a signal
processing circuit electrically connected to the first and second piezoelectric elements 16 and 20,
respectively. The first side electrode 21 is connected to the electrode land 5, and the electrode
land 5 is connected to the FET 12 although not shown in FIG. 1A. Similarly, the second
piezoelectric element 20 is connected to the second side electrode 22, and the second side
electrode 22 is connected to the FET 12A via an electrode land not shown. On the other hand, the
third side electrode 23 is connected to the electrode land 6 shown in FIG. 1A, and is connected to
the FET 12 and the FET 12A through the electrode land 6. As shown in FIG. 1A, the first and
second piezoelectric elements 16 and 20 of the impact and acoustic sensor 1 are connected in
series. Then, one end of the first piezoelectric element 16 is connected to the signal processing
circuit 26 via the first side electrode 21 described above. One end of the second piezoelectric
element 20 is connected to the signal processing circuit 26 via the second side electrode 22. One
ends of the first and second piezoelectric elements 16 and 20 connected to each other are
connected in common, and connected to the signal processing circuit 26 by the third side
electrode 23. Therefore, the sensor portion consisting of the first and second piezoelectric
elements 16 and 20 constitutes a three-terminal type sensor having three output terminals.
[0036]
FIG. 3 is a diagram showing a circuit configuration including the first and second piezoelectric
elements 16 and 20 of the impact and acoustic sensor 1 and the signal processing circuit 26. As
shown in FIG. As shown in Fig. 3, in the package 2, the aforementioned FET 12 and another FET
12A are incorporated. Only the FET 12 is illustrated in FIG. The FETs 12 and 12A are provided to
amplify the outputs of the first and second piezoelectric elements 16 and 20, respectively. The
FET 12 and the FET 12A may not necessarily be provided.
[0037]
The input ends of the signal processing circuit 26 are the first to third side electrodes 21 to 23
described above. The first side electrode 21 is connected to the gate terminal of the FET 12.
Similarly, the second side electrode 22 is connected to the gate terminal of the FET 12A. The
drain electrodes of the FETs 12 and 12A are connected to the operational amplifiers 27 and 29
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via the coupling capacitors 31 and 32, respectively. The output end of the operational amplifier
27 is connected to one input end of the A / D converter 28. The output end of the operational
amplifier 29 is connected to the other input end of the A / D converter 28.
[0038]
The source electrodes of the first and second FETs 12 and 12A are connected to the ground
potential.
[0039]
In addition, an adder / subtractor 33 is connected to the subsequent stage of the A / D converter
28, and the adder / subtractor 33 is connected to the first output terminal 34.
The first output terminal 34 outputs an output signal based on the detected sound. The second
output terminal 35 outputs an output signal based on the detected shock.
[0040]
In the present embodiment, the output signal of the first piezoelectric element 16 is given to the
first side electrode 21 which is the first input terminal of the signal processing circuit 26. This
output signal is amplified by the operational amplifier 27 and converted into a digital signal by
the A / D converter 28. Similarly, the output signal of the second piezoelectric element 20 is
given to the second side electrode 22 which is the third input terminal of the signal processing
circuit 26, and the output signal is digitalized in the A / D converter 28. It is converted to a
signal.
[0041]
The signal extracted from the first piezoelectric element 16 is processed as described above, and
the signal supplied to the adder / subtractor 33 is x, the signal extracted from the second
piezoelectric element 20 is processed as described above, A signal given to the adder-subtractor
33 is y. The adder / subtractor 33 calculates ax + by or ax−by. Here, a and b are arbitrary
complex numbers. Note that a and b may be real numbers.
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[0042]
ax + by corresponds to an output signal when a sound is detected, and is output from the output
terminal 34. ax-by is output from the second output terminal 35 as a signal when an impact or
vibration is detected.
[0043]
That is, in the present embodiment, by processing the outputs of the first and second
piezoelectric elements 16 and 20 by the signal processing circuit 26, not only sound can be
detected, but also shock and vibration can be detected. It is assumed. This principle will be
described with reference to FIGS. 4 (a) and 4 (b).
[0044]
As shown in FIG. 4A, in the portion where the first and second piezoelectric elements 16 and 20
are stacked, as shown by arrow F1, when acceleration is applied, that is, impact in the direction
shown by arrow F1 The first and second piezoelectric elements 16 and 20 are displaced in phase.
For example, as shown in FIG. 4A, the direction in which the main surface of the first
piezoelectric element 16 extends is not orthogonal to the direction in which the main surface of
the second piezoelectric element 20 extends, in this case, Being arranged in parallel, if an
acceleration having a component perpendicular to the main surface is applied downward from
above the main surface, the first piezoelectric element 16 is bent downward and the second
piezoelectric element 20 is similarly similarly The first piezoelectric element 16 is bent
downward in the same bending direction as the first piezoelectric element 16.
[0045]
Therefore, by calculating ax-by from the output signals x and y of the first and second
piezoelectric elements 16 and 20 connected in series, shock or vibration can be detected.
[0046]
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On the other hand, in the shock and acoustic sensor 1 shown in FIG. 1 (a), when sound is guided
from the through hole 4a into the package 2, as shown by arrows B1 and B2 in FIG. 1 (a), the
first piezoelectric In the element 16 and the second piezoelectric element 20, sound pressure is
applied from the outer surface toward the space side in which both are opposed.
Therefore, as shown in FIG. 4B, the first piezoelectric element 16 and the second piezoelectric
element 20 are displaced in opposite phase due to the sound pressure. Therefore, by calculating
ax + by from the output signals of the first and second piezoelectric elements 16 and 20
connected in series, an output signal based on the above sound can be extracted.
[0047]
That is, in the present embodiment, the first and second piezoelectric elements 16 and 20 are
displaced in the opposite phase when a sound is applied in the package 2, and are displaced in
the same phase when an impact or acceleration is applied. The first and second piezoelectric
elements 16 and 20 are disposed as follows.
[0048]
More specifically, in the first embodiment, as described above, the plate-like first and second
piezoelectric elements 16 and 20 are opposed to each other across the space A so that their main
surfaces are parallel to each other. ing.
The space A is sealed by a rectangular frame-shaped holding member 18 and adhesive layers 17
and 19. Accordingly, the space A is an acoustically closed space and forms a rear air chamber of
the piezoelectric elements 16 and 20. In addition, when a plate-shaped piezoelectric vibrator
vibrates, a back air chamber shall mean the closed space located in the surface on the opposite
side to the side which a sound pressure is added.
[0049]
In addition, the space closed acoustically shall mean the space which does not permeate |
transmit a sound wave substantially between the inside of this space, and the outside of space.
Such a space is not limited to a sealed space, but includes a small through hole for reducing the
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pressure difference between the inside and the outside provided in a portion separating the
inside of the outside space from the outside of the space.
[0050]
In the present embodiment, as described above, the output signals of the first and second
piezoelectric elements 16 and 20 are converted into digital signals by the A / D converter 28. It
is also good. Furthermore, after performing some modulation processing such as frequency
modulation, arithmetic processing equivalent to the addition and subtraction may be performed.
Further, although the FET is incorporated in the sensor package and the other signal processing
circuits are out of the package in this embodiment, the whole or other partial configuration of the
signal processing circuit may be incorporated in the sensor package. Of course, it is not
necessary to use an FET as an amplification circuit, and part or all of a signal processing circuit
may be integrated in an IC.
[0051]
When the piezoelectric element deforms, a volume change occurs in the rear air chamber. Along
with that, the piezoelectric element receives pressure as a reaction force, so the sensitivity of the
piezoelectric element is lowered. The amount of decrease in sensitivity generally depends on the
amount of deformation of the piezoelectric element and the volume of the rear air chamber. In
the present embodiment, the rear air chamber is common to the first and second piezoelectric
elements 16 and 20. Therefore, the decrease in acoustic detection sensitivity occurs equally in
the first and second piezoelectric elements 16 and 20. Therefore, S / N at the time of detecting
an impact as an impact sensor can be raised.
[0052]
On the other hand, in the case of detecting an impact or vibration, the volume of the space A
between the two piezoelectric elements hardly changes because the first and second piezoelectric
elements 16 and 20 deform in phase. Therefore, it is hard to produce the fall of vibration
detection sensitivity, and it is hard to produce the sensitivity difference of the 1st and 2nd
piezoelectric elements 16 and 20. Therefore, in the case of detecting a sound, the S / N of the
sound detection signal can be increased because the vibration signal removal performance is
excellent.
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[0053]
The sound detected in the present embodiment is not limited to the sound of the audio
frequency, and includes the high frequency signal from the low frequency signal of several Hz or
less to the ultrasonic wave region.
[0054]
From the viewpoint of the noise removal effect, preferably, it is desirable to perform fine
adjustment in the above addition and subtraction processing.
The sensitivity of the first and second piezoelectric elements due to the material variation of the
piezoelectric element, the variation in processing process, the pressure received as a reaction
force with the volume change of the back air chamber when the piezoelectric element is
deformed, and the acoustic resistance. A difference can occur. If sensitivity differences occur,
simple addition and subtraction such as x + y and x−y reduce the noise removal effect. In
addition, the gain removal at the time of amplification by the signal processing circuit is similarly
reduced. On the other hand, the effect of canceling the signal based on the vibration can be
enhanced in the case of detecting the sound by performing fine adjustment in the addition and
subtraction processing so as to correct the sensitivity difference and the gain difference.
Similarly, in the case of detecting vibration, the cancellation effect of the output signal by the
acoustic signal can be enhanced. As such fine adjustment, there is a method of adjusting the
complex numbers a and b in the above addition and subtraction. In ordinary adjustment, a and b
are real numbers among complex numbers, and a sufficient effect can be obtained. About the
setting of said a and b, after producing impact and acoustic sensor 1, it may adjust according to
the output signal from a signal processing circuit. With regard to sound, a phase difference
occurs in the sound pressure applied to the first and second piezoelectric elements at a
frequency of approximately 10 kHz or more. In the high frequency part, a and b are complex
numbers, phase correction is performed, and addition and subtraction are performed, whereby
the function of removing an acoustic signal can be enhanced when functioning as an impact
sensor.
[0055]
FIG. 5 shows sensitivity frequency characteristics for detecting sound pressure in the impact and
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acoustic sensor of the above embodiment. The solid line indicates the sound pressure sensitivity,
and the broken line indicates the impact, that is, the sensitivity of acceleration that is noise. It can
be seen that the sound pressure can be measured with high sensitivity over a wide frequency
range around 100 Hz to 20000 Hz, while the sensitivity of the noise acceleration is at least 33
dB lower.
[0056]
That is, in the present embodiment, as described above, the rear air chamber is sandwiched
between the first and second piezoelectric elements 16 and 20. Therefore, even if the vibration
input changes, the piezoelectric element deforms in phase and the volume of the rear air
chamber does not change. Therefore, the deformation of the first and second piezoelectric
elements 16 and 20 is hardly hindered. Therefore, it is difficult to cause a decrease in
acceleration sensitivity, and at the same time, a difference in sensitivity does not easily occur.
Therefore, as shown in FIG. 5, it is possible to sufficiently reduce the acceleration sensitivity that
causes noise. That is, the S / N can be effectively increased.
[0057]
Moreover, FIG. 6 is a figure which shows the sensitivity of the acceleration at the time of
detecting an impact, ie, acceleration, and the characteristic of the sound pressure sensitivity as
noise in the impact and acoustic sensor of the said embodiment.
[0058]
As apparent from FIG. 6, even in the case of detecting the acceleration, it is understood that the
acceleration can be detected with high sensitivity over a wide frequency range.
On the other hand, it can be seen that the sound pressure sensitivity, which is noise in that case,
is 40 dB or more lower over a wide frequency range.
[0059]
That is, in the present embodiment, as described above, the first and second piezoelectric
04-05-2019
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elements 16 and 20 are common. Therefore, the decrease in acoustic detection sensitivity occurs
equally in the first and second piezoelectric elements 16 and 20. Therefore, the sound pressure
sensitivity to noise can be sufficiently lowered. Further, as described above, with respect to
vibrations, the volume of the rear air chamber hardly changes, so that the acceleration sensitivity
hardly decreases. Therefore, as shown in FIG. 6, the sensitivity to acceleration can be effectively
enhanced, and the sound pressure sensitivity to noise can be sufficiently lowered. That is, S / N at
the time of detecting an impact as an impact sensor can be raised.
[0060]
Preferably, the surface density σ of the first and second piezoelectric elements 16 and 20 is in
the range of 0.01 to 1 kg / m <2>. This is explained below.
[0061]
The force received per unit area by the acoustic input of the sound pressure p (Pa) of the
piezoelectric elements 16 and 20 is fs, and the force received per unit area from the vibration
input of acceleration c (m / sec <2>) is fa Do. When the surface density σ [kg / m <2>] which is
the mass per unit area of the piezoelectric elements 16 and 20 is used, fs [N] = p [Pa] · 1 [m <2>],
fa [ N] = σ [kg / m <2>] · 1 [m <2>] · c [m / s <2>].
[0062]
The output voltage at the acoustic input is proportional to fs, and the output voltage for the
vibration input is proportional to fa. The sound pressure sensitivity is represented by the sound
pressure p = 1 [Pa], and the acceleration sensitivity is represented by the output voltage with
respect to c = 1 G = 9.8 [m / sec <2>]. Therefore, the ratio of acceleration sensitivity / sound
pressure sensitivity is fa / fs = 1 / (9.8 × σ). That is, the balance between the acceleration
sensitivity and the sound pressure sensitivity depends on the surface density σ.
[0063]
Here, in the case of fs = fa, ie, σ = p / c, as schematically shown in FIG. 7, the output voltages of
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the acoustic sensor and the vibration sensor become equal. When p and c are standard signal
levels of sound pressure and acceleration to be detected, it can be seen that the isolation between
signal and noise is most enhanced under the condition of σ = p / c.
[0064]
On the other hand, FIG. 8 is an example in the case of σ> p / c. In this case, it is understood that
noise due to vibration is likely to be introduced at the time of sound detection.
[0065]
As described above, the balance between the sound detection sensitivity and the acceleration
detection sensitivity can be adjusted by the surface density σ.
Therefore, it is desirable to adjust the sensitivity balance with the surface density σ so that the
signal voltages of the acoustic and impact sensors output when the standard values of the sound
pressure and acceleration to be detected are input are equal to each other. Thereby, the isolation
between the sound pressure signal or the acceleration signal and the acceleration signal or the
sound pressure signal as noise can be enhanced.
[0066]
For example, for a sound of 1 pa often used as a reference level and an acceleration of 1 G (9.8 m
/ sec <2>), σ = 1 / 9.8, that is, σ is about 0.1 kg / m <2>. When the above isolation is the best.
When the density of the piezoelectric elements 16 and 20 is 8 × 10 <-3> kg / m <3>, it is
understood that the thickness of the piezoelectric elements 16 and 20 may be preferably 13 μm.
[0067]
As described above, it can be understood that the area density σ may be in the range of 0.01 to
1 kg / m <2> in consideration of general use.
[0068]
In the above embodiment, although the three-terminal type impact and acoustic sensor is
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configured, as shown in FIG. 9, the four-terminal type impact and the first and second
piezoelectric elements 16 and 20 are individually extracted. It may be an acoustic sensor.
[0069]
FIG. 10 is a front cross-sectional view of an impact and acoustic sensor according to a second
embodiment of the present invention.
The impact and acoustic sensor 41 of the present embodiment is configured substantially the
same as the impact and acoustic sensor 1 shown in FIG.
The difference is that the through hole 4 a is not formed in the lid 4, and instead, the through
hole 3 a is formed in the substrate 3. That is, a portion for guiding the sound into the package 2
is provided not on the package 2 but on the substrate 3. Since the other points are the same, the
description of the first embodiment is incorporated by giving the same reference numerals to the
same parts.
[0070]
In the present embodiment, when the impact and acoustic sensor 41 is incorporated in the
device, there is no need to provide a clearance above the lid 4. Therefore, the height reduction of
the product in which the impact and acoustic sensor 41 is incorporated can be promoted.
Further, in the present embodiment, since the other structure is the same as that of the first
embodiment, the same effect as that of the first embodiment can be obtained.
[0071]
FIG. 11 is a front sectional view of an impact and acoustic sensor according to a third
embodiment of the present invention, and FIG. 12 is an exploded perspective view thereof.
[0072]
In the present embodiment, the spacer substrate 63 is stacked on the substrate 3 via the
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adhesive layer 62.
The first piezoelectric element 65 is stacked on the spacer substrate 63 via an adhesive layer 64
having a substantially circular opening. Although shown schematically in FIG. 11, as shown in
FIG. 12, the first piezoelectric element 65 is formed of a piezoelectric plate, and a circular first
electrode 65a and a first electrode are formed on the upper surface of the piezoelectric plate.
And a ring-shaped second electrode 65b provided so as to surround 65a.
[0073]
A holding member 67 is stacked on the first piezoelectric element 65 via an adhesive layer 66
having a circular opening member. The holding member 67 has a circular opening as the
adhesive layer 66 does. Then, a second piezoelectric element 69 is stacked on the holding
member 67 via an adhesive layer 68 having a circular opening. The second piezoelectric element
69 is configured in the same manner as the first piezoelectric element 65.
[0074]
A lid substrate 71 is stacked on the second piezoelectric element 69 via an adhesive layer 70
having a circular opening. A through hole 71 a is formed in the lid substrate 71. The through
hole 71 a is a portion that guides the sound into the package 2.
[0075]
That is, in the third embodiment, the internal space is formed by laminating the first and second
piezoelectric elements 65 and 69 and the lid substrate 71 without using the lid member 4. Here,
in order to guide the sound pressure to the lower surface of the lower first piezoelectric element
65, a sound through hole 72 shown in FIG. 11 is formed. The sound through hole 72 is formed to
penetrate the second piezoelectric element 69, the adhesive layer 68, the holding member 67,
the adhesive layer 66, and the first piezoelectric element 65.
[0076]
Therefore, as indicated by the arrow D in FIG. 11, the sound pressure introduced to the inside is
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also introduced to the space on the lower surface side of the first piezoelectric element 65.
[0077]
As described above, in the present invention, instead of the lid member 4 opened downward, the
lid substrate 71 is used, and the piezoelectric element and the adhesive layer are laminated to
remove the through hole for introducing the sound inside. It may form a closed internal space.
According to the present embodiment, the impact and acoustic sensor 61 can be obtained only
by laminating a plurality of sheet-like members. Therefore, the manufacturing process can be
simplified. In addition, with the impact and acoustic sensor 61, it is easy to promote
miniaturization and reduction in height.
[0078]
Also in the present embodiment, as in the first embodiment, since the portion where the first and
second piezoelectric elements face each other is a closed space, as in the first embodiment, the
shock and It becomes possible to detect sound reliably and with high accuracy.
[0079]
FIG. 13 is a front sectional view of an impact and acoustic sensor according to a fourth
embodiment of the present invention, and FIG. 14 is a perspective view thereof.
In the impact and acoustic sensor 81 of the present embodiment, as in the third embodiment, a
package is configured by laminating a plurality of sheet-like members. That is, the spacer
substrate 82 is stacked on the substrate 3. At the outer peripheral edge of the spacer substrate
82, a support portion 82a projecting upward is formed. The first piezoelectric element 83 is
stacked on the support portion 82a. The first piezoelectric element 83 is stacked with the second
piezoelectric element 85 via the spacer 84. The first and second piezoelectric elements 83 and
85 are configured in the same manner as in the first embodiment. Here, on the side of the spacer
84, a through hole 84a communicating with the outside is formed. The through hole 84a acts as
a sound through hole.
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[0080]
A lid substrate 86 is bonded to the upper surface of the second piezoelectric element 85. The lid
substrate 86 has a frame-shaped support portion 86 a at the outer periphery of the lower
surface. A frame-shaped support portion 86 a is joined to the upper surface of the second
piezoelectric element 85. In FIG. 13, it is pointed out that illustration of an adhesive layer and the
like for joining the respective members is omitted. A conductive film 87 is formed to cover the
outer surface of the laminated structure on the substrate 3.
[0081]
As in the present embodiment, a through hole 84 a to be a sound through hole may be provided
on the side surface of the package. Further, in the present embodiment, the through hole 84 a
which is a sound through hole is in communication with the space between the first and second
piezoelectric elements 83 and 85. Therefore, the sound pressure of the sound guided from the
through hole 84 a is received by the upper surface of the first piezoelectric element 83 and the
lower surface of the second piezoelectric element 85. Thus, sound pressure may be introduced
between the first and second piezoelectric elements facing each other.
[0082]
Also in the present embodiment, when the sound pressure is detected, the first and second
piezoelectric elements 83 and 85 are displaced in reverse phase, and when an impact is applied,
the first and second piezoelectric elements 83 and 85 It is displaced in the same phase.
Therefore, as in the first embodiment, sound and impact can be detected with high accuracy. In
addition, since the sound pressure by the sound is equally applied to the first and second
piezoelectric elements, the noise signal caused by the sound can be removed in a wide frequency
band as a function of the shock sensor. In the structure in which the space between the
diaphragms is closed acoustically, when the frequency rises to about 10 kHz or more, a phase
difference occurs in the sound reaching the outside position of the two diaphragms, and when it
is made to function as an impact sensor The removal effect is reduced. On the other hand, in the
present embodiment in which the sound is introduced into the space between the diaphragms,
the sound pressure applied to the two diaphragms becomes the same phase, and such a problem
does not occur, and a high noise removal effect is obtained in a wide frequency band. Be
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[0083]
FIG. 15 is a front sectional view of an impact and acoustic sensor according to a fifth
embodiment of the present invention. In the impact and acoustic sensor 91 of the present
embodiment, a spacer 93 having openings 93 a and 93 b is stacked on the substrate 92. The first
piezoelectric element 94 is stacked on the substrate 92 so as to close the opening 93 a. Similarly,
the second piezoelectric element 95 is stacked so as to close the opening 93 b.
[0084]
In addition, a lid substrate 96 is stacked on the top surfaces of the first and second piezoelectric
elements 94 and 95. The lid substrate 96 has recesses 96 a and 96 b on the lower surface. The
recess 96 a is formed to face the opening 93 a of the spacer 93. Similarly, the recess 96 b is
formed to face the opening 93 b. Therefore, in the impact and acoustic sensor 91, a package is
constituted by the substrate 92, the spacer 93, the portion of the first and second piezoelectric
elements 94 and 95 supported by the spacer 93 and the lid substrate 96, and the lid substrate
96 There is.
[0085]
As in the present embodiment, the first and second piezoelectric elements 94 and 95 may be
arranged in parallel so that the piezoelectric elements do not face each other. Here, in the recess
96 a closed by the first piezoelectric element 94, the through hole 96 c is formed in the lid
substrate 96 so as to face the first piezoelectric element 94. The through hole 96 c functions as a
sound through hole. Therefore, the opening 93a which is a closed space constitutes a back air
chamber.
[0086]
On the other hand, on the second piezoelectric element 95 side, a through hole 92 a is formed in
the substrate 92 so as to face the second piezoelectric element 95. The through hole 92a acts as
a sound through hole. Therefore, the space in which the recess 96 b is closed by the second
piezoelectric element 95 constitutes a rear air chamber of the second piezoelectric element 95.
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[0087]
Also in this embodiment, the first and second piezoelectric elements 94 and 95 are displaced in
the opposite phase when sound pressure is applied, and are displaced in the same phase when an
impact is applied. Therefore, the same effect as that of the first embodiment can be obtained. In
addition, since the first and second piezoelectric elements 94 and 95 are juxtaposed as described
above, the height can be reduced.
[0088]
DESCRIPTION OF SYMBOLS 1 ... Impact and acoustic sensor 2 ... Package 3 ... Substrate 3 a ...
Through hole 4 ... Lid material 4 a ... Through hole 5 7 ... Electrode land 8, 9 ... External electrode
11 ... Via hole electrode 12 ... FET 12 A ... FET 13 ... Conductivity Adhesive layer 14 Spacer 15
Adhesive layer 16 First piezoelectric element 16a Piezoelectric plate 16b First electrode 16c
Second electrode 17, 19 Adhesive layer 18 Holding member 20 Second Piezoelectric element
20a: piezoelectric plate 20b: first electrode 20c: second electrode 21: first side electrode 22:
second side electrode 23: third side electrode 24: fourth side electrode 25: external electrode
Reference Signs List 26 signal processing circuit 27, 29 operational amplifier 28 A / D converter
31, 32 capacitor 33 adder / subtractor 34 first output terminal 35 second output terminal 36
external electrode 41 impact and sound The Sensor 61 Impact and acoustic sensor 62 Adhesive
layer 63 Spacer substrate 64 Adhesive layer 65 First piezoelectric element 65a First electrode
65b Second electrode 66 Adhesive layer 67 Holding member 68 ... adhesive layer 69 ... second
piezoelectric element 70 ... adhesive layer 71 ... lid substrate 71a ... through hole 72 ... sound
through hole 72 ... lid substrate 81 ... acoustic sensor 82 ... spacer substrate 82a ... support
portion 83 ... first Piezoelectric element 84: Spacer 84a: Through hole 85: Second piezoelectric
element 86: Lid substrate 86a: Support portion 87: Conductive film 91: Acoustic sensor 92:
Substrate 92a: Through hole 93: Spacer 93a, 93b: Opening 94 First piezoelectric element 95:
Second piezoelectric element 96: Lid substrate 96a, 96b: Recess 96c: Through hole
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