JP2001083004A - Vibration converter and acceleration sensor equipped with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a superior acceleration sensor which has a relatively simple structure, high performance and is low cost. SOLUTION: A capacitor comprises a fixed electrode 25, having an electrode surface 25a, a metal vibrator 27 which faces the electrode surface 25a with a prescribed interval in parallel and comprises a flat surface 27a, and an electret layer 23 formed on the electrode surface 25a of the electrode 25. A vibrator converter 20 is provided comprising a cylindrical case 21, which comprising a flange-like fitting part 21b at a lower end outer peripheral part, houses the capacitor, a circuit board 35 which comprises a flat surface provided with a prescribed conductive path, an FET 33 which is placed on the board 35 and connected electrically to the vibrator 27, and an insulator 31 for insulating the vibration plate 27 from the case 21. The board 35 is fixed to the fitting part 21b of the case 21 by its end part by spot welding, etc., so that the FET 33 is housed in the case 21.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vibration converter for converting sound or vibration into an electric signal and an acceleration sensor having the vibration converter, and more particularly to a vibration converter capable of obtaining a stable output over a wide frequency band. And an acceleration sensor including the vibration transducer.

[0002]

2. Description of the Related Art Conventionally, there are known sound / vibration sensors which convert sound / vibration into electric signals by various methods such as an electromagnetic type, a piezoelectric type, and a semiconductor type and detect them. I have. Among such sound / vibration sensors, a capacitor-type sensor is generally used as a sensor suitable for an audio circuit microphone. This conventional condenser microphone has a flat frequency characteristic over a wide range as shown in FIG.

As an example of this condenser microphone, FIG. 14 shows an electret condenser microphone 10 using an electretized polymer film. As shown in FIG. 1, a conventional electret condenser microphone 10 includes a vibrating body 3 and a vibrating body 3.
And a metal back electrode 5 separated at a predetermined interval.
The vibrating body 3 and the back pole 5 are insulated from each other by an insulator 7 and housed in the metal case 1. A polymer film is fixed on one flat surface 5a of the back electrode 5, and an electret film 9 is formed into an electret. The electret film 9 is polarized so that the vibrating body 3 side becomes a negative electrode.

As described above, with the electret film 9 interposed therebetween,
The vibrating body 3 and the back pole 5 arranged at a predetermined interval form a capacitor. In the conventional microphone 10, when the vibrating body 3 vibrates, the capacitance of the capacitor changes. Therefore, the vibration can be detected by detecting the change in the capacitance.

[0005]

However, in the conventional sound / vibration sensor 10 as described above, its frequency characteristics are flat over a wide range in a low frequency band, and a stable output can be obtained. As shown in FIG. 13, there is a problem that a stable output cannot be obtained in a high frequency band. This is inconvenient when stable output is required in a specific frequency band, such as an acceleration sensor.

It is also desired that the assembling work of the vibrating body 3 and the back pole 5 and the insulator 7 arranged at a predetermined interval in the metal case 1 can be performed more easily and more accurately. Furthermore, in order to enable the conventional microphone 10 to be applied as a vibration detector included in an acceleration sensor or the like, it is desired that the airtightness of the metal case 1 be improved so that noise or the like does not enter the metal case 1. .

Accordingly, the present invention has been made in view of the above-mentioned problems, and has an excellent vibration having a relatively simple structure, low cost, and high performance capable of obtaining stable frequency characteristics over a wide range. It is an object to provide a transducer and an acceleration sensor including the vibration transducer.

[0008]

According to a first aspect of the present invention, there is provided a vibration transducer for converting vibration into an electric signal, comprising: a first electrode having an electrode surface; A vibrating body having a flat surface facing the electrode surface of the first electrode at a predetermined interval substantially in parallel with the vibrating body and capable of vibrating in a direction substantially perpendicular to the flat surface; A capacitor comprising: a second electrode formed on the first electrode; and an electret film interposed between the first and second electrodes;
A cylindrical case having a top surface, a brim-shaped mounting portion on the outer periphery of a lower end, and a conductive inner surface, a circuit board having a plane provided with a predetermined conductive path, and a plane of the circuit board An electrical impedance converter mounted on the first electrode and electrically connected to one of the first and second electrodes via the conductive path; and connecting the one electrode to the inner surface of the case. And an insulator for holding the capacitor in the case so as to electrically insulate the other electrode and the inner surface of the case, and wherein the circuit board includes the electrical impedance converter. Is mechanically fixed to the mounting portion of the case so as to be accommodated in the case, and is electrically connected via the conductive path.

The electret film has a persistent electric polarization characteristic and acts as a good dielectric. The electret film is interposed between the pair of electrodes (first and second electrodes) to form a capacitor. One of the pair of electrodes is formed on the vibrator. The capacitor thus formed changes in capacitance in response to vibration. The vibration is detected by detecting the change in capacitance. The output is taken out via an electrical impedance converter.

According to this structure, a pair of electrodes facing each other at a predetermined interval with the electret film interposed therebetween is disposed in a case having a flange-shaped mounting portion on the outer periphery of the lower end. Is electrically connected to the inside of the case, and an insulator for holding the other of the pair of electrodes so as to insulate the other from the case is further provided. Since it is fixed to the mounting portion of the case, it is possible to obtain an inexpensive and excellent vibration transducer having a relatively simple configuration and high performance capable of obtaining stable frequency characteristics over a wide area.

It is preferable that the vibrator is formed of a conductive thin film or a metal diaphragm. According to this configuration, one of the pair of electrodes can be integrated with the vibrator, and the configuration is further simplified. It is preferable that the circuit board and the mounting portion of the case are mechanically fixed and electrically connected by spot welding, laser welding, or the like. According to this configuration, the case and the circuit board can be securely fixed with a simple structure, and the airtightness inside the case can be enhanced.

The electret film is formed by fixing a polymer film or an electret material made of SiO _{2 on} one of the first and second electrodes,
An electret layer formed by electret formation is preferable. The electret material can be fixed by heat fusion or the like. The electrical impedance converter includes a field effect transistor. The case may have a sound hole formed in a top surface.

In addition, the circuit board has another plane opposite to the plane, a through hole passing through the plane and the other plane, and a conductive path formed in the other plane.
The conductive path on the plane and the conductive path on the other plane may be electrically connected via the through hole. This makes it possible to extract the output of the vibration transducer with a simple configuration.

Further, the circuit board may have an electric signal output section electrically connected to the conductive path on the other plane. The electric signal output unit can be formed, for example, by forming a groove in a protrusion formed at an end of the circuit board, and extending a conductive path on the other plane to the groove.
The electrical signal output unit thus formed can be electrically connected by soldering or the like, and can be mechanically fixed.
Reliability can be improved.

According to a seventh aspect of the present invention, in order to solve the above-mentioned problem, an acceleration sensor includes the vibration transducer according to any one of the first to sixth aspects, and converts an electric signal from the vibration detector into an electric signal. The acceleration is detected based on the detected acceleration.

According to this configuration, there is provided an acceleration sensor having the same functions and effects as those of the vibration transducer according to the first to sixth aspects. That is, it is possible to obtain an excellent acceleration sensor having a relatively simple configuration, a low cost, and high performance capable of obtaining stable frequency characteristics over a wide range.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION An acceleration sensor according to the present invention comprises a first electrode having an electrode surface and a plane opposed to the electrode surface of the first electrode at a predetermined interval substantially in parallel. A vibrating body having a vibrating body in a direction substantially perpendicular to the plane, a second electrode formed on the plane of the vibrating body, and being interposed between the first and second electrodes A capacitor including an electret film, a cylindrical case having a top surface, a flange-shaped mounting portion on a lower peripheral portion, and a conductive inner surface, and a plane provided with a predetermined conductive path. A circuit board, an electric impedance converter mounted on a plane of the circuit board, and electrically connected to one of the first and second electrodes via the conductive path; Of the case is insulated from the inner surface of the case, and the other is To connect poles the inner surface electrically of the case, and a vibration transducer for converting vibrations comprising, an insulator for holding the capacitor in the case into an electric signal. The circuit board of the vibration transducer is mechanically fixed to a mounting portion of the case and is electrically connected to the case via the conductive path so that the electric impedance transducer is housed in the case. . The acceleration sensor according to the present invention detects acceleration based on an electric signal from the vibration detector.

The electret film has a persistent electric polarization property and acts as a good dielectric. The electret film is interposed between the pair of electrodes to form a capacitor. One of the pair of electrodes is formed on the vibrator. The capacitor thus formed changes in capacitance in response to vibration. The vibration is detected by detecting the change in capacitance. The output is taken out via an electrical impedance converter.

According to this configuration, a pair of electrodes facing each other at a predetermined interval with the electret film interposed therebetween is disposed in a case having a flange-shaped mounting portion on the outer periphery of the lower end, and one of the pair of electrodes is provided. Is electrically connected to the inside of the case, and an insulator for holding the other of the pair of electrodes so as to insulate the other from the case is further provided. Thus, since it is fixed to the mounting portion of the case, it is possible to obtain an excellent acceleration sensor having a relatively simple configuration, a low cost, and high performance capable of obtaining stable frequency characteristics over a wide area.

Preferably, the vibrating body is formed of a metal vibrating plate. According to this configuration, one of the pair of electrodes can be integrated with the vibrator, and the configuration is further simplified. It is preferable that the circuit board and the mounting portion of the case are mechanically fixed and electrically connected by spot welding, laser welding, or the like. According to this configuration, the case and the circuit board can be securely fixed with a simple structure, and the airtightness inside the case can be enhanced.

The electret film is formed by fixing an electret material made of a polymer film or SiO _{2 on} one of the first and second electrodes,
An electret layer formed by electret formation is preferable. The electret material can be fixed by heat fusion or the like. The electrical impedance converter includes a field effect transistor.

Further, the circuit board has another plane opposite to the plane, a through hole passing through the plane and the other plane, and a conductive path formed in the other plane.
The conductive path on the plane and the conductive path on the other plane may be electrically connected via the through hole. This makes it possible to extract the output of the vibration transducer with a simple configuration.

Further, the circuit board may have an electric signal output section electrically connected to the conductive path on the other plane. The electric signal output unit can be formed, for example, by forming a groove in a protrusion formed at an end of the circuit board, and extending a conductive path on the other plane to the groove.
The electrical signal output unit thus formed can be electrically connected by soldering or the like, and can be mechanically fixed.
Reliability can be improved.

Alternatively, as another mode, a sound / vibration sensor having the same function and effect as the above-mentioned embodiment is provided by providing a sound hole in the top surface of the metal case and forming the vibrator by a conductive thin film. Can be obtained.

[0025]

First Embodiment Hereinafter, a first embodiment of a vibration converter for an acceleration sensor according to the present invention will be described with reference to FIGS. In all the drawings, similar components are denoted by the same reference symbols and symbols.

FIG. 1 shows a first example of the acceleration sensor according to the present invention.
It is sectional drawing of the vibration transducer 20 of an Example. Vibration transducer 2
0 converts the vibration received by the acceleration sensor into an electric signal,
Output. As shown in the figure, a vibration transducer 20 is separated from a fixed electrode 25 made of a disk-shaped metal plate having an electrode surface 25a and substantially in parallel with an electrode surface 25a of the fixed electrode 25 at a predetermined distance d. And opposing plane 27a
A vibrating body 27 made of a disk-shaped metal plate capable of vibrating in a direction substantially perpendicular to the plane 27a, and an electret layer 23 formed on the electrode surface 25a of the fixed electrode 25,
A spacer 2 made of a ring-shaped insulating member having a predetermined thickness d and interposed between the fixed electrode 25 and the metal vibrating body 27
9 is provided.

In this embodiment, the electrode surface 25 of the fixed electrode 25
The electret layer 23 is formed on the surface a of the vibrating body 27 in another embodiment. That is, the electret film may be interposed between the fixed electrode 25 and the vibrating body 27. The fixed electrode 25 has a plurality of through holes 25c. This through hole 25c is a hole for ventilation inside the sensor.

The electret layer 23 is formed by applying an electret material made of a polymer film to the electrode surface 25 of the fixed electrode 25.
It is fixed on the substrate a by heat fusion and formed into an electret. The polymer film electretized in this way has a persistent electric polarization characteristic and acts as a good dielectric. The electret layer 23 includes the vibrating body 2
Polarized so that the 7 side becomes a negative electrode. In the vibration converter 20 of the present embodiment, the fixed electrode 25 and the vibrating body 27 act as a pair of electrodes, and these form a capacitor together with the electret layer 23 which is a dielectric.

The polymer film as the electret material is preferably a polyester film, such as an ethylene tetrafluoride-propylene hexafluoride copolymer (FEP) film. In another embodiment, the electret layer 2
3, the fixed electrode 2 electret material formed of SiO ₂
5 may be fixed by heat fusion and formed into an electret. The thickness d of the spacer 29 is several tens μm.

In another embodiment, the vibrating body may be made of an insulating material, and the surface of the vibrating body may be plated or metal-deposited to have conductivity on the surface of the vibrating body. FIG. 2 shows a top view of the vibrating body 27 of the present embodiment. However, the present invention is not limited to this, and various shapes can be considered. As shown in FIG. 2, the vibrating body 27 has a disk shape with a predetermined thickness and has a predetermined area.
7b and a support portion 27 that supports the vibrating portion 27b so that it can vibrate
c, and a ring-shaped mounting portion 27d that supports the vibrating portion 27b integrally with the supporting portion 27c and enables mounting to the device. As another example, the vibration part 27b may be rectangular. Also, the vibrating body 27
May be a thin film vibrator formed of a conductive material.

Returning to FIG. 1, the vibration transducer 20 of the present embodiment
Is a top surface 21a and a brim-like mounting portion 21b on the outer periphery of the lower end.
And a circuit board 3 having a flat surface 35a provided with a predetermined conductive path (not shown).
5, a first metal ring 38 interposed between the diaphragm 27 and the top surface 21a of the metal case 21; an electric impedance converter 33 mounted on a flat surface 35a of the circuit board 35; And a second metal ring 39 interposed between the fixed electrode 25 and the fixed electrode 25.

As another embodiment, the case may be made of resin or the like, and the inside surface of the case may be plated or metal-deposited so that the inside surface of the case has conductivity.

The electric impedance converter 33 comprises a field effect transistor (hereinafter referred to as "FET").
The FET 33 converts the impedance of the output of the capacitor. The capacitor formed by the fixed electrode 25 and the vibrating body 27 of the vibration transducer 20 of the present embodiment has a small capacity of about several tens of pF due to air capacity. Therefore, since the impedance becomes high, impedance conversion is required. Theoretically, for a capacitor, ω = 0
(Ω = 2πf), an output can be obtained.
The limit is determined by the magnitude of the input impedance of the ET33.

Although the FET 33 of this embodiment is used in the common source system (two-wire system), it is needless to say that the FET 33 may be of the source follower system (three-wire system) which is more stable in performance.

The fixed electrode 25, the spacer 29, the vibrating body 27, the first and second metal rings 38 and 39,
The FET 33 is accommodated in the case 21 via the insulator 31, and these components are held down by a circuit board 35 having an end fixed to the mounting portion 21 b of the case 21.
The mounting portion 21b of the case 21 is fixed to the circuit board 35 by spot welding or laser welding. Nitrogen or the like may be sealed and sealed inside the case 21.

In this way, the vibrating body 27 is electrically connected to the top surface 21a of the metal case 21 via the first metal ring 38, while the fixed electrode 25 is insulated from the metal case 21 and On the other flat surface 25b where the electret layer 23 is not formed, the FET 33 on the circuit board 35 is connected via the second metal ring 39 and the conductive path.
Is electrically connected to

On the circuit board 35, other electrical components 43 such as resistors and capacitors are mounted. Circuit board 3
5 has two through holes 35c and 35d. These through holes 35c and 35d are for taking out wiring from one plane 35a of the circuit board 35 to the other plane 35b on the opposite side.
5c and 35d are sealed.

FIG. 3 is a bottom view of the vibration transducer 20 of this embodiment shown in FIG. As shown in the figure, on the other flat surface 35b of the circuit board 35, conductive paths 41a and 41b indicated by oblique lines in the figure are formed. The conductive paths 41a and 41 on the other plane 35b of the circuit board 35
1b denotes through holes 35c and 3c of the circuit board 35, respectively.
Via 5d, it is electrically connected to the electronic circuit component 43 on one flat surface 35a of the circuit board 35. Thus, the output of the vibration transducer 20 can be taken out to the outside with a simple configuration.

FIG. 4 is an equivalent electric circuit diagram of the vibration transducer 20 of the present embodiment shown in FIG. As shown in the figure, anions exist on the surface of the metal fixed electrode 25 due to the electret layer 23. C ₁ is a metal vibrator 27
4 shows a capacitor formed between the metal fixed electrode 25 and the metal fixed electrode 25. R is the load resistance, C ₂ denotes the coupling capacitor. The vibrating body 27 is grounded via a case 21 and a circuit board 35 via a first metal ring 38. The fixed electrode 25 is electrically connected to the input terminal 33a of the FET 33 via the second metal ring 39,
Output terminal 33b of the FET33 is electrically connected to the load resistor R and a coupling capacitor C _2. The output is taken out via the conductive paths 41a and 41b, respectively.

Hereinafter, the operation of the vibration transducer 20 according to the present embodiment will be described.

In this embodiment, when the acceleration sensor receives an external vibration, the metal vibrating body 27 vibrates in the direction of arrow D in FIG. 4, that is, in a direction substantially perpendicular to the plane of the vibrating body 27. At this time, assuming that the mass of the vibrating body 27 is m and the external vibration is acceleration G, F = m
A force of × G acts, and the force F causes the capacitor C ₁ to generate a capacitance change ΔC by an amount corresponding to the vibration change. That is, the capacitance of the capacitor is C ₁ = C ₁ ± ΔC. This capacitance change ΔC can be obtained as a voltage change ΔV, and the voltage change ΔV is subjected to electric impedance conversion by the FET 33 and taken out as an electric signal.

The sensitivity of the flat part of the frequency characteristic of the vibration transducer 20 of the present embodiment includes the equivalent effective area exhibited by the metal fixed electrode 25 and the metal vibrator 27, the equivalent gap between the metal fixed electrode 25 and the metal vibrator 27, It depends on the stray capacitance, the gain of the FET 33, and the like.

The vibration transducer 20 configured as above is
It has a frequency characteristic as shown in FIG. That is,
It has a high Q value near the resonance point f ₀ and shows flat characteristics in the middle and low frequency regions. As described above, the vibration can be detected at a specific frequency (resonance point f ₀ ) not only in the flat portion of the low frequency band but also in the high frequency band.
A vibration transducer having stable frequency characteristics over a wide area is provided. Therefore, the vibration transducer 20 of the present embodiment, even in the acceleration sensor, by the purpose of use, it is possible to select and use the vibration output of ₀ near the flat portion or the resonance point f.

According to this embodiment, the structure is relatively simple.
It is possible to provide an excellent vibration transducer of an acceleration sensor which has low manufacturing cost, can be mass-produced, and has high performance.

[0045]

Second Embodiment Next, a second embodiment of the vibration transducer of the acceleration sensor according to the present invention will be described with reference to FIGS.

FIG. 6 is a sectional view of the vibration transducer according to the second embodiment. As shown in the figure, the vibration transducer 50 of the second embodiment includes a circuit board 55 in addition to the same configuration as the vibration transducer 2 of the first embodiment shown in FIG.
As described above, the vibration converter 50 of the second embodiment has the two circuit boards 35 and 55 configured as a multilayer structure.

The circuit board 55 has one plane 55a facing the other plane 35b of the circuit board 35 and the other plane 55b on the opposite side. Further, two through holes 55c and 55d are formed in the circuit board 55. These through holes 55c and 55d are
5 for guiding the wiring from the through holes 35c and 35d to the other flat surface 55b of the circuit board 55, respectively. In this way, the output of the vibration transducer 50 can be guided to the outside of the vibration transducer 50.

FIG. 7 is a bottom view of the vibration transducer 50 of the second embodiment shown in FIG. As shown in the figure, conductive paths 57a and 57b indicated by oblique lines in the figure are formed on the other flat surface 55b of the circuit board 55. The conductive path 57a on the other flat surface 55b of the circuit board 55
Is connected to one plane 35 of the circuit board 35 through the through hole 55d of the circuit board 55 and the through hole 35d of the circuit board 35
a is electrically connected to the electronic circuit component 43 on a. The conductive path 57b on the other flat surface 55b of the circuit board 55 is connected to the through hole 55c of the circuit board 55 and the through hole 35 of the circuit board 35.
Through c, it is electrically connected to the electronic circuit component 43 on one flat surface 35a of the circuit board 35.

Further, the circuit board 55 has grooves 59a and 59b formed at the ends including the conductive paths 57a and 57b, respectively. The grooves 59a and 59b can be formed by forming a through hole in the circuit board 55 and then cutting off the through hole substantially at the center. FIG.
Are the grooves 59a and 59b of the vibration transducer 50 of the present embodiment.
FIG. 9 is a top view of the vibration converter 50 of the present embodiment. As shown in FIGS. 8 and 9, the surfaces of the grooves 59a and 59b are provided with conductive paths 57.
Conductive layers 61a and 61b are formed extending from a and 57b, respectively.

According to the vibration transducer 50 of the second embodiment configured as described above, the grooves 59a and 59b can be fixed to the device by soldering or the like. Performance can be improved, and the same operation and effect as those of the vibration converter 20 of the first embodiment can be obtained.

[0051]

Third Embodiment FIG. 10 is a sectional view showing a third embodiment of the vibration transducer of the acceleration sensor according to the present invention. As shown in the figure, the vibration transducer 70 of the third embodiment reverses the arrangement of the fixed electrode 25 and the vibrating body 27 in the configuration of the vibration transducer 20 of the first embodiment shown in FIG. In addition, the first metal ring 38 of the vibration transducer 20 of the first embodiment is omitted. In addition, the vibration transducer 7 of the third embodiment
Numeral 0 is provided with a fixed electrode 75 instead of the fixed electrode 25 of the vibration transducer 20 of the first embodiment.

The vibration converter 70 of the third embodiment having the above-described configuration can provide the same operation and effect as those of the vibration converter 20 of the first embodiment.

As another embodiment, the electret layer 23 of the third embodiment may be formed not on the fixed electrode 75 but on one flat surface 27a of the vibrating body 27.

[0054]

Fourth Embodiment FIG. 11 is a sectional view of a vibration converter of an acceleration sensor according to a fourth embodiment of the present invention. As shown in the figure, the vibration transducer 80 of the fourth embodiment has the same configuration except that the fixed electrode 75 is removed from the vibration transducer 70 of the third embodiment shown in FIG. . That is, it is directly covered with a polymer film so as to cover at least the top surface 21 a of the metal case 21 and is electretized to form the electret layer 23. In the vibration transducer 80 of the fourth embodiment configured as described above, the third
The same operation and effect as those of the vibration transducer 70 of the embodiment can be obtained.
Also, as shown in FIG.
May be formed so as to cover the entire inner surface of the metal case 21, and in this case, the insulator 31 can be omitted.

As another embodiment, the electret layer 23 of the fourth embodiment may be formed not on the top surface 21a of the metal case 21 but on one plane 27a of the vibrator 27. In this case, the insulator 31 is required.

[0056]

Fifth Embodiment FIG. 12 is a sectional view of a vibration transducer according to a fifth embodiment of the present invention. In particular, the vibration transducer 90 of the fifth embodiment is suitable for a sound sensor that detects sound. As shown in the figure, the vibration transducer 90 of the fifth embodiment has
Instead of the metal case 21 having the configuration of the vibration transducer 20 of the first embodiment shown in FIG. 1, a metal case 91 having a sound hole portion 91c substantially at the center of the top surface 91a, and a metal case of the first embodiment. A conductive film-shaped vibrating body 97 is provided instead of the vibrating body 27.

In the vibrating body 97 of this embodiment, when the equivalent area of the vibrating body 97 is S, a force F = P ×
S will be detected. Therefore, a configuration using a thin film or the like is preferable as shown in FIG. In the vibration transducer 90 of the fifth embodiment configured as described above, the first
The same operation and effect as those of the vibration converter 20 of the embodiment can be obtained.

In the first to fifth embodiments, by dividing the capacitor into a vibration converter having two capacitors, a voltage is applied to one of the capacitors.
A sound or vibration sensor having a self-diagnosis function can be configured by vibrating the vibrating body and detecting and extracting a voltage change caused by the vibration with the other capacitor. In this case, the same operation and effect as those of the above embodiment can be obtained.

[0059]

According to the present invention, a pair of electrodes which are opposed to each other at a predetermined interval with an electret film interposed therebetween are arranged in a case having a flange-shaped mounting portion on the outer periphery of the lower end. One of the pair of electrodes is electrically connected to the inside of the case, and an insulator for holding the other of the pair of electrodes so as to insulate the other from the case is further provided. Since the end portion is fixed to the mounting portion of the case, it is possible to obtain an excellent acceleration sensor having a relatively simple configuration, a low cost, and high performance capable of obtaining stable frequency characteristics over a wide area.

Since the vibrating body is made of a metal diaphragm,
One of the pair of electrodes can be integrated with the vibrator, and the configuration is further simplified. Further, since the flat plate and the mounting portion of the case are mechanically fixed and electrically connected by spot welding, laser welding, or the like, the case and the flat plate can be securely fixed with a simple structure. The airtightness inside the case can be enhanced.

Further, the circuit board has another plane opposite to the plane, a through hole passing through the plane and the other plane, and a conductive path formed in the other plane.
Since the conductive path on the plane and the conductive path on the other plane are electrically connected through the through hole, it is possible to take out the output of the vibration transducer with a simple configuration.

Further, since the circuit board has an electric signal output portion electrically connected to the conductive path on the other plane, the electric signal output portion is electrically connected to the conductive path by soldering or the like. Thus, mounting can be improved with a simple configuration, and reliability can be improved.

Further, according to the present invention, by providing a sound hole in the top surface of the metal case and forming the vibrating body with a conductive thin film, a vibration sensor suitable for a sound sensor having the same function and effect as the above invention is provided. A converter can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of a first embodiment of a vibration transducer included in an acceleration sensor according to the present invention.

FIG. 2 is a top view of a vibrating body of the vibration converter shown in FIG.

FIG. 3 is a bottom view of the vibration transducer shown in FIG. 1;

FIG. 4 is an equivalent electric circuit diagram of the vibration transducer shown in FIG.

FIG. 5 is a frequency characteristic diagram of the vibration converter of the acceleration sensor shown in FIG. 1;

FIG. 6 is a cross-sectional view of a second embodiment of the vibration transducer included in the acceleration sensor according to the present invention.

FIG. 7 is a bottom view of the vibration transducer shown in FIG. 6;

FIG. 8 is a partially enlarged perspective view of the vibration transducer shown in FIG.

FIG. 9 is a top view of the vibration transducer shown in FIG. 6;

FIG. 10 is a cross-sectional view of a third embodiment of the vibration transducer included in the acceleration sensor according to the present invention.

FIG. 11 is a sectional view of a fourth embodiment of the vibration transducer included in the acceleration sensor according to the present invention.

FIG. 12 is a sectional view of a vibration transducer according to a fifth embodiment of the present invention.

FIG. 13 is a diagram for explaining frequency characteristics of a general sound / vibration sensor.

FIG. 14 is a sectional view of a conventional sound / vibration sensor.

[Explanation of symbols]

 20, 50, 70, 80, 90 Vibration transducer 21, 91 Metal case (case) 21b, 91b Mounting portion 91c Sound hole 23 Electret layer (electret film) 25, 75 Fixed electrode (first electrode) 27, 97 Vibration Body (vibrator, second electrode) 29 Spacer 31 Insulator 33 FET (electrical impedance converter) 35, 55 Circuit board 38, 39 Metal ring 41a, 41b, 57a, 57b Conductive path 43 Electronic circuit component

Claims (7)

[Claims] 1. A vibration transducer for converting a vibration into an electric signal, comprising: a first electrode having an electrode surface, and being substantially parallel to and separated from the electrode surface of the first electrode by a predetermined distance. A vibrating body having an opposing plane and capable of vibrating in a direction substantially perpendicular to the plane, a second electrode formed on the plane of the vibrating body, and a vibrating body of the first and second electrodes A capacitor including an electret film interposed therebetween; a cylindrical case having a top surface, a brim-shaped mounting portion on the outer periphery of the lower end, and a conductive inner surface; and a predetermined conductive path provided. A circuit board having a flat surface; and a first and a second circuit board mounted on the flat surface of the circuit board.
An electrical impedance converter electrically connected to one of the electrodes through the conductive path, and insulating the one electrode from the inner surface of the case, and connecting the other electrode to the case. An insulator that holds the capacitor in the case so as to be electrically connected to the inner surface, wherein the circuit board accommodates the electric impedance converter in the case. A vibration transducer, which is mechanically fixed to the mounting portion and electrically connected through the conductive path. 2. The electret film according to claim 1, wherein the electret film is an electret layer formed by fixing an electret material made of a polymer film on one of the first and second electrodes and forming an electret. The vibration transducer according to claim 1, wherein 3. The circuit board has: another plane opposite to the plane; a through-hole penetrating the plane and the other plane; and a conductive path formed in the other plane. The vibration converter according to claim 1, wherein the conductive path on the plane and the conductive path on the other plane are electrically connected via the through hole. 4. The vibration transducer according to claim 3, wherein the circuit board has an electric signal output portion electrically connected to the conductive path on the other plane. 5. The vibration transducer according to claim 1, wherein the vibrator is made of a conductive thin film. 6. The vibration transducer according to claim 5, wherein the case has a sound hole formed in a top surface. 7. An acceleration sensor comprising the vibration transducer according to claim 1, wherein acceleration is detected based on an electric signal from the vibration detector.