JP2008072703A - Acoustic transducer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an acoustic transducer available as a speaker or a microphone, wherein acoustics of much higher sound pressure can be generated while attaining miniaturization and weight reduction. <P>SOLUTION: An acoustic transducer 1 is provided with: a housing 3 configured by forming a cavity part S1 that is opening outwardly; an approximately plate-shaped fixed electrode 7 which faces an opening 3a and forms a part of the housing 3; a diaphragm 5 which includes an electrode 29 and is disposed between the opening 3a and the fixed electrode 7; and an elastic deforming part 17 which can be elastically deformed, supporting the diaphragm 5 with respect to the housing 3 so as to vibrate the diaphragm in a thickness direction, wherein the fixed electrode 7 and the electrode 29 are electrically insulated from each other, the elastic deforming part 17 separates the diaphragm 5 from the fixed electrode 7 in a balanced state where no elastic force is generated therein, and can be elastically deformed to a position where the diaphragm 5 is brought into contact with the fixed electrode 7. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an acoustic transducer.

2. Description of the Related Art Conventionally, acoustic transducers such as speakers and microphones have been required to be reduced in size and weight. For example, Patent Document 1 discloses a technique using MEMS technology. In this type of acoustic transducer, the outer periphery of the fixed electrode and the diaphragm electrode are fixed to an annular housing so that the flat fixed electrode and the diaphragm electrode face each other with a space therebetween, and the fixed electrode and the diaphragm electrode are It is comprised so that it may be arrange | positioned inside a housing.
When the acoustic transducer having this configuration is used as a speaker, the diaphragm electrode is vibrated by elastic deformation by applying a voltage between the fixed electrode and the fixed electrode in accordance with an electric signal.
US Patent Application Publication No. 2003/0044029

However, in the conventional acoustic transducer described above, since the outer peripheral portion of the diaphragm electrode is fixed, there is a problem that sufficient amplitude cannot be obtained when used as a speaker, and sound with a large sound pressure is generated. I can't.
The present invention has been made in view of the above-described circumstances, and an object thereof is to provide an acoustic transducer that can vibrate a diaphragm with a larger amplitude while achieving a reduction in size and weight.

In order to solve the above problems, the present invention proposes the following means.
According to a first aspect of the present invention, there is provided a housing formed with a cavity portion that opens outward, a substantially plate-like fixed electrode that forms a part of the wall portion of the housing opposite to the opening portion, and an electrode. A diaphragm disposed between the opening and the fixed electrode, and an elastically deformable elastically deformable portion that supports the housing so as to vibrate the diaphragm in the thickness direction thereof. The fixed electrode and the electrode of the diaphragm are electrically insulated from each other, and the elastic deformation portion separates the diaphragm from the fixed electrode in an equilibrium state where no elastic force is generated in the elastic deformation portion. The acoustic transducer is characterized in that it can be elastically deformed to a position where the diaphragm contacts the fixed electrode.

  When the acoustic transducer according to the present invention is used as a speaker, a DC voltage is applied in advance between the fixed electrode and the electrode of the diaphragm, and the diaphragm is caused by electrostatic attraction acting between the diaphragm and the fixed electrode. Is fixed to the fixed electrode by adsorption. In this state, an elastic force is generated in the elastically deforming portion so as to separate the diaphragm from the fixed electrode. However, by making the electrostatic attractive force larger than the elastic force, the above-described adsorption fixing is performed. The state can be maintained. Further, since the electrode of the diaphragm and the fixed electrode are electrically insulated, no current flows between the electrode of the diaphragm and the fixed electrode in the adsorbed and fixed state.

  When sound is generated from the acoustic transducer, voltage application between the fixed electrode and the diaphragm is released. At this time, the vibration plate is separated from the fixed electrode by the elastic force of the elastic deformation portion, reaches the position where the elastic deformation portion is in an equilibrium state, and is further displaced to the opposite side of the adsorption fixing position by the inertia force of the vibration plate. To do. Even in this state, since the elastic force is generated in the elastic deformation portion, the elastic deformation portion and the inertial force of the vibration plate are displaced in the direction approaching the fixed electrode, and return to the suction fixing position again. become. As described above, sound is generated outward from the opening of the housing when the diaphragm vibrates.

  When the diaphragm vibrates and returns to the vicinity of the fixed electrode again, a larger voltage may be applied again between the fixed electrode and the electrode of the diaphragm. As a result, even when the vibration of the diaphragm is lost, energy is lost due to air resistance or the like, and even if the diaphragm cannot return to the suction and fixing position only by the elastic force of the elastically deforming portion and the inertial force of the diaphragm, the vibration is reliably generated. The plate can be adsorbed and fixed to the fixed electrode.

  According to a second aspect of the present invention, in the acoustic transducer according to the first aspect, a power supply unit that selectively applies an AC voltage and a DC voltage between the fixed electrode and the electrode of the diaphragm, and the AC voltage The acoustic transducer is characterized in that the frequency is equal to the resonance frequency of the diaphragm based on the elastic modulus of the elastic deformation portion and the weight of the diaphragm.

According to the acoustic transducer of the present invention, in the state where the diaphragm is arranged at the equilibrium position, the diaphragm is made efficient by applying an AC voltage having a frequency equal to the resonance frequency of the diaphragm, for example, by the power supply unit. It can be adsorbed and fixed to a fixed electrode well.
In other words, when the AC voltage is applied between the fixed electrode and the diaphragm electrode in a state where the diaphragm is arranged at an equilibrium position, the AC electric field generated between the fixed electrode and the diaphragm electrode causes Since the amplitude of the diaphragm gradually increases, the diaphragm can be brought closer to the fixed electrode. As described above, when the amplitude of the diaphragm becomes large and the diaphragm comes into contact with the fixed electrode, or when the diaphragm is sufficiently close to the fixed electrode, the power supply unit causes a gap between the fixed electrode and the electrode of the diaphragm. By applying a DC voltage, the diaphragm can be adsorbed and fixed to the fixed electrode.

The invention according to claim 3 is the acoustic transducer according to claim 1 or 2, wherein the diaphragm is brought into contact with the fixed electrode by applying the AC voltage or the DC voltage before the sound is generated. An acoustic transducer characterized by being adsorbed and fixed is provided.
In the acoustic transducer according to the present invention, before the sound is generated, the diaphragm is forcibly fixed against the elastic force of the elastic deformation portion in advance by selectively applying the AC voltage or the DC voltage described above. Therefore, when the diaphragm is vibrated and the diaphragm is vibrated to generate sound, the vibration displacement of the diaphragm is reliably increased using the elastic force. be able to.

  According to a fourth aspect of the present invention, in the acoustic transducer according to the first to third aspects, one of the diaphragm and the fixed electrode is configured by providing an electret film on a surface facing the other. A characteristic acoustic transducer is proposed.

According to the acoustic transducer of the present invention, a voltage is applied between the diaphragm and the fixed electrode so that a permanent charge in the electret film appears on the other of the diaphragm and the fixed electrode. In addition to the electrostatic attractive force based on the voltage application between them, an electrostatic attractive force acting between the electret film and the other of the diaphragm and the fixed electrode is also generated. That is, the diaphragm can be adsorbed and fixed to the fixed electrode even if the voltage applied between the diaphragm and the fixed electrode is lowered.
Further, when a voltage is applied so that a charge having the same polarity as the permanent charge in the electret film appears on the other of the diaphragm and the fixed electrode, a repulsive force can be generated between the diaphragm and the fixed electrode. Also, the acoustic transducer can be operated efficiently.

  According to a fifth aspect of the present invention, there is provided a housing formed with a hollow portion that opens outward, a substantially plate-like fixed electrode that faces the opening and forms a part of the wall portion of the housing, and the opening. A vibration plate disposed between a portion and the fixed electrode; and an elastically deformable elastically deformable portion that supports the housing so that the vibration plate can vibrate in a thickness direction thereof, and The elastically deforming portion is arranged to be spaced apart from the fixed electrode in an equilibrium state where no elastic force is generated in the elastically deforming portion, and can be elastically deformed to a position where the vibrating plate contacts the fixed electrode. An acoustic transducer is proposed in which the diaphragm includes an electret charged on one of positive and negative sides.

  When the acoustic transducer according to the present invention is used as a speaker, a static voltage acting between the diaphragm and the fixed electrode is previously applied to the fixed electrode so that a charge opposite to the permanent charge in the electret appears. The diaphragm is attracted and fixed to the fixed electrode by attractive force. In this state, an elastic force is generated in the elastically deforming portion so as to separate the diaphragm from the fixed electrode. However, by making the electrostatic attractive force larger than the elastic force, the above-described adsorption fixing is performed. The state can be maintained.

And when generating sound from this acoustic transducer, by canceling the voltage application, or by applying a voltage so that a charge having the same polarity as the permanent charge appears on the fixed electrode adsorbed by the diaphragm, The diaphragm is vibrated by the elastic force of the elastically deforming portion and its own inertial force, and returns to the suction fixing position. That is, sound is generated outward from the opening of the housing by the vibration of the diaphragm.
In addition, when the diaphragm vibrates and returns to the vicinity of the fixed electrode again, it is ensured by applying a larger voltage so that a charge having the same polarity as the permanent charge appears on the fixed electrode again. The diaphragm can be adsorbed and fixed to the fixed electrode.

According to the first and fifth aspects of the invention, the diaphragm is vibrated from the state in which the diaphragm is forcibly attracted and fixed against the elastic force of the elastic deformation portion. It becomes possible to vibrate. Therefore, it is possible to generate a sound having a larger sound pressure.
In addition, since the acoustic transducer according to these inventions has a simple configuration in which a fixed electrode, a diaphragm, and an elastically deforming portion are simply provided on the housing, it can be easily reduced in size and weight.

  According to the invention which concerns on Claim 2, even if the diaphragm is distribute | arranged to the position of an equilibrium state, a diaphragm can be efficiently adsorbed and fixed to a fixed electrode.

  According to the third aspect of the invention, since the diaphragm is forcibly adsorbed and fixed against the elastic force of the elastic deformation portion before the sound is generated, the elastic force is applied when the sound is generated. By utilizing this, the vibration displacement of the diaphragm can be reliably increased. Therefore, it is possible to reliably generate a sound with a large sound pressure.

  According to the fourth aspect of the present invention, the voltage applied between the diaphragm and the fixed electrode can be lowered, so that the acoustic transducer can be operated with power saving.

The acoustic transducer according to the first embodiment of the present invention will be described below with reference to FIGS. As shown in FIG. 1, the acoustic transducer 1 according to this embodiment is configured by disposing a diaphragm 5 inside a housing 3 formed with a cavity S1 opening outward. The housing 3 includes a substantially plate-like fixed electrode 7 that faces the opening 3a and forms the bottom wall portion of the housing 3, a substantially cylindrical side wall portion 9 disposed on the periphery of the surface 7a of the fixed electrode 7, and a side wall. It is comprised from the cover part 11 which is fixed to the upper part of the part 9 and has the opening part 3a.
The fixed electrode 7 is made of a conductive material, and is configured by providing an electret film 13 on a surface 7 a facing the diaphragm 5. The electret film 13 is covered with an electrical insulating film 15. In addition, as a specific material which comprises the electret film | membrane 13, organic materials, such as a fluororesin, inorganic materials, such as SiO2, etc. are mentioned, for example.

  The diaphragm 5 is disposed between the opening 3a and the fixed electrode 7 so as to be substantially parallel to the fixed electrode 7, and is supported with respect to the housing 3 by an elastic deformation portion 17 formed integrally therewith. ing. The elastically deformable portion 17 includes a substantially cylindrical bellows portion 19 and a thin-film-like flange portion 21 projecting radially outward from an upper end portion thereof, and the outer peripheral portion of the flange portion 21 is an upper portion of the side wall portion 9 and a lid body. It is sandwiched between the part 11 and fixed. As a result, the upper end portion of the bellows portion 19 is fixed to the periphery of the opening 3 a of the lid portion 11.

The lower end of the bellows part 19 is integrally connected to the outer peripheral edge of the diaphragm 5, and the diaphragm 5 is suspended from the peripheral edge of the opening 3 a of the lid part 11 by the bellows part 19. The bellows portion 19 is configured to be elastically deformed in the thickness direction so that the diaphragm 5 can vibrate in the thickness direction (AB direction).
In addition, the elastic deformation portion 17 is configured to dispose the diaphragm 5 away from the fixed electrode 7 in an equilibrium state where no elastic force is generated in the bellows portion 19. Further, the bellows portion 19 of the elastic deformation portion 17 can be elastically deformed and extended to a position where the diaphragm 5 contacts the fixed electrode 7 (see FIG. 3).
The diaphragm 5 and the elastic deformation portion 17 configured as described above can be integrally formed using, for example, a mold F shown in FIG. The mold F used here has a recess F2 that is recessed from the surface F1, and the inner peripheral surface of the recess F2 is formed in a bellows shape.

When the diaphragm 5 and the elastically deformable portion 17 are molded using the mold F, the concave portion F2 is formed with the polyimide film 23 formed in a thin film shape disposed on the surface F1 of the heated mold F. As shown in FIG. 2B, the polyimide film 23 is attached to the bottom surface of the recess F2 and the bellows-shaped inner peripheral surface by removing the air inside. Then, the bottomed cylindrical body 25 having the bellows portion 19 and the flange portion 21 are integrally formed by cooling the polyimide film 23 formed following the shape of the recess F2 and taking it out from the recess F2. Become.
Finally, as shown in FIG. 2 (c), a liquid glass epoxy resin 27 is placed on the bottom surface of the bottomed cylindrical body 25 and solidified, for example, so that it does not elastically deform at the lower end of the bellows portion 19. The diaphragm 5 can be formed.

As shown in FIG. 1, the diaphragm 5 has an electrode 29. The electrode 29 is formed on the surface 5 a of the diaphragm 5 facing the electret film 13 and the fixed electrode 7, and is connected to the wiring 31 formed on the outer peripheral surface of the bellows portion 19 and the surface of the flange portion 21. Yes. These electrodes 29 and wirings 31 can be formed, for example, by vapor deposition of gold plating.
The fixed electrode 7 and the electrode 29 of the diaphragm 5 are connected to a power supply unit 35, and the power supply unit 35 selectively applies an AC voltage and a DC voltage between the fixed electrode 7 and the electrode 29 of the diaphragm 5. Is configured to do. The power supply unit 35 can also turn on / off voltage application. Here, the frequency of the alternating voltage applied by the power supply unit 35 is equal to the resonance frequency of the diaphragm 5 based on the elastic modulus of the bellows part 19 and the weight of the diaphragm 5.

  As shown in FIG. 3, even if the bellows portion 19 is elastically deformed and the diaphragm 5 comes into contact with the fixed electrode 7, the electrode 29 of the diaphragm 5 is in contact with the insulating film 15 of the fixed electrode 7. The electrode 7 and the electrode 29 of the diaphragm 5 are electrically insulated from each other. Therefore, even if a voltage is applied between the fixed electrode 7 and the electrode 29 of the diaphragm 5 by the power supply unit 35 described above, an electrical short circuit does not occur between them.

The cavity S1 of the housing 3 is partitioned into a space S2 on the opening 3a side and a back air chamber S3 on the fixed electrode 7 side by the diaphragm 5 and the elastic deformation portion 17 having the above-described configuration.
Here, a plurality of holes 9 a, 9 a communicating the back air chamber S 3 outward are formed in the side wall portion 9, and the pressure increase / decrease in the back air chamber S 3 based on the vibration of the vibration plate 5 is increased. This prevents the vibration from being hindered. Further, by forming the holes 9 a and 9 a in the side wall portion 9, sound can be generated from the holes 9 a and 9 a by the vibration of the diaphragm 5.

Next, an operation when the acoustic transducer 1 configured as described above is used as a speaker will be described.
In the acoustic transducer 1, permanent charges are previously formed on the electret film 13 by high voltage or corona discharge. Specifically, for example, negative charges are collected on the surface side of the electret film 13 facing the diaphragm 5, and positive charges are collected on the back surface side of the electret film 13 in contact with the fixed electrode 7.
Before the sound is generated, the power supply unit 35 fixes the fixed electrode in a state where the bellows portion 19 of the elastically deforming portion 17 is extended by elastic deformation and the diaphragm 5 is brought into contact with the fixed electrode 7, as shown in FIG. A DC voltage is applied between the diaphragm 7 and the electrode 29 of the diaphragm 5, and the diaphragm 5 is attracted and fixed to the fixed electrode 7 by electrostatic attraction acting between the diaphragm 5 and the fixed electrode 7.

In this adsorption-fixed state, a DC voltage is applied so that charges having a polarity opposite to the permanent charge collected on the surface side of the electret film 13 are collected on the electrode 29 of the diaphragm 5. For example, when negative charges are collected on the surface side of the electret film 13, a voltage is applied to the diaphragm 5 so that positive charges are collected. Thereby, in addition to the electrostatic attractive force based on the voltage application, the electrostatic attractive force also acts between the electret film 13 and the diaphragm 5, so that the voltage applied between the diaphragm 5 and the fixed electrode 7 is reduced. Even in this case, the diaphragm 5 can be fixed to the fixed electrode 7.
In this state, an elastic force is generated in the bellows portion 19 so as to separate the diaphragm 5 from the fixed electrode 7. However, by making the total electrostatic attraction mentioned above larger than this elastic force. It is possible to maintain the above-described adsorption fixed state. In addition, since the fixed electrode 7 and the electrode 29 of the diaphragm 5 are electrically insulated by an insulating film, no current flows between the fixed electrode 7 and the electrode 29 of the diaphragm 5 in the adsorption fixed state. .

  When sound is generated from the acoustic transducer 1, the voltage application between the fixed electrode 7 and the diaphragm 5 by the power supply unit 35 is released in the state described above. At this time, the diaphragm 5 is separated from the fixed electrode 7 by the elastic force of the bellows part 19 and reaches a position where the bellows part 19 is in an equilibrium state as shown in FIG. As shown in FIG. 4, it is displaced to the opposite side of the position of the suction and fixation. Even in this state, since the elastic force is generated in the bellows part 19, the diaphragm 5 is displaced in a direction approaching the fixed electrode 7 by the elastic force of the bellows part 19 and the inertial force of the diaphragm 5. FIG. As shown in FIG. 4, the position is again returned to the suction fixing position. As described above, when the diaphragm 5 vibrates, sound is generated outward from the opening 3 a of the housing 3.

Further, when the diaphragm 5 vibrates and returns to the vicinity of the fixed electrode 7, a larger DC voltage may be applied again between the fixed electrode 7 and the electrode 29 of the diaphragm 5. As a result, even when the vibration of the vibration plate 5 is lost, energy is lost due to air resistance or the like, and the vibration plate 5 cannot return to the suction fixing position only by the elastic force of the bellows portion 19 and the inertial force of the vibration plate 5. The diaphragm 5 can be reliably fixed to the fixed electrode 7 by suction.
When sound is generated from the acoustic transducer 1, voltage is applied so that charges having the same polarity as the permanent charges collected on the surface side of the electret film 13 appear on the electrode 29 of the diaphragm 5 in the suction-fixed state. You may do it. In this case, since a repulsive force can be generated between the diaphragm 5 and the fixed electrode 7, the acoustic transducer 1 can be operated efficiently.

Further, in this acoustic transducer 1, when the diaphragm 5 is attracted and fixed to the fixed electrode 7 as shown in FIG. 3 from the state where the diaphragm 5 is arranged at the equilibrium position as shown in FIG. For example, an AC voltage having a frequency equal to the resonance frequency of the diaphragm 5 may be applied by the power supply unit 35.
That is, when the AC voltage is applied between the fixed electrode 7 and the electrode 29 of the diaphragm 5 in a state where the diaphragm 5 is arranged at an equilibrium position, the fixed electrode 7 and the electrode 29 of the diaphragm 5 Since the amplitude of the diaphragm 5 gradually increases due to the alternating electric field generated therebetween, the diaphragm 5 can be brought closer to the fixed electrode 7. When the diaphragm 5 comes into contact with the fixed electrode 7 or when the diaphragm 5 is sufficiently close to the fixed electrode 7, a DC voltage is applied between the fixed electrode 7 and the electrode 29 of the diaphragm 5 by the power supply unit 35. Thus, the diaphragm 5 can be fixed to the fixed electrode 7 by suction.
At the time of this adsorption fixation, it is necessary to apply a voltage to the extent that electrostatic attraction acts between the electrode 29 of the diaphragm 5 and the fixed electrode 7 arranged at the equilibrium position. However, even in this case, since the diaphragm 5 can be moved using the electrostatic attraction generated between the electrode 29 of the diaphragm 5 and the electret film 13, compared to the case without the electret film 13, The applied voltage can be kept low.

According to the acoustic transducer 1, the diaphragm 5 is vibrated from the state in which the diaphragm 5 is forcibly fixed to the fixed electrode 7 against the elastic force of the bellows portion 19 in advance before the sound is generated. The diaphragm 5 can be vibrated with amplitude. Therefore, the vibration displacement of the diaphragm 5 can be increased to generate a sound with a greater sound pressure.
Further, since the acoustic transducer 1 has a simple configuration in which the housing 3 is provided with the fixed electrode 7, the diaphragm 5, and the elastic deformation portion 17, the size and weight can be easily reduced.

Furthermore, even when the diaphragm 5 is arranged at a position in an equilibrium state, the diaphragm 5 is efficiently adsorbed to the fixed electrode 7 by applying an AC voltage having a frequency equal to the resonance frequency of the diaphragm 5 by the power supply unit 35. Can be fixed.
Further, by providing the electret film 13, an acoustic transducer such as an applied voltage for attracting and fixing the diaphragm 5 to the fixed electrode 7 from an equilibrium position, an applied voltage for holding the diaphragm 5 in the attracted and fixed state, etc. Since the applied voltage for operating 1 can be lowered, the acoustic transducer 1 can be operated with power saving.

In the first embodiment, the AC voltage is applied between the diaphragm 5 and the fixed electrode 7 before the sound is generated to fix the diaphragm 5 to the fixed electrode 7. However, the present invention is not limited to this. For example, only the DC voltage may be applied between the diaphragm 5 and the fixed electrode 7 so that the diaphragm 5 is attracted and fixed to the fixed electrode 7.
Moreover, in the said embodiment, although the electret film | membrane 13 was provided in the surface 7a which opposes the diaphragm 5, and the fixed electrode 7 was comprised, for example, the same electret film | membrane 13 is provided in the surface 5a which opposes the fixed electrode 7. The diaphragm 5 may be configured by providing it. In this configuration, it is preferable to arrange the electret film 13 so as to cover the electrode 29 of the diaphragm 5, and it is preferable to cover the electret film 13 with the insulating film 15 as in the above embodiment. Even in this configuration, similarly to the above embodiment, the voltage applied between the diaphragm 5 and the fixed electrode 7 can be lowered, so that the acoustic transducer 1 can be operated with power saving.

  Moreover, although the diaphragm 5 and the fixed electrode 7 are configured to be provided with the electret film 13, they may not be particularly provided. However, in this case, the insulating film 15 is formed on one of the surfaces 5 a and 7 a of the diaphragm 5 and the fixed electrode 7 facing each other, so that the fixed electrode 7 and the electrode 29 of the diaphragm 5 It is necessary not to short-circuit between them. Here, in order to attract the diaphragm 5 to the fixed electrode 7 with a low voltage, it is preferable to reduce the film thickness of the insulating film 15, and specifically to set the film thickness to several μm.

Furthermore, although the elastic deformation part 17 was formed with the polyimide film 23, it is not restricted to this, It should just be formed with the material which can be elastically deformed at least.
The diaphragm 5 is formed of the polyimide film 23 and the glass epoxy resin 27. However, the diaphragm 5 is not limited to this and may be formed in a substantially plate shape that does not elastically deform at least.
Furthermore, the electrode 29 of the diaphragm 5 is attached to the surface 5a of the diaphragm 5. However, the present invention is not limited to this. For example, the diaphragm 5 itself is formed of a conductive material. May function as an electrode.

  Next, a second embodiment according to the present invention will be described with reference to FIGS. The acoustic transducer according to the second embodiment is different from the first embodiment mainly in the configuration of the diaphragm and the elastic deformation portion. Here, the above differences will be mainly described, and the same components as those of the acoustic transducer 1 of the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

As shown in FIG. 5, the housing 43 constituting the acoustic transducer 41 of the second embodiment includes a lid 47 having a fixed electrode 7, a cylindrical side wall 45, and an opening 43 a similar to those of the first embodiment. I have.
However, the lid portion 47 is made of a conductive material and forms a counter electrode 49 that faces the fixed electrode 7. The fixed electrode 7 and the counter electrode 49 are connected to the power source unit 35 similar to that of the first embodiment. ing. That is, in the acoustic transducer 41, a voltage is applied between the fixed electrode 7 and the counter electrode 49. Moreover, the side wall part 45 is comprised so that the elastic deformation part 53 mentioned later may be fixed to the inside.

As shown in FIGS. 5 and 6, the diaphragm 51 is disposed between the lid body 47 including the opening 43 a and the fixed electrode 7 so as to be substantially parallel to the fixed electrode 7 and the counter electrode 49. Are supported with respect to the housing 43 by a plurality of (four in the illustrated example) elastic deformation portions 53, 53,. Note that the diameter dimension of the diaphragm 51 formed in a substantially circular shape in plan view as in the illustrated example is larger than the diameter dimension of the opening 43a.
Each elastically deforming portion 53 is formed to extend in the surface direction from the periphery of the diaphragm 51, and the tip portion thereof is fixed to the side wall portion 45 of the housing 43. Each elastic deformation portion 53 is formed so as to meander from the diaphragm 51 toward the side wall portion 45 as shown in the drawing, and is configured to be easily elastically deformable. The plurality of elastic deformation portions 53, 53,... Are arranged at equal intervals in the circumferential direction of the diaphragm 51 and are formed integrally with the diaphragm 51.

  The vibration plate 51 can vibrate in its own thickness direction (CD direction) by elastically deforming the elastic deformation portion 53, and the vibration deformation portion 53 is configured such that the vibration plate 51 is fixed electrode 7 or counter electrode. 49 can be elastically deformed and extended to a position in contact with 49. The elastically deforming portion 53 is arranged so that the diaphragm 51 is separated from the fixed electrode 7 and the counter electrode 49 in an equilibrium state where no elastic force is generated. Specifically, the diaphragm 51 is arranged at a position where the distances from both the fixed electrode 7 and the counter electrode 49 are equal in the equilibrium state.

The diaphragm 51 and the elastic deformation portion 53 are integrally formed by an electret 55 such as an organic material such as a fluororesin or an inorganic material such as SiO2. The diaphragm 51 and the elastic deformation portion 53 can be integrally formed by forming a resist pattern having the shape of the vibration plate 51 and the elastic deformation portion 53 on the substantially plate-like electret 55 and performing etching, for example. In addition, about the part which forms the elastic deformation part 53, it should just etch to the thinness which can be elastically deformed.
In addition, since the diaphragm 51 is formed by the electret 55 that is a dielectric, even if the diaphragm 51 contacts the fixed electrode 7 or the counter electrode 49, the fixed electrode 7 or the counter electrode 49 and the diaphragm 51 There is no charge transfer between them.

  The acoustic transducer 41 includes partition plates 57, 57,... That project inward from the side wall portion 45 and block the gap formed between the diaphragm 51 and the side wall portion 45. The plates 57, 57,... And the diaphragm 51 generate an air flow between the space S2 on the opening 43a side forming the cavity S1 and the back air chamber S3 on the fixed electrode 7 side. Suppressed.

Next, an operation when the acoustic transducer 41 configured as described above is used as a speaker will be described. In the acoustic transducer 41, the diaphragm 51 made of the electret 55 is charged in advance to one of positive and negative by high voltage or corona discharge.
Further, a DC voltage is applied so that a charge opposite to the permanent charge in the electret 55 appears on the fixed electrode 7 in a state where the elastically deforming portion 53 is extended by elastic deformation and the diaphragm 51 is in contact with the fixed electrode 7. The diaphragm 51 is attracted and fixed to the fixed electrode 7 by electrostatic attraction acting between the diaphragm 51 and the fixed electrode 7. In this suction-fixed state, an elastic force that tries to separate the diaphragm 51 from the fixed electrode 7 is generated in the elastic deformation portion 53. By making the electrostatic attraction force larger than this elastic force, It is possible to maintain the above-described adsorption fixed state.

Then, when generating sound from the acoustic transducer 41, as in the case of the first embodiment, the voltage application by the power supply unit 35 is canceled in the above-described state, so that the diaphragm 51 has the elastic deformation portion 53. It will vibrate by the elastic force and its own inertial force and return to the position of adsorption fixation. That is, sound is generated outward from the opening 43 a of the housing 43 by the vibration of the diaphragm 51.
Further, when the diaphragm 51 vibrates and returns to the vicinity of the fixed electrode 7, the diaphragm 51 can be reliably fixed to the fixed electrode 7 by applying a DC voltage again.
When generating sound from the acoustic transducer 41, a voltage may be applied so that a charge having the same polarity as the permanent charge of the electret 55 appears on the fixed electrode 7 in the suction-fixed state. In this case, since the repulsive force can be generated between the diaphragm 51 and the fixed electrode 7, the acoustic transducer 41 can be operated efficiently.

Further, in the acoustic transducer 41, when the diaphragm 51 is attracted and fixed to the fixed electrode 7 from the state where the diaphragm 51 is arranged at the equilibrium position, for example, the resonance frequency of the diaphragm 51 by the power supply unit 35 is used. An AC voltage having the same frequency as that of the fixed electrode 7 and the counter electrode 49 may be applied.
In other words, when the AC voltage is applied between the fixed electrode 7 and the counter electrode 49 in a state where the diaphragm 51 is arranged at the equilibrium position, the counter electrode is connected between the fixed electrode 7 and the diaphragm 51. 49, the amplitude of the diaphragm 51 gradually increases due to an alternating electric field generated between the diaphragm 49 and the diaphragm 51, so that the diaphragm 51 can be brought closer to the fixed electrode 7 and the counter electrode 49. Then, when the diaphragm 51 comes into contact with the fixed electrode 7 or when the diaphragm 51 is sufficiently close to the fixed electrode 7, a direct current is applied to the fixed electrode 7 by the power supply unit 35 so that a charge having a polarity opposite to that of the electret 55 appears. The diaphragm 51 can be attracted to the fixed electrode 7 by applying a voltage.

  According to the acoustic transducer 41, the same effects as those of the first embodiment can be obtained. Further, in the case of this configuration, in a state where the diaphragm 51 is arranged at a balanced position, the power supply unit 35 applies an AC voltage having a frequency equal to the resonance frequency of the diaphragm 51 between the fixed electrode 7 and the counter electrode 49. By applying the voltage between them, not only the AC electric field generated between the fixed electrode 7 and the diaphragm 51 but also the AC electric field generated between the counter electrode 49 and the diaphragm 51 is used. Can be increased efficiently. Therefore, the diaphragm 51 can be adsorbed and fixed to the fixed electrode 7 in a shorter time than in the case of the first embodiment.

In the second embodiment, the entire lid part 47 forms the counter electrode 49 that faces the fixed electrode 7. However, the present invention is not limited to this, and at least the opening 43 a of the housing 43 in the lid part 47. As long as the peripheral portion of the elastic member 51 is a counter electrode facing the fixed electrode 7, the diaphragm 51 may be in contact with the counter electrode by elastic deformation of the elastic deformation portion 53.
The elastic deformation portion 53 is not limited to the meandering shape extending in the radial direction of the diaphragm 51 as described above, and may be, for example, a meandering shape extending in a direction along a part of the outer periphery of the diaphragm 51. It may be corrugated.

Furthermore, although the elastic deformation portion 53 is directly connected to the diaphragm 51, the present invention is not limited to this. For example, as shown in FIGS. 7 and 8, a part of the outer periphery of the diaphragm 51 is provided. May be connected to the diaphragm 51 via arcuate support portions 60 and 61 extending in a direction along the direction.
Here, each elastic deformation portion 53 shown in FIG. 7 is processed into a linear shape extending in the radial direction of the vibration plate 51, and is connected to the vibration plate 51 via the support portion 60. The support part 60 is disposed between two adjacent elastic deformation parts 53. One end of the support portion 60 is connected to the diaphragm 51 with a gap between one of the two adjacent elastic deformation portions 53, and the other end of the support portion 60 is connected to the other elastic deformation portion 53. ing. Moreover, the elastic deformation part 53 and the support part 60 are surrounded by the partition plate 57 so as to form a gap with the partition plate 57 processed so as to follow these shapes.

Thus, the diaphragm 51 is connected to the elastic deformation part 53 via the support part 60, and the amplitude of the vibration plate 51 is further increased by surrounding the elastic deformation part 53 and the support part 60 with the partition plate 57. Can do. Further, since the gap between the partition plate 57 and the elastically deforming portion 53 and the support portion 60 becomes an air resistance, when the diaphragm 51 moves from the fixed electrode 7 to the counter electrode 49, the back air chamber S3 on the fixed electrode 7 side. It is possible to suppress the flow of air toward.
Each elastically deforming portion 53 shown in FIG. 8 is formed to meander from the vibration plate 51 toward the side wall portion 45, and a support portion 61 extending in a direction along a part of the outer periphery of the vibration plate 51 is provided. And is connected to the diaphragm 51. By forming in this way, the amplitude of the diaphragm 51 can be further increased.

Furthermore, although the elastically deformable portion 53 is formed by the same electret 55 as that of the diaphragm 51, it is not limited to this, and may be the same material or a different member, and at least elastically deformable as a result of selection of the shape and material. It only has to be.
In addition, although the diaphragm 51 is entirely composed of the electret 55, the present invention is not limited to this, and it is sufficient that at least a part of the diaphragm 51 is formed by the electret 55.

  Furthermore, although the diaphragm 51 is an electrostatic capacity type in which at least a part thereof is formed by the electret 55, the present invention is not limited to this and may be a capacitor type. In this case, the diaphragm 51 may be formed of a conductive material and connected to the external electrode. When the diaphragm 51 is formed in this way, the diaphragm 51 can be vibrated by changing the voltage applied to the diaphragm 51, the fixed electrode 7 and the counter electrode 49.

  Furthermore, the acoustic transducer 41 having the configuration shown in FIGS. 5 to 8 can be configured using two substrates 70 and 80, for example, as shown in FIGS. That is, the acoustic transducer 91 shown in FIGS. 9 to 14 is an upper side of the acoustic transducer 41 according to the second embodiment that forms the side wall 45, the lid body 47, the counter electrode 49, the vibration plate 51, the elastic deformation portion 53, and the partition plate 57. A substrate 70 and a lower substrate 80 forming the fixed electrode 7 are included.

As shown in FIGS. 10 to 14, the upper substrate 70 is an insulating film 102 that forms the side wall 45 and the partition plate 57 in the second embodiment on the surface of the polysilicon substrate 101 in which the opening 43 a penetrating in the thickness direction is formed. And a stopper layer (second stopper layer) 110 are sequentially stacked, and the tip of the elastically deformable portion 53 extending in the radial direction from the diaphragm 51 side is fixed between the insulating film 102 and the stopper layer 110. ,It is configured.
Here, the insulating film 102 and the stopper layer 110 are formed of an insulating material. Further, by arranging the diaphragm 51 on the inner peripheral side of the partition plate 57, a space S2 similar to that of the second embodiment is formed. In addition, the code | symbol F in the example of illustration has shown the area | region corresponding to the side wall part 45 in 2nd Embodiment among the insulating films 102 and the stopper layer 110. FIG.

  Further, the upper substrate 70 is configured by forming an annular conductive layer 201 on the inner periphery of the surface of the polysilicon substrate 101. Here, the conductive layer 201 is formed so as to draw out the wiring to the outer edge of the surface of the polysilicon substrate 101 in order to be electrically connected to a power supply unit (not shown). That is, the polysilicon substrate 101 forms the lid portion 47 in the second embodiment, and the conductive layer 201 forms the counter electrode 49 in the second embodiment. In the acoustic transducer 91, since the vibration film 51 is formed of a conductive material, an insulating film 202 is formed on the surface of the conductive layer 201.

As shown in FIG. 9, the lower substrate 80 is disposed on the stopper layer 110, thereby forming the same space S3 as in the second embodiment. In the region F of the stopper layer 110, a recess 151 is formed for forming a hole 150 that allows the back air chamber S3 to communicate with the lower substrate 80 outward.
As shown in FIGS. 9, 13, and 14, the lower substrate 80 is configured by forming a conductive layer 401 on the surface of a polysilicon substrate 301 that is disposed to face the diaphragm 51. Here, the conductive layer 401 is formed so as to lead out the wiring to the outer edge of the surface of the polysilicon substrate 301 in order to be electrically connected to a power supply unit (not shown).

An insulating film 402 is formed on the surface of the conductive layer 401. Note that, in the illustrated example, a plurality of insulating films 402 formed in a circular shape or an annular shape are arranged at intervals, and the conductive layer 401 is exposed from the gap between the insulating films 402. The film 402 only needs to be formed on at least part of the surface of the conductive layer 401 facing the diaphragm 51.
The lower substrate 80 configured as described above constitutes the fixed electrode 7 in the second embodiment.

Next, an example of a method for manufacturing the acoustic transducer 91 will be described. When the acoustic transducer 91 is manufactured, the upper substrate 70 and the lower substrate 80 are individually manufactured in advance.
When manufacturing the upper substrate 70 shown in FIGS. 9 to 12, first, as shown in FIG. 15, the insulating film 102 is formed on the surface of the polysilicon substrate 101 having a thickness of 500 to 600 μm. Here, the insulating film 102 is preferably formed by sequentially stacking a silicon oxide layer and a silicon nitride layer from the bottom. The thickness of the insulating film 102 can be about 5 to 25 μm, preferably 10 μm.
Next, in order to form the partition plate 57 on the opening 43a side in the insulating film 102, as shown in FIGS. 16 and 17, etching is performed using the resist 103 as a mask to form a recess S. Note that the resist 103 is removed after the etching.

  Then, in order to form an annular conductive layer 201 on the surface of the polysilicon substrate 101 in which the recess S is formed, as shown in FIG. 18, the resist 104 is used as a mask so as to follow the shape of an opening 43a described later. Doping such as (phosphorus) is performed. After this doping, the resist 104 is removed and heat treatment is performed to form a conductive layer (diffusion layer) 201 on the polysilicon substrate 101 as shown in FIG. Note that a wiring portion (see FIG. 11) of the conductive layer 201 drawn from the annular portion of the conductive layer 201 to the outer edge of the surface of the polysilicon substrate 101 is also formed in this step.

Further, as shown in FIG. 20, in order to form an insulating film 202 on the conductive layer 201, about 100 to 250 mm of silicon oxide (pad oxidation) is formed on the surface side of the polysilicon substrate 101, and silicon nitride (insulating film). Is deposited about 1000 to 3000 mm. As shown in FIGS. 21 and 22, the insulating film 202 made of silicon oxide (pad oxidation) and silicon nitride (insulating film) is selectively formed using an annular resist 106 corresponding to the annular conductive layer 201 as a mask. It can be processed into a predetermined shape by etching. Note that the resist 106 may be removed after etching.
Then, as shown in FIG. 23, silicon oxide to be the first stopper layer 107 is deposited on the surface side of the polysilicon substrate 101, and the first stopper layer 107 is planarized as shown in FIG. For the planarization, for example, CMP (Chemical mechanical polishing) is used. Further, the planarization is performed until the insulating film 102 is exposed.

Thereafter, as shown in FIG. 25, in order to form the diaphragm 51 and the elastically deformable portion 53, a polysilicon film in which P (phosphorus) or the like is added as an impurity on the surface of the first stopper layer 107 and the insulating film 102 108 is deposited to about 0.5 μm. The polysilicon film 108 is selectively etched by anisotropic etching such as RIE (Reactive Ion Etching) using a photoresist mask 109 as shown in FIG. The deformed portion 53 is processed into a shape.
Then, as shown in FIG. 27, silicon oxide to be the second stopper layer 110 is deposited so as to cover the etched polysilicon film 108. Planarization is performed if necessary. If part of the partition plate 57 is preferably a conductor, a polysilicon film may be deposited as the second stopper layer 110.

Finally, the upper substrate 70 can be obtained by etching the deposited polysilicon substrate 101.
That is, as shown in FIG. 28, the first stopper layer 107 is formed on the back side of the polysilicon substrate 101 by anisotropic etching such as deep RIE using a photoresist mask 111 so as to have the shape of the opening 43a. The polysilicon substrate 101 is etched until it is exposed. On the other hand, on the surface side of the polysilicon substrate 101, the diaphragm 51 is anisotropically etched using a photoresist mask (not shown) so that the second stopper layer 110 has a shape such as the partition plate 57 and the depression 151. The second stopper layer 110 is selectively etched until the polysilicon film 108 forming the elastically deforming portion 53 is exposed.
After this etching, etching is performed to match the inner edge of the insulating film 202 made of silicon oxide (pad oxidation) and silicon nitride (insulating film) with the shape of the opening 43a. Further, as shown in FIG. 29, the silicon oxide (first stopper layer 107) around the diaphragm 51 is selectively etched away by wet etching using, for example, buffered hydrofluoric acid (Buffered HF). As described above, the manufacture of the upper substrate 70 is completed.

When manufacturing the lower substrate 80 shown in FIGS. 9, 13, and 14, the surface of the polysilicon substrate 301 having a thickness of 500 to 600 μm is doped with P (phosphorus) or the like in accordance with the shape of the diaphragm 51. The conductive layer 401 is formed, and the insulating film 402 may be formed over part of the conductive layer 401.
Finally, the upper substrate 70 and the lower substrate 80 are bonded together, whereby the manufacture of the acoustic transducer 91 is completed.

  In the above-described manufacturing method, the vibration plate 51 and the elastically deformable portion 53 are formed of the polysilicon film 108 to which P (phosphorus) or the like is added as an impurity. However, the present invention is not limited to this. A silicon film (SiN), a silicon oxynitride film (SiON film), a layer structure combining these materials, a layer structure in which the aforementioned polysilicon film 108 is covered with an insulating film such as a silicon nitride film or a silicon oxynitride film, or Alternatively, a silicon oxide film can be used. Capacitance type acoustic transducer 91 can be manufactured by a semiconductor process by charging diaphragm 51 made of such an insulating material to one of positive and negative by high voltage or corona discharge.

In this embodiment, one acoustic transducer 91 is disclosed. However, the present invention is not limited to this, and a plurality of acoustic transducers can be arranged in an array.
By arranging in this way, it is possible to configure a digital speaker that reproduces an analog waveform by a plurality of acoustic transducers. That is, a large sound pressure can be obtained by causing the acoustic transducers arranged in an array to function as if they were one speaker. It is also possible to simultaneously form a plurality of acoustic transducers on a single wafer using a semiconductor process.

In all the embodiments described above, the housings 3 and 43 are not limited to the fixed electrode 7, the side wall portions 9 and 45, and the lid body portions 11 and 47, but at least the cavity S 1 that opens outward. And the side wall portions 9 and 45 and the lid portions 11 and 47 may be integrally formed, for example.
In all the embodiments described above, the diaphragms 5 and 51 are arranged so as to be substantially parallel to the fixed electrode 7 and the counter electrode 49. However, at least the equilibrium state and the diaphragm 5 are attracted to the fixed electrode 7. In this state, the diaphragms 5 and 51 may be arranged so as to be substantially parallel to the fixed electrode 7 and the counter electrode 49. And the diaphragms 5 and 51 should just be substantially parallel including the inclination to the fixed electrode 7 or the counter electrode 49 in the state which this is vibrating.

  Moreover, all the acoustic transducers 1, 41, 91 described above are not limited to being used as speakers, but can also be used as microphones for detecting sound. That is, the sound that reaches the diaphragms 5 and 51 through the openings 3 a and 43 a of the housings 3 and 43 can be detected by the vibration of the diaphragms 5 and 51. For example, in the acoustic transducer 1 of the first embodiment, the vibration of the diaphragm 5 can be detected by a change in electrostatic capacitance between the fixed electrode 7 and the electrode 29 of the diaphragm 5. In the acoustic transducer 41 of the second embodiment, the vibration of the diaphragm 51 can be detected by a change in electrostatic capacitance between the diaphragm 51 and the fixed electrode 7 or the counter electrode 49.

  As mentioned above, although embodiment of this invention was explained in full detail with reference to drawings, the concrete structure is not restricted to this embodiment, The design change etc. of the range which does not deviate from the summary of this invention are included.

1 is a side sectional view showing a schematic configuration of an acoustic transducer according to a first embodiment of the present invention. It is a schematic sectional side view which shows an example of the manufacturing method of the diaphragm and elastic deformation part which comprise the acoustic transducer shown in FIG. FIG. 2 is a schematic cross-sectional side view showing a state in which the diaphragm is attracted and fixed to a fixed electrode in the acoustic transducer shown in FIG. 1. In the acoustic transducer shown in FIG. 1, it is a schematic sectional side view which shows the state by which the diaphragm was arrange | positioned in the position most distant from the fixed electrode. It is a sectional side view which shows schematic structure of the acoustic transducer based on 2nd Embodiment of this invention. 6 is a plan sectional view showing a schematic configuration of a diaphragm, an elastic deformation portion, and a partition plate as viewed from the opening side of the housing in the acoustic transducer shown in FIG. FIG. 7 is a plan sectional view showing a modification of the acoustic transducer shown in FIGS. FIG. 7 is a plan sectional view showing a modification of the acoustic transducer shown in FIGS. It is a sectional side view which shows schematic structure of the acoustic transducer which concerns on other embodiment of this invention. FIG. 10 is a side sectional view showing a schematic configuration of an upper substrate constituting the acoustic transducer of FIG. 9. It is BB arrow sectional drawing of FIG. It is a top view which shows the state which looked at the upper board | substrate of FIG. 10 from the diaphragm side. It is a sectional side view which shows schematic structure of the lower board | substrate which comprises the acoustic transducer of FIG. It is DD sectional view taken on the line of FIG. FIG. 11 is a cross-sectional view showing a state in which an insulating film is formed on the surface of a polysilicon substrate in the method for manufacturing the upper substrate shown in FIG. 10. FIG. 11 is a sectional view showing a state in which a resist is formed on an insulating film in the method for manufacturing the upper substrate shown in FIG. 10. FIG. 11 is a cross-sectional view showing a state after the insulating film is etched and the resist is removed in the method for manufacturing the upper substrate shown in FIG. 10. FIG. 11 is a cutaway view showing a state in which a resist is formed on the surface side of a polysilicon substrate in the method for manufacturing the upper substrate shown in FIG. 10. FIG. 11 is a cutaway view showing a state in which a conductive layer is formed on the surface of a polysilicon substrate in the method for manufacturing the upper substrate shown in FIG. 10. FIG. 11 is a cutaway view showing a state in which an insulating film is formed on the surface side of a polysilicon substrate in the method for manufacturing the upper substrate shown in FIG. 10. FIG. 11 is a cross-sectional view showing a state where an annular resist is formed on the surface of the insulating film in the method for manufacturing the upper substrate shown in FIG. 10. FIG. 11 is a cross-sectional view showing a state after the insulating film is etched and the resist is removed in the method for manufacturing the upper substrate shown in FIG. 10. FIG. 11 is a cross-sectional view showing a state in which a first stopper layer is formed on the surface side of a polysilicon substrate in the method for manufacturing the upper substrate shown in FIG. 10. FIG. 11 is a cross-sectional view showing a state in which the first stopper layer is planarized in the method for manufacturing the upper substrate shown in FIG. 10. FIG. 11 is a cross-sectional view showing a state in which a polysilicon film is deposited on the surface of the first stopper layer and the insulating film in the method for manufacturing the upper substrate shown in FIG. 10. FIG. 11 is a cross-sectional view showing a state in which a diaphragm and a resist for forming an elastic deformation portion are formed on a polysilicon film in the method for manufacturing the upper substrate shown in FIG. 10. FIG. 11 is a cross-sectional view showing a state in which a second stopper layer is formed on the diaphragm and the elastically deformed portion in the method for manufacturing the upper substrate shown in FIG. 10. FIG. 11 is a cross-sectional view showing a step of forming an opening in a polysilicon substrate in the method for manufacturing the upper substrate shown in FIG. 10. FIG. 11 is a side sectional view showing a state where an unnecessary stopper layer is removed in the method for manufacturing the upper substrate shown in FIG. 10.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,41,91 ... Acoustic transducer, 3,43 ... Housing, 3a, 43a ... Opening part, 5,51 ... Diaphragm, 7 ... Fixed electrode, 7a ... Surface, DESCRIPTION OF SYMBOLS 13 ... Electret film | membrane, 17, 53 ... Elastic deformation part, 29 ... Electrode, 35 ... Power supply part, 55 ... Electret, 80 ... Lower board | substrate (fixed electrode), S1 ..・ Cavity

Claims (5)

A housing formed with a cavity opening outward,
A substantially plate-like fixed electrode that forms part of the wall of the housing opposite to the opening;
A diaphragm having an electrode and disposed between the opening and the fixed electrode;
An elastically deformable elastically deformable portion that supports the housing so as to vibrate the diaphragm in its thickness direction;
The fixed electrode and the electrode of the diaphragm are electrically insulated from each other;
The elastically deforming portion is arranged to be spaced apart from the fixed electrode in an equilibrium state where no elastic force is generated in the elastically deforming portion, and can be elastically deformed to a position where the vibrating plate contacts the fixed electrode. An acoustic transducer. A power supply unit that selectively applies an AC voltage and a DC voltage between the fixed electrode and the electrode of the diaphragm;
2. The acoustic transducer according to claim 1, wherein the frequency of the AC voltage is equal to a resonance frequency of the diaphragm based on an elastic modulus of the elastic deformation portion and a weight of the diaphragm.   The acoustic transducer according to claim 2, wherein the diaphragm is adsorbed and fixed at a position in contact with the fixed electrode by applying the AC voltage or the DC voltage before the sound is generated.   The acoustic transducer according to any one of claims 1 to 3, wherein one of the diaphragm and the fixed electrode is configured by providing an electret film on a surface facing the other. A housing formed with a cavity opening outward,
A substantially plate-like fixed electrode that forms part of the wall of the housing opposite to the opening;
A diaphragm disposed between the opening and the fixed electrode;
An elastically deformable elastically deformable portion that supports the housing so that the diaphragm can vibrate in the thickness direction;
The elastically deforming portion is arranged to be spaced apart from the fixed electrode in an equilibrium state where no elastic force is generated in the elastically deforming portion, and can be elastically deformed to a position where the vibrating plate contacts the fixed electrode. And
An acoustic transducer, wherein the diaphragm includes an electret charged on one of positive and negative sides.

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