JP2007228472A - Electrostatic ultrasonic transducer, configuration method of electrostatic ultrasonic transducer, and ultrasonic speaker - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrostatic ultrasonic transducer for furthermore increasing an output sound pressure. <P>SOLUTION: The electrostatic ultrasonic transducer is characterized by including: a first fixed electrode formed with a plurality of throughholes; a second fixed electrode formed with a plurality of throughholes and in pairs with the first fixed electrode; a conductor layer sandwiched between the fixed electrodes in pairs, the conductor layer including a vibration membrane to which a DC bias voltage is applied, wherein a plurality of fixed electrode structures receiving an AC signal are laminated between the fixed electrodes in pairs in parallel in a way that positions of the throughholes corresponding to the fixed electrode structures are coincident with each other, and a vibration part of the vibration membrane of the other fixed electrode structure acts on excitation to a vibration part of the vibration membrane of the one fixed electrode structure forming a sound wave radiation face to an external part. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

  The present invention relates to an electrostatic ultrasonic transducer, a method for constructing an electrostatic ultrasonic transducer, and an ultrasonic speaker capable of increasing an output sound pressure as compared with a conventional electrostatic ultrasonic transducer. .

  The ultrasonic transducer can reproduce a sound having a sharp directivity by outputting a modulated wave obtained by modulating a carrier wave in an ultrasonic frequency band with an acoustic signal in an audible band.

  FIG. 7 is a diagram illustrating a configuration example of a conventional piezoelectric ultrasonic transducer. Most conventional ultrasonic transducers are resonant types using piezoelectric ceramics. A piezoelectric ultrasonic transducer uses a piezoelectric ceramic as a vibration element to perform both conversion from an electric signal to ultrasonic waves and conversion from ultrasonic waves to electric signals (transmission and reception of ultrasonic waves).

  The bimorph type ultrasonic transducer shown in FIG. 7 includes two piezoelectric ceramics 61 and 62, a cone 63, a case 64, leads 65 and 66, and a screen 67. The piezoelectric ceramics 61 and 62 are bonded to each other, and a lead 65 and a lead 66 are connected to a surface opposite to the bonded surface, respectively.

  Since the piezoelectric ultrasonic transducer utilizes the resonance phenomenon of piezoelectric ceramic, the transmission and reception characteristics of ultrasonic waves are good in a relatively narrow frequency band around the resonance frequency. However, since the piezoelectric transducer utilizes the sharp resonance characteristics of the element, a high sound pressure can be obtained, but the frequency band is very narrow. For this reason, an ultrasonic speaker using a piezoelectric transducer has a narrow reproducible frequency band, and there is a tendency that reproduced sound quality is poor as compared with a loudspeaker.

  Unlike the piezoelectric transducers described above, electrostatic ultrasonic transducers are conventionally known as broadband oscillation ultrasonic transducers that can generate high sound pressure over a high frequency band. FIG. 8 shows a configuration example of a broadband oscillation type electrostatic ultrasonic transducer. This electrostatic ultrasonic transducer is called a pull type because it works only in the direction in which the vibrating membrane is attracted to the fixed electrode side.

  The electrostatic ultrasonic transducer shown in FIG. 8 uses a dielectric 131 (insulator) such as PET (polyethylene terephthalate resin) having a thickness of about 3 to 10 μm as a vibrating body (vibrating film). An upper electrode 132 formed as a metal foil such as aluminum is integrally formed on the upper surface of the dielectric 131 by a process such as vapor deposition, and a lower electrode 133 formed of brass is formed on the lower surface of the dielectric 131. It is provided so that it may contact a part. The lower electrode 133 is connected to a lead 152 and fixed to a base plate 135 made of bakelite or the like. The upper electrode 132 is connected to a lead 153, and the lead 153 is connected to the DC bias power supply 150. A DC bias voltage for attracting the upper electrode of about 50 to 150 V is constantly applied to the upper electrode 132 by the DC bias power source 150, and the upper electrode 132 is attracted to the lower electrode 133 side. Reference numeral 151 denotes a signal source. The dielectric 131, the upper electrode 132, and the base plate 135 are caulked by the case 130 together with the metal rings 136, 137, and 138 and the mesh 139.

  On the surface of the lower electrode 133 on the dielectric 131 side, a plurality of minute grooves (uneven portions) having a non-uniform shape of about several tens to several hundreds of μm are formed. Since this minute groove becomes a gap between the lower electrode 133 and the dielectric 131, the electrostatic capacity distribution between the upper electrode 132 and the lower electrode 133 changes minutely. These random minute grooves are formed by manually roughing the surface of the lower electrode 133 with a file. An electrostatic ultrasonic transducer has a wide frequency characteristic by forming innumerable capacitors having different gap sizes and depths (Patent Documents 1 and 2).

As described above, the electrostatic ultrasonic transducer shown in FIG. 8 is conventionally known as a broadband ultrasonic transducer (Pull type) capable of generating a relatively high sound pressure over a wide frequency band. .
(See Patent Documents 1 and 2).
JP 2000-50387 A JP 2000-50392 A

  However, the sound pressure output from the conventional electrostatic ultrasonic transducer described above depends on the magnitude of the electrostatic force acting on the vibrating membrane, and the output sound pressure may not be sufficient. Recently, there has been a strong demand for miniaturization and high performance of devices, and some structural ingenuity has been required to achieve further increase in sound pressure in electrostatic ultrasonic transducers.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an electrostatic ultrasonic transducer, an electrostatic ultrasonic transducer capable of further increasing the output sound pressure in the electrostatic ultrasonic transducer. An object of the present invention is to provide a method of constructing an acoustic transducer and an ultrasonic speaker.

The present invention has been made to solve the above problems, and an electrostatic ultrasonic transducer according to the present invention includes a first fixed electrode in which a plurality of through holes are formed, and a pair of the first fixed electrode and the first fixed electrode. A second fixed electrode having a plurality of through holes formed therein, a conductive layer sandwiched between the pair of fixed electrodes, and a vibrating membrane to which a DC bias voltage is applied to the conductive layer, A plurality of fixed electrode structures to which an AC signal is applied between a pair of fixed electrodes are stacked in parallel so that the positions of the corresponding through holes of each fixed electrode structure coincide with each other, and the sound wave radiating surface to the outside is provided. It is characterized in that the vibration part of the vibration film of another fixed electrode structure exerts an exciting action on the vibration part of the vibration film of the fixed electrode structure to be formed.
In the electrostatic ultrasonic transducer configured as described above, for example, as shown in FIG. 1, a push-pull type in which a vibrating membrane 12 is sandwiched between upper and lower fixed electrodes 10 and 11 having radiation holes (through holes) 14. A plurality of fixed electrode structures are stacked in parallel. Then, the vibration part of the vibration film of the fixed electrode structure that forms the sound wave radiating surface to the outside is configured so that the vibration part of the vibration film of another fixed electrode structure exerts an exciting action.
As described above, the ultrasonic output sound pressure can be increased by laminating a plurality of fixed electrode structures so that a vibration action is generated in the vibrating portion of the vibrating membrane.

Further, the electrostatic ultrasonic transducer according to the present invention is configured such that the vibration of the vibration film facing the space is formed with respect to the space formed by the upper and lower through holes and the vibration film of the coupling portion of the laminated fixed electrode structure. An air vent structure is provided to allow the part to vibrate without receiving resistance by air.
In the electrostatic ultrasonic transducer having such a configuration, an air vent structure is provided so that the space formed by the upper and lower through holes and the vibration film of the joint portion of the fixed electrode structure is not a sealed space. That is, the vibrating portion of the vibrating membrane can be freely vibrated without receiving air resistance (air resistance when air is removed or sucked by vibration of the vibrating membrane) in the through-hole serving as a vibration space.
Thereby, even when the fixed electrode structure is laminated, the vibrating portion of the vibrating membrane can vibrate freely without receiving air resistance. For this reason, the ultrasonic output sound pressure can be increased.

In the electrostatic ultrasonic transducer according to the present invention, the vibration part of the vibration film of the other fixed electrode structure is vibrated with respect to the vibration part of the vibration film of the fixed electrode structure forming the sound wave emission surface to the outside. A phase shift means for adjusting the phase of the AC signal applied to the vibrating membrane of each of the fixed electrode structures so as to exert an action is provided.
With such a configuration, the fixed electrode structure of the vibration film of another fixed electrode structure exerts an excitation action on the vibration part of the vibration film of the fixed electrode structure that radiates sound waves to the outside. The phase of the AC signal applied to the vibrating membrane is adjusted.
Thereby, the phase of the AC signal applied to the vibration film of each fixed electrode structure can be set, and the vibration action can be generated in the vibration film. For this reason, the ultrasonic output sound pressure can be increased.

Further, the electrostatic ultrasonic transducer according to the present invention is configured such that the number of stacked layers of the fixed electrode structure is two, and two vibrating portions are formed on the radial axis of the through hole. The vibration part of the vibration film of the fixed electrode structure is configured to vibrate the vibration part of the vibration film of the other fixed electrode structure.
With such a configuration, the fixed electrode structure has two layers, and the vibration of the vibration film part of the other fixed electrode structure is vibrated by the vibration part of the vibration film of one fixed electrode structure. Thereby, the ultrasonic output sound pressure can be increased by making the fixed electrode structure of the electrostatic ultrasonic transducer into two layers.

The electrostatic ultrasonic transducer according to the present invention includes a first fixed electrode having a plurality of through holes and a plurality of through holes that are paired with the first fixed electrode. Two fixed electrodes and a vibration layer sandwiched between the pair of fixed electrodes and having a conductive layer to which a DC bias voltage is applied, and an AC signal is applied between the pair of fixed electrodes. A plurality of fixed electrode structures to be stacked in parallel so that the positions of the corresponding through-holes of each fixed electrode structure coincide with each other, and a vibrating part of the vibrating membrane of the fixed electrode structure that forms a sound wave radiating surface to the outside On the other hand, the present invention is characterized in that it includes a procedure in which a vibrating portion of a vibrating membrane having another fixed electrode structure exerts a vibrating action.
In the configuration method of the electrostatic ultrasonic transducer of such a procedure, for example, as shown in FIG. 1, push-pull in which the vibrating membrane 12 is sandwiched between upper and lower fixed electrodes 10 and 11 having radiation holes (through holes) 14. A plurality of mold fixed electrode structures are stacked in parallel. And the vibration part of the vibration film of the other fixed electrode structure exerts an exciting action on the vibration part of the vibration film of the fixed electrode structure that forms the sound wave radiating surface to the outside.
Thus, by laminating a plurality of fixed electrode structures, the ultrasonic output sound pressure can be increased.

In addition, an ultrasonic speaker according to the present invention includes any one of the electrostatic ultrasonic transducers described above.
As a result, the ultrasonic output sound pressure can be increased in the ultrasonic speaker.

  Next, the best mode for carrying out the present invention will be described with reference to the drawings.

[Description of push-pull type electrostatic ultrasonic transducer]
FIG. 1 is a diagram for explaining an electrostatic ultrasonic transducer called a push-pull type that is a constituent element of the ultrasonic transducer of the present invention. FIG. 1A is a diagram showing a cross-sectional structure of a push-pull type electrostatic ultrasonic transducer 1, and FIG. 1B shows a top view of the electrostatic ultrasonic transducer 1. The ultrasonic transducer of the present invention is characterized in that this push-pull type electrostatic ultrasonic transducer 1 is laminated.

  In FIG. 1, a push-pull type electrostatic ultrasonic transducer 1 is sandwiched between a pair of fixed electrodes 10 and 11 including a conductive member formed of a conductive material functioning as an electrode, and the pair of fixed electrodes 10 and 11. The vibration film 12 has a conductive layer (deposition film layer) 121, a pair of fixed electrodes 10 and 11, and a member (not shown) that holds the vibration film 12.

  The vibration film 12 includes an insulating layer 120 and a conductive layer 121 formed of a conductive material. The conductive layer 121 is unipolar (positive or negative) by a DC bias power supply 16. DC bias voltage) may be applied.

  In addition, the pair of fixed electrodes 10 and 11 have the same number and a plurality of radiation holes (stepped through holes) 14 at positions facing each other with the vibrating membrane 12 (see FIG. 1B). An AC signal is applied between the conductive members of the fixed electrodes 10 and 11 by AC signal sources 18A and 18B. Capacitors are formed on the fixed electrode 10 and the conductive layer 121, and on the fixed electrode 11 and the conductive layer 121, respectively.

  In the above configuration, in the ultrasonic transducer, a DC bias voltage having a single polarity (positive polarity in this example) is applied to the conductive layer 121 of the vibration film 12 by the DC bias power supply 16. On the other hand, an AC signal is applied to the pair of fixed electrodes 10 and 11 by the signal sources 18A and 18B. As a result, in the positive half cycle of the AC signal output from the signal sources 18A and 18B, since a positive voltage is applied to the fixed electrode 10, the surface portion 13A not sandwiched between the fixed electrodes of the vibrating membrane 12 is applied. The electrostatic repulsive force acts, and the surface portion 13A is pulled downward in FIG. At this time, since a negative voltage is applied to the opposed fixed electrode 11, an electrostatic attraction force acts on the back surface portion 13B which is the back surface side of the surface portion 13A of the vibration film 12, The back surface portion 13B is pulled further upward in FIG.

  Accordingly, the membrane portion of the vibrating membrane 12 that is not sandwiched between the pair of fixed electrodes 10 and 11 receives an electrostatic repulsive force and an electrostatic repulsive force in the same direction. Similarly, in the negative half cycle of the AC signal output from the signal sources 18A and 18B, the surface portion 13A of the vibrating membrane 12 has an electrostatic attraction force upward in FIG. 1 and the back surface portion 13B. In FIG. 1, an electrostatic repulsive force acts on the upper side, and a film portion not sandwiched between the pair of fixed electrodes 10 and 11 of the vibrating membrane 12 receives an electrostatic repulsive force and an electrostatic repulsive force in the same direction. In this way, the direction in which the electrostatic force changes alternately while the vibrating membrane 12 receives the electrostatic repulsive force and the electrostatic repulsive force in the same direction according to the change in polarity of the AC signal. An acoustic signal having a sound pressure level sufficient to obtain a parametric array effect can be generated.

  In this way, the ultrasonic transducer is called a push-pull type because the vibrating membrane 12 receives a force from the pair of fixed electrodes 10 and 11 and vibrates. The push-pull type electrostatic ultrasonic transducer is capable of simultaneously satisfying wide bandwidth and high sound pressure compared to the pull type electrostatic ultrasonic transducer that only acts on the vibrating membrane. have.

  In the electrostatic ultrasonic transducer shown in FIG. 1, the fixed electrodes 10 and 11 may be made of a conductive material. For example, SUS, brass, iron, or nickel may be used alone. In addition, since it is necessary to reduce the weight, a desired hole processing is performed on a glass epoxy substrate or a paper phenol substrate generally used for circuit boards, and then plating is performed with nickel, gold, silver, copper, or the like. It is also possible. In this case, in order to prevent warping after molding, it is also effective to devise plating on the both surfaces. However, in consideration of insulation, it is desirable that some kind of insulation treatment be performed on the vibration film side of each fixed electrode. For example, a convex portion insulated with a liquid solder resist, a photosensitive film, a photosensitive coating material, a non-conductive paint, an electrodeposition material, or the like is formed.

  As described above, in the push-pull type electrostatic ultrasonic transducer, a high voltage DC bias voltage is applied to the vibration film, and an AC voltage is applied to the fixed electrode, so that the fixed electrode-vibration film The membrane part vibrates due to the electrostatic force (attraction and repulsive force) acting on. In this case, in order to realize the vibration of the ultrasonic band, it is necessary to reduce the hole diameter of the vibration part to several mm or less, and by providing a large number of vibration holes, a transducer with high followability and high output is configured. There is a need. Note that the shape of the fixed electrode is not limited to a circle but may be an arbitrary shape such as a square.

[Description of Configuration Example of Electrostatic Ultrasonic Transducer of the Present Invention]
FIG. 2 is a diagram showing a configuration example of the ultrasonic transducer of the present invention, and shows a part of the electrostatic ultrasonic transducer of the present invention. 2A is a diagram illustrating a cross-sectional structure, and FIG. 2B is a bottom view. Note that the cross-sectional structure illustrated in FIG. 2A illustrates a cross section in the XY direction indicated by a dashed-dotted line in FIG.

  The ultrasonic transducer 2 of the present invention is configured by laminating an upper fixed electrode structure 3 and a lower fixed electrode structure 4 via an insulating material 19 in FIG.

  The upper fixed electrode structure 3 has the same configuration and function as the fixed electrode structure of the push-pull electrostatic ultrasonic transducer 1 shown in FIG. The lower fixed electrode structure 4 has the same configuration and function as the upper fixed electrode structure 3, except that air vent holes 31A and 31B are provided and an air vent structure is provided.

  As shown in FIG. 2, the lower fixed electrode structure 4 includes a pair of fixed electrodes 20, 21 including a conductive member formed of a conductive material functioning as an electrode, like the upper fixed electrode structure 3. The vibrating film 22 includes a conductive layer (deposited film layer) 221 sandwiched between a pair of fixed electrodes 20 and 21.

  The vibration film 22 includes an insulating layer 220 and a conductive layer 221 formed of a conductive material. Further, the pair of fixed electrodes 20 and 21 have the same number and a plurality of radiation holes (stepped through holes) 24 at positions facing each other through the vibration film 22.

  With the above configuration, the vibrating portions 25A and 25B of the vibrating membrane are formed in parallel on the ultrasonic radiation axis CL, and the other vibrating portion 25B is assisted (for excitation) with respect to one vibrating portion 25A. . With such a configuration, it is possible to increase the output sound pressure in the vibration section 25A (the mechanism of this excitation will be described later). In the example shown in FIG. 2, the lower fixed electrode structure 4 is used as an assist for the upper fixed electrode structure 3, but the opposite may be used.

  FIG. 3 is a diagram showing an example of an air vent hole in the fixed electrode structure on the lower side of the electrostatic ultrasonic transducer shown in FIG. The right side of FIG. 3 is an enlarged perspective view showing a part of the lower fixed electrode structure 4 and shows only the air vent holes for easy understanding of the drawing. The membrane is omitted.

  As shown in FIG. 3, the fixed electrode 20 of the lower fixed electrode structure 4 communicates with the radiation hole (stepped through hole) 24 as a vent hole in FIG. It is done. In addition, a vertical air vent hole 31B is provided in FIG. 3 that communicates with the air vent 31A.

  By supplying air to the surfaces of the vibrating portions of the vibrating membrane 22 and the vibrating membrane 12 from the air vent holes 31A and 31B, the vibrating surfaces of the vibrating membrane 22 and the vibrating membrane 12 have an air resistance (excludes air by vibration of the vibrating membrane or It is configured to vibrate freely without being affected by air resistance during suction. Note that the structure of the air vent holes 31A and 31B is not limited to the example shown in FIG. 3, and any structure can be used as long as the vibration surfaces of the vibration film 22 and the vibration film 12 are not affected by air resistance. It may be a structure.

  FIG. 4 is a diagram showing an example of a driving method of the electrostatic ultrasonic transducer according to the present invention. Similarly to the upper fixed electrode structure 3, the lower fixed electrode structure 4 also has a single-polarity (positive polarity in this example) DC bias voltage applied to the conductive layer 221 of the vibration film 22 by the DC bias power supply 26. Applied. On the other hand, an AC signal (a signal obtained by modulating a carrier wave signal in an ultrasonic frequency band with an audible frequency wave signal) is applied to the pair of fixed electrodes 20 and 21 from the signal sources 28A and 28B.

  Next, the mechanism of increasing the sound pressure by the vibration structure in the present invention will be described by taking one radiation hole (through hole) of the electrostatic ultrasonic transducer having such a laminated structure as an example.

  FIG. 5 is a view for explaining the mechanism of the excitation action in the electrostatic ultrasonic transducer of the present invention. The example shown in FIG. 5 is an example in which two vibrating portions (A) and (B) are formed on the radial axis of the vibrating membrane. Note that, for the sake of simplification of the drawings, the fixed electrode and the air vent hole are omitted.

  Consider a transducer that emits ultrasonic waves, with the right side from the vibrating part (A) in FIG. There is a vibration part (B) having a role of exciting the vibration part (A).

  The mechanism of the excitation depends on the distance between the vibration part (A) and the vibration part (B), and the vibration part (A), (with the distance according to the drive frequency (frequency of the carrier wave signal in the ultrasonic frequency band), ( It is necessary to arrange B). For example, when the drive frequency is 60 kHz (λ = about 5.7 mm), the distance is an odd multiple of a quarter wavelength (about 1.425 mm), and the drive phase of the vibration part (A) is vibrated. By delaying the portion (B), the vibration amplitude of the vibration portion (A) can be increased.

  FIGS. 5B and 5C show how the magnitude of the vibration waveform of the vibration part (A) changes depending on the presence or absence of vibration by the vibration part (B). FIG. 5B shows a case where there is no vibration by the vibration part (B), and FIG. 5C shows a case where there is vibration by the vibration part (B). As shown in FIG. 5C, when there is excitation by the vibration part (B), the vibration amplitude of the vibration part (A) increases.

  When the drive phase of the vibration part (A) is delayed with respect to the vibration part (B), for example, in the drive circuit shown in FIG. 4, the phase of the AC signal of the upper signal sources 18A and 18B is reduced. It is only necessary to provide a phase shift means for delaying the signal sources 28A and 28B.

  Further, by providing an air vent hole in the space C formed by the vibration part (A) and the vibration part (B), the air between the vibration part (A) and the vibration part (B) can move freely. The vibration amplitude of the vibration part (A) can be increased by the vibration action without being affected by air resistance. In this way, an increase in the sound pressure of the ultrasonic output can be realized.

[Description of configuration example of ultrasonic speaker]
FIG. 6 is a diagram showing a configuration example of an ultrasonic speaker using the electrostatic ultrasonic transducer of the present invention. An ultrasonic speaker applies amplitude modulation (AM modulation) to an ultrasonic wave called an audio signal (audible frequency signal) on an ultrasonic wave called a carrier wave, and when it is released into the air, the original audio signal is self-regenerated in the air due to air nonlinearity. That's it. In other words, since sound waves are coarse and dense waves that propagate using air as a medium, the dense and sparse portions of the air appear prominently in the process of the modulated ultrasonic waves propagating, and the dense portions have high sound speed and sparseness. Since the speed of sound is slow in this part, the modulation wave itself is distorted. As a result, the waveform is separated into a carrier wave (ultrasonic wave) and an audible wave (original audio signal). This is the principle that only listening can be heard and is generally called the pametric array effect.

  The ultrasonic speaker 41 shown in FIG. 6 generates a carrier wave in the ultrasonic frequency band and outputs the carrier wave signal source 42, and an audio frequency wave signal source (audio signal source) that generates a signal wave in the audio frequency band. 43, a modulator 44, a phase shift circuit 46, power amplifiers 45 and 47, and an electrostatic ultrasonic transducer 2 in which fixed electrode structures 3 and 4 are laminated.

  In the above configuration, modulation is performed by modulating the carrier wave in the ultrasonic frequency band output from the carrier wave signal source 42 by the modulator 44 using the audio signal wave output from the audible frequency wave signal source 43 and amplifying it by the power amplifier 45 The assist-side fixed electrode structure 4 in the electrostatic ultrasonic transducer 2 is driven by the signal. The output of the modulator 44 is input to the phase shift circuit 46, and the modulated signal whose phase is delayed by the phase shift circuit 46 (the phase is delayed so that an excitation action occurs in the diaphragm) Amplified by the amplifier 47 and applied to the fixed electrode structure 3. As a result, the vibration part of the vibration film of the fixed electrode structure 3 is vibrated by the vibration part of the vibration film of the fixed electrode structure 4.

  In this way, the modulated signal is converted into a sound wave of a finite amplitude level by the electrostatic ultrasonic transducer 2, and this sound wave is radiated into the medium (in the air) and is audible to the original by the nonlinear effect of the medium (air). The signal sound in the frequency band is self-regenerated.

  As described above, in the electrostatic ultrasonic transducer according to the present invention, the sound pressure of the ultrasonic output can be increased by forming the fixed electrode structure of the push-pull electrostatic ultrasonic transducer into a laminated structure. Can do. Further, the number of stacked fixed electrode structures is not limited to two, and may be three or more.

  Although the embodiments of the present invention have been described above, the electrostatic ultrasonic transducer of the present invention is not limited to the above-described illustrated examples, and various modifications can be made without departing from the scope of the present invention. Of course, it can be added.

Explanatory drawing of a push-pull type electrostatic ultrasonic transducer. The figure which shows the structural example of the electrostatic type ultrasonic transducer of this invention. The figure which shows the example of the air vent structure in a fixed electrode structure. The figure which shows the example of the drive method of the electrostatic type ultrasonic transducer of this invention. Explanatory drawing of the mechanism of the vibration of the electrostatic type ultrasonic transducer of this invention. The figure which shows the structural example of an ultrasonic speaker. The figure which shows the structural example of a piezoelectric type ultrasonic transducer. The figure which shows the structural example of the conventional electrostatic ultrasonic transducer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 ... Electrostatic ultrasonic transducer, 3 ... Upper fixed electrode structure 4 ... Lower fixed electrode structure 10, 11, 20, 21 ... Fixed electrode, 12, 22 ... Vibration membrane, 121, 221 ... Conductive Layers, 120, 220 ... insulating layers, 14, 24 ... radiation holes (through holes), 16, 26 ... DC bias power supply, 18A, 18B, 28A, 28B ... AC signal source, 19 ... insulating materials, 31A, 31B ... air vent Hole: 41 ... Ultrasonic speaker, 42 ... Carrier wave signal source, 43 ... Audio frequency wave signal source, 44 ... Modulator, 45, 47 ... Power amplifier, 46 ... Phase shift circuit

Claims (6)

A first fixed electrode having a plurality of through holes, a second fixed electrode having a plurality of through holes paired with the first fixed electrode, and a conductive layer sandwiched between the pair of fixed electrodes A plurality of fixed electrode structures in which an AC signal is applied between the pair of fixed electrodes,
Laminated in parallel so that the positions of the corresponding through holes of each fixed electrode structure coincide,
The static part is characterized in that the vibration part of the vibration film of the other fixed electrode structure exerts an excitation action on the vibration part of the vibration film of the fixed electrode structure that forms the sound wave radiating surface to the outside. Electric ultrasonic transducer. The vibration part of the vibration film facing the space can vibrate without receiving resistance due to air with respect to the space formed by the upper and lower through holes and the vibration film of the coupling part of the laminated fixed electrode structure. The electrostatic ultrasonic transducer according to claim 1, further comprising an air vent structure for performing the operation. The vibration of each of the fixed electrode structures is such that the vibration part of the vibration film of another fixed electrode structure exerts an exciting action on the vibration part of the vibration film of the fixed electrode structure that forms the sound wave emission surface to the outside. The electrostatic ultrasonic transducer according to claim 1, further comprising phase shift means for adjusting a phase of an AC signal applied to the film. The number of stacks of the fixed electrode structure is two, and it is configured such that two vibration parts are formed on the radial axis of the through hole,
The static part according to any one of claims 1 to 3, wherein the vibration part of the vibration film of one fixed electrode structure is configured to vibrate the vibration part of the vibration film of the other fixed electrode structure. Electric ultrasonic transducer. A first fixed electrode having a plurality of through holes, a second fixed electrode having a plurality of through holes paired with the first fixed electrode, and a conductive layer sandwiched between the pair of fixed electrodes A plurality of fixed electrode structures to which an AC signal is applied between the pair of fixed electrodes, and a vibration film to which a DC bias voltage is applied to the conductive layer.
A procedure for laminating in parallel so that the positions of the corresponding through holes of each fixed electrode structure are matched,
And a configuration in which a vibrating portion of a vibrating membrane of another fixed electrode structure exerts an excitation action on a vibrating portion of a vibrating membrane of a fixed electrode structure that forms an external sound wave radiating surface. A configuration method of an electrostatic ultrasonic transducer. An ultrasonic speaker comprising the electrostatic ultrasonic transducer according to claim 1.

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