JP2005354473A5 - - Google Patents

Description

Ultrasonic transducer and ultrasonic speaker using the same

  The present invention relates to an electrostatic ultrasonic transducer that generates a constant high sound pressure over a wide frequency band, and an ultrasonic speaker using the same.

Most of conventional ultrasonic transducers are resonant types using piezoelectric ceramics.
Here, FIG. 10 shows a configuration of a conventional ultrasonic transducer. Most of conventional ultrasonic transducers are resonant types using piezoelectric ceramics as vibration elements. The ultrasonic transducer shown in FIG. 10 performs both the conversion from an electric signal to an ultrasonic wave and the conversion from an ultrasonic wave to an electric signal (transmission and reception of an ultrasonic wave) using a piezoelectric ceramic as a vibration element. The bimorph ultrasonic transducer shown in FIG. 10 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 resonance type ultrasonic transducer uses the resonance phenomenon of the piezoelectric ceramic, the transmission and reception characteristics of the ultrasonic wave are good in a relatively narrow frequency band around the resonance frequency.

Unlike the resonant ultrasonic transducer shown in FIG. 10 described above, an electrostatic ultrasonic transducer is conventionally known as a broadband oscillation ultrasonic transducer capable of generating a high sound pressure over a high frequency band. 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.
FIG. 11 shows a specific configuration of a broadband oscillation type ultrasonic transducer (Pull type).

The electrostatic ultrasonic transducer shown in FIG. 11 uses a dielectric 131 (insulator) such as PET (polyethylene terephthalate resin) having a thickness of about 3 to 10 μm as a vibrating body. 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 is 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. The DC bias power supply 150 constantly applies a DC bias voltage for attracting the upper electrode of about 50 to 150 V to the upper electrode 132 so that 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 of about several tens to several hundreds μm having a non-uniform shape 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. In the electrostatic ultrasonic transducer, the frequency characteristics of the ultrasonic transducer shown in FIG. 7 are shown by a curve Q1 in FIG. 8 by forming innumerable capacitors having different gap sizes and depths. Broadband.

In the ultrasonic transducer having the above configuration, a rectangular wave signal (50 to 150 Vp-p) is applied between the upper electrode 12 and the lower electrode 133 in a state where a DC bias voltage is applied to the upper electrode 132. Yes. Incidentally, as shown by the curve Q1 in FIG. 8, the frequency characteristic of the resonance type ultrasonic transducer has a center frequency (resonance frequency of the piezoelectric ceramic) of, for example, 40 kHz, and ± 5 kHz with respect to the center frequency that is the maximum sound pressure. -30 dB with respect to the maximum sound pressure at a frequency of. On the other hand, the frequency characteristics of the broadband oscillation type ultrasonic transducer having the above configuration are flat from 40 kHz to near 100 kHz, and are about ± 6 dB compared to the maximum sound pressure at 100 kHz (see Patent Documents 1 and 2). .
JP 2000-50387 A JP 2000-50392 A

As described above, unlike the resonance ultrasonic transducer shown in FIG. 10, the electrostatic ultrasonic transducer shown in FIG. 11 can generate a relatively high sound pressure over a wide frequency band. It is known as a broadband ultrasonic transducer (Pull type).
However, as shown in FIG. 12, the maximum value of the sound pressure is 120 dB or less for the electrostatic ultrasonic transducer as compared to 130 dB or more for the resonance ultrasonic transducer, and the sound pressure is low as an ultrasonic speaker. Sound pressure was slightly insufficient to use.

Here, the ultrasonic speaker will be described. By applying AM modulation to an ultrasonic frequency band signal called a carrier wave with an audio signal (audible frequency band signal) and driving the ultrasonic transducer with this modulation signal, the ultrasonic wave was modulated with the audio signal of the signal source. The sound wave of the state is radiated into the air, and the original audio signal is self-regenerated in the air due to the nonlinearity of air.

In other words, since sound waves are coarse and dense waves that propagate using air as a medium, the dense and sparse parts of the air appear prominently in the process of the modulated ultrasonic waves propagating, and the dense parts 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), and we humans audible sound below 20 kHz (original audio signal) This is the principle that only listening can be heard, and it is generally called the parametric array effect.

In order for the above parametric effect to appear sufficiently, an ultrasonic sound pressure of 120 dB or more is required. However, it is difficult to achieve this value with an electrostatic ultrasonic transducer, and ceramic piezoelectric elements such as PZT, PVDF, etc. The polymer piezoelectric element has been used as an ultrasonic transmitter.
However, since the piezoelectric element has a sharp resonance point regardless of the material, and is practically used as an ultrasonic speaker by being driven at the resonance frequency, the frequency region where a high sound pressure can be secured is extremely narrow. That is, it can be said that it is a narrow band.

Generally, the maximum human audible frequency band is said to be 20 Hz to 20 kHz, and has a band of about 20 kHz. That is, in an ultrasonic speaker, it is impossible to faithfully demodulate the original audio signal unless a high sound pressure is ensured over a frequency band of 20 kHz in the ultrasonic region. It can be easily understood that it is difficult to faithfully reproduce (demodulate) this 20 kHz wide band with a conventional resonance type ultrasonic speaker using a piezoelectric element.

In fact, in an ultrasonic speaker using a conventional resonance type ultrasonic transducer, (1) the reproduction frequency is narrow with a narrow band, and (2) the demodulated sound is distorted if the AM modulation degree is increased too much, so the maximum is only about 0.5. The degree of modulation cannot be increased. (3) When the input voltage is increased (when the volume is increased), the vibration of the piezoelectric element becomes unstable and the sound is broken. When the voltage is further increased, the piezoelectric element itself is liable to be destroyed, and (4) it is difficult to make an array, enlargement, and miniaturization.

On the other hand, the ultrasonic speaker using the electrostatic ultrasonic transducer (Pull type) shown in FIG. 11 can substantially solve the above-mentioned problems of the prior art, but it can cover a wide band, but the demodulated sound is not generated. There was a problem that the absolute sound pressure was insufficient for the volume to be sufficient.
In the Pull type ultrasonic transducer, the electrostatic force works only in the direction of attracting only to the fixed electrode side, and the symmetry of vibration of the vibration film (corresponding to the upper electrode 132 in FIG. 7) is not maintained. When used for an acoustic speaker, there has been a problem that the vibration of the diaphragm directly generates an audible sound.

Furthermore, in order to realize stable membrane vibration, a DC bias voltage of several hundred volts is used to adsorb the bulk material of the vibrating thin film of the upper electrode and the lower electrode (fixed electrode), and 100 V for vibrating the thin film. Needed an AC voltage exceeding. These voltages are high voltages, leading to an increase in size / power / cost of the apparatus as well as danger.
In addition, if the voltage applied between the vibrating thin film and the fixed electrode is suppressed, the membrane vibration becomes unstable and causes vibration with irregular amplitude and phase at each location. Could not be released as sonic energy

  The present invention has been made in view of such circumstances, and can generate an acoustic signal having a sufficiently high sound pressure level to obtain a parametric array effect over a wide frequency band, and the membrane vibration of the diaphragm An object of the present invention is to provide an ultrasonic transducer and an ultrasonic speaker using the ultrasonic transducer that effectively utilize energy (acoustic energy).

Ultrasonic transducer of the present invention in order to achieve the above object, a second fixed electrode having a first fixed electrode having a plurality of holes, a plurality of holes forming the first fixed electrode and the counter, wherein first clamping or are held by the fixed electrode and the pair of fixed electrodes and a second fixed electrode Rutotomoni has a conductive layer, and a vibrating membrane to which a DC bias voltage to the conductive layer is applied, the a, wherein the plurality of holes of the second fixed electrode are all at a position opposite to the plurality of holes of the first fixed electrode through the vibrating membrane, or the majority is formed, the fixation of the pair between the electrodes an AC signal is applied, and having an acoustic reflector on the first surface of the pair of fixed electrodes.

In the ultrasonic transducer according to the present invention having the above-described configuration, the first fixed electrode and the second fixed electrode have a plurality of holes at opposing positions, and a DC bias voltage is applied to the conductive layer of the vibrating membrane. Thus, since an AC signal as a drive signal is applied to the pair of fixed electrodes including the first and second fixed electrodes, the vibration film sandwiched between the pair of fixed electrodes has a direction corresponding to the polarity of the AC signal. Since the electrostatic attractive force and the electrostatic repulsive force are simultaneously received in the same direction, the vibration of the vibrating membrane can be made large enough to obtain a parametric effect, and the symmetry of the vibration is ensured. Sound pressure can be generated over a wide frequency band.
Further, acoustic signals (ultrasonic waves) in the ultrasonic frequency band are output from the plurality of holes of the first and second fixed electrodes to the front side and the back side of the ultrasonic transducer due to the vibration of the vibrating membrane. The acoustic signal output to the back surface (first surface) side of the ultrasonic transducer is radiated to the front side of the ultrasonic transducer in a state where the phases are aligned by the acoustic reflector, so that it is radiated to the front side of the ultrasonic transducer. In addition to ultrasonic waves, ultrasonic waves radiated to the back surface (first surface) side of the ultrasonic transducer can be used, and the membrane vibration energy of the vibration membrane can be effectively utilized to the maximum.

In the ultrasonic transducer according to the present invention, the acoustic reflector may be configured such that the ultrasonic waves radiated from the openings of the plurality of holes on the first surface of the ultrasonic transducer all pass through the same length path. It is arranged at a position radiated to the second surface of the transducer.
In the ultrasonic transducer of the present invention configured as described above, the acoustic reflector is configured such that the ultrasonic waves radiated from the openings of the first surface of the ultrasonic transducer all have the same length in the path of the ultrasonic transducer . Since it is arranged to be radiated to the second surface, the acoustic signal output to the first surface side of the ultrasonic transducer is in front of the ultrasonic transducer (first 2) , the ultrasonic wave radiated not only on the second surface (front surface) side of the ultrasonic transducer but also on the first surface ( back surface ) side of the ultrasonic transducer . Sound waves can also be used, and the diaphragm vibration energy of the diaphragm can be utilized to the maximum extent possible.

The ultrasonic transducer of the present invention, the acoustic reflector, the located one end to the center position of the first surface of the ultrasonic transducer, the first surface of the ultrasonic transducer to said center position as a reference A pair of first reflectors disposed at an angle of 45 ° with respect to both sides and having the other end coincident with the end of the ultrasonic transducer; and the ends of the pair of first reflectors; A pair of second reflectors each having a right angle and connected in the outer direction of the first reflector and having a length equal to the length of the first reflector is provided.

In the ultrasonic transducer of the present invention configured as described above, one end of the ultrasonic wave radiated to the back surface of the ultrasonic transducer is located at the center position of the first surface (back surface) of the ultrasonic transducer , and the center position is As a reference, a horizontal direction is provided by a pair of first reflectors arranged at an angle of 45 ° with respect to both sides of the first surface of the ultrasonic transducer and having the other end coincident with the end of the ultrasonic transducer. And is connected to the outside of the first reflecting plate at an angle perpendicular to the end portions of the pair of first reflecting plates and has a length equivalent to the length of the first reflecting plate. The light is reflected toward the front surface of the ultrasonic transducer by the pair of second reflecting plates, and reflected so that the reflection paths have the same path length. Therefore, since the acoustic signal output to the first surface ( back surface ) side of the ultrasonic transducer is radiated in front of the ultrasonic transducer in a state where the phases are aligned by the acoustic reflector, Not only the radiated ultrasonic waves but also the ultrasonic waves radiated to the back side of the ultrasonic transducer can be used, and the membrane vibration energy of the vibrating membrane can be effectively utilized to the maximum extent.

In the ultrasonic transducer of the present invention, one end of the acoustic reflector is located at one end of the first surface of the ultrasonic transducer , and the first end of the ultrasonic transducer from the one end . A first reflector that is disposed at an angle of 45 ° in the direction of the other end of the one surface, and has a length that the other end coincides with the other end of the ultrasonic transducer; and the first reflector And a second reflecting plate connected to the outside of the first reflecting plate at a right angle to the other end of the first reflecting plate and having a length equivalent to the length of the first reflecting plate.
In the ultrasonic transducer of the present invention having such a configuration, ultrasonic waves emitted to the first surface of the ultrasonic transducer (back) is one end of the first surface of the ultrasonic transducer (rear) One end of the ultrasonic transducer is disposed at an angle of 45 ° from the one end to the other end of the first surface ( back surface ) of the ultrasonic transducer, and the other end is the other end of the ultrasonic transducer. The reflected light is reflected in the horizontal direction by the first reflecting plate having a length that matches the portion, and the reflected wave forms an angle perpendicular to the other end of the first reflecting plate and is outside the first reflecting plate. It is reflected by a second reflector that is connected in the direction and has a length equal to the length of the first reflector, and is emitted in phase with the front surface of the ultrasonic transducer. Therefore, not only the ultrasonic wave radiated to the front surface side of the ultrasonic transducer but also the ultrasonic wave radiated to the back surface side of the ultrasonic transducer can be used, and the membrane vibration energy of the vibration membrane can be utilized to the maximum extent. .

The ultrasonic transducer of the present invention, the acoustic reflector, the at 45 ° angle to both sides of the first surface of the ultrasonic transducer with respect to the center position of the first surface of the ultrasonic transducer A first reflector having a conical shape, the end of which has a generatrix whose length coincides with the end of the ultrasonic transducer, and an angle perpendicular to the generatrix of the first reflector. And a frustoconical second reflector having a generatrix having a length equivalent to the length of the first reflector connected to the outside of the first reflector. of the ultrasonic transducer, the first surface ultrasonic waves emitted (the back) of the ultrasonic transducer, both of the reference to the center position of the rear ultrasonic transducer ultrasonic transducer first face (back) Is reflected at a horizontal direction by a first reflecting plate having a conical shape having a generatrix whose length is coincident with the end of the ultrasonic transducer. A second truncated conical shape having a bus bar having a length equal to the length of the first reflector plate connected to the outside of the first reflector plate at an angle perpendicular to the bus bar of the first reflector plate. And is radiated to the front surface of the ultrasonic transducer in a phase-aligned state. Therefore, not only the ultrasonic wave radiated to the front surface side of the ultrasonic transducer but also the ultrasonic wave radiated to the back surface side of the ultrasonic transducer can be used, and the membrane vibration energy of the vibration membrane can be utilized to the maximum extent. .

The ultrasonic transducer according to a sixth aspect of the present invention is the ultrasonic transducer according to any one of the first to fifth aspects, wherein the size of the concavo-convex shape of the reflecting surface of the acoustic reflector is the ultrasonic wave. It is less than the wavelength of the ultrasonic wave radiated from the transducer.
In the ultrasonic transducer of the present invention configured as described above, the size of the uneven shape of the reflection surface of the acoustic reflector is equal to or less than the wavelength of the ultrasonic wave radiated from the ultrasonic transducer, so that the ultrasonic wave is not absorbed. , Can be reflected effectively.

The ultrasonic transducer of the present invention, the hole where the pair of fixed electrodes has is characterized by a cylindrical through-hole.
In the ultrasonic transducer of the present invention having such a configuration, ultrasonic waves generated by the vibration of the vibrating film are radiated via the cylindrical through-hole having a pair of fixed electrodes. The cylindrical through-hole has the advantage that production is simplest, electrostatic force acting between the conductive layer of the vibrating film to the vibrating film facing the electrode portion is not present in the fixed electrode side It has the disadvantage of being weak.

In the ultrasonic transducer according to the present invention, the holes of the pair of fixed electrodes are through holes in which concentric cylindrical holes of at least two types having different diameters and depths are connected . .
The ultrasonic transducer of the present invention is configured as a pair of fixed electrodes has a through-hole continuous concentric cylindrical holes of at least two kinds of different size, each diameter and depth. Therefore, since the fixed electrode portion parallel to the edge portion of each of the two or more types of concentric cylindrical holes of the pair of fixed electrodes is configured to face the conductive layer of the vibrating membrane, a parallel capacitor is formed. The Accordingly, the vibration film can be vibrated greatly because the portion of the vibration film facing the edge of each hole is lifted and a pulling force is applied at the same time.

The ultrasonic transducer of the present invention, the hole where the pair of fixed electrodes has is characterized in that cross-section is tapered.
In the ultrasonic transducer according to the present invention configured as described above, since the pair of fixed electricity has a through hole having a tapered cross section, the tapered portion of the fixed electrode is opposed to the conductive layer of the vibrating membrane. The parallel capacitor is formed.
Accordingly, the vibration film portion facing the taper portion of the fixed electrode is lifted and at the same time a pulling force acts, so that the vibration of the vibration film can be increased.

In the ultrasonic transducer according to the present invention, the holes of the pair of fixed electrodes are through holes having a rectangular plane.
In the ultrasonic transducer of the present invention having such a configuration, ultrasonic waves generated by the vibration of the vibrating membrane, a plane having a pair of fixed electrodes is emitted through the rectangular through-hole. Static This plane is rectangular through hole has the advantage that production is simplest, acting between the conductive layer of the vibrating film to the vibrating film facing the electrode portion is not present in the fixed electrode side It has the disadvantage that power is weak.

In the ultrasonic transducer according to the present invention, the holes formed in the pair of fixed electrodes are rectangular holes having at least two types of sizes formed on the same center line and having the same length and different widths and depths. It is the through-hole which continued.
In the ultrasonic transducer of the present invention configured as described above, the pair of fixed electrodes are formed on the same center line, and are connected with rectangular holes of at least two types of sizes having the same length and different widths and depths. having a through-hole. Accordingly, since the fixed electrode portion parallel to the edge portion of each of the two or more types of rectangular holes of the pair of fixed electrodes is configured to face the conductive layer of the vibrating membrane, a parallel capacitor is formed. The Therefore, the vibration film can be vibrated greatly because the part of the vibration film facing the edge of each hole is lifted and the pulling force acts at the same time.

The ultrasonic transducer of the present invention, a rectangular through hole in which the pair of fixed electrodes has is characterized in that cross-section is tapered.
In the ultrasonic transducer according to the present invention configured as described above, the pair of fixed electrodes has a through hole having a rectangular plane and a tapered cross section. Therefore, the tapered portion of the fixed electrode is a conductive layer of the vibrating membrane. Therefore, a parallel capacitor is formed.
Accordingly, the vibration film portion facing the taper portion of the fixed electrode is lifted and at the same time a pulling force acts, so that the vibration of the vibration film can be increased.

The ultrasonic transducer of the present invention is characterized in that the hole of the fixed electrode has a larger hole diameter and a shallower depth on the vibration film side than the opposite side of the vibration film.
In the ultrasonic transducer of the present invention configured as described above, since the hole of the fixed electrode has a larger hole diameter on the vibration film side and a shallower depth than the opposite side of the vibration film, the two or more types described above Since the parallel capacitor is formed by configuring the fixed electrode portion parallel to the edge portion of each concentric cylindrical hole of the size to face the conductive layer of the vibrating membrane, electrostatic force acting on the conductive layer of the vibrating membrane is formed. The suction force and electrostatic repulsion can be increased.

The ultrasonic transducer according to the present invention is characterized in that the rectangular hole of the fixed electrode has a larger width and a shallower depth on the vibration film side than the opposite side of the vibration film.
In the ultrasonic transducer of the present invention having such a configuration, a rectangular hole having the fixed electrode, the width in the direction of the vibrating film side of the opposite side of the diaphragm is large, so and the depth is shallow, the two or more Since the parallel capacitor is formed by configuring the fixed electrode portion parallel to the edge portion of each rectangular hole of the size or the taper portion of the fixed electrode to face the conductive layer of the vibration membrane, the vibration membrane The electrostatic attractive force and electrostatic repulsive force acting on the conductive layer can be increased.

In the ultrasonic transducer according to the present invention, the plurality of through holes may have the same size.
In the ultrasonic transducer of the present invention configured as described above, each of the pair of fixed electrodes has a through hole of the same size. Therefore, drilling is easy and the manufacturing cost can be reduced.

The ultrasonic transducer according to the present invention is characterized in that the plurality of through holes have the same size at positions facing each other and have a plurality of hole sizes.
In the ultrasonic transducer of the present invention configured as described above, the pair of fixed electrodes have the same size at the opposed positions and have through holes having a plurality of hole sizes. Therefore, drilling is easy and the manufacturing cost can be reduced.

The ultrasonic transducer according to the present invention is characterized in that the pair of fixed electrodes are made of a single conductive member.
In the ultrasonic transducer of the present invention configured as described above, the pair of fixed electrodes can be formed of a single conductive member, for example, a conductive material such as SUS, brass, iron, or nickel.

The ultrasonic transducer according to the present invention is characterized in that the pair of fixed electrodes includes a plurality of conductive members.
In the ultrasonic transducer of the present invention configured as described above, the pair of fixed electrodes can be formed of a plurality of conductive members.

In the ultrasonic transducer according to the present invention, the pair of fixed electrodes includes a conductive member and an insulating member.
In the ultrasonic transducer according to the present invention configured as described above, the pair of fixed electrodes includes a conductive member and an insulating member. For example, after forming a desired hole in an insulating member such as a glass epoxy substrate or a paper phenol substrate, the fixed electrode is formed of a conductive member and an insulating member by plating with nickel, gold, silver, copper, or the like. be able to. Thereby, the weight of the ultrasonic transducer can be reduced.

In the ultrasonic transducer of the present invention, the vibration film is a thin film having electrode layers on both surfaces of an insulating polymer film.
In the ultrasonic transducer of the present invention configured as described above, the vibrating membrane has electrode layers on both sides of the insulating polymer film. In this case, an insulating layer is provided on the fixed electrode side facing the vibration film, as will be described later. Therefore, the vibration film can be easily manufactured.

In the ultrasonic transducer of the present invention, the vibration film is a thin film formed such that an electrode layer is sandwiched between two insulating polymer films.
In the ultrasonic transducer of the present invention configured as described above, the vibration film is formed so that the electrode layer is sandwiched between insulating layers (insulating polymer film). Accordingly, the insulation treatment on the fixed electrode side becomes unnecessary, and the manufacture of the ultrasonic transducer becomes easy. In addition, it becomes easy to ensure the symmetry of the arrangement of the fixed electrodes with respect to the vibration membrane.

The ultrasonic transducer according to the present invention is characterized in that the vibrating membrane is formed by using two thin films having an electrode layer on one side of an insulating polymer film, and the electrode layers are in close contact with each other. To do.
In the ultrasonic transducer of the present invention configured as described above, the vibration film is formed by using two thin films having electrode layers on one side of the insulating polymer film and bringing the electrode layers into close contact with each other. Therefore, the vibration film can be easily manufactured.

The ultrasonic transducer according to the present invention is characterized in that the vibrating membrane uses an electret film.
In the ultrasonic transducer of the present invention configured as described above, an electret film is used as the vibration film. In this case, an insulating layer is formed on the fixed electrode side. Therefore, the vibration film can be easily manufactured.

In addition, the ultrasonic transducer according to the present invention has a vibrating membrane having electrode layers on both sides of the insulating polymer film, or a vibrating membrane using an electret film, on each vibrating membrane side of the pair of fixed electrodes. An electrical insulation treatment is performed.
In the ultrasonic transducer of the present invention configured as described above, when using a vibrating membrane having conductive layers (electrode layers) on both sides of an insulating layer (insulating film) as the vibrating membrane, or using an electret film as the vibrating membrane Is electrically insulated on the vibrating membrane side of the fixed electrode. Therefore, a double-sided electrode vapor-deposited film having an electrically conductive layer (electrode layer) on both sides of an insulating layer (insulating film) or an electret film can be used as a vibration film.

In the ultrasonic transducer according to the present invention, a DC bias voltage having a single polarity is applied to the vibrating membrane.
In the ultrasonic transducer of the present invention configured as described above, a single-polarity DC bias voltage is applied to the vibrating membrane. Therefore, since the electric charge of the same polarity is always accumulated in the electrode layer of the vibrating membrane, the vibrating membrane is electrostatically attracted according to the polarity of the voltage of the fixed electrode that is changed by the AC signal applied to the pair of fixed electrodes. Vibrates under force and electrostatic repulsion.

In the ultrasonic transducer according to the present invention, the member that holds the fixed electrode and the vibration film is made of an insulating material.
In the ultrasonic transducer of the present invention configured as described above, the member that holds the fixed electrode and the vibration film is formed of an insulating material. Therefore, electrical insulation between the fixed electrode and the vibrating membrane is maintained.

The ultrasonic transducer according to the present invention is characterized in that the vibrating membrane is fixed by applying tension in four perpendicular directions on the plane of the membrane.
In the ultrasonic transducer of the present invention configured as described above, the vibrating membrane is fixed by applying tension in four directions at right angles on the plane of the membrane. Therefore, conventionally, it was necessary to apply a DC bias voltage of several hundred volts to the vibrating membrane to attract the vibrating membrane to the fixed electrode side. Thus, the DC bias voltage can be reduced because the same effect as that of the tensile tension that the DC bias voltage has conventionally performed is brought about.

An ultrasonic speaker according to the present invention includes any of the ultrasonic transducers described above, a signal source that generates a signal wave in an audible frequency band, and a carrier wave supply that generates and outputs a carrier wave in the ultrasonic frequency band. And a modulation means for outputting a modulation signal obtained by modulating the carrier wave with a signal wave in an audible frequency band outputted from the signal source, the ultrasonic transducer comprising the pair of fixed electrodes and the vibrating membrane characterized in that it is driven by the pre-Symbol modulation signal applied between the electrode layers.

In the ultrasonic speaker of the present invention configured as described above, an audible frequency band signal wave is generated by the signal source, and an ultrasonic frequency band carrier wave is generated and output by the carrier wave supply means. Further, the carrier wave is modulated by the audible frequency band signal wave output from the signal source by the modulation means, and the modulation signal output from the modulation means is between the pair of fixed electrodes and the electrode layer of the vibrating membrane. And the ultrasonic transducer is driven. Further, the ultrasonic wave radiated to the back surface of the ultrasonic transducer is reflected by an acoustic reflector installed on the back surface of the ultrasonic transducer, and is radiated to the front surface of the ultrasonic transducer in a state where the phases are aligned.
Therefore, since the ultrasonic speaker of the present invention is configured using the ultrasonic transducer having the above-described configuration, it can generate an acoustic signal having a sound pressure level high enough to obtain a parametric array effect over a wide frequency band, Since the membrane vibration energy of the vibration membrane can be effectively utilized to the maximum, the power can be reduced.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The configuration of an ultrasonic transducer to which the present invention is applied is shown in FIG. FIG. 1A shows a configuration of an ultrasonic transducer, and FIG. 1B shows a plan view in which a part of the ultrasonic transducer is broken.
In FIG. 1, an ultrasonic transducer 1 to which the present invention is applied includes a pair of fixed electrodes 10A and 10B including a conductive member formed of a conductive material functioning as an electrode, and a pair of fixed electrodes. The diaphragm 12 includes a pair of fixed electrodes 10A and 10B and a member (not shown) for holding the diaphragm.

The vibrating membrane 12 is formed of an insulator 120 and has an electrode layer 121 formed of a conductive material. The electrode layer 121 has a single polarity (positive or negative polarity) by a DC bias power supply 16. Any of these may be applied), and an alternating current signal output from the signal source 18 is applied so as to be superimposed on the direct current bias voltage.

Further, the pair of fixed electrodes 10A and 10B have the same number and a plurality of holes 14 at positions facing each other with the vibrating membrane 12 therebetween, and the signal source 18 exchanges AC between the conductive members of the pair of fixed electrodes 10A and 10B. A signal is applied.
The fixed electrode 10A and the electrode layer 121, and the fixed electrode 10B and the electrode layer 121 are each formed with a capacitor.

In the above configuration, the ultrasonic transducer 1 receives an AC signal output from the signal source 18 to the electrode layer of the vibrating membrane 12 to a DC bias voltage having a single polarity (positive polarity in this embodiment) by the DC bias power supply 16. Applied in a superimposed state.
On the other hand, an AC signal is applied from the signal source 18 to the pair of fixed electrodes 10A and 10B.

As a result, in the positive half cycle of the AC signal output from the signal source 18, since a positive voltage is applied to the fixed electrode 10A, the surface portion 12A not sandwiched between the fixed electrodes of the vibrating membrane 12 An electrostatic repulsion force acts, and the surface portion 12A is pulled downward in FIG.
Further, at this time, since a negative voltage is applied to the opposed fixed electrode 10B, an electrostatic attraction force acts on the back surface portion 12B which is the back surface side of the surface portion 12A of the vibration film 12, The back surface part 12B is pulled further downward in FIG.

  Therefore, the membrane portion of the vibrating membrane 12 that is not sandwiched between the pair of fixed electrodes 10A and 10B 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 source 18, the electrostatic attracting force is applied to the upper surface portion 12 </ b> A of the vibrating membrane 12 in FIG. In FIG. 1, the electrostatic repulsive force acts upward, and the film portion not sandwiched between the pair of fixed electrodes 10 </ b> A and 10 </ b> B of the vibrating membrane 12 receives the electrostatic repulsive force and the 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.

Thus, the ultrasonic transducer 1 to which the present invention is applied is called a push-pull type because the vibrating membrane 12 vibrates by receiving a force from the pair of fixed electrodes 10A and 10B.
The ultrasonic transducer 1 to which the present invention is applied satisfies the broadband property and the high sound pressure simultaneously as compared with the conventional electrostatic ultrasonic transducer (Pull type) in which only the electrostatic attraction force acts on the vibration membrane. Have the ability.

FIG. 8 shows frequency characteristics of an ultrasonic transducer to which the present invention is applied. In the figure, a curve Q3 is a frequency characteristic of the ultrasonic transducer to which the present invention is applied. As can be seen from the figure, a higher sound pressure level can be obtained over a wider frequency band than the frequency characteristics of the conventional broadband electrostatic ultrasonic transducer. Specifically, it can be seen that a sound pressure level of 120 dB or more that can obtain a parametric effect in a frequency band of 20 kHz to 120 kHz can be obtained.

In the ultrasonic transducer 1 to which the present invention is applied, since the thin vibration film 12 sandwiched between the pair of fixed electrodes 10A and 10B receives both electrostatic attractive force and electrostatic repulsive force, not only large vibrations are generated. Since the symmetry of vibration is ensured, a high sound pressure can be generated over a wide band.

Next, the configuration of the ultrasonic transducer according to the first embodiment of the present invention is shown in FIG. The configuration of the ultrasonic transducer 55 according to the first embodiment of the present invention is shown in FIG. 1 except that the reflection of the acoustic wave is provided on the back surface of the ultrasonic transducer (corresponding to the first surface of the present invention) . The configuration is the same. That is, the ultrasonic transducer 55 according to the first embodiment of the present invention includes a pair of fixed electrodes 10A and 10B including a conductive member formed of a conductive material functioning as an electrode, and the pair of fixed electrodes 10A and 10B. The vibration film 12 is sandwiched and has a conductive layer 121 to which a DC bias voltage is applied. The member (not shown) that holds the pair of fixed electrodes 10A and 10B and the vibration film 12 is provided. The pair of fixed electrodes 10A and 10B have the same number and a plurality of holes at positions facing each other with the vibrating membrane 12 therebetween, and an ultrasonic wave to which an AC signal is applied between the conductive members of the pair of fixed electrodes 10A and 10B. It is a transducer, and the acoustic reflector 20 is installed on the back surface (first surface) of the ultrasonic transducer.

In addition, the acoustic reflector 20 is disposed on the front surface of the ultrasonic transducer 55 (corresponding to the second surface of the present invention) along the path of the same length of all the ultrasonic waves radiated from the respective openings on the back surface of the ultrasonic transducer 55. It is arranged to be emitted.
That is, one end of the acoustic reflector 20 is located at the center position M of the back surface (first surface) of the ultrasonic transducer 55, and the angle is 45 ° with respect to both sides of the back surface of the ultrasonic transducer 55 with reference to the center position. The pair of first reflecting plates 200 and 200 having a length that is disposed and the other end of which coincides with the end portions X1 and X2 of the ultrasonic transducer 55 and the end portions of the pair of first reflecting plates 200 and 200 are perpendicular to each other. A pair of second reflectors each having an angle and connected to the outer side of the first reflector and having a length equivalent to the length of the first reflector.

  In the above configuration, the first reflectors 200, 200 are arranged at an angle of 45 ° with respect to both sides of the center M on the back surface of the ultrasonic transducer 55, and the length to the point where the end coincides with the end of the ultrasonic transducer 55. Is needed. The ultrasonic waves emitted from the back surface of the ultrasonic transducer 55 by the first reflectors 200 and 200 are reflected in the horizontal direction.

Next, by connecting the second reflectors 202 and 202 connected at a right angle to the first reflectors 200 and 200 to the outside of the first reflectors 200 and 200, respectively, the ultrasonic waves are converted into ultrasonic waves. The transducer 55 is emitted from the side or top and bottom to the front. This second reflector length is also required to be equal to the first reflector length. What is important here is that all the ultrasonic waves radiated from the back surface of the ultrasonic transducer 55 have the same length path. This is because the same path length means that the phases of the ultrasonic waves emitted from the back surface are all aligned.

Further, the reason why the sound wave can be handled geometrically as shown in FIG. 2 is that the sound wave to be emitted is an ultrasonic wave and therefore has a very strong directivity. Another point that needs to be mentioned is the time difference between the ultrasonic wave emitted from the front surface of the ultrasonic transducer 55 and the ultrasonic wave reflected from the back surface and emitted to the front surface.

Ultrasonic waves emitted from a point a distance away from the center of the transducer, assuming that the transducer is circular and its radius is r, the distance to reach the transducer front is approximately 2r, ie the diameter of the transducer. Of course, the distance a must satisfy the following formula.
0 ≦ a ≦ r (1)

Now, if the transducer diameter is about 10cm and the sound velocity is 340m / sec, the time difference between the ultrasonic wave emitted from the front and the ultrasonic wave emitted from the back and reaching the front is about 0.29msec. Because there is a time difference that humans cannot perceive, there is no problem. That is, ultrasonic waves emitted from the front and back surfaces of the transducer can be used effectively.

Next, FIG. 3 shows a configuration of an ultrasonic transducer according to the second embodiment of the present invention. The only difference from the first embodiment in the configuration is the configuration of the reflector, and the other configurations are the same as those in the first embodiment.
In FIG. 3, in the ultrasonic transducer according to this embodiment, the acoustic reflector 30 has one end A located at one end (X1 or X2: X1 in this embodiment) of the back surface of the ultrasonic transducer 55. The other end B is disposed at an angle of 45 ° from the one end X1 toward the other end X2 of the back surface of the ultrasonic transducer 55, and the other end B has a length that coincides with the other end X2 of the ultrasonic transducer 55. The first reflector (AB) 300 and the other end B of the first reflector 300 are connected at an angle perpendicular to the outer side of the first reflector 300 and have a length equivalent to the length of the first reflector. And a second reflector (BC) 302 having a thickness.

In the above configuration, the ultrasonic waves radiated from the back surface of the ultrasonic transducer 55 are reflected in the horizontal direction by the first reflecting plate 300, and further reflected by the first reflecting plate 302, so that the phases are aligned on the front surface of the ultrasonic transducer 55. Will be emitted.
Also in this embodiment, the same effect as the ultrasonic transducer according to the first embodiment can be obtained.

Next, FIG. 4 shows a configuration of an ultrasonic transducer according to the third embodiment of the present invention. The present embodiment is different from the first and second embodiments in terms of configuration only in the configuration of the reflector, and the other configurations are the same as those in the first and second embodiments. To do.

In FIG. 4, in the ultrasonic transducer 55 according to the third embodiment, the acoustic reflector 40 is at an angle of 45 ° with respect to both sides of the back surface of the ultrasonic transducer 55 with reference to the center position M on the back surface of the ultrasonic transducer 55. A conical first reflector 400 having bus bars JK, JL whose length is coincident with the end of the ultrasonic transducer, and an angle perpendicular to the bus of the first reflector 400. In addition, the second reflecting plate 402 having a truncated cone shape having a generatrix having a length equivalent to the length of the first reflecting plate connected to the outside of the first reflecting plate 400 is provided.
Also in this embodiment, the same effect as the ultrasonic transducer according to the first and second embodiments can be obtained.

  FIG. 5 is a perspective view showing an external configuration of the acoustic reflector in the ultrasonic transducer according to the first embodiment and the second embodiment.

Next, the fixed electrode of the ultrasonic transducer according to this embodiment will be described. FIG. 6 shows some configuration examples (cross-sectional views) of a cylindrical fixed electrode (only one of a pair of fixed electrodes).
6 (a) is a through hole type, specifically, the holes in which the pair of fixed electrodes 10A, 10B has is a cylindrical through hole. The fixed electrode having the through hole is the simplest to manufacture, but has no portion corresponding to the electrode facing the vibrating membrane 12, and thus has a drawback that the electrostatic force is weak.

FIG. 6B shows the structure of a fixed electrode having a two-stage through-hole structure. That is, the holes in which the pair of fixed electrodes 10A, 10B has is a through hole continuous size concentric cylindrical holes of (two in this embodiment) at least two kinds of different respective diameters and depths. Hole which the fixed electrode having the hole diameter towards the vibrating film side is large, and the depth is shallower.
In this case, a place parallel to the flange portion of each hole is opposed to the vibration film 12, and this portion constitutes a parallel plate capacitor.

Therefore, at the same time that the heel portion of the vibrating membrane 12 is lifted, a pulling force acts, so that the membrane vibration can be increased. FIG. 6C shows a through hole having a tapered cross section. The effect when this shape is adopted as the fixed electrode is the same as the effect obtained by the configuration in FIG.

FIG. 7 shows several configuration examples of the fixed electrode having a groove-shaped through hole (only one of the pair of fixed electrodes). FIG. 7A shows a through-slot hole type, and the holes of the pair of fixed electrodes 10A and 10B are through-holes having a rectangular plane. The fixed electrode having this through hole is the simplest to produce, but has no drawback in that the electrostatic force is weak because there is no portion corresponding to the electrode facing the vibrating membrane 12.

FIG. 7B shows a configuration of a fixed electrode having a two-stage through-slot structure. That is, the holes of the pair of fixed electrodes 10A and 10B are formed on the same center line, and the planes of at least two types (two types in this embodiment) having the same length and different widths and depths are rectangular. It is a through hole with a series of holes.
In this case, as in the case of the round hole shape, the place parallel to the flange portion of each slot faces the vibrating membrane 12, and this constitutes a parallel plate capacitor.
Accordingly, since the heel portion of the vibration film 12 is lifted and a force to be pulled down acts, the film vibration of the vibration film 12 can be increased.

FIG. 7C shows a tapered through-slot hole. That is, the rectangular through hole formed in the pair of fixed electrodes 10A and 10B has a tapered cross section. When this shape is adopted as the fixed electrode, the same effect as that of the fixed electrode having the configuration shown in FIG.
In the configuration example of FIG. 7 (b), (c) , a rectangular hole having the fixed electrode, the width in the direction of the vibrating film side is large, and is configured to and depth becomes shallower.

Also, FIG. 6, shown in the configuration shown in FIG. 7, the plurality of through holes provided in the fixed electrode may be each the same size.
Further, the plurality of through holes may have the same size at positions facing each other, and may have a plurality of hole sizes.

The fixed electrode constituting the ultrasonic transducer according to this embodiment may be constituted by a single conductive member or may be formed by a plurality of conductive members.
Further, the fixed electrode constituting the ultrasonic transducer according to the present embodiment may be composed of a conductive member and an insulating member.

Specifically, the material of the fixed electrode of the ultrasonic transducer according to the present embodiment is only required to be conductive, and for example, a single structure of SUS, brass, iron, or nickel is possible.
In addition, since it is necessary to reduce the weight, a desired hole is drilled in a glass epoxy board or paper phenol board that is generally used for circuit boards, and then plated 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 apply plating to the substrate on both sides.

However, when a double-sided electrode vapor deposition film or an electret film is used for the vibration film 12, in the ultrasonic transducer 1 shown in FIG. 1, some insulation treatment is required on the vibration film 12 side of the pair of fixed electrodes 10A and 10B. Become. For example, it is necessary to perform an insulating thin film treatment with alumina, silicon polymer material, amorphous carbon film, SiO ₂ or the like.

  Next, the vibration film 12 will be described. The function of the vibrating membrane 12 is to always accumulate charges of the same polarity (which may be + polarity or-polarity) and to vibrate by electrostatic force between the fixed electrodes 10A and 10B that change with an AC voltage. A specific configuration example of the vibrating membrane 12 in the ultrasonic transducer according to the embodiment of the present invention will be described with reference to FIG.

FIG. 8A shows a cross-sectional structure of the vibrating membrane 12 having the electrode layer 121 by performing electrode vapor deposition on both surfaces of the insulating film 120. The central insulating film 120 is made of a polymer material such as polyethylene terephthalate (PET), polyester, polyethylene naphthalate (PEN), polyphenylene sulfide (PPS), etc. preferable.

  The electrode deposition material for forming the electrode layer 121 is most commonly Al, and Ni, Cu, SUS, Ti, etc. are desirable from the standpoints of compatibility with the polymer material and cost. The thickness of the insulating polymer film as the insulating film 120 forming the vibration film 12 cannot be uniquely determined because the optimum value varies depending on the driving frequency, the hole size provided in the fixed electrode, etc., but generally it is not less than 1 μm and not more than 100 μm. The range seems to be sufficient.

The thickness of the electrode deposition layer as the electrode layer 121 is also preferably in the range of 40 nm to 200 nm. If the electrode thickness is too thin, almost no charge can be accumulated, and if it is too thick, the film becomes hard and the amplitude is reduced. The electrode material may be a transparent conductive film ITO / In, Sn, Zn oxide or the like.

FIG. 8B shows a structure in which the electrode layer 121 is sandwiched between insulating polymer films as the insulating film 120. The thickness of the electrode layer 121 at this time is preferably in the range of 40 nm to 200 nm as in the case of FIG. Further, the material and thickness of the insulating film 120 sandwiching the electrode layer 121 are also polyethylene terephthalate (PET), polyester, polyethylene naphthalate (PEN) in the same manner as the double-sided electrode deposition film of FIG. Polyphenylene sulfide (PPS) is preferably 1 μm or more and 100 μm or less.

FIG. 8 (c) shows a case where two single-sided electrode vapor-deposited films are bonded together so that the electrode surfaces are in contact. The conditions of the insulating film and the electrode part at this time are preferably the same conditions as those of the other vibration films described above.
Further, the vibrating membrane 12 requires a DC bias voltage of several hundred volts, but the bias voltage is reduced by fixing the vibrating membrane 12 with tension in four directions at right angles on the membrane surface when the membrane unit is manufactured. it can.

This is because a tension is applied to the film in advance to bring about the same effect as the tensile tension that the bias voltage has conventionally been responsible for, which is a very effective means for lowering the voltage.
Also in this case, Al is the most common film electrode material, and Ni, Cu, SUS, Ti, etc. are desirable from the standpoint of compatibility with the polymer material and cost. Further, a transparent conductive film ITO / In, Sn, Zn oxide or the like may be used.

Next, as the fixing material for the fixed electrode or the diaphragm, plastic materials such as acrylic, bakelite, and polyacetal (polyoxymethylene) resin (POM) are preferable from the viewpoint of light weight and non-conductivity.

  Next, the configuration of the ultrasonic speaker according to the embodiment of the present invention is shown in FIG. The ultrasonic speaker according to the present embodiment uses any of the ultrasonic transducers (FIGS. 2 to 4) including the acoustic reflector according to the above-described embodiments of the present invention as the ultrasonic transducer 55. .

5, the ultrasonic speaker according to the present embodiment includes an audio frequency wave oscillation source (signal source) 51 that generates a signal wave in an audio frequency band, and a carrier that generates and outputs a carrier wave in the ultrasonic frequency band. A wave oscillation source (carrier wave supply means) 52, a modulator (modulation means) 53, a power amplifier 54, and an ultrasonic transducer 55 are included. The ultrasonic transducer 55 is provided with an acoustic reflector (not shown) according to an embodiment of the present invention.
The modulator 53 modulates the carrier wave output from the carrier wave oscillation source 52 with the signal wave of the audio frequency band output from the audio frequency wave oscillation source 51, and supplies the modulated wave to the ultrasonic transducer 55 via the power amplifier 54. To do.

  In the above configuration, the carrier wave in the ultrasonic frequency band output from the carrier wave oscillation source 52 by the signal wave output from the audible frequency wave oscillation source 51 is modulated by the modulator 53 and the modulated signal amplified by the power amplifier 54 is used. The ultrasonic transducer 55 is driven. As a result, the modulated signal is converted into a sound wave of a finite amplitude level by the ultrasonic transducer 55, and this sound wave is radiated into the medium (in the air), and the signal sound in the original audible frequency band due to the nonlinear effect of the medium (air). Is self-regenerating.

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 propagation of the modulated ultrasonic waves, and the dense portions have high sound speed and sparseness. Since the sound speed of such a portion is slow, the modulation wave itself is distorted. As a result, the waveform is separated into a carrier wave (ultrasonic frequency band), and a signal wave (signal sound) in an audible frequency band is reproduced.

When sound waves are radiated from the ultrasonic transducer 55, the sound waves (ultrasonic frequency band) radiated from the front surface of the ultrasonic transducer 55 are radiated as they are in front of the ultrasonic transducer. The sound wave (ultrasonic frequency band) radiated from the back surface is reflected by an acoustic reflector (not shown), and the paths of all the reflected waves are equal. Radiated.
Therefore, since the membrane vibration energy of the vibration membrane in the ultrasonic transducer 55 can be utilized to the maximum extent, the voltage of the signal source can be lowered, and an ultrasonic speaker with reduced power can be realized.

Further, as described above, when a high sound pressure broadband property is secured, it can be used as a speaker for various purposes. Ultrasound is strongly attenuated in the air and attenuates in proportion to the square of its frequency. Therefore, when the carrier frequency (ultrasonic wave) is low, it is possible to provide a loudspeaker that has a small attenuation and can reach far away in the form of a beam.
On the contrary, if the carrier frequency is high, the attenuation is severe, so that the parametric array effect does not occur sufficiently, and a speaker in which the sound spreads can be provided. These are very effective functions because the same ultrasonic speaker can be used according to the application.

  In addition, dogs who often live with humans as pets can listen to sounds up to 40kHz, and cats can listen to sounds up to 100kHz, so if you use a higher carrier frequency, there will be no effect on pets. Also have. In any case, the fact that it can be used at various frequencies brings many advantages.

  According to the ultrasonic speaker according to the embodiment of the present invention, the ultrasonic wave according to the embodiment of the present invention can generate an acoustic signal having a sound pressure level sufficiently high to obtain a parametric array effect over a wide frequency band. Since the transducer is used, a signal sound with high fidelity (audible frequency band) can be reproduced over a wide frequency band.

  The ultrasonic transducer according to the embodiment of the present invention can be used for various sensors, for example, a distance measuring sensor, and as described above, a sound source for a directional speaker and an ideal impulse signal generation source. Etc. are available.

The figure which shows the structure of the ultrasonic transducer to which this invention is applied. 1 is a diagram showing a configuration of an ultrasonic transducer according to a first embodiment of the present invention. The figure which shows the structure of the ultrasonic transducer based on 2nd Embodiment of this invention. The figure which shows the structure of the ultrasonic transducer based on 3rd Embodiment of this invention. The perspective view which shows the external appearance structure of an acoustic reflector. Explanatory drawing which shows the specific example of the shape of the fixed electrode in the ultrasonic transducer | transducer which concerns on each embodiment of this invention. Explanatory drawing which shows the specific example of the penetration groove | channel structure of the fixed electrode in the ultrasonic transducer | transducer which concerns on each embodiment of this invention. Explanatory drawing which shows the specific example of the structure of the diaphragm in the ultrasonic transducer | transducer which concerns on each embodiment of this invention. The block diagram which shows the structure of the ultrasonic speaker which concerns on each embodiment of this invention. The figure which shows the structure of the conventional resonance type ultrasonic transducer. The figure which shows the specific structure of the conventional electrostatic broadband oscillation type ultrasonic transducer. The figure which showed the frequency characteristic of the ultrasonic transducer which concerns on each embodiment of this invention with the frequency characteristic of the conventional ultrasonic transducer.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Ultrasonic transducer, 10A, 10B ... Fixed electrode, 12 ... Vibration membrane, 14 ... Hole, 16 ... DC bias power supply, 18 ... Signal source, 20, 30, 40 ... Acoustic reflector 51 ... Audio frequency wave oscillation source, 52 ... Carrier wave oscillation source, 53 ... Modulator, 54 ... Power amplifier, 55 ... Ultrasonic transducer, 120 ... Insulating film, 121 ... Electrode layer,

Claims (7)

A first fixed electrode having a plurality of holes;
A second fixed electrode having a plurality of holes paired with the first fixed electrode;
It said first clamping or are held by the fixed electrode and the pair of fixed electrodes and a second fixed electrode Rutotomoni has a conductive layer, and a vibrating membrane to which a DC bias voltage to the conductive layer is applied,
Have,
The plurality of holes of the second fixed electrode are all or most formed at positions facing the plurality of holes of the first fixed electrode through the vibration film, and the gap is between the pair of fixed electrodes. AC signal is applied ,
An ultrasonic transducer comprising an acoustic reflector on a first surface of the pair of fixed electrodes . In the acoustic reflector, all the ultrasonic waves radiated from the openings of the plurality of holes in the first surface of the ultrasonic transducer are radiated to the second surface of the ultrasonic transducer through a path having the same length. The ultrasonic transducer according to claim 1, wherein the ultrasonic transducer is disposed at a position . The acoustic reflector is
One end is located at the center position of the first surface of the ultrasonic transducer , and the other end is disposed at an angle of 45 ° with respect to both sides of the first surface of the ultrasonic transducer with respect to the center position. A pair of first reflectors having a length that matches the end of the acoustic transducer;
A pair of second layers having a length equal to the length of the first reflector plate connected to the outside of the first reflector plate at an angle perpendicular to the end portions of the pair of first reflector plates. The ultrasonic transducer according to claim 2, further comprising: a reflector. The acoustic reflector is
Wherein located at one end or at one end of the first surface of the ultrasonic transducer, the arrangement at the other angle end direction at 45 ° to the first surface of the ultrasonic transducer from one end the A first reflector having a length at which the other end coincides with the other end of the ultrasonic transducer;
A second reflector having a right angle to the other end of the first reflector and connected to the outside of the first reflector and having a length equivalent to the length of the first reflector. The ultrasonic transducer according to claim 2. The acoustic reflector is
Wherein are arranged at an angle of 45 ° to either side of the first surface of the ultrasonic transducer with respect to the center position of the first surface of the ultrasonic transducer, consistent with the ends of its ends the ultrasonic transducer A first conical reflector having a length of generating line;
A frustoconical second having a generatrix with a length equal to the length of the first reflector connected to the outside of the first reflector at an angle perpendicular to the generatrix of the first reflector A reflector,
The ultrasonic transducer according to claim 2, comprising:   The ultrasonic transducer according to any one of claims 1 to 5, wherein the size of the concave-convex shape of the reflection surface of the acoustic reflector is equal to or less than the wavelength of the ultrasonic wave emitted from the ultrasonic transducer. The ultrasonic transducer according to any one of claims 1 to 6,
  A signal source for generating a signal wave in an audible frequency band;
  A carrier wave supply means for generating and outputting a carrier wave in an ultrasonic frequency band;
  Modulation means for outputting a modulated signal obtained by modulating the carrier wave with an audible frequency band signal wave output from the signal source;
  The ultrasonic speaker is driven by the modulation signal applied between the pair of fixed electrodes and the electrode layer of the vibrating membrane.