JP4867662B2 - Electrostatic ultrasonic transducer, ultrasonic speaker, and audio signal reproduction method for electrostatic ultrasonic transducer - Google Patents

Description

  The present invention relates to an electrostatic ultrasonic transducer used in a directivity acoustic radiation device, and in particular, in an electrostatic ultrasonic transducer, an area of a vibrating portion of a vibrating membrane and an opening that radiates an acoustic signal. Electrostatic ultrasonic transducer, ultrasonic speaker equipped with electrostatic ultrasonic transducer, and audio signal reproducing method of electrostatic ultrasonic transducer, which can increase area and obtain large amplitude with low voltage The present invention relates to a display device including an ultrasonic speaker and a directional acoustic system.

  As an ultrasonic transducer used for an acoustic radiation device with sharp directivity, a piezoelectric type and an electrostatic type have been proposed. Piezoelectric ultrasonic transducers have the drawback that sound reproducibility is poor because the resonance point is sharp and it is difficult to widen the bandwidth (see, for example, Patent Documents 1 and 2).

  On the other hand, electrostatic ultrasonic transducers do not have sharp resonance of the diaphragm itself, and use of the air column resonance phenomenon of an acoustic tube enables a wider bandwidth and excellent sound reproducibility (good sound quality). Has advantages (for example, see Patent Document 3).

  FIG. 10 is a diagram showing a conventional electrostatic ultrasonic transducer 3. FIG. 1A shows a cross section of the electrostatic ultrasonic transducer 3. The electrostatic ultrasonic transducer 3 includes a vibrating membrane 30 having a vibrating electrode (conductive layer) 32, and each of the vibrating membrane 30. It has a pair of fixed electrode which consists of the front side fixed electrode 60A and the back side fixed electrode 60B which were provided facing the surface. The vibration film 30 is formed so that a vibration electrode (conductive layer) 32 forming an electrode is sandwiched between dielectric films (insulating films) 31 and 33.

  The front-side fixed electrode 60A that sandwiches the vibration film 30 is provided with a plurality of through holes 61A, and the back-side fixed electrode 60B is opposed to each through-hole 61A provided in the front-side fixed electrode 60A. Are provided with through holes 61B having the same shape. The front-side fixed electrode 60A and the back-side fixed electrode 60B are supported by a support member 62 with a predetermined gap from the vibrating membrane 30, respectively, so that the vibrating membrane 30 and the fixed electrode are opposed to each other with a gap. The support member 62 is formed. FIG. 10B shows a one-sided plan view of the transducer, and a plurality of through holes 61A are arranged in a honeycomb shape on the front-side fixed electrode 60A.

  The DC power source 36 is a power source for applying a DC bias voltage to the vibration electrode 32, and AC signals 37 </ b> A and 37 </ b> B are applied to the front side fixed electrode 60 </ b> A and the back side fixed electrode 60 </ b> B in order to drive the vibration film 30. Signal. With the above configuration, the front side fixed electrode 60A and the back side fixed electrode 60B of the electrostatic ultrasonic transducer 3 are supplied with AC signals 37A and 37B having the same amplitude and opposite phases with respect to the center tap. Applied.

In this way, the direction in which the electrostatic force works alternately changes while the vibrating membrane 30 receives electrostatic attraction and 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 the parametric array effect can be generated. As described above, the electrostatic ultrasonic transducer 3 shown in FIG. 10 has a push-pull type electrostatic super-vibration because the vibrating membrane 30 vibrates by receiving a force from the pair of fixed electrodes 60A and 60B. It is called a sonic transducer.
JP-A 61-296897 JP 2000-287297 A JP 2006-93932 A

  The above-described electrostatic ultrasonic transducer has advantages in that it can have a wide band and has excellent sound reproducibility (good sound quality) compared to a resonant ultrasonic transducer.

  However, in this electrostatic ultrasonic speaker, the vibration part area of the membrane is as small as, for example, less than 15% of the acoustic radiation surface area of the transducer, so vibration energy cannot be effectively released into the air as acoustic energy. I had a problem. Ultrasonic speakers are required to release high acoustic energy into the air, but further enhancement of the sound level has been desired even in an electrostatic system that can obtain a relatively high sound pressure. Furthermore, in the electrostatic system, in order to obtain a high sound pressure output, a signal having a high voltage of 200 V or more is required, and a reduction in voltage has been a problem.

  In order to cope with such a problem, the applicant of the present application is currently applying for the electrostatic ultrasonic transducer shown in FIG. FIG. 11A shows a plan view of one electrode 70 of the pair of electrodes 70 and 70A sandwiching the vibrating membrane as viewed from the vibrating membrane side. FIG. 11B is a cross-sectional view of the electrostatic ultrasonic transducer, and is a cross-sectional view in the XX ′ direction in FIG.

  In this electrostatic ultrasonic transducer, a circular through hole 71 is provided in an electrode (base material) 70 made of a non-conductive material, and a cross bridge portion 72 facing the vibrating membrane 30 is formed in the circular through hole 71. It is provided. The cross bridge portion 72 is formed such that its length (length in the depth direction of the through hole) has a predetermined interval (for example, 5 to 6 μm) with respect to the surface of the vibrating membrane 30 when it is not vibrating. An electrode layer 73 is formed on the surface of the cross bridge portion 72 facing the vibration film 30. Similarly, a through hole 71A, a cross bridge portion 72A, and an electrode layer 73A are formed in the other electrode 70A. A DC bias voltage is applied to the vibration electrode 32 of the vibration film 30, and an AC signal is applied between the cross-shaped electrode layer 73 and the electrode layer 73 </ b> A.

  Such a structure makes it possible to efficiently convert electrical energy into membrane vibration energy (to obtain a large amplitude acoustic signal). However, the problem of increasing the acoustic radiation area has not been solved.

  The present invention has been made to solve such a problem, and an object of the present invention is to increase the area of a vibrating portion of a vibrating membrane and to provide an opening for emitting an acoustic signal in an electrostatic ultrasonic transducer. An electrostatic ultrasonic transducer, an ultrasonic speaker including the electrostatic ultrasonic transducer, and an electrostatic ultrasonic transducer, which can increase the area and obtain a large amplitude acoustic signal with a low voltage signal An audio signal reproducing method, a display device including an ultrasonic speaker, and a directional acoustic system are provided.

The present invention has been made to solve the above problems, and an electrostatic ultrasonic transducer of the present invention includes a first electrode having a slit-like through hole and a second electrode having a slit-like through hole. A pair of electrodes, wherein the through hole of the first electrode and the through hole of the second electrode are arranged to make a pair, and the first electrode and the second electrode A vibration layer sandwiched between and having a conductive layer, to which a DC bias voltage is applied to the conductive layer,
The pair of electrodes includes an electrode layer disposed in the longitudinal direction of the through hole inside the through hole, and an ultrasonic frequency band carrier wave is transmitted between the electrode layers of the pair of electrodes in an audible frequency band. A modulated wave modulated by a signal wave is applied.
In the electrostatic ultrasonic transducer having the above-described configuration, a plurality of slit-shaped (rectangular) through holes (openings) are provided in each of the pair of electrodes that sandwich the vibration film, and the inside of the slit-shaped through holes is An electrode layer facing the vibrating membrane with a predetermined distance is disposed in the longitudinal direction of the through hole.
Thereby, for example, the shape of the through hole (vibration shape of the vibrating membrane) can be changed from the circular shape shown in FIG. 11 to the rectangular shape (slit shape) shown in FIG. For this reason, while increasing the vibration area of a diaphragm, the area of the opening which radiates | emits an acoustic signal can be increased, and a large amplitude acoustic signal can be obtained with a low voltage signal. As a result, the electrical / acoustic energy conversion efficiency can be improved and high sound pressure can be obtained.

The electrostatic ultrasonic transducer according to the present invention is characterized in that is formed in the through hole of the first electrode and the through hole of the second electrode.
In the electrostatic ultrasonic transducer having the above-described configuration, a plurality of slit-like (rectangular) through holes are provided in each of the pair of electrodes that sandwich the vibration film, and the vibration film is parallel to the longitudinal direction of the through hole. A bridge portion having a diaphragm facing surface facing the surface in the depth direction of the through hole with respect to the surface at the time of non-vibration, and an electrode layer is provided on the diaphragm facing surface of the bridge portion. Form.
Thereby, while being able to form an electrode and a bridge | bridging part integrally, an electrode layer can be formed easily.

The electrostatic ultrasonic transducer according to the present invention is characterized in that the first electrode, the second electrode, and the bridge portion are formed of a non-conductive material.
In the electrostatic ultrasonic transducer having the above configuration, the first electrode, the second electrode, and the bridge portion are formed of a nonconductive material, and the electrode layer is formed on the vibration film facing surface of the bridge portion.
Thereby, the electrode of the electrostatic ultrasonic transducer can be formed of a material such as plastic, and the electrostatic ultrasonic transducer can be manufactured at a low cost and at a low cost.

In the electrostatic ultrasonic transducer according to the present invention, at least one of the first electrode and the second electrode may be a reinforcing member that crosses the through hole in the short direction inside the through hole. It is characterized by having.
In the electrostatic ultrasonic transducer having the above-described configuration, the through hole is formed in the through hole in at least one of the first electrode and the second electrode which are a pair of electrodes sandwiching the vibration film. A reinforcing member that crosses in the short direction is provided.
Thereby, in addition to the effect of increasing the vibration area of the vibration film and increasing the area of the opening that radiates the acoustic signal, the strength of the electrode of the electrostatic ultrasonic transducer can be increased. For this reason, it is possible to manufacture an electrostatic ultrasonic transducer having a large area (for example, 50 mm × 50 mm or more).

The electrostatic ultrasonic transducer according to the present invention is characterized in that the vibration film has a multi-layered conductive layer.
In the electrostatic ultrasonic transducer having the above configuration, the conductive layer (vibrating electrode) of the vibrating membrane is formed in multiple layers.
Thereby, the electrostatic force applied to the diaphragm can be increased, the amplitude of the diaphragm can be increased, and the sound pressure level of the output acoustic signal can be increased.

The electrostatic ultrasonic transducer according to the present invention is characterized in that an acoustic reflector is provided on the back surface of the electrostatic ultrasonic transducer.
In the electrostatic ultrasonic transducer having the above configuration, an acoustic reflector is installed on the back surface of the electrostatic ultrasonic transducer, and the ultrasonic waves emitted from the back surface of the electrostatic ultrasonic transducer are reflected on the front surface. For example, the acoustic reflector is disposed so that all the ultrasonic waves radiated from the respective openings on the back surface of the electrostatic ultrasonic transducer are radiated to the front surface of the electrostatic ultrasonic transducer through a path having the same length.
Thereby, the ultrasonic wave emitted from the front surface and the back surface of the electrostatic ultrasonic transducer can be effectively used.

In the electrostatic ultrasonic transducer according to the present invention, one end of the acoustic reflector is located at a center position on the back surface of the electrostatic ultrasonic transducer, and both sides of the back surface of the electrostatic ultrasonic transducer are based on the center position. A pair of first reflectors arranged at an angle of 45 ° with respect to the other end of the electrostatic ultrasonic transducer, and the ends of the pair of first reflectors; A pair of second reflectors each having a right angle and being connected to the outer side of the first reflector and having a length equivalent to the length of the first reflector, To do.
In the electrostatic ultrasonic transducer having the above-described configuration, the acoustic reflector is configured such that all the ultrasonic waves radiated from the openings on the back surface of the electrostatic ultrasonic transducer are radiated to the front surface of the ultrasonic transducer through the same length path. Placed in. That is, the first reflecting plate is disposed at an angle of 45 ° with respect to both sides of the center M on the back surface of the ultrasonic transducer, and the length of the first reflecting plate coincides with the end of the ultrasonic transducer. The ultrasonic wave emitted from the back surface of the ultrasonic transducer is reflected in the horizontal direction by the first reflecting plate. Next, by connecting the second reflecting plate connected at a right angle to the first reflecting plate to the outside of the first reflecting plate, the ultrasonic wave is emitted to the front surface of the ultrasonic transducer. The second reflector length is also required to be equal to the first reflector length. In this way, all the ultrasonic waves radiated from the back surface of the ultrasonic transducer are reflected along the same length path, and the phases of the ultrasonic waves emitted from the back surface to the front surface are all aligned.
Thereby, the ultrasonic wave emitted from the front surface and the back surface of the transducer can be effectively used.

The ultrasonic speaker of the present invention modulates a carrier wave in the ultrasonic frequency band with a signal wave output from a signal source that generates a signal wave in the audible frequency band, and an electrostatic ultrasonic transducer is modulated with the modulated wave. An ultrasonic speaker that reproduces signal sound in an audible frequency band by driving, wherein the electrostatic ultrasonic transducer includes a first electrode having a slit-like through hole and a first electrode having a slit-like through hole. A pair of the first electrode and the second electrode, the second electrode, the through hole of the first electrode and the through hole of the second electrode arranged in a pair. And a vibration film that has a conductive layer and is applied with a DC bias voltage to the conductive layer, and the pair of electrodes are disposed in the longitudinal direction of the through hole inside the through hole. Having an electrode layer To the electrode layers in the pair of electrodes is characterized in that modulated wave obtained by modulating the carrier wave in the ultrasonic frequency band by signal waves in the audio frequency band is applied.
In the ultrasonic speaker of the present invention configured as described above, in the ultrasonic speaker that modulates the carrier wave in the ultrasonic frequency band with the signal wave in the audible frequency band and drives the electrostatic ultrasonic transducer with the modulated wave, An electrostatic ultrasonic transducer having a slit-like through-hole and an electrode layer facing the vibration film inside the through-hole is used.
As a result, the vibration area of the vibration film of the electrostatic ultrasonic transducer used in the ultrasonic speaker can be increased, and the area of the opening that radiates the acoustic signal can be increased. As a result, it is possible to realize an ultrasonic speaker that can generate an acoustic signal having a sufficiently high sound pressure level to obtain a parametric array effect over a wide frequency band.

The method of reproducing an audio signal of an electrostatic ultrasonic transducer according to the present invention includes: a first electrode having a slit-like through hole; a second electrode having a slit-like through hole; The through hole and the through hole of the second electrode are arranged to make a pair, and are sandwiched between a pair of electrodes composed of the first electrode and the second electrode, and have a conductive layer A vibrating membrane to which a DC bias voltage is applied to the conductive layer, and the pair of electrodes has an electrode layer disposed in the longitudinal direction of the through hole inside the through hole. A procedure for generating a signal wave in an audible frequency band by a signal source, a procedure for generating a carrier wave in an ultrasonic frequency band by a carrier wave supply source, and a signal in the audible frequency band. Modulated by waves And a step of driving the electrostatic ultrasonic transducer by applying the modulation signal between the electrode layers of the pair of electrodes.
In the audio signal reproducing method of the electrostatic ultrasonic transducer including such a procedure, the carrier wave in the ultrasonic frequency band is modulated by the signal wave in the audible frequency band, and the electrostatic ultrasonic transducer is driven by the modulated wave. In the ultrasonic speaker, an electrostatic ultrasonic transducer having an electrode layer having a slit-like through hole in the electrode and facing the vibration film inside the through hole is used.
As a result, the vibration area of the vibration film of the electrostatic ultrasonic transducer used in the ultrasonic speaker can be increased, and the area of the opening that radiates the acoustic signal can be increased. As a result, it is possible to generate an acoustic signal having a sound pressure level that is sufficiently high to obtain a parametric array effect over a wide frequency band.

The display device of the present invention modulates a carrier wave signal in an ultrasonic frequency band with an audio signal supplied from an acoustic source, and drives an electrostatic ultrasonic transducer with the modulated signal to generate a signal sound in an audible frequency band. A display device comprising: an ultrasonic speaker to be reproduced; and a projection optical system that projects an image on a projection surface, wherein the electrostatic ultrasonic transducer of the ultrasonic speaker has a slit-shaped through hole. 1 electrode, a second electrode having a slit-like through hole, the through hole of the first electrode and the through hole of the second electrode are arranged in pairs, and the first electrode A vibration film sandwiched between a pair of electrodes composed of one electrode and the second electrode and having a conductive layer, and a DC bias voltage is applied to the conductive layer, the pair of electrodes, Inside the through hole A modulation wave obtained by modulating a carrier wave in an ultrasonic frequency band with a signal wave in an audible frequency band is applied between the electrode layers of the pair of electrodes. Features.
In the display device having the above-described configuration, an ultrasonic speaker including an electrostatic ultrasonic transducer having a slit-like through hole in the electrode and an electrode layer facing the vibration film inside the through hole is used. And the audio | voice signal supplied from an acoustic source is reproduced | regenerated by this ultrasonic speaker.
As a result, the acoustic signal can be reproduced so as to be emitted from a virtual sound source formed in the vicinity of a sound wave reflecting surface such as a screen with sufficient sound pressure and wide band characteristics. For this reason, it is possible to easily control the reproduction range of the acoustic signal.

Further, the directional acoustic system of the present invention modulates a carrier wave signal in an ultrasonic frequency band with a signal in a first sound range among audio signals supplied from an acoustic source, and an electrostatic ultrasonic transducer is modulated with the modulated signal. An ultrasonic speaker that drives and reproduces a signal sound in an audible frequency band; and a low-frequency sound reproduction speaker that reproduces a signal in a second sound range lower than the first sound range among sound signals supplied from the acoustic source; The electrostatic ultrasonic transducer of the ultrasonic speaker includes: a first electrode having a slit-like through hole; a second electrode having a slit-like through hole; When the through hole of the first electrode and the through hole of the second electrode are arranged so as to make a pair, and are sandwiched between a pair of electrodes composed of the first electrode and the second electrode When A vibration layer to which a DC bias voltage is applied to the conductive layer, and the pair of electrodes includes an electrode layer disposed in the longitudinal direction of the through hole inside the through hole. And a modulated wave obtained by modulating a carrier wave in an ultrasonic frequency band with a signal wave in an audible frequency band is applied between the electrode layers of the pair of electrodes.
In the directional acoustic system having the above configuration, an ultrasonic speaker including an electrostatic ultrasonic transducer having a slit-like through hole in the electrode and an electrode layer facing the vibration film inside the through hole is used. . The ultrasonic speaker reproduces an audio signal in the middle / high range (first range) of the audio signal supplied from the acoustic source. In addition, a sound signal in the low sound range (second sound range) among the sound signals supplied from the acoustic source is reproduced by a low sound reproduction speaker.
Therefore, it is possible to reproduce the mid-high range sound so that it can be emitted from a virtual sound source formed in the vicinity of a sound wave reflecting surface such as a screen with sufficient sound pressure and wide band characteristics. Further, since the sound in the low frequency range is directly output from the low sound reproduction speaker provided in the sound system, the low frequency range can be reinforced and a more realistic sound field environment can be created.

First, an outline of the electrostatic ultrasonic transducer of the present invention will be described.
In order to increase the sound pressure level of the acoustic signal radiated from the electrostatic ultrasonic transducer, it is necessary to increase the vibration amplitude and vibration area of the vibrating membrane, which increases the electrostatic force acting on the membrane and the vibration area. It is important to increase the ratio. In the present invention, the bridge structure for increasing the membrane amplitude is improved, and the vibration shape of the vibration membrane is changed from the circular shape shown in FIG. 11 to the rectangular shape (slit shape) shown in FIG. While increasing a vibration area, the area of the opening part which radiates | emits an acoustic signal is increased. As a result, the electrical / acoustic energy conversion efficiency can be improved and a high sound pressure acoustic signal can be obtained.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[First Embodiment]
FIG. 1 is a diagram showing a configuration example of an electrostatic ultrasonic transducer according to the first embodiment of the present invention. 1A is a cross-sectional view, and FIG. 1B is a plan view of the electrode viewed from the vibrating membrane side.

  The electrostatic ultrasonic transducer 1 of the present invention includes a vibrating membrane 30, a front electrode (first electrode) 10 and a rear electrode (second electrode) 20, which are a pair of electrodes sandwiching the vibrating membrane 30, and It consists of the circuit which drives.

  The front electrode 10 includes a diaphragm supporting portion 11 for sandwiching the diaphragm 30, an opening 13 that is a slit-shaped (rectangular) through-hole, and an inside of the opening (through-hole) 13. It is formed with the bridge part 12 arrange | positioned in parallel with the longitudinal direction. The bridge portion 12 is disposed such that the bottom surface (vibrating film facing surface facing the vibrating film 30) maintains a predetermined distance (for example, 5 to 6 μm) from the film surface of the vibrating film 30 when not vibrating. The An electrode layer 14 is formed on the vibration film facing surface of the bridge portion 12 that faces the vibration film 30.

  Similarly, the back electrode 20 includes a diaphragm supporting portion 21 for sandwiching the diaphragm 30, an opening 23 that is a slit-like (rectangular) through-hole, and an inside of the opening (through-hole) 23. And the bridge portion 22 arranged in parallel with the longitudinal direction of the through hole. The bridge portion 22 is disposed such that the bottom surface (vibrating membrane facing surface facing the vibrating membrane 30) maintains a predetermined distance (for example, 5 to 6 μm) from the membrane surface of the vibrating membrane 30 when not vibrating. The An electrode layer 24 is formed on the vibration film facing surface of the bridge portion 22 that faces the vibration film 30.

  In addition, the thickness of the front side electrode 10 and the back side electrode 20 is about 1.5 mm, for example. Further, as shown in FIG. 1B, the width of the slit-shaped through hole is, for example, about 1.5 mm, and the width of the bridge portion is about 0.5 mm.

  The front side electrode 10 and the back side electrode 20 are formed of a non-conductive base material (various plastics, glass, ceramics, etc.), and plating (printing) of metal (gold, silver, copper, aluminum, etc.) as the electrode layers 14, 24. , Vapor deposition, paste, and the like. An AC voltage of about 10 to 300 V is applied to the electrode layers 14 and 24 by AC signals 37A and 37B on the circuit side.

  The vibration film 30 is formed by covering a vibration electrode (conductive layer) 32 with dielectric films (insulators) 31 and 32. For example, a metal film processed on one side of a polymer film (dielectric film) having a thickness of several microns is laminated with an adhesive. As the material of the polymer film, for example, poly (ethylene terephthalate) (PET), aramid, poly ester, poly (ethylene naphthalate) (PEN), poly (phenylene sulfide) (PPS) or the like is used. Al (aluminum) is the most common material for the metallized portion forming the vibration electrode 32, and Ni, Cu, SUS, Ti, or the like may be used. The thickness of the metallized portion is preferably about 100 to 1500 mm. A DC bias voltage of 10 to 300 V is applied from the DC power supply 36 on the circuit side to the metallized portion (vibrating electrode 32) of the vibrating membrane.

  The operation of the electrostatic ultrasonic transducer 1 having the above configuration is basically the same as that of the electrostatic ultrasonic transducer 3 shown in FIG. 10, and an acoustic signal is generated by the push-pull operation of the vibration film 30. In other words, in the electrostatic ultrasonic transducer 1, the pair of electrodes 10, 20 has the same number and a plurality of slit-like openings (through holes) 13, 23 at positions facing each other via the vibration film 30. Between the electrode layers 14 and 24 of the bridge portions 12 and 22 of the pair of electrodes 10 and 20, AC signals 37A and 37B whose phases are mutually inverted by a signal source 37 are applied. Capacitors are formed between the electrode layer 14 and the vibrating electrode 32 and between the electrode layer 24 and the vibrating electrode 32, respectively. Also, a unipolar (positive polarity in this embodiment) DC bias voltage is applied to the vibrating electrode 32 of the vibrating membrane 30 by a DC power source 36.

As a result, in the positive half cycle of the AC signal 37A output from the signal source 37, since a positive voltage is applied to the electrode layer 14 of the bridge portion 12 of the front electrode 10, the electrodes 10 of the vibrating membrane 30 Electrostatic repulsive force acts on the surface portion 15A not sandwiched by 20, and the surface portion 15A is pulled downward in FIG.
Further, at this time, the AC signal 37B becomes a negative cycle, and a negative voltage is applied to the electrode layer 24 of the bridge portion 22 of the opposing back side electrode 20, so that the back surface of the surface portion 15A of the vibration film 30 is An electrostatic attraction force acts on the back surface portion 15B which is the side, and the back surface portion 15B is pulled further downward in FIG.

  Therefore, the film portion of the vibration film 30 that is not sandwiched between the pair of electrodes 10 and 20 receives an electrostatic attractive force and an electrostatic repulsive force (electrostatic repulsive force) in the same direction. Similarly, in the negative half cycle of the AC signal output from the signal source 37, the electrostatic attraction force is applied upward in FIG. 1 to the front surface portion 15A of the vibration film 30, and the rear surface portion 15B In FIG. 1, an electrostatic repulsive force acts on the upper side, and a film portion not sandwiched between the pair of electrodes 10 and 20 of the vibration film 30 receives an electrostatic attractive 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 30 receives the electrostatic attractive force and the electrostatic repulsive force in the same direction according to the change in the polarity of the AC signal. An acoustic signal having a sound pressure level sufficient to obtain a parametric array effect can be generated. The acoustic signal radiated from the vibration film 30 is radiated to the outside as a plane wave through the slit-shaped openings 13 and 23.

  FIG. 2 is a view showing a modification of the electrostatic ultrasonic transducer according to the present invention. 2A, 2 </ b> B, and 2 </ b> C are plan views of the front side electrode as viewed from the diaphragm side. The back side electrode has the same configuration.

  The front electrode 10 shown in FIG. 2A is the same as the front electrode 10 shown in FIG. 1B, and is the most basic configuration example of the electrostatic ultrasonic transducer of the present invention.

  A front side electrode 40 shown in FIG. 2 (B) has a reinforcing member 41 for reinforcing a base material (for example, plastic) forming the electrode at the center portion in the longitudinal direction of the slit-like through hole. The example added to the direction orthogonal to the longitudinal direction of is shown. In this example, the electrode layer facing the vibration film is divided into the electrode layer 42A and the electrode layer 42B by the reinforcing member 41, but the length of the reinforcing member 41 (depth of the through hole) is shown. The length of the direction) is the same as the length of the bridge portion (the length of the through hole in the depth direction), and the surface of the bridge portion (the surface facing the vibrating membrane) and the surface of the reinforcing member 41 are aligned with each other. Can also be formed as a continuous surface.

  In addition, the front-side electrode 50 shown in FIG. 2C has two reinforcing members 51 and 52 for reinforcing a base material (for example, plastic) forming the electrode, and slit-like through holes are equally long. The example added so that it becomes. In this example, the electrode layer facing the vibration film is divided into the electrode layer 53A, the electrode layer 53B, and the electrode layer 53C by the reinforcing members 51 and 52. The length (length in the depth direction of the through hole) is the same length (length in the depth direction of the through hole) as the bridge portion, and the surface of the bridge portion (surface facing the vibration film) and the reinforcing member 51, By combining the surfaces of 52, the electrode layer can be formed as a continuous surface.

  As described above, when the transducer area is small, a slit-like rectangular hole (through hole) as shown in FIG. 2A may be formed. However, the transducer area becomes large and it is necessary to ensure the mechanical strength of the electrode. If there is, the base material is reinforced in the direction perpendicular to the longitudinal direction of the through hole in the middle of the slit, as shown in FIGS. Thereby, the strength of the electrode of the electrostatic ultrasonic transducer can be increased, and an electrostatic ultrasonic transducer having a large area (for example, 50 mm × 50 mm or more) can be manufactured.

  The structure of the electrostatic ultrasonic transducer according to the present invention has been described above. The features of the electrostatic ultrasonic transducer according to the present invention are as shown in FIGS. 2 (A), (B), and (C). It is important to form a through-hole (opening) in a rectangular shape (slit shape) in the electrode, and particularly important to form an electrode pattern in a bridge shape so that an electrode layer can be formed at the center of the rectangular vibrating membrane It is configured to leave a base material (bridge portion) to be left. This means that the bridge structure for the round hole shown in FIG. 11 is expanded to a rectangular hole.

  In the structure shown in FIG. 11, the electrode layer is formed in a cross-bridge shape with respect to a round hole (for example, φ0.75 mm), but the aperture ratio (area ratio where acoustic energy is radiated) is 15% or less. . On the other hand, when the electrode layer of the bridge structure is applied to the rectangular through hole as in the electrostatic ultrasonic transducer of the present invention, the vibration area of the vibration film can be increased by about 3 times and about 3 times. An aperture ratio of (45%) can be obtained. The meaning of this number is that the rectangular bridge structure of the present invention can emit three times as much acoustic energy when both the round hole and the rectangular hole have the same membrane amplitude.

  Further, in the electrodes 10 and 20 of the electrostatic ultrasonic transducer of the present invention shown in FIG. 1, the configuration of the bridge portion in the through hole is simpler than that of the electrode 70 of the electrostatic ultrasonic transducer shown in FIG. This makes it easy to manufacture the electrode.

  In order to further increase the electrostatic force, it is also effective to make the vibration film 30A have a laminated structure of three or more layers. That is, like the electrostatic ultrasonic transducer 2 shown in FIG. 3, by forming the vibration film 30A by laminating the two vibration electrodes 32, 34 and the dielectric films 31, 33, 35, the electrostatic force can be reduced. It can be increased to increase the membrane amplitude.

  As described above, in the electrostatic ultrasonic transducer of the present invention, the vibration area of the vibration film is increased by making the vibration shape of the vibration film a rectangular shape (slit shape), and the aperture of the acoustic signal is radiated. The area is increased. For this reason, a large amplitude acoustic signal can be obtained with a low voltage signal. As a result, the electrical / acoustic energy conversion efficiency can be improved and a high sound pressure acoustic signal can be obtained.

[Second Embodiment]
Next, a configuration example of an electrostatic ultrasonic transducer according to the second embodiment of the present invention is shown in FIG. The configuration of the electrostatic ultrasonic transducer according to the second embodiment of the present invention is the same as the configuration shown in FIG. 1 except that an acoustic reflector is installed on the back surface of the electrostatic ultrasonic transducer 1. .

  That is, the electrostatic ultrasonic transducer according to this embodiment is characterized in that acoustic reflectors 101 and 102 are installed on the back surface of the electrostatic ultrasonic transducer 1 shown in FIG.

The acoustic reflectors 101 and 102 radiate the ultrasonic waves radiated from the respective openings 23 of the back-side electrode 20 of the electrostatic ultrasonic transducer 1 to the front surface of the electrostatic ultrasonic transducer 1 through paths having the same length. Are arranged to be.
That is, one end of the acoustic reflector is located at the center position M of the back surface of the electrostatic ultrasonic transducer 1 and an angle of 45 ° with respect to both sides of the back surface of the electrostatic ultrasonic transducer 1 with respect to the center position. And the other end of the pair of first reflectors 101 and 101 having a length matching the ends X1 and X2 of the electrostatic ultrasonic transducer 1 and the ends of the pair of first reflectors 101 and 101. A pair of second reflectors 102 and 102, each of which is connected to the outside of the first reflector plate at an angle perpendicular to the first portion and has a length equivalent to the length of the first reflector plate. Yes.

  In the above configuration, the first reflectors 101 and 101 are arranged at an angle of 45 ° with respect to both sides of the center M on the back surface of the ultrasonic transducer 1, and the length to the point where the end coincides with the end of the ultrasonic transducer 1. Is needed. The ultrasonic waves emitted from the back surface of the ultrasonic transducer 1 by the first reflecting plates 101 and 101 are reflected in the horizontal direction.

  Next, by connecting the second reflectors 102 and 102 connected at a right angle to the first reflectors 101 and 101 to the outside of the first reflectors 101 and 101, respectively, the ultrasonic waves are electrostatically discharged. Is emitted to the front surface of the ultrasonic transducer 1. The 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 electrostatic ultrasonic transducer 1 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 that the sound wave can be handled geometrically as shown in FIG. 4 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 electrostatic ultrasonic transducer 1 and the ultrasonic wave reflected from the rear surface and emitted to the front surface.

The ultrasonic wave emitted from a point a distance away from the center of the transducer is assumed to be circular and its radius is r, and the distance to reach the transducer front surface is approximately 2r, that is, the diameter of the transducer. Of course, the distance a must satisfy the following equation.
0 ≦ a ≦ r (1)

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

[Third Embodiment]
Next, FIG. 5 shows a configuration example of an ultrasonic speaker using an electrostatic ultrasonic transducer according to the third embodiment of the present invention. The ultrasonic speaker according to the present embodiment has the above-described electrostatic ultrasonic transducer of the present invention (FIG. 1), that is, has a slit-like through hole (opening), and an electrode layer is provided at the bridge portion in the through hole. It is composed of a provided Push-Pull type electrostatic ultrasonic transducer.

5, the ultrasonic speaker according to the present embodiment includes an audio frequency wave oscillation source 201 that generates a signal wave in an audio frequency band, and a carrier wave oscillation source 202 that generates and outputs a carrier wave in the ultrasonic frequency band. A modulator 203, a power amplifier 204, and an electrostatic ultrasonic transducer 205.
The modulator 203 modulates the carrier wave output from the carrier wave oscillation source 202 with the signal wave in the audible frequency band output from the audio frequency wave oscillation source 201, and outputs the electrostatic ultrasonic transducer via the power amplifier 204. 205.

  In the above configuration, the carrier wave in the ultrasonic frequency band output from the carrier wave oscillation source 202 by the signal wave output from the audible frequency wave oscillation source 201 is modulated by the modulator 203 and the modulated signal amplified by the power amplifier 204 is used. The electrostatic ultrasonic transducer 205 is driven. As a result, the modulated signal is converted into a sound wave of a finite amplitude level by the electrostatic ultrasonic transducer 205, and this sound wave is radiated into the medium (in the air), and the original audible frequency band due to the nonlinear effect of the medium (air). The signal sound is regenerated.

  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.

  As the electrostatic ultrasonic transducer 205, the electrostatic ultrasonic transducer 1 of the present invention shown in FIG. 1 is used, and an acoustic signal having a high sound pressure can be output with a wide bandwidth. For this reason, it becomes possible to utilize as a speaker for various uses.

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 an ultrasonic speaker in which the sound reaches far as a beam with little attenuation.
On the contrary, if the carrier frequency is high, the attenuation is severe, so that the parametric array effect does not occur sufficiently and an ultrasonic 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.

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

[Fourth Embodiment]
Next, the electrostatic ultrasonic transducer of the present invention, that is, a Push-Pull type electrostatic ultrasonic transducer having a slit-like through hole (opening) and having an electrode layer in a bridge portion in the through hole. A directional acoustic system using an ultrasonic speaker constituted by (FIG. 1) will be described. Hereinafter, the electrostatic ultrasonic transducer is also simply referred to as “ultrasonic transducer”.

  Hereinafter, a projector (display device) will be described as an example of a directional acoustic system according to the present invention. FIG. 6 shows a usage state of the projector according to the present invention. As shown in the figure, the projector 301 is installed behind the viewer 303, projects an image on a screen 302 installed in front of the viewer 303, and uses the ultrasonic speaker mounted on the projector 301 to screen 302. A virtual sound source is formed on the projection plane and the sound is reproduced.

An appearance configuration of the projector 301 is shown in FIG. The projector 301 includes a projector main body 320 including a projection optical system that projects an image on a projection surface such as a screen, and ultrasonic transducers 324A and 324B that can oscillate sound waves in an ultrasonic frequency band, and is supplied from an acoustic source. And an ultrasonic speaker that reproduces a signal sound in an audible frequency band from a sound signal. In the present embodiment, in order to reproduce a stereo audio signal, ultrasonic transducers 324A and 324B constituting ultrasonic speakers are mounted on the left and right with a projector lens 331 constituting a projection optical system interposed therebetween in the projector body.
Further, a low-pitched sound reproduction speaker 323 is provided on the bottom surface of the projector main body 320. Reference numeral 325 denotes a height adjusting screw for adjusting the height of the projector main body 320, and reference numeral 326 denotes an exhaust port for the air cooling fan.

  Further, in the projector 301, a Push-Pull electrostatic ultrasonic transducer according to the present invention (a slit-shaped through hole and a static electrode having an electrode layer formed on a bridge portion in the through hole) is used as an ultrasonic transducer constituting an ultrasonic speaker. Electric type ultrasonic transducer) is used, and an acoustic signal in a wide frequency band (sound wave in an ultrasonic frequency band) can be oscillated at a high sound pressure. For this reason, by conventionally changing the frequency of the carrier wave to control the spatial reproduction range of the reproduction signal in the audible frequency band, an acoustic effect that can be obtained in a stereo surround system or 5.1ch surround system is conventionally required. Thus, it is possible to realize a projector that can be realized without requiring a large-scale sound system and is easy to carry.

  Next, an electrical configuration of the projector 301 is shown in FIG. The projector 301 includes an operation input unit 310, a reproduction range setting unit 312, a reproduction range control processing unit 313, an audio / video signal reproduction unit 314, a carrier wave oscillation source 316, modulators 318A and 318B, power amplifiers 322A and 322B, and static An ultrasonic speaker including electric ultrasonic transducers 324A and 324B, a high-pass filter 317A and 317B, a low-pass filter 319, a mixer 321, a power amplifier 322C, a low-frequency sound reproduction speaker 323, and a projector main body 320. ing. The ultrasonic transducers 324A and 324B are Push-Pull electrostatic ultrasonic transducers according to the present invention (electrostatic ultrasonic transducers having slit-like through holes and having electrode layers formed in bridge portions in the through holes. ).

  The projector main body 320 includes a video generation unit 332 that generates a video and a projection optical system 333 that projects the generated video on a projection surface. The projector 301 is configured by integrating an ultrasonic speaker and a bass reproduction speaker 323 and a projector main body 320.

  The operation input unit 310 has various function keys including a numeric keypad, numeric keys, and a power key for turning the power on and off. The reproduction range setting unit 312 can input data specifying a reproduction range of a reproduction signal (signal sound) by a user operating the operation input unit 310 with a key. The frequency of the carrier wave that defines the reproduction range of the signal is set and held. The reproduction range of the reproduction signal is set by designating a distance that the reproduction signal reaches in the radial axis direction from the sound wave emission surfaces of the ultrasonic transducers 324A and 324B.

The reproduction range setting unit 312 can set the frequency of the carrier wave by the control signal output from the audio / video signal reproduction unit 314 according to the video content.
Further, the reproduction range control processing unit 313 refers to the setting contents of the reproduction range setting unit 312 and changes the frequency of the carrier wave generated by the carrier wave oscillation source 316 so as to be within the set reproduction range. It has a function of controlling the oscillation source 316.
For example, when the distance corresponding to the carrier wave frequency of 50 kHz is set as the internal information of the reproduction range setting unit 312, the carrier wave oscillation source 316 is controlled to oscillate at 50 kHz.

The reproduction range control processing unit 313 stores in advance a table indicating the relationship between the distance that the reproduction signal reaches in the radial axis direction from the sound wave emitting surfaces of the ultrasonic transducers 324A and 324B that define the reproduction range and the frequency of the carrier wave. It has a storage part. The data in this table is obtained by actually measuring the relationship between the frequency of the carrier wave and the reach distance of the reproduction signal.
The reproduction range control processing unit 313 obtains the frequency of the carrier wave corresponding to the distance information set with reference to the table based on the setting content of the reproduction range setting unit 312 and oscillates the carrier wave so as to be the frequency. Control the source 316.

The audio / video signal reproduction unit 314 is, for example, a DVD player that uses a DVD as a video medium. Among the reproduced audio signals, the R channel audio signal is sent to the modulator 318A via the high-pass filter 317A. The signal is output to the modulator 318B via the high-pass filter 317B, and the video signal is output to the video generation unit 332 of the projector main body 320.
The R channel audio signal and the L channel audio signal output from the audio / video signal reproduction unit 314 are combined by the mixer 321 and input to the power amplifier 322C via the low-pass filter 319. . The audio / video signal reproduction unit 314 corresponds to an acoustic source.

The high-pass filters 317A and 317B have a characteristic of passing only the frequency components in the middle and high sound range (first sound range) in the R channel and L channel audio signals, respectively. Only the low frequency range (second range) frequency component of the audio signal of the channel is passed.
Accordingly, among the R channel and L channel audio signals, the mid and high range audio signals are reproduced by the ultrasonic transducers 324A and 324B, respectively, and among the R channel and L channel audio signals, the low range audio signals are low frequencies. It is reproduced by the reproduction speaker 323.

  The audio / video signal reproduction unit 314 is not limited to a DVD player, and may be a reproduction device that reproduces a video signal input from the outside. In addition, the audio / video signal reproduction unit 314 instructs the reproduction range setting unit 312 to dynamically change the reproduction range of the reproduced sound in order to produce an acoustic effect corresponding to the reproduced video scene. Has a function of outputting a control signal.

The carrier wave oscillation source 316 has a function of generating a carrier wave having a frequency in the ultrasonic frequency band designated by the reproduction range setting unit 312 and outputting the carrier wave to the modulators 318A and 318B.
The modulators 318A and 318B AM modulate the carrier wave supplied from the carrier wave oscillation source 316 with the audio signal in the audible frequency band output from the audio / video signal reproduction unit 314, and each of the modulated signals is a power amplifier 322A. , 322B.

  The ultrasonic transducers 324A and 324B are driven by modulation signals output from the modulators 318A and 318B via the power amplifiers 322A and 322B, respectively, and convert the modulation signals into sound waves of a finite amplitude level and radiate them into the medium. And has a function of reproducing a signal sound (reproduction signal) in an audible frequency band.

The video generation unit 332 includes a display such as a liquid crystal display and a plasma display panel (PDP), a drive circuit that drives the display based on a video signal output from the audio / video signal reproduction unit 314, and the like. A video obtained from the video signal output from the audio / video signal reproduction unit 314 is generated.
The projection optical system 333 has a function of projecting an image displayed on the display onto a projection surface such as a screen installed in front of the projector main body 320.

  Next, the operation of the projector 301 having the above configuration will be described. First, data (distance information) instructing the reproduction range of the reproduction signal is set in the reproduction range setting unit 312 from the operation input unit 310 by the user's key operation, and a reproduction instruction is given to the audio / video signal reproduction unit 314.

As a result, distance information defining the reproduction range is set in the reproduction range setting unit 312, and the reproduction range control processing unit 313 takes in the distance information set in the reproduction range setting unit 312 and stores it in the built-in storage unit. The carrier wave oscillation source 316 is controlled so as to obtain the frequency of the carrier wave corresponding to the set distance information with reference to the set table and to generate the carrier wave of the frequency.
As a result, the carrier wave oscillation source 316 generates a carrier wave having a frequency corresponding to the distance information set in the reproduction range setting unit 312 and outputs the carrier wave to the modulators 318A and 318B.

  On the other hand, the audio / video signal reproduction unit 314 outputs the R channel audio signal of the reproduced audio signal to the modulator 318A via the high pass filter 317A, and the L channel audio signal to the modulator 318B via the high pass filter 317B. In addition, the R channel audio signal and the L channel audio signal are output to the mixer 321, and the video signal is output to the video generation unit 332 of the projector main body 320.

Therefore, the high-pass filter 317A inputs the mid-high range audio signal of the R channel audio signal to the modulator 318, and the high-pass filter 317B converts the mid-high range audio signal of the L channel audio signal to the modulator 318B. Is input.
The R channel audio signal and the L channel audio signal are synthesized by the mixer 321, and the low frequency audio signal of the R channel audio signal and the L channel audio signal is input to the power amplifier 322 C by the low pass filter 319. Is done.

The video generation unit 332 generates a video by driving the display based on the input video signal, and displays the video. The image displayed on the display is projected onto a projection surface, for example, the screen 302 shown in FIG. 6 by the projection optical system 333.
On the other hand, the modulator 318A AM-modulates the carrier wave output from the carrier wave oscillation source 316 with the mid-high range audio signal in the R channel audio signal output from the high-pass filter 317A, and outputs it to the power amplifier 322A. .
Further, the modulator 318B AM-modulates the carrier wave output from the carrier wave oscillation source 316 with the mid-high range audio signal in the L channel audio signal output from the high pass filter 317B, and outputs the result to the power amplifier 322B. .

The modulation signals amplified by the power amplifiers 322A and 322B are applied between the electrode layer 14 of the front-side electrode 10 and the electrode layer 24 (see FIG. 1) of the back-side electrode 20 of the ultrasonic transducers 324A and 324B, respectively. The modulated signal is converted into a sound wave (acoustic signal) of a finite amplitude level and radiated to a medium (in the air), and an ultrasonic transducer 324A reproduces an audio signal in the mid-high range in the R channel audio signal. Then, the ultrasonic transducer 324B reproduces the mid-high range audio signal in the L channel audio signal.
In addition, the low frequency sound signal in the R channel and the L channel amplified by the power amplifier 322C is reproduced by the low sound reproduction speaker 323.

  As described above, in the propagation of ultrasonic waves radiated into the medium (in the air) by the ultrasonic transducer, the sound speed increases at a portion where the sound pressure is high and the sound speed is slow at a portion where the sound pressure is low. Become. As a result, waveform distortion occurs.

  When a signal (carrier wave) in the radiated ultrasonic band is modulated (AM modulation) with a signal in the audible frequency band, the signal wave in the audible frequency band used for modulation is super It is formed so as to be self-demodulated separately from the carrier wave in the sonic frequency band. At this time, the spread of the reproduction signal becomes a beam shape due to the characteristics of ultrasonic waves, and the sound is reproduced only in a specific direction completely different from that of a normal speaker.

  The beam-like reproduction signal output from the ultrasonic transducer 324 constituting the ultrasonic speaker is radiated toward the projection surface (screen) on which the image is projected by the projection optical system 333, and is reflected and diffused by the projection surface. In this case, until the reproduction signal is separated from the carrier wave in the radial axis direction (normal direction) from the sound wave emitting surface of the ultrasonic transducer 324 according to the frequency of the carrier wave set in the reproduction range setting unit 312. And the beam width (beam divergence angle) of the carrier wave are different, the reproduction range changes.

  FIG. 9 shows a reproduction signal reproduction state by an ultrasonic speaker including the ultrasonic transducers 324A and 324B in the projector 301. In the projector 301, when the ultrasonic transducer is driven by the modulation signal obtained by modulating the carrier wave with the audio signal, if the carrier frequency set by the reproduction range setting unit 312 is low, the sound wave emitting surface of the ultrasonic transducer 324 To the direction of the radiation axis (the distance until the reproduction signal is separated from the carrier wave in the normal direction of the sound wave radiation surface, that is, the distance to the reproduction point becomes long.

Therefore, the reproduced reproduction signal beam in the audible frequency band reaches the projection plane (screen) 302 without being relatively expanded, and is reflected on the projection plane 302 in this state. Becomes a audible range A indicated by a dotted arrow, and a reproduction signal (reproduced sound) can be heard only in a relatively narrow and narrow range from the projection plane 302.

  On the other hand, when the carrier frequency set by the reproduction range setting unit 312 is higher than the case described above, the sound wave radiated from the sound wave emission surface of the ultrasonic transducer 324 is narrower than when the carrier frequency is low. However, the distance until the reproduction signal is separated from the carrier wave in the radial direction (normal direction of the acoustic wave emission surface) from the sound wave emission surface of the ultrasonic transducer 324, that is, the distance to the reproduction point is shortened.

  Therefore, the reproduced reproduction signal beam in the audible frequency band spreads before reaching the projection plane 302 and reaches the projection plane 302, and is reflected on the projection plane 302 in this state. 9 is an audible range B indicated by a solid arrow, and a reproduction signal (reproduced sound) can be heard only in a relatively close and wide range from the projection plane 302.

  As described above, in the projector of the present invention, the push-pull type electrostatic ultrasonic transducer (the electrostatic ultrasonic transducer having a slit-like through hole and having an electrode layer formed in the bridge portion in the through hole). The sound signal can be reproduced so as to be emitted from a virtual sound source formed in the vicinity of a sound wave reflecting surface such as a screen with a sufficient sound pressure level and wide band characteristics. For this reason, the reproduction range can be easily controlled.

  The projector described above is used for viewing images on a large screen. Recently, large-screen liquid crystal televisions and large-screen plasma televisions are rapidly spreading, and those large-screen televisions are also used. The ultrasonic speaker of the present invention can be used effectively.

  That is, by using the ultrasonic speaker according to the present invention for a large screen television, it becomes possible to radiate an audio signal locally toward the front of the large screen television.

  The embodiment of the present invention has been described above, but the electrostatic ultrasonic transducer, the ultrasonic speaker, and the display device of the present invention are not limited to the illustrated examples described above, and the gist of the present invention is described. Of course, various changes can be made without departing from the scope.

The figure which shows the structural example of the electrostatic type ultrasonic transducer of this invention. The figure which shows the other structural example of the electrostatic ultrasonic transducer of this invention. The figure which shows the example which made the vibration electrode of the vibration film into the multilayer. The figure which shows the example which provided the reflecting plate in the back surface of an electrostatic type ultrasonic transducer. The block diagram which shows the structure of the ultrasonic speaker by this invention The figure which shows the use condition of the projector by this invention. The figure which shows the external appearance structure of the projector shown in FIG. FIG. 7 is a block diagram showing an electrical configuration of the projector shown in FIG. 6. Explanatory drawing of the reproduction | regeneration state of the reproduction signal by an ultrasonic transducer. The figure which shows the structure of the conventional push pull type electrostatic ultrasonic transducer. The figure which shows the example which provided the electrode layer of the bridge | bridging structure in the circular through-hole.

Explanation of symbols

1, 2, 3 ... electrostatic ultrasonic transducer, 10 ... front side electrode, 11 ... vibrating membrane support, 12 ... bridge, 13 ... opening (through hole), DESCRIPTION OF SYMBOLS 14 ... Electrode layer, 20 ... Back side electrode, 21 ... Vibration-membrane support part, 22 ... Bridge part, 23 ... Opening part (through-hole), 24 ... Electrode layer, 30 , 30A ... vibration film, 31, 33, 35 ... dielectric film, 32, 34 ... vibration electrode, 36 ... DC power supply, 37 ... signal source, 37A, 37B ... AC Signal, 40 ... front side electrode, 41 ... reinforcing member, 42A, 42B ... electrode layer, 50 ... front side electrode, 51, 52 ... reinforcing member, 53A, 53B, 53C ... -Electrode layer, 60A ... front side fixed electrode, 60B ... back side fixed electrode, 61A, 61B ... through hole, 6 ... Support members, 70, 70A ... Electrodes, 71, 71A ... Through holes, 72, 72A ... Cross bridge parts, 73, 73A ... Electrode layers, 101, 102 ... Reflecting plates , 201 audible frequency wave oscillation source, 202, carrier wave oscillation source, 203, modulator, 204, power amplifier, 205, electrostatic ultrasonic transducer, 301, projector. , 302 ... screen (projection plane), 303 ... viewer, 310 ... operation input unit, 312 ... reproduction range setting unit, 313 ... reproduction range control processing unit, 314 ... audio / Video signal reproduction unit, 316, carrier wave oscillation source, 317A, 317B, high pass filter, 318A, 318B, modulator, 319, low pass filter, 320, projector main body 321 ... Mixer, 322A, 322B ... Power amplifier, 322C ... Power amplifier, 323 ... Low-frequency speaker, 324A, 324B ... Ultrasonic transducer, 331 ... Projector lens, 332 ..Image generation unit, 333 ... Projection optical system

Claims (7)

A first electrode having a slit-like through hole;
A second electrode having a slit-like through hole;
The through hole of the first electrode and the through hole of the second electrode are arranged so as to make a pair, and are sandwiched between a pair of electrodes composed of the first electrode and the second electrode And a vibration layer having a conductive layer and a DC bias voltage applied to the conductive layer,
The pair of electrodes has an electrode layer disposed in the longitudinal direction of the through hole inside the through hole,
A modulated wave obtained by modulating a carrier wave in an ultrasonic frequency band with a signal wave in an audible frequency band is applied between the electrode layers of the pair of electrodes ,
An electrostatic ultrasonic transducer. Inside the through hole of the first electrode and the through hole of the second electrode, the through hole is parallel to the longitudinal direction of the through hole and the surface of the vibrating membrane is not vibrating. Having a bridge portion provided with a diaphragm facing surface opposed to each other with a predetermined interval in the depth direction;
The electrode layer is formed on the vibration film facing surface of the bridge portion ;
2. The electrostatic ultrasonic transducer according to claim 1, wherein The first electrode, the second electrode, and the bridge portion are formed of a non-conductive material ;
The electrostatic ultrasonic transducer according to claim 2. At least one of the first electrode and the second electrode,
Having a reinforcing member that crosses the through hole in a short direction inside the through hole ;
The electrostatic ultrasonic transducer according to any one of claims 1 to 3. The vibration film has a conductive layer formed in multiple layers ,
The electrostatic ultrasonic transducer according to any one of claims 1 to 4, wherein: A carrier wave in the ultrasonic frequency band is modulated by a signal wave output from a signal source that generates a signal wave in the audible frequency band, and an electrostatic ultrasonic transducer is driven by the modulated wave, thereby generating a signal sound in the audible frequency band. An ultrasonic speaker for reproducing
The electrostatic ultrasonic transducer is
A first electrode having a slit-like through hole;
A second electrode having a slit-like through hole;
The through hole of the first electrode and the through hole of the second electrode are arranged so as to make a pair, and are sandwiched between a pair of electrodes composed of the first electrode and the second electrode And a vibration layer having a conductive layer and a DC bias voltage applied to the conductive layer,
The pair of electrodes has an electrode layer disposed in the longitudinal direction of the through hole inside the through hole,
A modulated wave obtained by modulating a carrier wave in an ultrasonic frequency band with a signal wave in an audible frequency band is applied between the electrode layers of the pair of electrodes ,
Ultrasonic speaker characterized by. A first electrode having a slit-like through hole;
A second electrode having a slit-like through hole;
The through hole of the first electrode and the through hole of the second electrode are arranged so as to make a pair, and are sandwiched between a pair of electrodes composed of the first electrode and the second electrode And a vibration layer having a conductive layer and a DC bias voltage applied to the conductive layer,
The pair of electrodes uses an electrostatic ultrasonic transducer having an electrode layer disposed in the longitudinal direction of the through hole inside the through hole,
Generating a signal wave of an audible frequency band by a signal source;
A procedure for generating a carrier wave in an ultrasonic frequency band by a carrier wave source;
Generating a modulated signal obtained by modulating the carrier wave with a signal wave in the audible frequency band;
A procedure for driving the electrostatic ultrasonic transducer by applying the modulation signal between the electrode layers of the pair of electrodes;
A method of reproducing an audio signal of an electrostatic ultrasonic transducer, comprising:

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