JP2008258864A - Electrostatic ultrasonic transducer, ultrasonic speaker, sound signal reproducing method of electrostatic ultrasonic transducer, display device, and directional acoustic system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrostatic ultrasonic transducer, wherein a pair of electrodes can hold a vibrating membrane with equal force and stable membrane vibration can be obtained. <P>SOLUTION: The electrostatic ultrasonic transducer includes a first electrode having a through hole, a second electrode having a through hole, and the vibrating membrane which is held between a pair of electrodes comprising the first electrode and the second electrode and has a conductive layer, wherein the through hole of the first electrode and the through hole of the second electrode are arranged so as to form a pair and direct current bias voltage is applied to the conductive layer, wherein a plate-like fixed member and the pair of electrodes are fixed integrally by allowing a projecting part of the plate-like fixed member having recessed shape to abut on the vicinity of a central part of either of the pair of electrodes on the surface opposite to the vibrating membrane, and a modulation wave obtained by modulating a carrier wave of an ultrasonic frequency band is applied between the pair of electrodes. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to an electrostatic ultrasonic transducer used in a directivity acoustic radiation device, and more specifically, an electrostatic ultrasonic transducer capable of obtaining stable membrane vibration, and the electrostatic ultrasonic transducer The present invention relates to an ultrasonic speaker provided with the above, an audio signal reproducing method for an electrostatic ultrasonic transducer, a display device provided with the 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 a drawback that sound reproducibility is poor because the resonance point is sharp and it is difficult to increase the bandwidth (for example, Patent Document 1).
2).

On the other hand, the electrostatic ultrasonic transducer does not have a sharp resonance of the diaphragm itself, and can be broadened by using the air column resonance phenomenon of an acoustic tube and has excellent sound reproducibility (good sound quality).
(For example, refer to Patent Document 3).

FIG. 13 is a diagram showing a conventional electrostatic ultrasonic transducer 3. FIG.
Shows a cross section of the electrostatic ultrasonic transducer 3. The electrostatic ultrasonic transducer 3 has a vibrating membrane 30 having a vibrating electrode (electrode layer) 32, and faces each surface of the vibrating membrane 30. A pair of fixed electrodes including a front-side fixed electrode 60A and a back-side fixed electrode 60B are provided. The vibration film 30 is formed so that a vibration electrode (electrode layer) 32 forming an electrode is sandwiched between dielectric films (insulating films) 31 and 33.

The front-side fixed electrode 60A that sandwiches the vibrating membrane 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. 13B 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 (Push-Pu) because the vibrating membrane 30 vibrates by receiving a force from the pair of fixed electrodes 60A and 60B.
ll) type electrostatic ultrasonic transducer.
JP-A 61-296897 JP 2000-287297 A JP 2006-93932 A

The electrostatic ultrasonic transducer described above has the advantages of being capable of widening the band and having excellent sound reproducibility (good sound quality) as compared to the resonant ultrasonic transducer.

However, with this electrostatic ultrasonic transducer, due to its structure, it is difficult to hold the vibrating membrane with a pair of electrodes with a uniform force, resulting in a gap between the pair of electrodes.
It was difficult to sandwich the vibrating membrane with a uniform force and a uniform distance between the pair of electrodes.
In an electrostatic ultrasonic transducer, it is necessary to release high acoustic energy into the air by virtue of a stable vibration of the vibrating membrane. However, in a conventional electrostatic ultrasonic transducer, a vibrating membrane is required. There was a limit to the stable vibration.

The present invention has been made in view of such circumstances, and an electrostatic ultrasonic transducer capable of holding a vibrating membrane with a uniform force between a pair of electrodes and obtaining stable membrane vibration, and the electrostatic ultrasonic transducer. It is an object of the present invention to provide an ultrasonic speaker including an ultrasonic transducer, an audio signal reproducing method of an electrostatic ultrasonic transducer, a display device including an ultrasonic speaker, and a directional acoustic system.

In order to achieve the above object, an electrostatic ultrasonic transducer of the present invention includes a first electrode having a through hole, a second electrode having a through hole, the through hole of the first electrode, and the Second
The through hole of the electrode of the first electrode is disposed so as to make a pair and is sandwiched between a pair of electrodes composed of the first electrode and the second electrode, and has a conductive layer, and a DC bias voltage is applied to the conductive layer. And a convex portion of a plate-shaped fixing member having a convex shape around a central portion of the surface of either one of the pair of electrodes opposite to the vibrating membrane. The plate-shaped fixing member and the pair of electrodes are integrally fixed so as to contact each other, and a carrier wave in an ultrasonic frequency band is modulated between the pair of electrodes by a signal wave in an audible frequency band. A modulated wave is applied.
With the above configuration, the vicinity of the center of the back surface of one of the pair of electrodes sandwiching the diaphragm is in contact with the convex portion of the plate-like fixing member, and the peripheral portion of the pair of electrodes is screwed by the plate-like fixing member. It is fixed so that it can be pressed. As a result, the pair of electrodes in the electrostatic ultrasonic transducer is configured so that the acoustic radiation surface is slightly convex. As a result, a substantially uniform force is applied between the pair of electrodes, and the vibrating membrane has a uniform force (distance). And stable membrane vibration can be obtained.

Further, in the electrostatic ultrasonic transducer according to the present invention, the plate-like fixing member has a surface of the plate-like fixing member that is in contact with a surface of one of the pair of electrodes opposite to the vibration film. Is formed in a convex curved surface.
With the above-described configuration, the vicinity of the center of the back surface of one of the pair of electrodes sandwiching the diaphragm is brought into contact with the convex surface of the plate-like fixing member, and the peripheral portion of the pair of electrodes is screwed by the plate-like fixing member. It is fixed so that it can be pressed down. As a result, the pair of electrodes in the electrostatic ultrasonic transducer is configured so that the acoustic radiation surface is slightly convex. As a result, a substantially uniform force is applied between the pair of electrodes, and the vibrating membrane has a uniform force (distance). And stable membrane vibration can be obtained.

Further, in the electrostatic ultrasonic transducer according to the present invention, the plate-like fixing member has a surface of the plate-like fixing member that is in contact with a surface of one of the pair of electrodes opposite to the vibration film. It has a protrusion in the center part of.
With the above configuration, the vicinity of the center of the back surface of one of the pair of electrodes sandwiching the vibration film is in contact with the protrusion formed at the center of the plate-shaped fixing member, and the peripheral portion of the pair of electrodes is the plate-shaped The fixing member is fixed so as to be pressed by a screw or the like. As a result, the pair of electrodes in the electrostatic ultrasonic transducer is configured so that the acoustic radiation surface is slightly convex. As a result, a substantially uniform force is applied between the pair of electrodes, and the vibrating membrane has a uniform force (distance). And stable membrane vibration can be obtained.

The 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 of the first electrode, and the The through hole of the second electrode is disposed so as to make a pair, and is sandwiched between a pair of electrodes composed of the first electrode and the second electrode, and has a conductive layer. A vibrating membrane to which a DC bias voltage is applied, and the pair of electrodes has an electrode layer disposed in the longitudinal direction of the through hole inside the through hole, and one of the pair of electrodes The plate-shaped fixing member and the pair of electrodes are integrated with each other so that the convex portion of the plate-shaped fixing member having a convex shape is in contact with the vicinity of the central portion of the surface of the one electrode opposite to the vibrating membrane. And the electrode layer in the pair of electrodes To 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.
With the above configuration, the vicinity of the center of the back surface of one of the pair of electrodes sandwiching the diaphragm is in contact with the convex portion of the plate-like fixing member, and the peripheral portion of the pair of electrodes is screwed by the plate-like fixing member. It is fixed so that it can be pressed. As a result, the pair of electrodes in the electrostatic ultrasonic transducer is configured so that the acoustic radiation surface is slightly convex. As a result, a substantially uniform force is applied between the pair of electrodes, and the vibrating membrane has a uniform force (distance). And stable membrane vibration can be obtained.

Further, in the electrostatic ultrasonic transducer according to the present invention, the plate-like fixing member has a surface of the plate-like fixing member that is in contact with a surface of one of the pair of electrodes opposite to the vibration film. Is formed in a convex curved surface.
With the above-described configuration, the vicinity of the center of the back surface of one of the pair of electrodes sandwiching the diaphragm is brought into contact with the convex surface of the plate-like fixing member, and the peripheral portion of the pair of electrodes is screwed by the plate-like fixing member. It is fixed so that it can be pressed down. As a result, the pair of electrodes in the electrostatic ultrasonic transducer is configured so that the acoustic radiation surface is slightly convex. As a result, a substantially uniform force is applied between the pair of electrodes, and the vibrating membrane has a uniform force (distance). And stable membrane vibration can be obtained.

Further, in the electrostatic ultrasonic transducer according to the present invention, the plate-like fixing member has a surface of the plate-like fixing member that is in contact with a surface of one of the pair of electrodes opposite to the vibration film. It has a protrusion in the center part of.
With the above configuration, the vicinity of the center of the back surface of one of the pair of electrodes sandwiching the vibration film is in contact with the protrusion formed at the center of the plate-shaped fixing member, and the peripheral portion of the pair of electrodes is the plate-shaped The fixing member is fixed so as to be pressed by a screw or the like. As a result, the pair of electrodes in the electrostatic ultrasonic transducer is configured so that the acoustic radiation surface is slightly convex. As a result, a substantially uniform force is applied between the pair of electrodes, and the vibrating membrane has a uniform force (distance). And stable membrane vibration can be obtained.

In the electrostatic ultrasonic transducer according to the present invention, the vibrating membrane is parallel to the longitudinal direction of the through hole inside the through hole of the first electrode and the through hole of the second electrode. A bridge portion having a diaphragm facing surface facing the surface in the depth direction of the through hole with respect to the surface during non-vibration, and the electrode layer on the diaphragm facing surface of the bridge portion Is formed.
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 during 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, 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 bridge portion is opposed to the vibration film. An electrode layer is formed on the surface.
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 includes a first electrode having a through hole, a second electrode having a through hole, the through hole of the first electrode, and the second electrode. The through hole is disposed in a pair and is sandwiched between a pair of electrodes composed of the first electrode and the second electrode, and has a conductive layer, and a DC bias voltage is applied to the conductive layer. The first electrode and the second electrode each have a counter electrode portion facing the vibration film inside the through hole, and any of the pair of electrodes The plate-shaped fixing member and the pair of electrodes are arranged so that the convex portion of the plate-shaped fixing member having a convex shape is in contact with the vicinity of the central portion of the surface of the other electrode opposite to the vibrating membrane. In addition to being fixed integrally, a carrier in an ultrasonic frequency band is interposed between the pair of electrodes. Wherein the modulated wave obtained by modulating the waves at the signal wave in the audio frequency band is applied.
With the above configuration, the vicinity of the center of the back surface of one of the pair of electrodes sandwiching the diaphragm is in contact with the convex portion of the plate-like fixing member, and the peripheral portion of the pair of electrodes is screwed by the plate-like fixing member. It is fixed so that it can be pressed. As a result, the pair of electrodes in the electrostatic ultrasonic transducer is configured so that the acoustic radiation surface is slightly convex. As a result, a substantially uniform force is applied between the pair of electrodes, and the vibrating membrane has a uniform force (distance). And stable membrane vibration can be obtained.
Further, a counter electrode portion is disposed in the through hole so as to face the vibration region of the vibration film (the portion of the vibration film facing the through hole).
Thereby, the film | membrane amplitude amount of the vibration area | region of a vibration film can be increased.

In the electrostatic ultrasonic transducer according to the present invention, the counter electrode portion is a counter electrode portion having a bridge structure that bridges the outer peripheral portion and the inside of the through hole.
With the above configuration, a counter electrode portion having a bridge structure that bridges the outer peripheral portion of the through hole and the inside thereof is disposed in the through hole so as to face the vibration region of the vibration film (the portion of the vibration film facing the through hole). .
Thereby, the film | membrane amplitude amount of the vibration area | region of a vibration film can be increased.

Also. In the electrostatic ultrasonic transducer according to the present invention, the bridge structure is a cross structure.
Thereby, the film | membrane amplitude amount of the vibration area | region of a vibration film can be increased.

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. Two electrodes, the through hole of the first electrode and the second electrode
The through hole of the electrode is disposed in a pair and is sandwiched between a pair of electrodes composed of the first electrode and the second electrode, and has a conductive layer, and a DC bias is applied to the conductive layer. And the pair of electrodes have an electrode layer disposed in the longitudinal direction of the through hole inside the through hole, and any one of the pair of electrodes The plate-shaped fixing member and the pair of electrodes are integrated with each other such that the convex portion of the plate-shaped fixing member having a convex shape abuts near the central portion of the surface of the electrode opposite to the vibration film. In addition to being fixed, 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 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.
Also, the vicinity of the back center of one of the pair of electrodes sandwiching the vibration membrane of the electrostatic ultrasonic transducer used in the ultrasonic speaker is in contact with the convex portion of the plate-like fixing member, and the pair of electrodes Is fixed so that the peripheral portion thereof is pressed by a screw or the like by the plate-like fixing member.
As a result, the pair of electrodes in the electrostatic ultrasonic transducer is configured so that the acoustic radiation surface is slightly convex. As a result, a substantially uniform force is applied between the pair of electrodes, and the vibrating membrane has a uniform force (distance). And stable membrane vibration can be obtained.

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, and the penetration of the first electrode. A hole and the through hole of the second electrode are arranged to make a pair, and sandwiched between a pair of electrodes consisting of the first electrode and the second electrode, and having a conductive layer, A vibration film to which a DC bias voltage is applied to the conductive layer, and the pair of electrodes includes an electrode layer disposed in a longitudinal direction of the through hole inside the through hole, The plate-like fixing member and the pair of electrodes are arranged so that the convex portion of the plate-like fixing member having a convex shape is in contact with the vicinity of the central portion of the surface of either one of the electrodes opposite to the vibrating membrane. And are fixed together,
Using an electrostatic ultrasonic transducer, 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 the audible carrier wave A step of generating a modulation signal modulated by a signal wave in a frequency band, and a step of driving the electrostatic ultrasonic transducer by applying the modulation signal between the electrode layers of the pair of electrodes. Features.
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.
Also, the vicinity of the back center of one of the pair of electrodes sandwiching the vibration membrane of the electrostatic ultrasonic transducer used in the ultrasonic speaker is in contact with the convex portion of the plate-like fixing member, and the pair of electrodes Is fixed so that the peripheral portion thereof is pressed by a screw or the like by the plate-like fixing member.
As a result, the pair of electrodes in the electrostatic ultrasonic transducer is configured so that the acoustic radiation surface is slightly convex. As a result, a substantially uniform force is applied between the pair of electrodes, and the vibrating membrane has a uniform force (distance). And stable membrane vibration can be obtained.

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 plate-shaped fixing member having an electrode layer arranged in the longitudinal direction of the through-hole, and having a convex shape around the central portion on the surface opposite to the vibrating membrane of one of the pair of electrodes The plate-shaped fixing member and the pair of electrodes are integrally fixed so that the convex portions of the pair are in contact with each other, and an ultrasonic frequency carrier wave is audible between the electrode layers of the pair of electrodes. A modulated wave modulated by a signal wave in a band is applied.
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.
Also, the vicinity of the back center of one of the pair of electrodes sandwiching the vibration membrane of the electrostatic ultrasonic transducer used in the ultrasonic speaker is in contact with the convex portion of the plate-like fixing member, and the pair of electrodes Is fixed so that the peripheral portion thereof is pressed by a screw or the like by the plate-like fixing member.
As a result, the pair of electrodes in the electrostatic ultrasonic transducer is configured so that the acoustic radiation surface is slightly convex. As a result, a substantially uniform force is applied between the pair of electrodes, and the vibrating membrane has a uniform force (distance). And stable membrane vibration can be obtained.

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 the 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; The through hole of one electrode and the through hole of the second electrode are arranged so as to make a pair, and sandwiched between a pair of electrodes composed of the first electrode and the second electrode 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. Then, the plate-shaped fixing member having a convex shape abuts on the vicinity of the center portion of the surface on the opposite side of the vibrating membrane of one of the pair of electrodes, so that the plate-like The fixing member and the pair of electrodes are integrally fixed, 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. It is characterized by that.
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, among the audio signals supplied from the acoustic source, an audio signal in a low sound range (second sound range) 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.
Also, the vicinity of the back center of one of the pair of electrodes sandwiching the vibration membrane of the electrostatic ultrasonic transducer used in the ultrasonic speaker is in contact with the convex portion of the plate-like fixing member, and the pair of electrodes Is fixed so that the peripheral portion thereof is pressed by a screw or the like by the plate-like fixing member.
As a result, the pair of electrodes in the electrostatic ultrasonic transducer is configured so that the acoustic radiation surface is slightly convex. As a result, a substantially uniform force is applied between the pair of electrodes, and the vibrating membrane has a uniform force (distance). And stable membrane vibration can be obtained.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. An example of the configuration of an electrostatic ultrasonic transducer according to an embodiment of the present invention is shown in FIG. In the figure, reference numeral 1 denotes an electrostatic ultrasonic transducer, and the electrostatic ultrasonic transducer 1 has a through hole (not shown).
A first electrode 10 having a through hole, a second electrode 20 having a through hole not shown), and the first electrode 1.
The through hole of 0 and the through hole of the second electrode 20 are arranged so as to make a pair, and are sandwiched between a pair of electrodes composed of the first electrode 10 and the second electrode 20, and a conductive layer (not shown) And a vibration film 30 to which a DC bias voltage is applied to the conductive layer.

The pair of electrodes 10 and 20 is formed of a conductive material, or has an electrode layer facing the vibration film 30 inside the through hole, and one of the pair of electrodes 10 and 20 The convex portion of the plate-like fixing member 25 having a convex shape (for example, a convex curved surface) around the central portion of the surface of the electrode (second electrode 20 in the present embodiment) on the side opposite to the vibrating membrane 30. The plate-like fixing member 25 and the pair of electrodes 10 and 2 are arranged so that the curved surfaces (for example, convex curved surfaces) are in contact with each other.
0 is integrally fixed by the screw 28. The plate-like fixing member 25 is composed of the pair of electrodes 10.
, 20 and a member having rigidity equal to or higher than that.

With the above-described configuration, the vicinity of the center of the back surface of one of the pair of electrodes sandwiching the vibrating membrane comes into contact with the convex portion (for example, convex curved surface) of the plate-like fixing member 25, and the pair of electrodes 10, 20 Is fixed by the plate-like fixing member 25 so as to be pressed by the screw 28. As a result, the pair of electrodes 10 and 20 in the electrostatic ultrasonic transducer 1 is configured such that the acoustic radiation surface is slightly convex, and as a result, a substantially uniform force is applied between the pair of electrodes 10 and 20, and the vibrating membrane 30 is held with a uniform force (distance), and stable membrane vibration can be obtained.

Note that when the electrostatic ultrasonic transducer 1 is driven, a DC bias voltage is applied to the conductive layer of the vibration film 30, and between the pair of electrodes 10, 20 or between the pair of electrodes 10, 20. 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 in FIG.

Next, another configuration of the electrostatic ultrasonic transducer according to the embodiment of the present invention is shown in FIG. In the figure, the configuration differs from the electrostatic ultrasonic transducer shown in FIG. 1 only in the shape of the plate-like fixing member, and the other configurations are the same.
In the electrostatic ultrasonic transducer 1 shown in FIG. 2, the plate-like fixing member 26 is different from the vibrating membrane 30 of one of the pair of electrodes 10 and 20 (second electrode 20 in the present embodiment). A protrusion 26A is provided at the center of the surface of the plate-like fixing member 26 that comes into contact with the opposite surface. 29
Is a screw hole.

With the above-described configuration, the vicinity of the center of the back surface of one of the pair of electrodes 10 and 20 sandwiching the vibration film 30 abuts on the protrusion 26A formed at the center of the plate-like fixing member 26, and the pair of electrodes 10
, 20 is fixed by the plate-like fixing member 26 so as to be pressed by the screw 28. As a result, the pair of electrodes in the electrostatic ultrasonic transducer is configured so that the acoustic radiation surface is slightly convex, and as a result, a substantially uniform force is applied between the pair of electrodes 10 and 20, and the vibrating membrane 30 is uniform. It is held by force (distance) and stable membrane vibration can be obtained.
In the example of FIGS. 1 and 2, the first electrode 10, the second electrode, and the plate-like fixing member (25 or 26) are integrally fixed by screws, but the present invention is not limited to this. It may be fixed with an adhesive or the like.

Further, the plate-like fixing member that applies stress to the first electrode 10 and the second electrode so that the acoustic radiation surface is convex and is fixed integrally is not limited to the shape shown in FIGS. 1 and 2. For example, as shown in FIG. 3, it may be a plate-like fixing member having a belt-like protrusion 27A having a semicircular cross section at the center. FIG.
The first electrode 10 and the second electrode 20 of the electrostatic ultrasonic transducer 1 may be fixed integrally with the plate-like fixing member shown in FIG. 3 instead of the plate-like fixing member shown in FIG. 1. The same effect as that obtained by the configuration of FIG. 2 can be obtained. Reference numeral 29 denotes a screw hole.

The electrostatic ultrasonic transducer fixing structure according to the present embodiment shown in FIGS. 1 to 3 described above can be applied to all of the electrostatic ultrasonic transducers shown in FIG. Is also applicable. Since the configuration and operation of the electrostatic ultrasonic transducer have already been described for the electrostatic ultrasonic transducer of FIG. 13, the description thereof is omitted here. The electrostatic ultrasonic transducer in FIGS. 1 to 3 is a push-pull (
Fig. 2 conceptually shows a Push-Pull type electrostatic ultrasonic transducer.

Next, a specific configuration example of an electrostatic ultrasonic transducer to which the present invention (a structure in which a pair of electrodes are integrally fixed by a plate-like fixing member as shown in FIGS. 1 to 3) is applied is shown in FIG. Shown in However, the state fixed with the plate-shaped reinforcing member is omitted.
4A is a cross-sectional view, and FIG. 4B is a plan view of the electrode viewed from the vibrating membrane side.

An electrostatic ultrasonic transducer 1 to which the present invention is applied includes a vibrating membrane 30 and a pair of electrodes that sandwich the vibrating membrane 30, a front side electrode (first electrode) 10 and a back side electrode (second electrode) 20. And a circuit for driving it.

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. As shown in FIG. 4B, 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 non-conductive base materials (various plastics, glass,
The electrode layers 14 and 24 are made of metal (gold, silver, copper, aluminum, etc.).
It is set as the structure which gave plating, printing, vapor deposition, paste, etc. of this. 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. Examples of the polymer film material include poly-ethylene terephthalate (PET), aramid, poly-ester, poly-ethylene naphthalate (
PEN), polyphenylene sulfide (PPS), or the like is used. The material of the metallized portion forming the vibrating electrode 32 is most commonly Al (aluminum), and other materials such as Ni, Cu, S
US, Ti, etc. may be used. The thickness of the metallized portion is preferably about 100 to 1500 mm. The metallized portion (vibrating electrode 32) of the vibrating membrane is 10 to 300 from the DC power supply 36 on the circuit side.
A DC bias voltage of V is applied.

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. 13, and an acoustic signal is generated by the push-pull operation of the vibration film 30. That is, in the electrostatic ultrasonic transducer 1, a pair of electrodes 10,
20 has the same number and a plurality of slit-like openings (through holes) 13 and 23 at positions facing each other with the vibrating membrane 30 therebetween. Tier 1
4 and 24 are supplied with AC signals 37A and 37B whose phases are mutually inverted by a signal source 37. 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 An electrostatic repulsive force acts on the surface portion 15A that is not sandwiched between 20 and the surface portion 15A.
A 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 reversed. 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 suction force is applied upward to the front surface portion 15A of the vibration film 30 in FIG. The electrostatic repulsive force acts on the upper side of FIG.
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 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 a slit-shaped opening 1.
3 and 23 radiate to the outside as a plane wave.

FIG. 5 is a diagram showing a modification of the electrostatic ultrasonic transducer to which the present invention is applied. FIGS. 5A, 5 </ b> B, and 5 </ 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 side electrode 10 shown in FIG. 5A is the same as the front side electrode 10 shown in FIG. 4B, and is the most basic configuration example of the electrostatic ultrasonic transducer to which the present invention is applied. is there.

A front-side electrode 40 shown in FIG. 5B is a base material (for example, plastic) that forms an electrode.
In the central portion in the longitudinal direction of the slit-shaped through hole, the reinforcing member 41 for reinforcing
The example added to the direction orthogonal to the longitudinal direction of a through-hole 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. 5C 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. 5A 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.

As described above, the structure of the electrostatic ultrasonic transducer to which the present invention is applied has been described.
An example of the electrostatic ultrasonic transducer to which the present invention shown in FIG. 4 is applied is shown in FIG.
As shown in A), (B), and (C), a through hole (opening portion) is formed in a rectangular shape (slit shape) in a pair of electrodes, and particularly important is the center of the rectangular diaphragm. On the other hand, a base material (bridge portion) for forming an electrode pattern in a bridge shape is left so that an electrode layer can be formed. This means that the bridge structure for the round hole shown in FIG. 7 is expanded to a rectangular hole.

Here, the configuration of the electrostatic ultrasonic transducer in which the electrode layer having the bridge structure is provided in the circular through hole shown in FIG. 7 will be described. FIG. 7A shows a pair of electrodes 70 and 7 sandwiching the vibration film.
The top view which looked at one electrode 70 of 0A from the diaphragm side is shown. FIG. 7B shows a cross-sectional view of the electrostatic ultrasonic transducer, which is a cross-sectional view in the XX ′ direction in FIG. 7A.

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, the other electrode 70A has a through hole 71A, a cross bridge portion 72A,
And electrode layer 73A is formed. 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).

In the structure shown in FIG. 7, 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 approximately tripled,
An aperture ratio of about 3 times (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. 4, 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, as in the electrostatic ultrasonic transducer 2 shown in FIG. 6, 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.

In addition, the electrostatic ultrasonic transducer to which the present invention is applied includes a first electrode having a slit-like through hole, a second electrode having a slit-like through hole, and the through-hole of the first electrode. A hole and the through hole of the second electrode are arranged to make a pair, and sandwiched between a pair of electrodes consisting of the first electrode and the second electrode, and having a conductive layer, A vibration film to which a DC bias voltage is applied to the conductive layer, and the pair of electrodes includes an electrode layer disposed in a longitudinal direction of the through hole inside the through hole, The plate-like fixing member and the pair of electrodes are arranged so that the convex portion of the plate-like fixing member having a convex shape is in contact with the vicinity of the central portion of the surface of either one of the electrodes opposite to the vibrating membrane. Are fixed together and in the pair of electrodes The serial electrode layers modulated wave obtained by modulating the carrier wave in the ultrasonic frequency band by signal waves in the audio frequency band is applied.

With the above configuration, the vicinity of the center of the back surface of one of the pair of electrodes sandwiching the diaphragm is in contact with the convex portion of the plate-like fixing member, and the peripheral portion of the pair of electrodes is screwed by the plate-like fixing member. It is fixed so that it can be pressed. As a result, the pair of electrodes in the electrostatic ultrasonic transducer is configured so that the acoustic radiation surface is slightly convex. As a result, a substantially uniform force is applied between the pair of electrodes, and the vibrating membrane has a uniform force (distance). And stable membrane vibration can be obtained.

Further, in the electrostatic ultrasonic transducer according to the present invention, the plate-like fixing member has a surface of the plate-like fixing member that is in contact with a surface of one of the pair of electrodes opposite to the vibration film. Is formed in a convex curved surface.
With the above-described configuration, the vicinity of the center of the back surface of one of the pair of electrodes sandwiching the diaphragm is brought into contact with the convex surface of the plate-like fixing member, and the peripheral portion of the pair of electrodes is screwed by the plate-like fixing member. It is fixed so that it can be pressed down. As a result, the pair of electrodes in the electrostatic ultrasonic transducer is configured so that the acoustic radiation surface is slightly convex. As a result, a substantially uniform force is applied between the pair of electrodes, and the vibrating membrane has a uniform force (distance). And stable membrane vibration can be obtained.

Further, in the electrostatic ultrasonic transducer according to the present invention, the plate-like fixing member has a surface of the plate-like fixing member that is in contact with a surface of one of the pair of electrodes opposite to the vibration film. Has a protrusion at the center.
With the above configuration, the vicinity of the center of the back surface of one of the pair of electrodes sandwiching the vibration film is in contact with the protrusion formed at the center of the plate-shaped fixing member, and the peripheral portion of the pair of electrodes is the plate-shaped The fixing member is fixed so as to be pressed by a screw or the like. As a result, the pair of electrodes in the electrostatic ultrasonic transducer is configured so that the acoustic radiation surface is slightly convex. As a result, a substantially uniform force is applied between the pair of electrodes, and the vibrating membrane has a uniform force (distance). And stable membrane vibration can be obtained.

Next, FIG. 8 shows a configuration example of an ultrasonic speaker using an electrostatic ultrasonic transducer to which the present invention is applied. The ultrasonic speaker according to the present embodiment has the above-described electrostatic ultrasonic transducer of the present invention (FIG. 4), 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. This electrostatic ultrasonic transducer is a plate-like fixing member shown in FIGS. 1 to 3, in which a pair of electrodes are integrally fixed so that the acoustic radiation surface has a convex shape. In the figure, this state is not shown for convenience.

In FIG. 8, the ultrasonic speaker according to the present embodiment includes an audio frequency wave oscillation source 201 that generates a signal wave in the 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 speed of sound is slow in this part, the modulation wave itself is distorted, resulting in a carrier wave (ultrasonic frequency band).
And the signal wave (signal sound) in the audible frequency band is reproduced.

As the electrostatic ultrasonic transducer 205, the electrostatic ultrasonic transducer 1 of the present invention shown in FIG. 4 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, there is little attenuation, and an ultrasonic speaker that can reach far away in the form of a beam can be provided.
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.

In addition, since the electrostatic ultrasonic transducer 1 of the present invention shown in FIG. 4 is used for this ultrasonic speaker, the back surface of one of the pair of electrodes sandwiching the vibration film of the electrostatic ultrasonic transducer. The vicinity of the center comes into contact with the convex portion of the plate-like fixing member, and the peripheral portions of the pair of electrodes are fixed by the plate-like fixing member so as to be pressed by a screw or the like. As a result, the pair of electrodes in the electrostatic ultrasonic transducer is configured so that the acoustic radiation surface is slightly convex,
As a result, a substantially uniform force is applied between the pair of electrodes, and the diaphragm is held with a uniform force (distance).
Stable membrane vibration can be obtained.

Next, the electrostatic ultrasonic transducer of the present invention, that is, having a slit-like through hole (opening), having an electrode layer in a bridge portion in the through hole, and a pair of electrodes integrated by a plate-like fixing member A directional acoustic system using an ultrasonic speaker composed of a push-pull type electrostatic ultrasonic transducer (FIG. 4) fixed in a fixed manner 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. 9 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 external 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.
Reference numeral 26 denotes an exhaust port for an 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 controlling the spatial reproduction range of the reproduction signal in the audible frequency band by changing the frequency of the carrier wave, a stereo surround system or 5.1ch
A sound effect that can be obtained by a surround system or the like can be realized without requiring a large-scale sound system that has been conventionally required, and a projector that is easy to carry can be realized.

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, and a power amplifier 322.
A, 322B and ultrasonic ultrasonic transducers 324A, 324B, high-pass filters 317A, 317B, low-pass filter 319, and mixer 3
21, a power amplifier 322C, a bass reproduction speaker 323, and a projector main body 32
0. It should be noted that the ultrasonic transducers 324A and 324B are P according to the present invention.
It is a ush-Pull type electrostatic ultrasonic transducer (electrostatic ultrasonic transducer having a slit-like through hole and having an electrode layer formed on a bridge portion in the through hole).

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 is operated by the user using the operation input unit 31
Data for designating the reproduction range of the reproduction signal (signal sound) can be input by keying 0, and when the data is inputted, the frequency of the carrier wave defining the reproduction range of the reproduction signal is It is set and retained. 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.

Also, 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 includes an ultrasonic transducer 324A that defines a reproduction range,
It has a storage unit in which a table showing the relationship between the distance that the reproduction signal reaches in the radial axis direction from the sound wave emitting surface of 324B and the frequency of the carrier wave is stored in advance. 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, and the R channel audio signal among the reproduced audio signals is the high-pass filter 31.
The audio signal of the L channel 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, respectively.
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. The audio / video signal playback unit 314
A function for outputting a control signal for instructing the reproduction range to the reproduction range setting unit 312 so as to dynamically change the reproduction range of the reproduction sound in order to produce an acoustic effect according to the scene of the reproduced video. Yes.

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 respectively connected to the modulators 318A and 318B.
Is driven by a modulation signal output from the power amplifiers 322A and 322B, and the modulation signal is converted into a sound wave of a finite amplitude level and radiated into the medium to reproduce a signal sound (reproduction signal) in an audible frequency band. It has a function.

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 from the operation input unit 310 by the user's key operation
Is set in the reproduction range setting unit 312, 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 so as to obtain a carrier wave frequency corresponding to the set distance information and generate a carrier wave of the frequency.
To control.
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 the result 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. 4) 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.
Also, the low-frequency audio signals in the R channel and L channel amplified by the power amplifier 322C are reproduced by the low tone 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. 12 shows a reproduction signal reproduction state by an ultrasonic speaker configured to include the ultrasonic transducers 324A and 324B in the projector 301. Projector 30
1, if the carrier frequency set by the reproduction range setting unit 312 is low when the ultrasonic transducer is driven by the modulation signal obtained by modulating the carrier wave with the audio signal, the ultrasonic wave is emitted from the sound wave emitting surface of the ultrasonic transducer 324. The distance until the reproduction signal is separated from the carrier wave in the radiation axis direction (normal direction of the sound wave emission 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. Therefore, the reproduction range is as shown in FIG. 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 becomes an audible range B indicated by a solid arrow, and the projection plane 302
Thus, the reproduction signal (reproduction sound) can be heard only in a relatively close and wide range.

As described above, in the projector according to the present invention, the push-pull type electrostatic ultrasonic transducer (having slit-like through holes, having an electrode layer in the bridge portion in the through holes, and the pair of electrodes being a plate Using an ultrasonic speaker composed of an electrostatic ultrasonic transducer that is integrally fixed so that the acoustic radiation surface is convex so that the acoustic radiation surface is convex. It has level and broadband characteristics, and 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. For this reason, the reproduction range can be easily controlled.
Further, in the projector according to the present invention, the convex portion of the plate-shaped fixing member hits the vicinity of the center of the back surface of one of the pair of electrodes sandwiching the vibration film of the electrostatic ultrasonic transducer used for the ultrasonic speaker. The peripheral portions of the pair of electrodes are fixed so as to be pressed by a screw or the like by the plate-shaped fixing member. As a result, the pair of electrodes in the electrostatic ultrasonic transducer is configured so that the acoustic radiation surface is slightly convex. As a result, a substantially uniform force is applied between the pair of electrodes, and the vibrating membrane has a uniform force (distance). And stable membrane vibration can be obtained.

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 the ultrasonic speaker of the present invention can be used effectively for these large-screen televisions.

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.

As mentioned above, although embodiment of this invention was described, the electrostatic ultrasonic transducer of this invention, an ultrasonic speaker, and a display apparatus are not limited only to the above-mentioned illustration example,
Of course, various modifications can be made without departing from the scope of the present invention.

The figure which shows the structural example of the electrostatic ultrasonic transducer which concerns on embodiment of this invention. The figure which shows the other structural example of the electrostatic type ultrasonic transducer which concerns on embodiment of this invention. The figure which shows the other structural example of the plate-shaped fixing member used for the electrostatic ultrasonic transducer which concerns on embodiment of this invention. The figure which shows the structural example of the electrostatic ultrasonic transducer to which this invention is applied. The figure which shows the other structural example of this invention electrostatic electrostatic transducer. 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 electrode layer of the bridge | bridging structure in the circular through-hole. 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. FIG. 10 is a diagram showing an external configuration of the projector shown in FIG. 9. FIG. 10 is a block diagram showing an electrical configuration of the projector shown in FIG. 9. 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.

Explanation of symbols

1, 2, 3 ... electrostatic ultrasonic transducer, 10 ... front side electrode, 11 ...
Vibration support part, 12 ... Bridge part, 13 ... Opening part (through hole), 14 ... Electrode layer, 20 ... Back side electrode, 21 ... Vibration support part, 22.・ Bridge part, 23 ...
Opening (through hole), 24 ... electrode layer, 25, 26, 27 ... plate-like fixing member, 30, 30A
... Vibrating membranes 31, 33, 35 ... Dielectric membranes, 32,34 ... Vibrating electrodes, 36 ...
DC power source 37 ... signal source 37A, 37B ... AC signal 40 ... front side electrode 41 ... reinforcing member 42A, 42B ... electrode layer 50 ... front side Electrode, 51, 5
2 ... Reinforcing member, 53A, 53B, 53C ... Electrode layer, 60A ... Front side fixed electrode, 60B ... Back side fixed electrode, 61A, 61B ... Through hole, 62 ... Support Member, 7
0, 70A ... Electrode, 71, 71A ... Through hole, 72, 72A ... Cross-bridge, 73, 73A ... Electrode layer, 101, 102 ... Reflector, 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 surface), 303... Viewer, 310.
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, 31
8A, 318B ... modulator, 319 ... low pass filter, 320 ... projector body, 321 ... mixer, 322A, 322B ... power amplifier, 322C ...
Power amplifier, 323... Bass reproduction speaker, 324A, 324B... Ultrasonic transducer, 331... Projector lens, 332.
・ Projection optics

Claims (17)

A first electrode having a through hole;
A second electrode having a through hole;
The through hole of the first electrode and the through hole of the second electrode are disposed so as to make a pair and are sandwiched between a pair of electrodes composed of the first electrode and the second electrode A vibrating membrane having a conductive layer, and a DC bias voltage applied to the conductive layer;
Including
The plate-like fixing member is arranged so that the convex portion of the plate-like fixing member having a convex shape comes into contact with the vicinity of the central portion of the surface of either one of the pair of electrodes on the side opposite to the vibrating membrane. And the pair of electrodes are integrally fixed,
An electrostatic ultrasonic transducer, wherein 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 pair of electrodes. The plate-like fixing member is characterized in that a surface of the plate-like fixing member that abuts on a surface of one of the pair of electrodes opposite to the vibrating membrane is formed as a convex curved surface. The electrostatic ultrasonic transducer according to claim 1. The plate-like fixing member has a protrusion at the center of the surface of the plate-like fixing member that abuts on the surface of one of the pair of electrodes opposite to the vibration film. Item 14. The electrostatic ultrasonic transducer according to Item 1. 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,
The plate-like fixing member is arranged so that the convex portion of the plate-like fixing member having a convex shape comes into contact with the vicinity of the central portion of the surface of either one of the pair of electrodes on the side opposite to the vibrating membrane. And the pair of electrodes are integrally fixed,
An electrostatic ultrasonic transducer, wherein 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. The plate-like fixing member is characterized in that a surface of the plate-like fixing member that abuts on a surface of one of the pair of electrodes opposite to the vibrating membrane is formed as a convex curved surface. The electrostatic ultrasonic transducer according to claim 4. The plate-like fixing member has a protrusion at the center of the surface of the plate-like fixing member that abuts on the surface of one of the pair of electrodes opposite to the vibration film. Item 5. The electrostatic ultrasonic transducer according to Item 4. 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 electrostatic ultrasonic transducer according to claim 4, wherein the electrode layer is formed on the vibration film facing surface of the bridge portion. The electrostatic ultrasonic transducer according to claim 7, wherein the first electrode, the second electrode, and the bridge portion are formed of a non-conductive material. At least one of the first electrode and the second electrode,
The electrostatic ultrasonic transducer according to any one of claims 4 to 8, further comprising a reinforcing member that crosses the through hole in a short direction inside the through hole. The electrostatic ultrasonic transducer according to claim 4, wherein the vibration film has a conductive layer formed in multiple layers. A first electrode having a through hole;
A second electrode having a through hole;
The through hole of the first electrode and the through hole of the second electrode are disposed so as to make a pair and are sandwiched between a pair of electrodes composed of the first electrode and the second electrode A vibrating membrane having a conductive layer, and a DC bias voltage applied to the conductive layer;
Including
The first electrode and the second electrode have a counter electrode portion facing the vibrating membrane inside the through hole,
The plate-like fixing member is arranged so that the convex portion of the plate-like fixing member having a convex shape comes into contact with the vicinity of the central portion of the surface of either one of the pair of electrodes on the side opposite to the vibrating membrane. And the pair of electrodes are integrally fixed,
A capacitive 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 pair of electrodes. The electrostatic ultrasonic transducer according to claim 11, wherein the counter electrode part is a counter electrode part having a bridge structure that bridges an outer peripheral part and an inside of the through hole. The electrostatic ultrasonic transducer according to claim 12, wherein the bridge structure is a cross structure. 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,
The plate-like fixing member is arranged so that the convex portion of the plate-like fixing member having a convex shape comes into contact with the vicinity of the central portion of the surface of either one of the pair of electrodes on the side opposite to the vibrating membrane. And the pair of electrodes are integrally fixed,
An ultrasonic speaker, wherein 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. 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,
The plate-like fixing member is arranged so that the convex portion of the plate-like fixing member having a convex shape comes into contact with the vicinity of the central portion of the surface of either one of the pair of electrodes on the side opposite to the vibrating membrane. And using the electrostatic ultrasonic transducer that is integrally fixed to the pair of electrodes,
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: An ultrasonic speaker that 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 reproduce a signal sound in an audible frequency band;
A projection optical system that projects an image onto a projection surface;
A display device comprising:
The ultrasonic ultrasonic transducer of the ultrasonic speaker 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,
The plate-like fixing member is arranged so that the convex portion of the plate-like fixing member having a convex shape comes into contact with the vicinity of the central portion of the surface of either one of the pair of electrodes on the side opposite to the vibrating membrane. And the pair of electrodes are integrally fixed,
A display device in which 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. The carrier signal in the ultrasonic frequency band is modulated by the signal in the first sound range among the audio signals supplied from the acoustic source, and the electrostatic ultrasonic transducer is driven by the modulated signal to reproduce the signal sound in the audible frequency band. An ultrasonic speaker,
A low-frequency sound reproduction speaker for reproducing a signal in a second sound range lower than the first sound range among the sound signals supplied from the acoustic source;
A directional acoustic system comprising:
The ultrasonic ultrasonic transducer of the ultrasonic speaker 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,
The plate-like fixing member is arranged so that the convex portion of the plate-like fixing member having a convex shape comes into contact with the vicinity of the central portion of the surface of either one of the pair of electrodes on the side opposite to the vibrating membrane. And the pair of electrodes are integrally fixed,
A directional acoustic system, wherein 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.

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