JP4868030B2 - Ultrasonic speaker, audio signal reproducing method, and superdirective acoustic system - Google Patents

Description

  The present invention relates to a push-pull type electrostatic ultrasonic transducer, which can generate the same sound pressure with less energy and can realize a low voltage (low power). Electric ultrasonic transducer, ultrasonic speaker using the same, electrostatic ultrasonic transducer design method, audio signal reproduction method using electrostatic ultrasonic transducer, electrostatic ultrasonic transducer design apparatus, electrostatic ultrasonic The present invention relates to a design program for an acoustic transducer, a method for manufacturing a fixed electrode of an electrostatic ultrasonic transducer, a superdirective acoustic system, and a display device.

  Conventionally, an electrostatic ultrasonic transducer is known as a broadband oscillation type ultrasonic transducer capable of generating a high sound pressure over a high frequency band. FIG. 7 shows a configuration example of a broadband oscillation type ultrasonic transducer. This electrostatic ultrasonic transducer is called a pull type because it works only in the direction in which the vibrating membrane is attracted to the fixed electrode side.

  The electrostatic ultrasonic transducer shown in FIG. 7 uses a dielectric 131 (insulator) such as PET (polyethylene terephthalate resin) having a thickness of about 3 to 10 μm as a vibrating body (vibrating film). An upper electrode 132 formed as a metal foil such as aluminum is integrally formed on the upper surface of the dielectric 131 by a process such as vapor deposition, and a lower electrode 133 formed of brass is formed on the lower surface of the dielectric 131. It is provided so that it may contact a part. The lower electrode 133 is nationally fixed to a base plate 135 made of bakelite or the like, to which the lead 152 is connected.

  The upper electrode 132 is connected to a lead 153, and the lead 153 is connected to the DC bias power supply 150. A DC bias voltage for attracting the upper electrode of about 50 to 150 V is constantly applied to the upper electrode 132 by the DC bias power source 150, and the upper electrode 132 is attracted to the lower electrode 133 side. Reference numeral 151 denotes a signal source.

  The dielectric 131, the upper electrode 132, and the base plate 135 are caulked by the case 130 together with the metal rings 136, 137, and 138 and the mesh 139.

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

  As described above, the electrostatic ultrasonic transducer shown in FIG. 7 is conventionally known as a broadband ultrasonic transducer (Pull type) capable of generating a relatively high sound pressure over a wide frequency band. .

  However, the maximum value of the sound pressure is somewhat low, for example, the sound pressure is as low as 120 dB or less, and the sound pressure is slightly insufficient for use as an ultrasonic speaker. An ultrasonic sound pressure of 120 dB or more is necessary for the parametric effect to sufficiently appear in an ultrasonic speaker. However, it is difficult to achieve this value with an electrostatic ultrasonic transducer (pull type). Polymer piezoelectric elements such as ceramic piezoelectric elements and PVDF have been used as ultrasonic transmitters. However, since the piezoelectric element has a sharp resonance point regardless of the material, and is practically used as an ultrasonic speaker by being driven at the resonance frequency, the frequency region where a high sound pressure can be secured is extremely narrow. That is, it can be said that it is a narrow band.

  In order to solve such a problem, an electrostatic ultrasonic transducer to which the design method of the present invention is applied as shown in FIG. 1 is currently proposed (Japanese Patent Application No. 2004-173946). Such a structure is generally referred to as a push-pull type, and the details of the structure and operation will be described later. In the ultrasonic transducer shown in FIG. Compared to the type ultrasonic transducer, it has the ability to satisfy both high bandwidth and high sound pressure at the same time.

  By the way, in the push-pull type electrostatic ultrasonic transducer shown in FIG. 1, it is particularly important to determine the height t (step height of the stepped hole) of the convex portions of the fixed electrodes 10A and 10B. It becomes a problem. The height t (step height of the stepped hole) of the fixed electrodes 10A and 10B is conventionally set to be large, for example, from 10 to 20 μm by observing the margin. It was. As described above, when the height t of the convex portion is increased, a higher drive AC voltage is required, and excessive energy is consumed, which is a problem. For this reason, provision of the method of designing the optimal convex part height t quantitatively from the value of desired sound pressure and drive frequency was calculated | required.

  If the optimum convex portion height t can be obtained quantitatively, an efficient configuration capable of obtaining a desired sound pressure with a small drive voltage can be realized. In other words, it is possible to generate the same sound pressure with less energy, and it is possible to reduce the voltage (lower power) of the electrostatic ultrasonic transducer.

JP 2000-50387 A JP 2000-50392 A

  As described above, in the push-pull type electrostatic ultrasonic transducer as shown in FIG. 1, the height t (step height of the stepped hole) of the fixed electrodes 10A and 10B is quantitatively designed. There was a need to provide a way to do this. If the optimum convex height t can be obtained quantitatively, an efficient configuration can be realized that can obtain a desired sound pressure with a small drive voltage, and the same sound pressure can be generated with less energy. It becomes. That is, it is possible to realize a low voltage (low power) of the electrostatic ultrasonic transducer.

The present invention has been made to solve such a problem. In a push-pull type electrostatic ultrasonic transducer, the height of the convex portion of the fixed electrode is quantitatively obtained, and the same with less energy than in the past. It is a first object of the present invention to provide an electrostatic ultrasonic transducer capable of generating sound pressure and achieving a low voltage (low power).
The present invention also provides an ultrasonic speaker using the push-pull type electrostatic ultrasonic transducer, a method for designing an electrostatic ultrasonic transducer, a design apparatus for an electrostatic ultrasonic transducer, an electrostatic ultrasonic transducer, and the like. A second object is to provide a design program for a sound wave transducer, a sound signal reproducing method, a manufacturing method, a superdirective acoustic system, and a projector.

The present invention has been made to solve the above problems, and an ultrasonic transducer according to the present invention includes a first electrode in which a through hole is formed, and a through hole that makes a pair with the through hole of the first electrode. And a second electrode to which an AC signal is applied between the first electrode and the pair of electrodes, and a conductive layer, and a DC bias voltage is applied to the conductive layer. And a holding member that holds the pair of electrodes and the vibrating membrane,
When the desired sound pressure to be output is P (dB) and the drive frequency is f (Hz), the one-side amplitude value of the membrane vibration in the diaphragm when the diaphragm is driven is a (m). The one-side amplitude value a of the membrane vibration is expressed by the following equation:
a = (1 / πf) √ {(I _O · 10 ^{P / 10} ) / 2ρ _O c},
Here, Io: 0.96 × 10 ⁻¹² (W / m ² ) in the standard sound intensity, ρo: 1.2 (kg / m ³ ) in the air density, c: about 340 (in the speed of sound in the air) m / S),
Sought by
Each of the pair of electrodes has a step portion on the outer periphery of the through hole on the vibration film side, and the height of the step portion in the vibration film side direction exceeds the one-side amplitude value a, and the one-side amplitude value a It is characterized by being set to a nearby value.
With such a configuration, for example, in the push-pull type electrostatic ultrasonic transducer shown in FIG. 1, when a desired sound pressure and driving frequency are given, the step height t of the stepped hole is optimally set. Formulate the formula. This equation is given by the following equation when the desired sound pressure is P (dB), the drive frequency is f (Hz), and the one-side amplitude a (m) of the membrane vibration.
a = (1 / πf) √ {t (I _O · 10 ^{P / 10} ) / 2ρ _O c},
Here, Io: 0.96 × 10 ⁻¹² (W / m ² ) in the standard sound intensity, ρo: 1.2 (kg / m ³ ) in the air density, c: about 340 (in the speed of sound in the air) m / S).
Then, the step height of the stepped hole of the fixed electrode is a value that exceeds the value of the membrane vibration amplitude obtained by the above formula and is as close as possible to the amplitude value (at least in a range where the membrane does not contact the electrode due to membrane vibration). An ultrasonic transducer with a fixed electrode designed by the above method is manufactured.
As a result, it is possible to design the optimum convex height t from the values of the desired sound pressure and the drive frequency. As a result, the electrostatic ultrasonic transducer has an efficient configuration. The sound pressure is obtained. In other words, it is possible to generate the same sound pressure as in the prior art with less energy, and it is possible to realize a low voltage (low power) of the electrostatic ultrasonic transducer.

The ultrasonic transducer designing method of the present invention includes a first electrode in which a through hole is formed, and a through hole that is paired with the through hole of the first electrode. A second electrode to which an AC signal is applied, a vibration film sandwiched between the pair of electrodes and having a conductive layer, and a DC bias voltage applied to the conductive layer, and the pair of fixed electrodes, A holding member for holding the vibrating membrane;
When the desired sound pressure to be output is P (dB) and the drive frequency is f (Hz), the one-side amplitude value of the membrane vibration in the diaphragm when the diaphragm is driven is a (m). The one-side amplitude value a of the membrane vibration is expressed by the following equation:
a = (1 / πf) √ {(I _O · 10 ^{P / 10} ) / 2ρ _O c},
Here, Io: 0.96 × 10 ⁻¹² (W / m ² ) in the standard sound intensity, ρo: 1.2 (kg / m ³ ) in the air density, c: about 340 (in the speed of sound in the air) m / S),
Calculated by
Each of the pair of electrodes has a step portion on the outer periphery of the through hole on the vibration film side, and the height of the step portion in the vibration film side direction exceeds the one-side amplitude value a, and the one-side amplitude value a It is characterized by being set to a nearby value.
With such a procedure, for example, in the push-pull type electrostatic ultrasonic transducer shown in FIG. 1, when a desired sound pressure and a driving frequency are given, the step height t of the stepped hole is optimally set. Formulate the formula. This equation is given by the following equation when the desired sound pressure is P (dB), the drive frequency is f (Hz), and the one-side amplitude a (m) of the membrane vibration.
a = (1 / πf) √ {t (I _O · 10 ^{P / 10} ) / 2ρ _O c},
Here, Io: 0.96 × 10 ⁻¹² (W / m ² ) in the standard sound intensity, ρo: 1.2 (kg / m ³ ) in the air density, c: about 340 (in the speed of sound in the air) m / S).
Then, the step height of the stepped hole of the fixed electrode is a value that exceeds the value of the membrane vibration amplitude obtained by the above formula and is as close as possible to the amplitude value (at least in a range where the membrane does not contact the electrode due to membrane vibration). An ultrasonic transducer with a fixed electrode designed by the above method is manufactured.
As a result, it is possible to design the optimum convex portion (stepped portion) height t from the values of the desired sound pressure and the driving frequency, and as a result, the electrostatic ultrasonic transducer has an efficient configuration, so that it is less. A desired sound pressure can be obtained with the driving voltage. In other words, it is possible to generate the same sound pressure as in the prior art with less energy, and it is possible to realize a low voltage (low power) of the electrostatic ultrasonic transducer.

In the electrostatic ultrasonic transducer designing apparatus of the present invention, the first electrode in which a through hole is formed and the through hole that makes a pair with the through hole of the first electrode are formed, and the first electrode A second electrode to which an AC signal is applied between the electrodes, a vibration film sandwiched between the pair of electrodes and having a conductive layer, and a DC bias voltage is applied to the conductive layer, and the pair of electrodes A holding member that holds the fixed electrode and the vibrating membrane;
When the desired sound pressure to be output is P (dB) and the drive frequency is f (Hz), the one-side amplitude value of the membrane vibration in the diaphragm when the diaphragm is driven is a (m). The one-side amplitude value a of the membrane vibration is expressed by the following equation:
a = (1 / πf) √ {(I _O · 10 ^{P / 10} ) / 2ρ _O c},
Here, Io: 0.96 × 10 ⁻¹² (W / m ² ) in the standard sound intensity, ρo: 1.2 (kg / m ³ ) in the air density, c: about 340 (in the speed of sound in the air) m / S),
Computing means for calculating by
A step part as a vibration film sandwiching part on the outer periphery of the through hole on each vibration film side of the pair of electrodes, the height of the step part in the vibration film side direction exceeds the one-side amplitude value a; Setting means for setting a value in the vicinity of the one-side amplitude value a;
It is characterized by having.
With the above-described configuration, the calculation means allows the one-side amplitude of the membrane vibration in the diaphragm when the diaphragm is driven when the desired sound pressure to be output is P (dB) and the drive frequency is f (Hz). When the value is a (m), the one-side amplitude value a of the membrane vibration is expressed by the following equation: a = (1 / πf) √ {(I _O · 10 ^{P / 10} ) / 2ρ _O c}, where Io: reference 0.96 × 10 ⁻¹² (W / m ² ) in acoustic intensity, ρo: 1.2 in air density (kg / m ³ ), c: about 340 (m / S) in sound speed in air The calculating and setting means has a step portion as a vibration film sandwiching portion on the outer periphery of the through hole on each vibration membrane side of the pair of electrodes, and the height of the step portion in the vibration film side direction is set to the one side A value exceeding the amplitude value a and in the vicinity of the one-side amplitude value a (at least in a range where the vibrating membrane does not contact the electrode due to membrane vibration) Set.
As a result, it is possible to design the optimum convex portion (stepped portion) height t from the values of the desired sound pressure and the driving frequency, and as a result, the electrostatic ultrasonic transducer has an efficient configuration, so that it is less. A desired sound pressure can be obtained with the driving voltage. In other words, it is possible to generate the same sound pressure as in the prior art with less energy, and it is possible to realize a low voltage (low power) of the electrostatic ultrasonic transducer.

Further, the electrostatic ultrasonic transducer design program according to the present invention includes a first electrode having a through hole formed therein and a through hole that is paired with the through hole of the first electrode. A second electrode to which an AC signal is applied between the electrodes, a vibration film sandwiched between the pair of electrodes and having a conductive layer, and a DC bias voltage is applied to the conductive layer, and the pair of electrodes A holding member that holds the fixed electrode and the vibrating membrane;
When the desired sound pressure to be output is P (dB) and the drive frequency is f (Hz), the one-side amplitude value of the membrane vibration in the diaphragm when the diaphragm is driven is a (m). The one-side amplitude value a of the membrane vibration is expressed by the following equation: a = (1 / πf) √ {(I _O · 10 ^{P / 10} ) / 2ρ _O c}, where Io: 0.96 × in the reference sound intensity 10 ⁻¹² (W / m ² ), ρo: 1.2 in air density (kg / m ³ ), c: about 340 (m / S) in the sound speed in the air, Each of the pair of electrodes has a step portion on the outer periphery of the through hole on the vibration film side, and the height of the step portion in the vibration film side direction exceeds the one-side amplitude value a, and the one-side amplitude value a The gist is to cause the computer to execute the second step of setting to a nearby value.
In the above configuration, when the desired sound pressure to be output is P (dB) and the driving frequency is f (Hz), the one-side amplitude value of the membrane vibration in the diaphragm when the diaphragm is driven is a ( m) Then, the one-side amplitude value a of the membrane vibration is expressed by the following equation: a = (1 / πf) √ {(I _O · 10 ^{P / 10} ) / 2ρ _O c}, where Io is the reference acoustic intensity 0.96 × 10 ⁻¹² (W / m ² ), ρo: 1.2 (kg / m ³ ) in the density of air, and c: about 340 (m / S) in the speed of sound in the air A step portion as a vibration film sandwiching portion on the outer periphery of the through hole on each vibration film side of each of the pair of electrodes, and the height of the step portion in the vibration film side direction is set to the one-side amplitude value a. And a value in the vicinity of the one-side amplitude value a (at least in a range where the vibrating membrane does not contact the electrode due to membrane vibration) By causing the computer to execute a design program for an electric ultrasonic transducer for causing the computer to execute the second step, an optimum convex (step) height t can be determined from the values of the desired sound pressure and the driving frequency. As a result, the electrostatic ultrasonic transducer has an efficient configuration, so that a desired sound pressure can be obtained with a smaller driving voltage. In other words, it is possible to generate the same sound pressure as in the prior art with less energy, and it is possible to realize a low voltage (low power) of the electrostatic ultrasonic transducer.

In the ultrasonic speaker according to the present invention, the first electrode in which a through hole is formed and a through hole that is paired with the through hole of the first electrode are formed, and an alternating current is formed between the first electrode and the ultrasonic electrode. A second electrode to which a signal is applied; a vibration film sandwiched between the pair of electrodes and having a conductive layer, and a DC bias voltage is applied to the conductive layer; the pair of electrodes and the vibration film; A holding member for holding
When the desired sound pressure to be output is P (dB) and the drive frequency is f (Hz), the one-side amplitude value of the membrane vibration in the diaphragm when the diaphragm is driven is a (m). The one-side amplitude value a of the membrane vibration is expressed by the following formula: a = (1 / πf) √ {(I _O · 10 ^{P / 10} ) / 2ρ _O c}, where Io: 0.96 × in the reference sound intensity 10 ⁻¹² (W / m ² ), ρ o: 1.2 (kg / m ³ ) in the density of air, c: about 340 (m / S) in the speed of sound in the air, each of the pair of electrodes A step portion is provided on the outer periphery of the through hole on the diaphragm side, and the height of the step portion in the vibration film side direction is set to a value that exceeds the one-side amplitude value a and is close to the one-side amplitude value a. It is characterized by this.
Accordingly, since the ultrasonic speaker has an efficient configuration, a desired sound pressure can be obtained with a smaller voltage. That is, it is possible to generate the same sound pressure as that of the conventional ultrasonic speaker with less energy, and it is possible to realize a lower voltage (lower power) of the ultrasonic speaker.

The method of reproducing an audio signal of an electrostatic ultrasonic transducer according to the present invention includes a first electrode having a through hole formed therein and a through hole that is paired with the through hole of the first electrode. A second electrode to which an alternating current signal is applied between the first electrode, a vibration film sandwiched between the pair of electrodes and having a conductive layer, and a DC bias voltage is applied to the conductive layer; When the diaphragm is driven when the desired sound pressure to be output is P (dB) and the drive frequency is f (Hz), having a pair of electrodes and a holding member that holds the diaphragm A (m), the one-side amplitude value a of the membrane vibration is expressed as follows: a = (1 / πf) √ {(I _O · 10 ^{P / 10} ) / 2ρ _O c}, where, Io: baseline acoustic Intensity at ^{0.96 × 10 -12 (W / m} 2), ρo: empty The step is formed on the outer periphery of the through hole on the vibrating membrane side of each of the pair of electrodes, and is obtained by: 1.2 (kg / m ³ ) in the air density, c: about 340 (m / S) in the sound speed in the air An electrostatic ultrasonic transducer characterized in that the height of the stepped portion in the vibrating membrane side direction is set to a value exceeding the one-side amplitude value a and in the vicinity of the one-side amplitude value a. 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 modulating the carrier wave by a signal wave in the audible frequency band And a step of driving the electrostatic ultrasonic transducer by applying the modulation signal between the fixed electrode and the electrode layer of the vibrating membrane. To do.
In the audio signal reproduction method of the electrostatic ultrasonic transducer including such a procedure, an audible frequency band signal wave is generated by the signal source, and an ultrasonic frequency band carrier wave is generated by the carrier wave supply source and output. Is done. Then, the carrier wave is modulated by the signal wave in the audible frequency band, and this modulated signal is applied between the fixed electrode and the electrode layer of the vibrating membrane, and the electrostatic ultrasonic transducer is driven.
Accordingly, the electrostatic ultrasonic transducer having the above-described configuration can output an acoustic signal having a sound pressure level high enough to obtain a parametric array effect over a wide frequency band, and reproduce an audio signal.

In the method of manufacturing an electrostatic ultrasonic transducer according to the present invention, a first electrode having a through hole formed therein and a through hole that makes a pair with the through hole of the first electrode are formed. A second electrode to which an AC signal is applied between the electrodes, a vibration film sandwiched between the pair of electrodes and having a conductive layer, and a DC bias voltage is applied to the conductive layer, and the pair of electrodes A mask member having a through hole pattern formed on a conductor plate for forming a fixed electrode portion of the pair of electrodes, and having an electrode and a holding member for holding the vibrating membrane; The first step of forming a through hole in the conductor plate, the vibration when the desired sound pressure output from the electrostatic ultrasonic transducer is P (dB) and the drive frequency is f (Hz). A piece of membrane vibration in the vibrating membrane when the membrane is driven The amplitude value Then a (m), one side amplitude value a of the membrane vibration, the following equation, a = (1 / πf) √ {(I O · 10 P / 10) / 2ρ O c}, where, Io: 0.96 × 10 ⁻¹² (W / m ² ) at the reference sound intensity, ρo: 1.2 (kg / m ³ ) at the air density, c: about 340 (m / S) at the speed of sound in the air, And the height of the stepped portion in the vibration film side direction exceeds the one-side amplitude value a, and the one-side amplitude is obtained. A second step of forming a value in the vicinity of the value a;
It is characterized by having.

In the manufacturing method of the electrostatic ultrasonic transducer of the present invention comprising the above steps, a mask member in which a pattern of a plurality of through holes is formed on a conductor plate for forming a fixed electrode portion of a pair of fixed electrodes is coated. Then, a plurality of through holes are formed in the conductor plate by an etching process. Then, when the desired sound pressure output by the electrostatic ultrasonic transducer is P (dB) and the drive frequency is f (Hz), the vibration of the diaphragm in the diaphragm when the diaphragm is driven When the one-side amplitude value is a (m), the one-side amplitude value a of the membrane vibration is expressed by the following equation: a = (1 / πf) √ {(I _O · 10 ^{P / 10} ) / 2ρ _O c} (where Io : 0.96 × 10 ⁻¹² (W / m ² ) at the reference sound intensity, ρo: 1.2 (kg / m ³ ) at the air density, c: about 340 (m / S) at the speed of sound in the air ) And the height of the stepped portion, which is the diaphragm sandwiching portion provided on the outer periphery of the through hole on the diaphragm side of each of the pair of fixed electrodes, exceeds the one-side amplitude value a and in the vicinity of the one-side amplitude value a (At least in a range where the vibrating membrane does not contact the electrode due to membrane vibration).
As a result, the height of the convex part of the fixed electrode can be obtained quantitatively, and the same sound pressure can be generated with less energy than in the past, and the electrostatic ultrasonic transducer designed to reduce the voltage (lower power). Is obtained.

In the method of manufacturing an electrostatic ultrasonic transducer according to the present invention, a non-conductive photosensitive resist as a vibration film sandwiching portion forming material is formed to a predetermined thickness on the conductor plate in which the through hole is formed. A third step, a fourth step of covering and exposing a vibration film sandwiching portion forming mask member in which a pattern of the vibration film sandwiching portion is formed on the surface of the non-conductive photosensitive resist, and the vibration film And a fifth step of removing the unnecessary photosensitive resist by development by peeling the nipping portion forming mask member.
In the manufacturing method of the electrostatic ultrasonic transducer of the present invention comprising the above steps, a non-conductive photosensitive resist as a vibration film sandwiching portion forming material is formed to a predetermined thickness on a conductive plate in which a through hole is formed. A third step of covering the surface of the non-conductive photosensitive resist with a vibration film sandwiching portion forming mask member on which a pattern of the vibration film sandwiching portion is formed, and exposing the vibration member. A film sandwiching portion forming mask member is peeled off, and a fifth step of removing the unnecessary photosensitive resist by development is included, so that the steps after metal electroforming, which has been conventionally required, can be dispensed with, so that the manufacturing process It is shortened and manufacturing cost can be reduced. Further, a solvent or the like (mainly a strong alkali solvent) used in the residual resist peeling step is not required, and the environment can be improved.

Also, the method for manufacturing an electrostatic ultrasonic transducer according to the present invention is a screen printing plate in which a mask member for forming the vibration film sandwiching portion forming material is arranged on the surface of the conductor plate in which the through hole is formed. And a third step of setting the liquid vibration film sandwiching portion forming material, and setting the screen printing plate and the liquid vibration film sandwiching portion forming material on the surface of the conductor plate on which the through hole is formed, A fourth step of applying the vibration film holding portion forming material to a portion where the mask member is not applied while moving the screen, and after applying the vibration film holding portion forming material to a portion where the mask member is not applied, the screen A fifth step of removing the printing plate and drying the vibration film sandwiching portion forming material remaining on the surface of the conductive plate.
In the manufacturing method of the electrostatic ultrasonic transducer of the present invention comprising the above steps, a screen printing plate in which a mask member for forming the vibration film sandwiching portion is arranged on the surface of the conductor plate in which the through hole is formed, and A third step of setting the liquid vibration film sandwiching portion forming material in liquid form, and setting the screen printing plate and the liquid vibration film sandwiching portion forming member on the surface of the conductor plate in which the plurality of through holes are formed, A fourth step of applying the diaphragm holding portion forming member to a portion where the mask member is not applied while moving the squeegee; and after applying the diaphragm holding portion forming material to a portion where the mask member is not applied, A fifth step of removing the screen printing plate and drying the vibration film sandwiching portion forming material remaining on the surface of the conductive plate, so that the steps after metal electroforming that have been conventionally required are unnecessary. Can further since there is no need also steps such development carried out by photolithography, the manufacturing process can be greatly shortened, and can greatly reduce the production cost.

In the superdirective acoustic system of the present invention, the first electrode in which a through hole is formed and the through hole that is paired with the through hole of the first electrode are formed, and the first electrode is provided between the first electrode and the first electrode. A second electrode to which an AC signal is applied, a vibration film sandwiched between the pair of electrodes and having a conductive layer, and a DC bias voltage is applied to the conductive layer, the pair of electrodes and the vibration A membrane member in the diaphragm when the diaphragm is driven when a desired sound pressure to be output is P (dB) and a drive frequency is f (Hz). When the amplitude value of one side of vibration is a (m), the amplitude value a of one side of membrane vibration is given by the following equation: a = (1 / πf) √ {(I _O · 10 ^{P / 10} ) / 2ρ _O c}, where , Io: baseline acoustic Intensity at ^{0.96 × 10 -12 (W / m} 2), ρo: a density of the air 1.2 (kg / m ), C: from about 340 at the speed of sound in air (m / S), obtained by having a step portion in the through hole outer periphery of the vibrating film side of each of the pair of electrodes, the vibrating film side direction of the step portion Is set to a value in the vicinity of the one-side amplitude value a and in the vicinity of the one-side amplitude value a, by an ultrasonic speaker configured using an electrostatic ultrasonic transducer, Is a super directional acoustic system that reproduces a sound signal supplied from a sound source and forms a virtual sound source in the vicinity of a sound wave reflection surface such as a screen, and reproduces a mid-high range signal among the sound signals supplied from the sound source. And a low-frequency sound reproduction speaker that reproduces a low-frequency sound of a sound signal supplied from the acoustic source.
In the superdirective acoustic system having the above configuration, when the desired sound pressure output by the electrostatic ultrasonic transducer is P (dB) and the drive frequency is f (Hz), the vibration membrane is driven. When the one-side amplitude value of the membrane vibration in the vibrating membrane is a (m), the one-side amplitude value a of the membrane vibration is expressed by the following equation: a = (1 / πf) √ {(I _O · 10 ^{P / 10} ) / 2ρ _O c}, where Io: 0.96 × 10 ⁻¹² (W / m ² ) in reference sound intensity, ρo: 1.2 (kg / m ³ ) in air density, c: speed of sound in air About 340 (m / S), and the height of the stepped portion that is the diaphragm sandwiching portion provided on the outer periphery of the through hole on each diaphragm side of the pair of fixed electrodes exceeds the one-side amplitude value a, And a value in the vicinity of the one-side amplitude value a (at least in a range where the vibrating membrane does not contact the electrode due to membrane vibration). An ultrasonic speaker composed of an electrostatic ultrasonic transducer set to (1) is used. The ultrasonic speaker reproduces an audio signal in the middle / high range among the audio signals supplied from the acoustic source. Further, among the audio signals supplied from the acoustic source, the audio signal in the low frequency range is reproduced by a low tone 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.

In the display device of the present invention, a first electrode in which a through hole is formed and a through hole that is paired with the through hole of the first electrode are formed, and an AC signal is provided between the first electrode and the first electrode. A vibration film that is sandwiched between the pair of electrodes, has a conductive layer, and a DC bias voltage is applied to the conductive layer, and the pair of electrodes and the vibration film One side of membrane vibration in the diaphragm when the diaphragm is driven when the desired sound pressure to be output is P (dB) and the drive frequency is f (Hz) When the amplitude value is a (m), the one-side amplitude value a of the membrane vibration is expressed by the following equation: a = (1 / πf) √ {(I _O · 10 ^{P / 10} ) / 2ρ _O c}, where Io: 0.96 × 10 ⁻¹² (W / m ² ) in reference sound intensity, ρo: 1.2 (kg / m ³ ) in air density, c: empty The sound velocity in the air is determined by about 340 (m / S), and a step portion is provided on the outer periphery of the through hole on each vibration membrane side of the pair of electrodes, and the height of the step portion in the vibration membrane side direction is determined. The electrostatic ultrasonic transducer is characterized in that it is set to a value that exceeds the one-side amplitude value a and is in the vicinity of the one-side amplitude value a, and is audible frequency from an audio signal supplied from an acoustic source. It has an ultrasonic speaker that reproduces a band signal sound, and a projection optical system that projects an image on a projection surface.
In the display device configured as described above, when the desired sound pressure output from the electrostatic ultrasonic transducer is P (dB) and the drive frequency is f (Hz), the vibration film when the vibration film is driven A (m), the one-side amplitude value a of the membrane vibration is expressed by the following equation: a = (1 / πf) √ {(I _O · 10 ^{P / 10} ) / 2ρ _O c}, Here, Io: 0.96 × 10 ⁻¹² (W / m ² ) in the standard sound intensity, ρo: 1.2 (kg / m ³ ) in the air density, c: about 340 (in the speed of sound in the air) m / S), and the height of the stepped portion, which is the diaphragm sandwiching portion provided on the outer periphery of the through hole on each diaphragm side of the pair of fixed electrodes, exceeds the one-side amplitude value a and the one-side Set to a value in the vicinity of the amplitude value a (at least in a range where the vibrating membrane does not contact the electrode due to membrane vibration) An ultrasonic speaker composed of an electrostatic ultrasonic transducer 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.

The schematic block diagram of the ultrasonic transducer to which the design method of this invention is applied. The enlarged view of the convex part of the fixed electrode of the electrostatic ultrasonic transducer shown in FIG. Wave equation derivation conceptual diagram. Sound intensity derivation conceptual diagram. The figure which shows the example of calculation of a film | membrane amplitude. The figure which shows the structural example of an ultrasonic speaker. The figure which shows the structural example of a pull type electrostatic ultrasonic transducer. The figure which shows 1st Embodiment of the manufacturing method of an ultrasonic transducer. The figure which shows 2nd Embodiment of the manufacturing method of an ultrasonic transducer. The figure which shows the relationship between the thickness of the insulating layer of a vibration film, the thickness of a vibration film clamping part, and an electrostatic capacitance. FIG. 3 is a diagram illustrating a usage state of the projector according to the embodiment of the invention. FIG. 12 is a diagram showing an external configuration of the projector shown in FIG. 11. FIG. 13 is a block diagram showing an electrical configuration of the projector shown in FIG. 12. Explanatory drawing of the reproduction | regeneration state of the reproduction signal by an ultrasonic transducer. The manufacturing process figure which shows the conventional manufacturing method of an ultrasonic transducer. The figure which shows the problem on the structure of the ultrasonic transducer by the conventional manufacturing method. Explanatory drawing which shows the characteristic improvement by the manufacturing method of this invention. The block diagram which shows the structure of the design apparatus of the electrostatic type ultrasonic transducer which concerns on embodiment of this invention. The flowchart which shows the content of the design program of the electrostatic type ultrasonic transducer which concerns on embodiment of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[Summary of Invention]
In the present invention, in the push-pull type electrostatic ultrasonic transducer shown in FIG. 1, when a desired sound pressure and a driving frequency are given, the step height of the stepped hole (corresponding to the vibration film sandwiching portion). Formulas for optimally setting t are formulated. In this equation, the one-side amplitude value a (m) of the membrane vibration when the desired sound pressure is P (dB) and the drive frequency is f (Hz) is given by the following equation.

Here, Io: 0.96 × 10 ⁻¹² (W / m ² ) as a reference sound intensity,
ρo: Air density of 1.2 (kg / m ³ ), c: Sound velocity in air of about 340 (m / S),

  Then, a value exceeding the one-side amplitude value a of the membrane vibration obtained by the above formula and as close as possible to the amplitude value a (at least in a range where the vibrating membrane does not contact the electrode due to membrane vibration) Designed as a step height t to produce an ultrasonic transducer. In addition, an ultrasonic transducer having an identification electrode designed by the above method is used for an ultrasonic speaker.

[Description of an example of an ultrasonic transducer to which the design method of the present invention is applied]
FIG. 1 is a schematic configuration diagram of a push-pull type electrostatic ultrasonic transducer to which a design method according to the present invention is applied.

  In FIG. 1, a push-pull type electrostatic ultrasonic transducer 1 to which the design method of the present invention is applied includes a pair of fixed electrodes 10A, 10B including a conductive member formed of a conductive material functioning as an electrode, The vibrating membrane 12 is sandwiched between a pair of fixed electrodes and has an electrode layer (conductive layer) 121, and a pair of fixed electrodes 10A and 10B and a member (not shown) that holds the vibrating membrane.

  The vibrating membrane 12 is formed of an insulator 120 and has an electrode layer 121 formed of a conductive material. The electrode layer 121 has a single polarity (positive or negative polarity) by a DC bias power supply 16. DC bias voltage is applied, and phase inversion between the pair of fixed electrodes 10A and 10B output from the signal source 18 is superimposed between the DC bias voltage. The AC signals 18A and 18B are applied.

  The pair of fixed electrodes 10A and 10B have the same number and a plurality of through holes (stepped through holes) 14 at positions facing each other with the vibrating membrane 12 therebetween, and the conductive members of the pair of fixed electrodes 10A and 10B. Between them, AC signals 18A and 18B whose phases are mutually inverted by the signal source 18 are applied. The fixed electrode 10A and the electrode layer 121, and the fixed electrode 10B and the electrode layer 121 are each formed with a capacitor.

  In the above-described configuration, the ultrasonic transducer 1 is applied to the electrode layer 121 of the vibrating membrane 12 with respect to the mutual phase output from the signal source 18 to a single polarity (positive polarity in this example) DC bias voltage by the DC bias power supply 16. The inverted AC signals 18A and 18B are applied in a superimposed state.

  On the other hand, an AC signal is applied from the signal source 18 to the pair of fixed electrodes 10A and 10B. As a result, in the positive half cycle of the AC signal 18A output from the signal source 18, since a positive voltage is applied to the fixed electrode 10A, the surface portion 12A not sandwiched between the fixed electrodes of the vibrating membrane 12 is applied to the surface portion 12A. The electrostatic repulsive force acts, and the surface portion 12A is pulled downward in FIG.

  At this time, the AC signal 18B is in a negative cycle, and a negative voltage is applied to the opposing fixed electrode 10B. Therefore, the back surface portion 12B, which is the back surface side of the surface portion 12A of the vibration film 12, has The electrostatic attraction force acts, and the back surface portion 12B is pulled further downward in FIG.

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

  Thus, the ultrasonic transducer 1 is called a push-pull type because the vibrating membrane 12 vibrates by receiving a force from the pair of fixed electrodes 10A and 10B. The push-pull type ultrasonic transducer 1 has the ability to satisfy both high bandwidth and high sound pressure at the same time as compared with the pull type electrostatic ultrasonic transducer that only acts on the vibrating membrane only by electrostatic attraction force. Yes.

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

Incidentally, an enlarged view of the convex portion of the fixed electrode of the electrostatic ultrasonic transducer shown in FIG. 1 is shown in FIG. As shown in FIG. 2, it can be seen that the vibration film 12 may come into contact with the fixed electrode unless the step height t of the convex portion is equal to or greater than the film amplitude of the vibration film 12. Therefore, it can be seen that the membrane amplitude of the vibrating membrane 12 may be calculated in order to design the height of the convex portion (the step height of the stepped hole) t. In other words, if the height of the convex portion (the step height of the stepped hole) t is set to a value close to the membrane amplitude (at least in a range where the vibrating membrane does not contact the electrode due to membrane vibration), the optimum design is achieved with less energy. It can be seen that a desired sound pressure can be generated, and a low voltage (low power) can be realized.
Hereinafter, a method for calculating the membrane amplitude of the vibrating membrane 12 will be described.

[Calculation of membrane amplitude of vibration membrane (calculation of wave equation)]
As a first procedure for calculating the membrane amplitude of the vibrating membrane, a wave equation is derived (related to aerial acoustics). Although there is no direct relationship between the relationship between membrane amplitude and sound pressure, it is a derivation of an important formula for understanding the definition of important variables that will be used frequently in the future. (First volume), Ito Kei, Corona, P158-159).

  As shown in FIG. 3, the volume of the gas sandwiched between the plane x and the plane x + δx is between the plane (x + ξ) and (x + ξ + δx + δξ) at time t after the change occurs. Since it is sandwiched, the distance between the two surfaces surrounding the body weight changes from δx to δx + δξ. Therefore δξ is

  The change in layer thickness is

  It becomes. Therefore, the expansion coefficient (dimensionless amount) of this part is

  Therefore, the condensation rate (dimensionless amount) is

  Next, it is convenient to express the pressure in terms of the condensation rate s, that is, ξ,

  By using that

  Here, the equation of motion for the mass of the gas between the plane x and x + δx is established. The equation for the balance of forces acting on the unit area of this plane is

  Where δp is the magnitude of the pressure increase at the front surface of the plane. From formulas (6), (5) and (3),

  Equation (7) is a plane wave equation relating to sound.

[Calculation of membrane amplitude of vibration membrane (derivation of acoustic intensity of plane wave)]
As a second procedure for calculating the membrane amplitude of the vibration membrane, an energy flow flowing through the unit area of the wave front surface of the plane wave is obtained. For this purpose, as shown in FIG. 4, a cylinder having a cross-sectional area of S is assumed, and an embankment in which air in the cylinder is vibrated by a piston at one end is considered, and acoustic intensity is derived.

  In FIG. 4, the movement of the piston is expressed by equation (8).

  The air on the positive side of x is

  It is thought that the displacement becomes. In this case, the work that the piston does against the air is every second,

  And taking the time average, the first term in equation (10) is gone,

  It becomes. This value is equal to the energy of the sound wave contained in the volume cS, and this much energy is released from the piston into the air every second. However, since the sound wave propagates a distance of c per second, the wave front advances by c per second, and the air in the volume of cS per second is newly oscillated. In this way, the wave front surface of the sound wave propagates energy at the rate shown in the equation (11). This is called energy flow. Therefore, the energy carried by the unit area of the wave front is every second,

In sound, this is called power density or sound intensity and is represented by I. On the other hand, the sound pressure P (dB) and the sound intensity I (W / m ³ ) are related by the following equation.

Here, Io is a standard sound intensity of 0.96 × 10 ⁻¹² (W / m ² ).

  From the equations (12) and (13), the membrane amplitude value a is expressed by the following equation.

Expression (14) is an expression for calculating the film amplitude necessary for the design.
Now, in the case of an ultrasonic speaker, the sound pressure needs to be 130 dB or more, so consider the case where the sound pressure P in equation (14) is 130, 140, 150 (dB). When the frequency of the carrier ultrasonic wave is 40, 50, 60 (kHz), the amplitude value a is as shown in FIG.

  For example, when it is desired to obtain a sound pressure of 140 (dB) by driving at 50 kHz, the membrane amplitude needs to be 2.18 μm. Therefore, in order for the membrane vibration not to come into contact with the fixed electrode and for the electrostatic force to work efficiently, it is desirable to set the height t of the fixed electrode convex portion to 2.18 μm or more and as close to 2.18 μm as possible. .

[Description of configuration example of ultrasonic speaker]
FIG. 6 shows a general configuration example of an ultrasonic speaker using an ultrasonic transducer according to the above design method. An ultrasonic speaker applies AM modulation to an ultrasonic wave called a carrier wave with an audio signal (audible area signal), and when it is released into the air, the original audio signal is self-reproduced in the air due to air nonlinearity. It is.
In other words, since the sound wave is a close-packed wave that is transmitted using air as a medium, in the process in which the modulated ultrasonic wave propagates, dense and sparse parts of the air remarkably appear, and the dense part has a high speed of sound. Since the sound speed of the sparse part is slow, the modulation wave itself is distorted. As a result, the waveform is separated into a carrier wave (ultrasonic wave) and an audible wave (original audio signal). Signal), and is generally called the parametric array effect.

  In FIG. 6, an ultrasonic speaker 40 includes an audio frequency wave signal oscillation source (audio signal source) 41 that generates a signal wave in the audio frequency band, and a carrier wave signal that generates and outputs a carrier wave in the ultrasonic frequency band. A source 42, a modulator 43, a power amplifier 44, and an ultrasonic transducer 45 are included. Here, in this embodiment, the “audible frequency band” refers to a frequency band of 20 kHz or less, and the “ultrasonic frequency band” refers to a frequency band exceeding 20 kHz.

  The modulator 43 modulates the carrier wave output from the carrier wave signal source 42 with the signal wave of the audible frequency band output from the audible frequency wave signal oscillation source 41, and transmits it to the ultrasonic transducer 45 via the power amplifier 44. Supply.

  In the above-described configuration, the carrier wave in the ultrasonic frequency band output from the carrier wave signal source 42 by the audio signal wave output from the audible frequency wave signal oscillation source 41 is modulated by the modulator 43 and amplified by the power amplifier 44. The ultrasonic transducer 45 is driven by the signal. As a result, the modulated signal is converted into a sound wave of a finite amplitude level by the ultrasonic transducer 45, and this sound wave is radiated into the medium (in the air), and the signal sound in the original audible frequency band due to the nonlinear effect of the medium (air). Is self-regenerating. That is, since the sound wave is a close-packed wave that propagates using air as a medium holiday, in the process in which the modulated ultrasonic wave propagates, a dense portion and a sparse portion of the air appear prominently, and the dense portion has a high sound speed, Since the sound speed is slow in the sparse part, the modulation wave itself is distorted. As a result, the waveform is separated into the carrier wave (ultrasonic frequency band), and the signal wave (signal sound) in the audible frequency band is reproduced.

As described above, in the push-pull type electrostatic ultrasonic transducer shown in FIG. 1, by formulating the film amplitude when the drive frequency and the desired sound pressure are given, the surface of the demarcated electrode is improved. The shape (projection-shaped vibrating membrane sandwiching portion) can be designed quantitatively. Conventionally, since the height of the convex portion of the fixed electrode was 10 to 20 μm, a high driving AC voltage was required.
However, if the design method of the present invention is used, the membrane amplitude can be determined if the desired sound pressure and drive frequency are determined, and the optimum convex portion height t can be designed from the value, resulting in an efficient configuration. .
For this reason, a desired sound pressure can be obtained with a smaller voltage. In other words, it is possible to generate the same sound pressure as in the prior art with less energy, and to realize a low voltage (low power).

[Description of Method for Manufacturing Fixed Electrode of Electrostatic Ultrasonic Transducer of the Present Invention]
Next, a method for manufacturing the fixed electrode portion of the Push-Pull electrostatic ultrasonic transducer of the present invention will be described.
First, a manufacturing process in the case where the fixed electrode portion of the ultrasonic transducer is manufactured by a conventional method by photolithography will be described with reference to FIG. In the figure, first, a conductor plate (copper, stainless steel is used, but copper is suitable for nickel electroforming) 10 is covered with a mask member 11 on which a plurality of through hole patterns are formed. Through holes 14 are formed in the conductor plate 10C by etching (FIGS. 15A and 15B).
Next, after the through hole 14 is formed in the conductor plate 10C, the mask member 11 is peeled off to obtain the conductor plate 10C having the through hole 14 (FIG. 15C).

  Here, the diameter of the through hole 14 opened in the conductor plate 10C by etching has a restriction in relation to the thickness of the conductor plate 10C. For example, when the minimum diameter of the through hole 14 used in the ultrasonic transducer according to the embodiment of the present invention is 0.25 mm, the thickness of the through hole 14 having this diameter is 0.25 mm or less. . Therefore, when a fixed electrode with a thickness of 0.25 mm or more is required, several sheets of a 0.25 mm-thick metal plate with through holes 14 formed by etching are prepared in advance, and the necessary number of sheets are stacked. Then, metal bonding is performed by thermocompression bonding or diffusion bonding, and the fixed electrodes having a desired thickness are manufactured.

Next, a photosensitive resist as a pretreatment material is used to form a vibration film sandwiching portion (stepped portion) constituting the fixed electrode on the conductive plate 10C (or the laminated conductive plate) having the through holes 14 formed therein. (Coating in the case of liquid, laminating in the case of film) 23 is attached, and then exposure is performed with the mask member 21 for forming the vibration film sandwiching portion covered (FIG. 15D).
As the photosensitive resist 23, a liquid resist or a dry film generally used for forming a temporary intermediate structure by etching, plating, or the like is used. In this component, the through hole 14 is sealed. Therefore, it is more effective to use a dry film.

When the unnecessary resist is removed by development, only the surface of the conductive plate 10C where the vibration film sandwiching portion (step portion) of the fixed electrode is formed is exposed (FIG. 15E).
Next, a metal (for example, nickel) is laminated on the exposed surface of the conductor plate 10C to a desired height by electroforming (FIG. 15 (f)). In this case, the height of the diaphragm sandwiching portion of the fixed electrode, that is, the step portion provided on the outer periphery of the through hole is set as follows.
That is, when the desired sound pressure output from the electrostatic ultrasonic transducer is P (dB) and the drive frequency is f (Hz), one side of the membrane vibration in the diaphragm when the diaphragm is driven When the amplitude value is a (m), the one-side amplitude value a of the membrane vibration is expressed by the following equation: a = (1 / πf) √ {(I _O · 10 ^{P / 10} ) / 2ρ _O c}, where Io: 0.96 × 10 ⁻¹² (W / m ² ) at the reference sound intensity, ρo: 1.2 (kg / m ³ ) at the air density, c: about 340 (m / S) at the speed of sound in the air, The height of the step portion, which is a diaphragm sandwiching part provided on the outer periphery of the through hole on each diaphragm side of the pair of fixed electrodes, exceeds the one-side amplitude value a and in the vicinity of the one-side amplitude value a (At least in a range where the vibrating membrane does not contact the electrode due to membrane vibration).
When the residual resist 24 is peeled after the electroforming process is completed, a desired fixed electrode is completed (FIG. 15 (g)).

Problems of the fixed electrode when manufactured by the above conventional manufacturing process are shown below.
(1) A thin film cannot be used for the vibrating membrane When the fixed electrode is manufactured in the conventional manufacturing process described above, that is, when the vibrating membrane sandwiching portion of the fixed electrode is made of a conductive material, the metal vapor deposition layer (= conductive) of the vibrating membrane is used. The maximum clearance between the layer) and the fixed electrode is the thickness of the insulating layer of the vibrating membrane.
Here, the insulating layer of the vibrating electrode film used in the ultrasonic transducer according to the embodiment of the present invention is made of polyethylene terephthalate (PET), polyethylene sulfide (PPS), polypropylene (PP), polyimide (PI), or the like.

Here, the dielectric breakdown strength of each material is as follows.
PET, PPS, PI: 200V / μm
PP: 300V / μm
The voltage applied to this transducer is several hundred volts to several kilovolts for both the fixed electrode and the vibrating electrode film.
Therefore, in the conventional configuration, for example, when PET is used for the insulating layer of the vibration film, a film thickness of at least 10 μm is necessary to apply a voltage of 2 kV, and a film thinner than this cannot be used as the vibration film. Become.
(2) Easily causes dielectric breakdown.
The edge portion of the fixed electrode formed by the etching process is very sharp. In addition, burrs of several to several tens of microns or the like are generated at places where additional machining (machining) is performed. Further, it has been confirmed that the etched metal is easily distorted, and at least a few tens of μm of warp remains even when thermocompression bonding or diffusion bonding is performed.
In this way, when the vibrating electrode film is securely held in a state where the fixed electrode is warped, the edge portion of the vibrating film holding portion 20 in the fixed electrode is formed on the insulating layer 120 of the vibrating film 12 as shown in FIG. Bite.

In the conventional configuration, since the diaphragm sandwiching portion 20 is formed of a conductive material, the minimum gap between the electrode layer 121 of the diaphragm 12 and the conductive portion of the fixed electrode is d1 in the figure, and the gap is narrowed by the amount of intrusion. The dielectric breakdown strength is reduced.
For example, when the insulating layer 120 is PET, it is difficult to apply a voltage of 200 V or more when d1 is reduced to about 1 μm.
(3) The capacitance is large, and energy is wasted.
The input power is determined by the electrostatic capacity, and as the gap between the electrode layer 121 of the vibrating membrane 12 and the fixed electrode is narrowed, that is, as the insulating layer 120 of the vibrating electrode film is thinner, the electrostatic capacity increases and the input power increases.
On the other hand, the electrostatic force acting on the vibrating membrane 12 that contributes most to the main characteristics (= sound pressure) of the ultrasonic transducer is that the area of the metal surface of the fixed electrode exposed as the vibrating membrane sandwiching portion and the level difference of the vibrating membrane sandwiching portion (= Gap between conductor and diaphragm).
Therefore, if a vibrating membrane with a thin insulating layer is used, the electrostatic force increases, but at the same time, the capacitance increases significantly, so that the energy efficiency is not good.

As described above, when a fixed electrode of an ultrasonic transducer is manufactured by a conventional manufacturing process, (1) a thin film cannot be used for the diaphragm, and (2) between the fixed electrode and the conductive layer of the diaphragm. (3) The capacitance formed between the conductive layer of the vibrating membrane and the fixed electrode is large, and energy is wasted.
These problems are solved by the manufacturing method of the ultrasonic transducer described below.

(First Embodiment of Method for Manufacturing Fixed Electrode of Electrostatic Ultrasonic Transducer of the Present Invention (Photolithographic Method))
FIG. 8 shows a first embodiment of a method for manufacturing a fixed electrode of an electrostatic ultrasonic transducer according to the present invention.
In FIG. 8, first, a conductor plate (copper, stainless steel is used, but copper is suitable for nickel electroforming) 10 is covered with a mask member 11 in which a plurality of through hole patterns are formed. Through holes 14 are formed in the conductor plate 10C by etching (FIGS. 8A and 8B).
Next, after the through hole 14 is formed in the conductor plate 10C, the mask member 11 is peeled off to obtain the conductor plate 10C having the through hole 14 (FIG. 8C). Next, the conductor plates 10C are stacked to obtain a desired thickness. Of course, when the desired thickness can be obtained with one conductive plate 10C, there is no need to stack the conductive plates 10C.

Next, a photosensitive resist (coating treatment in the case of liquid, in the case of a film) for forming a step constituting the vibration film sandwiching portion on the conductive plate 10C (or laminated conductive plates) with the through holes 14 formed therein. Is applied with a laminating process 22, and is then covered with a mask member 21 for forming a diaphragm holding portion and exposed (FIG. 8D).
The photosensitive resist 22 as the vibration film sandwiching portion forming material used here must be able to be permanently configured as the vibration film sandwiching portion and be non-conductive. In the case of liquid, photosensitive polyimide coating material (= photosensitive coating material used in semiconductor manufacturing, coated with a metal plate by spin coating) is used in the case of liquid, and in the case of film, the material is considered to be effective. There are a photosensitive solder resist film, a photosensitive polyimide film, and the like used for a substrate package.

  When the vibration film sandwiching portion forming mask member 21 is peeled off and the unnecessary photosensitive resist 22 is removed by development, only the surface of the conductive plate 10C serving as the fixed electrode portion is exposed, and the other portions are non-conductive photosensitive. The resist 22 remains, and a desired fixed electrode is completed (FIG. 8E).

  In the method of manufacturing the fixed electrode of the ultrasonic transducer comprising the above steps, the vibration film holding portion of the fixed electrode for holding the vibration film is formed of an insulating material by a photolithography method. Since the subsequent steps can be made unnecessary, the manufacturing process can be shortened and the manufacturing cost can be reduced. Further, a solvent or the like (mainly a strong alkali solvent) used in the residual resist peeling step is not required, and the environment can be improved.

(Second Embodiment of Method for Manufacturing Fixed Electrode of Electrostatic Ultrasonic Transducer of the Present Invention (Screen Printing Method))
Next, FIG. 9 shows a second embodiment of a method (manufacturing process) for manufacturing a fixed electrode of an electrostatic ultrasonic transducer according to the present invention.

In FIG. 9, first, a conductor plate (copper, stainless steel is used, but copper is suitable for nickel electroforming) 10 is covered with a mask member 11 in which a plurality of through hole patterns are formed. Through holes 14 are formed in the conductor plate 10C by etching (FIGS. 9A and 9B).
Next, after the through hole 14 is formed in the conductor plate 10C, the mask member 11 is peeled off to obtain the conductor plate 10C having the through hole 14 (FIG. 9C).
Next, the conductor plates 10C are stacked to obtain a desired thickness. Of course, when the desired thickness can be obtained with one conductive plate 10C, there is no need to stack the conductive plates 10C.

A screen printing plate 30 and a liquid vibration film sandwiching portion forming material 32 for forming a vibration film sandwiching portion in the fixed electrode are formed on the conductor plate 10C (or laminated conductor plates) with the through holes 14 formed therein. Then, the squeegee 31 is moved to apply the vibration film sandwiching portion forming material 32 to the portion of the screen printing plate 30 where the mask member is not applied (FIG. 9D).
Here, the diaphragm holding portion forming material 32 considered to be effective can be configured as a diaphragm holding section permanently and is non-conductive. For example, a liquid solder for a package generally used in a circuit board Masking ink used as a resist or a resist for sandblasting. In particular, a solder resist for a flexible printed circuit board is relatively soft (having a pencil hardness of about HB to 3H), and thus is effective for firmly holding the vibrating electrode film.

When the screen printing plate 30 is removed after the application of the vibration film sandwiching portion forming material 32 to the portion of the screen printing plate 30 where the mask member is not applied, a non-conductive layer (on the vibration film sandwiching portion on the conductive plate 10C). = Vibration film clamping portion forming material 32) remains and is dried to obtain a desired fixed electrode (FIG. 9 (e)).
As described above, when the vibration film sandwiching portion of the fixed electrode is formed of an insulating material by a screen printing method, it is possible to eliminate the steps required after metal electroforming, which has been conventionally required, and further, a development step performed by a photolithography method is completely necessary. Therefore, the manufacturing process is greatly shortened and the manufacturing cost can be greatly reduced.

  As another method for manufacturing an ultrasonic transducer, a resist is formed in advance so that a conductive portion is exposed only in a portion to be coated, and non-conductive ink (non-conductive paint) is ejected with an inkjet head and applied. Alternatively, it is also possible to use a method in which the resist is peeled off after coating or electrodeposition by dipping in an electrodeposited polyimide material and electrodeposition coating.

As described above, the following effects can be obtained by forming the vibration film sandwiching portion of the fixed electrode of the electrostatic ultrasonic transducer with a non-conductive material (insulating material).
(1) The selection range of the film thickness for forming the vibration film is expanded.
The thickness of the insulating layer is increased by the level difference (several μm to several tens of μm) of the vibration film sandwiching portion of the fixed electrode formed of a non-conductive material, and even a thin film of 10 μm or less as a vibration film is a problem. And can be used at high voltage.

For example, when a 3 μm PET film is used for the insulating layer of the vibrating electrode film, the conventional fixed electrode configuration (where the entire fixed electrode is formed of a conductive material) is an upper limit value of a voltage that can be applied with 600 V, but is not electrically conductive. By applying a conductive material, for example, even when the step of the vibration film sandwiching portion is 3 μm, the clearance between the fixed electrode surface and the conductive layer of the vibration film is 6 μm, so a voltage of 1 kV or more can be applied. It becomes.
Further, for example, when a voltage of 3 kV is applied with a step of the vibration film holding portion of the fixed electrode being 20 μm, a conventional fixed electrode configuration requires a 15 μm insulating layer (PET). If a non-conductive material is used to form the part, a 1 μm PET film (clearance: 21 μm) is sufficient.
(2) It is possible to avoid a dielectric breakdown between the fixed electrode and the conductive layer of the vibrating membrane due to the breakage of the vibrating membrane.
That is, when the diaphragm holding portion 20 of the fixed electrodes 10A and 10B is made of a non-conductive material, the step d2 (several μm to several tens of μm) of the diaphragm holding portion 20 is added as an insulating layer in FIG. Therefore, since the minimum gap between the electrode layer 121 of the vibrating membrane 12 and the fixed electrode portion (conductive portion) 10 of the fixed electrode is (d1 + d2), even if the edge portion penetrates deeply into the insulating layer 120 of the vibrating membrane 12, insulation is achieved. Breaking strength is sufficiently ensured, there is no occurrence of problems as in the prior art, and even a thin vibrating electrode film can be handled without problems.

In addition, even when a part of the fixed electrode 10A or 10B is completely in contact with the electrode layer 121 of the vibration film 12, or completely penetrates the vibration film 12 and is in contact with the opposite fixed electrode, the conductive portions are in contact with each other. There is nothing, and a decrease in insulation strength and a short circuit due to structural distortion of the fixed electrode can be completely prevented.
(3) The energy efficiency can be improved by reducing the capacitance.

Compared to the case where the fixed electrode is entirely made of a conductive material as in the past, when the diaphragm holding part is made of a non-conductive material, the conductive part (fixed) of the fixed electrode is not changed without changing the electrostatic force acting on the diaphragm. Only the capacitance between the electrode part 10) and the electrode part 10) can be reduced.
For example, in the structure of the transducer of the present invention (FIG. 17), the insulating layer 120 of the vibration film 12 is PET (relative dielectric constant 3.2), the thickness is t1, and the vibration film sandwiching portion 20 is polyimide (relative dielectric constant). 3.5), the thickness (= step difference of the diaphragm sandwiching section 20) is t2, the outer diameter of the diaphragm sandwiching section 20 is φD1, and the inner diameter is half the outer diameter. Capacitance ratios are shown in FIGS.
As is clear from the figure, as the thickness t1 of the insulating layer 120 of the vibration film 12 becomes thinner, the effect of reducing the electrostatic capacitance by forming the vibration film holding part 20 with an insulating material becomes larger. The greater the thickness t2, the greater the capacitance reduction effect.
From the above, since only the input power can be reduced without changing the electrostatic force, an ultrasonic transducer with improved energy efficiency can be realized.

[Description of Configuration Example of Superdirective Acoustic System or Display Device According to the Present Invention]
Next, when the desired ultrasonic pressure output by the electrostatic ultrasonic transducer of the present invention, that is, the electrostatic ultrasonic transducer is P (dB) and the drive frequency is f (Hz), the vibrating membrane is When the one-side amplitude value of the membrane vibration in the diaphragm when driven is a (m), the one-side amplitude value a of the membrane vibration is expressed by the following equation: a = (1 / πf) √ {(I _O · 10 ^{P / 10} ) / 2ρ _O c}, where Io: 0.96 × 10 ⁻¹² (W / m ² ) in reference sound intensity, ρo: 1.2 (kg / m ³ ) in air density, c: The height of the step portion, which is a diaphragm sandwiching portion provided on the outer periphery of the through hole on the diaphragm side of each of the pair of fixed electrodes, is obtained by the speed of sound in the air of about 340 (m / S). A value exceeding the value a and in the vicinity of the one-side amplitude value a A super-directional acoustic system using an ultrasonic speaker constituted by using a Push-Pull type electrostatic ultrasonic transducer set in a range that does not come into contact with the ultrasonic wave will be described.

  Hereinafter, a projector will be described as an example of a superdirective acoustic system or a display device according to the present invention. FIG. 11 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, and reference numeral 326 denotes an exhaust port for the air cooling fan.

Further, the projector 301 uses the Push-Pull electrostatic ultrasonic transducer according to the present invention as an ultrasonic transducer constituting the ultrasonic speaker, and a wide frequency band acoustic signal (sound wave in the ultrasonic frequency band). Can oscillate at high sound pressure.
For this reason, by conventionally changing the frequency of the carrier wave to control the spatial reproduction range of the reproduction signal in the audible frequency band, an acoustic effect that can be obtained in a stereo surround system or 5.1ch surround system is conventionally required. Thus, it is possible to realize a projector that can be realized without requiring a large-scale sound system and is easy to carry.

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

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

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

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

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

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

The high-pass filters 317A and 317B have characteristics that allow only the frequency components in the middle and high frequencies in the R-channel and L-channel audio signals to pass, and the low-pass filters are low-frequency filters in the R-channel and L-channel audio signals. It has the characteristic of passing only the frequency component of the sound range.
Accordingly, among the R channel and L channel audio signals, the mid and high range audio signals are reproduced by the ultrasonic transducers 324A and 324B, respectively, and among the R channel and L channel audio signals, the low range audio signals are low frequencies. It is reproduced by the reproduction speaker 323.

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

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

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

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

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

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

  On the other hand, the audio / video signal reproduction unit 314 outputs the R channel audio signal of the reproduced audio signal to the modulator 318A via the high pass filter 317A, and the L channel audio signal to the modulator 318B via the high pass filter 317B. In addition, the R channel audio signal and the L channel audio signal are output to the adder 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 combined by an adder 321, and a low frequency audio signal of the R channel audio signal and the L channel audio signal is supplied to a power amplifier 322 C by a low pass filter 319. Entered.

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. 11 by the projection optical system 333.
On the other hand, the modulator 318A AM-modulates the carrier wave output from the carrier wave oscillation source 316 with the mid-high range audio signal in the R channel audio signal output from the high-pass filter 317A, and outputs it to the power amplifier 322A. .
Further, the modulator 318B AM-modulates the carrier wave output from the carrier wave oscillation source 316 with the mid-high range audio signal in the L channel audio signal output from the high pass filter 317B, and outputs the result to the power amplifier 322B. .

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

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

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

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

  FIG. 15 shows a reproduction signal reproduction state by an ultrasonic speaker including the ultrasonic transducers 324A and 324B in the projector 301. In the projector 301, when the ultrasonic transducer is driven by the modulation signal obtained by modulating the carrier wave with the audio signal, if the carrier frequency set by the reproduction range setting unit 312 is low, the sound wave emitting surface of the ultrasonic transducer 324 To the direction of the radiation axis (the distance until the reproduction signal is separated from the carrier wave in the normal direction of the sound wave radiation surface, that is, the distance to the reproduction point becomes long.

  Therefore, the reproduced beam of the reproduced signal 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. 14, the audible range B is indicated by a solid arrow, and a playback signal (reproduced sound) can be heard only in a relatively close and wide range from the projection plane 302.

  As described above, the projector according to the present invention uses the ultrasonic speaker using the Push-Pull type electrostatic ultrasonic transducer according to the present invention, so that the acoustic signal has sufficient sound pressure and wideband characteristics. Thus, it 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.

[Description of Configuration Example of Electrostatic Ultrasonic Transducer Design Device According to the Present Invention]
Next, the design apparatus for the electrostatic ultrasonic transducer according to the present invention described above will be described. FIG. 18 shows the configuration of an electrostatic ultrasonic transducer designing apparatus according to an embodiment of the present invention. In the figure, an electrostatic ultrasonic transducer designing apparatus according to an embodiment of the present invention includes an input device 401, a processing device 402, and a storage device 403 in which an electrostatic ultrasonic transducer design program is stored. , A display device 404 and an output device 405. The input device 401, the processing device 402, the storage device 403, the display device 404, and the output device 405 are connected to each other via the bus 400.

The input device 401 has input means such as a keyboard and a mouse, and is used to input values of various parameters necessary for designing an electrostatic ultrasonic transducer.
The storage device 403 stores an electrostatic ultrasonic transducer design program. The design program includes a first electrode having a plurality of through-holes, a second electrode having a plurality of through-holes paired with the first electrode, and the pair of electrodes. , A vibration film having a conductive layer, to which a DC bias voltage is applied to the conductive layer, and a holding member that holds the pair of fixed electrodes and the vibration film, and an alternating current is provided between the pair of electrodes. A program of an electrostatic ultrasonic transducer to which a signal is applied, where the desired sound pressure to be output is P (dB) and the driving frequency is f (Hz). When the one-side amplitude value of the membrane vibration in the vibrating membrane is a (m), the one-side amplitude value a of the membrane vibration is expressed by the following equation: a = (1 / πf) √ {(I _O · 10 ^{P / 10} ) / 2ρ _O c}, where, Io: baseline acoustic Intensity at 0.96 × ^{10 -12} (W / ^{2), ρo:} 1.2 at a density of air ^{(kg / m 3), c} : a first step of calculating, from about 340 at the speed of sound in air (m / S),, of each of said pair of electrodes There is a step portion as a vibration film sandwiching portion on the outer periphery of the through hole on the vibration membrane side, and the height of the step portion in the vibration film side direction exceeds the one-side amplitude value a and in the vicinity of the one-side amplitude value a And causing the computer to execute the second step of setting the value of. The contents of this design program are shown in FIG.

The processing device 402 reads out the design program for the electrostatic ultrasonic transducer stored in the storage device 403 and executes the design program. The processing device 402 comes to the calculation means and setting means of the present invention.
The display device 404 displays various data and the contents of the design process.
The output device is, for example, a printer, and prints out various data and the contents of the design processing process based on an output instruction.

The operation of the electrostatic ultrasonic transducer designing apparatus according to the embodiment of the present invention having the above configuration will be described with reference to the flowchart shown in FIG. In FIG. 19, after the design program is started, values of various parameters necessary for designing the electrostatic ultrasonic transducer shown in FIG. 1 are input by the input device 401 (step 501). Next, the processing device 402 uses the vibration film when the vibration film is driven when the desired sound pressure output from the electrostatic ultrasonic transducer is P (dB) and the drive frequency is f (Hz). A (m), the one-side amplitude value a of the membrane vibration is expressed by the following equation: a = (1 / πf) √ {(I _O · 10 ^{P / 10} ) / 2ρ _O c}, Here, Io: 0.96 × 10 ⁻¹² (W / m ² ) in the standard sound intensity, ρo: 1.2 (kg / m ³ ) in the air density, c: about 340 (in the speed of sound in the air) m / S). (step 502).
Further, the processing apparatus 402 has a step portion as a vibration film sandwiching portion on the outer periphery of the through hole on each vibration membrane side of the pair of electrodes, and the height of the step portion in the vibration film side direction is set to the one side A value exceeding the amplitude value a and in the vicinity of the one-side amplitude value a is set (step 503). The design data obtained by the design process in this way is output from the processing device 402 to the display device 404 and the output device 405, displayed on the display screen of the display device 404, and printed from the printer as the output device 405. Out.

  Although the embodiments of the present invention have been described above, the electrostatic ultrasonic transducer of the present invention, the audio signal reproduction method using the electrostatic ultrasonic transducer, the method of manufacturing the electrostatic ultrasonic transducer, the ultrasonic speaker, the ultrasonic The directional acoustic system, display device, electrostatic ultrasonic transducer design method, electrostatic ultrasonic transducer design device, and electrostatic ultrasonic transducer design program are not limited to the above-described illustrated examples. Of course, various changes can be made without departing from the scope of the present invention.

  The ultrasonic transducer according to the embodiment of the present invention can be used for various sensors, for example, a distance measuring sensor, and as described above, a sound source for a directional speaker and an ideal impulse signal generation source. Etc. are available. It is also useful for superdirective acoustic systems and display devices such as projectors.

  DESCRIPTION OF SYMBOLS 1 ... Push-pull type electrostatic ultrasonic transducer, 10 ... Fixed electrode part, 10A, 10B ... Fixed electrode, 10C ... Conductor board, 11 ... Mask member, 12 ... Vibration film, 12A ... Front surface part, 12B ... Back surface Part 14, through hole (stepped through hole) 16, DC bias power source 18, signal source 20, vibration film clamping part 21, vibration film clamping part forming mask member 22, 23 photosensitive resist, 24 ... residual resist, 30 ... screen printing plate, 31 ... squeegee, 32 ... vibrating film clamping part forming material, 40 ... ultrasonic speaker, 41 ... audible frequency wave signal oscillation source, 42 ... carrier wave signal source, 43 ... modulator 44 ... Power amplifier 45 ... Electrostatic ultrasonic transducer 120 ... Insulator 121 ... Electrode layer 301 ... Projector 302 ... Screen (projection surface) 303 ... Viewer 3 DESCRIPTION OF SYMBOLS 0 ... Operation input part, 312 ... Reproduction | regeneration range setting part, 313 ... Reproduction | regeneration range control process part, 314 ... Audio / video signal reproduction | regeneration part, 316 ... Carrier wave oscillation source, 317A, 317B ... High-pass filter, 318A, 318B ... Modulator 319, low pass filter, 320, projector main body, 321, adder, 322A, 322B, 322C, power amplifier, 323, low sound reproduction speaker, 324A, 324B, electrostatic ultrasonic transducer, 331, projector lens, 332,. Image generation unit, 333 ... projection optical system, 400 ... bus, 401 ... input device, 402 ... processing device, 403 ... storage device, 404 ... display device, 405 ... output device

Claims (3)

A first electrode in which a through hole is formed; a second electrode in which a through hole that is paired with the through hole of the first electrode is formed; and an AC signal is applied between the first electrode and the first electrode; A vibration film sandwiched between the pair of electrodes and having a conductive layer, a DC bias voltage being applied to the conductive layer, and a holding member for holding the pair of electrodes and the vibration film,
When the desired sound pressure to be output is P (dB) and the drive frequency is f (Hz), the one-side amplitude value of the membrane vibration in the diaphragm when the diaphragm is driven is a (m). The one-side amplitude value a of the membrane vibration is expressed by the following equation:
a = (1 / πf) √ {(I _O · 10 ^{P / 10} ) / 2ρ _O c},
Here, Io: 0.96 × 10 ⁻¹² (W / m ² ) in the standard sound intensity, ρo: 1.2 (kg / m ³ ) in the air density, c: about 340 (in the speed of sound in the air) m / S),
Sought by
Each of the pair of electrodes has a step portion on the outer periphery of the through hole on the vibration film side, and the height of the step portion in the vibration film side direction exceeds the one-side amplitude value a, and the one-side amplitude value a An electrostatic ultrasonic transducer characterized by being set to a nearby value;
A signal source for generating a signal wave in an audible frequency band;
A carrier wave supply means for generating and outputting a carrier wave in an ultrasonic frequency band;
Modulation means for modulating the carrier wave with an audible frequency band signal wave output from the signal source;
The ultrasonic speaker, wherein the electrostatic ultrasonic transducer is driven by a modulation signal output from the modulation means applied between the fixed electrode and the electrode layer of the vibrating membrane. A first electrode in which a through hole is formed; a second electrode in which a through hole that is paired with the through hole of the first electrode is formed; and an AC signal is applied between the first electrode and the first electrode; A vibration film sandwiched between the pair of electrodes and having a conductive layer, a DC bias voltage being applied to the conductive layer, and a holding member for holding the pair of electrodes and the vibration film,
When the desired sound pressure to be output is P (dB) and the drive frequency is f (Hz), the one-side amplitude value of the membrane vibration in the diaphragm when the diaphragm is driven is a (m). The one-side amplitude value a of the membrane vibration is expressed by the following equation:
a = (1 / πf) √ {(I _O · 10 ^{P / 10} ) / 2ρ _O c},
Here, Io: 0.96 × 10 ⁻¹² (W / m ² ) in the standard sound intensity, ρo: 1.2 (kg / m ³ ) in the air density, c: about 340 (in the speed of sound in the air) m / S),
Sought by
Each of the pair of electrodes has a step portion on the outer periphery of the through hole on the vibration film side, and the height of the step portion in the vibration film side direction exceeds the one-side amplitude value a, and the one-side amplitude value a While using an electrostatic ultrasonic transducer characterized by being set to a nearby value,
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 fixed electrode and the electrode layer of the vibrating membrane;
A method of reproducing an audio signal of an electrostatic ultrasonic transducer, comprising: A first electrode in which a through hole is formed; a second electrode in which a through hole that is paired with the through hole of the first electrode is formed; and an AC signal is applied between the first electrode and the first electrode; A vibration film sandwiched between the pair of electrodes and having a conductive layer, a DC bias voltage being applied to the conductive layer, and a holding member for holding the pair of electrodes and the vibration film,
When the desired sound pressure to be output is P (dB) and the drive frequency is f (Hz), the one-side amplitude value of the membrane vibration in the diaphragm when the diaphragm is driven is a (m). The one-side amplitude value a of the membrane vibration is expressed by the following equation:
a = (1 / πf) √ {(I _O · 10 ^{P / 10} ) / 2ρ _O c},
Here, Io: 0.96 × 10 ⁻¹² (W / m ² ) in the standard sound intensity, ρo: 1.2 (kg / m ³ ) in the air density, c: about 340 (in the speed of sound in the air) m / S),
Sought by
Each of the pair of electrodes has a step portion on the outer periphery of the through hole on the vibration film side, and the height of the step portion in the vibration film side direction exceeds the one-side amplitude value a, and the one-side amplitude value a A sound source supplied from an acoustic source is reproduced by an ultrasonic speaker configured using an electrostatic ultrasonic transducer characterized by being set to a nearby value, and a virtual sound source is placed near a sound wave reflecting surface such as a screen. A super-directional acoustic system that forms
An ultrasonic speaker that reproduces a mid-high range signal among audio signals supplied from the acoustic source;
A low-pitched sound reproduction speaker that reproduces a low-frequency sound of the sound signal supplied from the acoustic source;
A superdirective acoustic system characterized by comprising:

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