JP2008048003A - Electrostatic ultrasonic transducer, ultrasonic speaker using the same, drive control method of electrostatic ultrasonic transducer, audio signal reproduction method, superdirective acoustic system, and display device - Google Patents

Abstract

An electrostatic ultrasonic transducer capable of stabilizing, improving or repairing sound pressure characteristics is provided.
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 electrode layer sandwiched between the pair of electrodes A vibrating membrane to which a DC bias voltage is applied to the electrode layer, and a holding member that holds the pair of electrodes and the vibrating membrane, and the pair of electrodes and the electrode layer of the vibrating membrane, An electrostatic ultrasonic transducer to which an AC signal is applied between the control means (20, 20), which continuously changes one or both of the level of the DC bias voltage and the frequency of the AC signal. 22).
[Selection] Figure 2

Description

  The present invention relates to an electrostatic ultrasonic transducer that generates a constant high sound pressure over a wide frequency band, an ultrasonic speaker using the same, a drive control method for an electrostatic ultrasonic transducer, an audio signal reproduction method, and a super-directional signal. The present invention relates to a sex sound system and a display device.

    Most of conventional ultrasonic transducers are resonant types using piezoelectric ceramics.

  Here, the configuration of a conventional ultrasonic transducer is shown in FIG. Most of conventional ultrasonic transducers are resonant types using piezoelectric ceramics as vibration elements. The ultrasonic transducer shown in FIG. 15 performs both conversion from an electric signal to ultrasonic waves and conversion from ultrasonic waves to electric signals (transmission and reception of ultrasonic waves) using a piezoelectric ceramic as a vibration element. The bimorphic ultrasonic transducer shown in FIG. 15 is composed of two piezoelectric ceramics 61 and 62, a cone 63, a case 64, leads 65 and 66, and a screen 67.

  The piezoelectric ceramics 61 and 62 are bonded to each other, and a lead 65 and a lead 66 are connected to a surface opposite to the bonded surface, respectively.

  Since the resonance type ultrasonic transducer uses the resonance phenomenon of the piezoelectric ceramic, the transmission and reception characteristics of the ultrasonic wave are good in a relatively narrow frequency band around the resonance frequency.

Unlike the resonant ultrasonic transducer shown in FIG. 15 described above, an electrostatic ultrasonic transducer is conventionally known as a broadband oscillation ultrasonic transducer capable of generating a high sound pressure over a high frequency band. This electrostatic ultrasonic transducer is called a pull type because it works only in the direction in which the vibrating membrane is attracted to the fixed electrode side.
FIG. 16 shows a specific configuration of a broadband oscillation type ultrasonic transducer (Pull type).

  The electrostatic ultrasonic transducer shown in FIG. 16 uses a dielectric 131 (insulator) such as PET (polyethylene terephthalate resin) having a thickness of about 3 to 10 μm as a vibrating body. An upper electrode 132 formed as a metal foil such as aluminum is integrally formed on the upper surface of the dielectric 131 by a process such as vapor deposition, and a lower electrode 133 formed of brass is formed on the lower surface of the dielectric 131. It is provided so that it may contact a part. The lower electrode 133 is connected to a lead 152 and is fixed to a base plate 135 made of bakelite or the like.

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

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

  On the surface of the lower electrode 133 on the dielectric 131 side, a plurality of minute grooves of about several tens to several hundreds μm having a non-uniform shape are formed. Since this minute groove becomes a gap between the lower electrode 133 and the dielectric 131, the electrostatic capacity distribution between the upper electrode 132 and the lower electrode 133 changes minutely.

  These random minute grooves are formed by manually roughing the surface of the lower electrode 133 with a file. In the electrostatic ultrasonic transducer, the frequency characteristics of the ultrasonic transducer shown in FIG. 16 are shown by a curve Q1 in FIG. 17 by forming an infinite number of capacitors having different gap sizes and depths. It is broadband.

  In the ultrasonic transducer having the above configuration, a rectangular wave signal (50 to 150 Vp-p) is applied between the upper electrode 132 and the lower electrode 133 in a state where a DC bias voltage is applied to the upper electrode 132. Yes. Incidentally, as shown by a curve Q2 in FIG. 17, the frequency characteristic of the resonance type ultrasonic transducer has a center frequency (resonance frequency of the piezoelectric ceramic) of, for example, 40 kHz, and ± 5 kHz with respect to the center frequency that is the maximum sound pressure. -30 dB with respect to the maximum sound pressure at a frequency of.

On the other hand, the frequency characteristic of the broadband oscillation type ultrasonic transducer having the above configuration is flat from 40 kHz to near 100 kHz, and is about ± 6 dB compared to the maximum sound pressure at 100 kHz (see Patent Documents 1 and 2). .
JP 2000-50387 A JP 2000-50392 A

  As described above, unlike the resonant ultrasonic transducer shown in FIG. 15, the electrostatic ultrasonic transducer shown in FIG. 16 can generate a relatively high sound pressure over a wide frequency band. It is known as a broadband ultrasonic transducer (Pull type).

  However, as shown in FIG. 17, the maximum value of the sound pressure is 120 dB or less for the electrostatic ultrasonic transducer as compared with the resonance ultrasonic transducer of 130 dB or more. Sound pressure was slightly insufficient for use.

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

  In other words, since sound waves are coarse and dense waves that propagate using air as a medium, the dense and sparse parts of air appear prominently in the process of propagation of modulated ultrasonic waves. Since the speed of sound is slow in this part, the modulation wave itself is distorted. As a result, the waveform is separated into a carrier wave (ultrasonic wave) and an audible wave (original audio signal). This is the principle that only listening can be heard, and it is generally called the parametric array effect.

  In order for the above parametric effect to appear sufficiently, an ultrasonic sound pressure of 120 dB or more is required. However, it is difficult to achieve this value with an electrostatic ultrasonic transducer, and ceramic piezoelectric elements such as PZT, PVDF, etc. The polymer piezoelectric element has been used as an ultrasonic transmitter.

  However, since the piezoelectric element has a sharp resonance point regardless of the material, and is practically used as an ultrasonic speaker by being driven at the resonance frequency, the frequency region where a high sound pressure can be secured is extremely narrow. That is, it can be said that it is a narrow band.

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

  Actually, in an ultrasonic speaker using a conventional resonance type ultrasonic transducer, (1) a narrow band and poor reproduction sound quality, (2) if the AM modulation degree is increased too much, the demodulated sound is distorted, so about 0.5 at the maximum. (3) When the input voltage is increased (when the volume is increased), the vibration of the piezoelectric element becomes unstable and the sound is broken. When the voltage is further increased, the piezoelectric element itself is liable to be destroyed, and (4) it is difficult to make an array, enlargement, and miniaturization.

  On the other hand, the ultrasonic speaker using the electrostatic ultrasonic transducer (Pull type) shown in FIG. 16 can substantially solve the above-mentioned problems of the conventional technology, but can cover a wide band, but has sufficient demodulated sound. However, there was a problem that the absolute sound pressure was insufficient for the sound volume to be high.

  In the pull-type electrostatic ultrasonic transducer, the electrostatic force works only in the direction in which the electrostatic force is attracted only to the fixed electrode side, and the symmetry of vibration of the vibrating membrane (corresponding to the upper electrode 132 in FIG. 17) is not maintained. Therefore, when used for an ultrasonic speaker, there has been a problem that the vibration of the vibrating membrane directly generates an audible sound.

  On the other hand, we have already proposed an electrostatic ultrasonic transducer capable of generating an acoustic signal having a sound pressure level high enough to obtain a parametric array effect over a wide frequency band (Japanese Patent Laid-Open No. 2005-2005). -354472). In this electrostatic ultrasonic transducer, a vibrating membrane having a conductive layer is sandwiched between a pair of fixed electrodes having through holes formed at opposing positions, and a pair of fixed electrodes is applied with a DC bias voltage applied to the vibrating membrane. Is configured to apply an AC signal.

  This electrostatic ultrasonic transducer is called a Push-Pull type electrostatic ultrasonic transducer, and an electrostatic attraction force is applied in a direction in which the vibration film sandwiched between a pair of fixed electrodes corresponds to the polarity of an AC signal. And electrostatic repulsion simultaneously in the same direction and at the same time, the vibration of the diaphragm can be made large enough to obtain the parametric array effect, and the symmetry of the vibration is ensured. High sound pressure can be generated over a wide frequency band as compared with the Pull type electrostatic ultrasonic transducer.

In the Push-Pull type electrostatic ultrasonic transducer described above, in the conventional driving method, first, a predetermined time (for example, 5 to 10 seconds) is applied to the vibrating membrane gradually to DC 250 V, and then fixed. to the electrode side, a predetermined time is applied (e.g., 5-10 seconds) gradually AC 250V _P-P, have made driving control in consideration of the electrical load relief of the vibrating membrane.

  However, due to the influence of the type (material, thickness, etc.) of the vibrating membrane and the configuration (structure, material, etc.) of the fixed electrode, it takes time to stabilize the driving state in the conventional driving control, or is not stable. As the driving time became longer, problems such as a decrease in sound pressure characteristics occurred.

  This is presumed to be because the vibration film does not reach the normal vibration state or becomes unstable.

  The present invention has been made in view of such circumstances, and an electrostatic ultrasonic wave capable of stabilizing, improving or repairing sound pressure characteristics by controlling an application method of an AC voltage or a DC voltage. It is an object of the present invention to provide a transducer, an ultrasonic speaker using the same, a drive control method for an electrostatic ultrasonic transducer, an audio signal reproduction method, a superdirective acoustic system, and a display device.

  In order to achieve the above object, a drive control method for an electrostatic ultrasonic transducer according to the present invention includes a first electrode having a through hole and a through hole that is paired with the through hole of the first electrode. A second electrode, a vibration film sandwiched between the pair of electrodes and having an electrode layer, to which a DC bias voltage is applied to the electrode layer, and a holder for holding the pair of electrodes and the vibration film A drive control method for an electrostatic ultrasonic transducer in which an AC signal is applied between the pair of electrodes and the electrode layer of the vibrating membrane, the level of the DC bias voltage and the AC One or both of the signal frequencies are continuously changed.

  In the drive control method of the electrostatic ultrasonic transducer of the present invention having the above-described configuration, either one or both of the level of the DC bias voltage and the frequency of the AC signal are continuously changed.

  Thus, the sound pressure characteristics can be stabilized, improved or repaired by forcibly applying vibration to the vibration film to stabilize or improve the vibration state of the vibration film.

  Further, the drive control method for the electrostatic ultrasonic transducer according to the present invention reduces the frequency of the AC signal when the DC bias voltage is set to a predetermined level and applied to the electrode layer of the vibrating membrane. A predetermined frequency is set after continuously changing from a high frequency to a high frequency.

  In the drive control method of the electrostatic ultrasonic transducer of the present invention having the above-described configuration, the frequency of the AC signal is set while the DC bias voltage is set to a predetermined level and applied to the electrode layer of the vibrating membrane. Is continuously changed from a low frequency to a high frequency, and then set to a predetermined frequency.

  Thus, the sound pressure characteristics can be stabilized, improved or repaired by forcibly applying vibration to the vibration film to stabilize or improve the vibration state of the vibration film.

  In addition, the drive control method for the electrostatic ultrasonic transducer according to the present invention may be configured such that the alternating current signal having a predetermined frequency is applied to the pair of fixed electrodes and the electrode layer of the vibrating membrane at a predetermined level. The bias voltage is once changed to increase to a set voltage in a predetermined time, and then the DC bias voltage is decreased to a low voltage and changed again to increase to the set voltage. It is characterized by being set to a value.

  In the drive control method of the electrostatic ultrasonic transducer of the present invention having the above-described configuration, under the state where the alternating current signal having a predetermined frequency is applied to the pair of fixed electrodes and the electrode layer of the vibrating membrane at a predetermined level, The DC bias voltage is once changed to increase to a set voltage in a predetermined time, and then the DC bias voltage is decreased to a low voltage and again changed to increase to the set voltage. Set to the voltage value of.

  Thus, the sound pressure characteristics can be stabilized, improved or repaired by forcibly applying vibration to the vibration film to stabilize or improve the vibration state of the vibration film.

  In the electrostatic ultrasonic transducer drive control method of the present invention, the frequency of the AC signal and the DC bias voltage are simultaneously and continuously changed within a predetermined time, and then set to predetermined values, respectively. When changing, the frequency of the AC signal is continuously changed from a low frequency to a high frequency, then set to a predetermined frequency, and the DC bias voltage is temporarily increased to the set voltage in a predetermined time. Next, the DC bias voltage is lowered to a low voltage, changed so as to rise again to the set voltage, and then set to a predetermined voltage value.

  In the drive control method for an electrostatic ultrasonic transducer of the present invention having the above-described configuration, the frequency of the AC signal and the DC bias voltage are changed simultaneously and continuously within a predetermined time, and then each predetermined value is obtained. When the frequency of the AC signal is continuously changed from a low frequency to a high frequency, the frequency is set to a predetermined frequency, and the DC bias voltage is once increased to the set voltage at a predetermined time. Next, the DC bias voltage is lowered to a low voltage, changed so as to be raised again to the set voltage, and then set to a predetermined voltage value.

  Thus, the sound pressure characteristics can be stabilized, improved or repaired by forcibly applying vibration to the vibration film to stabilize or improve the vibration state of the vibration film.

  In the drive control method for an electrostatic ultrasonic transducer according to the present invention, the AC signal is a sine wave signal.

  In the drive control method for an electrostatic ultrasonic transducer according to the present invention, the AC signal is a modulated wave signal obtained by modulating an ultrasonic frequency band signal with an audible frequency band signal.

  The drive control method for an electrostatic ultrasonic transducer according to the present invention is characterized in that the drive control of the electrostatic ultrasonic transducer is performed at the start of driving.

  As a result, at the start of driving the electrostatic ultrasonic transducer, the sound pressure characteristic can be stabilized, improved, or repaired by stabilizing or improving the vibration state of the vibration film.

  Also, the drive control method for the electrostatic ultrasonic transducer according to the present invention is such that the drive control of the electrostatic ultrasonic transducer is performed every time the drive time of the electrostatic ultrasonic transducer reaches a predetermined time. Features.

  In this way, the sound pressure characteristics can be further stabilized, improved, or repaired by stabilizing or improving the vibration state of the diaphragm by performing drive control of the electrostatic ultrasonic transducer a plurality of times. Is possible.

  The electrostatic ultrasonic transducer according to the present invention includes 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, A vibration film sandwiched between a pair of electrodes and having an electrode layer, to which a DC bias voltage is applied to the electrode layer; and a holding member that holds the pair of electrodes and the vibration film. An electrostatic ultrasonic transducer in which an AC signal is applied between an electrode and an electrode layer of the vibrating membrane, wherein one or both of the level of the DC bias voltage and the frequency of the AC signal are continuous. It has the control means to change automatically.

  In the electrostatic ultrasonic transducer (Push-Pull electrostatic ultrasonic transducer) of the present invention having the above-described configuration, a pair of electrodes in which through holes are formed, and the electrode layer is sandwiched between the pair of electrodes. An alternating current signal is applied between the electrode layer and the electrode layer of the vibrating membrane to which a direct current bias voltage is applied to the electrode layer, and one of the level of the direct current bias voltage and the frequency of the alternating current signal is controlled by the control means , Or both are changed continuously.

  Thus, the sound pressure characteristics can be stabilized, improved or repaired by forcibly applying vibration to the vibration film to stabilize or improve the vibration state of the vibration film.

  In the electrostatic ultrasonic transducer according to the present invention, the control means sets the DC bias voltage to a predetermined level and lowers the frequency of the AC signal under the condition that the DC bias voltage is applied to the electrode layer of the vibrating membrane. A predetermined frequency is set after continuously changing from a high frequency to a high frequency.

  In the electrostatic ultrasonic transducer (Push-Pull electrostatic ultrasonic transducer) of the present invention having the above-described configuration, the DC bias voltage is set to a predetermined level by the control means, and the electrode of the vibrating membrane Under the state of being applied to the layer, the frequency of the AC signal is continuously changed from a low frequency to a high frequency, and then set to a predetermined frequency.

  Thus, the sound pressure characteristics can be stabilized, improved or repaired by forcibly applying vibration to the vibration film to stabilize or improve the vibration state of the vibration film.

  The electrostatic ultrasonic transducer according to the present invention may be configured such that the control unit applies the AC signal having a predetermined frequency to the pair of fixed electrodes and the electrode layer of the vibrating membrane at a predetermined level. The DC bias voltage is once changed to increase to a set voltage in a predetermined time, and then the DC bias voltage is decreased to a low voltage and changed again to increase to the set voltage. It is set to a voltage value.

  In the electrostatic ultrasonic transducer (Push-Pull electrostatic ultrasonic transducer) of the present invention having the above-described configuration, the control means sends the AC signal having a predetermined frequency to the pair of fixed electrodes at a predetermined level. Under a state where the DC bias voltage is applied to the electrode layer of the vibrating membrane, the DC bias voltage is once changed to increase to a set voltage in a predetermined time, and then the DC bias voltage is decreased to a low voltage, and again, the After changing the voltage so as to increase to the set voltage, the voltage is set to a predetermined voltage value.

  Thus, the sound pressure characteristics can be stabilized, improved or repaired by forcibly applying vibration to the vibration film to stabilize or improve the vibration state of the vibration film.

  In the electrostatic ultrasonic transducer according to the present invention, the control means may change the frequency of the AC signal and the DC bias voltage simultaneously and continuously within a predetermined time, and then to a predetermined value. When setting, the frequency of the AC signal is continuously changed from a low frequency to a high frequency, and then set to a predetermined frequency, and the DC bias voltage is once increased to a set voltage at a predetermined time. Then, the DC bias voltage is lowered to a low voltage, changed so as to rise again to the set voltage, and then set to a predetermined voltage value.

  In the electrostatic ultrasonic transducer (Push-Pull electrostatic ultrasonic transducer) of the present invention having the above-described configuration, the frequency of the AC signal and the DC bias voltage are simultaneously controlled within a predetermined time by the control means. And when changing to a predetermined value after changing continuously, the frequency of the AC signal is continuously changed from a low frequency to a high frequency, and then set to a predetermined frequency, and the DC bias voltage is set. Is once changed to increase to a set voltage in a predetermined time, and then the DC bias voltage is decreased to a low voltage, and again changed to increase to the set voltage, and then to a predetermined voltage value. Set.

  Thus, the sound pressure characteristics can be stabilized, improved or repaired by forcibly applying vibration to the vibration film to stabilize or improve the vibration state of the vibration film.

  In the electrostatic ultrasonic transducer according to the present invention, the AC signal is a sine wave signal.

  In the electrostatic ultrasonic transducer according to the present invention, the AC signal is a modulated wave signal obtained by modulating an ultrasonic frequency band signal with an audible frequency band signal.

  The electrostatic ultrasonic transducer according to the present invention is characterized in that the control means performs drive control of the electrostatic ultrasonic transducer at the start of driving.

  As a result, at the start of driving the electrostatic ultrasonic transducer, the sound pressure characteristic can be stabilized, improved, or repaired by stabilizing or improving the vibration state of the vibration film.

  In the electrostatic ultrasonic transducer according to the present invention, the control means performs drive control of the electrostatic ultrasonic transducer every time the drive time of the electrostatic ultrasonic transducer reaches a predetermined time. It is characterized by.

  In this way, the sound pressure characteristics can be further stabilized, improved, or repaired by stabilizing or improving the vibration state of the diaphragm by performing drive control of the electrostatic ultrasonic transducer a plurality of times. Is possible.

  The ultrasonic speaker according to the present invention includes a first electrode having a through hole, a second electrode having a through hole paired with the through hole of the first electrode, and the pair of electrodes. A vibration film that is sandwiched between the electrode layers, a DC bias voltage is applied to the electrode layer, and a holding member that holds the pair of electrodes and the vibration film, and the pair of electrodes and the An electrostatic ultrasonic transducer in which an AC signal is applied between an electrode layer of a vibrating membrane, and continuously changes one or both of the level of the DC bias voltage and the frequency of the AC signal An electrostatic ultrasonic transducer having a control means, a signal source for generating an audible frequency band signal wave, a carrier wave supply means for generating and outputting a carrier wave in an ultrasonic frequency band, and the carrier wave Coming out of the signal source The electrostatic ultrasonic transducer is output from the modulation means applied between the electrode and the electrode layer of the vibrating membrane. It is driven by a modulation signal.

  Thereby, it is possible to realize an ultrasonic speaker with improved sound pressure characteristics.

  Also, in the audio signal reproduction method using the electrostatic ultrasonic transducer according to the present invention, the first electrode in which the through hole is formed and the second electrode in which the through hole that makes a pair with the through hole of the first electrode is formed. An electrode layer, a vibration film sandwiched between the pair of electrodes and having an electrode layer to which a DC bias voltage is applied, and a holding member for holding the pair of electrodes and the vibration film. An electrostatic ultrasonic transducer in which an AC signal is applied between the pair of electrodes and the electrode layer of the vibrating membrane, wherein either one of the level of the DC bias voltage and the frequency of the AC signal Or an electrostatic ultrasonic transducer having a control means for continuously changing both, a procedure for generating a signal wave in an audible frequency band by a signal source, and an ultrasonic frequency band by a carrier wave supply means A procedure for generating and outputting a carrier wave, a procedure for generating a modulation signal obtained by modulating the carrier wave with a signal wave in the audible frequency band by a modulation means, and the electrode between the electrode and the electrode layer of the diaphragm And a step of driving the electrostatic ultrasonic transducer by applying a modulation signal.

  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 electrode and the electrode layer of the vibration film, and the electrostatic ultrasonic transducer is driven.

   As a result, the electrostatic ultrasonic transducer having the above-described configuration can reduce the influence of distortion of the membrane vibration, increase the membrane vibration, and at a sufficiently high sound pressure level and distortion to obtain a parametric array effect over a wide frequency band. It is possible to output an audio signal and reduce an audio signal.

  In addition, the super-directional acoustic system of the present invention includes a first electrode having a through hole, a second electrode having a through hole that is paired with the through hole of the first electrode, and the pair. A vibration film sandwiched between the electrodes and having an electrode layer to which a DC bias voltage is applied, and a holding member for holding the pair of electrodes and the vibration film, and the pair of electrodes A capacitive ultrasonic transducer in which an AC signal is applied between the electrode layer of the vibrating membrane and the level of the DC bias voltage and the frequency of the AC signal, or both of them continuously A sound source supplied from an acoustic source is reproduced by an ultrasonic speaker configured using an electrostatic ultrasonic transducer having a control means for changing to a supersonic wave source, and a virtual sound source is formed in the vicinity of a sound wave reflecting surface such as a screen. Oriented An acoustic system that reproduces a mid-high range audio signal among audio signals supplied from the acoustic source, and reproduces a low-range audio signal among audio signals supplied from the acoustic source And a low-pitched sound reproducing speaker.

  In the superdirective acoustic system having the above-described configuration, the first electrode having a through hole, the second electrode having a through hole paired with the through hole of the first electrode, and the pair of electrodes A vibration film that is sandwiched between the electrode layers, a DC bias voltage is applied to the electrode layer, and a holding member that holds the pair of electrodes and the vibration film, and the pair of electrodes and the An electrostatic ultrasonic transducer in which an AC signal is applied between an electrode layer of a vibrating membrane, and continuously changes one or both of the level of the DC bias voltage and the frequency of the AC signal An ultrasonic speaker composed of an electrostatic ultrasonic transducer having a control means 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 reflect sound in the mid- and high-sound range with sufficient sound pressure and wideband characteristics with reduced sound pressure characteristics and improved sound pressure characteristics. Playback can be performed so as to be emitted from a virtual sound source formed near the surface. 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.

  Further, the display device of the present invention includes a first electrode having a through hole, a second electrode having a through hole paired with the through hole of the first electrode, and the pair of electrodes. A vibration film sandwiched between and having an electrode layer to which a DC bias voltage is applied; and a holding member that holds the pair of electrodes and the vibration film, the pair of electrodes and the vibration An electrostatic ultrasonic transducer in which an AC signal is applied to an electrode layer of a film, and continuously changes one or both of the level of the DC bias voltage and the frequency of the AC signal. An ultrasonic speaker configured to include an electrostatic ultrasonic transducer having a control means and reproducing a signal sound in an audible frequency band from an audio signal supplied from an acoustic source; and a projection optical system that projects an image on a projection surface; Having And features.

   In the display device having the above-described configuration, the first electrode having a through hole, the second electrode having a through hole paired with the through hole of the first electrode, and the pair of electrodes are sandwiched between the pair of electrodes. And a vibrating membrane to which a DC bias voltage is applied to the electrode layer, and a holding member that holds the pair of electrodes and the vibrating membrane, the pair of electrodes and the vibrating membrane An electrostatic ultrasonic transducer in which an AC signal is applied between the electrode layer and a control means for continuously changing one or both of the level of the DC bias voltage and the frequency of the AC signal An ultrasonic speaker composed of an electrostatic ultrasonic transducer having the above is used. And the audio | voice signal supplied from an acoustic source is reproduced | regenerated by this ultrasonic speaker.

  As a result, the sound signal can be reproduced so as to be emitted from a virtual sound source formed in the vicinity of a sound wave reflection surface such as a screen with sufficient sound pressure and wide band characteristics in a state where the sound pressure characteristics are improved. For this reason, it is possible to easily control the reproduction range of the acoustic signal. In addition, directivity control of sound radiated from the ultrasonic speaker can be performed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[Configuration example of electrostatic ultrasonic transducer according to the present invention]
FIG. 1 shows the configuration of an electrostatic ultrasonic transducer according to an embodiment of the present invention. FIG. 1A shows a configuration of an electrostatic ultrasonic transducer, and FIG. 1B shows a plan view in which a part of the ultrasonic transducer is broken.

  In FIG. 1, an electrostatic ultrasonic transducer 1 according to an embodiment of the present invention is sandwiched between a pair of fixed electrodes 10A and 10B including a conductive member formed of a conductive material functioning as an electrode, and the pair of fixed electrodes. The vibration film 12 having the electrode layer 121, the pair of fixed electrodes 10A and 10B, and a member (not shown) for holding the vibration film are included.

  The vibration film 12 is formed of an insulator (insulating layer) 120 and has an electrode layer 121 formed of a conductive material. The electrode layer 121 is unipolar (positive polarity) by a DC bias power supply 16. DC bias voltage may be applied to the fixed electrode 10 </ b> A and the fixed electrode 10 </ b> B superimposed on the DC bias voltage and output from the signal source 18. The AC signals 18A and 18B whose phases are reversed from each other are applied between the electrode layer 121 and the AC signals 18A and 18B.

  Further, the pair of fixed electrodes 10A and 10B have the same number and a plurality of through holes 14 at positions facing each other with the vibrating membrane 12 therebetween, and a signal source 18 is provided between the conductive members of the pair of fixed electrodes 10A and 10B. AC signals 18A and 18B whose phases are reversed from each other are applied. Reference numeral 16 denotes a DC bias power source.

  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. Note that the configuration of a control unit that controls the signal source 18 and the DC bias power supply 16 and a storage unit that stores a table indicating the control characteristics of the control unit are omitted in FIG.

  In the above-described configuration, the ultrasonic transducer 1 is mutually output from the signal source 18 to the electrode layer 121 of the vibration film 12 by the DC bias power supply 16 to a single polarity (positive polarity in this embodiment) DC bias voltage. The AC signals 18A and 18B whose phases are inverted are applied in a superimposed state.

  On the other hand, AC signals 18A and 18B whose phases are reversed from each other are 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, since the AC signal 18B has a negative cycle and a negative voltage is applied to the opposed fixed electrode 10B, the back surface portion 12B, which is the back surface side of the surface portion 12A of the vibrating membrane 12, An electrostatic attraction force acts, and the back surface portion 12B is pulled downward in FIG.

  Therefore, the film portion not sandwiched between the pair of fixed electrodes 10 </ b> A and 10 </ b> B of the vibration film 12 receives an electrostatic attractive force and an electrostatic repulsive force (electrostatic repulsive force) in the same direction. Similarly, in the negative half cycle of the AC signal output from the signal source 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 that is not sandwiched between the pair of fixed electrodes 10A and 10B of the vibrating membrane 12 receives the electrostatic attractive 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 attractive force and the electrostatic repulsive force in the same direction according to the change in the polarity of the AC signal. An acoustic signal having a sound pressure level sufficient to obtain a parametric array effect can be generated.

  Thus, the ultrasonic transducer 1 according to the embodiment of the present invention is called a push-pull type because the vibrating membrane 12 vibrates by receiving a force from the pair of fixed electrodes 10A and 10B.

  The ultrasonic transducer 1 according to the embodiment of the present invention has a wide band and high sound pressure at the same time as compared with the conventional electrostatic ultrasonic transducer (Pull type) in which only the electrostatic attraction force acts on the vibrating membrane. Have the ability to meet.

  FIG. 17 shows frequency characteristics of the ultrasonic transducer according to the embodiment of the present invention. In the figure, a curve Q3 is a frequency characteristic of the ultrasonic transducer according to the present embodiment. As can be seen from the figure, a higher sound pressure level can be obtained over a wider frequency band than the frequency characteristics of the conventional broadband electrostatic ultrasonic transducer. Specifically, it can be seen that a sound pressure level of 120 dB or higher that provides a parametric effect in a frequency band of 20 kHz to 120 kHz can be obtained.

  In the ultrasonic transducer 1 according to the embodiment of the present invention, the thin vibration film 12 sandwiched between the pair of fixed electrodes 10A and 10B receives both the electrostatic attractive force and the electrostatic repulsive force. In addition, since the symmetry of vibration is ensured, a high sound pressure can be generated over a wide band.

  Next, FIG. 2 shows a configuration of a main part of the electrostatic ultrasonic transducer according to the embodiment of the present invention. As shown in the figure, the electrostatic ultrasonic transducer according to the embodiment of the present invention includes a DC bias voltage supplied from the DC bias power supply 16 to the electrode layer 121 of the vibrating membrane 12 and an AC signal output from the signal source 18. A control unit 20 that controls the frequency of the control unit 20 and a storage unit 22 that stores control data indicating the control characteristics of the control unit 20.

  The storage unit 22 stores table data (FIGS. 3 to 5) indicating control characteristics when the electrostatic ultrasonic transducer is activated, and table data (FIG. 6) indicating control characteristics performed when a predetermined time has elapsed after activation. To FIG. 8) are stored.

  The control unit 20 refers to the table data stored in the storage unit, and determines the DC bias voltage supplied from the DC bias power supply 16 to the electrode layer 121 of the vibrating membrane 12 and the frequency of the AC signal output from the signal source 18. Control. The control unit 20 and the storage unit 22 correspond to the control means of the present invention.

[Driving method of electrostatic ultrasonic transducer according to the present invention]
Next, a driving method of the electrostatic ultrasonic transducer according to the embodiment of the present invention will be described with reference to FIGS. Driving control of the electrostatic ultrasonic transducer according to the embodiment of the present invention is performed based on the control characteristics shown in FIGS. The control characteristics of FIGS. 3 to 8 are stored in the storage unit 22 as table data. The control unit 20 refers to the table data stored in the storage unit 20, and the control characteristics of the electrostatic ultrasonic transducer 1. Drive control is performed.

  FIG. 3 shows the case where the DC ultrasonic bias voltage is applied to the electrode layer 121 of the vibrating membrane 12 when the electrostatic ultrasonic transducer 1 is driven from the stopped state, and is applied to the fixed electrodes 10A and 10B by the signal source 18. It is the figure which showed the table data of the frequency control table which changes the frequency of an alternating current signal continuously with the graph. Here, in the present embodiment, the AC signal output from the signal source 18 is either a sine wave signal or a modulated wave signal.

In this control table, the control for setting the frequency of the AC signal to a predetermined frequency (for example, 60 kHz) for 10 seconds is performed by continuously increasing the frequency of the AC signal from a low frequency (for example, 40 kHz) to a high frequency (for example, 300 kHz). Complete within.
FIG. 4 shows a direct current applied to the electrode layer 121 of the vibrating membrane 12 in a state where an alternating current signal is applied to the fixed electrodes 10A and 10B by the signal source 18 when the electrostatic ultrasonic transducer 1 is driven from a stopped state. It is the figure which showed the table data of the DC bias voltage table which changes a bias voltage continuously with the graph.

  In this control table, the DC voltage is once increased from 0 V to a set voltage (for example, 250 VV) within a predetermined time, and immediately after that, the DC voltage is lowered to a low voltage (for example, 100 V) and again to the set voltage (for example, 250 V). The control to raise continuously is completed within 10 seconds.

  FIG. 5 shows the DC bias voltage applied to the electrode layer 121 of the vibrating membrane 12 by the DC bias power supply 16 and the signal source 18 applied to the fixed electrodes 10A and 10B when the electrostatic ultrasonic transducer 1 is driven from the stopped state. It is the figure which showed the table data of the drive control table which changes the frequency of the alternating current signal to apply continuously with the graph. Here, the AC signal output from the signal source 18 is either a sine wave signal or a modulated wave signal in this embodiment.

  In this control table, the control for setting the frequency of the AC signal to a predetermined frequency (for example, 60 kHz) for 10 seconds is performed by continuously increasing the frequency of the AC signal from a low frequency (for example, 40 kHz) to a high frequency (for example, 300 kHz). Complete within.

  At the same time, the DC bias voltage is raised from 0V to a set voltage (for example, 250V) within a predetermined time, and immediately after that, the DC current bias voltage is lowered to a low voltage (for example, 100V) and again to the set voltage (for example, 250V). The control to raise continuously is completed within 10 seconds.

  The vibration state of the vibrating membrane 12 can be stabilized by any drive control performed by the control unit 20 and the storage unit 22 based on the control characteristics shown in FIGS. The pressure characteristics can be stabilized or improved.

  FIG. 6 is a graph showing table data of a frequency control table that continuously changes only the frequency of the AC signal applied from the signal source 18 to the fixed electrodes 10A and 10B when a certain predetermined driving time is reached. It is. This drive control is performed with a predetermined DC bias voltage applied to the electrode layer 121 of the vibration film 12. Here, the AC signal output from the signal source 18 is either a sine wave signal or a modulated wave signal in this embodiment.

  In this control table, the frequency of the AC voltage is continuously increased from a set frequency (for example, 60 kHz) to a high frequency (for example, 300 kHz), and then continuously decreased to return to the original set frequency (for example, 60 kHz). Is completed within 10 seconds.

   FIG. 7 is a graph showing table data of a DC voltage table that continuously changes only the DC bias voltage applied to the electrode layer 121 of the vibrating membrane 12 when a certain predetermined driving time is reached. This drive control is performed in a state where an AC signal is applied to the fixed electrodes 10A and 10B by the signal source 18 at a predetermined frequency.

  In this control table, the control for dropping the DC bias voltage from the set voltage (for example, 250 V) to the low voltage (for example, 100 V) and continuously increasing the DC bias voltage again to the set voltage (for example, 250 V) is completed within 10 seconds.

  In FIG. 8, when a certain predetermined driving time is reached, the frequency of the DC voltage applied to the electrode layer 121 of the vibrating membrane 12 from the DC bias power supply 16 and the frequency of the AC voltage applied to the fixed electrodes 10A and 10B are continuously obtained. It is a graph of the drive control table to change. Here, the AC signal output from the signal source 18 is either a sine wave signal or a modulated wave signal in this embodiment.

  In this control table, the frequency of the AC voltage is continuously increased from a set frequency (for example, 60 kHz) to a high frequency (for example, 300 kHz), and then continuously decreased to return to the original set frequency (for example, 60 kHz). Is completed within 10 seconds.

  At the same time, the DC bias voltage applied to the electrode layer 121 of the vibrating membrane 12 by the DC bias power supply 16 is reduced from a set voltage (for example, 250 V) to a low voltage (for example, 100 V) and continuously up to the set voltage (for example, 250 V) again. The control to raise and return is completed within 10 seconds.

  The vibration state of the diaphragm 12 can be returned to a stable state by any drive control performed by the control unit 20 and the storage unit 22 based on the control characteristics shown in FIGS. The sound pressure characteristics can be stabilized or restored.

  FIG. 9 shows the sound pressure characteristics when the conventional drive control is performed, and the DC bias voltage applied to the electrode layer 121 of the vibrating membrane 12 in the case of driving the ultrasonic transducer from the stopped state shown in FIG. The sound pressure characteristics when the control is performed according to the drive control table that continuously changes the frequency of the AC signal applied to the fixed electrodes 10A and 10B are shown. Here, the scale of the vertical axis is 10 dB.

  When the drive control of the present invention is carried out, the sound pressure is increased in all frequency bands compared to the prior art, and in particular, the main drive frequency band of the electrostatic ultrasonic transducer according to the embodiment of the present invention is 40 to 40. At 70 kHz, it is increased by about 3 to 5 dB, and it can be seen that this drive control is effective in improving the sound pressure.

  Note that the effect of this drive control can be increased by increasing the number of times, so that the drive control tables shown in FIGS. 5 to 8 are used according to the use conditions of the electrostatic ultrasonic transducer. It is good to repeat a plurality of times, shorten the time required for one control, and repeat a plurality of times within 5 to 10 seconds.

Further, in the case of driving the electrostatic ultrasonic transducer 1 from the stopped state, conventionally, the DC 250V was applied to the vibrating film 12 First, AC 250V _P-P then the fixed electrode 10A, with respect 10B side However, it is also possible to stabilize or improve the vibration state of the vibration film 12 by reversing this order.

That is, first fixed electrode 10A, by applying an AC 250V _P-P with respect 10B side, leave the state gave fine vibration to advance the vibrating film 12, by applying a DC 250V with respect to the vibration film 12 thereafter The problem that the vibration film 12 is held in the state of being attracted to the fixed electrodes 10A and 10B and sufficient vibration cannot be obtained can be avoided.

[Configuration example of ultrasonic speaker according to the present invention]
Next, the configuration of an ultrasonic speaker according to an embodiment of the present invention is shown in FIG. The ultrasonic speaker according to the present embodiment uses the above-described electrostatic ultrasonic transducer (FIGS. 1 and 2) according to the present embodiment as the ultrasonic transducer 55.

  In FIG. 10, an ultrasonic speaker 50 according to the present embodiment generates and outputs an audio frequency wave oscillation source (signal source) 51 that generates a signal wave in the audio frequency band and a carrier wave in the ultrasonic frequency band. A carrier wave oscillation source (carrier wave supply means) 52, a modulator (modulation means) 53, a power amplifier 54, and an ultrasonic transducer (electrostatic ultrasonic transducer) 55 are included.

  The modulator 53 modulates the carrier wave output from the carrier wave oscillation source 52 with the signal wave of the audio frequency band output from the audio frequency wave oscillation source 51, and supplies the modulated wave to the ultrasonic transducer 55 via the power amplifier 54. To do.

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

  In other words, sound waves are coarse and dense waves that propagate using air as a medium, so that in the process of modulated ultrasonic waves, the dense and sparse portions of air appear prominently, and the dense portions have high sound speed and sparseness. Since the sound speed of such a portion is slow, the modulation wave itself is distorted. As a result, the waveform is separated into a carrier wave (ultrasonic frequency band), and a signal wave (signal sound) in an audible frequency band is reproduced.

  As described above, when a high sound pressure broadband property is ensured, it can be used as a speaker for various purposes. Ultrasound is strongly attenuated in the air and attenuates in proportion to the square of its frequency. Therefore, when the carrier frequency (ultrasonic wave) is low, it is possible to provide an ultrasonic speaker in which the sound reaches far as a beam with little attenuation.

  On the contrary, if the carrier frequency is high, the attenuation is severe, so that the parametric array effect does not occur sufficiently and an ultrasonic speaker in which the sound spreads can be provided. These are very effective functions because the same ultrasonic speaker can be used according to the application.

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

  The ultrasonic speaker according to the embodiment of the present invention can generate an acoustic signal having a sufficiently high sound pressure level to obtain a parametric array effect over a wide frequency band.

  In the ultrasonic speaker of the present invention, the DC bias voltage applied to the electrode layer of the vibrating membrane of the electrostatic ultrasonic transducer, and the frequency of the AC signal applied between the pair of electrodes and the electrode layer. Since either one or both of them are continuously changed, an ultrasonic speaker with improved sound pressure characteristics can be realized.

[Description of configuration example of superdirective acoustic system according to the present invention]
Next, the electrostatic ultrasonic transducer of the present invention, that is, a first electrode in which a through hole is formed, and a second electrode in which a through hole that is paired with the through hole of the first electrode is formed A vibration that is sandwiched between the pair of electrodes and has an electrode layer, a DC bias voltage is applied to the electrode layer, and an AC signal is applied between the pair of electrodes and between the electrode layers A holding member for holding the membrane, the pair of electrodes, and the vibrating membrane, and laminating an electrode pattern corresponding to a plurality of driving functions on each of the first and second electrodes, A push-pull type electrostatic having control means for controlling to apply a voltage according to a driving condition defining the driving function between the electrode pattern formed by stacking and the electrode layer of the vibrating membrane. Type ultrasonic transducer, or An electrode having a concavo-convex portion on the surface, an electrode layer provided on the surface of the electrode, a DC bias voltage is applied to the electrode layer, and an AC signal is transmitted between the electrode layer of the vibrating membrane and the electrode. An electrode pattern formed by laminating an electrode pattern according to a drive function on the electrode, the electrode pattern having a vibration film driven by application, and a member holding the electrode and the vibration film; And a pull type electrostatic ultrasonic transducer having a control means for applying a voltage corresponding to a driving condition defining the driving function between the electrode layer of the vibrating membrane and the electrode layer of the vibrating membrane A super-directional acoustic system using an ultrasonic speaker will be described.

Hereinafter, a projector will be described as an example of a superdirective acoustic system according to the present invention. Note that the super-directional acoustic system according to the present invention is not limited to a projector and can be widely applied to display devices that reproduce audio and video.
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 the result to the power amplifier 322A. .

  Further, the modulator 318B AM-modulates the carrier wave output from the carrier wave oscillation source 316 with the mid-high range audio signal in the L channel audio signal output from the high pass filter 317B, and outputs the result to the power amplifier 322B. .

  The 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 or Pull type electrostatic ultrasonic transducer according to the present invention, and the acoustic signal is transmitted with sufficient sound pressure. It has a broadband characteristic and can be reproduced so as to be emitted from a virtual sound source formed in the vicinity of a sound wave reflecting surface such as a screen. For this reason, the reproduction range can be easily controlled. Further, as described above for the electrostatic ultrasonic transducer, the vibration region of the vibration film is divided into a plurality of blocks, and an alternating current is applied between the electrode layer of the vibration film and each block of the vibration electrode pattern. It is possible to control the directivity of the sound emitted from the ultrasonic speaker by controlling the phase of the signal so that a predetermined phase difference is provided between adjacent blocks.

  The embodiment of the present invention has been described above, but the electrostatic ultrasonic transducer and the ultrasonic speaker of the present invention are not limited to the above illustrated examples, and do not depart from the gist of the present invention. Of course, various changes can be made.

  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.

The figure which shows the structure of the electrostatic ultrasonic transducer which concerns on embodiment of this invention. The figure which shows the structure of the principal part of the electrostatic ultrasonic transducer shown in FIG. The figure which showed an example of the table data of the frequency control table which changes continuously the frequency of the alternating current signal applied to a pair of fixed electrode at the time of starting of an electrostatic ultrasonic transducer. The figure which showed in a graph the example of the table data of the DC bias voltage table which changes continuously the DC bias voltage applied to the electrode layer of a diaphragm at the time of starting of an electrostatic ultrasonic transducer. An example of table data of a drive control table that continuously changes the frequency of the DC bias voltage applied to the electrode layer of the vibrating membrane and the frequency of the AC signal applied to the pair of fixed electrodes when the electrostatic ultrasonic transducer is activated. The figure shown with the graph. The figure which showed in a graph the example of the table data of the frequency control table which changes only the frequency of the alternating current signal applied to a pair of fixed electrode continuously at the time of reaching a certain predetermined drive time. The figure which showed in a graph the example of the table data of the DC voltage table which changes only the DC bias voltage applied to the electrode layer of a diaphragm continuously at the time of reaching a predetermined drive time. A graph showing an example of table data of a drive control table that continuously changes the frequency of the DC voltage applied to the electrode layer of the vibrating membrane and the frequency of the AC voltage applied to the pair of fixed electrodes when a predetermined driving time is reached. Figure shown. The figure which compares and compares the sound pressure characteristic when drive control of the conventional electrostatic ultrasonic transducer is implemented, and the sound pressure characteristic when drive control of the electrostatic ultrasonic transducer by this invention is implemented. The figure which shows the structural example of an ultrasonic speaker. 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. 12 is a block diagram showing an electrical configuration of the projector shown in FIG. 11. Explanatory drawing of the reproduction | regeneration state of the reproduction signal by an ultrasonic transducer. The figure which shows the structure of the conventional resonance type ultrasonic transducer. The figure which shows the specific structure of the conventional electrostatic broadband oscillation type ultrasonic transducer. The figure which showed the frequency characteristic of the electrostatic ultrasonic transducer which concerns on embodiment of this invention with the frequency characteristic of the conventional ultrasonic transducer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electrostatic ultrasonic transducer, 10A, 10B ... Fixed electrode, 12 ... Vibration film, 12A ... Front surface part, 12B ... Back surface part, 14 ... Through-hole, 16 ... DC bias power supply, 18 ... Signal source, 20 ... Control Unit 22, storage unit, 50 ultrasonic speaker, 51 audible frequency wave oscillation source, 52 carrier wave signal source, 53 modulator, 54 power amplifier, 55 ultrasonic transducer, 120 insulator, 121. Electrode layer, 301 ... projector, 302 ... screen (projection plane), 303 ... viewer, 310 ... operation input unit, 312 ... playback range setting unit, 313 ... playback range control processing unit, 314 ... audio / video signal playback unit, 316: Carrier wave oscillation source, 317A, 317B ... High pass filter (HPF), 318A, 318B ... Modulator, 319 ... Low pass filter (LPF), 3 DESCRIPTION OF SYMBOLS 0 ... Projector body, 321 ... Adder, 322A, 322B, 322C ... Power amplifier, 323 ... Low-frequency sound reproduction speaker, 324A, 324B ... Electrostatic ultrasonic transducer, 331 ... Projector lens, 332 ... Video generation unit, 333 ... Projection optical system

Claims (20)

A first electrode having a through hole formed therein;
A second electrode having a through hole that is paired with the through hole of the first electrode;
A vibration film sandwiched between the pair of electrodes and having an electrode layer, to which a DC bias voltage is applied to the electrode layer; and a holding member for holding the pair of electrodes and the vibration film; A drive control method for an electrostatic ultrasonic transducer in which an AC signal is applied between the electrode and the electrode layer of the vibrating membrane,
Either of the level of the said DC bias voltage and the frequency of the said AC signal, or both are changed continuously, The drive control method of the electrostatic ultrasonic transducer characterized by the above-mentioned.   Under the state where the DC bias voltage is set to a predetermined level and applied to the electrode layer of the vibrating membrane, the frequency of the AC signal is continuously changed from a low frequency to a high frequency, and then set to a predetermined frequency. The drive control method for an electrostatic ultrasonic transducer according to claim 1.   In a state where the AC signal having a predetermined frequency is applied to the pair of fixed electrodes and the electrode layer of the vibrating membrane at a predetermined level, the DC bias voltage is temporarily changed to a set voltage so as to increase in a predetermined time. The electrostatic bias according to claim 1, wherein the DC bias voltage is lowered to a low voltage, changed so as to rise again to the set voltage, and then set to a predetermined voltage value. Drive control method of a type ultrasonic transducer.   When the frequency of the AC signal and the DC bias voltage are simultaneously and continuously changed within a predetermined time and then set to a predetermined value, the frequency of the AC signal is continuously changed from a low frequency to a high frequency. Is changed to a predetermined frequency, and the DC bias voltage is once changed to increase to a set voltage in a predetermined time, and then the DC bias voltage is decreased to a low voltage, and again, 2. The drive control method for an electrostatic ultrasonic transducer according to claim 1, wherein the voltage is set to a predetermined voltage value after being changed to increase to the set voltage.   5. The electrostatic ultrasonic transducer drive control method according to claim 1, wherein the AC signal is a sine wave signal.   5. The drive control of an electrostatic ultrasonic transducer according to claim 1, wherein the AC signal is a modulated wave signal obtained by modulating an ultrasonic frequency band signal with an audible frequency band signal. Method.   5. The drive control method for an electrostatic ultrasonic transducer according to claim 1, wherein the drive control of the electrostatic ultrasonic transducer is performed at the start of driving.   5. The electrostatic type according to claim 1, wherein the drive control of the electrostatic ultrasonic transducer is performed every time the drive time of the electrostatic ultrasonic transducer reaches a predetermined time. Ultrasonic transducer drive control method. A first electrode having a through hole formed therein;
A second electrode having a through hole that is paired with the through hole of the first electrode;
A vibration film sandwiched between the pair of electrodes and having an electrode layer, to which a DC bias voltage is applied to the electrode layer; and a holding member for holding the pair of electrodes and the vibration film; An electrostatic ultrasonic transducer in which an AC signal is applied between the electrode and the electrode layer of the vibrating membrane,
An electrostatic ultrasonic transducer comprising control means for continuously changing one or both of the level of the DC bias voltage and the frequency of the AC signal.   The control means sets the DC bias voltage to a predetermined level, and continuously changes the frequency of the AC signal from a low frequency to a high frequency while being applied to the electrode layer of the vibrating membrane. The electrostatic ultrasonic transducer according to claim 9, wherein the electrostatic ultrasonic transducer is set to a frequency of   The control means is configured to apply the DC bias voltage once to a set voltage for a predetermined time in a state where the AC signal having a predetermined frequency is applied to the pair of fixed electrodes and the electrode layer of the vibrating membrane at a predetermined level. 10. The voltage is changed so as to increase, and then the DC bias voltage is decreased to a low voltage, changed to increase again to the set voltage, and then set to a predetermined voltage value. The electrostatic ultrasonic transducer according to 1.   The control means changes the frequency of the AC signal and the DC bias voltage simultaneously and continuously within a predetermined time and then sets the frequency of the AC signal to a low frequency. After continuously changing from a high frequency to a high frequency, the frequency is set to a predetermined frequency, and the DC bias voltage is temporarily changed to a set voltage so as to increase in a predetermined time, and then the DC bias voltage is changed to a low voltage. The electrostatic ultrasonic transducer according to claim 9, wherein the electrostatic ultrasonic transducer is set to a predetermined voltage value after being lowered and changed again so as to be raised to the set voltage.   The electrostatic ultrasonic transducer according to claim 9, wherein the AC signal is a sine wave signal.   The electrostatic ultrasonic transducer according to claim 9, wherein the AC signal is a modulated wave signal obtained by modulating a signal in an ultrasonic frequency band with a signal in an audible frequency band.   The electrostatic ultrasonic transducer according to claim 9, wherein the control unit performs drive control of the electrostatic ultrasonic transducer at the start of driving.   The control means performs drive control of the electrostatic ultrasonic transducer every time the drive time of the electrostatic ultrasonic transducer reaches a predetermined time. The electrostatic ultrasonic transducer as described. 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; and an electrode layer sandwiched between the pair of electrodes; A vibration film to which a DC bias voltage is applied to the electrode layer; and a holding member that holds the pair of electrodes and the vibration film; and an alternating current between the pair of electrodes and the electrode layer of the vibration film. An electrostatic ultrasonic transducer to which a signal is applied, comprising: a control means for continuously changing either or both of the level of the DC bias voltage and the frequency of the AC signal A transducer;
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 according to claim 1, wherein the electrostatic ultrasonic transducer is driven by a modulation signal output from the modulation means applied between the 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; and an electrode layer sandwiched between the pair of electrodes; A vibration film to which a DC bias voltage is applied to the electrode layer; and a holding member that holds the pair of electrodes and the vibration film; and an alternating current between the pair of electrodes and the electrode layer of the vibration film. An electrostatic ultrasonic transducer to which a signal is applied, comprising: a control means for continuously changing either or both of the level of the DC bias voltage and the frequency of the AC signal While using a transducer,
Generating a signal wave of an audible frequency band by a signal source;
A procedure for generating and outputting a carrier wave in the ultrasonic frequency band by the carrier wave supply means;
Generating a modulated signal obtained by modulating the carrier wave with a signal wave in the audible frequency band by a modulation means;
A procedure for driving the electrostatic ultrasonic transducer by applying the modulation signal between the electrode and the electrode layer of the vibrating membrane;
A method of reproducing an audio signal using an electrostatic ultrasonic transducer. 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; and an electrode layer sandwiched between the pair of electrodes; A vibration film to which a DC bias voltage is applied to the electrode layer; and a holding member that holds the pair of electrodes and the vibration film; and an alternating current between the pair of electrodes and the electrode layer of the vibration film. An electrostatic ultrasonic transducer to which a signal is applied, comprising: a control means for continuously changing either or both of the level of the DC bias voltage and the frequency of the AC signal A superdirective acoustic system that reproduces an audio signal supplied from an acoustic source by an ultrasonic speaker configured using a transducer and forms a virtual sound source in the vicinity of a sound wave reflecting surface such as a screen,
An ultrasonic speaker that reproduces an audio signal in a middle and high range among audio signals supplied from the acoustic source;
A low-pitched sound reproduction speaker that reproduces a low-frequency sound signal among the sound signals supplied from the acoustic source;
A superdirective acoustic system characterized by 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; and an electrode layer sandwiched between the pair of electrodes; A vibration film to which a DC bias voltage is applied to the electrode layer; and a holding member that holds the pair of electrodes and the vibration film; and an alternating current between the pair of electrodes and the electrode layer of the vibration film. An electrostatic ultrasonic transducer to which a signal is applied, comprising: a control means for continuously changing either or both of the level of the DC bias voltage and the frequency of the AC signal Comprising a transducer,
An ultrasonic speaker that reproduces a signal sound in an audible frequency band from an audio signal supplied from an acoustic source;
A projection optical system that projects an image onto a projection surface;
A display device comprising:

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