JP2005223820A - Ultrasonic transducer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic transducer capable of increasing the magnitude of a vibrating membrane during vibration, and reducing the DC bias voltage and the AC signal voltage. <P>SOLUTION: The ultrasonic transducer comprises an upper electrode 10 composed of a vibrating membrane 2, formed by insulating materials and a conductive film 3 formed on the vibrating membrane, and a lower electrode 12, having a plurality of irregularities formed on a plane facing the vibrating membrane 2. The upper electrode and the lower electrode are adhered to each other. The ultrasonic transducer generates ultrasonic waves, by applying an AC signal between the upper electrode and the lower electrode. A resonance pipe unit 20 is prepared with a plurality of air holes 201, forming a both end aperture pipe resonating at the desired frequency in a plate 200. The resonance pipe unit 20 is fixed on the surface of the upper electrode 10. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electrostatic ultrasonic transducer that generates a constant high sound pressure over a wide frequency band, and more particularly, an ultrasonic wave that can generate strong ultrasonic waves by applying the resonance principle of sound waves. It relates to a transducer.

Most of conventional ultrasonic transducers are resonant types using piezoelectric ceramics.
Here, FIG. 10 shows a configuration of a conventional ultrasonic transducer. Most of conventional ultrasonic transducers are resonant types using piezoelectric ceramics as vibration elements. The ultrasonic transducer shown in FIG. 10 performs both the conversion from an electric signal to an ultrasonic wave and the conversion from an ultrasonic wave to an electric signal (transmission and reception of an ultrasonic wave) using a piezoelectric ceramic as a vibration element. The bimorph ultrasonic transducer shown in FIG. 10 includes two piezoelectric ceramics 61 and 62, a cone 63, a case 64, leads 65 and 66, and a screen 67.

The piezoelectric ceramics 61 and 62 are bonded to each other, and a lead 65 and a lead 66 are connected to a surface opposite to the bonded surface, respectively.
Since the resonance type ultrasonic transducer uses the resonance phenomenon of the piezoelectric ceramic, the transmission and reception characteristics of the ultrasonic wave are good in a relatively narrow frequency band around the resonance frequency.

  Unlike the resonant ultrasonic transducer shown in FIG. 10 described above, an electrostatic ultrasonic transducer is conventionally known as a broadband oscillation ultrasonic transducer capable of generating a high sound pressure over a high frequency band. FIG. 11 shows a specific configuration of the broadband oscillation type ultrasonic transducer. The electrostatic ultrasonic transducer shown in FIG. 11 uses a dielectric 131 (insulator) such as PET (polyethylene terephthalate resin) having a thickness of about 3 to 10 μm as a vibrating body. An upper electrode 132 formed as a metal foil such as aluminum is integrally formed on the upper surface of the dielectric 131 by a process such as vapor deposition, and a lower electrode 133 formed of brass is formed on the lower surface of the dielectric 131. It is provided so that it may contact a part. The lower electrode 133 is connected to a lead 152 and is fixed to a base plate 135 made of bakelite or the like.

The upper electrode 132 is connected to a lead 153, and the lead 153 is connected to the DC bias power supply 150. The DC bias power supply 150 constantly applies a DC bias voltage for attracting the upper electrode of about 50 to 150 V to the upper electrode 32 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. 11 are represented by a curve Q1 in FIG. 12 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 32 and the lower electrode 33 in a state where a DC bias voltage is applied to the upper electrode 32. Yes. Incidentally, as shown by a curve Q2 in FIG. 12, the frequency characteristic of the resonance type ultrasonic transducer has a center frequency (resonance frequency of the piezoelectric ceramic) of, for example, 40 kHz, and ± 5 kHz with respect to the center frequency that is the maximum sound pressure. -30 dB with respect to the maximum sound pressure at a frequency of. On the other hand, the frequency characteristics of the broadband oscillation type ultrasonic transducer having the above configuration are flat from 40 kHz to near 100 kHz, and are about ± 6 dB compared to the maximum sound pressure at 100 kHz (see Patent Documents 1 and 2). .

  Here, in the broadband oscillation type ultrasonic transducer, it is necessary to increase the amplitude of the vibration film of the upper electrode in order to obtain a high sound pressure level for the following reason. That is, the sound pressure level (SPL) of the ultrasonic wave radiated from the ultrasonic transducer is as follows: the device area is S, the vibration speed of the vibrating membrane is v, and the applied voltage applied between the upper electrode and the lower electrode is V. Then, there is a relationship of SPL∝S · v · V. In order to increase the sound pressure level, any one or all of the device area S, the vibration velocity v of the diaphragm, and the applied voltage V may be increased. However, considering the miniaturization of the ultrasonic transducer, the device area S, I do not want to increase the applied voltage V.

Therefore, in order to satisfy the requirement to increase the sound pressure level, it is necessary to increase the vibration velocity v of the diaphragm. Here, the vibration speed v of the diaphragm depends on the vibration frequency and amplitude, but in order to increase the vibration speed of the diaphragm, and thus the sound pressure level, from the necessity of obtaining a high sound pressure level over a wide frequency band, It can be seen that it is necessary to increase the amplitude of the vibrating membrane. However, it is difficult to increase the amplitude of the diaphragm, and a method for increasing the sound pressure generated without changing the amplitude is desired.
JP 2000-50387 A JP 2000-50392 A

However, in the conventional broadband oscillation type ultrasonic transducer, since the upper electrode thin film and the lower electrode bulk material are adsorbed by using a DC bias voltage of several tens to several hundreds V, There is a problem that sufficient amplitude of the vibrating membrane cannot be obtained. Furthermore, the vibration film in the upper electrode is driven by an AC signal of several hundred volts.
In addition, since this DC bias voltage is a high voltage, and the AC signal as a signal applied to the upper electrode thin film and the lower electrode is also a high voltage, the size of the apparatus is increased while the danger is increased. Invite power and cost.

  The present invention has been made in view of such circumstances, and the sound pressure can be increased by using a resonance phenomenon without changing the amplitude of the vibrating membrane during vibration, and the DC bias voltage and the AC signal can be increased. An object of the present invention is to provide an ultrasonic transducer in which voltage is reduced.

  In order to achieve the above object, an invention according to claim 1 is directed to an upper electrode comprising a vibration film formed of an insulator and a conductive film formed on the vibration film, and facing the vibration film of the upper electrode. A lower electrode having a plurality of projections and depressions on the surface to be adhered, the upper electrode and the lower electrode are brought into close contact with each other, and an ultrasonic signal is generated by applying an AC signal between the upper electrode and the lower electrode An ultrasonic transducer is characterized in that a resonance tube unit in which a plurality of vent holes for forming a double-ended opening tube that resonates at a desired frequency is provided on a plate material is fixed on the surface of the upper electrode.

  The invention according to claim 2 is an upper electrode composed of a vibration film formed of an insulator and a conductive film formed on the vibration film, and a plurality of irregularities on a surface of the upper electrode facing the vibration film, A lower electrode formed, and the upper electrode and the lower electrode are brought into close contact with each other to form a vent hole communicating from the inside of a plurality of cavities formed between the upper electrode and the lower electrode. An ultrasonic transducer that generates an ultrasonic wave by applying an AC signal between the upper electrode and the lower electrode, and has a plurality of vent holes that form a double-ended opening tube that resonates at a desired frequency with the plate material A resonance tube unit provided with is fixed to the surface of the upper electrode.

The invention according to claim 3 is a lower electrode having a plurality of irregularities formed on both sides;
Two upper electrodes comprising a vibrating film formed of an insulator and opposed to each other on both surfaces of the lower electrode; and the two upper electrodes, A plurality of cavities are formed at the upper and lower ends of the lower electrode by closely contacting the lower electrode, and the cavity formed at the upper end of the lower electrode among the plurality of cavities, and the lower electrode immediately below the cavity Resonance formed by forming a plurality of vent holes that form a double-ended opening tube that resonates at a desired frequency in a plate material. A tube unit is fixed to the two upper electrode surfaces.

  According to a fourth aspect of the present invention, in the ultrasonic transducer according to any one of the first to third aspects, the resonance tube unit is formed of a material that does not absorb ultrasonic waves of the desired frequency that resonates. Features.

  According to a fifth aspect of the present invention, in the ultrasonic transducer according to any one of the first to fourth aspects, the length in the depth direction of the vent hole formed in the resonance tube unit is a wavelength of the ultrasonic wave that resonates. It is characterized by being an integral multiple of the length of the half wavelength.

  The invention according to claim 6 is the ultrasonic transducer according to claim 4, wherein the surface shape of the resonance tube unit is such that the length of each resonance tube in the depth direction is toward the center. It is formed in a concave shape so as to be short.

  According to a seventh aspect of the present invention, in the ultrasonic transducer according to the fourth or fifth aspect, the surface shape of the resonance tube unit is such that the length of each resonance tube in the depth direction is toward the center. It is formed in a convex shape so as to be long.

  According to an eighth aspect of the present invention, in the ultrasonic transducer according to the fourth or fifth aspect, the surface shape of the resonance tube unit has a depth of each resonance tube from one end to the other end of the plate member. It is characterized by being inclined so that the length in the vertical direction changes linearly.

  According to a ninth aspect of the present invention, the vent hole formed in the ultrasonic transducer according to any one of the first to eighth aspects is formed at a position corresponding to the concave portion formed in the lower electrode. It is characterized by that.

  A tenth aspect of the present invention is the ultrasonic transducer according to any one of the first to ninth aspects, wherein an open end correction gap is provided between the resonance tube unit and the upper electrode. To do.

  The invention according to claim 11 is an ultrasonic speaker comprising the ultrasonic transducer according to any one of claims 1 to 9.

  As described above, according to the ultrasonic transducer of the present invention, the upper electrode composed of the vibration film formed of an insulator and the conductive film formed on the vibration film, and the vibration film of the upper electrode It has a lower electrode with a plurality of irregularities formed on the opposing surface. The upper electrode and the lower electrode are brought into close contact with each other, and an ultrasonic signal is generated by applying an AC signal between the upper electrode and the lower electrode. The ultrasonic transducer is configured to be fixed on the surface of the upper electrode with a resonance tube unit in which a plurality of vent holes forming a double-ended opening tube that resonates at a desired frequency are provided on the plate material. Sometimes the sound pressure can be increased by the resonance phenomenon without changing the amplitude of the diaphragm, and the DC bias voltage and the AC signal voltage can be reduced.

  Therefore, by constructing an ultrasonic speaker using this ultrasonic transducer, the sound pressure can be increased by the resonance phenomenon without changing the amplitude of the diaphragm during vibration, and the DC bias voltage and AC signal voltage can be reduced. Therefore, it is possible to realize an ultrasonic speaker.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows the configuration of the ultrasonic transducer according to the first embodiment of the present invention. The ultrasonic transducer according to this embodiment is obtained by adding a resonance tube unit 20 to the conventional ultrasonic transducer shown in FIG. 11, and the ultrasonic transducer body has the same configuration as that shown in FIG.
In FIG. 1, an ultrasonic transducer 1 includes an upper electrode 10 including a vibration film 2 formed of an insulator (dielectric material) and a conductive film 3 formed on the vibration film 2, and a vibration film of the upper electrode 10. 2 and a lower electrode 12 having a plurality of irregularities formed on the surface facing the electrode 2.
A resonance tube unit 20 is fixed on the surface of the upper electrode 10.

As the vibration film 2, a dielectric (insulator) such as PET (polyethylene terephthalate resin) having a thickness of about 3 to 10 μm is used. A conductive film 3 formed as a metal foil such as aluminum is integrally formed on the upper surface of the vibration film 2 by a process such as vapor deposition, and a lower electrode 12 formed of brass is formed on the lower surface of the vibration film 2. It is provided so that it may contact a part. The lower electrode 12 is connected to a lead 41 and is fixed to a base plate 14 made of bakelite or the like.

A lead 40 is connected to the conductive film 3 of the upper electrode 10, and the lead 40 is connected to a DC bias power supply 30. The DC bias power supply 30 always applies a DC bias voltage for attracting the upper electrode to the conductive film 3 of the upper electrode 10 so that the upper electrode 10 is attracted to the lower electrode 12 side. 32 is a signal source.
The vibration film 2, the conductive film 3, and the base plate 14 are caulked by a case 18 together with the metal rings 15, 16, and 17 and the resonance tube unit 20.

The resonance tube unit 20 is provided with a plurality of both-end opening tubes that resonate at a desired frequency on the plate member 200, and the vent hole 201 is located at a position corresponding to the recess formed in the lower electrode 12. As many as are formed. The board | plate material 200 is comprised with the rigid body, for example. However, even a rigid body may be a metal, ceramic, plastic, or the like as long as it can reflect an ultrasonic wave having a desired resonance frequency without being absorbed. FIG. 2 is a plan view of the resonance tube unit 20 and shows an example of the arrangement of the vent holes 201. The arrangement of the vent holes 201 is not necessarily arranged regularly as shown in FIG. 2, and is arranged corresponding to the concave shape and position of the lower electrode 12.

By arranging the vent hole functioning as a resonance tube in this way, the sound pressure level of the ultrasonic wave radiated from the ultrasonic transducer 1 can be improved more efficiently by utilizing the resonance phenomenon.
FIG. 3 is a front sectional view illustrating the resonance tube unit 20 in more detail. In the figure, “a” indicates the length of the vent hole 201 as a resonance tube, and in this embodiment, a state in which a wave of ½ wavelength propagates is illustrated. The minimum wavelength unit that causes the resonance phenomenon is ½ wavelength, and the theoretical formula of the resonance phenomenon of the both-end opening tube is as follows.
λ = mc / f (1)
Where f is the resonant ultrasonic frequency, c is the speed of sound (about 340 m / s), λ is the wavelength, and m is a natural number.

Accordingly, FIG. 2 shows a configuration in which the resonance tube unit is made most compact, but a in FIG. 3 may take any value as long as it is a natural number multiple of a half wavelength. For example, if the ultrasonic frequency generated in the ultrasonic transducer 1 is 40 kHz, the wavelength is 8.5 mm. Therefore, if there is a resonance tube length of 4.25 mm, the generated ultrasonic wave is generated. The sound pressure level can be improved by resonating.

Since ultrasonic waves are generated, the wavelength is 17 mm when 20 kHz is taken as a reference. Therefore, it is only necessary to have a half of the resonant tube length of 8.5 mm. Considering that the resonance phenomenon occurs every half wavelength, the resonance phenomenon occurs in 20 kHz increments from 20 kHz to higher frequencies. This means that the frequency can be used. This means that it can be used without sacrificing the broadband frequency characteristics that are characteristic of electrostatic transducers. When changing the ultrasonic wave with a finer step size, the fundamental frequency may be set to 10 kHz or 5 kHz, and the resonance tube size may be determined according to the above concept according to the basic frequency.

In FIG. 1, there is a slight gap between the resonance tube unit 20 and the upper electrode 10, but this is for performing open end correction, and generally requires about 0.6 times the radius of the resonance tube.
Further, when using this principle, it is assumed that the inner diameter of the resonance tube is sufficiently smaller than the sound wave length and that a plane wave is generated in the tube. In the case of the present invention, the generated ultrasonic wave is a plane wave and the inner diameter of the tube is about 100 μm at most, so that the oscillation ultrasonic wave is sufficiently small with respect to a wavelength of 17 mm when the frequency is 20 kHz. .

Furthermore, as a method of obtaining a continuous resonance frequency instead of a discrete resonance frequency, as shown in FIG. 4, the surface shape of the resonance tube unit 20A is set so that the length in the depth direction of each resonance tube 201A is in the center. It can be realized by forming a smooth concave surface so as to become shorter as it goes.
Further, in order to obtain a continuous resonance frequency, as shown in FIG. 5, the surface shape of the resonance tube unit 20B is smooth so that the length in the depth direction of each resonance tube 201B becomes longer toward the center. It can also be realized by forming a convex surface.

Furthermore, as a method for obtaining a continuous resonance frequency, the planar shape of the resonance tube unit is rectangular, and the surface shape of the resonance tube unit 20C (20D) is changed from one end of the plate as shown in FIGS. To the other end, the resonance tube 201C (201D) can be realized by being inclined so that the length in the depth direction changes linearly.
However, when the resonance tube unit shown in FIGS. 4 to 7 is used, if attention is paid to only a certain moment, the tubes that resonate are limited, and it is difficult to cause an overall resonance phenomenon.

According to the ultrasonic transducer of the first embodiment of the present invention, the upper electrode composed of the vibration film formed of an insulator and the conductive film formed on the vibration film, and the vibration film of the upper electrode It has a lower electrode with a plurality of irregularities formed on the opposing surface. The upper electrode and the lower electrode are brought into close contact with each other, and an ultrasonic signal is generated by applying an AC signal between the upper electrode and the lower electrode. The ultrasonic transducer is configured to be fixed on the surface of the upper electrode with a resonance tube unit in which a plurality of vent holes forming a double-ended opening tube that resonates at a desired frequency are provided on the plate material. Sometimes the sound pressure can be increased by the resonance phenomenon without changing the amplitude of the diaphragm, and the DC bias voltage and the AC signal voltage can be reduced.

Next, an ultrasonic transducer according to the second embodiment of the present invention will be described. In the ultrasonic transducer according to the second embodiment, the resonance tube unit shown in any of FIGS. 2 to 7 is fixed to the upper electrode surface in the ultrasonic transducer shown in FIG. Thereby, the same effect as that obtained by the ultrasonic transducer according to the first embodiment can be obtained.
The configuration of the ultrasonic transducer 1A according to the second embodiment shown in FIG. 8 will be described. In the present embodiment, the resonance tube unit is not shown for convenience of explanation. In FIG. 8, the ultrasonic transducer 1 </ b> A is opposed to the upper electrode 50 including the vibration film 42 formed of an insulator and the conductive film 43 formed on the vibration film 42, and the vibration film 42 of the upper electrode 50. A lower electrode 52 having a plurality of irregularities formed on the surface, a DC bias power supply 30 and a signal source 32 are provided.

A constant DC bias voltage is always applied between the upper electrode 50 and the lower electrode 52 by the DC bias power supply 30 that can adjust the voltage, and the convex portion 52A of the lower electrode 52 is generated by the electrostatic force generated by this electric field. The upper electrode 50 is adsorbed to the upper electrode 50 and is in a close contact state except for the cavity 54 formed between the upper electrode 50 and the lower electrode 52.
The lower electrode 52 is formed with a vent hole 56 communicating from the cavity 54 to the outside.

Further, an AC signal (frequency is an ultrasonic frequency band of 20 kHz or more) which is a signal voltage by the signal source 32 in a state of being superimposed on a DC bias voltage by the DC bias power supply 30 between the upper electrode 50 and the lower electrode 52. Is applied.
The vent hole 56 functions as a compression resistance reducing means for reducing the compression resistance of air generated when the vibrating membrane 42 vibrates in the cavity portion 54.

  In the above configuration, when a DC bias voltage is applied between the conductive film 43 of the upper electrode 50 and the lower electrode 52 by the DC bias power supply 30, the convex portion 52A of the lower electrode 52 is adsorbed to the upper electrode 50. In this state, an alternating current signal is applied from the signal source 32 so as to be superimposed on a direct current bias voltage between the conductive film 43 and the lower electrode 52 of the upper electrode 50, whereby the vibration film 42 of the upper electrode 50 is driven by the alternating current signal. Vibrate.

At this time, pressure is applied to the air in the cavity portion 54 according to the vibration of the vibration film 42, but since this air flows smoothly through the vent hole 56 communicating with the outside, a larger vibration ( Amplitude).
By using the above-described resonance tube unit (any one of FIGS. 2 to 7) applied to the first embodiment for the ultrasonic transducer 1A configured as described above, the sound pressure level of the emitted ultrasonic waves Can be improved by utilizing the resonance phenomenon.

Next, an ultrasonic transducer according to a third embodiment of the invention will be described. The ultrasonic transducer according to the third embodiment is such that the resonance tube unit shown in any of FIGS. 2 to 7 is fixed to the upper electrode surface in the ultrasonic transducer shown in FIG. Thereby, the same effect as that obtained by the ultrasonic transducer according to the first embodiment can be obtained.
The configuration of the ultrasonic transducer 1B according to the third embodiment shown in FIG. 9 will be described. In the present embodiment, the resonance tube unit is not shown for convenience of explanation.

In FIG. 9, an ultrasonic transducer 1B includes a lower electrode 112 having a plurality of concaves and convexes on both surfaces, a vibration film 101 formed of an insulator disposed on both surfaces of the lower electrode 112, and the vibration film 101. Two upper electrodes 100A, 100B made of a conductive film 102 formed on 101, a DC bias power supply 118, a signal source 120, one of the two upper electrodes 100, 100, for example, face the upper electrode 100B. And a cone 125 provided at a position where

A plurality of cavities 114A (upper end side of the lower electrode) and 114B (lower end side of the lower electrode) are formed at the upper and lower ends of the lower electrode 112 by closely contacting the two upper electrodes 100A, 100B and the lower electrode 112. .
Of the hollow portions 114A and 114B formed at the upper and lower ends of the lower electrode 112, a hollow portion 114A formed at the upper end of the lower electrode 112 and a hollow portion 114B formed at the lower end of the lower electrode 112 immediately below the lower portion In each case, a communicating air hole 116 is formed in the lower electrode 112.

A constant DC bias voltage is applied to the lower electrode 112 by a DC bias power supply 118 capable of adjusting the voltage.
Further, an AC signal (frequency is an ultrasonic frequency band of 20 kHz or higher) is applied between the two upper electrodes 100A and 100B by the signal source 120.

The cone 125 provided at a position facing one side of the upper electrode 100B has a function of reflecting ultrasonic waves generated downward in the drawing upward by the reflection surfaces 125A and 125B. In the arrangement of the cone 125 in this embodiment, the cone 125 functions to diverge the ultrasonic waves generated downward, but the reflective surface 130C of the cone 125 is positioned so as to face the upper electrode 100B. In some cases, the cone 125 functions to converge the ultrasonic wave generated downward toward the front.
As the material of the cone, a material having a large difference in acoustic impedance from air, for example, a hard solid (metal, ceramic, plastic) or the like is desirable.

  In the above configuration, when a constant DC bias voltage is applied to the lower electrode 112 by the DC bias power supply 118, an AC signal is applied between the upper electrodes 100A and 100B by the signal source 120, whereby the two upper electrodes 100A and 100A. The conductive film 102 of 100B is driven and vibrates. At this time, when a positive AC voltage is applied to the conductive film 102 of the upper electrode 100A, a negative AC voltage is applied to the conductive film 102 of the upper electrode 100B. In this case, since a positive DC bias voltage is applied to the lower electrode 112, the vibration film 101 of the upper electrode 100A at the position facing the cavity 114A formed on the upper end side of the lower electrode 112 It receives a repulsive force from 112 and is displaced upward in the figure.

At this time, the vibration film 101 of the upper electrode 100B at the position facing the cavity 114B formed on the lower end side of the lower electrode 112 receives an attractive force from the lower electrode 112 and is displaced upward in the figure. .
Similarly, when a negative AC voltage is applied to the conductive film 102 of the upper electrode 100A, a positive AC voltage is applied to the conductive film 102 of the upper electrode 100B. In this case, since a positive DC bias voltage is applied to the lower electrode 112, the vibration film 101 of the upper electrode 100A at the position facing the cavity 114A formed on the upper end side of the lower electrode 112 It receives a suction force from 112 and is displaced downward in the figure.

At this time, the vibration film 101 of the upper electrode 100B at the position facing the cavity 114B formed on the lower end side of the lower electrode 112 receives a repulsive force from the lower electrode 112 and is displaced downward in the figure. .
Thus, when an AC signal is applied from the signal source 120 between the conductive films 102 and 102 of the upper electrodes 100A and 100B, the vibration film 101 of the upper electrode 100A is moved upward according to the polarity of the applied AC signal. When the vibration film 101 of the upper electrode 100B is displaced upward, the vibration film 101 of the upper electrode 100A is also displaced downward. Since the conductive films 102 and 102 of the upper electrodes 100A and 100B are displaced in the same direction, the air trapped in the cavity 114A and the cavity 114B moves through the air holes 116, and the cavity 114A and The volume change of the air trapped in 114B can be suppressed, and therefore the spring effect due to the volume expansion rate of the air is reduced, and a larger membrane vibration is obtained.

  By using the above-described resonance tube unit (any one of FIGS. 2 to 7) applied to the first embodiment for the ultrasonic transducer 1B configured as described above, that is, depending on the purpose of use, the upper electrode By fixing a resonance tube unit (any one of FIGS. 2 to 7) on the surface of one or both of 100A and 100B, the sound pressure level of the radiated ultrasonic wave can be obtained using the resonance phenomenon. Can be improved.

  In addition, by applying the ultrasonic transducer according to the first to third embodiments to an ultrasonic speaker, the amplitude of the vibration film can be increased during vibration, and the DC bias voltage and the AC signal voltage can be reduced. A sound wave speaker can be realized.

1 is a diagram showing a configuration of an ultrasonic transducer according to a first embodiment of the present invention. The top view of the resonance tube unit in the ultrasonic transducer | vibrator which concerns on 1st Embodiment of this invention shown in FIG. The longitudinal cross-sectional view of the resonance tube unit shown in FIG. The longitudinal cross-sectional view which shows the structural example which formed the planar shape of the resonance tube unit in concave shape. The longitudinal cross-sectional view which shows the structural example which formed the planar shape of the resonance tube unit in the convex surface shape. The longitudinal cross-sectional view which shows the structural example formed so that the planar shape of a resonance tube unit might change to linear form. The longitudinal cross-sectional view which shows the other structural example formed so that the planar shape of a resonance tube unit might change to linear form. The figure which shows the structure of the ultrasonic transducer based on 2nd Embodiment of this invention. The figure which shows the structure of the ultrasonic transducer based on 3rd Embodiment of this invention. The figure which shows the structure of the conventional resonance type ultrasonic transducer. The figure which shows the structure of the conventional broadband oscillation type ultrasonic transducer. The figure which shows the frequency characteristic of the sound pressure level of an ultrasonic transducer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1A, 1B ... Ultrasonic transducer, 2 ... Vibration film, 3 ... Conductive film, 10 ... Upper electrode, 12 ... Lower electrode, 14 ... Base plate, 15, 16, 17 ... Metal ring, 18 ... Case, 20 ... Resonance tube unit, 30 ... DC bias power supply, 32 ... Signal source

Claims (11)

An upper electrode comprising a vibration film made of an insulator and a conductive film formed on the vibration film; and a lower electrode having a plurality of irregularities formed on a surface of the upper electrode facing the vibration film. An ultrasonic transducer that generates an ultrasonic wave by applying an alternating signal between the upper electrode and the lower electrode, and bringing the upper electrode and the lower electrode into close contact with each other,
An ultrasonic transducer characterized in that a resonance tube unit in which a plurality of vent holes for forming a double-ended opening tube that resonates at a desired frequency is provided on a plate material is fixed on the surface of the upper electrode. An upper electrode comprising a vibration film made of an insulator and a conductive film formed on the vibration film; and a lower electrode having a plurality of irregularities formed on a surface of the upper electrode facing the vibration film. The upper electrode and the lower electrode are provided with a vent hole communicating with the outside from the inside of a plurality of cavities formed between the upper electrode and the lower electrode by bringing the upper electrode and the lower electrode into close contact with each other. An ultrasonic transducer that generates an ultrasonic wave by applying an AC signal between
An ultrasonic transducer characterized in that a resonance tube unit in which a plurality of vent holes for forming a double-ended opening tube that resonates at a desired frequency is provided on a plate material is fixed on the surface of the upper electrode. A lower electrode having a plurality of irregularities formed on both sides;
On both surfaces of the lower electrode, there are two upper electrodes composed of a vibration film arranged oppositely and formed of an insulator and a conductive film formed on the vibration film,
A plurality of cavities are formed at the upper and lower ends of the lower electrode by bringing the two upper electrodes and the lower electrode into close contact with each other, and a cavity formed at the upper end of the lower electrode among the plurality of cavities, An ultrasonic transducer in which air holes communicating with the cavity formed at the lower end of the lower electrode immediately below are formed,
An ultrasonic transducer characterized in that a resonance tube unit in which a plurality of ventilation holes for forming a double-end opening tube that resonates at a desired frequency is provided on a plate material is fixed on the surface of the two upper electrodes.   4. The ultrasonic transducer according to claim 1, wherein the resonance tube unit is formed of a material that does not absorb the ultrasonic wave having the desired frequency to resonate. 5.   The length in the depth direction of the vent hole formed in the resonance tube unit is an integral multiple of the half-wave length of the wavelength of the ultrasonic wave to resonate. The described ultrasonic transducer.   6. The surface shape of the resonance tube unit is formed in a concave shape so that the length in the depth direction of each resonance tube becomes shorter toward the center portion. The described ultrasonic transducer.   The surface shape of the resonance tube unit is formed in a convex shape so that the length in the depth direction of each resonance tube becomes longer toward the center portion. The described ultrasonic transducer.   The surface shape of the resonance tube unit is formed so as to be inclined so that the length in the depth direction of each resonance tube changes linearly from one end to the other end of the plate member. The ultrasonic transducer according to claim 4.   The ultrasonic transducer according to any one of 1 to 8, wherein a vent hole formed in the resonance tube unit is formed at a position corresponding to the concave portion formed in the lower electrode.   The ultrasonic transducer according to claim 1, wherein an open end correction gap is provided between the resonance tube unit and the upper electrode. An ultrasonic speaker comprising the ultrasonic transducer according to claim 1.

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