JP2009095048A - Ultrasonic loudspeaker - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic transducer which magnifies amplitude of a vibrating diaphragm during being vibrated and reduces a direct-current bias voltage. <P>SOLUTION: The ultrasonic transducer 1 has an upper electrode 10 comprised of the vibrating diaphragm 2 formed by an insulator and a conductive film 3 formed on the vibrating diaphragm 2 and a lower electrode 12 forming a plurality of concaves and convexes on a face opposing the vibrating diaphragm 2 of the upper electrode 10 and generates an ultrasonic wave by firmly sticking the upper electrode 10 to the lower electrode 12 and by applying an alternating-current signal between the upper electrode 10 and the lower electrode 12. An air hole 16 communicating to the outsides from the insides of a plurality of cavity portions 14 formed between the upper electrode 10 and the lower electrode 12 is provided in the lower electrode 12 by firmly sticking the upper electrode 10 to the lower electrode 12. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  In the electrostatic ultrasonic transducer that generates a constant high sound pressure over a wide frequency band, the present invention can improve energy efficiency and generate strong ultrasonic waves by increasing the amplitude of the vibrating membrane. The present invention relates to an ultrasonic transducer.

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. 6 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 bimorph type ultrasonic transducer shown in FIG. 6A 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.
On the other hand, the unimorph type ultrasonic transducer shown in FIG. 6B is a piezoelectric ceramic composed of one piezoelectric ceramic 71, a case 72, leads 73 and 74, internal wiring 75, and glass 76. 71 is connected to a lead 73 via an internal wiring 75 and is grounded to a case 72.
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. 6 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. 7 shows a specific configuration of the broadband oscillation type ultrasonic transducer. The electrostatic ultrasonic transducer shown in FIG. 7 uses a dielectric 131 (insulator) such as PET (polyethylene terephthalate resin) having a thickness of about 3 to 10 μm as a vibrating body. 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 33 is connected to a lead 52 and is fixed to a base plate 35 made of bakelite or the like.

The upper electrode 32 is connected to a lead 53, and the lead 53 is connected to a DC bias power supply 50. A DC bias voltage for upper electrode adsorption of about 50 to 150 V is always applied to the upper electrode 32 by the DC bias power source 50 so that the upper electrode 32 is attracted to the lower electrode 33 side. Reference numeral 51 denotes a signal source.
The dielectric 31, the upper electrode 32, and the base plate 35 are caulked by the case 30 together with the metal rings 36, 37, and 38 and the mesh 39.

  On the surface of the lower electrode 33 on the dielectric 31 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 33 and the dielectric 31, the electrostatic capacity distribution between the upper electrode 32 and the lower electrode 33 changes minutely. These random minute grooves are formed by manually rubbing the surface of the lower electrode 33 with a file. In the electrostatic ultrasonic transducer, the frequency characteristic of the ultrasonic transducer 22 becomes a wide band as shown by a curve Q1 in FIG. 8 by forming innumerable capacitors having different gap sizes and depths. ing.

  In the ultrasonic transducer 14 having the above configuration, a rectangular wave signal (output of the driver 12: 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. It has come to be. Incidentally, as shown by the curve Q2 in FIG. 8, 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.
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.
Further, this DC bias voltage is a high voltage, which has led to an increase in size, power and cost of the apparatus as well as danger.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an ultrasonic transducer capable of increasing the amplitude of a vibrating membrane during vibration and reducing the DC bias voltage. .

In the first aspect of the present invention, the 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, An ultrasonic transducer that generates an ultrasonic wave by applying an alternating current signal between the upper electrode and the lower electrode, the lower electrode formed, the upper electrode and the lower electrode are in close contact with each other, A compression resistance reducing means for reducing the compression resistance of air generated when the vibrating membrane vibrates in 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; It is characterized by that.
According to the first aspect of the present invention, air generated by the vibration film during vibration in 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. Since the compression resistance reducing means for reducing the compression resistance is provided, the vibration film becomes smooth during the vibration, and the amplitude of the vibration film can be increased.

According to a second aspect of the present invention, there is provided an upper electrode composed of a vibration film formed of an insulator and a conductive film formed on the vibration film, and unevenness is formed on a surface of the upper electrode facing the vibration film. An ultrasonic transducer having a plurality of formed lower electrodes, generating an ultrasonic wave by bringing the upper electrode and the lower electrode into close contact with each other and applying an AC signal between the upper electrode and the lower electrode. In addition, the lower electrode is provided with a vent hole communicating 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. .
According to the second aspect of the present invention, the lower electrode is provided with a vent hole communicating with the outside through 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. Since it is provided on the electrode, the flow of air is smooth when the vibrating membrane vibrates, and the amplitude of the vibrating membrane can be increased.

According to a third aspect of the present invention, there is provided a lower electrode having a plurality of concavities and convexities formed on both surfaces, a vibration film formed of an insulator disposed opposite to both surfaces of the lower electrode, and the vibration film on the vibration film. Ultrasonic waves in which a plurality of hollow portions are formed at upper and lower ends of the lower electrode by bringing the two upper electrodes and the lower electrode into close contact with each other. A transducer, a hollow portion formed at the upper end of the lower electrode among the hollow portions formed at the upper and lower ends of the lower electrode, and a hollow portion formed at the lower end of the lower electrode immediately below the transducer, A vent hole that communicates is formed.
According to the third aspect of the present invention, the vibration film constituting the upper electrode is provided on both surfaces of the lower electrode, the cavity formed at the upper end of the cavity formed at the upper and lower ends of the lower electrode, and the Since the air holes communicating with the hollow portions formed at the lower ends of the lower electrodes immediately below are formed, the vibrating membranes of the two upper electrodes are set in accordance with the polarity of the AC signal applied between the two upper electrodes. By displacing in the same direction, the volume change of the air trapped in the cavity formed at the upper and lower ends of the lower electrode can be suppressed, and therefore the spring effect due to the volume expansion rate of the air is reduced, and more A large membrane vibration can be obtained.

According to a fourth aspect of the present invention, in the ultrasonic transducer according to the third aspect, the contact surfaces of the two upper electrodes and the lower electrode are fixed by bonding.
According to the invention described in claim 4, since the contact surfaces between the two upper electrodes and the lower electrode are fixed by bonding, the contact surfaces between the two upper electrodes and the lower electrode are adsorbed. The DC bias voltage can be reduced, and the power supply device, which has been large in the past, can be reduced in size.

According to a fifth aspect of the present invention, in the ultrasonic transducer according to the third aspect of the present invention, the ultrasonic transducer includes a pressing means for pressing a contact surface between the two upper electrodes and the lower electrode.
According to invention of Claim 5, since it has a press means which presses and fixes the contact surface of two upper electrodes and lower electrodes, for adsorbing the contact surface of two upper electrodes and lower electrodes The DC bias voltage can be reduced, and the power supply device, which has been large in the past, can be reduced in size.

According to a sixth aspect of the present invention, in the ultrasonic transducer according to any of the third to fifth aspects, a constant DC bias voltage is applied to the lower electrode, and an AC signal voltage is applied between the two upper electrodes. Is applied.
According to the sixth aspect of the present invention, the constant DC bias voltage is applied to the lower electrode, and the AC signal voltage is applied between the two upper electrodes disposed at the upper and lower ends of the lower electrode. The vibration film of the upper electrode disposed at the upper and lower ends of the electrode can be vibrated efficiently.

The invention according to claim 7 is the ultrasonic transducer according to any one of claims 3 to 6, wherein the cone diverges or converges sound waves forward to a position facing one of the two upper electrodes. It is characterized by having.
According to the seventh aspect of the invention, since the cone for diverging or converging the sound wave forward is provided at a position facing one of the two upper electrodes, the vibration of the vibrating membrane constituting the two upper electrodes The generated ultrasonic power can be used effectively.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows the configuration of an ultrasonic transducer according to the first embodiment of the present invention. In the figure, the ultrasonic transducer 1 according to the first embodiment includes an upper electrode 10 composed of a vibration film 2 formed of an insulator and a conductive film 3 formed on the vibration film 2, and an upper electrode 10. The lower electrode 12 having a plurality of irregularities formed on the surface facing the vibration film 2, a DC bias power source 18, and a signal source 20 are provided.
A constant DC bias voltage is always applied between the upper electrode 10 and the lower electrode 12 by a DC bias power supply 18 capable of adjusting the voltage, and the convex portion A of the lower electrode 12 is generated by the electrostatic force generated by this electric field. The upper electrode 10 is adsorbed to the upper electrode 10 and is in close contact except for the cavity 14 formed between the upper electrode 10 and the electrode 12.
The lower electrode 12 is formed with a vent hole 16 communicating from the cavity 14 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 20 in a state of being superimposed on a DC bias voltage by the DC bias power supply 18 between the upper electrode 10 and the lower electrode 12. Is applied.
The vent hole 16 functions as a compression resistance reducing means for reducing the compression resistance of air generated when the vibrating membrane 2 vibrates in the cavity portion 14.
In the above configuration, when a DC bias voltage is applied between the conductive film 3 and the lower electrode 12 of the upper electrode 10 by the DC bias power supply 18, the convex portion 12 </ b> A of the lower electrode 12 is adsorbed to the upper electrode 10. In this state, an alternating current signal is applied from the signal source 20 while being superimposed on a direct current bias voltage between the conductive film 3 of the upper electrode 10 and the lower electrode 12, so that the vibration film 2 of the upper electrode 10 is driven by the alternating current signal, Vibrate.

At this time, pressure is applied to the air in the cavity portion 14 according to the vibration of the vibrating membrane. However, since this air flows smoothly through the vent hole 16 communicating with the outside, a larger vibration (amplitude) is generated in the vibrating membrane 2. ) Is obtained.
FIG. 3 shows a state during operation of the conventional ultrasonic transducer and the ultrasonic transducer according to the first embodiment of the present invention. FIG. 3 is a simplified illustration of only one cavity formed between the upper electrode and the lower electrode in the ultrasonic transducer.
As shown in FIG. 3A, in the conventional electrostatic ultrasonic transducer, the air in the cavity 14 acts as a damper (spring) during operation, so the amplitude of the membrane vibration of the upper electrode 10 is reduced. On the other hand, in the ultrasonic transducer according to the first embodiment of the present invention, since the lower electrode 12 is provided with the vent hole 16 communicating from the cavity portion 14 to the outside, the vibrating membrane of the upper electrode 10 is in vibration. The air flow in the cavity 14 becomes smooth, and the amplitude of the membrane vibration increases.

The cross-sectional structure of the ultrasonic transducer 1 according to the first embodiment shown in FIG. 1 is actually caulked by a case 20 as shown in FIG.
The cross-sectional structure of the ultrasonic transducer according to the first embodiment is not limited to that shown in FIG. 2A, and the lower electrode 12 is fixed on the base plate 22 as shown in FIG. Alternatively, all the air holes 14 provided in the lower electrode 12 may be configured to communicate with the recesses 24 that communicate with the outside provided in the base plate 22.
Further, as shown in FIG. 2C, the lower electrode 12 is fixed on the base plate 30, and each of the plurality of vent holes 14 provided in the lower electrode 12 communicates with the outside provided in the base plate 22. You may comprise so that it may connect to the channel | path 24 provided directly under each ventilation hole 14. FIG.

Next, FIG. 4 shows a configuration of an ultrasonic transducer according to the second embodiment of the present invention. In the figure, the ultrasonic transducer 1A according to the second embodiment includes a lower electrode 112 having a plurality of irregularities formed on both surfaces, and a vibration formed by an insulator disposed on both surfaces of the lower electrode 112 so as to face each other. One of the two upper electrodes 100A and 100B made of the film 101 and the conductive film 102 formed on the vibration film 101, the DC bias power supply 118, the signal source 120, and the two upper electrodes 100 and 100, for example, , And a cone 125 provided at a position facing the upper electrode 100B.
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 the present 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.

  FIG. 5 shows a method of fixing the upper electrode and the lower electrode of the ultrasonic transducer according to the second embodiment. In the ultrasonic transducer according to the second embodiment shown in FIG. 4, the vibrating membranes of the upper electrodes 100A and 100B alternately receive both upper and lower forces according to the polarity of the AC signal, so that they are always attracted to the lower electrode 112. I don't mean. Therefore, another method for replacing the electrostatic attraction force is required. In FIG. 5, the electrode structure is shown in a simplified manner, but is the same as the electrode structure of the ultrasonic transducer shown in FIG.

The method of fixing the upper electrode and the lower electrode shown in FIG. 5A is to fix by bonding the contact surfaces of the two upper electrodes 100A, 100B and the lower electrode 112 in the ultrasonic transducer 1A.
The fixing method of the upper electrode and the lower electrode shown in FIG. 5B is the same (same) shape as the shape of the cavity 114A, 114B of the lower electrode 112, for example, the mesh electrode 140 and the upper electrode 100A, A method of fixing 100B to the lower electrode 112 is illustrated. The material of the mesh is preferably a material that is soft and smooth so as not to damage the electrode, such as fiber or plastic. The mesh member 140 corresponds to the pressing means of the present invention.

By fixing the upper electrode and the lower electrode by the method shown in FIG. 5, a DC bias voltage for adsorbing the upper electrode to the lower electrode can be eliminated.
The frequency characteristics of the ultrasonic transducers according to the first embodiment and the first embodiment are as shown by the curve Q1 in FIG. 8, and the sound pressure level is constant and large over a wide frequency band.

  As described above, according to the ultrasonic transducer according to the first embodiment of the present invention, 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. Since the lower electrode is provided with a vent hole communicating from the inside to the outside, the air flow is smooth when the vibration membrane vibrates, and the amplitude of the vibration membrane can be increased.

  In addition, according to the ultrasonic transducer according to the second embodiment of the present invention, the vibration film constituting the upper electrode is provided on both surfaces of the lower electrode, and is formed at the upper end of the cavity formed at the upper and lower ends of the lower electrode. Since the air hole that connects the formed hollow portion and the hollow portion formed at the lower end of the lower electrode immediately below the formed hollow portion is formed, the vibration film of the two upper electrodes is applied between the two upper electrodes. By changing in the same direction according to the polarity of the AC signal, it is possible to suppress the volume change of the air trapped in the cavity formed at the upper and lower ends of the lower electrode, and therefore depending on the volume expansion rate of the air The spring effect is reduced and a larger membrane vibration is obtained.

Furthermore, according to the ultrasonic transducer according to the second embodiment, the contact surfaces between the two upper electrodes and the lower electrode are fixed by bonding, so the contact surfaces between the two upper electrodes and the lower electrode are fixed. The direct-current bias voltage for adsorption can be reduced, and the power supply device, which has been large-scale in the past, can be reduced in size.
Furthermore, according to the ultrasonic transducer according to the second embodiment, since there is a pressing means for pressing and fixing the contact surface between the two upper electrodes and the lower electrode, the contact surface between the two upper electrodes and the lower electrode is provided. The direct-current bias voltage for adsorption can be reduced, and the power supply device, which has been large-scale in the past, can be reduced in size.

  Furthermore, according to the ultrasonic transducer according to the second embodiment, a constant DC bias voltage is applied to the lower electrode, and an AC signal voltage is applied between the two upper electrodes arranged at the upper and lower ends of the lower electrode. Therefore, the vibration film of the upper electrode arranged at the upper and lower ends of the lower electrode can be vibrated efficiently.

  Further, according to the ultrasonic transducer according to the second embodiment, since the cone for diverging or converging the sound wave forward is provided at a position facing one of the two upper electrodes, the vibration film constituting the two upper electrodes Therefore, it is possible to effectively use the ultrasonic output generated by the vibration.

  The ultrasonic transducer according to the present invention can be used for various sensors for position measurement, sound sources for directional speakers, impulse signal generation sources, and the like.

1 is a diagram showing a configuration of an ultrasonic transducer according to a first embodiment of the present invention. Sectional drawing which shows the specific example of the electrode structure of the ultrasonic transducer | vibrator which concerns on 1st Embodiment of this invention shown in FIG. Explanatory drawing which shows the state at the time of operation | movement of the conventional ultrasonic transducer and the ultrasonic transducer which concerns on 1st Embodiment of this invention. The figure which shows the structure of the ultrasonic transducer based on 2nd Embodiment of this invention. Explanatory drawing which shows the fixing method of the upper electrode and lower electrode of an ultrasonic transducer which concern on 2nd Embodiment of this invention. The figure which shows the structure of the conventional ultrasonic transducer. The block diagram which shows the specific structure of a broadband oscillation type ultrasonic transducer. The characteristic view which shows the frequency characteristic of the sound pressure level of an ultrasonic transducer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1A ... Ultrasonic transducer 2, 101 ... Vibrating membrane 3, 102 ... Conductive film 10, 100A, 100B ... Upper electrode, 12, 112 ... Lower electrode, 14, 114A, 114B ... Cavity part 16, 116 ... Vents, 18, 118 ... DC bias power supply, 20, 120 ... Signal source, 125 ... Cone

Claims (7)

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,
A compression resistance reducing means for reducing the compression resistance of air generated when the vibrating membrane vibrates in 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 characterized by that. 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 wave characterized in that the lower electrode is provided with a vent hole communicating 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. Transducer. 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,
An ultrasonic transducer in which a plurality of cavities are formed at the upper and lower ends of the lower electrode by closely contacting the two upper electrodes and the lower electrode,
Out of the hollow portions formed at the upper and lower ends of the lower electrode, the hollow portions formed at the upper end of the lower electrode and the hollow portions formed at the lower end of the lower electrode immediately below are respectively provided with vent holes. An ultrasonic transducer characterized by being formed.   The ultrasonic transducer according to claim 3, wherein the contact surfaces of the two upper electrodes and the lower electrode are fixed by bonding.   The ultrasonic transducer according to claim 3, further comprising a pressing unit that presses and fixes the contact surface between the two upper electrodes and the lower electrode.   6. The ultrasonic transducer according to claim 3, wherein a constant DC bias voltage is applied to the lower electrode, and an AC signal voltage is applied between the two upper electrodes.   The ultrasonic transducer according to any one of claims 3 to 6, further comprising a cone for diverging or converging sound waves forward at a position facing one of the two upper electrodes.

Images