JP4706586B2 - Electrostatic ultrasonic transducer, method for manufacturing electrostatic ultrasonic transducer, and ultrasonic speaker - Google Patents

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, and a method for manufacturing the electrostatic 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. 8 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 bimofull type ultrasonic transducer shown in FIG. 8 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. 8 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. 9 shows a specific configuration of a broadband oscillation type ultrasonic transducer (Pull type).

  The electrostatic ultrasonic transducer shown in FIG. 9 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. 9 are as shown by a curve Q1 in FIG. 10 by forming innumerable 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 the curve Q2 in FIG. 10, 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. 8, the electrostatic ultrasonic transducer shown in FIG. 9 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. 10, 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, and the sound pressure is low as an ultrasonic speaker. 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. 9 can substantially solve the problems of the above-mentioned 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 vibration symmetry of the vibration film (corresponding to the upper electrode 132 in FIG. 9) 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 that is sufficiently high to obtain a parametric array effect over a wide frequency band. 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. In order to receive the electrostatic repulsive force 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 electrostatic ultrasonic transducer.

  FIG. 6 shows an electrode structure of such a push-pull type electrostatic ultrasonic transducer. 6A is a plan view of an electrode structure of a push-pull electrostatic ultrasonic transducer, and FIG. 6B is a cross-sectional view taken along the line AA in FIG. 6A. In FIG. 6, the fixed electrodes 110 </ b> A and 110 </ b> B are configured by a counter electrode portion 120 and a through hole 114, and the counter electrode portion 120 and the through hole 114 are provided in the same shape and at the same position. The vibrating membrane 112 is held in a structure sandwiched between two fixed electrodes 110A and 110B, and sound waves generated by the vibration of the vibrating membrane 112 are released into the air through the through hole 114.

  Here, since the diaphragm 112 is sandwiched between the two fixed electrodes 110A and 110B in a state of being bonded to the diaphragm 113, it is necessary to provide a clearance larger than the thickness of the diaphragm 113 on the fixed electrode side. In particular, a structure having convex portions as shown in FIG.

  In addition, ensuring good clamping of the vibrating membrane is a very important factor for the vibration and sound pressure characteristics of the electrostatic ultrasonic transducer, so the flatness of the electrode surface of the fixed electrode should be within a few μm. Finished.

  With the structure and the flatness of the electrode surface secured as described above, the positioning means is used to align the positions of the opposing electrode portions of the two fixed electrodes 110A and 110B, and then one electrode center portion and the outer periphery The ultrasonic transducer is manufactured by screwing the four corners and sandwiching the vibration membrane.

  However, if the screw tightening torque at the outer corner is too strong, or if the rigidity of the fixed electrode is insufficient, the electrode member is locally deformed, resulting in a gap between the fixed electrode and the diaphragm. In particular, there is a problem that the sandwiching property of the vibrating electrode film is deteriorated and the characteristics of the ultrasonic transducer are deteriorated.

  As described above, even if the flatness of the electrode surface is sufficiently ensured in the pre-assembly stage, the flatness cannot be maintained by the current manufacturing (assembly) method.

  The present invention has been made in view of such circumstances, and manufacture of an electrostatic ultrasonic transducer and an electrostatic ultrasonic transducer that maintain the flatness of the fixed electrode and improve the sandwichability of the vibration membrane. It is an object to provide a method and an ultrasonic speaker.

  In order to achieve the above object, according to the method of manufacturing an electrostatic ultrasonic transducer of the present invention, a first electrode in which a through hole is formed and a through hole that is paired with the through hole of the first electrode are formed. A second electrode, a vibration film sandwiched between the pair of electrodes and having a conductive layer, to which a DC bias voltage is applied to the conductive layer, a holding member for holding the pair of electrodes and the vibration film, And a method of manufacturing an electrostatic ultrasonic transducer in which an AC signal is applied between the pair of electrodes, wherein at least two of the pair of electrodes are used when the electrostatic ultrasonic transducer is assembled. A positional deviation preventing means having a positioning function is provided at more than one place, and a fixing means capable of adjusting the fixing strength is provided at the center of the pair of electrodes.

  In the manufacturing method of the electrostatic ultrasonic transducer according to the present invention having the above-described configuration, there is provided a displacement prevention means having a positioning function at least at two or more positions with respect to the pair of electrodes when the electrostatic ultrasonic transducer is assembled. At the same time, a fixing means capable of adjusting the fixing strength is provided at the center of the pair of electrodes.

  As a result, the deformation of the fixed electrode can be minimized, and the sandwichability of the diaphragm can be improved and stabilized.

  In the method of manufacturing an electrostatic ultrasonic transducer according to the present invention, the position shift prevention means is formed of a non-conductive material.

In the manufacturing method of the electrostatic ultrasonic transducer of the present invention having the above-described configuration, the fixed electrode is usually formed of a conductive material, and therefore, the misalignment prevention means is formed of an electrically insulating material. As the material, resin or ceramic is suitable, and in the case of resin, for example, high-strength resin such as PEEK or aramid resin is used.
Thereby, electrical insulation between the fixed electrodes facing each other can be ensured.

  In the method of manufacturing an electrostatic ultrasonic transducer according to the present invention, the displacement prevention means may be configured such that a rod is inserted into an insertion hole formed in a peripheral portion of the pair of electrodes, and the electrode surfaces of the pair of electrodes And an end of the rod are fixed with an adhesive.

  In the manufacturing method of the electrostatic ultrasonic transducer according to the present invention having the above-described configuration, a positioning rod is inserted into an insertion hole formed in a peripheral portion of the pair of electrodes, and the electrode surfaces of the pair of electrodes and the Positioning of the pair of electrodes is performed by a misregistration prevention means configured by fixing the end of the rod with an adhesive.

  As a result, the flatness of the electrode can be maintained, and the sandwichability of the vibrating membrane can be improved.

  Further, in the method of manufacturing an electrostatic ultrasonic transducer according to the present invention, the positional deviation preventing means is inserted into an insertion hole formed in a peripheral portion of the pair of electrodes, and has a collar portion at one end. A female pin that is formed in a shape, and a male pin that has a flange at one end and is fitted into the female pin, and the female pin and the male pin are fitted in the female pin. In addition, a slight gap is provided between at least one of the flanges of the male pin and the electrode surface.

  In the manufacturing method of the electrostatic ultrasonic transducer according to the present invention having the above-described configuration, it is inserted into the insertion hole formed in the peripheral edge portion of the pair of electrodes, and has a collar portion at one end, and is formed in a cylindrical shape. The female pin and the male pin having a flange at one end and the male pin inserted into the female pin constitute the misalignment preventing means, and the female pin and the male pin are engaged with each other. In addition, a slight gap is provided between at least one of the male pins and the electrode surface.

  Thereby, when a pair of electrodes are fixed, fixing stress to the electrodes can be prevented from acting.

  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 a conductive layer to which a DC bias voltage is applied to the conductive layer; a pair of electrodes; and a holding member that holds the vibration film, the pair of electrodes An electrostatic ultrasonic transducer to which an alternating current signal is applied between the pair of electrodes, a positional deviation preventing means having a positioning function provided at least at two or more locations, and the pair of electrodes It has the fixing means which is provided in the center part and whose fixing strength can be adjusted.

  In the electrostatic ultrasonic transducer according to the present invention having the above-described configuration, when the electrostatic ultrasonic transducer is assembled, positional deviation preventing means having a positioning function is provided at least at two or more positions with respect to the pair of electrodes. A fixing means capable of adjusting the fixing strength is provided at the center of the pair of electrodes.

  Thereby, the deformation of the electrode can be suppressed to the minimum, and the sandwichability of the vibration film can be improved and stabilized.

  Further, the electrostatic ultrasonic transducer according to the present invention is characterized in that the position shift prevention means is formed of a non-conductive material.

In the electrostatic ultrasonic transducer of the present invention having the above-described configuration, the fixed electrode is usually formed of a conductive material, and therefore, the misalignment prevention means is formed of an electrically insulating material. As the material, resin or ceramic is suitable, and in the case of resin, for example, high-strength resin such as PEEK or aramid resin is used.
Thereby, electrical insulation between the fixed electrodes facing each other can be ensured.

  In the electrostatic ultrasonic transducer according to the present invention, the displacement prevention means may be configured such that a rod is inserted through an insertion formed in a peripheral portion of the pair of electrodes, and the electrode surface of the pair of electrodes and the rod The end portion is fixed with an adhesive.

  In the electrostatic ultrasonic transducer according to the present invention having the above-described configuration, a positioning rod is inserted through an insertion hole formed in a peripheral portion of the pair of electrodes, and the electrode surfaces of the pair of electrodes and the ends of the rods The pair of electrodes are positioned by the displacement prevention means configured by fixing the portion with an adhesive.

  As a result, the flatness of the electrode can be maintained, and the sandwichability of the vibrating membrane can be improved.

  Further, in the electrostatic ultrasonic transducer according to the present invention, the position shift prevention means is formed in a cylindrical shape having a flange portion at one end, which is inserted into an insertion hole formed in a peripheral portion of the pair of electrodes. The female pin and the male pin in a state where the female pin and the male pin are fitted to each other. A slight gap is provided between at least one of the ridges and the electrode surface.

  In the manufacturing method of the electrostatic ultrasonic transducer according to the present invention having the above-described configuration, it is inserted into the insertion hole formed in the peripheral edge portion of the pair of electrodes, and has a collar portion at one end, and is formed in a cylindrical shape. The female pin and the male pin having a flange at one end and the male pin inserted into the female pin constitute the misalignment preventing means, and the female pin and the male pin are engaged with each other. In addition, a slight gap is provided between at least one of the male pins and the electrode surface.

  Thereby, when a pair of electrodes are fixed, fixing stress to the electrodes can be prevented from acting.

  An ultrasonic speaker according to the present invention includes any one of the electrostatic ultrasonic transducers described above, a signal source that generates an audible frequency band signal wave, and a carrier wave that generates and outputs an ultrasonic frequency carrier wave. Supply means, and modulation means for modulating the carrier wave with a signal wave in an audible frequency band output from the signal source, and the electrostatic ultrasonic transducer is controlled by a modulation signal output from the modulation means. It is driven.

  In the ultrasonic speaker of the present invention configured as described above, an audible frequency band signal wave is generated by the signal source, and an ultrasonic frequency band carrier wave is generated and output by the carrier wave supply means. Further, the carrier wave is modulated by the audible frequency band signal wave output from the signal source by the modulation means, and the modulation signal output from the modulation means is between the electrode of the ultrasonic transducer and the electrode layer of the vibration film. Applied and driven.

  As described above, since the ultrasonic speaker of the present invention is configured by using the electrostatic ultrasonic transducer having the above-described configuration, it generates an acoustic signal having a sound pressure level high enough to obtain a parametric array effect over a wide frequency band. Therefore, an ultrasonic speaker that can be used can be realized.

  In addition, the electrode is provided with a displacement prevention means having a positioning function in at least two places, and by tightening one central portion of the electrode with a fixing means, the deformation of the electrode is minimized, and the vibrating membrane Can be improved. As a result, an excellent vibration characteristic of the vibration membrane can be obtained, vibration distortion of the electrostatic ultrasonic transducer can be reduced, and an ultrasonic speaker with improved sound pressure and sound quality can be realized.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows the structure of an electrostatic ultrasonic transducer according to an embodiment of the present invention. FIG. 1A is a plan view of an electrode structure of a push-pull electrostatic ultrasonic transducer, and FIG. 1B is a cross-sectional view taken along the line AA in FIG. The electrode structure of the Push-Pull electrostatic ultrasonic transducer shown in FIG. 1 is the same as that of the Push-Pull electrostatic ultrasonic transducer shown in FIG. Basically the same. In FIG. 1, the fixed electrodes 10 </ b> A and 10 </ b> B are configured by a counter electrode portion 20 and a through hole 14, and the counter electrode portion 20 and the through hole 14 are provided in the same shape and at the same position. The vibrating membrane 12 is held in a structure sandwiched between two fixed electrodes 10A and 10B, and sound waves generated by the vibration of the vibrating membrane 12 are released into the air through the through holes 14.

  Here, since the diaphragm 12 is sandwiched between the two fixed electrodes 10A and 10B in a state of being bonded to the diaphragm frame 13, it is necessary to provide a clearance larger than the thickness of the diaphragm frame 113 on the fixed electrode side. Similar to the example, a structure having convex portions as shown in FIG.

  The fixed electrodes 10A and 10B are provided with a fixed portion at the center of the fixed electrode. The fixing means 17 is a combination with a screw or a nut, and the fixing torque is controlled by adjusting the tightening torque. It has become.

On the outer peripheral portions of the fixed electrodes 10A and 10B, at least two or more positions are provided with a displacement prevention means 15 having a positioning function. The insertion holes provided for positioning on the fixed electrodes 10A and 10B side are desirably arranged diagonally in order to improve the positioning accuracy by separating the distance as much as possible. A rod such as a pilot pin that constitutes the misalignment prevention means is inserted into these insertion holes, and the counter electrode positions of the fixed electrodes are aligned and fixed.
Here, the fixed electrodes 10A and 10B are usually made of a conductive material, and the positional deviation prevention means 15 is made of an insulating material in order to ensure electrical insulation between the opposed fixed electrodes 10A and 10B. Resin or ceramic is appropriate as the material, and in the case of resin, high strength resin such as PEEK or aramid resin is desirable.
As a method for fixing the misalignment prevention means 15, it is desirable to adopt a method in which fixing stress is not easily applied to the fixed electrode side. 2 and 3 show a configuration example of the position slip prevention means 15. 2 and 3 show the configuration of the main part of the present invention including the position shift prevention means in the electrostatic ultrasonic transducer shown in FIG. 1, and FIG. 2 (A) and FIG. The plan views, FIGS. 2B and 3B are cross-sectional views along the line AA.
FIG. 2 shows a configuration example in which the misregistration prevention means is fixed by an adhesive method, and FIG. 3 shows a configuration example in which the misregistration prevention means is fixed by a fitting method. In any of the above methods, the diameter of the rod or pin constituting the misalignment prevention means 15 and the positioning hole diameter of the fixed electrodes 10A and 10B are controlled by fitting tolerances, so that the fixed electrodes 10A and 10B are fixed. The stress is extremely small. However, in the case of a simple pilot pin type rod, there is a possibility that the rod may fall off, and in order to prevent this, as shown in FIG. 2, the contact portion with the fixed electrodes 10A and 10B, that is, a pair of pairs The electrode surfaces of the fixed electrodes 10A and 10B and the end of the rod 15A are fixed with an adhesive (for example, a UV curable adhesive) 15B.
On the other hand, a slight volume shrinkage occurs when the adhesive is cured, and this may act as a fixed stress on the fixed electrodes 10A and 10B. Therefore, as a method for suppressing the fixing stress as much as possible, as shown in FIG. 3, the misalignment prevention means 15 is formed with two bodies, one of which is fitted with the positioning holes of the fixed electrodes 10A and 10B, and the size is controlled by the tolerance. A cylindrical female pin 19A is used, and the other is a male pin 10B with a hook. When both pins are fitted, fitting or adhesive fixing is used together. When the pins are completely fitted, a slight gap is provided between the flanges of these pins and the fixed electrodes 10A and 10B, thereby fixing the fixed electrode 10A. , 10B can completely avoid the effect of fixed stress.

The effects of the configuration of the electrostatic ultrasonic transducer and the manufacturing method thereof according to the embodiment of the present invention described above on the device characteristics will be described below.
There is a capacitance as a parameter that contributes to the characteristics of the electrostatic ultrasonic transducer, and the ideal state is that the measured value in the assembled state matches the theoretical capacitance. Here, the capacitance indicates how much the diaphragm is sandwiched by the fixed electrode, and the planar state of the electrode surface of the fixed electrode greatly contributes.
That is, when a very good flat surface can be maintained, the vibrating membrane can be firmly held between the electrode surfaces, and the capacitance matches the theoretical value.
On the other hand, when the fixed electrode is deformed and the flatness of the electrode surface is lost, a gap is generated between the vibrating membrane and the capacitance is reduced.
Here, the flatness of the fixed electrode is greatly influenced by the fixing method, and it is a point of the present invention to reduce this influence as much as possible.

  Therefore, a simulation was performed to verify the effect of the above-described fixing method according to the present invention. For each of the conventional fixing method and the fixing method of the present invention, numerical analysis was performed to clarify the difference between the two. For the analysis software, general-purpose structure software “I-DEAS NX10” was used.

[Analysis model]
The one side of the fixed electrode shown in FIG. 6 is three-dimensionalized. The model created with a fixed electrode thickness of 1.5 mm and an insertion hole diameter of φ0.75 mm is divided into tetrahedral elements, the number of elements is 165117, the number of nodes Is 47109.
[Analysis conditions]
The material properties of the fixed electrode are as shown in Table 1.

拘束条件：
２枚の固定電極を対向させて締め付ける場合に、図７中、点線で示した、挿通孔が設けられている電極面の内側と外側のエッジにおいて、厚み方向の変位は生じないが、平面方向では変形による変位が起こる可能性があるため、厚み方向は並進固定、平面方向は並進自由とした。なお、回転の自由度については、全て固定した。

Restraint condition:
When two fixed electrodes are tightened to face each other, displacement in the thickness direction does not occur at the inner and outer edges of the electrode surface provided with the insertion holes, which are indicated by dotted lines in FIG. Since there is a possibility of displacement due to deformation, the thickness direction is fixed in translation and the plane direction is free to translate. Note that all the degrees of freedom of rotation were fixed.

Loading condition:
A tightening force (11 kg) corresponding to a tightening torque (4.4 cN / m) of a screw for fixing the two fixed electrodes was applied as a surface pressure (3320 mN / mm ² ) to the screw fixing portion.
Table 2 shows the maximum amount of displacement of the electrode surface in the conventional fixing method, which is a total of five fastenings including one fixed electrode central part and four fixed electrode outer peripheral parts. The thickness of the fixed electrode is 1.5 mm and the material is aluminum, and the case of stainless steel is also shown for comparison.

ここで、最大変位発生箇所は、何れの材質においても、固定電極外周部の固定部位に近い外周側であり、アルミニウムでは０．０１ｍｍもの変位が発生する。よって固定電極と振動膜との間に大きな隙間が生じ、結果的に振動特性が劣化し、音圧が低下あるいは不安定となる。

Here, the maximum displacement occurrence location is the outer peripheral side near the fixed portion of the outer peripheral portion of the fixed electrode in any material, and a displacement of 0.01 mm occurs in aluminum. Therefore, a large gap is generated between the fixed electrode and the vibration membrane, resulting in deterioration of vibration characteristics and sound pressure being lowered or unstable.

  Table 3 shows the maximum amount of displacement of the electrode surface when the fixed electrode central portion is tightened at one place, which is the fixing method of the present invention. The tightening force was set to 11 kg as in the conventional fixing method.

最大変位発生箇所は、何れの材質においても、固定電極外周部の固定部に近い外周側ではあるが、アルミニウムでも０．００１ｍｍの変位しか発生せず、固定電極と振動電極膜の隙間は非常に小さく抑えられている。よって、振動電極膜はしっかりと固定電極で挟持されるため、振動特性が改善あるいは安定し、音圧が向上あるいは安定する。

Although the maximum displacement occurrence point is the outer peripheral side near the fixed part of the fixed electrode outer peripheral part in any material, only 0.001 mm of displacement is generated even with aluminum, and the gap between the fixed electrode and the vibrating electrode film is very large. It is kept small. Therefore, since the vibrating electrode film is firmly held between the fixed electrodes, the vibration characteristics are improved or stabilized, and the sound pressure is improved or stabilized.

As described above, in the conventional configuration, a large deformation occurs at the screw fixing portions at the four corners of the fixed electrode, and the influence extends to the vicinity of the outside of the electrode surface.
On the other hand, in the configuration of the present invention, deformation at the screw fixing portion at the center of the electrode is very small, and deformation of the electrode surface is also small.

[Description of Configuration Example of Electrostatic Ultrasonic Transducer According to the Present Invention]
FIG. 4 shows the overall configuration of the electrostatic ultrasonic transducer according to the embodiment of the present invention. 4A shows the overall configuration of the electrostatic ultrasonic transducer, and FIG. 4B shows a plan view in which a part of the electrostatic ultrasonic transducer shown in FIG. 4A is broken. ing. The electrode structure of this electrostatic ultrasonic transducer is as shown in FIGS.

  In FIG. 4, an electrostatic ultrasonic transducer 1 according to an embodiment of the present invention includes a pair of fixed electrodes 10A and 10B including a conductive member formed of a conductive material functioning as an electrode, and a pair of fixed electrodes 10A, The vibration film 12 is sandwiched between 10B and has an electrode layer 121, and a pair of fixed electrodes 10A and 10B and a member (not shown) for holding the vibration film.

  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.
The fixed electrode 10A and the electrode layer 121, and the fixed electrode 10B and the electrode layer 121 are each formed with a capacitor.

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

  On the other hand, AC signals 18A and 18B whose phases are inverted 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, The 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. This is also true for the negative half cycle of the AC signal output from the signal source 18, as shown in FIG. In FIG. 4, the electrostatic repulsive force acts on the upper side, and the film portion not sandwiched between the pair of fixed electrodes 10 </ b> A and 10 </ b> B of the vibrating membrane 12 receives the electrostatic 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. 10 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, the configuration of the ultrasonic speaker according to the embodiment of the present invention is shown in FIG. The ultrasonic speaker according to the present embodiment uses the above-described electrostatic ultrasonic transducer (FIG. 4) according to the present embodiment as the ultrasonic transducer 55.

  5, the ultrasonic speaker according to the present embodiment includes an audio frequency wave oscillation source (signal source) 51 that generates a signal wave in an audio frequency band, and a carrier that generates and outputs a carrier wave in the ultrasonic frequency band. A wave oscillation source (carrier wave supply means) 52, a modulator (modulation means) 53, a power amplifier 54, and an 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, since sound waves are coarse and dense waves that propagate using air as a medium, the dense and sparse portions of the air appear prominently in the process of propagation of the modulated ultrasonic waves, and the dense portions have high sound speed and sparseness. Since the sound speed of such a portion is slow, the modulation wave itself is distorted. As a result, the waveform is separated from the carrier wave (ultrasonic frequency band), and the signal wave (signal sound) in the 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.

As described above, according to the electrostatic ultrasonic transducer according to the embodiment of the present invention, the fixed electrode is provided with the misalignment preventing means having the positioning function in at least two or more locations. By tightening one central portion of the electrode with a fixing means, deformation of the fixed electrode can be minimized, and the sandwiching property of the vibrating electrode film can be improved and stabilized.
As a result, an excellent vibration characteristic of the vibrating electrode film can be obtained, vibration distortion of the ultrasonic transducer can be reduced, and an ultrasonic speaker with improved sound pressure and sound quality can be realized.

  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 top view and sectional drawing which show the structure of the electrostatic type ultrasonic transducer which concerns on embodiment of this invention. The partial top view and sectional drawing which show an example of a structure of the principal part of this invention containing the position slip prevention means in the electrostatic ultrasonic transducer shown in FIG. The fragmentary top view and sectional drawing which show the other example of a structure of the principal part of this invention containing the position slip prevention means in the electrostatic ultrasonic transducer shown in FIG. The figure which shows the whole structure of the electrostatic ultrasonic transducer which concerns on embodiment of this invention. The block diagram which shows the structure of the ultrasonic speaker which concerns on embodiment of this invention. The top view and sectional drawing which show an example of the electrode structure of a Push-Pull type electrostatic ultrasonic transducer. The figure for demonstrating the conditions of the simulation for verifying the effect of the electrostatic ultrasonic transducer which concerns on embodiment of this invention. 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 ultrasonic transducer | vibrator which concerns on embodiment of this invention with the frequency characteristic of the conventional ultrasonic transducer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Ultrasonic transducer, 10 ... Fixed electrode part, 10A, 10B ... Fixed electrode, 12 ... Vibration film, 13 ... Vibration film frame, 14 ... Through-hole, 15 ... Misalignment prevention means, 15A ... Rod, 15B ... Adhesive 16 ... DC bias power source, 17 ... fixing means, 18 ... signal source, misalignment prevention means, 19A ... female pin, 19B ... male pin 20 ... counter electrode part, 51 ... audio frequency wave oscillation source, 52 ... carrier Wave oscillation source, 53 ... modulator, 54 ... power amplifier, 55 ... ultrasonic transducer, 120 ... insulating film (insulating layer), 121 ... electrode layer,

Claims (9)

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 vibrating membrane sandwiched between the pair of electrodes and having a conductive layer, and a DC bias voltage applied to the conductive layer;
A holding member for holding the pair of electrodes and the vibrating membrane;
A method of manufacturing an electrostatic ultrasonic transducer in which an AC signal is applied between the pair of electrodes,
At the time of assembling the electrostatic ultrasonic transducer, with respect to the pair of electrodes, at least two or more locations are provided with a displacement prevention means having a positioning function,
A method for manufacturing an electrostatic ultrasonic transducer, characterized in that a fixing means capable of adjusting a fixing strength is provided at a central portion of the pair of electrodes.   2. The method of manufacturing an electrostatic ultrasonic transducer according to claim 1, wherein the displacement prevention means is formed of a non-conductive material.   The misalignment prevention means is configured such that a rod is inserted into an insertion hole formed in a peripheral portion of the pair of electrodes, and an electrode surface of the pair of electrodes and an end of the rod are fixed with an adhesive. The method for manufacturing an electrostatic ultrasonic transducer according to claim 1, wherein: The misregistration prevention means includes
A female pin inserted into an insertion hole formed in the peripheral edge of the pair of electrodes, and having a flange at one end and formed in a cylindrical shape;
A male pin having a collar at one end and fitted into the female pin;
Have
The present invention is characterized in that a slight gap is provided between at least one of the female pin and the male pin and the electrode surface in a state where the female pin and the male pin are fitted. Item 3. A method for manufacturing an electrostatic ultrasonic transducer according to Item 1 or 2. 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 vibrating membrane sandwiched between the pair of electrodes and having a conductive layer, and a DC bias voltage applied to the conductive layer;
A holding member for holding the pair of electrodes and the vibrating membrane;
An electrostatic ultrasonic transducer in which an AC signal is applied between the pair of electrodes,
Position misalignment prevention means having a positioning function provided in at least two locations with respect to the pair of electrodes,
A fixing means provided at a central portion of the pair of electrodes, the fixing strength being adjustable;
An electrostatic ultrasonic transducer characterized by comprising:   6. The electrostatic ultrasonic transducer according to claim 5, wherein the displacement prevention means is made of a non-conductive material.   The misalignment prevention means is configured such that a rod is inserted into an insertion hole formed in a peripheral portion of the pair of electrodes, and an electrode surface of the pair of electrodes and an end of the rod are fixed with an adhesive. The electrostatic ultrasonic transducer according to any one of claims 5 and 6. The misregistration prevention means includes
A female pin inserted into an insertion hole formed in the peripheral edge of the pair of electrodes, and having a flange at one end and formed in a cylindrical shape;
A male pin having a collar at one end and fitted into the female pin;
Have
The present invention is characterized in that a slight gap is provided between at least one of the female pin and the male pin and the electrode surface in a state where the female pin and the male pin are fitted. Item 7. The electrostatic ultrasonic transducer according to any one of Items 5 and 6. The electrostatic ultrasonic transducer according to any one of claims 5 to 8,
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;
Have
The ultrasonic speaker is characterized in that the electrostatic ultrasonic transducer is driven by a modulation signal output from the modulation means.

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