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JP2007082052

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DESCRIPTION JP2007082052
PROBLEM TO BE SOLVED: To provide an electrostatic ultrasonic transducer in which sound
pressure is improved by improving electrostatic force with a simple configuration. SOLUTION: A
first fixed electrode 10A in which a plurality of through holes 14 are formed, a second fixed
electrode 10B in which a plurality of through holes 14 paired with the first fixed electrode are
formed, and the pair Membrane 12 sandwiched between the fixed electrodes and having
conductive layers 120 on both sides of the insulating film 121, to which a DC bias voltage is
applied by the DC bias power source 16 on the conductive layer, the pair of fixed electrodes and
the diaphragm An electrostatic ultrasonic transducer having an AC signal applied thereto by the
signal source 18 between the pair of fixed electrodes, wherein each of the first and second fixed
electrodes is An insulating film layer is formed on the vibrating film side. [Selected figure] Figure
1
Electrostatic ultrasonic transducer and method of manufacturing the same
[0001]
The present invention relates to an electrostatic ultrasonic transducer generating constant high
sound pressure over a wide frequency band and an ultrasonic speaker using the same.
[0002]
Conventional ultrasonic transducers are mostly resonant type using piezoelectric ceramic.
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Here, the configuration of a conventional ultrasonic transducer is shown in FIG. Conventional
ultrasonic transducers are mostly resonant type using piezoelectric ceramic as a vibrating
element. The ultrasonic transducer shown in FIG. 9 uses piezoelectric ceramic as a vibrating
element to perform both conversion from an electrical signal to ultrasonic waves and conversion
from ultrasonic waves to electrical signals (transmission and reception of ultrasonic waves). The
bimoful type ultrasonic transducer shown in FIG. 9 is composed of two piezoelectric ceramics 61
and 62, a cone 63, a case 64, leads 65 and 66, and a screen 67.
[0003]
The piezoelectric ceramics 61 and 62 are bonded to each other, and the lead 65 and the lead 66
are connected to the surface opposite to the bonding surface, respectively. Since the resonance
type ultrasonic transducer utilizes the resonance phenomenon of piezoelectric ceramic, the
transmission and reception characteristics of the ultrasonic wave become good in a relatively
narrow frequency band around the resonance frequency.
[0004]
Unlike the resonant ultrasonic transducer shown in FIG. 9 described above, the electrostatic
ultrasonic transducer is conventionally known as a broadband ultrasonic transducer capable of
generating 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. FIG. 10 shows a specific configuration of the
broadband oscillation type ultrasonic transducer (Pull type).
[0005]
The ultrasonic transducer of the electrostatic type shown in FIG. 10 uses a dielectric 131
(insulator) such as PET (poly-ethylene-terephthalate resin) having a thickness of about 3 to 10
μm as a vibrator. For the dielectric 131, the upper electrode 132 formed as a metal foil such as
aluminum is integrally formed on the upper surface thereof by a process such as evaporation,
and the lower electrode 133 formed of brass is the lower surface of the dielectric 131 It is
provided to contact the part. The lower electrode 133 is connected to the lead 152 and fixed to a
base plate 135 made of Bakelite or the like.
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[0006]
Further, a lead 153 is connected to the upper electrode 132, and the lead 153 is connected to a
DC bias power supply 150. A DC bias voltage for attracting the upper electrode of about 50 to
150 V is constantly applied to the upper electrode 132 by the DC bias power supply 150 so that
the upper electrode 132 is attracted to the lower electrode 133 side. 151 is a signal source.
[0007]
The dielectric 131 and the upper electrode 132 and the base plate 135 are crimped 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 side of the dielectric 131, a plurality of microgrooves of
approximately several tens to several hundreds of μm having an uneven shape are formed. Since
this minute groove serves as an air gap between the lower electrode 133 and the dielectric 131,
the distribution of capacitance between the upper electrode 132 and the lower electrode 133
changes minutely.
[0008]
The random minute grooves are formed by manually roughening 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. 10 are as shown by curve Q1 in FIG. 11 by thus
forming an infinite number of capacitors having different sizes and depths of the air gaps. It is
broadband.
[0009]
In the ultrasonic transducer configured as described above, a rectangular wave signal (50 to 150
Vp-p) is applied between the upper electrode 12 and the lower electrode 133 in a state where a
DC bias voltage is applied to the upper electrode 132. There is. Incidentally, as shown by a curve
Q2 in FIG. 11, the frequency characteristic of the resonance type ultrasonic transducer has a
center frequency (resonance frequency of the piezoelectric ceramic) of, for example, 40 kHz, ± 5
kHz with respect to the center frequency which is the maximum sound pressure. At a frequency
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of -30 dB relative to the maximum sound pressure. On the other hand, the frequency
characteristic of the broadband oscillation type ultrasonic transducer of the above configuration
is flat from 40 kHz to 100 kHz, and is about ± 6 dB at 100 kHz as compared to the maximum
sound pressure (see Patent Documents 1 and 2) . Japanese Patent Laid-Open No. 2000-50387
Japanese Patent Laid-Open No. 2000-50392
[0010]
As described above, unlike the resonant ultrasonic transducer shown in FIG. 9, the electrostatic
ultrasonic transducer shown in FIG. 10 can generate relatively high sound pressure over a wide
frequency band conventionally. It is known as a broadband ultrasound transducer (Pull type).
However, as shown in FIG. 11, the sound pressure of the electrostatic ultrasonic transducer is
120 dB or less lower than that of the resonance ultrasonic transducer of 130 dB or more as
shown in FIG. The sound pressure was slightly short to use it.
[0011]
Here, the ultrasonic speaker will be described. An ultrasonic wave is modulated by an audio
signal of a signal source by AM-modulating a signal in an ultrasonic frequency band called a
carrier wave with an audio signal (a signal in an audible frequency band) and driving an
ultrasonic transducer with this modulation signal. The sound waves of the state are emitted into
the air, and the non-linearity of the air causes the original audio signal to self-reproduce in the
air.
[0012]
That is, since the sound wave is a compressional wave propagating through air as a medium, in
the process of propagation of the modulated ultrasonic wave, dense and sparse portions of air
become prominent, and the dense portion has a high speed of sound and is sparse. As the speed
of sound is slowed, the modulation wave itself is distorted, so that the waveform is separated into
the carrier wave (ultrasonic wave) and the audio wave (original audio signal), and we human
beings the audible sound below 20 kHz (original audio signal) The principle is that you can hear
only, and is generally called parametric array effect.
[0013]
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Although ultrasonic sound pressure of 120 dB or more is necessary for the above-mentioned
parametric effect to fully appear, it is difficult to achieve this value with electrostatic ultrasonic
transducers, and ceramic piezoelectric elements such as PZT and PVDF, etc. are exclusively used.
Polymer piezoelectric elements have been used as ultrasound transmitters.
However, since the piezoelectric element has a sharp resonance point regardless of the material
and is driven at the resonance frequency and put into practical use as an ultrasonic speaker, the
frequency range where high sound pressure can be secured is extremely narrow. That is, it can
be said that it is a narrow band.
[0014]
Generally, the maximum audio frequency band of human beings is said to be 20 Hz to 20 kHz,
and has a band of about 20 kHz. That is, in the ultrasonic speaker, it is impossible to faithfully
demodulate the original audio signal unless a high sound pressure is secured over the 20 kHz
frequency band in the ultrasonic region. It will be easily understood that it is difficult to faithfully
reproduce (demodulate) this wide band of 20 kHz at the very bottom of a conventional resonance
type ultrasonic speaker using a piezoelectric element.
[0015]
In fact, in the ultrasonic speaker using the conventional ultrasonic transducer of the resonance
type, (1) the band is narrow and the reproduction sound quality is bad, (2) if the AM modulation
degree is too large, the demodulation sound is distorted by at most 0.5 (3) When the input
voltage is increased (when the volume is raised), the vibration of the piezoelectric element
becomes unstable and the sound is broken. When the voltage is further increased, the
piezoelectric elements themselves are easily broken. (4) It is difficult to achieve array formation,
upsizing, downsizing, and thus cost increase.
[0016]
On the other hand, the ultrasonic speaker using the electrostatic ultrasonic transducer (Pull type)
shown in FIG. 8 can almost solve the problems of the above-mentioned prior art, but it can cover
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a wide band but the demodulation sound is sufficient. There was a problem that the absolute
sound pressure was insufficient to achieve a good volume. Further, in the Pull-type ultrasonic
transducer, the electrostatic force works only in the direction of attracting the electrode to the
fixed electrode side, which corresponds to a vibrating film (corresponding to the upper electrode
132 in FIG. 10). When used in an ultrasonic speaker, there is a problem that the vibration of the
vibrating membrane directly generates an audible sound, since the symmetry of the vibration of
(a) is not maintained.
[0017]
In contrast, we have already proposed ultrasound transducers that can generate acoustic signals
at sound pressure levels high enough to obtain parametric array effects over a wide frequency
band. The configuration of this ultrasonic transducer is shown in FIG. In FIG. 12, the ultrasonic
transducer is sandwiched between a pair of fixed electrodes 10A and 10B in which through holes
14 are formed opposite to a diaphragm 12 having a conductive layer 121, and a DC bias is
applied to the diaphragm 12 by a DC power supply 16. The alternating current signals 18A and
18B are applied to the pair of fixed electrodes by the signal source 18 in the state where the
voltage is applied. In addition, 120 is an insulating film which forms a diaphragm, 17 forms a
part of a pair of fixed electrodes 10A and 10B, has a function of holding the diaphragm 12 and
electrostatic force between the diaphragm 13 and It is a counter electrode formation object
which has the function to form the counter electrode part 19 which is the part to act.
[0018]
This ultrasonic transducer is called a Push-Pull type ultrasonic transducer, and the vibrating
membrane sandwiched by a pair of fixed electrodes has the same electrostatic attraction and
electrostatic repulsion in the direction according to the polarity of the AC signal. In order to
receive in the direction and simultaneously, the vibration of the vibrating membrane can not only
be made large enough to obtain the parametric array effect, but also the symmetry of the
vibration is secured, so that it can be compared to the conventional Pull type ultrasonic
transducer. High sound pressure can be generated over a wide frequency band.
[0019]
By the way, in a Push-Pull type ultrasonic transducer, the strength of the electrostatic force
acting on the vibrating film largely depends on the distance between the fixed electrode surface
and the conductive layer on the vibrating film side, and theoretically it is inversely proportional
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to the square of the distance Do.
Therefore, in order to reduce the distance as much as possible, it is effective to reduce the
thickness of the counter electrode portion provided on the fixed electrode and to make the
vibrating film thinner, but the Push-Pull type ultrasonic transducer already proposed at present
There was a limit in the configuration of FIG. For example, assuming that the minimum thickness
of the counter electrode portion is 6 μm and the thickness of one side is 9 μm based on the
conductive layer of the vibrating membrane, the distance between the fixed electrode surface and
the conductive layer of the vibrating membrane is 15 μm. It is a condition where stable and
reliable driving is possible. Therefore, the distance between the fixed electrode and the
conductive layer of the vibrating membrane can not be further shortened.
[0020]
The present invention has been made in view of such circumstances, and it is an object of the
present invention to provide an electrostatic ultrasonic transducer in which sound pressure is
improved by improving electrostatic force with a simple configuration, and a method of
manufacturing the same. To aim.
[0021]
In order to achieve the above object, in the electrostatic ultrasonic transducer according to the
present invention, a first fixed electrode in which a plurality of through holes are formed, and a
plurality of through holes paired with the first fixed electrode are formed. A second fixed
electrode, a vibrating film sandwiched by the pair of fixed electrodes and having conductive
layers on both sides of the insulating film, and a DC bias voltage being applied to the conductive
layer, the pair of fixed electrodes, and An electrostatic ultrasonic transducer having a holding
member for holding a vibrating membrane, and an alternating current signal being applied
between the pair of fixed electrodes, wherein each vibrating membrane in the first and second
fixed electrodes An insulating film layer is formed on the side.
[0022]
In the electrostatic ultrasonic transducer according to the present invention having the above
configuration, a plurality of holes are formed at positions facing the first fixed electrode and the
second fixed electrode, and a DC bias voltage is applied to the conductive layer of the diaphragm.
Since the AC signal which is a drive signal is applied to the pair of fixed electrodes consisting of
the first and second fixed electrodes in the above state, the vibrating film sandwiched between
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the pair of fixed electrodes has the polarity of the AC signal. In the corresponding direction, the
electrostatic attraction force and the electrostatic repulsion force are simultaneously received in
the same direction, so that not only the vibration of the vibrating membrane can be made large
enough to obtain a parametric effect, but also the symmetry of the vibration is ensured
Therefore, high sound pressure can be generated over a wide frequency band.
Furthermore, since the vibrating film has conductive layers on both sides of the insulating film,
and an insulating film layer is formed on the vibrating film side of each of the first and second
fixed electrodes, the conductive film of the fixed electrode and the vibrating film is conductive.
The distance between the layers can be shortened so far, the electrostatic force acting on the
vibrating membrane can be improved, and therefore the sound pressure can be improved.
[0023]
In the electrostatic ultrasonic transducer according to the present invention, an insulating
coating layer is also formed on the inner wall of the through hole of the first and second fixed
electrodes.
[0024]
In the electrostatic ultrasonic transducer of the present invention having the above configuration,
an insulating coating layer is also formed on the inner wall of the through hole of the first and
second fixed electrodes.
Therefore, when the vibrating membrane vibrates, the risk of the conductive layer of the
vibrating membrane and the fixed electrode coming into contact can be avoided, and the
reliability can be improved.
[0025]
In the electrostatic ultrasonic transducer according to the present invention, an insulating
coating layer is formed on the entire surface of the first and second fixed electrodes including the
inner wall of the through hole.
[0026]
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In the electrostatic ultrasonic transducer of the present invention having the above configuration,
an insulating coating layer is formed on the entire surface of the first and second fixed electrodes
including the inner wall of the through hole.
Therefore, the conductive portion of the fixed electrode can be prevented from being exposed to
the outside, and an electrostatic ultrasonic transducer with high safety can be realized.
[0027]
In the electrostatic ultrasonic transducer according to the present invention, in the electrostatic
ultrasonic transducer according to any one of the above, the insulating coating layer is any of a
photosensitive coating material, a nonconductive paint, and an electrodeposition material. It is
characterized in that it is formed of
[0028]
In the electrostatic ultrasonic transducer of the present invention having the above-described
structure, the insulating coating layer is formed using any of a photosensitive coating material, a
nonconductive paint, and an electrodeposition material.
Therefore, the insulating layer can be formed on the surface of the fixed electrode or the entire
surface of the fixed electrode including the inner wall of the through hole by vapor deposition,
spin coating, or electrodeposition on the fixed electrode (conductor) having the through hole.
[0029]
In the method of manufacturing an electrostatic ultrasonic transducer according to the present
invention, a first fixed electrode having a plurality of through holes formed therein, and a
plurality of through holes forming a pair with the first fixed electrode are formed. And a pair of
fixed electrodes held by the pair of fixed electrodes and having conductive layers on both
surfaces of the insulating film, to which a DC bias voltage is applied to the conductive layer, the
pair of fixed electrodes and the vibrating membrane And a holding member for holding an
electric current signal between the pair of fixed electrodes, wherein the first and second fixed
electrodes are electrically conductive. A first step of covering the mask member having the
pattern of the plurality of holes formed therein and forming a through hole by etching, and a
second step of peeling the mask member after the through hole is formed A piece of the
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conductor in which the through hole is formed A third step of forming an insulating film layer
having a predetermined film thickness, a through hole on the conductor on which the insulating
film layer is formed, and a mask member for masking a region near the through hole on the
conductor surface Set a counter electrode forming material for forming an insulating counter
electrode forming body for exposing the conductor portion facing the vibrating film on the
surface of the conductor and moving the squeegee Removing the mask member after the
application of the counter electrode forming material is completed in the fourth step of applying
the counter electrode forming material to a portion of the conductor surface not masked by the
mask member; And a fifth step of drying the counter electrode assembly formed on the
conductor.
[0030]
In the method of manufacturing an electrostatic ultrasonic transducer according to the present
invention having the above configuration, the first and second fixed electrodes forming a pair
cover a mask member in which a pattern of the plurality of holes is formed on a conductor. A
first step of forming a through hole by etching, a second step of peeling the mask member after
the through hole is formed, and a predetermined film on one surface of the conductor in which
the through hole is formed A third step of forming a thick insulating coating layer, a through hole
on the conductor on which the insulating coating layer is formed, and a mask member for
masking a region in the vicinity of the through hole are placed on the conductive surface And, a
counter electrode forming material for forming an insulating counter electrode forming body for
exposing the conductor portion facing the vibrating film is set on the conductor surface, and the
squeegee is moved to set the counter electrode Forming material on the surface of the conductor
Removing the mask member after the application of the counter electrode forming material is
completed in the fourth step of applying the unmasked portion by the mask member and the
fourth step, and the facing formed on the conductor It manufactures by the 5th process of drying
an electrode formation body.
[0031]
According to the manufacturing method of the electrostatic ultrasonic transducer of the present
invention having the above-described configuration, not only the vibration of the vibrating film
can be made sufficiently large to obtain the parametric effect, but also the symmetry of the
vibration is secured. An electrostatic ultrasonic transducer capable of generating high sound
pressure over a wide frequency band is obtained.
Further, in the method of manufacturing an electrostatic ultrasonic transducer according to the
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present invention having the above configuration, the insulating coating layer is formed on one
surface of the conductor of the fixed electrode.
Therefore, according to the method of manufacturing the electrostatic ultrasonic transducer of
the present invention having the above configuration, the risk that the conductive layer of the
vibrating membrane contacts the fixed electrode can be avoided when the vibrating membrane
vibrates. An electrostatic ultrasonic transducer with improved reliability can be obtained.
[0032]
Further, in the method of manufacturing an electrostatic ultrasonic transducer according to the
present invention, in the method of manufacturing the electrostatic ultrasonic transducer, the
inner wall of the through hole of the first and second fixed electrodes instead of the third step.
Also, the method has a third step of forming an insulating film layer.
[0033]
In the method of manufacturing an electrostatic ultrasonic transducer according to the present
invention having the above configuration, an insulating coating layer is also formed on the inner
wall of the through hole of the first and second fixed electrodes.
Therefore, when the vibrating membrane vibrates, the risk of contact between the conductive
layer of the vibrating membrane and the fixed electrode can be avoided, and an electrostatic
ultrasonic transducer with improved reliability can be obtained.
[0034]
Further, in the method of manufacturing an electrostatic ultrasonic transducer according to the
present invention, in the method of manufacturing the electrostatic ultrasonic transducer, the
conductor having the through hole formed therein is replaced with a predetermined one instead
of the third step. Forming an insulating coating layer of the thickness as described above on the
entire surface of the conductor including the inner wall of the through hole.
[0035]
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In the method of manufacturing an electrostatic ultrasonic transducer according to the present
invention having the above configuration, an insulating coating layer of a predetermined film
thickness covers the entire surface of the conductor including the inner wall of the through hole
with respect to the conductor in which the through hole is formed. It is formed.
Therefore, an insulating film layer is formed on the entire surface of the first and second fixed
electrodes including the inner wall of the through hole.
Therefore, the conductive portion of the fixed electrode can be prevented from being exposed to
the outside, and a highly safe electrostatic ultrasonic transducer can be obtained.
[0036]
Further, in the method of manufacturing an electrostatic ultrasonic transducer according to the
present invention, in the method of manufacturing an electrostatic ultrasonic transducer
according to any one of the above, the insulating coating layer comprises a photosensitive
coating material, a nonconductive paint, an electrodeposition material It is characterized in that it
is formed of
[0037]
According to the method of manufacturing an electrostatic ultrasonic transducer of the present
invention having the above configuration, the insulating coating layer is formed using any of a
photosensitive coating material, a nonconductive paint, and an electrodeposition material.
Therefore, the insulating layer can be formed on the surface of the fixed electrode or the entire
surface of the fixed electrode including the inner wall of the through hole by vapor deposition,
spin coating, or electrodeposition on the fixed electrode (conductor) having the through hole.
[0038]
Further, an ultrasonic speaker according to the present invention includes any one of the abovedescribed electrostatic ultrasonic transducers, a signal source that generates a signal wave in an
audio frequency band, and a carrier wave that generates and outputs a carrier wave in an
ultrasonic frequency band. A feeding means; and a modulation means for modulating the carrier
wave with a signal wave in an audible frequency band output from the signal source, the
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electrostatic ultrasonic transducer comprising the first and second fixed electrodes It is
characterized in that it is driven by a modulation signal outputted from the modulation means
applied between the diaphragm and the conductive layer.
[0039]
In the ultrasonic speaker according to the present invention having the above configuration, a
signal wave in the audible frequency band is generated by the signal source, and a carrier wave
in the ultrasonic frequency band is generated and output by the carrier wave supply means.
Further, the carrier wave is modulated by the signal wave in the audio frequency band outputted
from the signal source by the modulation means, and the modulation signal outputted from the
modulation means is applied between the fixed electrode and the electrode layer of the
diaphragm. And be driven.
[0040]
Since the ultrasonic speaker according to the present invention is configured using the
electrostatic ultrasonic transducer having the above configuration, it is possible to generate an
acoustic signal at a sound pressure level high enough to obtain a parametric array effect over a
wide frequency band. A sound wave speaker can be realized. Furthermore, since it was
configured using the electrostatic ultrasonic transducer of the above configuration, that is, the
vibrating film has a conductive layer on both sides of the insulating film, and each vibration in
the first and second fixed electrodes Since the insulating film layer is formed on the film side, the
distance between the fixed electrode and the conductive layer of the vibrating film can be made
shorter than before, and the electrostatic force acting on the vibrating film can be improved. Can
be improved.
[0041]
Hereinafter, embodiments of the present invention will be described in detail with reference to
the drawings. The configuration of an electrostatic ultrasonic transducer according to an
embodiment of the present invention is shown in FIG. FIG. 1 (A) shows the configuration of the
electrostatic ultrasonic transducer, and FIG. 1 (B) shows a plan view in which a part of the
04-05-2019
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ultrasonic transducer is broken. In FIG. 1, an electrostatic ultrasonic transducer 1 according to an
embodiment of the present invention is held between 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. And the vibrating film 12 having the conductive layers 121 on both
sides of the insulating film 120, and a member (not shown) for holding the pair of fixed
electrodes 10A and 10B and the vibrating film 12.
[0042]
The vibrating film 12 has an insulating film (insulator) 120 and a conductive layer 121 formed of
a conductive material on both sides thereof. The conductive layer 121 has a single polarity
(positive It may be either negative polarity or negative polarity. The DC bias voltage is applied to
the fixed electrode 10A and the fixed electrode 10B superimposed on the DC bias voltage, and
the AC signals 18A output from the signal source 18 are inverted in phase with each other. , 18 B
are applied between the conductive layer 121 and the conductive layer 121. The insulating film
(insulator) 120 of the vibrating membrane 12 is a polymer material (poly ethylene terephthalate
(PET), poly ester, poly ethylene naphthalate (PEN), aramid, poly phenylene) excellent in insulation
resistance. -It is formed of sulfide (PPS) or the like.
[0043]
Further, the pair of fixed electrodes 10A and 10B have the same number and plural holes 14 at
the positions facing each other through the diaphragm 12, and between the conductive members
of the pair of fixed electrodes 10A and 10B, the signal source 18 The phase-inverted alternating
current signals 18A and 18B are applied to the
[0044]
Further, 17 forms a part of the pair of fixed electrodes 10A and 10B and has a function of
sandwiching the vibrating film 12 and an opposing electrode portion (conductive portion is
exposed) which is a portion on which the electrostatic force acts between the vibrating film 13
The counter electrode forming body having a function of forming the part 19), and a stepped
hole is formed by the through hole 14 of the fixed electrode 10A or 10B and the counter
electrode forming body 19.
A capacitor is formed on each of the counter electrode portion 19 and the electrode layer 121 of
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the fixed electrode 10A and the counter electrode portion 19 and the electrode layer 121 of the
fixed electrode 10B.
[0045]
An enlarged view of a portion X in FIG. 1 is shown in FIG. Although not shown in FIG. 1, as shown
in FIG. 2, an insulating film layer 20 is formed on the surface of the conductive portion 10 of the
fixed electrodes 10A and 10B including the counter electrode portion 20. Thereby, the vibrating
film 12 vibrates and discharge (insulation breakdown) when the conductive layer 121
approaches the conductive portion 10 of the fixed electrodes 10A and 10B is prevented, and the
insulating property between the vibrating film 12 and the fixed electrodes 10A and 10B It can be
secured.
[0046]
Further, the counter electrode forming body sandwiching the vibrating film 12 is formed of an
insulating material (liquid solder resist, photosensitive coating material, nonconductive paint,
electrodeposition material, etc.) as in the prior art. As a material which constitutes insulating film
layer 20, polyimide, an epoxy system polymer material, etc. are effective, and the dielectric
breakdown withstand voltage of about 500V is securable with the thickness 2-3 micrometers. In
addition, as shown in FIG. 3, in order to obtain higher insulation, an insulating coating layer is
formed on one surface of the fixed electrode (surface configured as the counter electrode portion
20) including the side surface inside the through hole 14 of the fixed electrodes 10A and 10B.
20A may be formed, or, as shown in FIG. 4, the insulating film layer 20B may be formed on the
entire surface of the fixed electrode including the side surface inside the through hole 14 of the
fixed electrode 10A, 10B.
[0047]
In the above configuration, the ultrasonic transducer 1 is output from the signal source 18 to the
conductive layers 121 and 121 of the diaphragm 12 by the DC bias power supply 16 to a DC
bias voltage of a single polarity (positive in this embodiment). The AC signals 18A and 18B
whose phases are mutually inverted are applied in a superimposed state. On the other hand,
alternating current signals 18A and 18B which are mutually phase-inverted from the signal
source 18 are applied to the pair of fixed electrodes 10A and 10B.
04-05-2019
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[0048]
As a result, in the positive half cycle of the AC signal 18A output from the signal source 18, a
positive voltage is applied to the fixed electrode 10A, so the conductive layer on the surface side
not sandwiched by the fixed electrodes of the vibrating film 12 An electrostatic repulsive force
acts on 121, and the conductive layer 121 on the surface side is pulled downward in FIG. At this
time, the alternating current signal 18B has a negative cycle, and a negative voltage is applied to
the opposite fixed electrode 10B. Therefore, an electrostatic attraction force acts on the
conductive layer 121 on the back surface side of the vibrating film 12 The conductive layer 121
on the back side is pulled further downward in FIG.
[0049]
Therefore, the film portion of the vibrating film 12 which is not held by the pair of fixed
electrodes 10A and 10B simultaneously receives electrostatic repulsion and electrostatic
repulsion in the same direction. The same applies to the negative half cycle of the alternating
current signal output from the signal source 18 as well, the conductive layer 121 on the front
side of the vibrating membrane 12 in FIG. Electrostatic repulsion acts on the conductive layer
121 in the upper part of FIG. 1, and the membrane portion of the diaphragm 12 not sandwiched
by the pair of fixed electrodes 10A and 10B simultaneously and in the same direction has
electrostatic repulsion. It receives electrostatic repulsion. In this manner, the direction in which
the electrostatic force acts alternately changes while the diaphragm 12 simultaneously and in the
same direction is subjected to electrostatic repulsion and electrostatic repulsion according to the
change in polarity of the AC signal, so that a large membrane vibration is generated. That is, it is
possible to generate an acoustic signal of a sound pressure level sufficient to obtain a parametric
array effect.
[0050]
As described above, 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
compared with the conventional ultrasonic transducer (Pull type) of which only the electrostatic
04-05-2019
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attraction acts on the vibrating film. Have the ability to meet.
[0051]
The frequency characteristic of the ultrasonic transducer according to the embodiment of the
present invention is shown in FIG. In the same figure, curve Q3 is the frequency characteristic of
the ultrasonic transducer which relates to this execution form. As is clear from the figure, it can
be seen that high sound pressure levels can be obtained over a wider frequency band as
compared to the frequency characteristics of the conventional broadband electrostatic ultrasonic
transducer. Specifically, it can be seen that a sound pressure level of 120 dB or more at which a
parametric effect can be obtained in a frequency band of 20 kHz to 120 kHz can be obtained.
[0052]
In the ultrasonic transducer 1 according to the embodiment of the present invention, the
vibrating membrane 12 of the thin film sandwiched between the pair of fixed electrodes 10A and
10B receives both electrostatic attraction and electrostatic repulsion, so that only large vibration
occurs. Because the symmetry of vibration is secured, high sound pressure can be generated over
a wide band.
[0053]
Next, the manufacturing process of the fixed electrode in the Push-Pull type electrostatic
ultrasonic transducer according to the embodiment of the present invention will be described
with reference to FIG. 5 and FIG.
Here, a manufacturing process of one fixed electrode of the pair of fixed electrodes in the PushPull type electrostatic ultrasonic transducer will be described. In these figures, a mask member
102 in which a pattern of a plurality of holes is formed is coated on a conductor 100 which is a
base material of a fixed electrode, and a through hole is formed by etching (first step: FIG. 5 (a ),
(B)). Here, copper and stainless steel are used as the conductor 100, but copper is preferable for
nickel electroforming.
[0054]
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Then, after the through holes 104 are formed, the mask member 102 is peeled off to obtain the
conductor 100 having the through holes 104 (second step: FIG. 5C). Here, the diameter of the
through hole 104 opened by the etching process is restricted in relation to the thickness. For
example, the minimum diameter of the through hole used in the ultrasonic transducer according
to the embodiment of the present invention is 0.25 mm, and the thickness of the through hole
having this diameter is 0.25 mm or less. Therefore, when a fixed electrode of 0.25 mm or more
in thickness is required, several sheets of metal plates having a thickness of 0.25 mm with
through holes are prepared in advance, and these are required. Then, metal bonding is performed
by thermocompression bonding or diffusion bonding to fabricate a fixed electrode of a desired
thickness.
[0055]
Next, an insulating film layer 106 having a predetermined film thickness is formed on one
surface of the conductor (metal plate) 100 in which the through holes 104 are formed, using a
vapor deposition method or a spin coating method (third process: FIG. 5 (d-1)). Alternatively, for
the conductor 100 in which the through hole 104 is formed, an insulating film layer of a
predetermined film thickness is formed on the entire surface of the conductor 100 including the
inner wall of the through hole 104 using the electrodeposition method Process: FIG. 5 (d-2). In
the subsequent steps, an insulating film of a predetermined thickness is formed on one side of
the conductor (metal plate) 100 in which the through holes 104 shown in FIG. 5 (d-1) are
formed, using the vapor deposition method or the spin coating method. Assuming that the
process of forming the layer 106 has been performed, the process of completing the fixed
electrode will be described.
[0056]
Next, the through hole 104 on the conductor 100 on which the insulating coating layer 106 is
formed and the mask member 108 for masking the region near the through hole 104 are placed
on the surface of the conductor 100 and the surface of the conductor 100 A counter electrode
forming material 110 for forming an insulating counter electrode forming body for exposing a
conductor portion facing the vibration film is set on the upper, and the squeegee 112 is moved
along the mask member 108 to be a counter electrode. The forming material 110 is applied to a
portion of the surface of the conductor 100 which is not masked by the mask member 108
(fourth step: FIGS. 6E and 6F).
[0057]
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The counter electrode forming material considered to be effective can be permanently configured
as a counter electrode forming body and is non-conductive, for example, a liquid solder resist for
a package generally used for a circuit board or a resist for a sand blast Such as masking ink used
as
In particular, solder resists for flexible printed circuit boards are relatively soft (HB to 3H in
pencil hardness), so they have excellent adhesion to metals and various conductors (such as
conductive resins), and they are polymer films. It is very effective for the sandwiching property of
the vibrating membrane consisting of
[0058]
In the fourth step, the mask member 108 is removed after the application of the opposing
electrode forming material 110 is completed, and the opposing electrode forming body 114
formed on the conductor 100 is dried to complete the desired fixed electrode (fifth electrode).
Process: FIG. 6 (g).
[0059]
Next, the effects of using the electrostatic ultrasonic transducer according to the embodiment of
the present invention will be described with reference to FIG.
(1)Sound pressure can be improved by improving electrostatic force. In the configuration
shown in FIG. 7B (the configuration of the electrostatic ultrasonic transducer proposed prior to
the application of the present application), the surface of the fixed electrode 10A (or 10B) on the
vibrating film 12 side of the conductive portion 10 and the vibrating film 12 The distance to the
conductive layer 121 is determined by the thickness T1 of the insulating layer 120 of the
vibrating film 12 and the thickness T2 of the counter electrode forming body 17. For example,
when the thickness T1 of the insulating layer 120 is 9 μm and the thickness T2 of the counter
electrode forming body 17 is 6 μm, the distance between the electrodes is 15 μm.
[0060]
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19
On the other hand, in the configuration of the present invention shown in FIG. 7A, the distance
between the surface of the conductive portion 10 on the vibrating film 12 side of the fixed
electrode 10A (or 10B) and the conductive layer 121 of the vibrating film 12 is the counter
electrode. It is determined by the thickness t1 of the formed body 17 and the thickness t2 of the
insulating film layer 20. Even when the thickness t1 of the counter electrode forming body 17 is
6 μm as in the configuration of FIG. 7A, the thickness t2 of the insulating film layer 20 may be
about 3 μm, so the distance between electrodes can be suppressed to 9 μm. The electrostatic
force obtained as a result becomes 2.77 times (square of ratio of distance) to the conventional
configuration, and the sound pressure is improved by 4 dB or more.
[0061]
(2) The reliability can be improved. In the configuration shown in FIG. 7B, when the insulating
layer 120 of the vibrating film 12 is broken (scratch, crack, etc.), the inner conductive layer
(metal deposition film) 121 is exposed, and the damaged portion is damaged by the vibration.
However, the dielectric breakdown may occur when approaching the bare counter electrode
portion. On the other hand, in the configuration of the present invention, the entire surface of the
conductive portion 10 constituting the fixed electrode 10A (or 10B) is treated with an insulating
film, whereby the conductive layer 121 of the vibrating film 12 including the counter electrode
portion The risk of direct contact with the conductive portion 10 of the fixed electrode 10A (or
10B) is avoided, and dielectric breakdown hardly occurs. Therefore, the reliability can be
improved.
[0062]
(3) Safety (insulation) can be secured. In the configuration shown in FIG. 7 (b), since the
conductive portion 10 constituting the fixed electrode 10A (or 10B) is exposed on both outer
surfaces, it has been necessary to put it in a case with a safety net or the like. On the other hand,
as described in the manufacturing process of the fixed electrode of the present invention, if the
insulating coating layer is formed on the entire surface of the conductor including the inner wall
of the through hole by using the electrodeposition method, A configuration not exposed to the
outside can be easily realized, and a highly safe electrostatic ultrasonic transducer can be
realized. As described above, according to the electrostatic ultrasonic transducer according to the
present embodiment, safety (insulation) can be secured.
[0063]
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20
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
electrostatic ultrasonic transducer (FIG. 1) according to the above-described embodiment of the
present invention as an ultrasonic transducer 55.
[0064]
In FIG. 8, the ultrasonic speaker according to this embodiment includes an audio frequency wave
oscillation source (signal source) 51 that generates a signal wave in an audio wave frequency
band, and a carrier wave that generates and outputs a carrier wave in an 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 provided. The modulator 53
modulates the carrier wave output from the carrier wave oscillation source 52 with the signal
wave in the audio wave frequency band output from the audio frequency wave oscillation source
51, and supplies it to the ultrasonic transducer 55 via the power amplifier 54. Do.
[0065]
In the above configuration, the carrier wave in the ultrasonic frequency band output from the
carrier wave oscillation source 52 is modulated by the modulator 53 by the signal wave output
from the audio frequency wave oscillation source 51, and the modulation signal amplified by the
power amplifier 54 is used. The ultrasonic transducer 55 is driven. As a result, the modulated
signal is converted to a sound wave of a finite amplitude level by the ultrasonic transducer 55,
and this sound wave is emitted into the medium (in air) and the sound noise in the original audio
frequency band by the nonlinear effect of the medium (air). Is self-regenerating.
[0066]
That is, since the sound wave is a compression wave propagating through the air as a medium, in
the process of propagation of the modulated ultrasonic waves, the dense part and the sparse part
of the air appear prominently. As the speed of sound is slowed, the modulation wave itself is
distorted, so that the waveform is separated into the carrier wave (ultrasonic frequency band),
and the signal wave (sound signal) in the audible wave frequency band is reproduced.
04-05-2019
21
[0067]
As described above, when high sound pressure broadband is secured, it can be used as a speaker
in various applications.
Ultrasonic waves are highly attenuated in the air and decay in proportion to the square of their
frequency. Therefore, when the carrier frequency (ultrasound) is low, it is possible to provide an
ultrasonic speaker having a low attenuation and having a beam shape that allows sound to reach
far. Conversely, if the carrier frequency is high, the attenuation is severe, so that the parametric
array effect does not occur sufficiently, and it is possible to provide an ultrasonic speaker in
which the sound spreads. These are very effective functions because the same ultrasonic speaker
can be used according to the application.
[0068]
In addition, dogs that often live with humans as pets can listen to sounds up to 40 kHz and cats
up to 100 kHz, so if you use a carrier frequency higher than that, there is no effect on pets. It
also has an advantage. In any case, being available at various frequencies brings many benefits.
[0069]
The ultrasonic speaker according to the embodiment of the present invention can generate an
acoustic signal with a sound pressure level high enough to obtain a parametric array effect over
a wide frequency band. Moreover, since it comprised using the electrostatic-type ultrasonic
transducer of the said structure, that is, the said vibrating film has a conductive layer on both
surfaces of an insulating film, and each vibration in the said, 1st, 2nd fixed electrode Since the
insulating film layer is formed on the film side, the distance between the fixed electrode and the
conductive layer of the vibrating film can be made shorter than before, and the electrostatic force
acting on the vibrating film can be improved. Can be improved.
[0070]
The electrostatic 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 or an ideal impulse. It can be used as a signal source or
04-05-2019
22
the like.
[0071]
FIG. 1 shows a configuration of an electrostatic ultrasonic transducer according to an
embodiment of the present invention.
FIG. 2 is an enlarged view of a portion X in the electrostatic ultrasonic transducer according to
the embodiment of the present invention shown in FIG. 1. The figure which shows the structure
of the principal part of the electrostatic-type ultrasonic transducer which concerns on other
embodiment of this invention. The figure which shows the structure of the principal part of the
electrostatic-type ultrasonic transducer which concerns on further another embodiment of this
invention. The flow chart which shows an example of the manufacturing process of the
electrostatic ultrasonic transducer concerning the embodiment of the present invention. The flow
chart which shows an example of the manufacturing process of the electrostatic ultrasonic
transducer concerning the embodiment of the present invention. The figure for demonstrating
the effect obtained by using the electrostatic-type ultrasonic transducer which concerns on
embodiment of this invention. FIG. 1 is a block diagram showing the configuration of an
ultrasonic speaker according to an embodiment of the present invention. The figure which shows
the structure of the conventional resonance type ultrasonic transducer. FIG. 8 is a diagram
showing a specific configuration of a conventional electrostatic broadband ultrasonic transducer.
The figure which showed the frequency characteristic of the electrostatic ultrasonic transducer
which concerns on embodiment of this invention with the frequency characteristic of the
conventional ultrasonic transducer. The figure which shows the structure of a Push-Pull type
electrostatic-type ultrasonic transducer.
Explanation of sign
[0072]
DESCRIPTION OF SYMBOLS 1 ... Electrostatic-type ultrasonic transducer, 10A, 10B ... Fixed
electrode, 12 ... Vibrating film, 14 ... Through hole, 16 ... DC bias power supply, 18 ... Signal
source, 51 ... Audio frequency wave oscillation source, 52 ... Carrier wave oscillation Source 53
Modulator 54 Power Amplifier 55 Ultrasonic Transducer 120 Insulating Film 121 Conducting
Layer.
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