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JP2007088680

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DESCRIPTION JP2007088680
PROBLEM TO BE SOLVED: To provide an electrostatic ultrasonic transducer ensuring the
electrical safety without the conductive part being exposed on the surface. 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 A vibrating membrane 12 having a conductive layer 121 sandwiched between the fixed
electrodes and a DC bias voltage applied to the conductive layer by a DC bias power supply 16, a
pair of fixed electrodes, and a holding member for holding the vibrating membrane. An
electrostatic ultrasonic transducer in which an alternating current signal is applied by the signal
source 16 between the pair of fixed electrodes, wherein a base material of the first and second
fixed electrodes is the non-conductor 10; A conductive film 20 is formed on the surface of the
non-conductive material to be the counter electrode unit 21 facing the vibrating film, and the
step 17 of the counter electrode unit is formed of an insulator. [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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1
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. 6 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
bimorph type ultrasonic transducer shown in FIG. 6 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. 6 described above, the electrostatic
ultrasonic transducer is conventionally known as a broadband oscillation type 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. 7 shows a specific
configuration of the broadband oscillation type ultrasonic transducer (Pull type).
[0005]
The ultrasonic transducer of the electrostatic type shown in FIG. 7 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. 7 are as shown by a curve Q1 in FIG. 8 by thus
forming an infinite number of capacitors having different sizes and depths of 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. 8, the frequency characteristic of the resonance type ultrasonic transducer has a
center frequency (resonance frequency of the piezoelectric ceramic) of, for example, 40 kHz and
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± 5 kHz with respect to the center frequency which is the maximum sound pressure. At a
frequency 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. 6, the electrostatic
ultrasonic transducer shown in FIG. 7 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. 8, the sound pressure is lower at 120 dB or less for the electrostatic
ultrasonic transducer compared to 130 dB or more for the resonant ultrasonic transducer 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)
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shown in FIG. 8 can almost solve the problems of the above-mentioned prior art, but it can cover
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, electrostatic force acts only in a direction to attract only to the fixed electrode side,
which corresponds to a vibrating film (corresponding to the upper electrode 132 in FIG. 7).
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. 9, the ultrasonic
transducer is sandwiched between a pair of fixed electrodes 10A and 10B using a base material
in which a through hole 14 is formed at a position facing the vibrating film 12 having the
conductive layer 121 as a conductive material. In the state where the DC bias voltage is applied
by the DC power supply 16, the AC signals 18A and 18B are applied by the signal source 18 to
the pair of fixed electrodes. Reference numeral 120 denotes an insulating film for forming the
vibrating film 12, and 17 denotes a part of the pair of fixed electrodes 10A and 10B, and has a
function of holding the vibrating film 12 and electrostatic force between the vibrating film 13
and Is a counter electrode forming body having a function of forming a counter electrode portion
19 which is a portion on which
[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 such a Push-Pull type electrostatic ultrasonic transducer, the base material of the
fixed electrode is a conductive material, and the conductive part is largely exposed on the
surface, so that it is in an extremely dangerous state. It was necessary to fit in a case with a safety
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net.
[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 ensuring the electrical safety
without the conductive portion being exposed on the surface, and a method of manufacturing the
same. I assume.
[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 conductive film sandwiched between the pair of fixed electrodes, and a vibrating film
to which a DC bias voltage is applied to the conductive layer, a pair of fixed electrodes, and a
holding film for holding the vibrating film A member, and an electrostatic ultrasonic transducer
to which an alternating current signal is applied between the pair of fixed electrodes, wherein the
base material of the first and second fixed electrodes is a non-conductive material, and the
vibration is A conductive film is formed on the surface of the non-conductive material to be a
counter electrode portion facing the film, and a step portion of the counter electrode portion is
formed of an insulator.
[0022]
In the electrostatic ultrasonic transducer of the present invention having the above configuration,
a plurality of through 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
an 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 applied state, the vibrating film sandwiched between the pair
of fixed electrodes has the polarity of the AC signal. In the direction according to, electrostatic
attraction force and electrostatic repulsion force are simultaneously received in the same
direction.
Therefore, not only the vibration of the vibrating membrane can be made sufficiently large to
obtain a parametric effect, but also the symmetry of the vibration is ensured, so that high sound
pressure can be generated over a wide frequency band.
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Furthermore, a base material of the first and second fixed electrodes is a non-conductive
material, and a conductive film is formed on the non-conductive surface to be a counter electrode
portion facing the vibrating film, and the counter electrode portion Since the step portion is
formed of an insulator, it is possible to realize an electrostatic ultrasonic transducer that secures
the electrical safety without the conductive portion being exposed on the surface of the
transducer.
[0023]
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. A vibrating
film to which a fixed electrode and a pair of fixed electrodes are sandwiched and having a
conductive layer, and a DC bias voltage is applied to the conductive layer, and a holding member
holding the pair of fixed electrodes and the vibrating film A method of manufacturing an
electrostatic ultrasonic transducer, wherein an alternating current signal is applied between the
pair of fixed electrodes, wherein the first and second fixed electrodes have the plurality of holes
in a non-conductive material. A first step of forming a through hole by sandblasting or etching, a
second step of removing the mask member after the through hole is formed, and Non-conductive
material with through holes After the third step of forming a metal thin film of a predetermined
thickness on the surface, and laminating a nonconductive photosensitive resist material on the
non-conductor on which the metal thin film is formed, the above-mentioned on the upper surface
of the photosensitive resist A mask member for masking the through hole and a region facing the
region in the vicinity of the through hole is placed on the upper surface of the photosensitive
resist, and a fourth step of exposing and exposing the mask member is removed and developed.
The method is characterized in that the metal thin film is manufactured by the fifth step of
forming a counter electrode forming body on a non-conductor formed on the surface.
[0024]
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 in a nonconductive
material. A first step of forming a through hole by sandblasting or etching, a second step of
peeling the mask member after the through hole is formed, and a nonconductive material in
which the through hole is formed After the third step of forming a metal thin film of a
predetermined thickness on one side, and laminating a nonconductive photosensitive resist
material on the nonconductor on which the metal thin film is formed, the above-mentioned on
the upper surface of the photosensitive resist A mask member for masking the through hole and
a region facing the region in the vicinity of the through hole is placed on the upper surface of the
04-05-2019
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photosensitive resist, and a fourth step of exposing and exposing the mask member is removed
and developed. , Said Genus thin film is fabricated by a fifth step of forming a counter electrode
formed body on non-conductive formed on the surface.
[0025]
According to the manufacturing method of the electrostatic ultrasonic transducer of the present
invention having the above 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. Thus, there is provided an electrostatic ultrasonic transducer capable of generating high
sound pressure over a wide frequency band.
Further, according to the manufacturing method of the electrostatic ultrasonic transducer of the
present invention having the above configuration, the base material of the fixed electrode is
made non-conductive, the counter electrode portion is formed of a metal deposition film, and the
step portion of the counter electrode portion Since the (counter electrode forming body) is
formed of an insulator, the conductive portion (voltage marking portion) of the fixed electrode is
not exposed to the surface, which is extremely safe electrically.
[0026]
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. A vibrating
film to which a fixed electrode and a pair of fixed electrodes are sandwiched and having a
conductive layer, and a DC bias voltage is applied to the conductive layer, and a holding member
holding the pair of fixed electrodes and the vibrating film A method of manufacturing an
electrostatic ultrasonic transducer having an AC signal applied between the pair of fixed
electrodes, wherein the first and second fixed electrodes pass through the plurality of nonconductive members. A first step of covering a mask member having a pattern of holes formed
thereon and forming a through hole by sandblasting or etching; and a second step of peeling the
mask member after the through hole is formed; Non-conductive in which the through hole is
formed A third step of forming a metal thin film having a predetermined film thickness on one
side of the metal layer, a through hole on the nonconductive layer on which the metal thin film is
formed, and a mask member for masking a region near the through hole. A squeegee is formed
by setting a counter electrode forming material for forming an insulating counter electrode
forming body which is a stepped portion of a counter electrode portion which is placed on the
surface and which faces the vibrating film on the non-conductor surface. In the fourth step of
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moving to apply the counter electrode forming material to a portion of the non-conductor surface
which is not masked by the mask member, and in the fourth step, the mask after the application
of the counter electrode forming material is completed And a fifth step of removing the member
and drying the counter electrode forming body formed on the non-conductive material.
[0027]
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 are
mask members in which a pattern of the plurality of through holes is formed in a non-conductive
material. A first step of coating and forming a through hole by sandblasting or etching, a second
step of peeling the mask member after the through hole is formed, and a non-conductive material
in which the through hole is formed A third step of forming a metal thin film having a
predetermined film thickness on one side of the metal layer, a through hole on the
nonconductive layer on which the metal thin film is formed, and a mask member for masking a
region near the through hole. A squeegee is formed by setting a counter electrode forming
material for forming an insulating counter electrode forming body which is a stepped portion of
a counter electrode portion which is placed on the surface and which faces the vibrating film on
the non-conductor surface. Move the counter electrode type Removing the mask member after
the application of the counter electrode forming material is completed in the fourth step of
applying the material on the portion of the non-conductive surface that is not masked by the
mask member, and in the fourth step; It manufactures by the 5th process of drying the counter
electrode formation body formed on the conductor.
[0028]
According to the manufacturing method of the electrostatic ultrasonic transducer of the present
invention having the above 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. Thus, there is provided an electrostatic ultrasonic transducer capable of generating high
sound pressure over a wide frequency band.
Further, according to the manufacturing method of the electrostatic ultrasonic transducer of the
present invention having the above configuration, the base material of the fixed electrode is
made non-conductive, the counter electrode portion is formed of a metal deposition film, and the
step portion of the counter electrode portion Since the (counter electrode forming body) is
formed of an insulator, the conductive portion (voltage marking portion) of the fixed electrode is
not exposed to the surface, which is extremely safe electrically.
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Furthermore, according to the manufacturing method of the electrostatic ultrasonic transducer of
the present invention having the above configuration, when using glass as a base material of the
fixed electrode, the screen printing method does not need to apply a large stress to the glass.
There is an effect that the risk of breaking the fixed electrode is cut with very little.
[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. A vibrating
film to which a fixed electrode and a pair of fixed electrodes are sandwiched and having a
conductive layer, and a DC bias voltage is applied to the conductive layer, and a holding member
holding the pair of fixed electrodes and the vibrating film A method of manufacturing an
electrostatic ultrasonic transducer, wherein an alternating current signal is applied between the
pair of fixed electrodes, wherein the first and second fixed electrodes are based on a nonconductive material, A through hole is formed in advance with a predetermined diameter and
pitch, and a conductive layer is formed on both of its both surfaces, and an outer peripheral
portion of the through hole is formed on one surface of the printed board coated with the resist
over the entire surface of the conductive layer. For stripping the resist at Mask for forming a first
step of applying a resist for a resist, and a pattern for masking a region other than the region
facing the outer peripheral portion of the through hole on the resist for peeling of a printed
substrate on which the resist for peeling is applied A second step of coating a member on the
peeling resist and performing exposure and development; and a third step of peeling the resist in
a portion not masked with the peeling resist by the resist peeling treatment; After the completion
of the third step, it is characterized in that it is manufactured by the fourth step of removing the
remaining peeling resist.
[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
have non-conductive materials as a base material, and through holes with a predetermined
diameter and pitch in advance. A peeling layer for peeling off the resist at the outer peripheral
portion of the through hole on one side of a printed substrate which is formed, the conductive
layer is formed on the entire surface, and the entire surface of the conductive layer is coated with
the resist A mask member having a first step of applying a resist, and a pattern for masking a
region other than the region facing the outer peripheral portion of the through hole on the
peeling resist of the printed substrate on which the peeling resist is applied A second step of
coating on the resist for stripping and performing exposure and development processing, and the
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above-mentioned portion of the portion not masked with the resist for stripping by resist
stripping processing. A third step of peeling off the resist, after the end third step, is
manufactured by a fourth step of removing the peeling the remaining resist.
[0031]
According to the manufacturing method of the electrostatic ultrasonic transducer of the present
invention having the above 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. Thus, there is provided an electrostatic ultrasonic transducer capable of generating high
sound pressure over a wide frequency band.
Further, according to the manufacturing method of the electrostatic ultrasonic transducer of the
present invention having the above configuration, the base material of the fixed electrode is
made non-conductive, the counter electrode portion is formed of a metal deposition film, and the
step portion of the counter electrode portion Since the (counter electrode forming body) is
formed of an insulator, the conductive portion (voltage marking portion) of the fixed electrode is
not exposed to the surface, which is extremely safe electrically.
Furthermore, according to the manufacturing method of the electrostatic ultrasonic transducer of
the present invention having the above configuration, since the printed circuit board to which the
conductive layer (copper foil) and the resist processing are applied in advance is used, the
number of manufacturing steps is small. And the manufacturing cost can be reduced.
[0032]
The ultrasonic speaker according to the present invention generates and outputs the electrostatic
ultrasonic transducer according to claim 1, a signal source for generating a signal wave of an
audio frequency band, and a carrier wave of an ultrasonic frequency band. Carrier wave supply
means, and modulation means for modulating the carrier wave with a signal wave of audio
frequency band outputted from the signal source, and the electrostatic ultrasonic transducer
comprises the first and second fixed elements. It is characterized in that it is driven by a
modulation signal outputted from the modulation means applied between the electrode and the
conductive layer of the vibrating membrane.
[0033]
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12
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 the electrode layer of the first and second fixed electrodes and the
diaphragm. And is applied and driven.
[0034]
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 the electrostatic ultrasonic transducer of the above configuration is used, that
is, in the electrostatic ultrasonic transducer, the base material of the first and second fixed
electrodes forming a pair is a nonconductive body, and the vibrating film is A conductive film is
formed on the surface of the non-conductive material to be the opposing electrode portion facing
the electrode, and the step portion of the opposing electrode portion is formed of an insulator, so
that the conductive portion is not exposed to the surface of the transducer Ultrasonic speaker
with high target safety can be realized.
[0035]
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.
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13
1 (A) shows the configuration of the electrostatic ultrasonic transducer, and FIG. 1 (B) is a view of
only one fixed electrode of the electrostatic ultrasonic transducer viewed from the vibrating film
side, and FIG. 1 (C) is The top view which fractured a part of electrostatic type ultrasonic
transducer is shown. 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 and
a pair of fixed electrodes, and a vibrating film 12 having a conductive layer 121 and a pair of
fixed electrodes. It has electrodes 10A and 10B and a member (not shown) for holding the
vibrating membrane 12.
[0036]
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 film 12 interposed
therebetween. In the pair of fixed electrodes 10A and 10B, the base material is the
nonconductive 10, and the conductive film 20 is formed on the surface of the nonconductive 10
serving as the opposite electrode facing the vibrating film 12, and the opposite electrode A
counter electrode forming body 17 to be a step portion of is formed of an insulator (for example,
any of a liquid solder resist, a photosensitive coating material, a nonconductive paint, an
electrodeposition material and the like).
[0037]
The vibrating film 12 is formed of an insulating film (insulator) 120 and has a conductive layer
121 formed of a conductive material. That is, in order to secure insulation with the conductive
film 20 provided on the fixed electrodes 10A and 10B, the vibrating film 12 has a metal
deposition layer (conductive layer) 121 serving as an electrode portion at the central portion,
and both surfaces thereof. A sandwich structure is formed by covering the film with an insulating
film 120 such as a polymer film excellent in insulation resistance.
[0038]
The conductive layer 121 in the vibrating film 12 may be either single polarity (positive or
negative) by the DC bias power supply 16. The DC bias voltage is applied to the conductive film
20 of the fixed electrode 10A and the fixed electrode 10B superimposed on the DC bias voltage
04-05-2019
14
and the phase inversion of each other output from the signal source 18 is performed. The
alternating current signals 18A and 18B are applied to the conductive layer 121.
[0039]
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.
[0040]
Reference numeral 17 denotes a part of the pair of fixed electrodes 10A and 10B, which has a
function of sandwiching the vibrating film 12 and an opposing electrode portion (conductive film
20 which is a portion where electrostatic force acts between the vibrating film 13). It is a counter
electrode forming body having a function of forming the exposed portion 21), 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 in the counter electrode portion 21 and the conductive layer 121 of the
fixed electrode 10A, and the counter electrode portion 21 and the electrode layer 121 of the
fixed electrode 10B, respectively.
[0041]
Here, the non-conductor 10, which is the base material of the fixed electrodes 10A and 10B, is
glass, glass epoxy, ceramics or the like, through holes 14 are provided in this, and an insulating
material is used to make the counter electrode larger in diameter than the through holes. By
forming the forming portion 17, it is possible to form the doughnut-shaped counter electrode
portion 21 (FIG. 1 (B)). Further, it is also possible to form the doughnut-shaped counter electrode
portion 21 by peeling the resist in a predetermined region from a printed circuit board (a singlesided board or a double-sided board) in which the through holes 14 are provided in advance.
[0042]
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15
In the above-described configuration, the ultrasonic transducers 1 are mutually output from the
signal source 18 to the conductive layer 121 of the vibrating membrane 12 by the DC bias power
supply 16 to a DC bias voltage of a single polarity (positive in this embodiment). The phaseinverted alternating current signals 18A and 18B 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.
[0043]
As a result, in the positive half cycle of the alternating current signal 18A output from the signal
source 18, a positive voltage is applied to the fixed electrode 10A. Electrostatic repulsion acts
and the surface portion 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, so
that an electrostatic attraction force acts on the back surface portion of the vibrating film 12, and
the back surface The part is pulled further downward in FIG.
[0044]
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. Similarly, for the negative half cycle of the alternating current
signal output from the signal source 18, the electrostatic attraction force is applied to the surface
portion of the vibrating film 12 in FIG. The electrostatic repulsive force acts on the upper side
and the upper side, and the film portion of the vibrating film 12 not sandwiched by the pair of
fixed electrodes 10A and 10B receives the electrostatic repulsive force and the electrostatic
attractive force simultaneously and in the same direction. In this manner, the direction in which
the electrostatic force acts alternately changes while the diaphragm 12 simultaneously and in the
same direction receives electrostatic repulsion and electrostatic attraction in accordance with the
change in polarity of the AC signal, so that the large film Vibration, ie an acoustic signal at a
sound pressure level sufficient to obtain a parametric array effect, can be generated.
[0045]
According to the electrostatic ultrasonic transducer according to the embodiment of the present
invention, the base material of the first and second fixed electrodes is a non-conductive material,
and the non-conductive surface serving as an opposing electrode portion facing the vibrating film
Since the conductive film is formed and the step portion of the counter electrode portion is
04-05-2019
16
formed of an insulator, an electrostatic ultrasonic transducer is realized which secures the
electrical safety without the conductive portion being exposed on the surface of the transducer.
be able to.
[0046]
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 attraction acts on the vibrating film. Have
the ability to meet.
[0047]
The frequency characteristics of the ultrasonic transducer according to the embodiment of the
present invention are shown in FIG. In the figure, the curve Q3 is the frequency characteristic of
the inducer according to the present embodiment. 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.
[0048]
In the electrostatic ultrasonic transducer 1 according to the embodiment of the present
invention, the vibration film 12 of the thin film sandwiched between the pair of fixed electrodes
10A and 10B receives both the electrostatic attraction force and the electrostatic repulsion force.
Not only generation but also symmetry of vibration is ensured, so high sound pressure can be
generated over a wide band.
[0049]
04-05-2019
17
Next, an example of 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.
The fixed electrodes in conventional electrostatic ultrasonic transducers are manufactured by
covering a metal plate, which is a conductive material, with a mask material to form through
holes by etching, and laminating and bonding these by diffusion bonding or thermocompression
bonding. . On the other hand, in the manufacturing process of the fixed electrode made of the
non-conductive material in the electrostatic ultrasonic transducer according to the embodiment
of the present invention, the glass plate 200 is used as the non-conductive material instead of the
metal plate (FIG. 2 (a)) ).
[0050]
A sand blast method or an etching method is applied to this glass plate 200 to process through
holes. The sandblasting method will be described as an example. A plurality of mask members
202 having through-hole patterns formed of a resist material for sandblasting are coated on a
nonconductive glass plate 200, and a plurality of abrasives are applied to the glass plate 200 by
air blasting or shot blasting. The through holes 204 are formed (first step: FIG. 2 (b)). After the
through holes 204 are formed, the mask member 202 formed of a resist material for
sandblasting is peeled off to obtain the base member of the fixed electrode composed of the
nonconductive body 200 having the through holes 204 (second step) : FIG.2 (c).
[0051]
A metal (for example, aluminum, nickel, copper or the like) is vacuum deposited on one side of
the base member to form a metal thin film 206 having a predetermined film thickness to be a
counter electrode (third step: FIG. 2D). Thus, on the glass plate 200 in which the through holes
204 and the metal thin film 206 are formed, in the next step, a step (counter electrode forming
body) constituting the counter electrode portion is formed. In this process, a resist material or
coating material that can form a permanent structure and is nonconductive is used. Resist
materials considered to be effective are photosensitive films for packaging and photosensitive
polyimide films used for printed circuit boards.
04-05-2019
18
[0052]
After laminating the resist film 208 and the metal thin film 206 having the through holes 204 on
the surface of the glass plate 200, the resist film 208 is covered with the mask material 210 for
forming the counter electrode portion and exposed. And by performing development, only a
counter electrode surface is exposed and a nonelectroconductive layer is formed in the other part
(the 4th, 5th processes: FIG.2 (e), (f)). The fixed electrode produced in this manner is electrically
very safe without the voltage application part being exposed on the surface.
[0053]
Further, although the above description (content of FIG. 2) is the case where the
photolithography method is applied to the resist film, a method of applying the screen printing
method to the liquid resist is also effective. For example, a mask material used as a solder resist
for packages generally used in printed circuit boards or a resist for sand blasting is simply
applied by screen printing with a uniform thickness using a plate for forming a counter electrode
portion. Is possible.
[0054]
Next, another example of 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. A manufacturing process of a non-conductive fixed electrode in
the case of using the screen printing method will be described based on FIG. The process of
producing the intermediate of the fixed electrode consisting of the non-conductive body (glass
plate) 200 in which the through hole 204 and the metal thin film 206 are formed is exactly the
same as the example shown in FIG. And the redundant description is omitted (first to third steps:
FIGS. 3 (a) to 3 (d)).
[0055]
A through hole on a glass plate 200 as a nonconductive body in which a metal thin film 206 is
formed and a mask member 208 which is a screen plate for masking a region near the through
hole is formed on the surface of the glass plate 200 on which the metal thin film 206 is formed.
04-05-2019
19
And a counter electrode forming material 210 for forming an insulating counter electrode
forming body which is a step portion of the counter electrode portion facing the vibrating film on
the surface of the glass plate 200. Next, the squeegee 212 is moved to apply the counter
electrode forming material 210 to a portion of the surface of the glass plate 200 on which the
metal thin film 206 is formed, which is not masked by the mask member 208 (fourth step: FIG.
3E). .
[0056]
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, as a liquid solder resist
for a package generally used for a circuit board or a resist for sand blasting It is a masking ink
etc. used. In particular, since the solder resist for flexible printed circuit boards is relatively soft
(hardness of pencil is about HB), it has excellent adhesion strength to glass, various metals and
resin materials, and sandwiching the vibrating film made of polymer film Very effective in sex.
[0057]
Subsequently, when the mask member (screen plate) 208 is removed after the application of the
counter electrode forming material 210 is completed, the counter electrode forming body 214
which is a nonconductive layer remains in the other part except the counter electrode portion.
Next, a desired fixed electrode is completed by drying the counter electrode forming body 214
formed on the glass plate 200 (fifth step: FIG. 3F). As mentioned above, in these manufacturing
methods mentioned above, the amount of level | step differences of the counter electrode
formation body 214 which can be formed can be selected comparatively freely in the range of 5
micrometers-40 micrometers, and flatness is very good with 10% or less of thickness.
[0058]
When photolithography is applied to the resist film, there is a risk that the glass plate may be
damaged when laminating the resist film, but since the screen printing method does not need to
apply a large stress to the glass, the damage is caused. It is advantageous in that the risk of doing
so can be extremely reduced.
[0059]
04-05-2019
20
Moreover, when using glass epoxy or ceramics instead of a metal plate, a base member is
produced using the shaping | molding die for shape | molding as a plate with a through-hole of a
predetermined | prescribed hole diameter, One side of this base member A metal (eg, aluminum,
nickel, copper, etc.) is vacuum deposited to form a metal thin film to be a counter electrode.
Thereafter, as described based on FIG. 3, the desired fixed electrode is finished using the screen
printing method.
[0060]
Furthermore, the fixed material can be manufactured by peeling the resist material of a
predetermined place with respect to the universal printed circuit board to which the copper foil
and the resist process were given beforehand, and forming a counter electrode part. Still another
example of 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.
[0061]
The manufacturing process of the fixed electrode using a printed circuit board is demonstrated
based on FIG. In the figure, through holes 310 are provided in advance in a printed circuit board
30 using Bakelite or glass epoxy material as the non-conductor 300 as a predetermined diameter
and pitch (preferably in a honeycomb arrangement). A conductive layer 301 is formed of copper
foil on the entire surface of the printed board 30, and the entire surface of the conductive layer
301 is covered with a resist (synthetic resin film) 302 (FIG. 4 (a)) (FIG. The above is the
configuration of a general printed circuit board).
[0062]
Here, the thickness of the conductive layer (copper foil) 301 is not particularly specified, and
may be 35 μm or 70 μm which is generally used in a power supply system. On the other hand,
the thickness of the resist (synthetic resin film) 302 is preferably about 5 to 10 μm which is
effective as the thickness of the counter electrode portion and which can be realized by a screen
04-05-2019
21
printing method generally used as a resist processing method. A peeling resist 303 for peeling
the resist 302 on the outer peripheral portion of the through hole is applied to one surface of the
printed board 30 (first step: FIG. 4B).
[0063]
Next, the mask member 304 on which the pattern for masking the area other than the area
facing the outer peripheral part of the through hole 310 on the peeling resist 303 of the printed
substrate 30 on which the peeling resist 303 is applied is formed is the peeling resist 303 When
the film is coated and exposed and developed, the peeling resist 303 remains in the area other
than the area to be peeled. (Second step: FIG. 4 (b), (c)). Peel off the resist 302 in a portion not
masked with the peeling resist 303 by the resist peeling treatment (third step: FIG. 4D)
[0064]
After completion of the third step, the remaining peeling resist 303 is removed. When the
peeling resist is removed, the resist 302 which has not been peeled remains as the opposite
electrode forming body 305, and the fixed electrode using the printed circuit board as a base is
completed. (Fourth step: FIG. 4 (e)). The fixed electrode formed in this manner is electrically very
sensitive because the resist (synthetic resin film) 302 is still formed on the entire back surface
exposed to the outside (the surface not subjected to the resist peeling process). It's safe. As
described above, according to the method of manufacturing the electrostatic ultrasonic
transducer according to the embodiment of the present invention, the base material of the fixed
electrode is formed of a non-conductive material, and the conductive processing is performed
only on necessary portions. The site to which the high voltage is applied is not exposed to the
surface, and an electrically very safe electrostatic ultrasonic transducer is obtained.
[0065]
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.
04-05-2019
22
[0066]
In FIG. 5, the ultrasonic speaker according to the present embodiment includes an audio
frequency wave oscillation source (signal source) 51 for generating a signal wave in the audio
wave frequency band, and a carrier wave for generating and outputting 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
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.
[0067]
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.
[0068]
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.
[0069]
As described above, when high sound pressure broadband is secured, it can be used as a speaker
in various applications.
04-05-2019
23
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.
[0070]
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.
[0071]
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. Further, since the ultrasonic speaker is configured using the electrostatic
ultrasonic transducer having the above configuration, that is, the base material of the first and
second fixed electrodes forming a pair is made to be a non-conductive material, and it is opposed
to the diaphragm A conductive film is formed on the non-conductive surface which is to be the
electrode portion, and the step portion of the counter electrode portion is formed of an insulator,
so that the electrical safety without the conductive portion being exposed on the surface of the
transducer It is possible to realize the secured ultrasonic speaker.
[0072]
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
the like.
[0073]
04-05-2019
24
FIG. 1 shows a configuration of an electrostatic ultrasonic transducer according to an
embodiment of the present invention.
FIG. 7 is a process chart showing an example of a manufacturing process of a fixed electrode in a
Push-Pull type electrostatic ultrasonic transducer according to an embodiment of the present
invention. FIG. 8 is a process chart showing another example of the manufacturing process of the
fixed electrode in the Push-Pull type electrostatic ultrasonic transducer according to the
embodiment of the present invention. FIG. 8 is a process chart showing still another example of
the manufacturing process of the fixed electrode in the Push-Pull type electrostatic ultrasonic
transducer according to the embodiment of the present 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
[0074]
DESCRIPTION OF SYMBOLS 1 ... electrostatic-type ultrasonic transducer, 10A, 10B ... fixed
electrode, 12 ... vibrating membrane, 14 ... through hole, 16 ... DC bias power supply, 17 ...
counter electrode formation body (step part) 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.
04-05-2019
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