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JP2009105934

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DESCRIPTION JP2009105934
The object of the present invention is to provide an electrostatic ultrasonic transducer capable of
achieving low power consumption and capable of obtaining a high sound pressure and a voltage
applied between electrodes lower than that of the prior art. A first electrode (10A) having a
through hole (14), a second electrode (10B) having a through hole paired with the through hole
of the first electrode, and the first and second electrodes A vibrating film 12 is sandwiched
between a pair of electrodes and has an electrode layer 121, and a DC bias voltage is applied to
the electrode layer, and an electrode layer 101 is formed on the periphery of the through holes
of the pair of electrodes. An alternating current signal is applied between the pair of electrodes
and the electrode layer of the vibrating membrane. [Selected figure] Figure 1
Ultrasonic speaker, sound signal reproduction method, superdirective sound system
[0001]
The present invention relates to a directional electrostatic ultrasonic transducer that generates a
constant high sound pressure over a wide frequency band, a directional ultrasonic speaker using
the same, an audio signal reproduction method, and The present invention relates to a directional
acoustic system and a display device.
[0002]
Most conventional ultrasonic transducers as directional sharp acoustic radiation devices are
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. 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
bimorph 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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2
[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. 9 are as shown by curve Q1 in FIG. 10 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 having the above configuration, a rectangular wave signal (50 to
150 Vp-p) is applied between the upper electrode 132 and the lower electrode 133 in a state
where a DC bias voltage is applied to the upper electrode 132. 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
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kHz, ± 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) .
[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 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, and the dense part 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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4
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. 10 can almost solve the problems of the above-mentioned prior art, but it can
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cover a wide band but the demodulated sound is sufficient. There was a problem that the
absolute sound pressure was insufficient to achieve a good volume. Further, in the pull-type
electrostatic ultrasonic transducer, the electrostatic force works only in the direction of attracting
the electrode to the fixed electrode side, and the diaphragm (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]
On the other hand, we have already proposed an electrostatic ultrasonic transducer capable of
generating an acoustic signal at a sound pressure level high enough to obtain a parametric array
effect over a wide frequency band (see Patent Document 3). . The configuration of this
electrostatic ultrasonic transducer is shown in FIG. FIG. 12 (A) shows the configuration of the
electrostatic ultrasonic transducer, and FIG. 12 (B) shows a plan view of a part of the electrostatic
ultrasonic transducer. In FIG. 12, the electrostatic ultrasonic transducer 1 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 has an electrode layer 121. The
vibrating membrane 12 and a member (not shown) for holding the pair of fixed electrodes 10A
and 10B and the vibrating membrane 12 are included.
[0018]
The vibrating film 12 is formed of an insulator (insulating layer) 120 and has an electrode layer
121 formed of a conductive material. The electrode layer 121 has a single polarity (positive
polarity) by the DC bias power supply 16. However, any one of negative polarity may be used.
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 electrode layer 121 and the
electrode layer 121.
[0019]
Further, the pair of fixed electrodes 10A and 10B have the same number and a plurality of
through holes 14 at the positions facing each other through the vibrating film 12, and between
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the conductive members of the pair of fixed electrodes 10A and 10B is a signal source 18 The
alternating current signals 18A and 18B whose phases are mutually inverted are applied. 16 is a
DC bias power supply. The fixed electrode 10A and the electrode layer 121, and the fixed
electrode 10B and the electrode layer 121 each have a capacitor. A configuration of a control
unit that controls the signal source 18 and the DC bias power supply 16 and a storage unit in
which a table indicating control characteristics of the control unit is stored are omitted in FIG. 12.
The electrostatic ultrasonic transducer 1 is sandwiched between a pair of fixed electrodes 10A
and 10B in which through holes are formed at opposing positions of a vibrating film 12 having a
conductive layer 121. The alternating current signals 18A and 18B are applied from the signal
source 18 to the pair of fixed electrodes 10A and 10B in the state where the bias voltage is
applied.
[0020]
This electrostatic ultrasonic transducer is referred to as a Push-Pull type electrostatic ultrasonic
transducer, and the vibrating film sandwiched by a pair of fixed electrodes has an electrostatic
attraction force in the direction according to the polarity of the AC signal. Because the vibration
of the vibrating membrane can be made sufficiently large to obtain the parametric array effect
because the vibration and electrostatic repulsion are simultaneously received in the same
direction and in the same direction, the symmetry of the vibration is secured. High sound
pressure can be generated over a wide frequency band as compared to a pull-type electrostatic
ultrasonic transducer.
[0021]
As described above, as an ultrasonic transducer applied to a directional acoustic radiation device
(for example, an ultrasonic speaker), as described above, a piezoelectric method and an
electrostatic method have been proposed. Since the resonance point is sharp and it is difficult to
broaden the frequency band, there is a drawback that the sound reproducibility is poor (see
Patent Documents 4 and 5).
On the other hand, the electrostatic type has the advantage that the resonance of the diaphragm
itself is not sharp, and the use of the air column resonance phenomenon of the acoustic tube
enables wide band and excellent sound reproduction (good sound quality). (See Patent Document
3).
[0022]
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JP-A-2000-50387 JP-A-2000-50392 JP-A-2005-354472 JP-A-61-296897 JP-A-2000-287297
[0023]
However, when applying an ultrasonic transducer to an ultrasonic speaker, the output sound
pressure of the ultrasonic transducer is required to be high, but even if the ultrasonic transducer
of the electrostatic type that can obtain a relatively high sound pressure is further high-pitched
Pressure was desired.
Furthermore, in the electrostatic type ultrasonic transducer, in order to obtain a high sound
pressure output, a high voltage of 200 V or more is required for the voltage applied between the
electrodes, and it has been a problem to be solved to lower the voltage.
[0024]
The present invention has been made in view of such circumstances, and it is an electrostatic
ultrasonic transducer which achieves low power consumption and can obtain high sound
pressure with a voltage applied between electrodes lower than that of the prior art. It is an object
of the present invention to provide an ultrasonic speaker, an audio signal reproduction method, a
superdirective acoustic system and a display device using the same.
[0025]
In order to achieve the above object, an electrostatic ultrasonic transducer according to the
present invention comprises a first electrode having a through hole, a second electrode having a
through hole, the through hole of the first electrode, and the first through hole of the first
electrode. The through holes of the two electrodes are arranged in pairs, and are sandwiched
between a pair of electrodes consisting of the first electrode and the second electrode, and have
an electrode layer, and a DC bias is applied to the electrode layer A vibrating membrane to which
a voltage is applied, and the pair of electrodes has an electrode layer at a position located on the
peripheral edge portion of the through hole, and between the pair of electrodes and the electrode
layer of the vibrating membrane It is characterized in that an alternating current signal is
applied.
Here, in the specification and claims of the present application, the through hole refers to a
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8
columnar space through which a sound wave generated in the thickness direction of the first
electrode and the second electrode passes. Do.
[0026]
In the electrostatic ultrasonic transducer (Push-Pull type ultrasonic transducer) of the present
invention having the above-described configuration, the pair of electrodes is located at the
peripheral edge of the through hole, which is a portion necessary for applying electrostatic force.
An electrode layer is formed at the place where the Thereby, the electrode layer area of the pair
of electrodes can be reduced, and the capacitance formed by the pair of electrodes and the
electrode layer of the vibrating membrane can be reduced. Therefore, when the electrostatic
ultrasonic transducer is used as a capacitive load, the load impedance is increased, and flows
between each of the pair of electrodes in the electrostatic ultrasonic transducer and the electrode
layer of the vibrating membrane. The current is reduced, and voltage reduction and power
consumption can be achieved at the time of driving the electrostatic ultrasonic transducer.
[0027]
In the electrostatic ultrasonic transducer according to the present invention, the first electrode
having a through hole, the second electrode having a through hole, the through hole of the first
electrode, and the second electrode of the second electrode A through hole is disposed to form a
pair and is sandwiched between a pair of electrodes consisting of the first electrode and the
second electrode, and has an electrode layer, and a DC bias voltage is applied to the electrode
layer A vibrating membrane, the base material of the pair of electrodes is a non-conductive
material, and the pair of electrodes has a stepped portion at the periphery of the through hole,
and is opposed to the electrode layer of the vibrating membrane An electrode layer is provided
on the surface of the step portion, and an alternating current signal is applied between the pair
of electrodes and the electrode layer of the vibrating membrane.
[0028]
In the electrostatic ultrasonic transducer (Push-Pull type ultrasonic transducer) of the present
invention configured as described above, the base material of the pair of electrodes is a nonconductive material, and the peripheral portion of the through hole of the pair of electrodes is It
has a step, and has an electrode layer on the surface of the step facing the electrode layer of the
vibrating membrane.
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Thereby, the electrode layer area of the pair of electrodes can be reduced, and the capacitance
formed by the pair of electrodes and the electrode layer of the vibrating membrane can be
reduced. Therefore, when the electrostatic ultrasonic transducer is used as a capacitive load, the
load impedance is increased, and flows between each of the pair of electrodes in the electrostatic
ultrasonic transducer and the electrode layer of the vibrating membrane. The current is reduced,
and voltage reduction and power consumption can be achieved at the time of driving the
electrostatic ultrasonic transducer.
[0029]
In the electrostatic ultrasonic transducer according to the present invention, the first electrode
having a through hole, the second electrode having a through hole, the through hole of the first
electrode, and the second electrode of the second electrode A through hole is disposed to form a
pair and is sandwiched between a pair of electrodes consisting of the first electrode and the
second electrode, and has an electrode layer, and a DC bias voltage is applied to the electrode
layer The base material of the pair of electrodes is a conductive material, and the pair of
electrodes has a convex shape only in the electrode portion, and the base material having the
through hole, and the insertion hole It consists of an empty non-conductive member, and the
convex-shaped electrode portion of the base material is fitted in the insertion hole of the nonconductive member, and the electrode layer of the pair of electrodes and the vibrating membrane
And an AC signal is applied between them.
[0030]
In the electrostatic ultrasonic transducer (Push-Pull type ultrasonic transducer) of the present
invention configured as described above, the base material of the pair of electrodes is a
conductive material, and each of the pair of electrodes is the vibrating film Only the electrode
portion for applying an electrostatic force so as to increase the distance to the electrode layer is
formed in a convex shape, and comprises the base material having a through hole, and a
nonconductive member having a through hole. The convex-shaped electrode portion of the base
material is integrally formed by being fitted to the insertion hole of the nonconductive member.
This makes it possible to increase the distance between the electrode layer of the pair of
electrodes and the electrode layer of the vibrating film other than the portion to which
electrostatic force is applied in the pair of electrodes, and the pair of electrodes and the vibrating
film The capacitance formed with the electrode layer of the above can be reduced. Therefore,
when the electrostatic ultrasonic transducer is used as a capacitive load, the load impedance is
04-05-2019
10
increased, and flows between each of the pair of electrodes in the electrostatic ultrasonic
transducer and the electrode layer of the vibrating membrane. The current is reduced, and
voltage reduction and power consumption can be achieved at the time of driving the electrostatic
ultrasonic transducer.
[0031]
In the electrostatic ultrasonic transducer according to the present invention, the first electrode
having a through hole, the second electrode having a through hole, the through hole of the first
electrode, and the second electrode of the second electrode A through hole is disposed to form a
pair and is sandwiched between a pair of electrodes consisting of the first electrode and the
second electrode, and has an electrode layer, and a DC bias voltage is applied to the electrode
layer The pair of electrodes includes an electrode layer at a location located inside the through
hole, and an alternating current signal is applied between the pair of electrodes and the electrode
layer of the diaphragm. It is characterized by Here, in the present specification and claims, the
inside of the through hole refers to the inside of a columnar space through which the sound wave
generated in the thickness direction of the first electrode and the second electrode passes. It shall
be pointed.
[0032]
In the electrostatic ultrasonic transducer (Push-Pull type ultrasonic transducer) of the present
invention configured as described above, the pair of electrodes is located inside the through hole,
which is a portion necessary for applying an electrostatic force. It has an electrode layer in the
place. Thereby, the electrode layer area of the pair of electrodes can be reduced, and the
capacitance formed by the pair of electrodes and the electrode layer of the vibrating membrane
can be reduced. Therefore, when the electrostatic ultrasonic transducer is used as a capacitive
load, the load impedance is increased, and flows between each of the pair of electrodes in the
electrostatic ultrasonic transducer and the electrode layer of the vibrating membrane. The
current is reduced, and voltage reduction and power consumption can be achieved at the time of
driving the electrostatic ultrasonic transducer.
[0033]
In the electrostatic ultrasonic transducer according to the present invention, the first electrode
having a through hole, the second electrode having a through hole, the through hole of the first
electrode, and the second electrode of the second electrode A through hole is disposed to form a
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pair and is sandwiched between a pair of electrodes consisting of the first electrode and the
second electrode, and has an electrode layer, and a DC bias voltage is applied to the electrode
layer And a base material of the pair of electrodes is a non-conductive material, and the pair of
electrodes is positioned inside the through hole and is a bridge-like base facing the electrode
layer of the vibrating film. An electrode layer is provided on the surface of the material portion,
and an alternating current signal is applied between the pair of electrodes and the electrode layer
of the vibrating membrane.
[0034]
In the electrostatic ultrasonic transducer (Push-Pull type ultrasonic transducer) of the present
invention configured as described above, the base material of the pair of electrodes is a nonconductive material, and is positioned inside the through hole of the pair of electrodes And an
electrode layer is formed on the surface of the base material portion formed in a bridge shape so
as to face the electrode layer of the vibrating membrane.
Thereby, the electrode layer area of the pair of electrodes can be reduced, and the capacitance
formed by the pair of electrodes and the electrode layer of the vibrating membrane can be
reduced. Therefore, when the electrostatic ultrasonic transducer is used as a capacitive load, the
load impedance is increased, and flows between each of the pair of electrodes in the electrostatic
ultrasonic transducer and the electrode layer of the vibrating membrane. The current is reduced,
and voltage reduction and power consumption can be achieved at the time of driving the
electrostatic ultrasonic transducer.
[0035]
In the electrostatic ultrasonic transducer according to the present invention, the first electrode
having a through hole, the second electrode having a through hole, the through hole of the first
electrode, and the second electrode of the second electrode A through hole is disposed to form a
pair and is sandwiched between a pair of electrodes consisting of the first electrode and the
second electrode, and has an electrode layer, and a DC bias voltage is applied to the electrode
layer The base material of the pair of electrodes is a conductive material, and the pair of
electrodes is formed in a bridge shape so that only the electrode portion has a convex shape and
faces the electrode layer of the diaphragm. The base material and the non-conductive member
having an insertion hole formed therein, wherein the convex electrode part of the base material
is fitted into the insertion hole of the non-conductive member, and the pair AC signal is applied
between the electrode of the electrode and the electrode layer of the vibrating membrane And
features.
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[0036]
In the electrostatic ultrasonic transducer (Push-Pull type ultrasonic transducer) according to the
present invention, the base material of the pair of electrodes is a conductive material, and the
pair of electrodes are electrodes of the vibrating film. Only the electrode portion for applying an
electrostatic force so as to increase the distance to the layer has a convex shape, and the base
material formed in a bridge shape so as to face the electrode layer of the vibrating film, and an
open hole The non-conductive member is integrally formed by fitting the convex-shaped
electrode portion of the base material into the insertion hole of the non-conductive member.
This makes it possible to increase the distance between the electrode layer of the pair of
electrodes and the electrode layer of the vibrating film other than the portion to which
electrostatic force is applied in the pair of electrodes, and the pair of electrodes and the vibrating
film The capacitance formed with the electrode layer of the above can be reduced. Therefore,
when the electrostatic ultrasonic transducer is used as a capacitive load, the load impedance is
increased, and flows between each of the pair of electrodes in the electrostatic ultrasonic
transducer and the electrode layer of the vibrating membrane. The current is reduced, and
voltage reduction and power consumption can be achieved at the time of driving the electrostatic
ultrasonic transducer.
[0037]
Further, in the ultrasonic speaker according to the present invention, a first electrode having a
through hole, a second electrode having a through hole, the through hole of the first electrode,
and the through hole of the second electrode Are arranged in a pair and are sandwiched between
a pair of electrodes consisting of the first electrode and the second electrode, and have an
electrode layer, and a vibrating film to which a DC bias voltage is applied to the electrode layer
An electrostatic type in which an alternating current signal is applied between the pair of
electrodes and the electrode layer of the vibrating film. Ultrasonic transducer, signal source for
generating signal wave in audio frequency band, carrier wave supply means for generating and
outputting carrier wave in ultrasonic frequency band, and audio frequency output from the signal
source for the carrier wave And modulation means for modulating the signal wave of the Serial
electrostatic ultrasonic transducer, characterized in that it is driven by a modulated signal output
from said modulation means is applied between the electrode layer of the vibrating film and the
electrode.
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[0038]
In the ultrasonic speaker of the present invention having the above configuration, in the pair of
electrodes in the electrostatic ultrasonic transducer to be used, a portion located at the
peripheral portion of the through hole, which is a portion necessary for applying an electrostatic
force. Since the electrode layer is provided, the area of the electrode layer of the pair of
electrodes can be reduced, and the capacitance formed by the pair of electrodes and the
electrode layer of the vibrating membrane can be reduced.
Therefore, when the electrostatic ultrasonic transducer is used as a capacitive load, the load
impedance is increased, and flows between each of the pair of electrodes in the electrostatic
ultrasonic transducer and the electrode layer of the vibrating membrane. The current is reduced,
and voltage reduction and power consumption can be achieved at the time of driving the
electrostatic ultrasonic transducer. That is, the same sound pressure as that of the conventional
ultrasonic speaker can be generated with less energy, and the power consumption of the
ultrasonic speaker can be reduced.
[0039]
Further, according to the sound signal reproducing method by the electrostatic ultrasonic
transducer of the present invention, a first electrode having a through hole, a second electrode
having a through hole, the through hole of the first electrode, and the first through hole of the
first electrode The through holes of the two electrodes are arranged in pairs, and are sandwiched
between a pair of electrodes consisting of the first electrode and the second electrode, and have
an electrode layer, and a DC bias is applied to the electrode layer The pair of electrodes includes
an electrode layer at a position located at the periphery of the through hole, and an alternating
current is applied between the pair of electrodes and the electrode layer of the diaphragm. Using
an electrostatic ultrasonic transducer to which a signal is applied, generating a signal wave of an
audio frequency band by the signal source, and generating and outputting a carrier wave of an
ultrasonic frequency band by the carrier wave supply means And the modulation means A step of
generating a modulation signal in which the wave is modulated by the signal wave in the audio
frequency band, and applying the modulation signal between the electrode and the electrode
layer of the vibrating membrane to form the electrostatic ultrasonic transducer And a driving
step.
[0040]
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In the sound signal reproduction method of the electrostatic ultrasonic transducer including such
a procedure, the signal source generates a signal wave of an audio frequency band, and the
carrier wave source generates a carrier wave of an ultrasonic frequency band, and outputs Be
done.
Then, the carrier wave is modulated by the signal wave in the audio frequency band by the
modulation means, and this modulation signal is applied between the electrode and the electrode
layer of the vibrating film to drive the electrostatic ultrasonic transducer. As a result, the
electrostatic ultrasonic transducer of the above configuration allows the voltage applied between
the electrodes to be low and increase the film vibration, and the acoustic signal has a sound
pressure level high enough to obtain the parametric array effect over a wide frequency band. Can
be output to reproduce an audio signal.
[0041]
Further, in the superdirective acoustic system of the present invention, a first electrode having a
through hole, a second electrode having a through hole, the through hole of the first electrode,
and the penetration of the second electrode. A vibration is disposed so as to form a pair with a
hole and is sandwiched between a pair of electrodes consisting of the first electrode and the
second electrode, and has an electrode layer, and a DC bias voltage is applied to the electrode
layer A pair of electrodes including an electrode layer at a position located on the periphery of
the through hole, and an alternating current signal being applied between the pair of electrodes
and the electrode layer of the vibrating film An ultrasonic speaker configured using an electronic
ultrasonic transducer and reproducing an audio signal in the middle to high frequency range
among audio signals supplied from an acoustic source, and a voice in a low frequency range
among audio signals supplied from the acoustic source And a speaker for bass reproduction that
reproduces a signal Wherein the ultrasonic speaker reproduces an audio signal supplied from the
sound source, and forming a virtual sound source into a sound wave reflecting surface near the
screen or the like.
[0042]
In the superdirective acoustic system configured as described above, a first electrode having a
through hole, a second electrode having a through hole, the through hole of the first electrode,
and the through hole of the second electrode Are arranged in a pair and are sandwiched between
a pair of electrodes consisting of the first electrode and the second electrode, and have an
electrode layer, and a vibrating film to which a DC bias voltage is applied to the electrode layer
An electrostatic type in which an alternating current signal is applied between the pair of
04-05-2019
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electrodes and the electrode layer of the vibrating film. Use an ultrasound speaker consisting of
an ultrasound transducer.
Then, among the sound signals supplied from the sound source, the sound signal in the middle to
high range is reproduced by the ultrasonic speaker. Further, among the audio signals supplied
from the audio source, the audio signal in the low frequency range is reproduced by the bass
reproduction speaker. Therefore, with the sound in the middle to high range, the voltage applied
between the electrodes of the electrostatic ultrasonic transducer being lowered and the sound
pressure characteristics being improved, with sufficient sound pressure and broadband
characteristics, It can reproduce | regenerate so that it may be emitted from the virtual sound
source formed in the sound wave reflective surface vicinity, such as a screen. In addition, since
the sound in the low frequency range is directly output from the speaker for reproducing the low
frequency sound provided in the sound system, it is possible to reinforce the low frequency
range and create a more realistic sound field environment.
[0043]
In the display device of the present invention, a first electrode having a through hole, a second
electrode having a through hole, the through hole of the first electrode, and the through hole of
the second electrode are included. A vibrating membrane which is disposed in a pair and is
sandwiched between a pair of electrodes consisting of the first electrode and the second
electrode, and which has an electrode layer, to which a DC bias voltage is applied. The pair of
electrodes includes an electrode layer at a position located on the peripheral edge portion of the
through hole, and an electrostatic type super that an alternating current signal is applied
between the pair of electrodes and the electrode layer of the vibrating membrane It is
characterized in that it comprises an ultrasonic transducer including an acoustic transducer, and
an ultrasonic speaker that reproduces a signal sound in an audible frequency band from an audio
signal supplied from an acoustic source, and a projection optical system that projects an image
on a projection plane.
[0044]
In the display device having the above configuration, the first electrode having the through hole,
the second electrode having the through hole, and the through hole of the first electrode and the
through hole of the second electrode are paired. A vibrating membrane disposed so as to be
sandwiched between a pair of electrodes consisting of the first electrode and the second
electrode, and having an electrode layer, to which a DC bias voltage is applied. The pair of
electrodes has an electrode layer at a position located on the periphery of the through hole, and
04-05-2019
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an electrostatic ultrasonic transducer in which an alternating current signal is applied between
the pair of electrodes and the electrode layer of the vibrating membrane Using an ultrasonic
speaker configured to include
Then, the sound signal supplied from the sound source is reproduced by the ultrasonic speaker.
As a result, the acoustic signal can be reproduced to be emitted from a virtual sound source
formed in the vicinity of a sound wave reflection surface such as a screen with sufficient sound
pressure and wide band characteristics in a state where the sound pressure characteristic is
improved. Therefore, control of the reproduction range of the acoustic signal can be easily
performed. Moreover, it is possible to perform directivity control of the sound radiated from the
ultrasonic speaker.
[0045]
Hereinafter, embodiments of the present invention will be described in detail with reference to
the drawings. [Configuration Example of Electrostatic Ultrasonic Transducer According to the
Present Invention] The configuration of the electrostatic ultrasonic transducer according to the
first 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
ultrasonic transducer is broken.
[0046]
In FIG. 1, the electrostatic ultrasonic transducer 1 according to the first embodiment of the
present invention is a through electrode that forms a pair with the fixed electrode 10A (first
electrode) having the through hole 14 and the through hole 14 of the fixed electrode 10A. A
vibrating electrode 12 having an electrode layer 121, which is sandwiched between a fixed
electrode 10B (second electrode) having a hole 14 and a pair of fixed electrodes 10A and 10B
consisting of the fixed electrode 10A and the fixed electrode 10B, and a pair of fixed electrodes
10A , 10B and a member (not shown) for holding the vibrating membrane.
[0047]
The vibrating film 12 is formed of an insulator (insulation layer) 120, and an electrode layer 121
formed of a conductive material is formed in the middle of the insulator (insulation layer) 120.
04-05-2019
17
Specifically, the vibrating film 12 is metallized on one side of a polymer film (insulator) having a
thickness of several microns, and is laminated by an adhesive. As a material of the polymer film,
for example, poly ethylene terephthalate (PET), aramid, poly ester, poly ethylene naphthalate
(PEN), poly phenylene sulfide (PPS) or the like is used. The metallized material is most commonly
Al, and may be Ni, Cu, SUS, Ti or the like. The thickness of the metallization is preferably about
500 Å to 1,500 Å.
[0048]
These electrode layers 121 are single polarity (positive in this embodiment by the DC bias power
supply 16), but may be either positive or negative. The DC bias voltage of (1) is applied. A direct
current bias voltage of 50 to 300 V is applied to the metallized portion (electrode layer 121) of
the vibrating film 12 from the circuit side. Furthermore, alternating current signals 18A and 18B,
which are output from the signal source 18 and are mutually inverted in phase, are applied
between the plurality of electrode layers 121 to the fixed electrode 10A and the fixed electrode
10B superimposed on the DC bias voltage. It is supposed to be.
[0049]
Further, the pair of fixed electrodes 10A and 10B have the same number and a plurality of
through holes 14 at the positions facing each other with the vibrating film 12 interposed
therebetween. The base material 100 of the pair of fixed electrodes 10A and 10B is a nonconductive material, and the pair of electrodes 10A and 10B have stepped portions in the
peripheral portion of the through hole 14 of the pair of electrodes 10A and 10B. An electrode
layer 101 is formed of a conductive material on the surface of the step facing the electrode layer
121 of the vibrating film. As a nonelectroconductive material which is a base material of said pair
of fixed electrodes 10A and 10B, glass, a glass fiber material, a plastics, a hard rubber etc. can be
used, for example. In addition, copper, aluminum, nickel, gold, silver, chromium or the like can be
used as a conductive material for forming the electrode layer 101. An electrode layer 101 is
formed by plating, vapor deposition, printing, or the like on the surface of the step of the pair of
electrodes 10A, 10B formed of a base material.
[0050]
04-05-2019
18
Between the fixed electrode 10A and the electrode layer 121 of the vibrating membrane 12 and
between the fixed electrode 10B and the electrode layer 121 of the vibrating membrane 12,
alternating-current signals 18A and 18B mutually phase-reversed by the signal source 18 are
applied. It is supposed to be. An alternating current voltage (AC signal) of about 100 to 300 V is
applied to the pair of fixed electrodes 10A and 10B from the circuit side. 16 is a DC bias power
supply. A capacitor is formed by the fixed electrode 10A and the electrode layer 121, and the
fixed electrode 10B and the electrode layer 121, respectively. Note that configurations of a
control unit that controls the signal source 18 and the DC bias power supply 16 and a storage
unit in which a table indicating control characteristics of the control unit is stored are omitted in
FIG. 1.
[0051]
In the above configuration, in the ultrasonic transducer 1, a DC bias voltage of a single polarity
(positive in this embodiment) is applied to the electrode layer 121 of the diaphragm 12 by the
DC bias power supply 16. The AC signals 18A and 18B, which are output from the signal source
18 and whose phases are mutually inverted, are applied in a superimposed state. On the other
hand, alternating-current signals 18A and 18B mutually phase-inverted from the signal source
18 are applied between the fixed electrode 10A and the vibrating film 12 and between the fixed
electrode 10B and the electrode layer 121 of the vibrating film 12, respectively.
[0052]
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, so the surface portion 12A of
the vibrating film 12 which is not held by the fixed electrode The electrostatic repulsive force
acts, and the surface portion 12A 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, the back surface 12B on the back surface side of the front surface 12A of the
vibrating film 12 is The electrostatic attraction force acts, and the back surface portion 12B is
pulled further downward in FIG.
[0053]
Therefore, the film portion of the vibrating film 12 which is not held by the pair of fixed
04-05-2019
19
electrodes 10A and 10B receives the electrostatic attractive force and the electrostatic repulsive
force (electrostatic repulsive force) in the same direction. Similarly, for the negative half cycle of
the alternating current signal output from the signal source 18, the surface portion 12A of the
vibrating membrane 12 in FIG. In FIG. 1, electrostatic repulsion acts on the upper side, and the
film portion of the diaphragm 12 which is not sandwiched by the pair of fixed electrodes 10A
and 10B receives electrostatic attraction and repulsion in the same direction. In this manner, the
direction in which the electrostatic force acts alternately changes while the diaphragm 12
receives the electrostatic attraction force and the electrostatic repulsion in the same direction
according to the change in polarity of the AC signal, so that the large membrane vibration, ie, An
acoustic signal of a sound pressure level sufficient to obtain a parametric array effect can be
generated.
[0054]
Thus, the electrostatic 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. ing. The electrostatic ultrasonic transducer
1 according to the embodiment of the present invention has a wider band and higher sound
compared to the conventional ultrasonic transducer (Pull type) in which only the electrostatic
attraction force acts on the vibrating film. Has the ability to simultaneously meet the pressure.
[0055]
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.
[0056]
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
04-05-2019
20
a wide band.
[0057]
Here, an example of the structure of the fixed electrode 10A (first electrode) and the fixed
electrode 10B (second electrode) in FIG. 1 which is a feature of the present invention is shown in
FIG.
2 (A) is a plan view of one side of the fixed electrodes 10A and 10B, FIG. 2 (B) is a cross-sectional
view taken along the line XX 'in FIG. 2 (A), and FIG. 2 (C) is 2 (A). It is a figure which shows the
other example of the cross-sectional structure by XX 'cutting line. In FIG. 2, for convenience of
explanation, only seven through holes through which sound is emitted are shown. As shown in
FIG. 2, a step 100A is formed on the periphery of the through hole 14 in a base material 100 of a
nonconductive material, and an electrode layer 101 is formed on the surface of the step 100A.
[0058]
The method of processing the base material is appropriately selected depending on the material,
such as press, injection molding, machining, and the like. Conventionally, in addition to the
electrode layer, since the base material portion is also a conductive material, the capacitance
value of the capacitance formed between the pair of fixed electrodes 10A and 10B and the
electrode layer 121 of the vibrating film 12 is large, Low power consumption was difficult. In the
first embodiment of the present invention, the electrode area can be reduced and the capacitance
value of the capacitance can be reduced by making the base material of a nonconductive
material. As a result, power consumption can be reduced when the electrostatic ultrasonic
transducer is driven.
[0059]
In the electrode structure shown in FIGS. 2A and 2B, when the diameter of the through hole 14 is
φ0.75 mm, the outer diameter of the electrode layer 101 is φ1.5 mm, and the through hole
pitch is 1.625 mm, By configuring the base material 100 with a nonconductive material, the
capacitance value of the capacitance can be reduced by 20%. This means that the current is also
reduced by 20%, and the current flowing when a voltage equivalent to the conventional one is
04-05-2019
21
applied between the pair of fixed electrodes 10A and 10B and the electrode layer 121 of the
vibrating film 12 is a conventional example Therefore, the power consumption can also be 80%
of that of the conventional example.
[0060]
FIG. 2C shows another example (modified example of the first embodiment) of the cross-sectional
structure of the electrode taken along the line X-X 'in FIG. 2A. The configuration other than the
fixed electrode of the electrostatic ultrasonic transducer is basically the same as that of FIG. 1, so
this modification will be described with reference to FIGS. 1 and 2 (C). FIG. 13 is another example
of the electrode structure for reducing the capacitance value of the capacitance formed between
the pair of fixed electrodes 10A and 10B and the electrode layer 121 of the vibrating film 12 in
the electrostatic ultrasonic transducer 1. FIG. In FIG. 2C, the base materials 110 of the pair of
fixed electrodes 10A and 10B are different from the case of FIGS. 1, 2A and 2B, and are
conductive materials, and the pair of fixed electrodes 10A and 10B Each has a through hole 14
so as to increase the distance between the vibrating membrane 12 and the electrode layer 121,
and a base material 110 in which only an electrode portion 110A for applying an electrostatic
force is formed in a convex shape, and an insertion hole And 112 non-conductive members 111.
Each of the pair of fixed electrodes 10A and 10B is integrally configured by fitting the convexshaped electrode portion 110A of the base material 110 into the insertion hole 112 of the
nonconductive member 111. The other configurations are the same as those in FIGS. 1 and 2A.
[0061]
In the case of the electrode structure shown in FIG. 2C having the above configuration, the
electrode layers of the pair of fixed electrodes 10A and 10B other than the portion to which
electrostatic force is applied in the pair of fixed electrodes 10A and 10B The distance between
110A) and the electrode layer 121 of the vibrating membrane (see FIG. 1) can be increased, and
the capacitance formed by the pair of fixed electrodes and the electrode layer of the vibrating
membrane can be reduced. be able to. Therefore, when the electrostatic ultrasonic transducer is
used as a capacitive load, the load impedance is increased, and flows between each of the pair of
electrodes in the electrostatic ultrasonic transducer and the electrode layer of the vibrating
membrane. The current is reduced, and voltage reduction and power consumption can be
achieved at the time of driving the electrostatic ultrasonic transducer.
[0062]
04-05-2019
22
Next, an electrostatic ultrasonic transducer according to a second embodiment of the present
invention will be described. The electrostatic ultrasonic transducer according to the second
embodiment of the present invention is basically the same as the first embodiment except for the
structure of the pair of fixed electrodes 10A and 10B in FIG. The electrostatic ultrasonic
transducer according to the second embodiment will be described with reference to FIG. The
structure of the fixed electrode of the electrostatic ultrasonic transducer according to the second
embodiment of the present invention is shown in FIG. 3 (A) is a plan view of one side of the fixed
electrodes 10A and 10B, FIG. 3 (B) is a cross-sectional view along the line YY 'in FIG. 3 (A), and
FIG. 3 (C) is FIG. It is a figure which shows the other example of the cross-section with the YY
'cutting line in these.
[0063]
1 and 3A and 3B, the base material 200 of the pair of fixed electrodes 10A and 10B is a nonconductive material, and is located inside the through holes 214 of the pair of fixed electrodes
10A and 10B, An electrode layer 201 is formed on the surface of a base material portion 200A
formed in a bridge shape so as to face the electrode layer 121 of the vibrating film 12. Thereby,
the electrode layer area of the pair of fixed electrodes in the electrostatic ultrasonic transducer
can be reduced, and the capacitance formed by the pair of electrodes and the electrode layer of
the vibrating film can be reduced. Therefore, when the electrostatic ultrasonic transducer is used
as a capacitive load, the load impedance is increased, and flows between each of the pair of
electrodes in the electrostatic ultrasonic transducer and the electrode layer of the vibrating
membrane. The current is reduced, and voltage reduction and power consumption can be
achieved at the time of driving the electrostatic ultrasonic transducer.
[0064]
FIG. 3C shows another example (modification of the second embodiment) of the cross-sectional
structure of the electrode taken along the line Y-Y 'in FIG. 3A. 1 and 3C, the base material 210 of
the pair of fixed electrodes 10A and 10B in the electrostatic ultrasonic transducer 1 is a
conductive material, and each of the pair of fixed electrodes 10A and 10B is a vibrating film. A
base material 210 formed in a bridge shape so that only the electrode portion 210A for applying
an electrostatic force to have a long distance to the twelve electrode layers 121 and having a
convex shape and facing the electrode layer 121 of the diaphragm 12 And the non-conductive
member 211 having the insertion hole 212 formed therein, and the projection-shaped electrode
04-05-2019
23
portion 210A of the base material 210 is integrally fitted with the insertion hole 212 of the nonconductive member 211. .
[0065]
As a result, the distance between the electrode layer (electrode portion 210A) of the pair of
electrodes and the electrode layer 121 of the vibrating film 12 other than the portion to which
the electrostatic force acts in the pair of fixed electrodes 10A and 10B is increased. Thus, the
capacitance formed by the pair of electrodes 10A and 10B and the electrode layer 121 of the
vibrating film 12 can be reduced. Therefore, when the electrostatic ultrasonic transducer is used
as a capacitive load, the load impedance is increased, and flows between each of the pair of
electrodes in the electrostatic ultrasonic transducer and the electrode layer of the vibrating
membrane. The current is reduced, and voltage reduction and power consumption can be
achieved at the time of driving the electrostatic ultrasonic transducer.
[0066]
As described above, according to the electrostatic ultrasonic transducer (Push-Pull type
ultrasonic transducer) according to the embodiment of the present invention, it is necessary to
apply an electrostatic force to a pair of electrodes (fixed electrodes). The electrode layer is
formed at the peripheral portion of the through hole or at a portion located inside the through
hole. Thereby, the electrode layer area of the pair of electrodes can be reduced, and the
capacitance formed by the pair of electrodes and the electrode layer of the vibrating membrane
can be reduced. Therefore, when the electrostatic ultrasonic transducer is used as a capacitive
load, the load impedance is increased, and flows between each of the pair of electrodes in the
electrostatic ultrasonic transducer and the electrode layer of the vibrating membrane. The
current is reduced, and voltage reduction and power consumption can be achieved at the time of
driving the electrostatic ultrasonic transducer.
[0067]
In the embodiment of FIGS. 3A, 3B and 3C, the electrode layer (electrode portion) is formed on
the base material of the nonconductive material or the conductive material, but the present
invention is not limited to this. The through hole may be configured to be bridged by a bridgelike electrode without providing a base material for construction. Also in this case, the same
04-05-2019
24
effect as that of the second embodiment can be obtained.
[0068]
[Configuration Example of Ultrasonic Speaker According to the Present Invention] 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 (see FIG. 1) according to the above-described embodiment of the present
invention as the ultrasonic transducer 55.
[0069]
In FIG. 4, the ultrasonic speaker 50 according to the present embodiment generates and outputs
an audio frequency wave oscillation source (signal source) 51 that generates a signal wave in the
audio wave frequency band, and a carrier wave in the ultrasonic frequency band. A carrier wave
oscillation source (carrier wave supply means) 52, a modulator (modulation means) 53, a power
amplifier 54, and an ultrasonic transducer (electrostatic 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.
[0070]
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.
[0071]
That is, since the sound wave is a compression wave propagating through the air as a medium, in
04-05-2019
25
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.
[0072]
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.
[0073]
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.
[0074]
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, in the ultrasonic speaker according to the present invention
having the above configuration, in the pair of electrodes in the electrostatic ultrasonic transducer
to be used, the peripheral portion or the inside of the through hole, which is a portion necessary
for applying electrostatic force Since the electrode layer is formed at the position located in the
above, the electrode layer area of the pair of electrodes can be reduced, and the capacitance
formed by the pair of electrodes and the electrode layer of the vibrating film is reduced. be able
04-05-2019
26
to. Therefore, when the electrostatic ultrasonic transducer is used as a capacitive load, the load
impedance is increased, and flows between each of the pair of electrodes in the electrostatic
ultrasonic transducer and the electrode layer of the vibrating membrane. The current is reduced,
and voltage reduction and power consumption can be achieved at the time of driving the
electrostatic ultrasonic transducer. That is, the same sound pressure as that of the conventional
ultrasonic speaker can be generated with less energy, and the power consumption of the
ultrasonic speaker can be reduced.
[0075]
[Description of Configuration Example of Superdirective Acoustic System According to the
Present Invention] Next, the electrostatic ultrasonic transducer according to the present
invention, that is, a first electrode having a through hole, and the through hole of the first
electrode A second electrode having a pair of through holes, a vibrating film sandwiched between
a pair of electrodes consisting of the first and second electrodes and having an electrode layer, to
which a DC bias voltage is applied And forming an electrode layer at a position located at the
periphery or inside of the through holes of the pair of electrodes, and an alternating current
signal is applied between the pair of electrodes and the electrode layer of the vibrating film. A
superdirectional acoustic system using an ultrasonic speaker configured using a Pull-type
electrostatic ultrasonic transducer will be described.
[0076]
Hereinafter, a projector will be described as an example of the superdirective sound system
according to the present invention.
The superdirective acoustic system according to the present invention is not limited to a
projector, but can be widely applied to display devices that reproduce audio and video. FIG. 5
shows the use of the projector according to the present invention. As shown in the figure, the
projector 301 is installed behind the viewer 303 and projects an image on the screen 302
installed in front of the viewer 303, and the screen 302 by the ultrasonic speaker mounted on
the projector 301. The virtual sound source is formed on the projection plane of the to reproduce
the sound.
[0077]
04-05-2019
27
The external configuration of the projector 301 is shown in FIG. The projector 301 includes a
projector main body 320 including a projection optical system that projects an image on a
projection surface such as a screen, and ultrasonic transducers 324A and 324B capable of
oscillating sound waves in an ultrasonic frequency band, and is supplied from an acoustic source
And an ultrasonic speaker that reproduces a sound signal of an audible frequency band from an
audio signal. In the present embodiment, in order to reproduce a stereo sound signal, ultrasonic
transducers 324A and 324B which constitute ultrasonic speakers on the left and right sides of
the projector lens 331 which constitutes the projection optical system are mounted on the
projector main body. Furthermore, on the bottom surface of the projector main body 320, a bass
reproduction speaker 323 is provided. Reference numeral 325 denotes a height adjustment
screw for adjusting the height of the projector main body 320, and reference numeral 326
denotes an exhaust port for an air-cooling fan.
[0078]
Further, in the projector 301, the Push-Pull type electrostatic ultrasonic transducer according to
the present invention is used as an ultrasonic transducer constituting an ultrasonic speaker, and
a wide frequency band acoustic signal (sound wave of ultrasonic frequency band) Can be
oscillated at high sound pressure. For this reason, by changing the frequency of the carrier wave
to control the spatial reproduction range of the reproduction signal in the audio frequency band,
it is necessary to conventionally obtain the acoustic effect that can be obtained in the stereo
surround system, 5.1ch surround system, etc. It is possible to realize a projector that can be
realized without the need for a large-scale sound system and easy to carry.
[0079]
Next, the electrical configuration of the projector 301 is shown in FIG. The projector 301
includes an operation input unit 310, a reproduction range setting unit 312, a reproduction
range control processing unit 313, an audio / video signal reproduction unit 314, a carrier wave
oscillation source 316, modulators 318A and 318B, power amplifiers 322A and 322B, and The
ultrasonic speaker consisting of the electric ultrasonic transducers 324A and 324B, the high pass
filters 317A and 317B, the low pass filter 319, the adder 321, the power amplifier 322C, the
bass reproduction speaker 323, and the projector main body 320 are provided. doing. The
electrostatic ultrasonic transducers 324A and 324B are Push-Pull type electrostatic ultrasonic
transducers according to the present invention.
04-05-2019
28
[0080]
The projector body 320 includes an image generation unit 332 that generates an image, and a
projection optical system 333 that projects the generated image on a projection surface. The
projector 301 is configured by integrating an ultrasonic speaker, a bass reproduction speaker
323, and a projector main body 320.
[0081]
The operation input unit 310 has various function keys including a ten-key pad, numeric keys,
and a power key for turning the power on and off. The reproduction range setting unit 312 is
configured such that the user can input data for specifying the reproduction range of the
reproduction signal (signal sound) by key operation of the operation input unit 310, and when
the data is input, reproduction is performed. The frequency of the carrier wave that defines the
reproduction range of the signal is set and held. The setting of the reproduction range of the
reproduction signal is performed by designating the distance that the reproduction signal
reaches from the sound wave emission surface of the ultrasonic transducers 324A and 324B in
the radiation axis direction.
[0082]
Also, the reproduction range setting unit 312 can set the frequency of the carrier wave by the
control signal output from the audio / video signal reproduction unit 314 according to the
contents of the video. Further, the reproduction range control processing unit 313 refers to the
setting contents of the reproduction range setting unit 312, and changes the frequency of the
carrier wave generated by the carrier wave oscillation source 316 so as to become the set
reproduction range. It has a function of controlling the oscillation source 316. For example, when
the distance corresponding to the carrier wave frequency of 50 kHz is set as internal information
of the reproduction range setting unit 312, the carrier wave oscillation source 316 is controlled
to oscillate at 50 kHz.
[0083]
The reproduction range control processing unit 313 stores in advance a table indicating the
04-05-2019
29
relationship between the distance at which the reproduction signal reaches in the radiation axis
direction from the sound wave emitting surfaces of the ultrasonic transducers 324A and 324B
defining the reproduction range and the frequency of the carrier wave. Storage unit. The data of
this table can be obtained by actually measuring the relationship between the frequency of the
carrier wave and the reach distance of the reproduction signal. The reproduction range control
processing unit 313 obtains the frequency of the carrier wave corresponding to the distance
information set by referring to the above-mentioned table based on the setting contents of the
reproduction range setting unit 312, and carries out carrier wave oscillation so as to be the
frequency. Control source 316
[0084]
The audio / video signal reproduction unit 314 is, for example, a DVD player that uses a DVD as
a video medium, and among the reproduced audio signals, the R channel audio signal is
transmitted to the modulator 318A via the high pass filter 317A. The signal is output to the
modulator 318 B via the high pass filter 317 B, and the video signal is output to the video
generation unit 332 of the projector main body 320. Also, the R channel audio signal and the L
channel audio signal output from the audio / video signal reproduction unit 314 are synthesized
by the adder 321 and input to the power amplifier 322 C via the low pass filter 319. There is.
The audio / video signal reproduction unit 314 corresponds to an audio source.
[0085]
The high-pass filters 317A and 317B have the characteristic of passing only the frequency
components in the middle and high frequency range of the R channel and L channel audio
signals, respectively, and the low pass filters have low characteristics in the R channel and L
channel audio signals. It has the property of passing only frequency components in the sound
range. Therefore, among the audio signals of the R channel and L channel, the audio signals in
the middle to high range are reproduced by the ultrasonic transducers 324A and 324B,
respectively, and the audio signals of the bass region of the audio signals of the R channel and L
channel are bass It will be reproduced by the reproduction speaker 323.
[0086]
The audio / video signal reproduction unit 314 is not limited to a DVD player, and may be a
04-05-2019
30
reproduction device that reproduces a video signal input from the outside. Also, the audio / video
signal reproduction unit 314 instructs the reproduction range setting unit 312 to change the
reproduction range of the reproduction sound dynamically in order to obtain an acoustic effect
according to the scene of the video to be reproduced. Output control signal.
[0087]
The carrier wave oscillation source 316 has a function of generating a carrier wave of the
frequency of the ultrasonic frequency band instructed by the reproduction range setting unit 312
and outputting the carrier wave to the modulators 318A and 318B. Modulators 318A and 318B
AM modulate the carrier wave supplied from the carrier wave oscillation source 316 with the
audio signal of the audio frequency band output from the audio / video signal reproduction unit
314, and respectively modulate the modulated signal with the power amplifier 322A. , 322 B
have a function to output.
[0088]
The ultrasonic transducers 324A and 324B are driven by modulation signals output from the
modulators 318A and 318B via the power amplifiers 322A and 322B, respectively, convert the
modulation signals into sound waves of finite amplitude level and emit them into the medium
And has a function of reproducing a signal sound (reproduction signal) in the audio frequency
band.
[0089]
The video generation unit 332 includes a display such as a liquid crystal display or a plasma
display panel (PDP), and a drive circuit that drives the display based on the video signal output
from the audio / video signal reproduction unit 314. An image obtained from the video signal
output from the audio / video signal reproduction unit 314 is generated.
The projection optical system 333 has a function of projecting an image displayed on a display
on a projection surface such as a screen installed in front of the projector main body 320.
[0090]
04-05-2019
31
Next, the operation of the projector 301 configured as described above will be described. First,
data (distance information) instructing the reproduction range of the reproduction signal from
the operation input unit 310 is set in the reproduction range setting unit 312 by the key
operation of the user, and the audio / video signal reproduction unit 314 is instructed to
reproduce.
[0091]
As a result, distance information defining the reproduction range is set in the reproduction range
setting unit 312, and the reproduction range control processing unit 313 takes in the distance
information set in the reproduction range setting unit 312 and stores it in the built-in storage
unit. The frequency of the carrier wave corresponding to the set distance information is
determined with reference to the table, and the carrier wave oscillation source 316 is controlled
to generate the carrier wave of the frequency. As a result, the carrier wave oscillation source 316
generates a carrier wave of a frequency corresponding to the distance information set in the
reproduction range setting unit 312, and outputs the carrier wave to the modulators 318A and
318B.
[0092]
On the other hand, the audio / video signal reproduction unit 314 transmits the audio signal of R
channel among the reproduced audio signals to the modulator 318A through the high pass filter
317A and the audio signal of L channel through the high pass filter 317B. The audio signal of the
R channel and the audio signal of the L channel are output to the adder 321, and the video signal
is output to the video generation unit 332 of the projector main body 320, respectively.
[0093]
Therefore, the high-pass filter 317A inputs the voice signal of middle to high range among the
voice signals of the R channel to the modulator 318, and the high-pass filter 317B sets the voice
signal of middle to high range among the voice signals of the L channel to the modulator 318B.
Is input to
The R channel audio signal and the L channel audio signal are synthesized by the adder 321, and
the low pass filter 319 combines the R channel audio signal and the L channel audio signal with
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the power amplifier 322C. It is input.
[0094]
The video generation unit 332 drives the display based on the input video signal to generate and
display a video. The image displayed on the display is projected by the projection optical system
333 onto a projection surface, for example, the screen 302 shown in FIG. Modulator 318A, on
the other hand, AM modulates the carrier wave output from carrier wave oscillation source 316
with the middle-to-high range audio signal of the R channel audio signal output from high-pass
filter 317A, and outputs it to power amplifier 322A. . Also, the modulator 318B AM modulates
the carrier wave output from the carrier wave oscillation source 316 with the middle-to-high
range audio signal of the L channel audio signal output from the high-pass filter 317B, and
outputs it to the power amplifier 322B. .
[0095]
Modulated signals amplified by the power amplifiers 322A and 322B are applied between the
upper electrode 10A and the lower electrode 10B (see FIG. 1) of the ultrasonic transducers 324A
and 324B, respectively, and the modulated signals have finite amplitude levels. Sound waves
(acoustic signals) are converted and emitted to the medium (in air), and the ultrasonic transducer
324A reproduces medium to high frequency sound signals in the R channel sound signal, and the
ultrasonic transducer 324B The voice signal of the middle to high range in the voice signal of L
channel is reproduced. In addition, the audio signal of the bass range in the R channel and the L
channel amplified by the power amplifier 322 C is reproduced by the bass reproduction speaker
323.
[0096]
As described above, in the propagation of the ultrasonic wave radiated into the medium (in air)
by the ultrasonic transducer, the speed of sound becomes high in the high sound pressure area
and the speed of sound is slow in the low sound pressure area. Become. As a result, waveform
distortion occurs.
[0097]
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33
When the signal (carrier wave) of the emitting ultrasonic band is modulated (AM modulated) with
the signal of the audio frequency band, the signal wave of the audio frequency band used at the
time of modulation is super It is formed to be separated from the carrier wave in the sound wave
frequency band and to be self-demodulated. At this time, the spread of the reproduction signal is
in the form of a beam due to the characteristics of the ultrasonic waves, and the sound is
reproduced only in a specific direction which is completely different from that of a normal
speaker.
[0098]
The beam-like reproduction signal output from the ultrasonic transducer 324 constituting the
ultrasonic speaker is emitted by the projection optical system 333 toward a projection surface
(screen) on which an image is projected, and is reflected and diffused by the projection surface.
In this case, depending on the frequency of the carrier wave set in the reproduction range setting
unit 312, until the reproduction signal is separated from the carrier wave in the radiation axis
direction (normal direction) from the sound wave emission surface of the ultrasonic transducer
324 The reproduction range changes due to the difference in the distance d and the beam width
of the carrier wave (beam spread angle).
[0099]
The state at the time of reproduction | regeneration of the reproduction | regeneration signal by
the ultrasonic speaker comprised including ultrasonic transducer 324A, 324B in the projector
301 is shown in FIG. In the projector 301, when the ultrasonic transducer is driven by the
modulation signal in which the carrier wave is modulated by the audio signal, the acoustic wave
emission surface of the ultrasonic transducer 324 when the carrier frequency set by the
reproduction range setting unit 312 is low. The distance from the carrier wave to the separation
of the reproduction signal in the direction of the radiation axis (the normal direction of the sound
wave emission surface, ie, the distance to the reproduction point becomes long.
[0100]
Therefore, the beam of the reproduced signal of the reproduced audio frequency band reaches
the projection surface (screen) 302 without being relatively spread, and is reflected at the
projection surface 302 in this state, so that the reproduction range is as shown in FIG. The
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34
audible range A is indicated by a dotted arrow in FIG. 2 and the reproduced signal (reproduced
sound) can be heard only in a relatively far and narrow range from the projection plane 302.
[0101]
On the other hand, when the carrier frequency set by the reproduction range setting unit 312 is
higher than the case described above, the sound wave emitted from the sound wave emitting
surface of the ultrasonic transducer 324 is narrowed compared to the case where the carrier
frequency is low. However, the distance from the acoustic wave emission surface of the
ultrasonic transducer 324 to the separation of the reproduction signal from the carrier wave in
the radiation axis direction (normal direction of the sound emission surface), that is, the distance
to the reproduction point becomes short.
[0102]
Therefore, the beam of the reproduced signal in the audible frequency band is expanded before
reaching the projection plane 302 to reach the projection plane 302, and is reflected at the
projection plane 302 in this state, so that the reproduction range is as shown in FIG. The audio
range B indicated by a solid arrow at 8 is the audible range B, and the reproduced signal
(reproduced sound) can be heard only in a relatively close and wide range from the projection
plane 302.
[0103]
As described above, the projector of the present invention uses the ultrasonic speaker using the
Push-Pull type or Pull type electrostatic ultrasonic transducer according to the present invention,
and the acoustic signal has a sufficient sound pressure and It can be reproduced so as to be
emitted from a virtual sound source formed in the vicinity of a sound wave reflection surface
such as a screen with a wide band characteristic.
Therefore, control of the reproduction range can be easily performed.
In addition, as described above, the electrostatic ultrasonic transducer is divided into a plurality
of blocks in the vibration region of the vibration film, and alternating current is applied between
the electrode layer of the vibration film and each block of the vibration electrode pattern. It is
possible to perform directivity control of the sound radiated from the ultrasonic speaker by
controlling the phases of the signals so as to have predetermined phase differences between
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adjacent blocks.
The embodiment of the present invention has been described above, but the electrostatic
ultrasonic transducer and the ultrasonic speaker according to the present invention are not
limited to the above illustrated examples, and the scope without departing from the scope of the
present invention Of course, various modifications can be made within.
[0104]
The ultrasonic transducer according to the embodiment of the present invention can be used for
various sensors, for example, a distance measurement sensor, and as described above, a sound
source for a directional speaker or an ideal impulse signal source Etc. are available. Moreover, it
is useful also for a super-directional sound system and a display device such as a projector.
[0105]
FIG. 1 shows a configuration of an electrostatic ultrasonic transducer according to an
embodiment of the present invention. The top view and sectional drawing which show an
example of the structure of the fixed electrode in FIG. Sectional drawing which shows the other
example of the structure of the fixed electrode in FIG. The figure which shows the structural
example of an ultrasonic speaker. The figure which shows the use condition of the projector
which concerns on embodiment of this invention. FIG. 5 is a view showing an appearance
configuration of the projector shown in FIG. 4; FIG. 5 is a block diagram showing an electrical
configuration of the projector shown in FIG. 4. Explanatory drawing which shows the
reproduction | regeneration state of the reproduction | regeneration signal by an ultrasonic
transducer. 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
structural example of the conventional electrostatic-type ultrasonic transducer.
Explanation of sign
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[0106]
DESCRIPTION OF SYMBOLS 1 ... electrostatic-type ultrasonic transducer, 10A, 10B ... fixed
electrode, 12 ... vibrating membrane, 12A ... surface part, 12B ... back surface part, 14 ... through
hole, 16 ... DC bias power supply, 18 ... signal source, 50 ... super Sound wave speaker 51: audio
frequency wave oscillation source 52: carrier wave signal source 53: modulator 54: power
amplifier 55: ultrasonic transducer 120: insulator, 121: electrode layer 301: projector 302: 302
Screen (projection plane), 303, viewer, 310, operation input unit, 312, reproduction range setting
unit, 313, reproduction range control processing unit, 314, audio / video signal reproduction
unit, 316, carrier wave oscillation source, 317A, 317 B: high pass filter (HPF), 318 A, 318 B:
modulator, 319: low pass filter (LPF), 320: projector main body, 3 1 ... adder, 322A, 322B, 322C
... power amplifier, 323 ... low-frequency sound reproducing speaker, 324A, 324B ... electrostatic
ultrasonic transducer, 331 ... projector lens, 332 ... image generator, 333 ... projection optical
system.
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