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JP2013077992

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DESCRIPTION JP2013077992
Abstract: The present invention provides an ultrasonic speaker and a parametric speaker that can
increase the sound pressure of the entire parametric speaker and can efficiently produce sound
with high sound pressure with a small number of ultrasonic speakers. An ultrasonic sound
generator for a parametric speaker that generates ultrasonic waves, which is a plate-like
piezoelectric element 111 that expands and contracts by the application of a voltage in the
thickness direction, and the piezoelectric element 111 adheres to one main surface And a conical
cylindrical resonator 114 provided on the other principal surface of the diaphragm 112 and
resonating with the vibration of the diaphragm 112 to generate an ultrasonic wave, the resonator
114 comprising The resonance frequency is adjusted by the solidified body 114 a filled at the
bottom. Thereby, the dispersion ¦ variation in the resonant frequency of the ultrasonic sounding
body 110 can be reduced, and the sound pressure of the whole parametric speaker can be raised.
And it can be pronounced with high sound pressure efficiently with a small number of ultrasonic
sounders 110. [Selected figure] Figure 2
Ultrasonic speaker and parametric speaker
[0001]
The present invention relates to an ultrasonic speaker that generates ultrasonic waves, and a
parametric speaker provided with a plurality of the ultrasonic speaker.
[0002]
The ultrasonic speaker includes a piezoelectric vibrator in which a diaphragm and a piezoelectric
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element are bonded to each other.
When an AC voltage at a resonance frequency specific to the piezoelectric vibrator is applied to
the piezoelectric vibrator, the piezoelectric vibrator vibrates, and the ultrasonic speaker emits a
sound having the same frequency as the resonance frequency. The resonant frequency is
included in the ultrasonic band above 20 kHz.
[0003]
Furthermore, by attaching a conical cylindrical resonator to the piezoelectric vibrator, the sound
pressure of the generated ultrasonic wave can be increased, and the ultrasonic wave can have
directivity of 60 to 70 degrees in front. Although the ultrasonic speaker has the same structure
as the ultrasonic sensor, the ultrasonic sensor transmits and receives ultrasonic waves, and the
ultrasonic speaker only transmits the ultrasonic sensor. ing.
[0004]
The parametric speaker is configured by arranging a plurality of such ultrasonic sound
generators (see, for example, Patent Documents 1 and 2). The ultrasonic waves emitted by the
ultrasonic sound generators of each of the parametric speakers overlap in air and are
demodulated to audible sound when reaching a certain sound pressure or more. In addition,
since the audible sound is generated only at the central position where the ultrasonic waves
overlap, the parametric speaker functions as a sharp directional speaker.
[0005]
In addition, what is adjusting the resonance frequency is known as an ultrasonic sensor. For
example, in the ultrasonic sensor described in Patent Document 3, the resonance frequency is
adjusted by adjusting the angle between the side surface of the resonator and the diaphragm.
[0006]
Japanese Patent Application Laid-Open No. 60-167597 Japanese Patent Application Laid-Open
No. 62-296698 Japanese Patent Application Laid-Open No. 7-72006
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[0007]
The plurality of ultrasonic sound generators used in the parametric speaker are driven at a
common drive frequency to match the vibrations of the respective piezoelectric vibrators.
In the ultrasonic speaker, as shown in FIG. 5, the sound pressure is high when the drive
frequency is close to the resonance frequency, and the sound pressure is low when the drive
frequency is away from the resonance frequency.
[0008]
In the case of using a plurality of ultrasonic sounding bodies as parametric speakers, if there is
variation in the resonance frequency of each ultrasonic sounding body, the sound pressure
becomes low in the ultrasonic sounding body having a resonance frequency that is significantly
different from the drive frequency. And the sound pressure of the whole parametric speaker also
becomes low by the presence of the ultrasonic sounding body whose sound pressure is low.
[0009]
On the other hand, it is possible to increase the number of ultrasonic sounding bodies in advance,
assuming that the sound pressure of some ultrasonic sounding bodies decreases, but in that case,
the parametric speaker becomes too large. On the other hand, if the variation of the resonance
frequency of the ultrasonic sounding body is reduced, it is possible to eliminate the ultrasonic
sounding body with low sound pressure and to reduce the number of ultrasonic sounding bodies
used. Therefore, although it is conceivable to apply the frequency adjustment method of the
ultrasonic sensor described in Patent Document 3, since the directivity of each ultrasonic sensor
varies, this method is used in the case where plural ultrasonic sensors are used side by side like a
parametric speaker. Is unsuitable.
[0010]
The present invention has been made in view of such circumstances, and it is an ultrasonic
sounding body and a parametric speaker that can increase sound pressure of the entire
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parametric speaker and can efficiently produce high sound pressure with a small number of
ultrasonic sounding bodies. Intended to be provided.
[0011]
(1) In order to achieve the above object, the ultrasonic sounding body of the present invention is
an ultrasonic sounding body for a parametric speaker that generates ultrasonic waves, and has a
plate shape that expands and contracts by application of a voltage in the thickness direction. A
piezoelectric element, a diaphragm having the piezoelectric element bonded to one of the main
surfaces, and a conical cylindrical resonance provided on the other main surface of the
diaphragm to resonate with the vibration of the diaphragm to generate an ultrasonic wave The
resonator is characterized in that the resonant frequency is adjusted by a solidified body filled at
the bottom.
[0012]
As described above, by adjusting the resonance frequency of the resonator, it is possible to
reduce the variation in the resonance frequency of the ultrasonic speaker that constitutes the
parametric speaker.
As a result, the sound pressure of the entire parametric speaker can be increased.
And it can be pronounced with high sound pressure efficiently with a small number of ultrasonic
sounders.
[0013]
(2) Further, in the ultrasonic speaker according to the present invention, the coagulated body
filled in the bottom of the resonator is a silicon resin. Thus, the resonance frequency can be
adjusted easily and at low cost for each resonator.
[0014]
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(3) Further, the parametric speaker of the present invention is characterized in that a plurality of
the above-mentioned ultrasonic sound generators are provided, and the standard deviation of
their resonance frequencies is 50 Hz or less. As a result, the variation in the resonance frequency
of the ultrasonic speaker can be reduced, and the sound pressure of the entire parametric
speaker can be sufficiently increased.
[0015]
According to the present invention, the sound pressure of the entire parametric speaker can be
increased, and sound can be efficiently generated at a high sound pressure with a small number
of ultrasonic sound generators.
[0016]
It is a front view showing a parametric speaker of the present invention.
It is a sectional side view which shows the structure of the ultrasonic sounding body of this
invention. Each of (a) and (b) is a side view schematically showing one scene of the operation of
the ultrasonic speaker according to the present invention. It is a block diagram showing an
electrical configuration of a parametric speaker. It is a graph which shows the relationship of the
sound pressure with respect to the difference of a drive frequency and a resonance frequency.
[0017]
Next, embodiments of the present invention will be described with reference to the drawings. In
order to facilitate understanding of the description, the same reference numerals are given to the
same components in the respective drawings, and the overlapping description will be omitted.
[0018]
(Configuration of Parametric Speaker) FIG. 1 is a front view showing the parametric speaker 100.
FIG. The parametric speaker 100 generates a high intensity sound pressure modulated ultrasonic
wave and causes an audible sound to appear due to the non-linear characteristic of the ultrasonic
wave propagation in the air. In this way, it is possible to identify the direction or distance, give
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directivity, and transmit acoustic information. As shown in FIG. 1, the parametric speaker 100 is
configured by providing a plurality of ultrasonic sound generators 110 on a substrate 120. The
ultrasonic speaker 110 generates an ultrasonic wave based on the modulation signal. The
substrate 120 fixes and supports the ultrasonic sound generator 110. Note that FIG. 1 shows the
external configuration, and the electrical configuration is omitted.
[0019]
(Configuration of Ultrasonic Sounding Body) FIG. 2 is a side sectional view showing a
configuration of the ultrasonic sounding body 110. As shown in FIG. The ultrasonic speaker 110
is used for a parametric speaker to generate an ultrasonic wave. The ultrasonic speaker 110
generates a modulated ultrasonic signal by applying a voltage. The ultrasonic sound generator
110 is composed of a piezoelectric element 111, a diaphragm 112, lead wires 113 a and 113 b,
and a resonator 114.
[0020]
The piezoelectric element 111 is formed in a plate shape, and expands and contracts by
application of a voltage in the thickness direction. The piezoelectric element 111 is adhered to
one main surface of the diaphragm 112 and installed. In the piezoelectric element 111, the other
main surface of the diaphragm 112 is a vibrating surface, and the piezoelectric element 111 can
generate an ultrasonic wave through the vibrating surface.
[0021]
The resonator 114 is formed in a conical cylindrical shape, and is preferably made of aluminum
or an aluminum alloy. The conical cylindrical shape includes a parabolic shape or a funnel shape.
The resonator 114 is provided on the other main surface of the diaphragm 112 and resonates
with the vibration of the diaphragm 112 to generate an ultrasonic wave. The resonator 114 has
its resonant frequency adjusted by the solidified body 114 a filled at the bottom. As described
above, by adjusting the resonance frequency of the resonator, the variation in the resonance
frequency of the ultrasonic sound generator can be reduced. As a result, the sound pressure of
the entire parametric speaker can be increased. And it can be pronounced with high sound
pressure efficiently with a small number of ultrasonic sounders.
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[0022]
The solidified body 114a is preferably a silicone resin. Thus, the resonance frequency can be
adjusted easily and at low cost for each resonator. Thus, the ultrasonic speaker 110 whose
resonant frequency is adjusted can be used for the parametric speaker 100. In that case, the
standard deviation of the resonance frequency is preferably 50 Hz or less. Thereby, the sound
pressure of the whole parametric speaker can be raised enough.
[0023]
Electrodes are respectively formed on both main surfaces of the piezoelectric element 111, and
the piezoelectric body of the main body portion is polarized in the thickness direction. In the
diaphragm 112, the piezoelectric element 111 is bonded to one main surface. The diaphragm
112 is formed in a disk shape. The diaphragm 112 can be formed of, for example, a metal such
as brass, SUS304, 42 alloy or aluminum. The piezoelectric element 111 and the diaphragm 112
form a piezoelectric vibrator 115. The piezoelectric vibrator 115 is designed in advance to have a
constant resonance frequency.
[0024]
(Operation of Ultrasonic Sounding Body) FIGS. 3A and 3B are side views schematically showing
one scene of the operation of the ultrasonic sounding body 110 of the present invention. As
shown in FIGS. 3 (a) and 3 (b), the ultrasonic sound generator 110 bends and vibrates by
applying an alternating voltage to the electrodes on both main surfaces of the piezoelectric
element 111 polarized in the thickness direction. At that time, a voltage is applied with the
resonance frequency of the piezoelectric vibrator 115 as a driving frequency.
[0025]
(Production of Ultrasonic Sounding Body) A method of producing the ultrasonic sounding body
110 will be described. First, the materials of the piezoelectric element 111 and the vibration
plate 112 are determined for the piezoelectric vibrator 115, and their external shapes are also
designed.
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[0026]
A plate-like piezoelectric body is formed of a piezoelectric material, and electrodes are provided
to polarize, thereby forming the piezoelectric element 111. The piezoelectric element 111 is
bonded to one of the main surfaces of the diaphragm 112. Then, the lead wires 113a and 113b
are connected to the electrodes or diaphragm 112 at predetermined locations. The resonator
114 is bonded to the other main surface of the diaphragm 112. Thus, the ultrasonic speaker 110
can be manufactured.
[0027]
Next, the resonant frequency of the produced ultrasonic sound generator 110 is measured. Then,
a silicone resin is injected into the bottom of the resonator 114 with the resonance frequency
that is the lowest value of the ultrasonic sounding body 110 as a target value, and is solidified to
adjust the resonance frequency of each ultrasonic sounding body. When the silicon resin is put in
the resonator 114, the resonance frequency is lowered according to the amount, so that it is
possible to adjust the injection of the silicon resin for all the elements whose resonance
frequency is higher than the minimum value. On the other hand, since the change in resonance
frequency with respect to the amount of silicon resin can be grasped in advance, the amount of
silicon resin can be determined from the difference in target frequency to be adjusted before
adjustment, and can be injected in quantitative amounts by a dispenser. In this way, the
resonance frequencies of the plurality of ultrasonic sound generators 110 are adjusted to the
lowest value among them.
[0028]
(Electrical Configuration of Parametric Speaker) FIG. 4 is a block diagram showing an electrical
configuration of the parametric speaker 100. As shown in FIG. As shown in FIG. 4, the parametric
speaker 100 includes an oscillator 101, a modulator 102, an amplifier 105, and an ultrasonic
sound generator 110, through which ultrasonic waves are generated. The oscillator 101
oscillates a signal at a predetermined frequency in the ultrasonic band. The frequency to be
oscillated is a drive frequency for driving the piezoelectric element 111 when the oscillation
signal is transmitted to the ultrasonic sound generator 110, and is determined in advance
according to the application of the parametric speaker 100.
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[0029]
The modulator 102 AM modulates the oscillation signal with the audio signal. The modulation
may be DSB modulation, SSB modulation, or FM modulation instead of AM modulation. The
amplifier 105 amplifies the modulated oscillation signal and outputs it to the ultrasonic sound
generator 110. The ultrasonic speaker 110 converts the amplified oscillation signal into a sound
wave.
[0030]
The parametric speaker 100 configured as described above oscillates a signal of a frequency in
the ultrasonic band, modulates the oscillation signal with a desired sound signal, amplifies the
modulation signal, and converts it into a sound wave by the ultrasonic sound generator 110. And
radiate. In this way, directional sharp ultrasound can be emitted. For example, it can be used for
museums, aquariums, museums, amusement facilities, etc. because it can selectively send
information to people in a narrow area. In the future, it can also be used as traffic information.
[0031]
Example In accordance with the above-described manufacturing method, first, 50 ultrasonic
sounding bodies were manufactured for a parametric speaker without filling the silicon resin and
not adjusting the resonance frequency of each piezoelectric vibrator. And when these resonance
frequencies were measured and the standard deviation was calculated, it was 301 Hz.
[0032]
Next, a silicone resin was injected into the bottom of the resonator as a target value, with the
resonance frequency that is the average value of each ultrasonic sounding body set to solidify,
and the resonance frequency of each ultrasonic sounding body was adjusted. And when these
resonant frequencies were measured and the standard deviation was calculated, it was 42 Hz.
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[0033]
Table 1 shows the standard deviation of each resonance frequency before and after adjusting the
resonance frequency. As shown in Table 1, the adjustment using the silicone resin reduced the
standard deviation of the resonance frequency, and the variation could be suppressed. Therefore,
it could be demonstrated that the sound pressure can be improved if a parametric speaker is
manufactured using the adjusted ultrasonic sounding body.
[0034]
DESCRIPTION OF SYMBOLS 100 parametric speaker 101 oscillator 102 modulator 105 amplifier
110 ultrasonic sounding body 111 piezoelectric element 112 diaphragm 113a, 113b lead wire
114 resonator 114a solidified body 115 piezoelectric vibrator 120 board
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