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JP2014064204

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DESCRIPTION JP2014064204
Abstract: The present invention provides an ultrasonic speaker and a parametric speaker capable
of suppressing a temperature rise even if a sound pressure is increased by increasing an applied
voltage. An ultrasonic sound generator for a parametric speaker that generates ultrasonic waves,
wherein a piezoelectric element 111 and a piezoelectric element 111 using a piezoelectric
material having a mechanical quality factor Qm of 100 or more are formed on one main surface
A piezoelectric vibrator 115 formed of a bonded diaphragm 112, and a resonator 114 provided
on the other main surface of the diaphragm 112 and generating an ultrasonic wave by the
vibration of the diaphragm 112 are provided. Thus, even if the applied voltage is increased to
increase the sound pressure, the temperature rise can be suppressed. Moreover, since it is for
parametric speakers, it is not necessary to receive ultrasonic waves, and it is not necessary to
contain vibration in a short time, and it is possible to use a large Qm piezoelectric material.
[Selected figure] Figure 1
Ultrasonic speaker and parametric speaker
[0001]
The present invention relates to an ultrasonic speaker that generates ultrasonic waves and a
parametric speaker using the same.
[0002]
The ultrasonic speaker includes a piezoelectric vibrator in which a diaphragm and a piezoelectric
element are bonded to each other.
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When an alternating voltage near the resonance frequency specific to the piezoelectric vibrator is
applied to the piezoelectric element, the piezoelectric vibrator vibrates and emits an ultrasonic
wave. 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 in the forward direction. The ultrasonic sound generator is fixed by bonding node
portions that do not move in bending vibration of the piezoelectric vibrator with a silicon
adhesive or the like so as not to disturb the vibration as much as possible. 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]
On the other hand, a piezoelectric ceramic material having a high mechanical quality factor Qm
and having characteristics suitable for use as an ultrasonic transducer or the like is disclosed
(see, for example, Patent Document 3). The piezoelectric material described in Patent Document
3 contains Bi, Na, Ti, Ba, Mn, Nb and O, and has a general formula (1-x-y) (Bi0.5Na0.5) TiO3xBaTiO3-yBa (Mn1 / 1). It is a piezoelectric ceramic material represented by 3Nb2 / 3) O3.
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[0006]
Japanese Patent Application Laid-Open No. 60-167 597 Japanese Patent Application Laid-Open
No. 62-296698 Japanese Patent Application Laid-Open No. 2007-137704
[0007]
In the above-described ultrasonic speaker and ultrasonic sensor, high sound pressure can be
obtained by setting the driving frequency to the resonance frequency at which the piezoelectric
vibrator vibrates most.
However, although sound pressure can be obtained when driving at a resonance frequency, heat
generation of the piezoelectric vibrator is large. Further, as the temperature of the piezoelectric
vibrator rises, the resonance frequency is lowered as shown in FIG. 8 and the resonance
frequency is separated from the set driving frequency, so that the sound pressure is lowered.
[0008]
Since the ultrasonic sensor alternately performs transmission and reception by intermittent
driving, the temperature rise of the piezoelectric vibrator is small. On the other hand, since the
ultrasonic sound generator constitutes a parametric speaker and is driven continuously, the
temperature rise of the piezoelectric vibrator becomes large, and the sound pressure is reduced
due to the above-mentioned circumstances. Therefore, as an ultrasonic sounding body for
parametric speakers which is continuously driven, an ultrasonic sounding body which can emit a
high sound pressure ultrasonic wave and which can suppress a decrease in sound pressure with
a small temperature rise is desired.
[0009]
The present invention has been made in view of such circumstances, and it is an object of the
present invention to provide an ultrasonic sound generator and a parametric speaker capable of
suppressing a temperature rise even if the sound pressure is increased by increasing the applied
voltage. I assume.
[0010]
(1) In order to achieve the above object, an ultrasonic speaker according to the present invention
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is an ultrasonic speaker for a parametric speaker that generates ultrasonic waves, and is a
piezoelectric material having a mechanical quality factor Qm of 100 or more. A piezoelectric
element used and a piezoelectric vibrator formed by a vibrating plate having the piezoelectric
element bonded to one main surface, and the other main surface of the vibrating plate, and
ultrasonic waves are generated by the vibration of the vibrating plate And a resonator.
[0011]
As described above, since the ultrasonic speaker according to the present invention uses a
piezoelectric material having a mechanical quality factor Qm of 100 or more, the temperature
rise can be suppressed even if the sound pressure is increased by increasing the applied voltage.
it can.
In addition, since the ultrasonic speaker according to the present invention is for a parametric
speaker, it is not necessary to receive ultrasonic waves, there is no need to contain vibration in a
short time, and it becomes possible to use a large Qm piezoelectric material There is.
[0012]
(2) Further, the ultrasonic speaker according to the present invention is characterized in that the
piezoelectric material used for the piezoelectric element has a mechanical quality factor Qm of
600 or more.
Thus, even if the applied voltage is increased to increase the sound pressure, the temperature
rise can be suppressed.
[0013]
(3) Further, the ultrasonic speaker according to the present invention is characterized in that the
sound pressure of the generated ultrasonic wave can be maintained at 122.5 dB or more even
when the temperature rises by 20 ° C. As a result, a sufficiently large sound pressure can be
maintained when the temperature rise tolerance is 20 ° C.
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[0014]
(4) Further, the parametric speaker of the present invention comprises a flat substrate provided
with a wiring pattern, a support member provided on the substrate, and the above ultrasonic
sounding body supported by the support member. A plurality of ultrasonic sounding bodies are
provided, and by continuously driving the ultrasonic sounding bodies, an audible sound is caused
to appear due to non-linear characteristics when ultrasonic waves propagate.
[0015]
As described above, by configuring a parametric speaker with an ultrasonic sound generator
using a piezoelectric material having a large Qm, individual sound pressure of the ultrasonic
sound generator can be increased, and a small number of sound pressure can be sufficient. You
can get it.
As a result, the parametric speaker can be miniaturized.
[0016]
According to the present invention, even if the applied voltage is increased to increase the sound
pressure, the temperature rise of the ultrasonic transducer can be suppressed to a small value.
[0017]
It is a front view showing a parametric speaker of the present invention.
It is a side view which shows the structure of the ultrasonic sounding body of this invention. (A),
(b) is a side view which shows one scene of operation | movement of the ultrasonic sounding
body of this invention. It is a block diagram showing an electrical configuration of a parametric
speaker. It is a graph which shows an experimental result by the relation of temperature rise to
sound pressure. It is a graph which shows an experimental result by temperature rise to
mechanical quality factor Qm. It is a graph which shows an experimental result by the relation of
sound pressure to mechanical quality factor Qm. It is a graph which shows the relationship
between the resonance frequency in each temperature of a piezoelectric vibrator, and impedance.
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[0018]
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.
[0019]
(Configuration of Parametric Speaker) FIG. 1 is a front view showing the parametric speaker 100.
As shown in FIG. The parametric speaker 100 generates an ultrasonic wave modulated by a
strong sound pressure, and an audible sound appears due to the non-linear characteristic of the
propagation of the ultrasonic wave in the air. In this way, it is possible to identify the direction or
distance, give directivity, and transmit acoustic information.
[0020]
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.
[0021]
The ultrasonic sounding body 110 using a piezoelectric material having a large Qm constitutes
the parametric speaker 100, so that the individual sound pressure of the ultrasonic sounding
body 110 can be increased, and a sufficient number of sound pressures can be obtained with a
small number. be able to. As a result, the parametric speaker 100 can be miniaturized.
[0022]
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(Configuration of Ultrasonic Sounding Body) FIG. 2 is a side view showing a configuration of the
ultrasonic sounding body 110. As shown in FIG. The ultrasonic speaker 110 is used for the
parametric speaker 100 to generate an ultrasonic wave. Since the ultrasonic speaker 110 is for a
parametric speaker, it is not necessary to receive ultrasonic waves, and it is not necessary to
contain vibration in a short time, and it is possible to use a large Qm piezoelectric material. 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.
[0023]
The piezoelectric element 111 is formed in a plate shape using a piezoelectric material having a
mechanical quality factor Qm of 100 or more, and expands and contracts by application of a
voltage in the thickness direction. As described above, since the piezoelectric material having the
mechanical quality factor Qm of 100 or more is used, the temperature rise can be suppressed
even if the applied voltage is increased to increase the sound pressure.
[0024]
The piezoelectric material used for the piezoelectric element 111 preferably has a mechanical
quality factor Qm of 600 or more. As a result, even if ultrasonic waves with a sound pressure of
122.5 dB are generated, the temperature rise is 20 ° C. or less, and even if the applied voltage is
increased to raise the sound pressure, the temperature rise can be suppressed. More preferably,
the piezoelectric material used for the piezoelectric element 111 has a mechanical quality factor
Qm of 1000 or more. As a result, even if an ultrasonic wave with a sound pressure of 123 dB is
generated, the temperature rise is 20 ° C. or less.
[0025]
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 ultrasonic waves can be generated via the vibrating surface.
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[0026]
The resonator 114 is formed in a conical cylinder shape, and is made of, for example, aluminum
or an aluminum alloy. In addition, parabolic cylinder shape or funnel shape is contained in
conical cylinder 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. 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, for example, of a metal such as brass, SUS304, 42 alloy or
aluminum. The piezoelectric element 111 and the diaphragm 112 form a piezoelectric vibrator
115.
[0027]
Even in the case of the ultrasonic speaker 110, when a material having a large mechanical
quality factor Qm is selected as in the ultrasonic sensor, the tailing of the pulse waveform of the
ultrasonic wave is increased. The ultrasonic sensor can not determine the timing at which the
ultrasonic wave returned when the vibration of the vibrator is not settled when the ultrasonic
wave is reflected back to the obstacle or the like, and the sensor function can not be performed,
The tailing of the above pulse waveform is a problem. Then, in the ultrasonic sensor, the
vibration is reduced in a short time by using a small Qm material.
[0028]
On the other hand, the ultrasonic sounding body for parametric speakers is specialized for
transmission of ultrasonic waves, and the above problems do not occur. Since the ultrasonic
speaker 110 does not receive ultrasonic waves as in an ultrasonic sensor, it is not necessary to
quickly store the vibration, and it is preferable to vibrate using a large Qm material.
[0029]
(Operation of Ultrasonic Sounding Body) FIGS. 3A and 3B are side views showing one scene of
the operation of the ultrasonic sounding body 110 of the present invention. As shown in FIGS. 3
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(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. At this time, if the mechanical quality factor
Qm of the piezoelectric material is high, the electric energy is less likely to be consumed as heat,
and the temperature rise can be suppressed small even if the sound pressure is increased.
[0030]
(Method of Producing Ultrasonic Sounding Body) A method of producing the ultrasonic sounding
body 110 will be described. First, a plate-like piezoelectric body is formed of a piezoelectric
material having a Qm of 100 or more (more preferably 600 or more), 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 100 can be manufactured.
[0031]
(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.
[0032]
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
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wave.
[0033]
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.
[0034]
(Example) The ultrasonic sounding body was produced with the piezoelectric element using the
piezoelectric material of different Qm, the sound pressure was changed by adjusting the applied
voltage, and the temperature rise was measured about each continuously driven. 5 to 7 are
graphs showing experimental results from different points of view.
[0035]
FIG. 5 is a graph showing experimental results in terms of temperature rise relative to sound
pressure. FIG. 5 shows the temperature rise relative to the sound pressure at the time of
saturation, and indicates that the higher the sound pressure and the lower the temperature rise,
the better the characteristics. The ultrasonic sounding body (Qm 500 sample) using the Qm 500
piezoelectric material is closer to the ultrasonic sounding body (Qm 1350 sample) using the Qm
1350 piezoelectric material, and it can be seen that the higher the Qm, the better the property.
[0036]
FIG. 6 is a graph showing experimental results in terms of temperature rise with respect to the
mechanical quality factor Qm. FIG. 6 shows the sound pressure with respect to Qm at each
temperature rise. According to FIG. 6, for example, when the sound pressure is 117 dB, the
temperature rise of the ultrasonic sounding body (Qm60 sample) using the Qm60 piezoelectric
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material is 10.9 ° C., and the temperature rise of the Qm500 sample is 6.0 ° C. , Qm1350
sample temperature rise is 5.0 ° C. Therefore, it is understood that the temperature increase is
suppressed to a smaller value as the sample with larger Qm.
[0037]
FIG. 7 is a graph showing experimental results in terms of sound pressure with respect to the
mechanical quality factor Qm. According to FIG. 7, the temperature rise of 10 ° C. is 116.3 dB
for the Qm60 sample, 119.1 dB for the Qm500 sample, and 120.0 dB for the Qm1350 sample.
Thus, under the same temperature rise condition, the higher the mechanical quality factor Qm,
the higher the sound pressure.
[0038]
Assuming a practical time from the above result, there is a difference in the maximum sound
pressure that can be taken with respect to the temperature rise tolerance. For example, when the
temperature rise tolerance is up to + 20 ° C., the maximum sound pressure is 120.5 dB for the
Qm50 sample, 122.3 dB for the Qm 500 sample, and 123.7 dB for the Qm 1350 sample. In
addition, if it is 3 dB higher, one ultrasonic sounding body can emit an ultrasonic wave equivalent
to 1.4. Therefore, the larger the material Qm, the greater the sound pressure for a given
temperature rise tolerance. And the part | minute and the number of ultrasonic sounding bodies
can be decreased and a parametric speaker can be miniaturized.
[0039]
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 115 piezoelectric vibrator 120 board
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