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JP2012134592

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DESCRIPTION JP2012134592
An oscillation device capable of outputting a large volume while having a small occupied area is
provided. In an electro-acoustic transducer (100), an elastic member (120) for restraining a
piezoelectric element (110) is connected to a substrate (BP) at a spring portion (130). Therefore,
the piezoelectric element 110 and the elastic member 120 can be resiliently vibrated with
respect to the substrate BP, and the vibration can be enhanced by resonance. Therefore, highefficiency and high-volume output is possible, and cancellation and energy loss can be eliminated
even when arranged in an array, for example. [Selected figure] Figure 1
Oscillator and electronic device
[0001]
The present invention relates to an oscillation device using a piezoelectric element, and an
electronic device using the oscillation device.
[0002]
At present, in mobile phones which are electronic devices, development of thin and stylish mobile
phones having sound functions such as music reproduction and hands-free as a commercial
value has been activated.
Among the electro-acoustic transducers, there is a high demand for small, thin and high-quality
sound, and development of a thin electro-acoustic transducer of a piezoelectric type replacing the
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conventional electrodynamic type is actively made.
[0003]
As shown in FIG. 4, the piezoelectric electroacoustic transducer has a piezoelectric element 110
that moves in an expanding and contracting manner by the application of an electric field, and a
flat elastic member 120 that restrains one surface of the piezoelectric element 110. The sound
waves are reproduced using the 110 stretching movements. For this reason, it is superior to
slimming down compared with the electrodynamic type electroacoustic transducer comprised
from a magnet and a voice coil.
[0004]
At present, there are various proposals as the above-described electroacoustic transducers
(Patent Documents 1 and 2).
[0005]
JP 2002-300700 A JP 2004-112213 A
[0006]
However, the problem found by the inventor is efficiency.
As shown in FIG. 5, when a plurality of piezoelectric vibrators are arrayed, the sound waves
interfere in the vicinity of the radiation surface, so energy loss may occur due to canceling or the
directivity control may be difficult. The
For this reason, the inventor has found that a technique relating to an electroacoustic transducer
for ultrasonic waves that enables highly efficient and directional control is required.
[0007]
The present invention has been made in view of the problems as described above, and provides
an oscillating device capable of outputting a large sound volume with high efficiency, and an
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electronic device using such an oscillating device.
[0008]
The oscillation device of the present invention is an elastic member that has a piezoelectric
element that moves in an expanding and contracting manner by the application of an electric
field, a flat elastic member that restrains one surface of the piezoelectric element, and an elastic
member with emissivity in the direction orthogonal to the main surface of the piezoelectric
element. And at least opposing ridges individually formed on at least both ends of and coupled to
the substrate.
[0009]
A first electronic device of the present invention includes the oscillation device of the present
invention and an oscillation drive unit that causes the oscillation device to output sound waves in
an audible range.
[0010]
A second electronic device according to the present invention includes an oscillation device
according to the present invention, an oscillation drive unit that causes the oscillation device to
output an ultrasonic wave, and an ultrasonic wave detection that detects an ultrasonic wave
oscillated from the oscillation device and reflected by the object to be measured. And a distance
measuring unit for calculating the distance from the detected ultrasonic wave to the object to be
measured.
[0011]
In the oscillation device of the present invention, the elastic member for restraining the
piezoelectric element is connected to the substrate at the spring portion.
Therefore, the piezoelectric element and the elastic member can be resiliently vibrated with
respect to the substrate, and the vibration can be enhanced by resonance.
Therefore, high-efficiency and high-volume output is possible, and cancellation and energy loss
can be eliminated even when arranged in an array, for example.
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[0012]
It is a typical front view showing the structure of the electroacoustic transducer which is an
oscillation device of an embodiment of the invention.
It is a typical front view which shows the structure of the electroacoustic transducer of one
modification.
It is a typical front view which shows the structure of the electroacoustic transducer of another
modification. It is a typical front view which shows the structure of the electroacoustic
transducer of one prior art example. It is a typical perspective view showing the structure of a
plurality of electroacoustic transducers arranged in the shape of an array.
[0013]
As shown in FIG. 1, an electroacoustic transducer 100, which is an oscillation device according to
the present embodiment, includes a piezoelectric element 110 that stretches and contracts by
application of an electric field, and a flat elastic member 120 that restrains one surface of the
piezoelectric element 110. And at least oppositely projecting portions 130 individually formed on
at least both ends of the elastic member 120 and having elasticity in a direction orthogonal to
the main surface of the piezoelectric element and coupled to the substrate BP.
[0014]
The spring portion 130 is integrally formed with the elastic member 120, and the spring portion
130 is formed in a semicircular arc cross-sectional shape continuous with the flat elastic member
120 at one end.
Further, in the electro-acoustic transducer 100 of the present embodiment, one piezoelectric
element 110 is mounted on one surface of the elastic member 120 on the opposite side to the
substrate BP.
[0015]
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The piezoelectric element 110 is connected to a driver circuit 140 which is an oscillation drive
unit that causes the electroacoustic transducer 100 to output sound waves in an audible range.
Since the spring portion 130 is perpendicular to the amplitude direction of the piezoelectric
element 110, it acts as a spacer between the piezoelectric element 110 and the substrate BP.
[0016]
The mechanism of sound wave generation utilizes the stretching movement generated by the
application of an electric field to the piezoelectric element 110. Also, the frequency of ultrasonic
waves is limited to 20 kHz or more. Since the piezoelectric element 110 has a high mechanical
quality factor Q, energy is concentrated in the vicinity of the fundamental resonance, so a high
sound pressure level can be obtained at the fundamental resonance frequency, but the sound
pressure is attenuated in other frequency bands .
[0017]
In this configuration, since the ultrasonic wave limited to the specific frequency is oscillated, it is
rather advantageous that the mechanical quality factor Q of the piezoelectric element 110 is
high. In addition, since the fundamental resonance frequency of the piezoelectric vibrator is
affected by the shape of the piezoelectric element 110, the case where the resonance frequency
is adjusted to a high frequency band, for example, an ultrasonic wave band is advantageous in
downsizing.
[0018]
In this configuration, an ultrasonic wave modulated by FM (Frequency Modulation) or AM
(Amplitude Modulation) is oscillated, and the modulated wave is demodulated to reproduce an
audible sound by using a non-linear state (density state) of air. Sound is reproduced based on the
principle of so-called parametric speakers. In the electroacoustic transducer 100 according to the
present embodiment, the piezoelectric element 110 is configured to be limited to the oscillation
of the high frequency band, so that miniaturization can be achieved.
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[0019]
In the configuration as described above, the first feature of the electroacoustic transducer 100 of
the present embodiment is the point regarding implementation. Since the spring portions 130 at
both ends of the elastic member 120 which constrains the piezoelectric element 110 are directly
bonded to the substrate BP, a frame constituting the transducer is unnecessary, and the
mounting area can be reduced. In addition, since it can be easily joined to the empty space of the
substrate BP, restrictions such as the mounting position can be alleviated.
[0020]
The second feature relates to the area of the transducer. In the electro-acoustic transducer 100
of this configuration, the ultrasonic wave is oscillated, so the area can be reduced as compared
with the conventional electro-acoustic transducer that reproduces the audible sound.
[0021]
The third feature is the sound pressure level. In this configuration, by forming the projecting
portion 130 in the vertical direction in the elastic member 120, the apparent stroke of the elastic
member 120 can be lengthened, and vibration displacement can be enlarged.
[0022]
In the electro-acoustic transducer 100 of this configuration, sound reproduction is performed
using the principle of a parametric speaker that uses ultrasonic waves as a carrier wave of sound.
By utilizing this principle of parametric speaker, it is possible to form a superdirective sound
field. In order to control the directivity of sound waves, it is preferable to emit sound waves from
a plurality of transducers on the array as in the phase array method, and in the electro-acoustic
transducer 100 of this configuration as well, a plurality of them on the substrate BP. Can be
arranged to form an array of transducers.
[0023]
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As described above, in the electroacoustic transducer 100 of the present embodiment, the elastic
member 120 for restraining the piezoelectric element 110 is connected to the substrate BP at the
spring portion 130. Therefore, the piezoelectric element 110 and the elastic member 120 can be
resiliently vibrated with respect to the substrate BP, and the vibration can be enhanced by
resonance. Therefore, high-efficiency and high-volume output is possible, and cancellation and
energy loss can be eliminated even when arranged in an array, for example.
[0024]
The present invention is not limited to the present embodiment, and various modifications are
allowed without departing from the scope of the present invention. For example, in the abovedescribed embodiment, the unimorph-structured electroacoustic transducer 100 in which only
one upper surface of the elastic member 120 is constrained by one piezoelectric element 110 is
illustrated.
[0025]
However, as in the electroacoustic transducer 200 illustrated as an oscillation device in FIG. 2, an
oscillation device having a bimorph structure in which the upper surface and the lower surface of
the elastic member 120 are constrained by two piezoelectric elements 110 can be implemented.
In this case, high-volume output can be performed more efficiently without increasing the size of
the entire apparatus.
[0026]
Further, in the above embodiment, the piezoelectric element 110 is restricted to the upper
surface of the elastic member 120 on the side opposite to the substrate BP. However, the
piezoelectric element 110 may be restrained by the lower surface of the elastic member 120 on
the same side as the substrate BP, as in the electroacoustic transducer 300 illustrated as an
oscillation device in FIG. 3. In this case, dead space can be used to miniaturize the entire
apparatus.
[0027]
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Moreover, in the said form, it assumed that the piezoelectric element 110 consists of one
piezoelectric layer. However, the piezoelectric element may have a laminated structure in which
piezoelectric layers and electrode layers are alternately laminated (not shown).
[0028]
Furthermore, in the above-described embodiment, it has been exemplified that the spring portion
130 is formed in a semicircular arc cross-sectional shape which is continuous with the flat elastic
member 120 at one end. However, such a spike portion may be formed in a V-shaped crosssectional shape (not shown).
[0029]
Further, in the above-described embodiment, it has been illustrated that the pair of opposing
projecting portions 130 are individually formed at both ends of the elongated rectangular elastic
member 120. However, the spring portion may be connected to all four sides of the rectangular
elastic member 120 (not shown).
[0030]
Furthermore, in the above-described embodiment, it is assumed that the electronic apparatus has
a driver circuit 140, which is an oscillation drive unit, connected to the electroacoustic
transducer 100. However, such an electro-acoustic transducer 100, an oscillation drive unit for
causing the electro-acoustic transducer 100 to output an ultrasonic wave, and an ultrasonic wave
for detecting an ultrasonic wave oscillated from the electro-acoustic transducer 100 and
reflected by an object to be measured It is also possible to implement an electronic device (not
shown) such as a sonar having a detection unit and a distance measurement unit that calculates
the distance from the detected ultrasonic wave to the measurement object.
[0031]
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As a matter of course, the embodiment and the plurality of modifications described above can be
combined as long as the contents do not conflict with each other. Further, in the embodiment and
the modification described above, the structure and the like of each part are specifically
described, but the structure and the like can be variously changed as long as the present
invention is satisfied.
[0032]
100 electro-acoustic transducer 110 piezoelectric element 120 elastic member 130 springing
portion 140 driver circuit 200 electro-acoustic transducer 300 electro-acoustic transducer BP
substrate
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