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DESCRIPTION JP2012134594

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DESCRIPTION JP2012134594
An oscillation device capable of realizing a sufficient sound pressure level even in a small size
and thin shape is provided. In an electro-acoustic transducer 100 as an oscillation device, an axial
center member 130 having a specific gravity higher than that of a piezoelectric element 123
penetrates the centers of the piezoelectric element 123, an elastic member 122, and a vibrating
film 121 in a planar shape. For this reason, since this axial center member 130 plays a role of
weight and increases the inertial effect of the piezoelectric vibrator 120 composed of the
piezoelectric element 123, the elastic member 122 and the vibrating film 121, the vibration
amplitude can be increased. Therefore, a high sound pressure level can be secured in the small
and thin piezoelectric type electroacoustic transducer 100. [Selected figure] Figure 1
Oscillator and electronic device
[0001]
The present invention relates to an oscillation device using a piezoelectric vibrator, and an
electronic device using the oscillation device.
[0002]
In mobile phones, the development of thin and stylish mobile phones that use audio 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
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sound, and development of a thin electro-acoustic transducer of a piezoelectric type replacing the
conventional electrodynamic type is actively made. The piezoelectric type electroacoustic
transducer reproduces a sound wave using the expansion and contraction movement of the
piezoelectric element. For this reason, it is superior to slimming down compared with the
electrodynamic type electroacoustic transducer comprised from a magnet and a voice coil.
[0003]
At present, there are various proposals as the above-described electroacoustic transducer (Patent
Document 1).
[0004]
Japanese Patent Application Publication No. 2004-087662
[0005]
However, since a piezoelectric ceramic with high rigidity is used as a driving source for a
piezoelectric electroacoustic transducer, a high mechanical quality factor can be obtained, and a
high sound pressure level can be secured near the fundamental resonance frequency. There is a
problem that the sound pressure level is attenuated in the band.
That is, there are peaks and valleys in the acoustic characteristics, and it is difficult to secure a
high sound pressure level.
[0006]
The present invention has been made in view of the problems as described above, and provides
an oscillation device capable of securing a high sound pressure level, and an electronic device
using such an oscillation device.
[0007]
The oscillation device according to the present invention includes a frame-shaped support frame,
a flat vibration member supported by the support frame at an outer peripheral portion, and an
elastic member disposed on at least one surface of the vibration member and having higher
rigidity than the vibration member. It has a piezoelectric element disposed on at least one surface
of an elastic member and capable of expanding and contracting by the application of an electric
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field, and an axial center member which has a higher specific gravity than the piezoelectric
element and penetrates the center of the piezoelectric element in the direction orthogonal to the
main surface. .
[0008]
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 an ultrasonic
wave that is demodulated to a sound wave in the audible range.
[0009]
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.
[0010]
Note that the various components of the present invention do not necessarily have to be
independent entities individually, but a plurality of components are formed as one member, and
one component is formed of a plurality of members. That one component is a part of another
component, that a part of one component overlaps with a part of another component, and so on.
[0011]
In the oscillation device of the present invention, the axial center member whose specific gravity
is higher than that of the piezoelectric element penetrates the center of the piezoelectric element
in the direction orthogonal to the main surface.
For this reason, since this axial center member plays a role of weight and increases the inertial
effect of the piezoelectric vibrator including the piezoelectric element, the elastic member and
the vibrating member, the vibration amplitude can be increased.
Therefore, a high sound pressure level can be secured in the small and thin piezoelectric
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oscillation device.
[0012]
FIG. 1 is a schematic vertical front view showing a structure of an electro-acoustic transducer
that is an oscillation device according to an embodiment of the present invention.
It is a typical disassembled perspective view which shows the structure of an electroacoustic
transducer.
It is a schematic plan view which shows the structure of the electroacoustic transducer of one
modification.
[0013]
The electroacoustic transducer 100 which is an oscillation apparatus of this Embodiment is
demonstrated below with reference to FIG. 1 and FIG.
The electro-acoustic transducer 100 of the present embodiment includes a frame-shaped support
frame 110, a vibration film 121 which is a flat vibration member supported by the support frame
110 at an outer peripheral portion, and a vibration film 121 as illustrated. And a piezoelectric
element 123 disposed on at least one surface of the elastic member 122 and having a higher
specific gravity than the piezoelectric element 123. And an axial center member 130 penetrating
the center of the piezoelectric element 123 in the direction orthogonal to the main surface.
[0014]
More specifically, the axial center member 130 penetrates the piezoelectric element 123, the
elastic member 122, and the vibrating film 121.
An electrode layer 124 is also formed on both sides of the piezoelectric element 123, and the
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piezoelectric vibrator 120 is formed of the electrode layer 124, the piezoelectric element 123,
the elastic member 122, and the vibrating film 121. A driver circuit 140 which is an oscillation
drive unit is connected to such a piezoelectric vibrator 120.
[0015]
The axial center member 130 is made of a metal material such as brass, copper or tungsten
having a high specific gravity, and is fixed to the piezoelectric element 123, the elastic member
122, and the vibrating film 121, but is insulated from the electrode layer 124. . The piezoelectric
element 123, the elastic member 122 and the vibrating film 121 are formed in a similar shape
centering on the shaft center member 130, and are formed concentrically around the shaft
center member 130 as shown in FIG. The vibrating film 121 is formed to have a large diameter,
the elastic member 122 is formed to have a medium diameter, and the electrode layer 124 and
the piezoelectric element 123 are formed to have a small diameter.
[0016]
Further, in the electroacoustic transducer 100 of the present embodiment, for example, the
longitudinal elastic coefficient of the vibrating film 121 made of resin is 1/50 or less of the
longitudinal elastic coefficient of the elastic member 122 made of metal. The thickness ratio of
the film 121 is approximately 3: 1.
[0017]
The piezoelectric element 123 is not particularly limited as to both the inorganic material and the
organic material as long as it has a piezoelectric effect, but a material having high
electromechanical conversion efficiency, such as lead zirconate titanate (PZT) or barium titanate
(BaTiO3) Materials such as) can be used.
The thickness is not particularly limited, but preferably 10 μm to 1 mm.
[0018]
When a thin film having a thickness of less than 10 μm is used as a ceramic material which is a
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brittle material, chipping and breakage occur due to weak mechanical strength during handling,
making handling difficult. In addition, when a ceramic having a thickness of more than 1 mm is
used, the conversion efficiency for converting electrical energy into mechanical energy is
significantly reduced, and sufficient performance as the electroacoustic transducer 100 can not
be obtained. Generally, in a piezoelectric ceramic that produces an electrostrictive effect by the
input of an electrical signal, its conversion efficiency depends on the electric field strength. Since
this electric field strength is expressed by thickness / input voltage with respect to the
polarization direction, an increase in thickness inevitably causes a decrease in conversion
efficiency.
[0019]
In the piezoelectric element 123 of the present invention, an electrode layer 124 is formed on
the main surface to generate an electric field. The material is not particularly limited, but it is
possible to use, for example, silver or silver / palladium. Silver is used as a low-resistance
general-purpose electrode material and has advantages in manufacturing processes and costs,
and silver / palladium is a low-resistance material excellent in oxidation resistance, so it has
advantages in terms of reliability. is there.
[0020]
Further, the thickness of the electrode layer 124 is not particularly limited, but the thickness is
preferably 1 to 100 μm. If the thickness is less than 1 μm, since the film thickness is thin, it can
not be molded uniformly, and the conversion efficiency may be reduced. When the film thickness
of the electrode layer 124 exceeds 100 μm, there is no particular problem in manufacturing, but
the electrode layer 124 becomes a constraining surface with respect to the ceramic material of
the piezoelectric element 123 and the energy conversion efficiency is reduced. There is a point.
[0021]
The elastic member 122 is not particularly limited as long as it is a material having a high elastic
modulus to ceramic which is a brittle material such as metal or resin, but general materials such
as phosphor bronze and stainless steel are used from the viewpoint of processability and cost.
Ru. The thickness is preferably 5 to 1000 μm. If the thickness is less than 5 μm, the mechanical
strength is weak, the function as a constraining member is impaired, and there is a problem that
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the mechanical vibration characteristic of the vibrator varies among manufacturing lots due to
the decrease in processing accuracy.
[0022]
The vibrating film 121 is not particularly limited as long as it is a polymer material having a
longitudinal elastic modulus of 100 GPa or less, but from the viewpoint of versatility, use of
polyethylene terephthalate, polyethylene, urethane, silicone rubber, natural rubber, synthetic
rubber, etc. Is possible.
[0023]
In addition, when the thickness exceeds 1000 μm, there is a problem that the restraint to the
piezoelectric element 123 due to the increase in rigidity is intensified, and the vibration
displacement amount is attenuated.
Moreover, as for the elastic member 122 of this embodiment, it is preferable that the longitudinal
elastic modulus which is a parameter | index which shows the rigidity of material is 1-500 GPa.
As described above, when the rigidity of the elastic member 122 is excessively low or excessively
high, there is a problem that the characteristics and reliability of the mechanical oscillator are
impaired.
[0024]
The mechanism of sound wave generation utilizes the stretching movement generated by the
application of an electric field to the piezoelectric element 123. Also, the frequency of ultrasonic
waves is limited to 20 kHz or more. Since the piezoelectric element 123 has a high mechanical
quality factor Q, energy is concentrated in the vicinity of the fundamental resonance, so high
sound pressure levels can be obtained at the fundamental resonance frequency, but sound
pressure is attenuated in other frequency bands. I will.
[0025]
Since the electroacoustic transducer 100 of the present embodiment oscillates an ultrasonic
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wave limited to a specific frequency, it is rather advantageous that the mechanical quality factor
Q of the piezoelectric element 123 is high. In addition, since the fundamental resonance
frequency of the piezoelectric vibrator is affected by the shape of the piezoelectric element 123,
the case where the resonance frequency is adjusted to a high frequency band, for example, an
ultrasonic wave band is advantageous in downsizing.
[0026]
Note that the electroacoustic transducer 100 of the present embodiment oscillates an ultrasonic
wave that has been subjected to FM (Frequency Modulation) or AM (Amplitude Modulation)
modulation, and utilizes a non-linear state (density state) of air to generate a modulated wave.
Sound reproduction is performed based on the principle of so-called parametric speaker that
demodulates and reproduces audible sound. In the electroacoustic transducer 100 according to
the present embodiment, the piezoelectric element 123 is configured to be limited to oscillation
of a high frequency band, so that miniaturization can be achieved.
[0027]
In the configuration as described above, in the electro-acoustic transducer 100 of the present
embodiment, the axial center member 130 plays the role of a weight. That is, the inertial effect of
the piezoelectric vibrator 120 can be increased, and the vibration amplitude thereof can be
increased. Therefore, a high sound pressure level can be secured even with the small and thin
electroacoustic transducer 100.
[0028]
Further, in the electro-acoustic transducer 100 of the present embodiment, since the axial center
member 130 is disposed in the hole portion of the piezoelectric element 123 or the elastic
member 122, the shape is not lost. Even in the prior art, there has been a method of arranging
the weight at the center of the piezoelectric element 123 to increase the inertial effect, but in
order to attach the metal piece to the piezoelectric element 123, the shape is damaged and the
thickness direction of the vibrating surface is increased There were problems such as. In this
configuration, since the axial center member 130 is integrally formed, the shape is superior.
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[0029]
Moreover, in the structure of this invention, a division | segmentation vibration can be
suppressed. That is, by increasing the rigidity of the central portion of the piezoelectric element
123, it is possible to suppress the form of the divided vibration, and the acoustic characteristics
are improved. Furthermore, the electroacoustic transducer 100 of the present embodiment is
configured of a vibrating film 121 made of a resin that is rich in flexibility at the end where
stress is concentrated at the time of vibration. That is, since the impact energy at the time of
dropping can be absorbed by the vibrating film 121 made of resin, the drop strength can be
improved.
[0030]
Further, in the electro-acoustic transducer 100 of this configuration, an end portion between the
support frame 110 and the elastic member 122 is made of the resin of the vibration film 121. In
other words, the flexible film made of resin vibrating film 121 is located at the end of the
vibration, so that the movable range of the end is expanded, the vibration mode becomes more
like a piston, and the volume exclusion amount at the time of vibration is expanded. Do. Since the
sound pressure level depends on the volume displacement to air during vibration, the electroacoustic transducer 100 of the present configuration can realize advantageous characteristics.
[0031]
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 above
embodiment, the piezoelectric element 123, the elastic member 122 and the vibrating film 121
are formed in a similar shape centering on the shaft center member 130, and concentrically
around the shaft center member 130 as shown in FIG. It illustrated that it was formed.
[0032]
However, like the electroacoustic transducer 200 illustrated as an oscillation device in FIG. 3, the
electrode layer 210, the piezoelectric element 211, the elastic member 212, the vibrating film
213, and the support frame 220 are rectangular around the axial center member 130. It may be
formed in a square similar shape.
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[0033]
Further, in the above embodiment, the electro-acoustic transducer 100 having a monomorph
structure in which the elastic member 122 and the piezoelectric element 123 are disposed on
one side of the vibrating film 121 is illustrated.
However, while the first and second elastic members 122 are individually disposed on both
surfaces of the vibrating film 121, and the first piezoelectric element 123 is disposed on one
surface of the first elastic member 122, the second elasticity The second piezoelectric element
123 is disposed on the other surface of the member 122, and the first piezoelectric element 123,
the first elastic member 122, the vibrating film 121, the second elastic member 122, and the
second piezoelectric element 123 It is also possible to implement a bimorph structure in which
the axial center member 130 penetrates the center of the (not shown).
[0034]
In that case, by making the diameters of the pair of elastic members different, the structures of
the piezoelectric vibrators mounted one by one on both surfaces of the vibrating film can also be
made different. Further, the plate thicknesses of the pair of elastic members may be made
different while keeping the diameter the same, or the diameters and the plate thicknesses of the
pair of piezoelectric elements may be made different (none is shown).
[0035]
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.
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[0036]
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.
[0037]
DESCRIPTION OF SYMBOLS 100 electro-acoustic transducer 110 support frame 120
piezoelectric vibrator 121 vibration film 122 elastic member 123 piezoelectric element 124
electrode layer 130 axial center member 140 driver circuit 200 electro-acoustic transducer 210
electrode layer 211 piezoelectric element 212 elastic member 213 vibration film 220 support
flame
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