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DESCRIPTION JP2011228966

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DESCRIPTION JP2011228966
PROBLEM TO BE SOLVED: To provide an electroacoustic transducer having small size and high
quality characteristics and an electronic device using the same. SOLUTION: An electroacoustic
transducer according to the present invention comprises first and second actuators 1a and 1b
that generate an acoustic radiation when an input signal is respectively applied, and the first and
second actuators 1a and 1b It is characterized in that it comprises a support 3 supported so that
the radiation surfaces face each other with a predetermined gap therebetween. And it is
characterized by using the electroacoustic transducer of such a configuration as a sound source
of an electronic device. [Selected figure] Figure 1
Electro-acoustic transducer and electronic device using the same
[0001]
The present invention relates to an electroacoustic transducer and an electronic device using the
same, and more particularly to an electroacoustic transducer suitable for use in an electronic
device including a portable terminal such as a portable telephone.
[0002]
In recent years, the demand for portable terminals of mobile phones and laptop personal
computers has been increasing.
Under such circumstances, manufacturers are working on the development of so-called stylish
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portable terminals that make the acoustic function a commercial value, and the demand for largevolume, small-sized electroacoustic transducers used for such portable terminals is increasing.
[0003]
An electrodynamic electroacoustic transducer is used as an acoustic component of an electronic
device including a portable terminal such as a portable telephone. This electrodynamic
electroacoustic transducer is composed of a permanent magnet, a voice coil and a vibrating
membrane. The principle of operation is that a vibrating film such as an organic film fixed to a
voice coil vibrates to generate a sound wave by the action of a magnetic circuit of a stator using a
magnet.
[0004]
However, in the acoustic performance of the electroacoustic transducer, the sound pressure level,
which is a physically indicative quantity indicating the volume, is determined by the
displacement of the vibrating membrane against the air. That is, since the sound pressure level
depends on the radiation area and the amount of amplitude, in principle, it is impossible to
simultaneously achieve compactness and loudness, and there is a large problem in mounting on a
portable terminal where miniaturization is required. .
[0005]
In addition, it is necessary to increase vibration amplitude in order to secure an equivalent sound
pressure level while radiation area decreases. For example, in a low frequency band (500 Hz or
less) where the amount of energy for amplitude generation is large, in order to obtain a sound
pressure level of 80 dB or more at a measurement distance of 10 cm for a microphone, a
vibration amplitude of 1 mm or more is required and mounted in a small space In the electroacoustic transducer for portable telephones, implementation restrictions are imposed.
[0006]
Further, in the electrodynamic electroacoustic transducer, since a magnetic circuit is used as a
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drive source, it is necessary to generate a high magnetic flux density in order to obtain high
amplitude, and for that purpose, the volume of the magnet, In particular, it is necessary to secure
a sufficient thickness direction, which limits the reduction in thickness. For example, even an
electrodynamic electroacoustic transducer using a neodymium-based material with high
magnetizing force as a magnet, even the thinnest product has a thickness of 3 mm or more,
which is a major obstacle to promoting the stylishization of mobile phones. It has become.
[0007]
In addition, although thin electrokinetic electroacoustic transducers have been developed to
make the voice coil thin, there is a problem such as burnout in the magnetic circuit that passes a
large current, so that reliability can be ensured. There's a problem.
[0008]
On the other hand, there is a piezoelectric electroacoustic transducer as a method of providing a
thin electroacoustic transducer.
In this piezoelectric method, vibration amplitude is generated by an electrostrictive action by an
input of an electric signal by using a piezoelectric effect of a ceramic material. In this
piezoelectric type electroacoustic transducer, since the ceramic itself in which the upper and
lower layers are constrained by the electrode material vibrates, it is superior in thinning
compared to a magnetic circuit composed of a large number of members such as a magnet and a
voice coil.
[0009]
In addition, since the thin ceramic body increases the electric field strength with respect to a
constant input voltage, it is advantageous as a thin driving source. However, since the ceramic
material is a brittle material and has a small mechanical loss, the mechanical quality factor Q
tends to be higher than that of an electrodynamic electroacoustic transducer that generates an
amplitude from an organic film.
[0010]
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For example, in the electrodynamic electroacoustic transducer, Q is about 3 to 5 and in the
piezoelectric electroacoustic transducer, it is about 50 or so. Summarizing this, since the Q
indicates the sharpness at resonance, in the piezoelectric electroacoustic transducer, the sound
pressure is high near the fundamental resonance frequency, and the sound pressure is
attenuated in the other bands. It means to do. That is, peaks and valleys of the acoustic
characteristics occur in the sound pressure level frequency characteristics, and a sound of a
specific frequency is emphasized or lost, so that the sound quality sufficient for music
reproduction can not be obtained.
[0011]
In addition to acoustic characteristics, it also has problems with the radiation area. Also in the
piezoelectric electroacoustic transducer, as in the electrodynamic electroacoustic transducer, the
sound pressure level depends on the volume exclusion amount (the product of the radiation area
and the amplitude), so the radiation is possible even if thinness is possible There is a limit to the
reduction of the area, and it does not fulfill sufficient functions as an electroacoustic transducer
for a mobile phone. For this purpose, a revolutionary technology for producing high-quality and
compact electro-acoustic transducers is required.
[0012]
As an example of the piezoelectric type electroacoustic transducer, there is one disclosed in
Patent Document 1.
[0013]
Unexamined-Japanese-Patent No. 2009-295865
[0014]
As described above, an electro-acoustic transducer that is used as a sound source of a portable
terminal represented by a portable telephone is required to have a small size and high quality
characteristics.
[0015]
Then, this invention is providing the electroacoustic transducer which has such a small and high
quality characteristic, and an electronic device using the same.
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[0016]
In the electro-acoustic transducer according to the present invention, the first and second
actuators, which receive an input signal respectively to generate acoustic radiation, and the first
and second actuators face each other with their acoustic radiation surfaces facing each other
with a predetermined gap. And a supporting body.
[0017]
An electronic device according to the present invention is characterized by using the abovedescribed electroacoustic transducer.
[0018]
According to the present invention, the pair of actuators having the vibrators are arranged such
that the acoustic radiation surfaces of each other face each other with a predetermined gap, and
from the space formed by the actuators and the support, the vibrators are Since the sound waves
generated from the air are emitted into the atmosphere, there is an effect that small-sized and
high-quality sound reproduction becomes possible.
[0019]
It is a schematic sectional drawing of one embodiment of this invention.
It is a schematic perspective view (perspective view) of one embodiment of the present invention.
FIG. 2 is a cross-sectional view of a piezoelectric element used in the embodiment of the present
invention.
It is sectional drawing of the actuator used for embodiment of this invention.
It is a figure for demonstrating the operation | movement of one embodiment of this invention.
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It is a figure which shows the relationship between the sound wave in FIG. 5, and an interference
wave.
It is a figure explaining operation | movement of the piezoelectric element used for embodiment
of this invention.
It is a figure explaining operation | movement of the actuator used for embodiment of this
invention. It is a schematic sectional drawing of other embodiment of this invention. It is a figure
which shows the example of the acoustic characteristic of a division | segmentation vibration. It
is a figure which shows the example of a division | segmentation vibration. It is a figure for
describing other embodiment of this invention. It is a figure which shows the example of an
electrodynamic electroacoustic transducer. It is a schematic sectional drawing of other
embodiment of this invention. It is a figure which shows the example of an external appearance
of the mobile telephone to which this invention is applied. It is a figure which shows the example
of an external appearance of the personal computer to which this invention is applied.
[0020]
Hereinafter, embodiments of the present invention will be described in detail with reference to
the drawings. FIG. 1 is a schematic cross-sectional view of an embodiment of the present
invention, and FIG. 2 is a schematic perspective view (perspective view) thereof. As shown in
FIGS. 1 and 2, the piezoelectric electroacoustic transducers according to the embodiment of the
present invention are provided corresponding to the pair of piezoelectric elements 1a and 1b and
the piezoelectric elements 1a and 1b, respectively, and corresponding piezoelectric elements are
provided. It is comprised including the elastic members 2a and 2b which restrain an element, and
the support body 3 which supports the piezoelectric elements 1a and 1b restrained by the elastic
members 2a and 2b.
[0021]
The piezoelectric elements 1a and 1b are joined to the support 3 via the corresponding elastic
members 2a and 2b. The two elements 1a and 1b are arranged such that the acoustic emission
surfaces thereof face each other with a predetermined gap, and a hollow polyhedron (a
hexahedron in the example of the figure) is formed by the support 3 It is done. A through hole 4
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is provided on any one of the surfaces other than the surface supporting the multi-sided
piezoelectric element. The pair of piezoelectric elements 1a and 1b have the function of an
electromechanical transducer that generates an acoustic wave by the supply of an electrical
signal.
[0022]
Therefore, as shown in FIG. 3, the piezoelectric element 1 is composed of a piezoelectric material
11 and upper and lower electrodes 12 and 13 provided on both main surfaces thereof. Is
supposed to be
[0023]
With respect to the piezoelectric material 11, both inorganic materials and organic materials are
not particularly limited as long as they have a piezoelectric effect, but materials having high
electromechanical conversion efficiency, for example, crystalline zirconate titanate (PZT), etc. are
used be able to.
[0024]
The thickness of the piezoelectric material 11 is preferably 5 μ to 500 μ.
When a thin film having a thickness of 5 μm or less is used as a piezoelectric material composed
of polycrystals, sufficient electromechanical conversion efficiency can not be obtained because
the crystal order is low.
In addition, also in the case of using a ceramic having a thickness of more than 500 μm, the
conversion efficiency is poor, and a sufficient efficiency as a converter can not be obtained.
[0025]
In the case of a piezoelectric ceramic that produces an electrostrictive effect by the input of an
electrical signal, the conversion efficiency depends on the electric field strength. Since this
electric field strength is expressed by thickness / input voltage in the polarization direction, an
increase in thickness inevitably leads to a decrease in conversion efficiency.
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[0026]
Further, in the piezoelectric material 11, electrode layers 12 and 13 are formed on the main
surface in order to generate an electric field. The electrode material is not particularly limited as
long as it is a material having electrical conductivity, but it is preferable to use silver or silver /
palladium. Also, the thickness of the electrode material is not particularly limited, but preferably
1 to 50 μ. For example, if the thickness is less than 1 μm, the film thickness is too thin to form
uniformly on the electrode.
[0027]
In addition, there is also a method of applying in the form of paste, but in polycrystal such as
ceramic, since the surface state is so-called satin, the wet state at the time of application is bad,
and a uniform electrode film can not be formed. On the other hand, when the film thickness
exceeds 100 μm, molding becomes easy, but the electrode layer becomes a constraining surface,
and the energy conversion efficiency is lowered.
[0028]
Further, as shown in FIGS. 1 and 2, the piezoelectric element 1 shown in FIG. 3 is restrained by
the elastic material 2 (see the sectional view of FIG. 4). The elastic material 2 has a function of
propagating the vibration generated by the piezoelectric element 1 to the support 3 and a
function of enhancing shock stability when dropped.
[0029]
The elastic material 2 also has a function of adjusting the fundamental resonance frequency of
the piezoelectric element 1. The fundamental resonance frequency f of the mechanical oscillator
depends on the load weight m and the compliance C, as shown by the following equation: f = 1 /
{2πL (m · C) <1/2>}. Here, L is an equivalent inductance of the piezoelectric element.
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[0030]
In other words, since the compliance is the mechanical rigidity of the vibrator, this means that
the fundamental resonance frequency can be controlled by controlling the rigidity of the
piezoelectric element. For example, by selecting a material having a high elastic modulus or
reducing the thickness of the elastic material, it is possible to shift the fundamental resonance
frequency to a lower range.
[0031]
On the other hand, the fundamental resonance frequency can be shifted to a high frequency by
selecting a material having a high elastic modulus or increasing the thickness of the elastic
material. Until now, the basic resonant frequency was controlled by the shape and material of the
piezoelectric element, so there were problems in design restrictions, cost and reliability, but as in
the present invention, the elastic material which is a component The industrial value is great
because it can be easily adjusted to the desired fundamental resonance frequency by changing.
[0032]
The elastic material is not particularly limited as long as it is a material having a high elastic
modulus with respect to ceramic which is a brittle material such as metal and resin, but from the
viewpoint of processability and cost, general-purpose materials such as phosphor bronze and
stainless steel Is used.
[0033]
The thickness of the elastic material is preferably 5 to 1000 μm.
When the thickness is less than 5 μ, mechanical strength is weak, and the function as a
constraining member is impaired, and the processing accuracy of the vibrator is varied among
manufacturing lots due to the decrease in processing accuracy. In addition, when the thickness
exceeds 1000 μm, the restraint on the piezoelectric element due to the increase in rigidity is
strengthened, and the vibration displacement amount is attenuated.
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[0034]
Furthermore, the elastic material preferably has a longitudinal elastic modulus of 1 to 500 GPa,
which is an index indicating the rigidity of the material. As described above, when the stiffness of
the elastic material is excessively low or excessively high, the characteristics and reliability of the
mechanical oscillator are impaired.
[0035]
In the present embodiment, the piezoelectric element 1 is bonded to the support 3 with the
elastic member 2 interposed. The support 3 plays a role as a case for forming the electroacoustic
conversion, and also has a role to form an internal space above the hollow surrounded by two
transducers arranged in parallel.
[0036]
The shape of the support member 3 is not particularly limited as long as it can form a space, and
may be any shape such as a rectangular parallelepiped, another body, or a spherical surface. The
material of the support may be any material such as metal, resin, or a composite material of
metal and resin, but in order to efficiently propagate the vibration energy from the piezoelectric
element, On the other hand, it is preferable that the material has a certain degree of rigidity.
[0037]
Moreover, the support body 3 can use a several material. That is, when forming the hollow space,
it is not necessary to mold with an integral material, and it can be formed by joining constituent
members having a plurality of materials and shapes.
[0038]
In the electro-acoustic transducer of the present embodiment, the through hole 4 is formed on
any one side surface of the support 3 forming the internal space. The through hole 4 functions as
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a sound hole for emitting a sound wave to the atmosphere. For example, a sound wave generated
by the vibration of the piezoelectric element 1 a passes through the internal space and is emitted
to the outside air through the through hole 4. In addition, when the vibration is simultaneously
generated by the piezoelectric element 1a and the piezoelectric element 1b, they interfere with
each other in the internal space to amplify the sound wave. Since the amplified sound waves are
emitted to the outside through the through holes 4, a high sound pressure level can be obtained.
[0039]
In addition, the shape of the through hole 4 is not particularly limited, and may be any shape
such as a rectangle, a circle, or an ellipse. The through holes 4 are not particularly limited as long
as they can be formed on the side surface of the support 3. Further, the number of through holes
4 is not particularly limited, and a plurality of through holes may be formed.
[0040]
The manufacturing method of the above-mentioned electroacoustic transducer is demonstrated
below. First, a piezoelectric actuator which is a piezoelectric element has a configuration as
shown in FIG. The piezoelectric element 1 is a piezoelectric plate having an outer diameter of 5
mm and a thickness of 100 μm (0.1 mm), and upper and lower electrode layers each having a
thickness of 8 μm are formed on both surfaces thereof (see FIG. 3). The elastic member 2 was
formed of phosphor bronze having an outer diameter of 8 mm and a thickness of 100 μm (0.1
mm). Reference numeral 31 in FIG. 4 denotes a frame, and the piezoelectric actuator may be
fixed to the support 3 via the frame.
[0041]
The support 3 is made of SUS304, and the two piezoelectric actuators and the support 3 form an
internal space. Here, SUS is an abbreviation of Steel Use Stainless, and represents a stainless steel
material, and its 300 series is a Cr-Ni system. Further, the support 3 is a cube of vertical ×
horizontal × width = 21 × 21 × 21 mm, and is formed of SUS304 with a thickness of 0.5 mm.
Among the six faces of the cube shape, an opening of length x width = 20 x 20 mm was formed
in one face other than the two opposing faces to which the piezoelectric actuator was attached.
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[0042]
As shown in FIGS. 1 and 2, the piezoelectric elements 1a and 1b and the elastic members 2a and
2b are arranged concentrically at the center. A lead zirconate titanate ceramic was used for the
piezoelectric ceramic 11 constituting the piezoelectric element 1, and a silver / palladium alloy
(70% by weight: 30%) was used for the electrode layers 12 and 13.
[0043]
The piezoelectric ceramic 11 was produced by a green sheet method, and was fired in the
atmosphere over a temperature of 1100 ° C. for 2 hours, and then the piezoelectric material
layer was subjected to polarization treatment. The bonding between the piezoelectric element 1
and the elastic member 2 and the bonding between the support 3 were both performed using an
epoxy-based adhesive.
[0044]
Hereinafter, the operation principle of the above-described piezoelectric electroacoustic
transducer will be described. In this piezoelectric type electroacoustic transducer, a pair of
piezoelectric elements 1a and 1b are disposed with a predetermined interval so that the
respective acoustic radiation surfaces face each other, and by simultaneously driving these two
piezoelectric elements , Play the sound.
[0045]
That is, as shown in FIG. 5, the respective sound waves generated from the piezoelectric elements
1 a and 1 b interfere in the inner space of the support 3, and the sound waves are emitted to the
atmosphere through the through holes 4. As shown in FIG. 6, the sound waves are amplified by
the sound waves y1 and y2 having the same phase interfering with each other in the inner space
(y1 + y2). This doubles the sound wave generated from one vibrator, and the sound pressure
level is increased accordingly.
[0046]
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The sound pressure level P (dB) is expressed by the following equation: P = 10 log 10 {P '<2> / (2
× 10 <-5>) <2>} = 20 log 10 {P' / 2 × 10 <-5>} Since the effective sound pressure P '(Pa: Pascal)
depends on the radiation amount of the sound wave, if it is doubled, the sound pressure level of
about 6 dB increases. That is, by forming two vibrators on the side surface of the acoustic
element, it becomes possible to emit a loud sound without increasing the element shape.
[0047]
As shown in FIG. 7, the piezoelectric element 1 is formed of the piezoelectric plate (piezoelectric
ceramic) 11 having two main surfaces as described above, and the upper electrode layer 12 is
formed on each of the main surfaces of the piezoelectric plate 11. And the lower electrode layer
13 is formed. The polarization direction 100 of the piezoelectric plate 11 is not particularly
limited, but in the present embodiment, it is in the upper direction (the thickness direction of the
piezoelectric element 1) in the drawing shown by the arrow 100 in FIG.
[0048]
When an alternating voltage is applied to the upper electrode layer 12 and the lower electrode
layer 13 and an alternating electric field is applied, the piezoelectric element 1 configured in this
way, as shown in FIGS. A radial expansion / contraction motion is performed such that both
major surfaces simultaneously expand or contract. In other words, the piezoelectric element 1
performs a motion to repeat the first deformation mode in which the main surface is expanded
and the second deformation mode in which the main surface is reduced. It is the basic principle
of the electroacoustic transducer of the present invention that generates vibrations and
generates sound waves by repeating such motion.
[0049]
As described above, the electroacoustic transducer according to the present invention can also be
used as a sound source of an electronic device (for example, a mobile phone, a laptop personal
computer, a small game machine, etc.). Since the overall shape of the electroacoustic transducer
is not increased and the acoustic characteristics are improved, it can be used for portable
electronic devices.
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[0050]
Next, a second embodiment of the present invention will be described with reference to the
schematic cross sectional view of FIG. In FIG. 9, the parts equivalent to those in FIG. The present
embodiment is characterized in that the two piezoelectric elements 1a and 1b have different
shapes. That is, by making the shapes of the vibrators different from one another, each vibrator
has a different fundamental resonant frequency.
[0051]
For example, in the case of an electroacoustic transducer consisting of a single single transducer,
there is a problem that the reproduction band is narrow because a sound wave is generated
utilizing a single resonance characteristic, and in the vicinity of the resonance frequency In order
to maximize the acoustic energy, there is a problem that the sound pressure level is small in the
band lower than the fundamental resonance frequency, that is, in the low band, and there is no
heavy feeling of sound.
[0052]
As a means to solve this, there is a method of reducing the fundamental resonance frequency of
the electroacoustic transducer, but from the point of energy distribution, when energy is shifted
to the low range where a large amount of vibration energy is required, There is a problem that
the sound pressure level of 1 to 3 KHz decreases and the overall volume feeling decreases.
[0053]
Therefore, in the acoustic transducer according to the second embodiment of the present
invention, in order to maximize the sound pressure level in the specific frequency band, two
vibrators having different fundamental resonance frequencies are arranged, so a wide frequency
band is obtained. High sound pressure level can be realized.
[0054]
For example, in order to realize reproduction in a band of 100 Hz to 10 KHz where music
reproduction is possible, the volume of the low band can be increased by arranging a vibrator
having a fundamental resonance frequency of 500 Hz and 1 KHz. .
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[0055]
Further, in this electro-acoustic transducer, the characteristics of the sound pressure level
frequency can be flattened by adjusting the fundamental resonance frequencies of the two
vibrators.
This will be described in detail together with the relationship between the divided vibration and
the acoustic characteristics, and the description of the state of the divided vibration.
[0056]
As shown in FIG. 10, the divided vibration is formed by overlapping high-order vibration modes
generated after the fundamental resonance frequency with each other, and a large number of
vibration modes that move up and down are mixed in the radiation plane.
In this vibration, unlike the piston movement (vibration mode generated at the fundamental
resonance frequency) in which the entire surface translates in the same direction, the conversion
efficiency from the input acoustic signal to the acoustic vibration is before and after the
frequency at which the divided vibration occurs. Changes significantly, causing sounds other
than sound signals, not playing sound at a specific frequency, enhancing sound, or distorting the
sound, causing irregularities in sound pressure level frequency characteristics (Yamatani of
acoustic characteristics).
[0057]
For example, in the divided vibration shown in FIG. 11, vibration modes in which vibration modes
having different phases (in-phase and anti-phase) are regularly mixed are formed.
In acoustic radiation in this divided vibration, vibration modes mixed in the radiation plane and
having different phases (in-phase and anti-phase) interfere with each other in phase, and the
radiation sound is canceled.
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This means that the sound pressure is attenuated and a dip is generated. For this reason, how to
suppress the divisional vibration has been considered as an essential issue to realize the
flattening of the sound pressure level frequency.
[0058]
Therefore, in the present invention, by driving any one of the plurality of vibrators in accordance
with the frequency at which the sound peaks and valleys are generated, sound waves having an
opposite phase to cancel the sound pressure peak are generated. A sound pressure level
frequency characteristic can be flattened by generating an in-phase sound wave for repairing the
sound wave and causing the sound wave to interfere with each other.
[0059]
As described above, the electro-acoustic transducer according to the present embodiment can
also be used as a sound source of an electronic device (for example, a mobile phone, a laptop
personal computer, a small game machine, etc.).
In addition, since the shape of the entire electroacoustic transducer is not increased and the
acoustic characteristics are improved, the electroacoustic transducer can also be used for
portable electronic devices.
[0060]
Next, the third embodiment of the present invention will be described. In the present
embodiment, sound waves in the inaudible band, that is, ultrasonic waves are generated. Here, an
ultrasonic wave is generated from any one of the transducers, and an ultrasonic wave of the
same phase is generated at the same frequency which has been subjected to FM modulation or
AM modulation from another transducer. In other words, it is a parametric acoustic transducer.
The structure of the present embodiment is the same as that of the first embodiment.
[0061]
As shown in FIG. 12, two ultrasonic waves interfere in the inner space to generate heterodyne
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detection, and only AM modulation or FM modulation is generated as an audible wave. This
audible wave is radiated to the external space through the through hole, thereby enabling sound
reproduction. In the present embodiment, the frequency of generating the sound wave is not
particularly limited as long as it is 20 KHz or more. Further, the fundamental resonant frequency
of the vibrator depends on the outer peripheral shape of the piezoelectric ceramic. Therefore, by
shifting the reproduction frequency to a high frequency, the diameter of the vibrator can be
reduced, which is advantageous in that the shape of the electroacoustic transducer itself can be
miniaturized.
[0062]
As described above, the electro-acoustic transducer according to the present embodiment can
also be used as a sound source of an electronic device (for example, a mobile phone, a laptop
personal computer, a small game machine, etc.). In addition, since the shape of the entire
electroacoustic transducer is not increased and the acoustic characteristics are improved, the
electroacoustic transducer can also be used for portable electronic devices.
[0063]
Next, a fourth embodiment of the present invention will be described. In the electro-acoustic
transducer according to the present embodiment, a known MEMS (micro-electro-mechanical
system) actuator is used as a vibrator, and the configuration other than the vibrator is the same
as that of the first embodiment. .
[0064]
The piezoelectric MEMS actuator has a system using electrostatic force, electromagnetic force,
piezoelectric effect, or thermal distortion, and any system can be used. In this embodiment, a
system using the piezoelectric effect is used. The piezoelectric MEMS actuator comprises a
piezoelectric thin film layer, an upper movable electrode layer, and a lower movable electrode
layer. As in the first embodiment, this is a mechanism that generates vibration amplitude by the
piezoelectric effect, and is a mechanism that generates vibration amplitude by inputting an AC
signal to the electrode layer.
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[0065]
In addition, although a method etc. which can blow solid fusion particle etc. are mentioned to
manufacture of a MEMS actuator using an aerosol deposition method to an electrode layer, a
manufacturing method in particular is not limited. When this aerosol deposition method is used,
since the piezoelectric film can be easily adsorbed to a base material such as a curved surface,
the degree of freedom of the shape of the vibrator is increased, which is useful for improving the
characteristics of the electroacoustic transducer.
[0066]
The results of evaluation of the characteristics of the electroacoustic transducer according to the
present invention as described above will be described using the evaluation items of Evaluation 1
to Evaluation 3 as described below.
[0067]
(Evaluation 1) Measurement of sound pressure level frequency characteristics: The sound
pressure level when an AC voltage of 1 V was input was measured by a microphone placed at a
predetermined distance from the element.
The predetermined distance is 10 cm unless otherwise specified, and the frequency measurement
range is 10 Hz to 10 kHz.
[0068]
(Evaluation 2) Flatness Measurement of Sound Pressure Level Frequency Characteristic: The
sound pressure level when an AC voltage of 1 V was input was measured by a microphone
disposed at a predetermined distance from the element. The measurement range of the
frequency was 10 Hz to 10 kHz, and in the measurement range of 2 kHz to 10 kHz, the flatness
of the sound pressure level frequency characteristics was measured by the sound pressure level
difference between the maximum sound pressure level Pmax and the minimum sound pressure
level Pmin. As a result, the sound pressure level difference (referring to the difference between
the maximum sound pressure level Pmax and the minimum sound pressure level Pmin) was good
within 20 dB, and was not less than 20 dB. This predetermined distance is 10 cm unless
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otherwise stated.
[0069]
(Evaluation 3) Drop Impact Test: A drop impact stability test was conducted by causing a mobile
phone equipped with an electroacoustic transducer to drop spontaneously five times from 50 cm
immediately above. Specifically, breakage such as cracks after the drop impact test was visually
confirmed, and the sound pressure characteristics after the test were measured. As a result, the
sound pressure level difference (referring to the difference between the sound pressure level
before the test and the sound pressure level after the test) was 3 dB or less, and 3 dB or more.
[0070]
Example 1 The characteristics of the electroacoustic transducer described in the first
embodiment of the present invention were evaluated. The evaluation results are as follows.
Sound pressure level (1 kHz): 91 dB Sound pressure level (3 kHz): 88 dB Sound pressure level (5
kHz): 93 dB Sound pressure level (10 kHz): 85 dB Flatness of sound pressure level frequency
characteristics: Good Drop shock stability: Good
[0071]
As is clear from the above results, according to the electroacoustic transducer according to the
present embodiment, the sound pressure level frequency characteristic is flat and loud. In
addition, it has been demonstrated that the fundamental resonance frequency is 1 kHz or less,
the vibration amplitude is large, and the sound pressure level is over 80 dB in a wide frequency
band of 1 to 10 kHz.
[0072]
Comparative Example 1 As Comparative Example 1, an electrodynamic electroacoustic
transducer shown in FIG. 13 was produced. In the figure, (A) is a longitudinal cross-sectional
view, (B) is a part of the cross-sectional view of (A), 211 is a diaphragm, 212 is a voice coil, 213
is a frame, 214 is a pole piece , 215 and 216 are permanent magnets, and 217 is a yoke. Since
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such an electrodynamic electroacoustic transducer is well known, the description thereof is
omitted.
[0073]
[Results] Sound pressure level (1 kHz): 77 dB Sound pressure level (3 kHz): 75 dB Sound
pressure level (5 kHz): 76 dB Sound pressure level (10 kHz): 97 dB Flatness of sound pressure
level frequency characteristics: Good Drop shock stability: No
[0074]
Example 2 An electroacoustic transducer according to a second embodiment of the present
invention was produced.
[Results] Sound pressure level (1 kHz): 90 dB Sound pressure level (3 kHz): 95 dB Sound
pressure level (5 kHz): 90 dB Sound pressure level (10 kHz): 88 dB Flatness of sound pressure
level frequency characteristics: Good Drop shock stability: Good
[0075]
As apparent from the above results, according to the electro-acoustic transducer of this example,
the same characteristics as those of Example 1 above are obtained, and the sound pressure level
frequency characteristics are flat.
[0076]
Example 3 An electroacoustic transducer according to the third embodiment of the present
invention was produced.
[Results] Sound pressure level (1 kHz): 87 dB Sound pressure level (3 kHz): 91 dB Sound
pressure level (5 kHz): 85 dB Sound pressure level (10 kHz): 84 dB Flatness of sound pressure
level frequency characteristics: Good Drop shock stability: Good
[0077]
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As apparent from the above results, according to the electro-acoustic transducer of this example,
the same characteristics as those of Example 1 above are obtained, and the sound pressure level
frequency characteristics are flat.
[0078]
Example 4 An electroacoustic transducer according to the fourth embodiment of the present
invention was produced.
[Results] Sound pressure level (1 kHz): 84 dB Sound pressure level (3 kHz): 82 dB Sound
pressure level (5 kHz): 81 dB Sound pressure level (10 kHz): 80 dB Flatness of sound pressure
level frequency characteristics: Good Drop shock stability: Good
[0079]
As apparent from the above results, according to the electro-acoustic transducer of the present
example, it has the same characteristics as the first example, and the sound pressure level
frequency characteristic is flat.
[0080]
[Example 5] Here, as shown in the schematic perspective view of FIG. 14, according to the
present invention, the piezoelectric elements 1a and 1b have a configuration in which the outline
of the pair is not circular but rectangular. As an electroacoustic transducer by five embodiments,
it produced.
In FIG. 14, parts equivalent to those in FIGS. 1 and 2 are denoted by the same reference
numerals.
[0081]
[Results] Sound pressure level (1 kHz): 93 dB Sound pressure level (3 kHz): 95 dB Sound
pressure level (5 kHz): 91 dB Sound pressure level (10 kHz): 88 dB Sound pressure level
Frequency characteristic flatness: Good Drop shock stability: Good
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[0082]
As apparent from the above results, according to the electro-acoustic transducer of this example,
the same characteristics as those of Example 1 above are obtained, and the sound pressure level
frequency characteristics are flat.
[0083]
Example 6 In Example 6, the elastic member was changed from Example 1 above.
PET film was used as an elastic member.
[0084]
[Results] Sound pressure level (1 kHz): 83 dB Sound pressure level (3 kHz): 84 dB Sound
pressure level (5 kHz): 90 dB Sound pressure level (10 kHz): 84 dB Flatness of sound pressure
level frequency characteristics: Good Drop shock stability: Good
[0085]
As apparent from the above results, according to the electro-acoustic transducer of this example,
regardless of the material of the elastic member, it has the same sound pressure level as in
Example 1 above, and the sound pressure level frequency characteristic is flat. is there.
[0086]
Example 7 In Example 7, the piezoelectric material was changed from Example 1 above.
Polyvinylidene fluoride was used as a piezoelectric material.
[0087]
[Results] Sound pressure level (1 kHz): 80 dB Sound pressure level (3 kHz): 81 dB Sound
pressure level (5 kHz): 83 dB Sound pressure level (10 kHz): 87 dB Flatness of sound pressure
level frequency characteristics: Good Drop shock stability: Good
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[0088]
As apparent from the above results, according to the electro-acoustic transducer of this example,
regardless of the material of the piezoelectric material, it has the same sound pressure level as in
Example 1 above, and the sound pressure level frequency characteristics are flat. is there.
[0089]
Example 8 In Example 8, a general mobile phone as shown in FIG. 15 was prepared, and the
electroacoustic transducer (shown by a circle) of Example 1 above was mounted in the housing.
Specifically, the electro-acoustic transducer is attached to the inner surface of the casing of the
mobile phone.
[0090]
(Evaluation): A sound pressure level and frequency characteristics were measured by a
microphone placed at a position 10 cm away from the element.
In addition, a drop impact test was also conducted.
[0091]
[Results] Sound pressure level (1 kHz): 84 dB Sound pressure level (3 kHz): 85 dB Sound
pressure level (5 kHz): 88 dB Sound pressure level (10 kHz): 82 dB Drop impact test: Even after
five drops, the piezoelectric element still has cracks When the sound pressure level (1 kHz) was
measured after the test, it was 84 dB.
Flatness of sound pressure level frequency characteristics: Good
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[0092]
Example 9 A general mobile phone as shown in FIG. 15 was prepared as Example 9, and the
electro-acoustic transducer of Example 2 was mounted in this housing.
Specifically, this acoustic transducer is attached to the inside surface of the casing of the mobile
phone.
[0093]
(Evaluation): A sound pressure level and frequency characteristics were measured by a
microphone placed at a position 10 cm away from the element. In addition, a drop impact test
was also conducted.
[0094]
[Results] Sound pressure level (1 kHz): 82 dB Sound pressure level (3 kHz): 82 dB Sound
pressure level (5 kHz): 85 dB Sound pressure level (10 kHz): 84 dB Drop impact test: The
piezoelectric element still has cracks even after 5 drops When the sound pressure level (1 kHz)
was measured after the test, it was 78 dB. Flatness of sound pressure level frequency
characteristics: Good
[0095]
[Example 10] As Example 10, a general mobile phone as shown in FIG. 15 was prepared, and the
electro-acoustic transducer of Example 3 described above was mounted in this case. Specifically,
the electro-acoustic transducer is attached to the inner surface of the casing of the mobile phone.
[0096]
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(Evaluation): A sound pressure level and frequency characteristics were measured by a
microphone placed at a position 10 cm away from the element. In addition, a drop impact test
was also conducted.
[0097]
[Results] Sound pressure level (1 kHz): 84 dB Sound pressure level (3 kHz): 86 dB Sound
pressure level (5 kHz): 83 dB Sound pressure level (10 kHz): 81 dB Drop impact test: Even after
five drops, the piezoelectric element still has cracks When the sound pressure level (1 kHz) was
measured after the test, it was 78 dB. Flatness of sound pressure level frequency characteristics:
good
[0098]
Example 11 As Example 11, a general mobile phone as shown in FIG. 15 was prepared, and the
electro-acoustic transducer of Example 4 described above was mounted in this case. Specifically,
the electro-acoustic transducer is attached to the inner surface of the casing of the mobile phone.
[0099]
(Evaluation): A sound pressure level and frequency characteristics were measured by a
microphone placed at a position 10 cm away from the element. In addition, a drop impact test
was also conducted.
[0100]
[Results] Sound pressure level (1 kHz): 82 dB Sound pressure level (3 kHz): 85 dB Sound
pressure level (5 kHz): 81 dB Sound pressure level (10 kHz): 83 dB Drop impact test: Even after
five drops, the piezoelectric element still has cracks When the sound pressure level (1 kHz) was
measured after the test, it was 78 dB. Flatness of sound pressure level frequency characteristics:
Good
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[0101]
Example 12 As Example 12, a general desktop personal computer (PC) as shown in FIG. 16 was
prepared, and the electro-acoustic transducer of Example 1 described above was mounted in this
housing. Specifically, the electro-acoustic transducer is attached to the inner surface of the case
of the PC. (Evaluation): A sound pressure level and frequency characteristics were measured by a
microphone placed at a position 10 cm away from the element. In addition, a drop impact test
was also conducted.
[0102]
[Results] Sound pressure level (1 kHz): 80 dB Sound pressure level (3 kHz): 81 dB Sound
pressure level (5 kHz): 82 dB Sound pressure level (10 kHz): 81 dB Drop impact test: Even after
five drops, the piezoelectric element is still cracked When the sound pressure level (1 kHz) was
measured after the test, it was 78 dB. Flatness of sound pressure level frequency characteristics:
Good
[0103]
As mentioned above, the electro-acoustic transducer according to the present invention has at
least a pair of transducers, which are arranged such that the acoustic radiation surfaces face each
other with a predetermined gap, and a support It is characterized in that a space is formed. In
addition, a through hole is formed in a space in which a pair of transducers are formed to face
each other, and a sound wave generated from the transducer is radiated to the atmosphere
through the through holes.
[0104]
According to this configuration, the vibrator is an electromechanical transducer that generates an
amplitude by the input of an electric signal, and a sound wave is simultaneously generated from
the pair of vibrators, so that a high sound pressure level can be obtained. Further, according to
the present configuration, it is characterized in that an ultrasonic wave modulated by FM
modulation or AM modulation is generated from one vibrator and an ultrasonic wave of the same
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frequency is generated from another vibrator. That is, due to the interference between the FM or
AM modulated ultrasonic wave in space and the ultrasonic wave of the same frequency
generated from the opposing transducer, heterodyne detection occurs, an audible sound is
generated, and the air passes through the air into the atmosphere. It is emitted.
[0105]
According to this configuration, since the ultrasonic transducer is used, the size can be reduced
as compared with a transducer conventionally used for an electroacoustic transducer. Since the
fundamental resonance frequency depends on the outer circumference of the vibrator, the
ultrasonic vibrator is superior in miniaturization to a conventional vibrator having a fundamental
resonance frequency of about 1 KHz.
[0106]
Further, from the viewpoint of acoustic energy, an ultrasonic transducer having a higher
frequency can radiate equivalent energy with a low vibration amplitude, and is superior in design
as a mechanical transducer. Further, according to the present configuration, since an audible
sound is generated in a space formed by a plurality of transducers, it can be treated as one
electro-acoustic transducer, and therefore, in mounting on a small electronic device such as a
mobile phone. It is superior. As described above, according to the present invention, it is possible
to realize a small and high-quality electro-acoustic transducer.
[0107]
In the above embodiment, a pair of vibrators (actuators) is used, but one having a plurality of
vibrators arranged in an array can be used.
[0108]
1, 1a, 1b Piezoelectric element 2a, 2b Elastic material 3 Support 4 Through hole 12 Upper
electrode 13 Lower electrode
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