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DESCRIPTION JP2014160914

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DESCRIPTION JP2014160914
Abstract: [Problem] There is a need for a revolutionary technology for providing a piezoelectric
electroacoustic transducer capable of reproducing a small size and high sound quality, which is
an alternative to the electrodynamic electroacoustic transducer. A piezoelectric electroacoustic
transducer is a piezoelectric element, a frame supporting or containing the piezoelectric element,
and a diaphragm supported by the frame and directly or indirectly connected to the piezoelectric
element. And a diaphragm having a high rigidity portion formed to cross the diaphragm, and a
low rigidity portion formed between the high rigidity portion and the frame. [Selected figure]
Figure 1
Piezoelectric type electroacoustic transducer and electronic device using the same
[0001]
The present invention relates to a piezoelectric electroacoustic transducer and an electronic
device using the same.
[0002]
An electrodynamic electroacoustic transducer is used as an acoustic component of an electronic
device such as a mobile phone.
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
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film fixed to a voice coil is vibrated by the action of a magnetic circuit of a stator using a magnet
to generate an acoustic wave.
[0003]
By the way, in recent years, since the demand for portable terminals such as portable telephones
and laptop personal computers is increasing, the demand for downsizing of the electroacoustic
transducer is increasing. The sound pressure level, which is an important factor in the acoustic
performance of the electroacoustic transducer, is determined by the volume exclusion of the
vibrating membrane against air. Therefore, when the electroacoustic transducer is miniaturized,
the radiation surface area of the vibrating film is reduced, which causes a problem that the sound
pressure level is reduced.
[0004]
As a means of improving the sound pressure level, there is a method of increasing the generation
force of the magnetic circuit and increasing the amplitude of the vibrating film. However, this
means requires an increase in magnetic flux density and an increase in drive current, and there is
a problem that the thickness of the magnetic circuit is increased due to the increase in volume of
the permanent magnet and the thickening of the voice coil. Furthermore, there are problems
such as an increase in power consumption due to an increase in current amount.
[0005]
On the other hand, as means for realizing a small and thin electroacoustic transducer, there is a
piezoelectric electroacoustic transducer utilizing the piezoelectric effect of piezoelectric ceramics.
In this piezoelectric method, vibration amplitude is generated by the electrostrictive action by the
input of an electric signal using the piezoelectric effect of a ceramic material. In the piezoelectric
type electroacoustic transducer, the ceramic itself in which the upper and lower layers are
constrained by the electrode material vibrates, and this functions as a drive source. Therefore, an
electrokinetic comprising a magnetic circuit composed of many members such as a magnet and a
voice coil The number of members is smaller than that of the type electro-acoustic transducer,
which is advantageous in thinning.
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[0006]
Patent Document 1 discloses a speaker including a piezoelectric element and a diaphragm made
entirely of resin.
[0007]
JP, 2011-249990, A
[0008]
The following analysis is given by the present invention.
[0009]
Since the piezoelectric electroacoustic transducer uses a ceramic material with a low internal loss
as a vibration source, the mechanical quality factor Q tends to be higher than an electrodynamic
electroacoustic transducer that generates an amplitude through an organic film.
For example, the electrodynamic type is approximately 3 to 5 and the piezoelectric type is
approximately 50.
Since the mechanical quality factor Q indicates sharpness at resonance, in summary, the
piezoelectric electroacoustic transducer means that the sound pressure is high near the
fundamental resonance frequency and the sound pressure is attenuated in the other bands.
That is, in the frequency characteristics of the sound pressure level, peaks and valleys of the
acoustic characteristics are generated, and a sound of a specific frequency is emphasized or lost,
and there is a problem that sufficient sound quality can not be obtained for music reproduction
and the like.
[0010]
Moreover, in the speaker of patent document 1, there is a problem that the rigidity of the
diaphragm which is entirely made of resin is low and divided vibration is likely to occur.
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[0011]
On the other hand, since the diaphragm made of metal as a whole has a small internal loss, there
is a problem that the vibration continues for a long time and the timbre is easily disturbed.
[0012]
For this reason, there is a demand for a revolutionary technology for providing a piezoelectric
electroacoustic transducer capable of reproducing a small size and high sound quality, which is
an alternative to the electrodynamic electroacoustic transducer.
[0013]
The piezoelectric electroacoustic transducer according to the first aspect comprises a
piezoelectric element, a frame supporting or containing the piezoelectric element, and a
diaphragm supported by the frame and connected directly or indirectly to the piezoelectric
element. The diaphragm includes: a high rigidity portion formed to cross the diaphragm; and a
low rigidity portion formed between the high rigidity portion and the frame.
[0014]
The electronic device of the second viewpoint uses the piezoelectric electroacoustic transducer of
the first viewpoint as a speaker.
[0015]
The first viewpoint contributes to the provision of a piezoelectric electroacoustic transducer
capable of reproducing a small size and high sound quality, which is an alternative to the
electrodynamic electroacoustic transducer, and the second perspective relates to a small size and
high sound quality regeneration Contribute to the provision of electronic devices that can
[0016]
(A) is a top view of the piezoelectric-type electroacoustic transducer which concerns on
Embodiment 1, (B) is the same sectional view.
FIG. 6 is an exploded view of a piezoelectric electroacoustic transducer according to a second
embodiment.
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It is sectional drawing of the piezoelectric-type electroacoustic transducer which concerns on a
comparative example.
It is a graph which each shows the frequency characteristic of the sound pressure level of the
piezoelectric-type electroacoustic transducer of Embodiment 1, and the piezoelectric-type
electroacoustic transducer which concerns on a comparative example.
[0017]
Preferably, the high rigidity portion of the diaphragm is formed on the diagonal of the diaphragm
to form an X shape.
[0018]
Preferably, the low stiffness portion of the diaphragm is formed between the edge of the high
stiffness portion and the inner edge of the frame.
[0019]
Preferably, the central portion of one surface of the piezoelectric element is connected to the
central portion of the diaphragm or the high rigidity portion thereof via a connecting member.
More preferably, the center of one surface of the piezoelectric element is connected to the center
of the diaphragm or the high rigidity portion thereof via the connection member.
[0020]
Preferably, the other surface of the piezoelectric element is supported by the frame via at least an
elastic member.
[0021]
Preferably, the high rigidity portion of the diaphragm gradually widens from the center to the
end of the diaphragm.
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[0022]
Preferably, the high rigidity portion of the diaphragm is made of metal, and the low rigidity
portion of the diaphragm is made of resin.
[0023]
Preferably, the piezoelectric electroacoustic transducer of the embodiment is used as a
parametric speaker.
[0024]
An outline of an embodiment of the present invention will be described with reference to the
drawings.
The reference numerals of the drawings appended to this summary are added for convenience to
the respective elements as an example for aiding understanding, and the present invention is not
intended to be limited to the illustrated embodiments.
[0025]
Referring to FIG. 1, the piezoelectric electroacoustic transducer 1 is supported by the
piezoelectric element 2, a frame 4 supporting or containing the piezoelectric element 2, and the
frame 4, and is directly or indirectly connected to the piezoelectric element 2. And a diaphragm
3.
The diaphragm 3 has a high rigidity portion 3 a formed to cross the diaphragm 3 and a low
rigidity portion 3 b formed between the high rigidity portion 3 a and the frame 4.
[0026]
The high rigidity portion 3a enhances the rigidity of the diaphragm 3, prevents the divided
vibration of the diaphragm 3, and raises the sound pressure level.
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In addition, the vibration of the high rigidity portion 3a itself also helps the entire diaphragm 3 to
perform a piston movement.
By these actions, the sound pressure level is increased, and highly efficient reproduction is
possible.
The low rigidity portion 3 b attenuates the vibration of the diaphragm 3 and improves the sound
quality because the internal loss is large.
[0027]
In addition, the piezoelectric element 1 is restrained by the high rigidity portion (metal plate) 3a
of the diaphragm 3, and the high rigidity portion 3a is joined to the frame 4 via the low rigidity
portion 3b such as a resin film.
Thereby, the rigidity of the end portion of the diaphragm 3 where the stress is concentrated is
reduced, and the vibration movable range is expanded.
In addition, the low rigidity portion 3b damps the vibration and the mechanical quality factor Q is
reduced.
[0028]
Since a normal piezoelectric electroacoustic transducer has a plurality of vibration modes, the
generation of divided vibration results in a frequency sound pressure characteristic with peaks
and valleys.
According to the piezoelectric-type electroacoustic transducer 1 of the embodiment, the divided
vibration is suppressed by controlling the vibration mode by the diaphragm 3 configured of a
plurality of portions having different rigidity, and good acoustic characteristics can be obtained.
it can.
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[0029]
Preferably, as shown in FIG. 1, the piezoelectric-type electroacoustic transducer 1 includes the
piezoelectric element 2, the diaphragm 3 supported by the frame 4, and a connecting member 5
that connects the one surface of the piezoelectric element 2 and the diaphragm 3 And a metal
plate 6 joined to the other surface of the piezoelectric element 2 to restrain the other surface,
and an elastic member 7 connecting the metal plate 6 to the frame 4. The diaphragm 3 includes
a high rigidity portion 3a made of metal and a low rigidity portion 3b made of resin. The high
rigidity portion 3a is disposed on the diagonal of the diaphragm 3 or the vibration surface. The
low rigidity portion 3 b is joined to the outer edge of the high rigidity portion 3 a.
[0030]
The high rigidity portion is preferably formed of a metal thin film having a thickness of 100 μm
or less.
[0031]
Preferably, a connecting member is interposed between the piezoelectric element and the
diaphragm.
By propagating the vibration from the piezoelectric element (piezoelectric actuator) to the
diaphragm through the connecting member, stress can be concentrated on the diaphragm and
the displacement of the vibration can be expanded. Also, there is an advantage that the resonance
frequency can be easily controlled by adjusting the shape of the vibrating body.
[0032]
The piezoelectric electroacoustic transducer of the embodiment is small and highly efficient, and
is useful as an electroacoustic transducer for portable terminals. In addition, by using this as a
sound source of the parametric speaker, high-quality sound reproduction is possible. The
piezoelectric electroacoustic transducer of the embodiment can also reproduce ultrasonic waves
of 20 kHz or more. As described above, by setting the oscillation frequency to the ultrasonic
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band, it is possible to miniaturize the piezoelectric element or the piezoelectric type
electroacoustic transducer, and to control the directivity by utilizing the straightness of the
ultrasonic wave. It is possible to realize a privacy sound source limited only in the vicinity of the
position of. Therefore, the piezoelectric-type electroacoustic transducer of the embodiment can
be suitably used as a parametric speaker that transports an audio signal to ultrasonic waves and
demodulates them in the air.
[0033]
Therefore, the piezoelectric-type electroacoustic transducer has high industrial value as an
acoustic device for electronic devices that is small and thin, and can efficiently reproduce sound
with high sound pressure and high sound quality.
[0034]
The piezoelectric-type electroacoustic transducer of the embodiment is suitably applied to
general portable electronic devices such as portable terminals. For example, a portable telephone,
a smartphone, a game console, a tablet PC (Personal Computer), a notebook PC, a PDA (Personal
Data Assistants) : A portable information terminal), a digital camera, etc. are applied suitably.
[0035]
Preferably, the upper and lower main surfaces of the piezoelectric ceramic are constrained by the
electrodes to form a piezoelectric element.
In addition, preferably, the piezoelectric element is restrained by a metal plate and is joined to
the frame via the metal plate.
The resonance frequency of the piezoelectric element can be easily controlled by adjusting the
rigidity by changing the thickness or material of the metal plate. This metal plate may not be
formed of a single metal material but may be formed of a composite material with a resin or a
laminated material.
[0036]
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The resonance frequency of the piezoelectric element (mechanical oscillator) is controlled by the
shape, its weight and rigidity. Since it is difficult to process an ordinary piezoelectric element into
an arbitrary shape because the piezoelectric ceramic is a brittle material, the resonance
frequency is adjusted by a method such as adding a weight. In such a method, although the
resonance frequency can be reduced by the addition of weight, there is a problem that the
vibration amplitude is attenuated because the amplitude portion is restrained by a weight.
[0037]
In the diaphragm, the ratio of specific elastic modulus of high rigidity part to low rigidity part (=
specific elastic modulus of high rigidity part / specific elastic modulus of low rigidity part) is, for
example, several times to several thousand times, several times It is adjusted to be in the range of
several hundred times or in the range of several times to several tens times.
[0038]
In the diaphragm, the specific elastic modulus of the high rigidity portion is set to, for example,
an order of 10 <7> (E / ρ) m <2> / s <2> or more, and the specific elastic modulus of the low
rigidity portion is It is set to the order less than.
Preferably, the high rigidity portion is formed of a metal material such as stainless steel,
phosphor bronze, magnesium, aluminum, titanium, beryllium or an alloy thereof, and the low
rigidity portion is polyethylene type, polypropylene type, polystyrene type or polyamide type, or
It is formed of a resin material such as urethane. Also, the diaphragm may be formed of various
composite materials.
[0039]
The piezoelectric element can be composed of a piezoelectric ceramic and a pair of electrodes. As
the piezoelectric element, various types of piezoelectric elements can be used. For example, a
structure in which two piezoelectric elements are constrained by a metal material, that is, a
piezoelectric element having a so-called bimorph structure can be used. As the piezoelectric
ceramic of the piezoelectric element, PZT (lead titanium zirconate) or the like can be used.
[0040]
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The connection member can be formed of various materials such as metal and resin, and in the
case of metal, a relatively light metal is preferable, and for example, metal materials such as
magnesium, aluminum, titanium or beryllium or alloys thereof are exemplified. Ru. It is
preferable to form from
[0041]
Subsequently, an embodiment of the present invention will be described in detail with reference
to the drawings. In the following description, many specifics are made to aid the understanding
of the present invention for the purpose of explanation.
[0042]
FIG. 1A is a plan view of the piezoelectric electroacoustic transducer according to Embodiment 1,
and FIG. 1B is a cross-sectional view thereof. Referring to FIGS. 1A and 1B, the piezoelectric
electroacoustic transducer 1 is supported on the piezoelectric element 2, the frame 4 for
supporting or containing the piezoelectric element 2, and the end face of the frame 4 while being
piezoelectric And a diaphragm 3 which is directly or indirectly connected to the element 2 and
vibrates with the electrostrictive action of the piezoelectric element 2.
[0043]
In particular, referring to FIG. 1A, the diaphragm 3 is made of a metal high rigidity portion 3 a
formed so as to cross the diaphragm 3, and a resin formed between the high rigidity portion 3 a
and the frame 4. And the low rigidity portion 3b. The high rigidity portion 3 a is formed on the
diagonal of the diaphragm 3 and has an X shape. The low rigidity portion 3 b is formed between
the edge of the high rigidity portion 3 a and the inner edge of the frame 4. The high rigidity
portion 3a is formed gradually wider from the center to the end of the diaphragm 3.
[0044]
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The diaphragm 3 can be formed by laminating the rib-like high rigidity part 3 a and the film-like
low rigidity part 3 b. Alternatively, resin may be filled between the outer edge of the high rigidity
portion 3a and the inner edge of the frame 4 to form the low rigidity portion 3b in the same
layer as the high rigidity portion 3a. Preferably, the high rigidity portion 3a is joined to the frame
4 via the low rigidity portion 3b.
[0045]
The central portion of one main surface (one surface) of the piezoelectric element 2 is connected
to the central portion of the diaphragm 3 or the high rigidity portion 3 a via the connecting
member 5. In the illustrated embodiment, in particular, the center of one of the main surfaces of
the piezoelectric element is connected to the center of the diaphragm 3 or the high rigidity
portion 3a via the connecting member 5 having a circular cross section.
[0046]
The other main surface (other surface) of the piezoelectric element 2 is supported by the frame 4
via the metal plate 6 and the elastic member 7. The metal plate 6 restrains the other main
surface (other surface) of the piezoelectric element 2. Specifically, both ends of the piezoelectric
element 2 are supported on the inner wall of the frame 4 via the metal plate 6 and the plurality
of elastic members 7, 7.
[0047]
When the piezoelectric electroacoustic transducer 1 is mounted on an electronic device, the
frame 4 may be attached to the frame of the electronic device, or the frame 4 of the piezoelectric
electroacoustic transducer 1 may be integrated with the frame of the electronic device Good.
[0048]
The characteristic functions of the piezoelectric electroacoustic transducer 1 will be described.
The high rigidity portion 3a prevents the divided vibration of the diaphragm 3, and the high
rigidity portion 3a itself also vibrates and deforms, thereby helping the entire diaphragm 3 to
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perform a large piston movement. Since the low rigidity portion 3 b has a large internal loss, it
attenuates the vibration of the diaphragm 3 to reduce the mechanical quality factor Q and reduce
the rigidity of the end portion of the diaphragm 3 where the stress is concentrated. Expand the
movable range.
[0049]
Further, by propagating the vibration of the piezoelectric element 2 locally to the diaphragm 3
via the connecting member 5, stress is concentrated at the central portion or the center of the
diaphragm 3, and the vibration displacement of the diaphragm 3 is enlarged. It can be done.
[0050]
FIG. 2 is an exploded view of a piezoelectric electroacoustic transducer according to a second
embodiment.
In the second embodiment, the differences from the first embodiment will be mainly described,
and the description of the first embodiment will be appropriately referred to for the common
points of both the embodiments.
[0051]
Referring to FIG. 2, the piezoelectric electroacoustic transducer 11 is a flat plate-like connecting
member 15 joined to one electrode of the piezoelectric element 2 and a flat plate-like elastic
member joined to the other electrode of the piezoelectric element 2. It has 17 and. The
connecting member 15 is entirely bonded to one main surface of the piezoelectric element 2 to
restrain the piezoelectric element 2 with relatively high rigidity. The other main surface of the
piezoelectric element 1 is bonded to the elastic member 17 entirely, and the elastic member 17
elastically restrains the piezoelectric element 2.
[0052]
Further, the central portion of one main surface (one surface) of the piezoelectric element 2 is
connected to the central portion of the diaphragm 3 or the high rigidity portion 3 a via the
connection member 15.
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[0053]
Next, frequency characteristics of sound pressure levels of the piezoelectric electroacoustic
transducers of the first to third embodiments shown in FIG. 1 and the piezoelectric
electroacoustic transducer according to the comparative example shown in FIG. 3 were verified.
The high rigidity portion (metal portion) 3a of the diaphragm 3 is made of stainless steel, the low
rigidity portion 3b is made of polyethylene, the connection member 5 is made of urethane
rubber, and the piezoelectric ceramic 2a is made of PZT (lead titanium zirconate). .
[0054]
Referring to FIG. 3, in the piezoelectric-type electroacoustic transducer 31 of the comparative
example, a piezoelectric element 32 configured of a piezoelectric ceramic 32 a and a pair of
electrodes 32 b and 32 c sandwiching the piezoelectric ceramic 32 a, and one entire main
surface of the piezoelectric element 32 It has the metal diaphragm 33 joined between the
piezoelectric element 32 and the inner wall of the flame | frame 34 joined. The whole surface of
the metal diaphragm 33 is joined to the whole of one main surface of the piezoelectric element
31 to restrain the same. Both ends of the piezoelectric element 32 are supported on the inner
wall of the frame 34 via the metal diaphragm 33 and the elastic member 37, respectively.
[0055]
FIG. 4 is a graph showing frequency characteristics of sound pressure levels of the piezoelectric
electroacoustic transducer of the first embodiment and the piezoelectric electroacoustic
transducer according to the comparative example. Referring to FIG. 4, it can be seen that the
sound pressure level is generally higher in the first embodiment and there is no sharp peak.
Therefore, it can be seen that the piezoelectric type electroacoustic transducer according to the
first embodiment has small peaks and valleys of the acoustic characteristics and can reproduce
high-quality sound with high sound pressure without the sound of a specific frequency being
emphasized too much.
[0056]
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As mentioned above, although one embodiment etc. of the present invention were described, the
present invention is not limited to the above-mentioned one embodiment etc., in the range which
does not deviate from the fundamental technical idea of the present invention, the further
modification Substitutions or adjustments can be made.
[0057]
The disclosure of the above-mentioned patent documents is incorporated herein by reference.
Within the scope of the entire disclosure of the present invention (including the scope of the
claims), modifications and adjustments of the embodiments or examples are possible based on
the basic technical concept of the invention. In addition, various combinations or selections of
various disclosed elements (including the respective elements of the respective claims, the
respective elements of the respective embodiments and the examples, the respective elements of
the respective drawings, and the like) within the scope of the claims of the present invention Is
possible. That is, the present invention of course includes the entire disclosure including the
scope of the claims, and various modifications and alterations that can be made by those skilled
in the art according to the technical concept.
[0058]
1, 11 Piezoelectric Electroacoustic Transducer 2 Piezoelectric Element (Piezoelectric Actuator) 2a
Piezoelectric Ceramics 2b, 2c Electrode 3 Diaphragm 3a High Rigidity Section (Metal Section) 3b
Low Rigidity Section (Resin Section, Resin Film) 4 Frame 5 Connection Member 6 metal plate 7
elastic member 11 piezoelectric type electroacoustic transducer 15 connection member 17
elastic member
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