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DESCRIPTION JP2005286690

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DESCRIPTION JP2005286690
PROBLEM TO BE SOLVED: To obtain a piezoelectric film speaker capable of effectively using
vibration of a vibrating film for sound conversion and emitting effective sound. SOLUTION:
Expandable parts 4a and 4b are alternately provided so as to be front and back with respect to a
sound radiation direction, and the end parts of these expandable parts 4a and 4b are connected
by a rising part 5 to make a wave type diaphragm 1 . Each stretchable portion 4a, 4b has
stretchability in a direction perpendicular to the applied electric field, and electrodes 3a, 3b, 3c,
3d are formed on both sides of each stretchable portion 4a, 4b, and adjacent stretches are
formed. Electric fields of opposite phases are applied to the portions 4a and 4b. As a result, when
a signal whose polarity is reversed periodically is applied to the electrodes 3a, 3b, 3c, 3d, it
vibrates respiratoryly to generate a sound. [Selected figure] Figure 1
Piezoelectric film speaker and parametric speaker using the same
[0001]
The present invention relates to a piezoelectric film speaker that emits sound using a
piezoelectric film and a parametric speaker using the same.
[0002]
Conventionally, there is a piezoelectric film speaker in which a vibrating film made of a
piezoelectric film is formed in a wave shape, electrodes are formed on both the front and back
sides of this vibrating film, and an electric field such as an audio signal is applied to this
electrode. (See, for example, Patent Document 1).
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In such a piezoelectric film speaker, when an electric field is applied, the vibrating film expands
and contracts in the direction of the plane perpendicular to the electric field application direction
due to the piezoelectric effect. Then, by applying a signal such as an audio signal to the front and
back electrodes, sound was generated before and after the diaphragm.
[0003]
U.S. Pat. No. 6,411,015
[0004]
However, in the conventional piezoelectric film speaker, since the apex of the wave-shaped
diaphragm vibrates in the same phase (the expansion / contraction of the apex of the adjacent
diaphragms is performed in the same phase), the amplitude of the vibration is The maximum is at
the apex, and the amplitude decreases with distance from the apex.
In such a state, when the sound generated by the vibration is generated in the front and back
direction of the vibrating membrane, the amplitude can be strong and weak, and it is difficult to
say that the vibration of the vibrating membrane is effectively linked to the conversion to sound.
The
[0005]
The present invention has been made to solve the above problems, and it is possible to obtain a
piezoelectric film speaker capable of effectively using the vibration of a vibrating film for
converting sound and emitting effective sound. To aim.
[0006]
The piezoelectric film speaker according to the present invention is formed of a vibrating film
including extension portions alternately provided so as to be in front and back with respect to the
sound radiation direction and rising portions for connecting the end portions of adjacent
extension portions. The stretchable portion has stretchability in the direction perpendicular to
the applied electric field, and electrodes are formed on both sides of the stretchable portion so
that opposite stretch electric fields are applied to the adjacent stretchable portions. is there.
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[0007]
In the piezoelectric film speaker according to the present invention, since electric fields of
opposite phases are applied to the adjacent expansion and contraction parts, a respiratory
vibration phenomenon occurs due to the air in and out of the space formed by the expansion and
contraction parts and the rising parts. The vibration of can be effectively converted to sound.
[0008]
Embodiment 1
FIG. 1 is a cross-sectional view of an essential part showing a piezoelectric film speaker according
to a first embodiment of the present invention, but prior to this description, an entire
configuration of a vibrating film will be described.
[0009]
FIG. 2 is a perspective view of a vibrating film by the piezoelectric film speaker according to the
first embodiment of the present invention.
As shown in FIG. 2, the vibrating film 1 is constituted of a piezoelectric film 2 and an electrode 3
which are formed in a wave shape.
The piezoelectric film 2 is, for example, a composite piezoelectric material obtained by mixing a
polymer resin piezoelectric material such as polyvinylidene fluoride (PVDF) or a hard inorganic
piezoelectric material powder with a resin.
[0010]
As shown in FIG. 1, such a piezoelectric film 2 is alternately provided so as to be front and back
with respect to the sound radiation direction, and has cross-sectional arc-shaped expandable
portions 4a and 4b opposite to each other, and the expandable portions It is formed to have a
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rising portion 5 for connecting the ends of 4a and 4b. Further, strip-like electrodes 3a and 3b are
formed on the front and back of the arc-shaped stretchable portion 4a, and strip-like electrodes
3c and electrodes 3d are formed on the front and back of the stretchable portion 4b. In these
electrodes 3a to 3d, the electrodes 3a and 3d, and the electrodes 3b and 3c have the same
polarity. That is, when the electrode 3a and the electrode 3d are positive, the electrode 3b and
the electrode 3c are negative.
[0011]
FIG. 3 is a configuration diagram showing an example of connection of electrodes. The electrodes
3a to 3d disposed in the stretchable portions 4a and 4b are connected at one end as shown in the
drawing, and each constitute one electrode.
[0012]
The operation of the vibrating membrane 1 will be further described. As a premise, when an
electric field of + and 3b is applied to the electrode 3a and the electrode 3b of the stretchable
portion 4a, the piezoelectric film 2 stretches. In this state, as described above, an electric field ofand an electrode 3d of + are applied to the electrode 3c of the stretchable part 4b (the symbols +
and-in FIG. 1 indicate this state).
[0013]
Since the expansion and contraction part 4a is to be expanded, a force acts so as to expand the
arc part of the expansion and contraction part 4a in the left and right direction in FIG. On the
other hand, since the stretchable portion 4b is applied with an electric field reverse to that of the
stretchable portion 4a, the stretchable portion 4b contracts and a force acts so as to narrow the
arc portion of the stretchable portion 4b in the left and right direction in FIG. By these forces,
both ends of the stretchable part 4a are displaced so as to expand in the left-right direction, and
both ends of the stretchable part 4b are displaced so as to narrow in the left-right direction
Displacing in the direction).
[0014]
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By such an operation, the vibrating membrane 1 has a displacement distribution as shown by the
expansion-side displacement distribution line 6 in FIG. 1 (in the drawing, the expansion-side
displacement distribution line 6 is drawn exaggeratingly). As a result of the above, as shown by
two arrows 7 and 8 in FIG. 1, air enters the recess on the lower side of the stretchable portion 4a
(see arrow 8) and air exits the recess on the upper side of the stretchable portion 4b. The
phenomenon occurs (see arrow 7).
[0015]
On the other hand, when the polarities of the electrodes 3a to 3d are reversed, the displacement
distribution of the vibrating membrane 1 is as shown on the contraction side displacement
distribution line 9, and the movement of air is opposite to the above description. By the abovedescribed operation, when the electric field fluctuates and is applied in accordance with a signal
such as voice, a respiratory vibrational phenomenon occurs due to the movement of air, and a
sound is generated.
[0016]
Moreover, although the expansion-contraction part 4a, 4b demonstrated the example formed in
circular arc shape in the above description, it is not limited to this, A cross-sectional shape is a
part of quadratic curves, such as a straight line and elliptical arc. Even if it exhibits the same
operation. That is, as long as a space surrounded by the stretchable portions 4a and 4b and the
rising portion 5 is formed, the shapes of the stretchable portions 4a and 4b and the rising
portion 5 may be any shape.
[0017]
Further, in the present embodiment, in particular, since the shape of the stretchable portions 4a
and 4b is formed in an arc shape, the following effects can be obtained. That is, when the
diaphragm 1 is extended, the radius (curvature) of the arc is deformed so as to increase, and
when the diaphragm 1 is shrunk, the radius (curvature) of the arc is reduced. As a result of these
operations, the distance between the joint with the rising portion 5 is increased when it is
extended, and the distance between the joint with the rising portion 5 is decreased when it is
contracted. As a result of these, the deformation of the vibrating membrane 1 becomes large, and
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therefore, the volume change of the space becomes large, and the efficiency of the sound
radiation can be further improved. Furthermore, structural strength can be obtained compared to
a linear diaphragm or the like, and as a result, the diaphragm 1 can be made thinner, which is
advantageous as a piezoelectric film speaker.
[0018]
Further, the vibrating membrane 1 configured and operating as described above can change the
reproduction band of sound by changing the interval (pitch) of the wave-like mountain and the
dimensions of the stretchable portions 4a and 4b. That is, when the distance and size are
increased, the total displacement amount is increased, and the reproduction can be adapted to
the bass range. On the other hand, when the spacing and size are reduced, it becomes suitable for
high-range reproduction, and an electroacoustic transducer for ultrasonic band reproduction can
be obtained.
[0019]
There is a parametric speaker as an application object for ultrasonic band reproduction. FIG. 4 is
a block diagram of a parametric speaker using the piezoelectric film speaker of this embodiment
as an electroacoustic transducer. The parametric speaker emits an ultrasonic wave using a
configuration as shown in FIG. 4 to obtain an audible sound by utilizing a non-linear
phenomenon of air. That is, the parametric speaker converts an audible sound into an ultrasonic
wave and emits sound from the electroacoustic transducer to form a beam-like sound field and
reproduce it as an audible sound.
[0020]
The parametric speaker comprises an audio generator 10, an amplitude modulator 11, an
amplifier 12, a high frequency generator 13, and an electroacoustic transducer 14. An audio
signal generated by the audio generator 10 that generates an audible sound is multiplied in the
amplitude modulator 11 with an ultrasonic carrier signal for generating an ultrasonic wave from
the high frequency generator 13. Amplitude modulation is performed by this multiplication
processing to obtain a modulation signal. The modulated output signal of the amplitude
modulator 11 is amplified by the amplifier 12, supplied to the electroacoustic transducer 14, and
emitted as a sound wave from the electroacoustic transducer 14. This sound wave causes a non-
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linear interaction in the process of propagating in air as a finite amplitude sound wave which is a
strong ultrasonic wave, the low frequency component is self-demodulated, and can be heard by
the listener.
[0021]
By using the piezoelectric film speaker of the present embodiment for such a parametric speaker,
it is possible to contribute to the improvement of the efficiency as a parametric speaker. That is,
parametric speakers have lower conversion efficiency than general speakers, and the
improvement of the conversion efficiency is a major technical issue. By using the piezoelectric
film speaker of the present embodiment for the electroacoustic transducer, the demodulation
sound pressure can be increased as a parametric speaker. Therefore, by obtaining a large sound
pressure level, the range of use of the parametric speaker, which has conventionally been
available only for small sounds, can be expanded, and it can be used in various scenes such as
outdoors or places with a lot of noise.
[0022]
As described above, according to the first embodiment, the stretchable portions 4a and 4b
alternately provided to be forward and backward with respect to the sound radiation direction
and the end portions of the adjacent stretchable portions 4a and 4b are connected. The
stretchable portions 4a and 4b have stretchability in the direction perpendicular to the applied
electric field, and the electrodes 3 are formed on both sides of the stretchable portions 4a and
4b. Since electric fields of opposite phase to each other are applied to the adjacent stretchable
portions 4a and 4b, the vibration of the vibrating membrane can be effectively converted to
sound, and a large reproduced sound pressure level can be obtained.
[0023]
Further, according to the first embodiment, since the vibrating membrane is made of the polymer
resin piezoelectric material or the composite piezoelectric material, it is formed optimally as the
wave-like vibrating membrane comprising the stretchable portions 4 a and 4 b and the rising
portion 5. There is an effect that can be done.
[0024]
Further, according to the first embodiment, since the cross-sectional shape of the stretchable
portions 4a and 4b is configured to be a part of a straight line or a quadratic curve, the efficiency
of sound radiation due to the stretch of the diaphragm can be improved. There is an effect that it
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is advantageous as a membrane speaker.
[0025]
Further, according to the first embodiment, the electroacoustic conversion is performed on a
parametric speaker that converts an audible sound into an ultrasonic wave and emits the sound
from the electroacoustic transducer 14 to form a beam-like sound field and reproduce it as an
audible sound. Film 1 consisting of expansion and contraction parts 4a and 4b alternately
provided so as to be front and back with respect to the sound radiation direction and rising parts
5 for connecting the ends of adjacent expansion and contraction parts 4a and 4b And the
stretchable portions 4a and 4b have stretchability in a direction perpendicular to the applied
electric field, and form electrodes 3a, 3b, 3c and 3d on both sides of the stretchable portions 4a
and 4b, respectively. Since the expansion / contraction parts 4a and 4b are configured of
piezoelectric film speakers configured to apply electric fields of opposite phase to each other, it is
possible to increase the demodulation sound pressure as a parametric speaker, therefore,
parametrics It is possible to expand the range of applications over mosquitoes.
[0026]
It is principal part sectional drawing of the piezoelectric film speaker by Embodiment 1 of this
invention.
It is a perspective view of the vibrating membrane of the piezoelectric film speaker by
Embodiment 1 of this invention.
It is a block diagram which shows the example of a connection of the electrode in the
piezoelectric film speaker by Embodiment 1 of this invention.
It is a block diagram of the parametric speaker which used the piezoelectric film speaker by
Embodiment 1 of this invention for the electroacoustic transducer.
Explanation of sign
[0027]
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Reference Signs List 1 vibration film, 2 piezoelectric film, 3, 3a, 3b, 3c, 3d electrodes, 4a, 4b
stretchable portion, 5 rising portion, 14 electroacoustic transducer.
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