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DESCRIPTION JP2014003572

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DESCRIPTION JP2014003572
Abstract: An oscillation device capable of directivity control and capable of reducing power
consumption. SOLUTION: Piezoelectric films 21a and 21b which are disposed between a plurality
of piezoelectric elements 11a to 11c arranged to overlap each other in plan view and adjacent
piezoelectric elements 11a to 11c and joined to the piezoelectric elements 11a to 11c. And a
frame member 30 holding the edges of the piezoelectric films 21a and 21b, wherein the plurality
of piezoelectric elements 11a to 11c include ones having different resonance frequencies.
[Selected figure] Figure 1
Oscillator and electronic device
[0001]
The present invention relates to an oscillator and an electronic device.
[0002]
In mobile terminals such as mobile phones, 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 them, the demand for compact, thin and high sound quality is high for an oscillating
device such as an electroacoustic transducer. Patent Document 1 discloses a related technology.
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[0003]
JP, 2011-114597, A
[0004]
In the current situation where a portable terminal is used as an information terminal, there is a
large demand for a private sound that can be heard only by the user from the viewpoint of
privacy protection.
That is, there is a need for means for realizing a private sound with a small and thin oscillator. As
means for solving these demands, parametric speakers using ultrasonic waves have been
developed, but there are major issues in practical application to mobile phones.
[0005]
First is the problem of power consumption. Generally, a piezoelectric vibrator is used for the
vibration which oscillates an ultrasonic wave. The impedance of the piezoelectric element is
increased by shifting the frequency to a high frequency. For this reason, when oscillating an
ultrasonic wave, power consumption increases. On the other hand, the directivity of the sound
wave also tends to be higher as the high band shifts, and it is preferable to use a higher
frequency to realize the privacy sound source. Therefore, in the parametric speaker, the acoustic
characteristics and the power consumption are in a trade-off relationship.
[0006]
The second problem is sound pressure deterioration due to the interference of sound waves. In
the parametric speaker, sound waves are emitted from a plurality of transducers by a phased
array method in order to narrow down the directivity. Since a plurality of transducers are
arranged adjacent to each other, the sound waves interfere in the vicinity of the radiation surface,
causing energy loss due to canceling or the like, and it becomes difficult to control directivity.
[0007]
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For this reason, there is a need for an oscillation device capable of directivity control and capable
of reducing power consumption. In addition, although the subject of the oscillation apparatus
was demonstrated taking the example of a portable terminal here, the same subject exists in the
oscillation apparatus used with another electronic device.
[0008]
According to the present invention, a plurality of piezoelectric elements arranged to overlap with
each other in plan view, a piezoelectric film disposed between the adjacent piezoelectric elements
and joined to the piezoelectric elements, and holding the edge of the piezoelectric film There is
provided an oscillation device including: a frame member; and among the plurality of
piezoelectric elements, those having different resonance frequencies.
[0009]
Further, according to the present invention, an electronic device having the above-described
oscillation device is realized.
[0010]
According to the present invention, an oscillation device capable of directivity control and
capable of reducing power consumption is realized.
[0011]
It is an example of the cross-sectional schematic diagram of the oscillation apparatus of this
embodiment.
It is the perspective view which decomposed | disassembled the oscillation apparatus of FIG. 1 to
the up-down direction.
The electrode layers 41a to 41f are omitted.
It is another example of the cross-sectional schematic diagram of the oscillation apparatus of this
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embodiment. FIG. 6 is a diagram showing an oscillation device of Comparative Example 1; It is a
graph which shows the relationship between frequency and a sound pressure level.
[0012]
Hereinafter, embodiments of the electronic device and the oscillation device of the present
invention will be described using the drawings. The drawings are merely schematics for
explaining the configuration of the invention, and the sizes, shapes, numbers, ratios of sizes
between different members, and the like of the respective members are not limited to those
illustrated unless otherwise stated.
[0013]
FIG. 1 shows an example of a schematic cross-sectional view of the oscillation device of the
present embodiment. As illustrated, the oscillation device of the present embodiment has a
plurality of piezoelectric elements 11a to 11c, a plurality of piezoelectric films 21a and 21b, and
a frame member 30. Electrode layers 41a to 41f are positioned on both sides of each of the
plurality of piezoelectric elements 11a to 11c. Note that the on / off control unit 100 can be
further included.
[0014]
FIG. 2 is a perspective view of the oscillation device of FIG. 1 disassembled in the vertical
direction. The electrode layers 41a to 41f and the on / off control unit 100 are omitted.
[0015]
The piezoelectric elements 11a to 11c are formed of, for example, a piezoelectric ceramic such as
PZT. In addition, the "piezoelectric element" in the present embodiment is a concept excluding an
element formed in a film shape, a so-called piezoelectric film. The plurality of piezoelectric
elements 11a to 11c are arranged to overlap each other in plan view. Although the oscillation
device shown in FIGS. 1 and 2 has three piezoelectric elements 11a to 11c, the number of
piezoelectric elements is not limited to this.
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[0016]
Among the plurality of piezoelectric elements 11a to 11c, those having different fundamental
resonance frequencies are included. In the example shown in FIGS. 1 and 2, the planar shapes of
the plurality of piezoelectric elements 11a to 11c are common to the circle, but the sizes thereof
are different from each other. Such a configuration realizes a configuration in which the plurality
of piezoelectric elements 11a to 11c have different fundamental resonance frequencies. In the
example shown in FIGS. 1 and 2, the planar shape of the plurality of piezoelectric elements 11a
to 11c may be another shape such as a triangle, a quadrangle, another polygon, or an ellipse.
Further, by configuring the plurality of piezoelectric elements 11a to 11c to have different planar
shapes, a configuration in which the plurality of piezoelectric elements 11a to 11 have different
resonant frequencies may be realized. Furthermore, among the plurality of piezoelectric elements
11a to 11c, the plurality of piezoelectric elements 11a may be configured such that those having
different planar shapes and those having the same planar shape but different in size are mixed.
11c may have different resonance frequencies.
[0017]
In the example shown in FIGS. 1 and 2, although the plurality of piezoelectric elements 11a to
11c include only those having different resonance frequencies, those having the same resonance
frequency may be included. . The example is described below with reference to FIG.
[0018]
In the example shown in FIGS. 1 and 2, the plurality of piezoelectric elements 11 a to 11 c whose
planar shapes are circles are arranged such that the centers of the circles overlap each other in
plan view.
[0019]
The piezoelectric films 21a and 21b are films formed of a resin material having a piezoelectric
effect and an electrostrictive effect.
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This resin material is, for example, polyvinylidene fluoride. However, the piezoelectric films 21a
and 21b may be formed of another resin material such as polyvinyl chloride or
polytrifluoroethylene.
[0020]
The piezoelectric film 21a is disposed between the adjacent piezoelectric elements 11a and 11b,
and is joined to the piezoelectric elements 11a and 11b. The piezoelectric film 21b is disposed
between the adjacent piezoelectric elements 11b and 11c and is joined to the piezoelectric
elements 11b and 11c.
[0021]
In the example shown in FIGS. 1 and 2, the planar shapes of the plurality of piezoelectric films
21a and 21b are all circular, and the sizes thereof are the same. The planar shape of the plurality
of piezoelectric films 21a and 21b is larger than the planar shape of any of the plurality of
piezoelectric elements 11a to 11c. The plurality of piezoelectric films 21a and 21b are arranged
such that the centers of their circles overlap each other in plan view. The plurality of
piezoelectric films 21a and 21b are arranged such that the center of the circle overlaps the
center of the circle of the plurality of piezoelectric elements 11a to 11c in a plan view. Each of
the plurality of piezoelectric elements 11b and 11c is included in each of the plurality of
piezoelectric films 21a and 21b in plan view.
[0022]
The planar shape of the plurality of piezoelectric films 21a and 21b is not limited to a circle, and
may be a triangle, a quadrangle, another polygon such as another polygon, or an ellipse. The
resonant frequencies of the plurality of piezoelectric films 21a and 21b may be the same. The
resonant frequencies of the plurality of piezoelectric films 21a and 21b may be different from
the resonant frequencies of all of the plurality of piezoelectric elements 11a to 11c.
[0023]
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Electrode layers 41 b to 41 e are formed on two flat surfaces (front and back surfaces) of each of
the piezoelectric films 21 a and 21 b. Each of the electrode layers 41b to 41e is located between
any of the plurality of piezoelectric elements 11a to 11c and any of the piezoelectric films 21a
and 21b, and is electrically connected to any of the plurality of piezoelectric elements 11a to 11c.
. The planar shapes of the electrode layers 41b to 41e are all circular, and the size thereof is
equal to the size of the planar shapes of the piezoelectric films 21a and 21b. The planar shape
and size of the electrode layers 41b to 41e are not limited to this.
[0024]
Further, among the plurality of piezoelectric elements 11a to 11c, the electrode layers 41a and
41f are provided on exposed surfaces (surfaces not facing the piezoelectric films 21a and 21b) of
the two piezoelectric elements 11a and 11c located on the outermost side in the overlapping
direction. It is formed. The electrode layers 41a and 41f are electrically connected to the
piezoelectric elements 11a and 11c, respectively. The planar shape of the electrode layer 41a is a
circle, and the size thereof is equal to the size of the exposed surface of the piezoelectric element
11a. The planar shape of the electrode layer 41f is a circle, and the size thereof is equal to the
size of the exposed surface of the piezoelectric element 11c. The planar shapes and sizes of the
electrode layers 41a and 41f are not limited to this.
[0025]
That is, in each of the plurality of piezoelectric elements 11a to 11c, the electrode layers 41b to
41e are formed on both of the two planes (front and back). Further, in each of the plurality of
piezoelectric films 21a and 21b, the electrode layers 41b to 41e are formed on both of the two
planes (front and back). The means for bonding the plurality of piezoelectric elements 11a to 11c
and the plurality of piezoelectric films 21a and 21b to each other via the electrode layers 41b to
41e is not particularly limited, and may be realized using, for example, a conductive adhesive.
[0026]
The frame member 30 holds the edges of the plurality of piezoelectric films 21a and 21b. The
planar shape of the frame member 30 is a ring shape capable of containing the plurality of
piezoelectric films 21a and 21b (see FIG. 2). The frame member 30 holds the plurality of
piezoelectric films 21 a and 21 b in a state where the plurality of piezoelectric films 21 a and 21
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b are positioned inside the ring shape.
[0027]
The means by which the frame member 30 holds the plurality of piezoelectric films 21a and 21b
is not particularly limited, and may be realized using an adhesive such as an epoxy adhesive, for
example.
[0028]
The frame member 30 is made of, for example, a material such as brass or stainless steel.
[0029]
Wiring is connected to the plurality of electrode layers 41a to 41f.
The oscillation device of the present embodiment can include the on / off control unit 100 that
individually controls on / off of the plurality of piezoelectric elements 11a to 11c and the
plurality of piezoelectric films 21a and 21b.
[0030]
The on / off control unit 100 individually controls on / off of the plurality of piezoelectric
elements 11a to 11c and the plurality of piezoelectric films 21a and 21b, and oscillates in any of
the following modes (1) to (7): It can be done.
[0031]
(1) All the plurality of piezoelectric elements 11a to 11c are vibrated simultaneously.
(2) Only the piezoelectric elements 11a and 11b are vibrated simultaneously, and the
piezoelectric element 11c is not vibrated.
(3) Only the piezoelectric elements 11a and 11c are simultaneously vibrated, and the
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piezoelectric element 11b is not vibrated. (4) Only the piezoelectric elements 11b and 11c are
vibrated simultaneously, and the piezoelectric element 11a is not vibrated. (5) Only the
piezoelectric element 11a is vibrated, and the piezoelectric elements 11b and 11c are not
vibrated. (6) Only the piezoelectric element 11b is vibrated, and the piezoelectric elements 11a
and 11c are not vibrated. (7) Only the piezoelectric element 11c is vibrated, and the piezoelectric
elements 11a and 11b are not vibrated. In any of the embodiments (1) to (7), a predetermined
number of piezoelectric films can be additionally vibrated. Here, “to vibrate” means to vibrate
by applying a voltage to the piezoelectric element or the piezoelectric film through the electrode
layer and applying an electric field.
[0032]
FIG. 3 is a schematic cross-sectional view showing another example of the oscillation device of
the present embodiment. As illustrated, the oscillation device of this example includes five
piezoelectric elements 10a to 10e, four piezoelectric films 20a to 20d, and a frame member 30.
Electrode layers 40a to 40j are positioned on both sides of each of the five piezoelectric elements
10a to 10e. Although not shown, the on / off control unit 100 shown in FIG. 1 can be further
included.
[0033]
The oscillation device shown in FIG. 3 differs from the examples shown in FIGS. 1 and 2 in the
number of piezoelectric elements, piezoelectric films, and electrode layers.
[0034]
Further, in the oscillation device shown in FIG. 3, not only those having different resonance
frequencies but also those having the same resonance frequency are included in the five
piezoelectric elements 10a to 10e. It differs from the example shown in 2.
[0035]
That is, although the piezoelectric element 10a and the piezoelectric element 10e have the same
resonance frequency, they have resonance frequencies different from those of the other
piezoelectric elements 10b to 10d.
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The piezoelectric element 10b and the piezoelectric element 10d have the same resonance
frequency, but have different resonance frequencies from the other piezoelectric elements 10a,
10c and 10e.
The planar shapes of the piezoelectric elements 10a to 10e are all common to a circle. However,
although the size of the planar shapes of the piezoelectric element 10a and the piezoelectric
element 10e is the same, the size of the planar shapes of the other piezoelectric elements 10b to
10d is different. Further, although the planar shapes of the piezoelectric element 10b and the
piezoelectric element 10d have the same size, they are different from the planar shapes of the
other piezoelectric elements 10a, 10c and 10e.
[0036]
Further, in the oscillation device shown in FIG. 3, the five piezoelectric elements 10a to 10e
arranged so as to overlap with each other are arranged such that the planar shape becomes
smaller toward the end in the overlapping direction. It differs from the example shown.
[0037]
That is, the planar shape becomes smaller as the piezoelectric element 10c having the largest
planar shape is located in the middle and approaches the end in the overlapping direction from
there.
Specifically, the planar shape becomes smaller in the order of piezoelectric element 10c →
piezoelectric element 10b → piezoelectric element 10a. Further, the planar shape becomes
smaller in the order of the piezoelectric element 10 c → the piezoelectric element 10 d → the
piezoelectric element e.
[0038]
The on / off control unit (not shown) individually controls on / off of the five piezoelectric
elements 10a to 10e and the four piezoelectric films 20a to 20d, and any one of the following (1
') to (7') It can be oscillated in an aspect.
[0039]
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(1 ') All five piezoelectric elements 10a to 10e are vibrated simultaneously.
(2 ') Only the piezoelectric elements 10a, 10b, 10d and 10e are vibrated simultaneously, and the
piezoelectric element 10c is not vibrated. (3 ') Only the piezoelectric elements 10a, 10c and 10e
are vibrated simultaneously, and the piezoelectric elements 10b and 10d are not vibrated. (4 ')
Only the piezoelectric elements 10b to 10d are vibrated simultaneously, and the piezoelectric
elements 10a, 10c and 10e are not vibrated. (5 ') Only the piezoelectric elements 10a and 10e
are vibrated, and the piezoelectric elements 10b, 10c and 10d are not vibrated. (6 ') Only the
piezoelectric elements 10b, 10c and 10d are vibrated, and the piezoelectric elements 10a and
10e are not vibrated. (7 ') Only the piezoelectric element 10c is vibrated, and the piezoelectric
elements 10a, 10b, 10d and 10e are not vibrated. In any of the embodiments (1 ') to (7'), a
predetermined number of piezoelectric films can be additionally vibrated. Here, “to vibrate”
means to vibrate by applying a voltage to the piezoelectric element or the piezoelectric film
through the electrode layer and applying an electric field.
[0040]
The other configuration of the oscillator shown in FIG. 3 is the same as that of the oscillator
shown in FIGS. Therefore, the detailed description is omitted.
[0041]
Next, the operation and effect of the present embodiment will be described.
[0042]
In the present embodiment, a plurality of piezoelectric elements are disposed so as to overlap via
the piezoelectric film.
Among the plurality of piezoelectric elements, those having different resonance frequencies are
included. For example, the planar shape of the plurality of piezoelectric elements is a circle, and
the plurality of piezoelectric elements are arranged so as to overlap such that the centers of the
circles overlap in a plan view. The plurality of piezoelectric elements include ones having
different planar shapes from one another. Also, the resonant frequency of the piezoelectric film
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can be made different from any of the plurality of piezoelectric elements.
[0043]
For this reason, the oscillation device of this embodiment can simultaneously oscillate ultrasonic
waves having a plurality of frequencies. As described above, by demodulating the audio signal
using a plurality of ultrasonic waves as the carrier wave (by adding the bands of the demodulated
sound having different bands), it is possible to extend the band of the demodulated sound.
[0044]
Moreover, in the present embodiment, it is also possible to change the oscillating frequency by,
for example, an arbitrary setting by the user. That is, the oscillation device according to the
present embodiment individually controls on / off of the plurality of piezoelectric elements and
the piezoelectric film according to, for example, the setting of the user, and the plurality of
oscillation modes (the above (1) to (7), It can be oscillated in any of (1 ') to (7').
[0045]
There is a trade-off between the frequency of the ultrasound and the power consumption.
Determine the oscillating frequency in consideration of the directivity according to the scene to
be used, and set one of a plurality of oscillation modes realized by individually controlling on /
off of a plurality of piezoelectric elements and piezoelectric films By doing this, power
consumption can be reduced as compared to the case where oscillation is always performed with
all of the plurality of piezoelectric elements and piezoelectric films turned on. Further, by
oscillating only the necessary piezoelectric element and piezoelectric film, the interference of
sound waves can be suppressed, and energy loss can be reduced by canceling or the like.
[0046]
Further, in the present embodiment, the piezoelectric elements are joined via the piezoelectric
film. Here, the piezoelectric film is a resin material having an electrostrictive effect, and a
material such as polyvinylidene fluoride (PVDF (registered trademark)) can be used. The function
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plays the role of increasing the amount of vibration amplitude by driving in the same phase at
the time of vibration of the piezoelectric element. In addition, since the piezoelectric film itself is
a material having a large internal loss compared to the piezoelectric element, it has an effect of
reducing the machine Q. Usually, in the parametric speaker, the sound wave is reproduced only
at a specific frequency, but it is difficult to suppress the variation of the resonance frequency in
the manufacture of the piezoelectric element having a high mechanical Q. Here, by reducing the
machine Q with the piezoelectric film, it is possible to increase the amount of vibration amplitude
while improving the ease of manufacture.
[0047]
In the oscillation device of the present embodiment, it is desirable to reproduce (oscillate)
ultrasonic waves of 20 kHz or more. By setting the oscillation frequency to the ultrasonic band,
miniaturization of the oscillation device can be realized, and at the same time, directivity can be
controlled by utilizing the straightness of ultrasonic waves. As a result, it is possible to realize a
privacy sound source limited only in the vicinity of the position of the user. As an application
example, it can be used as a parametric speaker that allows an audio signal to be carried by
ultrasonic waves and demodulated in air.
[0048]
Also, as in the oscillation device shown in FIG. 3, when the plurality of piezoelectric elements
arranged so as to overlap with each other are arranged such that the planar shape becomes
smaller toward the end in the overlapping direction, the manufacturing becomes easy An effect is
obtained.
[0049]
The oscillation device of the present embodiment can be used, for example, as an electroacoustic
transducer.
The oscillation device of the present embodiment can be used for any electronic device, but when
used for a portable small electronic device, the problem of power consumption that can occur in
such a device can be effectively solved.
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[0050]
Here, FIG. 5 is a graph showing the relationship between frequency and sound pressure level.
Example 1 is data in the case where all of the plurality of piezoelectric elements are oscillated
simultaneously in the oscillation device of the structure of FIG. 3, and Example 2 is all of the
plurality of piezoelectric elements in the oscillation device of the structure of FIGS. It is data at
the time of making it oscillate simultaneously. Comparative Example 1 is data in the case where
all of the plurality of piezoelectric elements are oscillated simultaneously in the oscillation device
having the structure shown in FIG. In Comparative Example 1, metal plates 102a and 102b made
of phosphor bronze are used in place of the piezoelectric films 21a and 21b in Example 2. The
other configurations (frame member 103, piezoelectric elements 101a to 101c, and the like) of
Comparative Example 1 are the same as in Example 2.
[0051]
It can be seen from FIG. 5 that Example 1 and Example 2 can obtain a higher sound pressure
than Comparative Example 1. Further, it can be seen that in the second embodiment, high sound
pressure is obtained in a wide frequency band.
[0052]
10a to 10e Piezoelectric element 11a to 11c Piezoelectric element 20a to 20d Piezoelectric film
21a and 21b Piezoelectric film 30 Frame member 40a to 40j Electrode layer 41a to 41f
Electrode layer 100 On-off control unit
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