Abstract: PROBLEM TO BE SOLVED: To reduce variation in sound pressure in frequency
characteristics of sound pressure. SOLUTION: A sound generator comprises a film 3 serving as a
support plate, a frame member 5 provided on the outer peripheral portion of the film 3, and a
piezoelectric element 1 provided on the film 3 in the frame of the frame member 5. And the resin
layer 20 provided on the film 3 in the frame of the frame member 5, and the resin layer 20 has
the air bubbles 8. The air bubble 8 makes it possible to reduce peaks and dips in the frequency
characteristic of the sound pressure while suppressing a drop in the sound pressure, thereby
generating high-quality sound. [Selected figure] Figure 1B
Acoustic generator, acoustic generator and electronic device
The present invention relates to a sound generator, a sound generator and an electronic device.
Piezoelectric speakers are conventionally known as small-sized, low-current-driven acoustic
devices that use a piezoelectric body as an electroacoustic transducer, and are used, for example,
as acoustic generators to be incorporated into small electronic devices such as mobile computing
devices. It is done.
In general, an acoustic generator using a piezoelectric body as an electroacoustic transducer has
a structure in which a piezoelectric element in which an electrode of a silver thin film or the like
is formed on the piezoelectric body is attached to a metal diaphragm.
Such an acoustic generator generates a shape distortion in the piezoelectric element by applying
an alternating voltage to the piezoelectric element, and generates a sound by transmitting the
shape distortion of the piezoelectric element to a metal diaphragm to vibrate.
However, since an acoustic generator having a structure in which a piezoelectric element is
attached to a metal diaphragm is such that area bending vibration is generated by restraining a
piezoelectric element that spreads and vibrates with a metal plate whose area does not change. It
has been difficult to provide sound pressure characteristics with low conversion efficiency, small
size, and low resonance frequency.
In order to solve such problems, the applicant has proposed a sound generator using a resin film
as a diaphragm instead of a metal diaphragm (see, for example, Patent Document 1).
In this sound generator, a bimorph-type laminated piezoelectric element is sandwiched between a
pair of resin films in the thickness direction, and the resin film is fixed to a frame member in a
tensioned state.
Thereby, the sound conversion efficiency is improved, and high sound pressure can be generated.
JP, 2010-177867, A
However, the above-mentioned sound generator has variations in sound pressure in frequency
characteristics of sound pressure, and in order to further improve the sound quality, it is
necessary to reduce the variations in sound pressure.
The present invention is made in view of the above, and an object of the present invention is to
provide an acoustic generator, an acoustic generator, and an electronic device that can reduce
variation in sound pressure in frequency characteristics of sound pressure.
The sound generator according to the present invention comprises a film, a frame member
provided on an outer peripheral portion of the film, a piezoelectric element provided on the film
in the frame of the frame member, and a frame in the frame member. And a resin layer provided
on the film, wherein the resin layer has bubbles.
According to one aspect of the sound generator according to the present invention, it is possible
to reduce the variation in sound pressure in the frequency characteristic of sound pressure.
FIG. 1A is a plan view showing a first embodiment of a sound generator.
FIG. 1B is a cross-sectional view showing a first embodiment of a sound generator.
FIG. 2 is a partial cross-sectional view for explaining a first example of an effective placement
method of air bubbles in the resin layer of the sound generator of the first embodiment.
FIG. 3 is a partial cross-sectional view for explaining a second example of the effective
arrangement method of air bubbles in the resin layer of the sound generator of the first
embodiment.
FIG. 4 is a partial cross-sectional view for explaining a third example of the effective arrangement
FIG. 5 is a partial cross-sectional view for explaining a fourth example of the effective
arrangement method of the air bubbles in the resin layer of the sound generator of the first
FIG. 6 is a cross-sectional view schematically showing the sound generator of the second
FIG. 7 is a view schematically showing the electronic device of the third embodiment. FIG. 8 is a
graph showing an example of the frequency characteristic of sound pressure. FIG. 9 is a graph
showing an example of the frequency characteristic of sound pressure. FIG. 10 is a graph
showing an example of sound pressure frequency characteristics.
Hereinafter, embodiments of a sound generator, a sound generator and an electronic device
according to the present invention will be described in detail based on the drawings. Note that
this embodiment does not limit the present invention. And each form illustrated below as an
embodiment can be combined suitably in the range which does not contradict the shape and size
of each member which constitute a sound generator.
(1) First Embodiment [Structure of Sound Generator] First, a sound generator according to a first
embodiment of the present invention will be described based on FIGS. 1A and 1B. FIG. 1A is a
plan view of the first embodiment of the sound generator, and FIG. 1B is a cross-sectional view
taken along the line A-A 'of FIG. 1A. In FIG. 1A, the position of the piezoelectric element 1 which
is covered by the resin layer 20 and can not be seen in the + Z direction is indicated by a broken
line. Moreover, in FIG. 1B, in order to facilitate understanding, the thickness direction (Z-axis
direction) of the laminated piezoelectric element 1 is shown enlarged. Moreover, in FIG. 1A and
1B, illustration of the bubble 8 in resin 20 is abbreviate ¦ omitted.
The sound generator of the first embodiment shown in FIGS. 1A and 1B includes a film 3, a frame
member 5 provided on the outer peripheral portion of the film 3, and a piezoelectric element
provided on the film 3 in the frame of the frame member 5. 1 and the resin layer 20 provided on
the film 3 in the frame of the frame member 5.
The frame member 5 is constituted by a pair of frame members 5a and 5b, and as shown in FIG.
1B, the film 3 is held by holding the outer peripheral portion of the film 3 with the frame
members 5a and 5b under tension. Is fixed to the frame member 5, and the laminated
piezoelectric element 1 is disposed on the upper surface of the film 3.
Among them, the piezoelectric element 1 is formed in a plate shape and the upper and lower
main surfaces are formed in a square shape, a rectangular shape or a polygonal shape.
The piezoelectric element 1 is a laminate 13 in which four piezoelectric layers 7 (7a, 7b, 7c, 7d)
and three internal electrode layers 9 (9a, 9b, 9c) are alternately stacked. Including surface
electrode layers 15a and 15b formed on the upper and lower surfaces of the laminate 13 and
first to third external electrodes provided at the end of the laminate 13 in the longitudinal
direction (Y-axis direction) There is.
The first external electrode 17 is disposed at the end of the laminate 13 in the -Y direction, and is
connected to the surface electrode layers 15a and 15b and the internal electrode layer 9b.
A second external electrode 18 and a third external electrode (not shown) are disposed at an end
in the + Y direction of the laminate 13 at an interval in the X-axis direction. The second outer
electrode 18 is connected to the inner electrode layer 9a, and the third outer electrode (not
shown) is connected to the inner electrode 9c. The piezoelectric layer 7 is polarized in the
direction indicated by the arrow in FIG. 1B, so that when the piezoelectric layers 7a and 7b
contract, the piezoelectric layers 7c and 7d extend, and the piezoelectric layer 7a, When 7b
extends, a voltage is applied to the first external electrode 17, the second external electrode 18,
and the third external electrode so that the piezoelectric layers 7c and 7d contract. As described
above, the piezoelectric element 1 is a bimorph type piezoelectric element, and when an electric
signal is input, the piezoelectric element 1 bends and vibrates in the Z axis direction so that the
amplitude changes in the Y axis direction.
The upper and lower end portions of the second external electrode 18 are extended to the upper
and lower surfaces of the laminated body 13 to form folded external electrodes 18 a, and these
folded external electrodes 18 a are formed on the surface of the laminated body 13. The surface
electrode layers 15a and 15b are extended at a predetermined distance so as not to contact the
surface electrode layers 15a and 15b. Similarly, upper and lower end portions of a third external
electrode (not shown) are extended to the upper and lower surfaces of the laminate 13 to form
respective folded external electrodes (not shown), and these folded external electrodes are
formed. (Not shown) is extended at a predetermined distance from the surface electrode layers
15a and 15b so as not to contact the surface electrode layers 15a and 15b formed on the surface
of the laminate 13.
The four layers of the piezoelectric layer 7 and the three layers of the internal electrode layer 9
were formed by firing simultaneously in the laminated state, and the surface electrode layers 15
a and 15 b were formed into the laminated body 13. After that, it is formed by applying and
baking a conductor paste.
In the piezoelectric element 1, the main surface on the film 3 side and the film 3 are bonded by
the adhesive layer 21.
The thickness of the adhesive layer 21 is desirably 20 μm or less, and more desirably 10 μm or
less. When the thickness of the adhesive layer 21 is 20 μm or less, the vibration of the laminate
13 is easily transmitted to the film 3.
As an adhesive for forming the adhesive layer 21, known materials such as epoxy resin, silicon
resin, polyester resin and the like can be used. As a method of curing the resin used for the
adhesive, any method such as heat curing, photo curing or anaerobic curing may be used.
Furthermore, in the sound generator of the first embodiment, the resin is filled inside the frame
member 5 a so that the piezoelectric element 1 is embedded, and the resin layer 20 is formed.
For the resin layer 20, epoxy resin, acrylic resin, silicon resin, rubber, etc. can be adopted.
Further, the resin layer 20 is preferably applied in a state of completely covering the
piezoelectric element 1 from the viewpoint of suppressing peaks and dips, but it is not necessary
to completely cover the piezoelectric element 1. Furthermore, the region of the film 3 not
covered by the piezoelectric element 1 is also covered by the resin layer 20. The resin layer 20
does not necessarily have to cover the entire film 3. In some cases, the resin layer 20 may be
provided to cover a part of the film 3. The thickness of the resin layer 20 is set to, for example,
about 0.1 mm to 1 mm.
Thus, in the acoustic generator of the first embodiment, the resonance phenomenon can be
appropriately damped by providing the resin layer 20. By such a damping effect, it is possible to
suppress a resonance phenomenon and to suppress a peak or a dip in a frequency characteristic
of sound pressure which is generated due to the resonance phenomenon. As a result, it becomes
possible to flatten the frequency characteristic of sound pressure.
As the piezoelectric layer 7, existing piezoelectric ceramics such as lead-free piezoelectric
materials such as lead zirconate (PZ), lead zirconate titanate (PZT), Bi layer compounds, tungsten
bronze structure compounds, etc. can be used. . The thickness of the piezoelectric layer 7 is set to
10 to 100 μm from the viewpoint of low voltage drive.
The internal electrode layer 9 can be formed using various existing conductor materials, but it is
desirable to include a metal component consisting of silver and palladium and a material
component constituting the piezoelectric layer 7. Further, by incorporating the ceramic
component that constitutes the piezoelectric layer 7 in the internal electrode layer 9, it is
possible to reduce the stress due to the thermal expansion difference between the piezoelectric
layer 7 and the internal electrode layer 9. The internal electrode layer 9 may not contain a metal
component consisting of silver and palladium, and may not contain a material component
constituting the piezoelectric layer 7.
The surface electrode layers 15a and 15b and the first to third external electrodes can be formed
using various existing conductor materials, but it is desirable that the metal component made of
silver contain a glass component. By thus containing the glass component, strong adhesion can
be obtained between the piezoelectric layer 7 and the internal electrode layer 9 and the surface
electrode layer 15 and the first to third external electrodes.
The frame member 5 has a rectangular shape, and as shown in FIG. 1B, the frame member 5 is
configured by bonding two rectangular frame-shaped frame members 5a and 5b. The outer
peripheral portion of the film 3 is sandwiched between the frame members 5a and 5b, and the
film 3 is fixed in a tensioned state. The thickness of the frame members 5a and 5b is, for
example, about 100 to 1000 μm, and the length of one side of the inside of the frame is, for
example, about 20 mm to 200 mm. The material of the frame members 5a and 5b may be any
material that is less likely to be deformed than the resin layer 20. For example, hard resin, plastic,
engineering plastic, ceramics, etc. can be used. For example, stainless steel can be suitably used. .
The material, thickness, and the like of the frame members 5a and 5b are not particularly limited.
Further, the shape of the frame member 5 is not limited to a rectangular shape, and for example,
a part or all of the inner peripheral part or the outer peripheral part may be elliptical, or the
inner peripheral part or the outer peripheral part may be rhombus Good.
The film 3 is fixed to the frame members 5a and 5b in a state in which the film 3 is tensioned in
the surface direction by sandwiching the outer peripheral part of the film 3 between the frame
members 5a and 5b, and the film 3 serves as a diaphragm Plays. The thickness of the film 3 is,
for example, 10 to 200 μm, and the film 3 is made of, for example, a resin such as polyethylene,
polyimide, polypropylene or polystyrene, or a paper made of pulp, fibers or the like. Peaks and
dips can be suppressed by using these materials.
[Air Bubbles of Resin Layer] Subsequently, air bubbles in the resin layer 20 which the sound
generator of the first embodiment of the present embodiment has will be described. The resin
layer 20 of the first embodiment has air bubbles 8 as shown in FIGS. The size of the air bubble 8
(maximum value of the distance between two points located on the surface) is preferably, for
example, about 20 to 150 μm. Moreover, although a spherical shape is mentioned as a
representative example of the shape of the bubble 8, you may be another shape. In addition,
about the ratio which the bubble 8 occupies to the resin layer 20, it demonstrates in full detail in
the Example using FIGS. 8-11.
As described above, by providing the air bubbles 8 in the resin layer 20, the sound quality of the
sound generated from the sound generator can be improved. The reason why this effect can be
obtained can be estimated as follows, though it can not be specified clearly. When air bubbles
(voids) are present in the resin layer 20, stress generated by the vibration of the vibrator
constituted by the film 3 integrated with the piezoelectric element 1 and the resin layer 20 is
concentrated in the vicinity of the air bubbles 8. As a result, the local strain in the vicinity of the
bubble 8 becomes large, a part of the vibrational energy is absorbed by the bubble 8, and the Q
value at the resonance of the vibration system decreases. As a result, it is possible to reduce
peaks and dips in the frequency characteristics of sound pressure that are caused due to
resonance. As a result, the frequency characteristic of the sound pressure becomes flatter, and
the sound quality of the sound generated by the sound generator is improved. Furthermore, since
the sound quality can be improved without increasing the thickness of the resin layer 20, it is
also possible to avoid a decrease in the overall sound pressure. And since peaks and dips caused
by all the resonance modes can be reduced by the bubbles 8 contained in the resin layer 20, the
sound quality is improved over the entire frequency band where the sound pressure can be
obtained by the bending and bending vibration of the vibrator. be able to.
As described above, according to the sound generator of the first embodiment, the variation in
sound pressure in the frequency characteristic of sound pressure can be reduced, and the sound
quality can be improved. Next, an effective arrangement method of the air bubbles 8 in the resin
layer 20 will be described with reference to FIGS.
FIG. 2 is a partial cross-sectional view for explaining a first example of an effective arrangement
method of the air bubbles 8 in the resin layer 20 of the sound generator of the first embodiment
shown in FIGS. 1A and 1B. 4 shows an enlarged part of the vicinity of the boundary between the
frame member 5a and the resin layer 20.
In the example shown in FIG. 2, at least a part of the air bubbles 8 in the resin layer 20 is
provided in contact with the boundary between the frame member 5 a and the resin layer 20.
The boundary between the frame member 5a and the resin layer 20 is a portion where rigidity
changes in the sound generator, and therefore, a portion where stress concentrates when the
sound generator vibrates. By providing the air bubble 8 in the portion where the stress is
concentrated, the effect of the air bubble 8 absorbing vibration energy can be enhanced, so that
the sound quality of the sound generated from the sound generator can be effectively improved.
As described above, in the example illustrated in FIG. 2, at least a part of the air bubbles 8 in the
resin layer 20 is provided so as to be in contact with the part where the rigidity changes in the
sound generator. The sound quality of the sound can be effectively improved.
Further, in the example shown in FIG. 2, the air bubbles 8 arranged to be in contact with the
boundary between the frame member 5 a and the resin layer 20 are not completely spherical,
but are in the direction contacting with the boundary between the frame member 5 a and the
resin layer 20 (frame It is desirable to have a shape that extends in a direction parallel to the
boundary between the member 5a and the resin layer 20). That is, the air bubbles 8 arranged to
be in contact with the boundary between the frame member 5a and the resin layer 20 have a
long shape in the direction along the boundary between the frame member 5a and the resin layer
20 (the frame member 5a and It is desirable that the length in the direction along the boundary
with the resin layer 20 be larger than the length in the direction perpendicular to the boundary
between the frame member 5 a and the resin layer 20. Thereby, the area in which the air bubble
8 contacts the boundary between the frame member 5a and the resin layer 20 can be increased,
so the effect of absorbing the vibration energy is enhanced, and the sound quality of the sound
generated from the sound generator is improved. Can be improved. In the present specification,
when the sound generator is viewed in plan, it is viewed in plan from the thickness direction of
the resin layer 20 (Z-axis direction).
arrangement method of the air bubbles 8 in the resin layer 20 of the acoustic generator of the
first embodiment shown in FIGS. 1A and 1B. 4 shows an enlarged part of the vicinity of the
boundary between the piezoelectric element 1 and the resin layer 20.
provided in contact with the boundary between the piezoelectric element 1 and the resin layer
The boundary between the piezoelectric element 1 and the resin layer 20 is a portion where the
rigidity changes in the sound generator. Therefore, by providing at least a part of the air bubbles
8 in the resin layer 20 in contact with the boundary between the piezoelectric element 1 and the
resin layer 20, as in the first example described above, the sound generated from the acoustic
generator Sound quality can be effectively improved.
Further, in the example shown in FIG. 3, the bubbles 8 arranged to be in contact with the
boundary between the piezoelectric element 1 and the resin layer 20 are not completely
spherical, but expand in the direction in contact with the boundary between the piezoelectric
element 1 and the resin layer 20 It is desirable to have a shape like this. That is, the bubbles 8
arranged to be in contact with the boundary between the piezoelectric element 1 and the resin
layer 20 have a long shape in the direction along the boundary between the piezoelectric
element 1 and the resin layer 20 (the piezoelectric element 1 and the resin layer 20) It is
desirable that the length in the direction along the boundary with the resin layer 20 be larger
than the length in the direction perpendicular to the boundary between the piezoelectric element
1 and the resin layer 20). As a result, the area in which the air bubble 8 contacts the boundary
between the piezoelectric element 1 and the resin layer 20 can be increased, so the effect of
absorbing the vibration energy is enhanced, and the sound quality of the sound generated from
the sound generator Can be effectively improved.
film 3 and the resin layer 20.
provided in contact with the boundary between the film 3 and the resin layer 20.
The boundary between the film 3 and the resin layer 20 is a portion where the rigidity changes
in the sound generator. Therefore, by providing at least a part of the air bubbles 8 in the resin
layer 20 in contact with the boundary between the film 3 and the resin layer 20, as in the first
and second examples described above, from the acoustic generator The sound quality of the
generated sound can be effectively improved.
Further, in the example shown in FIG. 4, the air bubbles 8 disposed so as to be in contact with the
boundary between the film 3 and the resin layer 20 are not completely spherical, but in the
direction contacting with the boundary between the film 3 and the resin layer 20 It is desirable
that the shape is expanded in a direction parallel to the boundary with the resin layer 20). That
is, when viewed from a direction parallel to the boundary between the film 3 and the resin layer
20, the air bubbles 8 arranged to be in contact with the boundary between the film 3 and the
resin layer 20 are at the boundary between the film 3 and the resin layer 20 It is desirable that
the shape along the direction is long (the length along the boundary between the film 3 and the
resin layer 20 is larger than the length perpendicular to the boundary between the film 3 and the
resin layer 20). . As a result, the area in which the air bubble 8 contacts the boundary between
the film 3 and the resin layer 20 can be increased, so the effect of absorbing the vibration energy
of the air bubble 8 is enhanced, and the sound quality of the sound generated from the sound
generator is effective. Can be improved.
arrangement method of the air bubbles 8 in the resin layer 20 of the sound generator of the first
embodiment shown in FIGS. 1A and 1B. 4 shows an enlarged part of the vicinity of the boundary
between the film 3 and the resin layer 20.
In the example shown in FIG. 5, the air bubbles 8 in the resin layer 20 are arranged so as to be
unevenly distributed in the vicinity of the boundary between the film 3 and the resin layer 20 in
the thickness direction of the resin layer 20.
Further, the bubbles 8 in the resin layer 20 are arranged to be distributed more as they approach
the interface between the film 3 and the resin layer 20. That is, the number of air bubbles 8 is
arranged to increase as the interface between the film 3 and the resin layer 20 is approached. By
arranging the air bubbles 8 in this manner, the sound quality of the sound generated from the
sound generator can be effectively improved. The reason why this effect is obtained is estimated
as follows. That is, since the boundary between the film 3 and the resin layer 20 is a portion
where the rigidity changes in the sound generator, when the sound generator vibrates, the
portion near the boundary with the film 3 in the resin layer 20 is resin The strain (deformation)
becomes larger than that of the portion of the layer 20 which is far from the boundary with the
film 3. Therefore, it is effective by arranging so as to be localized near the boundary between the
film 3 and the resin layer 20, or arranging so that the number of the air bubbles 8 increases
toward the interface between the film 3 and the resin layer 20. The vibration energy can be
absorbed by the air bubbles 8. As a result, the Q value at the resonance of the vibration system
can be reduced, and peaks and dips in the frequency characteristics of the sound pressure
generated due to the resonance can be reduced, and a more flat frequency characteristic of the
sound pressure can be obtained. it can.
[Production method] An example of the production method of the sound generator of the present
invention will be described.
First, the piezoelectric element 1 is prepared.
First, a binder, a dispersant, a plasticizer, and a solvent are kneaded with powder of a
piezoelectric material to prepare a slurry. As a piezoelectric material, any of lead-based and nonlead-based can be used.
Next, the above-mentioned slurry is formed into a sheet to obtain a green sheet. Then, an internal
electrode paste is printed on the green sheet to form an internal electrode pattern, three green
sheets on which the electrode pattern is formed are stacked, and a green sheet on which the
electrode pattern is not printed is stacked. Then, a laminated molded body is produced.
Next, the laminate molded body is degreased and fired, and cut into a predetermined size,
whereby the laminate 13 can be obtained. The laminate 13 has its outer peripheral portion
processed as necessary, and the paste of the surface electrode layers 15a and 15b is printed on
both principal surfaces in the lamination direction of the laminate 13 and then, the longitudinal
direction of the laminate 13 (Y-axis direction) The first to third external electrodes are printed on
the both end faces of b) and the electrodes are baked at a predetermined temperature. Thus, the
piezoelectric element 1 shown in FIGS. 1A and 1B can be obtained.
Next, in order to impart piezoelectricity to the piezoelectric element 1, a direct current voltage is
applied through the first to third external electrodes to polarize the piezoelectric layer 7 of the
piezoelectric element 1. This polarization is performed by applying a DC voltage so as to be in the
direction indicated by the arrow in FIG. 1B.
Next, a film 3 to be a support is prepared, and the outer peripheral portion of the film 3 is
sandwiched between the frame members 5a and 5b, and the film 3 is fixed in a tensioned state.
After that, an adhesive is applied to the film 3 and the surface electrode 15a side of the
piezoelectric element 1 is pressed against the film 3. Thereafter, the adhesive is cured by
irradiating heat or ultraviolet light. Then, after the resin before curing is poured into the inside of
the frame member 5a and the air bubbles 8 are formed in a predetermined place, the resin is
cured to form the resin layer 20. In this way, the first form of the sound generator can be
obtained.
Various methods can be used as a method of forming the air bubbles 8 in the resin layer 20. For
example, a method may be used in which a resin before curing is poured into the inside of the
frame member 5a after the hollow resin spheres are disposed in desired locations. Alternatively,
a method may be used in which hollow resin spheres (cured or semi-cured) are mixed in the resin
before curing. In this case, for example, a resin containing hollow resin spheres is applied to a
desired place and dried, and then a resin not containing hollow resin spheres is poured and cured
to obtain the desired resin layer 20. It is possible to place the air bubbles 8 selectively in places.
Also, prepare a plurality of uncured resins having different amounts of hollow resin spheres
mixed (density of resin spheres in the resin), and order from the ones with many mixed resin
spheres (high density of resin spheres in resin) After coating and drying on a film, bubbles 8 can
be disposed as shown in FIG. 5 by pouring and curing an uncured resin not containing hollow
resin spheres. Thus, by using the hollow resin spheres prepared in advance, it becomes easy to
arrange the cells having the desired shape and size at the desired positions.
Alternatively, the resin before curing may be poured into the inside of the frame member 5a, and
gas may be injected into a desired location in the resin to form the air bubbles 8, and then the
resin may be cured. For example, the tip of a thin tube is applied to the interface between the
frame member 5a and the resin, and gas is intermittently injected through the tube while moving
the tip of the tube along the interface between the frame member 5a and the resin. By forming 8
and thereafter curing the resin, as shown in FIG. 2, the air bubbles 8 can be arranged to be in
contact with the boundary between the frame member 5 a and the resin layer 20. Similarly, the
tip of the tube is brought into contact with the interface between the piezoelectric element 1 and
the resin, and gas is intermittently injected through the tube while moving the tip of the tube
along the interface between the piezoelectric element 1 and the resin. By forming 8 and
thereafter curing the resin, as shown in FIG. 3, the air bubbles 8 can be arranged to be in contact
with the boundary between the piezoelectric element 1 and the resin layer 20. And similarly, the
tip of the tube is brought into contact with the interface between the film 3 and the resin, and
while the tip of the tube is moved along the interface between the film 3 and the resin, gas is
intermittently injected through the tube. By forming the air bubbles 8 by this, and then curing
the resin, the air bubbles 8 can be arranged to be in contact with the boundary between the film
3 and the resin layer 20 as shown in FIG.
For example, by using the method as described above, it is possible to arrange the air bubble 8 at
a desired position in the resin layer 20 as illustrated in FIGS. 2 to 5. In addition, the method of
arrange ¦ positioning the bubble 8 in the resin layer 20 is not limited to the method mentioned
above, You may use another method.
Moreover, although the case where the bimorph-type piezoelectric element 1 was provided in
one main surface of the film 3 was shown in FIG. 1B, it is not restricted to this. For example, the
same effect can be obtained by using a unimorph-type piezoelectric element in which a plate
made of metal or the like is attached to one main surface of the piezoelectric element that
vibrates in the plane direction instead of the bimorph-type piezoelectric element. Can. In addition,
piezoelectric elements that vibrate in a stretching direction in the plane direction may be
provided on both sides of the film 3, and unimorph type or bimorph type piezoelectric elements
may be provided on both sides of the film 3.
Moreover, although the example in which the resin layer 20 was provided in the inner side of the
frame member 5a so that the piezoelectric element 1 might be covered completely was shown in
FIG. 1B, it is not limited to this. For example, the resin layer 20 may be provided only on the film
3 so as not to completely cover the piezoelectric element 1.
Moreover, although the case where the shape of the part inside the frame member 5 is
substantially rectangular shape was shown in FIG. 1A, it is not restricted to this. For example, the
shape of the inner portion of the frame member 5 may be elliptical.
(2) Second Embodiment Next, a sound generator according to a second embodiment of the
present invention will be described with reference to FIG. FIG. 6 is a diagram showing the
configuration of the sound generation device 30 of the second embodiment of the present
invention. In FIG. 6, only the components necessary for the description are shown, and the
detailed configuration of the sound generator 10 and the general components are omitted.
The sound generation device 30 is a sound generation device such as a so-called speaker, and
includes, for example, a housing 31 and a sound generator 10 attached to the housing 31 as
shown in FIG. The housing 31 has a rectangular box-like shape, and has an opening 31a on one
surface. Such a housing 31 can be formed using, for example, known materials such as plastic,
metal, wood and the like. In addition, the shape of the housing 31 is not limited to a box shape of
a rectangular parallelepiped, and can be various shapes such as a cylindrical shape or a frustum
shape, for example.
The sound generator 10 is attached to the opening 31 a of the housing 31. The sound generator
10 is the sound generator of the first embodiment described above, and the description of the
sound generator 10 is omitted. Since the sound generator 30 having such a configuration
generates sound using the sound generator 10 that generates sound with high sound quality,
sound with high sound quality can be generated. Moreover, since the sound generator 30 can
resonate the sound generated from the sound generator 10 inside the housing 31, the sound
pressure in the low frequency band can be increased, for example. In addition, the place where
the sound generator 10 is attached can be set freely. Also, the sound generator 10 may be
attached to the housing 31 via another object.
(3) Third Embodiment Next, an electronic device according to a third embodiment of the present
invention will be described with reference to FIG. FIG. 7 is a diagram showing the configuration
of the electronic device 50 according to the third embodiment of the present invention. In FIG. 7,
only the components necessary for the description are shown, and the detailed configuration of
the sound generator 10 and the general components are omitted.
FIG. 7 shows the case where the electronic device 50 is a mobile terminal device such as a mobile
phone or a tablet terminal. As shown in FIG. 7, the electronic device 50 includes a housing 40,
the sound generator 10 attached to the housing 40, and an electronic circuit 60 connected to the
sound generator 10. The sound generator 10 is the sound generator of the first embodiment
described above, and the description of the sound generator 10 is omitted. The electronic circuit
60 includes, for example, a controller 50a, a transmitting / receiving unit 50b, a key input unit
50c, and a microphone input unit 50d. The electronic circuit 60 is connected to the sound
generator 10 and has a function of outputting an audio signal to the sound generator. The sound
generator 10 generates a sound based on an audio signal input from the electronic circuit 60.
The electronic device 50 further includes a display unit 50 e and an antenna 50 f, and these
devices are attached to the housing 40. Although FIG. 7 shows a state in which all the devices
including the controller 50a are housed in one housing 40, the housing form of each device is
not limited. In this embodiment, at least the sound generator 10 may be attached to the housing
40 directly or through another object, and the arrangement of the other components can be
freely set.
The controller 50 a is a control unit of the electronic device 50. The transmitting and receiving
unit 50b transmits and receives data via the antenna 50f based on the control of the controller
50a. The key input unit 50c is an input device of the electronic device 50, and receives a key
input operation by the operator. The microphone input unit 50d is also an input device of the
electronic device 50, and receives a voice input operation and the like by the operator. The
display unit 50 e is a display output device of the electronic device 50, and outputs display
information based on the control of the controller 50 a. The sound generator 10 then operates as
a sound output device in the electronic device 50. The sound generator 10 is connected to the
controller 50a of the electronic circuit 60, and emits a sound in response to the application of a
voltage controlled by the controller 50a.
Since the electronic device 50 having such a configuration generates sound using the sound
generator 10 that generates sound with high sound quality, it is possible to generate sound with
high sound quality.
By the way, in FIG. 7, although the electronic device 50 is described as being a portable terminal
device such as a smartphone, a portable telephone, a personal handy phone system (PHS), a
personal digital assistants (PDA), etc. It may be various electronic devices having a function of
emitting sound.
For example, a television, a personal computer, and a car audio device may be various products
such as a vacuum cleaner, a washing machine, a refrigerator, and a microwave oven, as a matter
In the present embodiment, the difference in frequency characteristics of the sound pressure
between the resin layer 20 not containing the bubbles 8 and the resin layer 20 containing the
bubbles 8 and the sound pressure due to the concentration of the bubbles 8 in the resin layer 20
The difference in frequency characteristics of
8 to 11 are graphs showing an example of the frequency characteristic of sound pressure.
Among these, FIG. 8 indicates the frequency characteristics of the sound pressure when the
volume ratio of the bubbles 8 to the entire volume of the resin layer 20 is 0%, that is, when the
resin layer 20 does not include the bubbles 8. Moreover, FIG. 9 points out the frequency
characteristic of the sound pressure in case the ratio of the volume of the air bubbles 8 to the
volume of the entire resin layer 20 is 10%. FIG. 10 shows the frequency characteristic of the
sound pressure in the case where the volume ratio of the bubbles 8 to the volume of the entire
resin layer 20 is 20%. FIG. 11 indicates the frequency characteristics of the sound pressure in the
case where the volume ratio of the bubbles 8 to the volume of the entire resin layer 20 is 30%.
The vertical axes of the graphs shown in FIGS. 8 to 11 indicate the sound pressure, and the
horizontal axes of the graphs indicate the frequency. The sound generators whose frequency
characteristics of the sound pressure shown in FIGS. 8 to 11 were measured had the same
configuration except for the concentration of the air bubbles 8, that is, the respective members
and the dimensions and materials thereof.
First, the graph shown in FIG. 8 and the graph shown in FIG. 9 are compared in order to explain
the difference in frequency characteristics of the sound pressure depending on the presence or
absence of the bubble 8. Peaks and dips located in the frequency band 210 of 700 Hz to 1 kHz,
the frequency band 220 of 1.5 kHz to 2.5 kHz, and the frequency band 230 of 6 kHz to 9 kHz in
FIG. 8 and the frequency band 310 of 700 Hz to 1 kHz shown in FIG. Comparing the peaks and
dips respectively located in the frequency band 320 of 1.5 kHz to 2.5 kHz and the frequency
band 330 of 6 kHz to 9 kHz, the peaks and dips in the graph of FIG. It can be seen that the dip is
clearly smaller. In addition, a decrease in the level is also observed for a peak located near 0.4
kHz and a peak located near 5 kHz to 6 kHz.
As described above, when the bubbles 8 are contained in the resin layer 20 at a volume
concentration of 10%, the peaks and dips become smaller in most of the frequency bands and the
flatness is improved compared to the case where the bubbles 8 are not included. It can be seen
that the frequency characteristic of sound pressure is improved.
Furthermore, the case where the bubbles 8 are contained at a volume concentration of 10% and
the case where the bubbles 8 are contained at a volume concentration of 20% are compared.
Peaks and dips located in the frequency band 310 of 700 Hz to 1 kHz and the frequency band
320 of 1.5 kHz to 2.5 kHz shown in FIG. 9 and the frequency band 410 of 700 Hz to 1 kHz
shown in FIG. Comparing the peaks and dips respectively located in the 5 kHz frequency band
420, it can be seen that the peaks and dips in the graph of FIG. 10 are clearly smaller than the
peaks and dips in the graph shown in FIG.
concentration of 20%, the peaks and dips become smaller and the flatness is improved as
compared to the case where the bubbles 8 are contained at a volume concentration of 10%. It
can be seen that the frequency characteristic of pressure is improved.
420 of 1.5 kHz to 2.5 kHz shown in FIG. 10, and the frequency band 510 of 700 Hz to 1 kHz
concentration of 30%, the peaks and dips become smaller and the flatness is improved compared
to the case where the bubbles 8 are contained at a volume concentration of 20%. It can be seen
that the frequency characteristic of pressure is improved.
From the above results, the variation in the sound pressure in the frequency characteristic of the
sound pressure can be suppressed more in the case where the bubbles 8 are included than in the
case where the bubbles 8 are not included in the resin layer 20, and more It can be seen that the
frequency characteristic of the sound pressure can be improved when the bubble 8 is included.
This confirms the effectiveness of the present invention.
1: Piezoelectric element 3: Film 5, 5a, 5b: Frame member 8: Bubble 10: Sound generator 20:
Resin layer 30: Sound generator 31, 40: Case 50: Electronic device 60: Electronic circuit