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DESCRIPTION JP2014017799

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DESCRIPTION JP2014017799
Abstract: To provide a planar electroacoustic transducer and a display device that are thin and
yet obtain sufficient sound volume and are excellent in acoustic characteristics. A piezoelectric
film that expands and contracts according to the state of an electric field, a visco-elastic support
that is disposed in close contact with one surface of the piezoelectric film, and visco-elasticity by
pressing the piezoelectric film against the visco-elastic support And a pressing member for
holding at least a part of the thickness of the support in a reduced state, and the piezoelectric
film is flat by the surface of the visco-elastic support at least at a portion except the pressing
portion pressed by the pressing member. The object is achieved by having a flat portion held in a
shape and an inclined portion connected to the pressing portion and the flat portion and
extending in a direction intersecting the pressing portion. [Selected figure] Figure 2
Electro-acoustic transducer and display device
[0001]
The present invention relates to an electroacoustic transducer such as a thin piezoelectric
speaker or a microphone using a piezoelectric film as a vibrator, and a display device using the
same.
[0002]
Sheet-like piezoelectric material such as polymer piezoelectric material such as uniaxially
stretched film of polyvinylidene fluoride (PVDF: Poly VinyliDene Fluoride) or polymer composite
piezoelectric material formed by dispersing powdery piezoelectric material with polymer material
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1
as matrix A so-called piezoelectric film, in which electrode layers are formed on both sides of the
film, has the property of expanding and contracting in response to an applied voltage.
In order to adopt this as a speaker, it is necessary to convert the stretching movement along the
film surface into vibration in the direction perpendicular to the film surface. The conversion from
the stretching movement to the vibration is achieved by holding the piezoelectric film in a curved
state, which enables the piezoelectric film to function as a speaker. However, since the
piezoelectric film itself is generally low in rigidity, it will be bent by its own weight when the area
of the speaker is large, and it will be difficult to hold it in a curved state, so there was a limit to
the enlargement of the speaker . In order to solve this problem, a device for mechanically biasing
the piezoelectric film has been made. For example, in Patent Document 1, thin film electrodes are
formed on both sides of a polymeric piezoelectric material sheet by vapor deposition or the like,
one end of the thin film electrode is fixed to a case via a backing, and the other thin film
electrode is mechanically biased. An electro-acoustic transducer (portable sound producing
device) is described which is in pressure contact with a conductive film formed on a given
member.
[0003]
In this patent document 1, a member having a loose curvature is described as a member for
giving a mechanical bias used for an electroacoustic transducer. Specifically, both ends in the
expansion and contraction direction of the piezoelectric film are fixed to a mounting plate
provided with clearances on both sides substantially parallel to the expansion and contraction
direction, and the thin film electrode on the opposite side to the sound wave radiation direction
of the piezoelectric film An arrangement is described in which the member having the curvature
is pressed to cause electrical conduction between the member having the loose curvature and the
ground plane.
[0004]
In the electro-acoustic transducer described in Patent Document 1, pressing the piezoelectric film
against a member having a loose curvature for applying mechanical bias causes the piezoelectric
film whose periphery is fixed to have a curved shape. In this electro-acoustic transducer, since
the elastic member has a loose curvature, it becomes possible to apply a constant mechanical
bias anywhere on the piezoelectric film, so that the expansion and contraction motion of the
piezoelectric film is not wasted, so that the back and forth motion can be achieved. A sound is
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generated according to the converted power supplied.
[0005]
Japanese Patent Application Laid-Open No. 53-59473
[0006]
As described above, in the electroacoustic transducer described in Patent Document 1, a constant
mechanical bias is provided at any place of the piezoelectric film by using a member having a
loose curvature for giving a mechanical bias. The expansion and contraction motion of the
piezoelectric film can be converted into the back and forth motion without waste.
In Patent Document 1, by having such a configuration, the electro-acoustic transducer can freely
select the tone over a wide frequency band, and reduce the number of parts and simplify the
configuration and reliability mechanism. It can be said that
[0007]
However, when the piezoelectric film is given a curvature, the piezoelectric film is curved, and
therefore, the installation place and the mounting method are restricted, and the wall is hung, or
it is installed on the back of a picture, a poster, a decorative plate, etc. Not suitable for In
addition, when the area of the speaker is increased, the thickness is increased even with a loose
curvature, and the original characteristics as a thin speaker are also lost.
[0008]
In order to compensate for such a problem, the curvature of the piezoelectric film may be
reduced (the radius of curvature is increased), but when it approaches a flat surface, the
expansion and contraction motion of the piezoelectric film can not move back and forth and no
sound is produced. (Volume) will be reduced. Therefore, a planar electroacoustic transducer
having a sufficiently thin thickness, high volume, and excellent acoustic characteristics has not
been realized.
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[0009]
An object of the present invention is to solve the problems of the prior art, and to provide a flattype electroacoustic transducer and a display device which are thin and excellent in acoustic
characteristics such as frequency characteristics and volume. .
[0010]
In order to achieve the above object, the present invention is disposed in close contact with a
piezoelectric film having two main surfaces facing each other, the main surface expanding and
contracting according to the state of an electric field, and one main surface of the piezoelectric
film And a pressing member for holding the thickness of at least a part of the viscoelastic support
thin by pressing the piezoelectric film against the viscoelastic support, and the main component
of the piezoelectric film A flat portion in which the piezoelectric film is held substantially linearly
by the surface of the visco-elastic support in at least a part except the pressing portion pressed
by the pressing member in a predetermined one direction parallel to the surface; An electroacoustic transducer is provided, characterized in that it has an inclined portion connected to the
portion and the flat portion and extending in a direction intersecting the pressing portion.
[0011]
In the present invention, the piezoelectric film preferably presses the whole of the viscoelastic
support.
The inclined portion has a curved curved portion connected to the flat portion and directed to
the pressing portion, and a rising portion connected to the curved portion and the pressing
portion and extending in a direction intersecting the pressing portion. Is preferred.
Furthermore, it is preferable that the curvature radius of a curved part is 1 mm-300 mm. Further,
it is preferable that an angle at which the rising portion and the pressing portion intersect is 10
° to 90 °. Moreover, it is preferable that the height of the flat part from a press part of a
piezoelectric film is 1 mm-10 mm.
[0012]
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Preferably, the pressing member presses at least a part of the peripheral portion of the
piezoelectric film to press the piezoelectric film against the viscoelastic support. Preferably, the
pressing member presses the entire periphery of the peripheral portion of the piezoelectric film
against the viscoelastic support.
[0013]
Further, the support has a support on which the visco-elastic support is mounted, the
piezoelectric film is disposed so as to cover the visco-elastic support, and the pressing member
presses the piezoelectric film against the visco-elastic support. Preferably, at least a portion of
the support is held in a thin state and fixed to the support. Moreover, it has a bottomed
cylindrical housing which accommodates a visco-elastic support in the state which one part
protruded, and while a piezoelectric film is arrange | positioned so that a visco-elastic support
and a case may be covered, Preferably, the member presses the piezoelectric film against the
housing so that the piezoelectric film presses the viscoelastic support so that at least a part of the
viscoelastic support is kept thin. Preferably, the pressing member presses the entire periphery of
the peripheral portion of the piezoelectric film against the housing. Preferably, the pressing
member presses at least a part of the peripheral portion of the piezoelectric film against the
housing.
[0014]
Also, the piezoelectric film has a sheet-like piezoelectric body made of a polymer composite
piezoelectric body or a polymer piezoelectric material, thin film electrodes formed on both sides
of the piezoelectric body, and a protective layer formed on the surface of the thin film electrode
Is preferred. Further, it is preferable that the polymer composite piezoelectric material is formed
by dispersing piezoelectric particles in a viscoelastic matrix made of a polymer material having
viscoelasticity at normal temperature. Moreover, it is preferable that the polymeric material
which has viscoelasticity at normal temperature is what has a cyanoethyl group. Furthermore, it
is preferable that the polymer material having viscoelasticity at normal temperature be
composed of cyanoethylated polyvinyl alcohol. Preferably, at least one of the thin film electrodes
of the piezoelectric film is formed in a region other than the pressing portion.
[0015]
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Preferably, the viscoelastic support has a sound absorbing effect. Preferably, the visco-elastic
support is a fiber material or a foam material. Preferably, the visco-elastic support is felt, glass
wool, and a combination of glass wool and felt, or foamed plastic.
[0016]
Here, the specific gravity of the felt material is preferably 50 to 500 kg / m <3>. Moreover, it is
preferable that a felt material consists of wool. Further, it is preferable that the felt material is a
wool felt containing rayon and / or polyester fiber. Moreover, it is preferable that specific gravity
of glass wool is 20-100 kg / m <3>. Further, the specific gravity of the foamed plastic is
preferably 16 to 100 kg / m <3>. In addition, it is preferable that the foamed plastic be made of
polyurethane.
[0017]
In addition, it is preferable that the surface of the viscoelastic support that is in close contact with
the piezoelectric film before being pressed by the piezoelectric film is a flat surface. The
thickness of the viscoelastic support before it is pressed by the piezoelectric film is preferably 1
to 50 mm. The pressing force of the viscoelastic support at the flat portion of the piezoelectric
film is preferably 0.02 to 0.2 MPa. In addition, it is preferable that the piezoelectric film and the
visco-elastic support have a circular shape, an oval shape, or a rectangular shape. In addition, it is
preferable to be driven by an amplifier whose output voltage approximates -6 dB / octave.
[0018]
Moreover, in order to achieve the said objective, this invention provides the display device which
used said electroacoustic transducer as a speaker part.
[0019]
According to the present invention having the above configuration, a piezoelectric film that
expands and contracts according to the state of an electric field, a visco-elastic support disposed
in close contact with one surface of the piezoelectric film, and a piezoelectric film are pressed
against the visco-elastic support And a pressing member for holding the thickness of at least a
portion of the visco-elastic support in a reduced state, and the piezoelectric film is a visco-elastic
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support at least at a portion except a pressing portion pressed by the pressing member. The flat
portion held flat by the surface of the above, and the inclined portion connected to the pressing
portion and the flat portion and extending in the direction crossing the pressing portion.
The visco-elastic support in the inclined portion is compressed in the thickness direction as it
approaches the pressing portion, but a mechanical bias substantially equal to that of the flat
portion is applied to the piezoelectric film by the static visco-elastic effect (stress relaxation).
Becomes possible. As a result, the mechanical bias can be kept constant anywhere in the
piezoelectric film, and the expansion and contraction movement of the piezoelectric film is
converted into forward and backward movement without waste, as in the case of using a member
having a loose curvature, It is possible to obtain a flat electroacoustic transducer that is thin and
yet has sufficient sound volume and is excellent in acoustic characteristics. In addition, since the
area other than the vicinity of the holding member is maintained flat, restrictions on the
installation place and the attachment method can be reduced, and it can be wall hanging or
installed on the back of a picture, a poster, a decoration plate, etc. it can.
[0020]
It is a perspective view which shows notionally an example of the electroacoustic transducer of
this invention. It is a schematic sectional drawing in the II-II line of the electroacoustic transducer
shown in FIG. It is a conceptual diagram for demonstrating the piezoelectric film of FIG. (A)-(D)
are conceptual diagrams for demonstrating the structure of the electroacoustic transducer of FIG.
It is a schematic sectional drawing for demonstrating the electroacoustic transducer shown in
FIG. It is a graph which shows notionally the relation between drive voltage and time. (A) is a top
view for demonstrating the operation | movement of an electroacoustic transducer shown in FIG.
1, (B) is a BB sectional view taken on the line of (A). (A) is a top view for demonstrating the
operation | movement of an electroacoustic transducer shown in FIG. 1, (B) is a BB sectional view
taken on the line of (A). (A) is a top view for demonstrating the operation | movement of an
electroacoustic transducer shown in FIG. 1, (B) is a BB sectional view taken on the line of (A). (A)
is a top view which shows notionally another example of the electroacoustic transducer of this
invention, (B) is the CC sectional view taken on the line of (A). It is sectional drawing which shows
notionally another example of the electroacoustic transducer of this invention. It is sectional
drawing which shows notionally another example of the electroacoustic transducer of this
invention. It is sectional drawing which shows notionally another example of the electroacoustic
transducer of this invention. (A) is a perspective view conceptually showing another example of
the electroacoustic transducer of the present invention, (B) is a cross-sectional view taken along
the line B-B of (A), (C) It is the CC sectional view taken on the line of A). (A) is a perspective view
conceptually showing another example of the electroacoustic transducer of the present invention,
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(B) is a cross-sectional view taken along the line B-B of (A), (C) It is the CC sectional view taken on
the line of A). It is a graph which shows the characteristic of the output voltage from a drive
amplifier. It is a graph which shows the result of having measured the relationship between a
sound pressure level and a frequency.
[0021]
Hereinafter, the electroacoustic transducer of the present invention will be described in detail
based on the preferred embodiments shown in the accompanying drawings.
[0022]
FIG. 1 conceptually shows an example of the electro-acoustic transducer of the present invention,
and FIG. 2 shows a cross-sectional view taken along line II-II of the electro-acoustic transducer
shown in FIG.
The electroacoustic transducer 40 shown in FIGS. 1 and 2 basically includes the piezoelectric film
10, a case 42, a ring 46, and a ring 44. Here, in the electro-acoustic transducer 40 of the present
invention, the piezoelectric film 10 is pressed against the visco-elastic support 46 by the ring 44
which is a pressing member, and the visco-elastic support 46 is compressed. It has a rising
portion (inclined portion) 40 a formed by pressing by the ring 44 and a substantially planar
region (flat portion 40 b) other than the rising portion 40 a.
[0023]
The case 42 is a holding member that holds the piezoelectric film 10 and the visco-elastic
support 46 together with the ring 44, and is a thin bottomed cylindrical casing made of plastic or
the like. The case 42 accommodates the viscoelastic support 46 in a cylinder. Also, the depth of
the tube portion is smaller than the height of the viscoelastic support 46.
[0024]
The visco-elastic support 46 has appropriate viscosity and elasticity, supports the piezoelectric
film 10, and provides a constant mechanical bias anywhere on the piezoelectric film, so that the
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stretching movement of the piezoelectric film can be performed back and forth without waste. It
is for conversion into (movement in the direction perpendicular to the plane of the film). In the
illustrated example, a felt material is used as the viscoelastic support 46. Further, in the
illustrated example, the viscoelastic support 46 has a cylindrical shape having an outer diameter
substantially equal to the inner diameter of the case 42, and is disposed in the cylinder of the
case 42. Further, the height of the viscoelastic support 46 is larger than the depth of the
cylindrical portion of the case 42.
[0025]
The material of the viscoelastic support 46 is not particularly limited as long as it has
appropriate viscosity and elasticity, and does not prevent the vibration of the piezoelectric film
and deforms suitably. Specifically, it is preferable to use a fiber material such as wool felt and
glass wool containing polyester fibers such as rayon and PET, or a foam material (foam plastic)
such as polyurethane. Here, the specific gravity of the felt is preferably in the range of 50 to 500
kg / m <3>, and more preferably 100 to 300 kg / m <3>. The specific gravity of glass wool is
preferably in the range of 20 to 100 kg / m <3>. Further, the specific gravity of the polyurethane
(foamed plastic) is preferably in the range of 16 to 100 kg / m <3>. Range of specific gravity of
felt when using felt as viscoelastic support 46, specific gravity of glass wool when using glass
wool as viscoelastic support 46, or specific gravity of polyurethane when using polyurethane as
viscoelastic support 46 In each of the above ranges, as described later, the shape of the
piezoelectric film 10 is formed, the rising portion 40a is formed in the peripheral portion, and
the substantially flat portion 40b is formed in the central portion. It can be shaped.
[0026]
The viscoelastic support 46 is also pressed toward the case 42 by the piezoelectric film 10 at the
portion corresponding to the flat portion 40 b, and the surface pressure with which the
viscoelastic support 46 presses the flat portion 40 b of the piezoelectric film 10. It is preferable
to set it as 0.02-0.2 Mpa.
[0027]
The piezoelectric film 10 is a circular thin film which has piezoelectricity and expands / contracts
in the in-plane direction according to the state of the electric field, and is disposed so as to cover
the viscoelastic support 46 and the case 42 as shown in FIG. It is done.
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Here, the peripheral portion of the piezoelectric film 10 is pressed against the edge of the case
42 by a ring 44 described later, and the central portion is pressed by the viscoelastic support 46
in the direction opposite to the case 42 side, In the region in the vicinity of the ring 44, the
curvature sharply changes to form a rising portion 40a which becomes lower toward the ring 44,
and a substantially planar flat portion 40b is formed in the central portion.
[0028]
In the inclined portion, the visco-elastic support is compressed in the thickness direction as it
gets closer to the pressing portion, but the static visco-elastic effect (stress relaxation) keeps the
mechanical bias constant anywhere in the piezoelectric film. Can. As a result, as in the case of
using a member having a loose curvature, the expansion and contraction movement of the
piezoelectric film is converted to the back and forth movement without waste, so a thin, sufficient
volume can be obtained, and a planar shape excellent in acoustic characteristics. Can be obtained.
Thereby, restrictions of the installation place and the attachment method can be reduced, and it
can be a wall hanging, or can be installed on the back of a picture, a poster, a decoration board or
the like.
[0029]
The height (height of the highest position from the pressing portion) h from the surface (pressing
portion) of the piezoelectric film 10 pressed by the ring 44 is preferably 1 mm to 10 mm. By
setting the height h in this range, a thin electroacoustic transducer can be obtained, and the
piezoelectric film 10 can sufficiently move back and forth (oscillate) when a drive voltage is
applied. Sound can be reproduced well and sufficient volume can be obtained.
[0030]
Further, the crossing angle between the rising portion 40 a and the pressing portion is preferably
10 ° to 90 °. By setting the angle of the rising portion 40a in this range, the flat portion 40b of
the piezoelectric film 10 can sufficiently move back and forth (oscillate) according to the
expansion and contraction of the piezoelectric film 10, so that the sound can be reproduced with
high accuracy. It is possible to obtain a sufficient volume.
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[0031]
FIG. 3 shows a schematic cross-sectional view showing a part of the piezoelectric film 10. The
piezoelectric film 10 basically includes a piezoelectric layer 12 made of a polymer composite
piezoelectric material, a thin film electrode 14 provided on one surface of the piezoelectric layer
12 and a thin film electrode 16 provided on the other surface, and a surface of the thin film
electrode 14 And a protective layer 20 provided on the surface of the thin film electrode 16.
[0032]
The piezoelectric layer 12 is, as described above, made of a polymer composite piezoelectric
material. The polymer composite piezoelectric material forming the piezoelectric material layer
12 is obtained by uniformly dispersing the piezoelectric material particles 26 in a visco-elastic
matrix 24 made of a polymer material having visco-elasticity at normal temperature. In addition,
preferably, the piezoelectric layer 12 is poled (polarized).
[0033]
In FIG. 3, the piezoelectric particles 26 in the piezoelectric layer 12 are dispersed in the
viscoelastic matrix 24 with regularity, but may be dispersed irregularly. Preferably,
cyanoethylated polyvinyl alcohol is used as the viscoelastic matrix 24 (viscoelastic matrix /
binder) of the polymer composite piezoelectric material constituting the piezoelectric layer 12.
Cyanoethylated vinyl alcohol (hereinafter also referred to as cyanoethylated PVA) is a polymer
material having viscoelasticity at normal temperature.
[0034]
Therefore, the piezoelectric layer 12 in which the visco-elastic matrix 24 is cyanoethylated PVA
has a high visco-elastic effect, and the polymer visco-elastic matrix / piezoelectric is produced
even in the vicinity of the ring 44 where the curvature changes rapidly. Since stress
concentration at the body particle interface is alleviated, it is very preferable without the
occurrence of cracks and the like inside the piezoelectric layer 12.
[0035]
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The viscoelastic matrix 24 is not limited to one composed of cyanoethylated PVA alone, and in
addition to cyanoethylated PVA, polyvinylidene fluoride and vinylidene fluoridetetrafluoroethylene which are high dielectric or ferroelectric polymers. Fluorine-based polymers
such as copolymers, vinylidene fluoride-trifluoroethylene copolymer, polyvinylidene fluoridetrifluoroethylene copolymer and polyvinylidene fluoride-tetrafluoroethylene copolymer, or
vinylidene cyanide -Vinyl acetate copolymer, cyanoethylcellulose, cyanoethylhydroxysucrose,
cyanoethylhydroxycellulose, cyanoethylhydroxypullulan, cyanoethyl methacrylate, cyanoethyl
acrylate, cyanoethyl hydroxyethyl cellulose, cyanoethyl amylose Cyanoethyl hydroxypropyl
cellulose, cyanoethyl dihydroxypropyl cellulose, cyanoethyl hydroxypropyl amylose, cyanoethyl
polyacrylamide, cyanoethyl polyacrylate, cyanoethyl pullulan, cyanoethyl polyhydroxy
methylene, cyanoethyl glycidol pullulan, cyano group such as cyanoethyl saccharose and
cyanoethyl sorbitol or cyanoethyl group Or at least one of a nitrile rubber and a synthetic rubber
such as chloroprene rubber may be added.
[0036]
Further, the viscoelastic matrix 24 is not limited to one containing cyanoethylated PVA, and for
example, a material having a cyanoethyl group such as cyanoethylated pullulan can be used.
The material used as the visco-elastic matrix 24 preferably has visco-elastic properties at normal
temperature.
[0037]
The piezoelectric particles 26 are particles of a piezoelectric.
The piezoelectric particles 26 are preferably made of ceramic particles having a perovskite
crystal structure. Examples of ceramic particles that constitute the piezoelectric particles 26
include lead zirconate titanate (PZT), lead zirconate titanate zirconate (PLZT), barium titanate
(BaTiO 3), and barium titanate and bismuth ferrite (for example, The solid solution (BFBT) with
BiFe3) etc. are illustrated.
[0038]
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The particle diameter of the piezoelectric particles 26 is not particularly limited, and may be
appropriately set according to the size of the piezoelectric film 10, the application of the
piezoelectric film 10, the characteristics required of the piezoelectric film 10, and the like. There
are no particular limitations on the quantitative ratio of the visco-elastic matrix 24 and the
piezoelectric particles 26 in the piezoelectric layer 12 (polymer composite piezoelectric). That is,
the quantitative ratio between the visco-elastic matrix 24 and the piezoelectric particles 26
depends on the size (size in the surface direction) and thickness of the piezoelectric film 10, the
application of the piezoelectric film 10, and the characteristics required for the piezoelectric film
10 And may be set as appropriate.
[0039]
The thickness of the piezoelectric layer 12 is not particularly limited, and may be set
appropriately according to the size of the piezoelectric film 10, the application of the
piezoelectric film 10, the characteristics required of the piezoelectric film 10, and the like. Here,
according to the study of the present inventor, the thickness of the piezoelectric layer 12 is
preferably 10 to 200 μm, particularly 30 to 100 μm. By setting the thickness of the
piezoelectric layer 12 in the above-mentioned range, it is possible to achieve favorable results in
that the strength of the piezoelectric film 10 can be secured and appropriate flexibility suitable
for back and forth movement (vibration) can be achieved. Can. Further, it is preferable that the
piezoelectric layer 12 be subjected to polarization processing (poling).
[0040]
Further, in the present embodiment, a polymer composite piezoelectric material is used as the
piezoelectric material layer 12, but the present invention is not limited to this, and a polymer
piezoelectric material having piezoelectricity such as PVDF (polyvinylidene fluoride) is used.
Materials may be used. Uniaxially stretched PVDF has an in-plane anisotropy in its piezoelectric
characteristics, whereas a polymer composite piezoelectric body has no in-plane anisotropy, so it
has a more preferable stretching motion than PVDF. It is preferable in that it can be converted
into back and forth movement, and sufficient sound volume and sound quality can be obtained.
[0041]
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In the piezoelectric film 10, the thin film electrode 14 is provided on one surface of the
piezoelectric layer 12, and the thin film electrode 16 is provided on the other surface. That is,
thin film electrodes are formed on both sides of the piezoelectric layer 12 so as to sandwich the
piezoelectric layer 12.
[0042]
The thin film electrodes 14 and 16 are electrodes for applying a drive voltage to the piezoelectric
layer 12. There are no particular limitations on the material for forming the thin film electrodes
14 and 16, and various conductors can be used. Specifically, C, Pd, Fe, Sn, Al, Ni, Pt, Au, Ag, Cu,
Cr, Mo and the like, and alloys thereof are exemplified. Further, the method of forming the thin
film electrode 14 is not particularly limited, and film formation by a vapor deposition method
(vacuum film formation method) such as vacuum evaporation or sputtering, a method of
adhering a foil formed of the above material, etc. Various known methods are available.
[0043]
Above all, the flexibility of the piezoelectric film 10, that is, the magnitude of the back and forth
movement can be secured, and a thin electrode layer which does not constrain the deformation
of the piezoelectric layer can be formed. The thin film is suitably used as the thin film electrodes
14 and 16.
[0044]
The thickness of the thin film electrodes 14 and 16 is not particularly limited, but is preferably 1
μm or less.
Also, the thicknesses of the thin film electrodes 14 and 16 are basically the same but may be
different.
[0045]
The thin film electrodes 14 and 16 are preferably as thin as possible, but in the case of the largesized piezoelectric film 10, the effect may be negligible, so the size of the piezoelectric film 10,
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14
the piezoelectric film It may be determined as appropriate according to the performance,
characteristics, handleability, etc. required for the item 10. The relationship between the
thickness of thin film electrodes 14 and 16 and the size of piezoelectric film 10 is the same as
the relationship between protective layers 18 and 20 and the size of piezoelectric film 10, which
will be described in detail later.
[0046]
In addition, the thin film electrode 14 and / or the thin film electrode 16 need not necessarily be
formed corresponding to the entire surface of the piezoelectric layer 12 (the protective layer 18
and / or 20). That is, at least one of the thin film electrode 14 and the thin film electrode 16 may
be smaller than, for example, the piezoelectric layer 12, and the piezoelectric layer 12 and the
protective film may be in direct contact with each other around the piezoelectric film 10. .
Specifically, it is permitted that the thin film electrode on the upper surface side (the sound
generation direction side) or the lower surface side is smaller than the inner diameter of the ring
44 as in an electroacoustic transducer 40 shown in FIG. Be
[0047]
A protective layer 18 is provided on the surface of the thin film electrode 14, and a protective
layer 20 is provided on the surface of the thin film electrode 16. The protective layers 18 and 20
protect the piezoelectric layer 12 and the thin film electrodes 14 and 16 and also function as a
support layer for supporting the piezoelectric film 10.
[0048]
The protective layers 18 and 20 are not particularly limited, and various sheet-like materials can
be used. As an example, various resin films (plastic films) are suitably exemplified. Among them,
polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC),
polyphenylene sulfite (PPS), polymethyl methacrylate (PMMA) and the like because of having
excellent mechanical strength and heat resistance. ), Polyether imide (PEI), polyimide (PI),
polyethylene naphthalate (PN), and cyclic olefin resins are preferably used.
[0049]
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The thickness of the protective layers 18 and 20 is not particularly limited. Also, the thicknesses
of the protective layers 18 and 20 are basically the same but may be different. Here, as in the
thin film electrode 14 and the like described above, if the rigidity of the protective layers 18 and
20 is high, expansion and contraction of the piezoelectric layer 12 will be restrained, and as a
result, the amplitude of the back and forth movement of the piezoelectric film will be small. .
Therefore, considering the performance of the electroacoustic transducer 40, the thinner the
protective layers 18 and 20, the better.
[0050]
On the other hand, as described above, since the protective layers 18 and 20 use resin films, the
thinner they are, the more difficult the handling becomes. The protective layers 18 and 20 also
function as a support for the piezoelectric film 10, but if the protective layer is too thin, it can not
exhibit sufficient functions as a protective layer and a support. In addition, if the piezoelectric
film 10 is required to have good mechanical strength and good handling as a sheet, the
protective layers 18 and 20 are advantageously thicker. However, when the protective layers 18
and 20 are thick and the rigidity is too high, not only the expansion and contraction of the
piezoelectric layer 12 is restrained but also the flexibility is impaired, so that the mechanical
strength and the good handling property as a sheet are Except where required, protective layers
18 and 20 are advantageously thinner. Therefore, the thickness of the protective layers 18 and
20 depends on the acoustic performance required for the piezoelectric film 10, that is, the
acoustic device, the handling required for the piezoelectric film 10, the mechanical strength
required for the piezoelectric film 10, etc. And may be set as appropriate.
[0051]
Here, according to the study of the inventor, if the thickness of the protective layer is equal to or
less than twice the thickness of the piezoelectric layer 12, it is preferable in terms of coexistence
of securing of rigidity and appropriate flexibility. You can get the result. For example, when the
thickness of the piezoelectric layer 12 is 50 μm and the protective layers 18 and 20 are made of
PET, the thickness of the protective layers 18 and 20 is preferably 100 μm or less, more
preferably 50 μm or less, and in particular 25 μm or less Is preferred.
[0052]
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As a method of manufacturing such a piezoelectric film 10, a coating obtained by dissolving
cyanoethylated PVA in a solvent, and further adding piezoelectric particles 26 such as PZT
particles, and stirring and dispersing is obtained on the protective layer 18. After casting
(coating) the sheet on which the thin film electrode 14 is formed and evaporating the organic
solvent and drying, the sheet on which the thin film electrode 16 is formed is laminated on the
protective layer 20, There is a method of manufacturing by thermocompression bonding.
Alternatively, a cyanoethylated PVA is heated and melted to prepare a melt obtained by adding /
dispersing the piezoelectric particles 26 thereto, and the thin sheet electrode (the thin film
electrode 14 is formed on the protective layer 18) by extrusion molding or the like. Sheet may be
extruded into a sheet and cooled to form the piezoelectric layer 12. Moreover, it is preferable to
perform polarization treatment (poling) of the piezoelectric layer 12 after drying the coating
material applied in the form of a sheet.
[0053]
The piezoelectric film 10 may be manufactured using the cut sheet-like material, but it is
preferable to use roll-to-roll manufacturing.
[0054]
The ring 44 is a pressing member for pressing the piezoelectric film 10, and is a circular plateshaped member formed of metal, plastic or the like and having a through hole at the center.
The outer diameter and the inner diameter of the ring 44 are substantially equal to the outer
diameter and the inner diameter of the case 42, respectively. The ring 44 is fixed to the case 42
in a state where the piezoelectric film 10 is pressed against the edge of the case 42. In addition,
there is no limitation in particular in the fixing method of the ring 44 and the case 42, Various
known fixing methods, such as a method of using screwing and a jig for fixing, can be used.
[0055]
Next, the assembly process of this electroacoustic transducer 40 is demonstrated using FIG. FIGS.
4A to 4D are conceptual perspective views for explaining the assembly process of the
electroacoustic transducer 40 shown in FIG.
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[0056]
As shown in FIG. 4A, a cylindrical visco-elastic support 46 is accommodated in the cylinder of the
case 42. Here, since the height of the visco-elastic support 46 is higher than the depth of the
cylindrical portion of the case 42, as shown in FIG. 4 (B), in the state before the ring 44 is fixed to
the case 42 The elastic support 46 protrudes from the upper surface (open surface) of the case
42.
[0057]
Next, as shown in FIG. 4B, the piezoelectric film 10 is disposed on the top surface of the
viscoelastic support 46 so as to cover the viscoelastic support 46 and the case 42. Furthermore,
as shown in FIG. 4C, the ring 44 is disposed to press the peripheral edge of the piezoelectric film
10 against the edge of the open surface of the case 42 from the upper side of the piezoelectric
film 10, and the ring 44 is The electroacoustic transducer 40 is assembled by fixing it to 42 (FIG.
4 (D)).
[0058]
Thus, in the electroacoustic transducer 40, the viscoelastic support 46 has a cylindrical shape
whose height (thickness) is thicker than the height of the inner surface of the case 42 (the depth
of the cylindrical portion). Therefore, in the electroacoustic transducer 40, in the peripheral
portion of the viscoelastic support 46 (in the vicinity of the ring 44), the viscoelastic support 46
is pressed downward by the piezoelectric film 10 and is held in a state where the thickness is
reduced. Be done. In the same manner, in the peripheral portion of the viscoelastic support 46,
the curvature of the piezoelectric film 10 changes rapidly, and a rising portion 40a is formed on
the piezoelectric film 10 so as to become lower toward the periphery of the viscoelastic support
46. Furthermore, the central region of the piezoelectric film 10 is pressed by the cylindrical
visco-elastic support 46 so as to be substantially planar.
[0059]
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Here, FIG. 5 shows a schematic cross-sectional view of the electroacoustic transducer 40 in a
state where the assembly is completed. Further, in FIG. 5, the viscoelastic support 46 a before
being mounted in the case 42 and before pressing the piezoelectric film 10 with the ring 44 is
indicated by a broken line. As shown in FIG. 5, the viscoelastic support 46 of the electroacoustic
transducer 40 after assembly is entirely pressed to the case 42 side by the piezoelectric film 10,
and the overall thickness is larger than that of the viscoelastic support 46a before assembly. It is
getting thinner. That is, in the electro-acoustic transducer after assembly, the viscoelastic support
46 is compressed not only at the rising portion 40a but also at the flat portion 40b, and the
thickness thereof is reduced. The viscoelastic support in the rising portion 40a is compressed in
the thickness direction as it approaches the pressing portion, but gives a mechanical bias to the
piezoelectric film which is substantially the same as that of the flat portion by the static
viscoelastic effect (stress relaxation). It is possible. As a result, the mechanical bias can be kept
constant anywhere in the piezoelectric film, and the expansion and contraction movement of the
piezoelectric film is converted into forward and backward movement without waste, as in the
case of using a member having a loose curvature, A thin, sufficient volume can be obtained, and a
planar electroacoustic transducer excellent in acoustic characteristics can be obtained.
[0060]
Next, the operation of the electroacoustic transducer 40 will be described with reference to FIGS.
6 and 7 to 9. FIG. 6 is a graph schematically showing a drive voltage applied to drive the
electroacoustic transducer 40. As shown in FIG. 7 (A) is a top view conceptually showing the
state of the electroacoustic transducer 40 at point a in FIG. 6, and FIG. 7 (B) is a cross section
taken along line B-B in FIG. 7 (A). FIG. 8 (A) is a top view conceptually showing the state of the
electroacoustic transducer 40 at point b in FIG. 6, and FIG. 8 (B) is a cross section taken along the
line B-B in FIG. 8 (A). FIG. 9 (A) is a top view conceptually showing the state of the electroacoustic
transducer 40 at point c in FIG. 6, and FIG. 9 (B) is a cross section taken along the line B-B in FIG.
9 (A). FIG. In FIGS. 7 to 9, for the sake of simplicity, the size of the thin film electrode 14 is
substantially equal to the size of the flat portion 40b. Also, illustration of the protective layers 18
and 20 is omitted.
[0061]
When a drive voltage shown in FIG. 6 is applied to the electroacoustic transducer 40, the
piezoelectric film 10 expands and contracts and moves back and forth according to the applied
drive voltage. Specifically, as shown in FIGS. 7A and 7B, the piezoelectric film 10 does not expand
or contract when the drive voltage is 0 as indicated by a point a, so that the viscoelastic support
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46 and the ring It is pressed by 44 and is formed in a shape having a rising portion 40a and a
flat portion 40b.
[0062]
Next, as in point b, when a positive drive voltage is applied, as shown in FIG. 8A, a region to
which a voltage is applied, that is, a region where the thin film electrode 16 is formed (flat
portion The piezoelectric film 10b of 40b contracts in the in-plane direction, and becomes
smaller than the flat portion 40b in the state of FIG. 7A. Therefore, in order to absorb this
contraction, as shown in FIG. 8B, the rising portion 40a of the piezoelectric film 10 changes its
angle in the falling direction (direction close to the plane). At that time, the viscoelastic support
46 held in a compressed state by the piezoelectric film 10 is further shrunk downward (case 42
side), so that the flat portion 40 b is held flat and the lower side (case 42 Move to the side). At
this time, if the viscoelastic support stores elastic energy accompanying compression at the
peripheral portion (rise portion), the force to push back the piezoelectric film works at the
peripheral portion, but the above-described viscoelastic effect Since the mechanical bias applied
to the piezoelectric film is substantially the same as that of the flat portion in the rising portion
40a by (stress relaxation), the contraction of the piezoelectric film is converted into the amount
of downward movement without waste. Here, the positive voltage is the voltage application
direction of the polarization process. Therefore, when a positive drive voltage is applied, the
piezoelectric film 10 extends in the film thickness direction and contracts in the in-plane
direction.
[0063]
On the other hand, when a negative drive voltage is applied as shown at point c, as shown in FIG.
8A, the piezoelectric film 10 in the region (flat portion 40b) where the thin film electrode 16 is
formed is in the in-plane direction And becomes larger than the flat portion 40b in the state of
FIG. 7 (A). Therefore, in order to absorb this extension, the rising portion 40a of the piezoelectric
film 10 changes its angle in the rising direction (the direction in which the crossing angle with
the pressing portion approaches 90 °). At this time, the viscoelastic support 46 held in a
compressed state by the piezoelectric film 10 extends upward (in the direction of sound
generation), so the flat portion 40 b is held upward while being held flat. Moving. At this time, if
the viscoelastic support stores elastic energy accompanying compression at the peripheral
portion (rising portion), a force acts to push back the piezoelectric film more than necessary at
the peripheral portion, as described above. Since the mechanical bias applied to the piezoelectric
film is almost the same as that of the flat portion in the rising portion 40a due to the viscoelastic
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effect (stress relaxation), the extension of the piezoelectric film is converted into the upward
moving amount without waste. Ru. The electroacoustic transducer 40 generates a sound by the
back and forth movement of the piezoelectric film 10.
[0064]
As described above, in an electroacoustic transducer using a conventional piezoelectric film, it is
necessary to give curvature to the piezoelectric film in order to obtain a sufficient volume.
However, when the piezoelectric film is given a curvature, the piezoelectric film is curved, and
therefore, the installation place and the mounting method are restricted, and the wall is hung, or
it is installed on the back of a picture, a poster, a decorative plate, etc. There was a problem that
it was not suitable to In addition, when the area of the speaker is increased, the thickness is
increased even with a loose curvature, and there is a problem that the features as an original thin
speaker are also lost.
[0065]
On the other hand, in the electroacoustic transducer according to the present invention, the
holding member holding the piezoelectric film and the visco-elastic support presses the
piezoelectric film against the visco-elastic support to make at least a part of the visco-elastic
support A driving voltage is applied to the piezoelectric film 10 since at least a part of the area
other than the area near the holding member of the piezoelectric film is formed substantially flat
while holding in a state where the thickness is reduced. At this time, the angle of the rising
portion 40a slightly changes according to the expansion and contraction of the piezoelectric film,
and the flat portion 40b can move back and forth, that is, vibrate and generate sound while
maintaining the flat surface. In addition, since the area other than the vicinity of the ring is
maintained flat, restrictions on the installation place and the attachment method can be reduced,
and the apparatus can be mounted on a wall or installed on the back of a picture, a poster, a
decoration plate, etc. .
[0066]
Although the electro-acoustic transducer 40 in the illustrated example has a circular shape for
the surface that generates sound, the present invention is not limited to this, and a square shape,
a rectangular shape, or an oval shape (elliptical shape, oval shape) And so on.
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21
[0067]
FIG. 10A is a top view showing another example of the electroacoustic transducer of the present
invention, and FIG. 10B is a cross-sectional view taken along the line C-C of FIG.
The electro-acoustic transducer 100 shown in FIGS. 10A and 10B basically has the same
configuration as the electro-acoustic transducer 40 shown in FIG. 2 except that the shape of the
surface that generates sound is square. Have. The electroacoustic transducer 100 includes a
piezoelectric film 102, a case 104, a viscoelastic support 106, and a frame 108.
[0068]
The piezoelectric film 102 is the same as the piezoelectric film 10 except that it is formed in a
square shape. The case 104 is a substantially rectangular box-shaped casing open on one side.
The visco-elastic support 106 is a visco-elastic support having elasticity and supporting the
piezoelectric film 102 and having a square columnar shape having a height higher than the
depth inside the case 104. The viscoelastic support 106 is housed inside the case 104, and the
end is compressed by the piezoelectric film 102 pressed by the frame 108, and the piezoelectric
film 102 is pressed in the sound generation direction. The frame 108 is a plate having a through
hole at the center and having the same shape as the upper end surface (open surface side) of the
case 104. The frame 108 is fixed in a state where the piezoelectric film 102 is pressed against
the end of the case 104.
[0069]
Therefore, in the electroacoustic transducer 100, in the peripheral portion of the viscoelastic
support 106, the viscoelastic support 106 is held in a state of being pressed downward by the
piezoelectric film 102 and having a reduced thickness. Similarly, in the peripheral portion of the
visco-elastic support 106, the curvature of the piezoelectric film 102 changes rapidly, and a
rising portion 100a is formed on the piezoelectric film 102 so as to become lower toward the
periphery of the visco-elastic support 106. Furthermore, the central region of the piezoelectric
film 102 is pressed against the viscoelastic support 106 in the form of a square pole, and a
(substantially) flat portion 100 b is formed.
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22
[0070]
As described above, even when the surface that generates sound has a square shape, when the
drive voltage is applied to the piezoelectric film 102, the angle of the rising portion 100a (flat
portion 100b) according to the expansion and contraction of the piezoelectric film 102. The
angle (with respect to the plane of the) changes slightly, and while the flat portion 100b
maintains a flat surface, back and forth movement, that is, vibration can be generated to generate
sound.
[0071]
Further, although the electroacoustic transducer 40 of the illustrated example presses the entire
peripheral area of the piezoelectric film 10 against the case 42 (that is, the visco-elastic support
46) by the ring 44, the present invention is not limited thereto. And at least two locations around
the piezoelectric film may be pressed against the case (viscoelastic support).
That is, the electro-acoustic transducer using the piezoelectric film 10 of the present invention
does not have the ring 44, and for example, at four places of the case 42, the piezoelectric film
10 is formed of A configuration in which pressing / fixing to the upper surface is also available.
In addition, the structure which presses the peripheral whole area of the piezoelectric film 10 can
form suitably a flat part and a standup part, and is preferable at the point which can improve the
reproducibility and sound volume of a sound more.
[0072]
Moreover, the electroacoustic transducer of this invention does not need to have a case which
accommodates a viscoelastic support body. That is, as the cross-sectional view of the electroacoustic transducer 110 in FIG. 11 conceptually shows an example, the viscoelastic support 106
is mounted on the rigid support plate 114, and the visco-elastic support 106 is The peripheral
portion of the visco-elastic support 106 is thinned by covering and mounting the piezoelectric
film 102 and pressing the piezoelectric film 102 against the visco-elastic support 106 with a
screw 118 to fix the peripheral portion of the visco-elastic support 106, and the piezoelectric
film A configuration having the raised and flat portions of 102 is also available.
[0073]
Alternatively, the piezoelectric film 102 is placed on the visco-elastic support 106 and the at
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23
least two substantially C-shaped support members 128 are mounted on the visco-elastic support
106, as schematically shown in the cross-sectional view of the electroacoustic transducer 120 of
FIG. The peripheral portion of the visco-elastic support 106 is made thinner by holding the
piezoelectric film 102 and the visco-elastic support 106 while pressing the peripheral portion of
the visco-elastic support 106 in the vertical direction, and the piezoelectric film 102 The rising
portion and the flat portion may be formed.
[0074]
Alternatively, a protective case for protecting the piezoelectric film may be used as a member
(ring, frame, etc.) for pressing the piezoelectric film.
[0075]
Furthermore, the electro-acoustic transducer using the piezoelectric film 10 of the present
invention is not limited to the configuration for pressing the peripheral portion, for example, the
center of the laminate of the viscoelastic support 46 and the piezoelectric film 10 It is also
possible to use a configuration in which the viscoelastic support 46 is held in a thin state by
pressing.
That is, in the electroacoustic transducer using the piezoelectric film 10 of the present invention,
the visco-elastic support is held by the piezoelectric film 10 so as to be held in a reduced
thickness, and by this pressing / holding, the piezoelectric film If the curvature of 10 fluctuates
rapidly and the rising portion 40a is formed on the piezoelectric film 10 and the flat portion 40b
is formed, various configurations can be used.
[0076]
In the above embodiment, although the piezoelectric film 10 is pressed against the viscoelastic
support 46 by the ring 44 to form the rising portion 40a and the flat portion 40b, the present
invention is not limited thereto. Alternatively, a curved portion may be formed between the rising
portion and the flat portion.
[0077]
FIG. 13 is a schematic cross-sectional view showing another example of the electroacoustic
14-04-2019
24
transducer of the present invention.
In the electro-acoustic transducer 130 shown in FIG. 13, the viscoelastic support 46 is changed
to a viscoelastic support 136 of different materials in the electro-acoustic transducer 40 shown
in FIG. 2, and between the rising portion and the flat portion Since the same configuration is
provided except that the curved portion is formed, the same portions are denoted by the same
reference numerals, and the following description will be mainly made on different portions.
[0078]
The electroacoustic transducer 130 has a piezoelectric film 10, a case 42, a visco-elastic support
136, and a ring 44.
The viscoelastic support 136 is the same as the viscoelastic support 46 except that glass wool is
used as a material, has a cylindrical shape having an outer diameter substantially equal to the
inner diameter of the case 42, and has a height of a cylinder of the case 42. Greater than the
depth of the department. Further, similarly to the viscoelastic support 46, the viscoelastic
support 136 is pressed and compressed by the piezoelectric film 10.
[0079]
Here, as shown in FIG. 13, when glass wool is used as the viscoelastic support 136, the
piezoelectric film 10 is pressed against the viscoelastic support 136 by the ring 44 because the
glass wool is softer than the felt material. Thus, the rising portion T, the flat portion H, and the
curved portion R between the rising portion T and the flat portion H are formed.
[0080]
Specifically, the electro-acoustic transducer 130 sharply rises from the pressing portion P where
the piezoelectric film 10 is pressed against the case 42 by the ring 44 and from the pressing
portion P, and extends in a direction intersecting the pressing portion P A rising portion T, a
curved curved portion R connected to the rising portion T and gently curved, and a flat portion H
connected to the curved portion R and substantially flat are formed.
[0081]
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25
As described above, even when the flat portion, the rising portion, and the curved portion are
formed, the angle of the rising portion T slightly changes according to the expansion and
contraction of the piezoelectric film 10 when the drive voltage is applied to the piezoelectric film
10 Thus, while the flat portion H maintains a flat surface, it can move back and forth to generate
a sound.
In addition, since the area other than the vicinity of the ring is maintained flat, restrictions on the
installation place and the attachment method can be reduced, and the apparatus can be mounted
on a wall or installed on the back of a picture, a poster, a decoration plate, etc. .
[0082]
The shape of the piezoelectric film when the piezoelectric film is pressed against the viscoelastic
support by the ring is the elastic modulus of the viscoelastic support, loss tangent, density,
rebound resilience, recovery rate, shape, elasticity of the piezoelectric film By appropriately
combining the rate, the loss tangent, and the like, an appropriate shape having a flat portion can
be obtained.
[0083]
In the above embodiment, the piezoelectric film 10 is pressed against the visco-elastic support 46
by the ring 44, whereby the rising portion 40a in the vicinity of the ring 44 and the flat portion
40b are formed. However, the present invention is not limited to this, and in the cross section in
a predetermined one direction perpendicular to the surface of the piezoelectric film, the flat
portion held substantially linearly and the rising portion in the vicinity of the pressing member It
may be configured to be formed.
[0084]
FIG. 14 is a perspective view conceptually showing another example of the electroacoustic
transducer of the present invention, and FIG. 14 (B) is a cross-sectional view taken along the line
B-B of (A). These are CC sectional view taken on the line of (A).
The electroacoustic transducer 140 shown in FIG. 14 has a piezoelectric film 142, a case 144, a
visco-elastic support 146, and a frame 148.
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[0085]
The piezoelectric film 142 is the same as the piezoelectric film 10 except that it is formed in a
rectangular shape.
The case 144 is a substantially rectangular box-shaped casing open on one side.
Further, in the case 144 of the illustrated example, a groove for disposing the O-ring 144a is
formed at the edge of the open surface.
[0086]
The visco-elastic support 146 is an elastic visco-elastic support having a rectangular column
shape whose height is higher than the depth inside the case 144 and supports the piezoelectric
film 142. The viscoelastic support 146 is accommodated inside the case 144, and the end is
compressed by the piezoelectric film 142 pressed by the frame 148, and the piezoelectric film
142 is pressed in the sound generation direction. The frame 148 is a plate-like pressing member
having a through hole at the center and having the same shape as the upper end surface (open
surface side) of the case 144. The frame 148 is fixed in a state where the piezoelectric film 142
is pressed against the end of the case 144.
[0087]
Here, in the electro-acoustic transducer 140, the shape of the piezoelectric film 142 (the shape of
the surface that generates sound) is a rectangular shape, and the short side direction is
sufficiently shorter than the longitudinal direction. Therefore, as shown in FIG. 14C, when viewed
in cross section in the longitudinal direction of the piezoelectric film 142, in the piezoelectric film
142, the visco-elastic support 146 is pressed by the piezoelectric film 142 in the vicinity of the
frame 148 and the thickness is Becomes thin and a rising portion 140a is formed. Further, the
central region of the piezoelectric film 142 is pressed by the viscoelastic support 146 to form a
substantially flat portion 140 b. On the other hand, as shown in FIG. 14B, when viewed in a cross
section in the width direction of the piezoelectric film 142, the piezoelectric film 142 is formed in
a curved shape without forming a flat portion.
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[0088]
In this manner, in the cross section of the predetermined one direction perpendicular to the
surface of the piezoelectric film, the flat portion held substantially linearly and the rising portion
in the vicinity of the pressing member are formed. Even when the drive voltage is applied to the
piezoelectric film 142, the angle of the rising portion 140a (the angle with respect to the surface
of the flat portion 140b) slightly changes according to the expansion and contraction of the
piezoelectric film 142, and the flat portion 140b is flat. The sound can be generated by moving
back and forth while maintaining the normal surface. In addition, since the area other than the
vicinity of the pressing member is maintained flat in the longitudinal direction, restrictions on the
installation place and the mounting method can be reduced, and installation on the back of a
wall, painting, poster, decoration plate, etc. You can do it.
[0089]
Further, as in the electro-acoustic transducer 140 shown in FIG. 14, it is preferable to dispose a
member having a damper effect such as an O-ring between the piezoelectric film and the case. As
a result, the vibration of the piezoelectric film can be prevented from being transmitted to the
case, and the acoustic characteristics can be improved.
[0090]
Further, in the above embodiment, the surface that generates sound is formed to be flat, but the
present invention is not limited to this, and the surface that generates sound may be formed to
be curved. .
[0091]
FIG. 15 (A) is a perspective view conceptually showing another example of the electroacoustic
transducer of the present invention, and FIG. 15 (B) is a sectional view taken along the line B-B of
FIG. (C) is the CC sectional view taken on the line of (A).
The electroacoustic transducer 150 shown in FIG. 15 has a piezoelectric film 152, a visco-elastic
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support 156, and a fixing ring 158.
[0092]
The piezoelectric film 152 is the same as the piezoelectric film 10 except that it is formed in a
rectangular shape. The short side of the piezoelectric film 152 has a length substantially equal to
the height of the cylindrical visco-elastic support 156, and the long side has a length
substantially equal to the circumferential length of the bottom of the visco-elastic support 156. is
there. In the illustrated example, the wires 152a and 152b connected to the thin film electrode
are formed on one short side of the piezoelectric film 152.
[0093]
The visco-elastic support 156 is a cylindrical visco-elastic support having elasticity. The
piezoelectric film 152 is wound around the circumferential surface of the viscoelastic support
156. Further, the fixing ring 158 is fixed to the circumferential surfaces on the two bottom sides
of the viscoelastic support 156 via the piezoelectric film 152 in a state of pressing the
viscoelastic support 156 in the radial direction. The fixing ring 158 is a ring-shaped member
having an inner diameter smaller than the outer diameter of the viscoelastic support 156, and is
a member that presses and fixes the piezoelectric film 152 and the visco-elastic support 156.
[0094]
Here, as shown in FIG. 15B, in the section of the viscoelastic support 156 in the height direction,
the piezoelectric film 152 is pressed by the piezoelectric film 152 in the vicinity of the fixing ring
158. Thus, the diameter is reduced and the rising portion 150a is formed. The central region of
the piezoelectric film 152 is pressed by the viscoelastic support 156 to form a substantially
cylindrical flat portion 150 b. On the other hand, as shown in FIG. 15C, when viewed in a radial
cross section of the visco-elastic support 156, the piezoelectric film 152 is formed in a circular
shape along the circumferential surface of the visco-elastic support 156.
[0095]
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As described above, by winding the piezoelectric film around the circumferential surface of the
cylindrical visco-elastic support and pressing both end portions on the bottom side with the
fixing ring, all 360 ° around the central axis of the visco-elastic support can be obtained. Sound
can be generated in the direction. Further, in the cross section in the height direction of the
visco-elastic support 156, since the flat portion 150b held substantially linearly and the rising
portion 150a near the pressing member are formed, the piezoelectric film 152 is formed. When
the driving voltage is applied to the flat portion 150b, the angle of the rising portion 150a (the
angle with respect to the surface of the flat portion 150b) slightly changes according to the
expansion and contraction of the piezoelectric film 152, and the flat portion 150b maintains the
flat surface. , Can move back and forth to generate sound. In addition, since the area other than
the vicinity of the pressing member is maintained flat in the height direction, restrictions on the
installation location and the mounting method can be reduced.
[0096]
Moreover, the electro-acoustic transducer of the present invention can not only be made thinner
as compared with a normal dynamic speaker etc., but also reproduces the sound with high
accuracy compared with the electro-acoustic transducer using a conventional piezoelectric film.
Since a sufficient sound volume can be obtained and acoustic characteristics are excellent, it can
be suitably used as a speaker of a thin display device such as a liquid crystal display device or an
organic EL display device. Specifically, a rectangular electroacoustic transducer as shown in FIG.
14 may be disposed on the side or lower side of the display area of the display device and used
as a speaker. Alternatively, the electro-acoustic transducer of the present invention may be
disposed on the side opposite to the display surface of the display device.
[0097]
Further, as the piezoelectric film of the electroacoustic transducer of the present invention, it is
particularly preferable to use a film having a viscoelasticity at normal temperature and using a
polymer material such as cyanoethylated PVA as a viscoelastic matrix. By using a piezoelectric
film using a visco-elastic matrix, the sound quality does not change much even if a load is applied
to the vibrating surface (piezoelectric film). Therefore, for example, it is put in the headrest of the
seat of the car and used as a device for preventing sleep (functions as a sensor and a speaker) or
is put in a pillow and used as a device for apnea syndrome be able to.
[0098]
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30
Hereinafter, the present invention will be described in more detail by way of specific examples of
the electroacoustic transducer.
[0099]
Example 1 The electro-acoustic transducer 40 shown in FIG. 2 was manufactured by the abovedescribed assembling method.
The inner diameter of the case 42 and the ring 44, that is, the size of the surface that generates
the sound, was Φ140 mm. Moreover, the depth of the cylindrical part of case 42 was 10 mm.
The piezoelectric film 10 had a size of Φ 150 mm and a thickness of 60 μm, the material of the
viscoelastic matrix of the piezoelectric layer 12 was cyanoethylated PVA, and the material of the
piezoelectric particles 26 was PZT. The thin film electrodes 14 and 16 were Cu thin films with a
thickness of 0.1 μm, and the protective layers 18 and 20 were PET films with a thickness of 4
μm. The viscoelastic support 46 was a felt material having a diameter of 140 mm, a height of 17
mm before assembly, and a density of 250 kg / m <3>. That is, the height of the visco-elastic
support 46 before assembly is 7 mm with reference to the edge of the case 42.
[0100]
The viscoelastic support 46 is placed in the cylindrical portion of the case 42, the piezoelectric
film 10 is disposed so as to cover the case 42 and the viscoelastic support 46, and the ring 44 is
covered from above the piezoelectric film 10. Were fixed to the case 42, and the electroacoustic
transducer 40 was produced.
[0101]
The shape of the surface of the piezoelectric film 10 of the electroacoustic transducer 40
manufactured in this manner was measured.
Specifically, the height based on the lower surface of the ring 44 was measured at each position
of 1 cm from one end on the center line of a predetermined one direction. That is, the position of
0 cm and the position of 14 cm are the positions (ends) adjacent to the ring 44, and the position
of 7 cm is the central portion of the piezoelectric film 10. The results are shown in Table 1.
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[0102]
As shown in Table 1 above, there is a sharp change between a position of 0 cm and a position of
1 cm, which is a position near the ring 44 which is a pressing member, and a position of 13 cm
to a position of 14 cm. It can be seen that the rising portion 40a is formed. At this time, the
inclination angle of the rising portion 40a was about 21.8 °. In addition, it can be seen that a
flat portion 40 b is formed between the position of 3 cm and the position of 11 cm, that is, the
central portion of the piezoelectric film 10 has a substantially constant height.
[0103]
Example 2 Next, in Example 2, the frequency characteristic was measured when a rectangular
electroacoustic transducer as shown in FIG. 10 was used as a speaker. Specifically, the size of the
case 104 and the frame 108, that is, the size of the surface that generates sound is 210 × 300
mm (A4 size). Moreover, the depth of case 104 was 12 mm. The piezoelectric film 102 was the
same as the piezoelectric film of Example 1 except that the piezoelectric film 102 was formed in
a rectangular shape corresponding to the shape of the case 104. The viscoelastic support 106
corresponds to the shape of the case 104 and is the same as the viscoelastic support of Example
1 except that the shape is accommodated in the inside of the case 104.
[0104]
The viscoelastic support 106 is placed inside the case 104, the piezoelectric film 102 is disposed
so as to cover the case 104 and the viscoelastic support 106, and the frame 108 is covered from
above the piezoelectric film 102 to form a frame. The electro-acoustic transducer 100 was
manufactured by fixing 108 to the case 104.
[0105]
A voltage was applied from the driving amplifier to the piezoelectric film of the electroacoustic
transducer 100 produced as described above, and the relationship between the frequency of the
sound generated and the sound pressure level (frequency characteristic) was measured.
The output voltage of the driving amplifier has a characteristic shown by a solid line in FIG.
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32
Specifically, a constant current circuit was incorporated to make the output voltage approximate
to -6 dB / octave (broken line). The measured results are shown in FIG.
[0106]
From the results of Example 1 and Example 2, the electroacoustic transducer of the present
invention is formed to be substantially flat in the piezoelectric film, and the sound pressure level
is sufficiently high at any frequency, and wide band and smooth frequency characteristics are
realized. I know what I can do. Further, it can be understood that by incorporating a constant
current circuit in the driving amplifier, it is possible to realize a wider band.
[0107]
Although the electro-acoustic transducer and display device of the present invention have been
described above in detail, the present invention is not limited to the above-described example,
and various improvements and modifications may be made without departing from the scope of
the present invention. Of course it is good.
[0108]
10, 102, 112, 122, 142, 152 Piezoelectric film 12 Piezoelectric layer 14 Thin film electrode 16
Thin film electrode 18 Protective layer 20 Protective layer 24 Viscoelastic matrix 26
Piezoelectric particles 40, 100, 110, 120, 130, 140, 150 Electro-acoustic transducers 40a, 100a,
140a, 150a rising portions 40b, 100b, 140b, 150b flat portions 42, 104, 144 case 44 rings 46,
106, 116, 126, 136, 146, 156 Frame 114 Support plate 118 Screw 128 Support member 144a
O-ring 158a, 158b Fixing ring
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33
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