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JP2002315095

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DESCRIPTION JP2002315095
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
piezoelectric acoustic transducer used in, for example, a mobile communication device such as a
portable telephone.
[0002]
2. Description of the Related Art A flat plate-like piezoelectric element 92 is attached to a
substantially central portion of a thin flat plate-like metal substrate 91 as a sound-producing
body used in a small electronic device such as a portable telephone as shown in FIG. A sound
generator 90 is known which has a structure in which a piezoelectric diaphragm 93 is formed,
and the outer peripheral portion of the piezoelectric diaphragm 93 is fixed to a case (frame
member) 94 using an adhesive.
[0003]
However, since such a sounding body 90 can not maintain a flat sound pressure level over a wide
frequency band, it can be used as a sounding body of sound of a specific frequency such as a
buzzer sound, but it can It was difficult to use as a sound generator for music.
Therefore, in order to solve this problem, for example, Japanese Unexamined Patent Publication
No. 11-7283 discloses a piezoelectric sounding body in which the vibration characteristic of a
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substrate is changed by forming a groove of a predetermined shape on a metal substrate. .
[0004]
However, the piezoelectric sounding body described in Japanese Patent Application Laid-Open
No. 11-7283 has a problem that the structure is complicated and the manufacturing cost is
increased.
[0005]
The present invention has been made in view of the problems of the prior art, and it is possible to
maintain a flat sound pressure level in a wide frequency band, and to reduce the manufacturing
cost. It is intended to provide a converter.
[0006]
According to the present invention, there is provided a piezoelectric acoustic transducer
comprising a piezoelectric diaphragm formed by bonding a piezoelectric element to a substrate,
and a case for holding the peripheral portion of the piezoelectric diaphragm. The substrate has a
sheet-like shape in which a conductor is formed on at least one of the front and back surfaces of
an insulator, and a predetermined pattern is formed on at least one of the conductors to make
the elastic modulus of the substrate nonuniform. A piezoelectric acoustic transducer is provided,
characterized in that:
[0007]
In such a piezoelectric acoustic transducer, by making the elastic modulus of the substrate
nonuniform, it is possible to maintain a flat sound pressure level in a wide frequency band.
Moreover, the piezoelectric acoustic transducer of the present invention is not complicated in
structure and easy to manufacture.
[0008]
In the piezoelectric acoustic transducer of the present invention, the conductor on which the
predetermined pattern is formed can also serve as a wire for applying a voltage to the
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piezoelectric element.
Also, in the case of using a substrate in which the conductor is formed on both the front and back
sides of the insulator in which the through holes are formed, when the conductor formed on the
front and back sides is conducted through this through hole The wiring for the application can be
reduced to simplify the structure.
Furthermore, it is also preferable to form one or a plurality of through holes of a predetermined
shape in the substrate, and to fill the through holes with a material having at least an elastic
modulus different from that of the insulator constituting the substrate. In this way, the substrate
is less likely to resonate, and the sound pressure level can be made flatter.
[0009]
In the piezoelectric acoustic transducer of the present invention, by pulling out a part of the
substrate to the outside of the case, it can be used as a part of the wiring, whereby the assembly
can be facilitated. As the substrate, a substrate having a laminated structure in which a plurality
of insulators and one or more conductors are stacked in the thickness direction can also be used.
In this case, the elastic modulus of at least one of the plurality of insulators is different from that
of the other insulator or conductor. Thus, the vibration characteristics of the substrate can be
changed to realize a piezoelectric acoustic transducer having a desired sound pressure level. In
addition, when an insulating resin is used as the insulator and a substrate using a metal
conductor is used as the conductor, manufacture is easy.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the piezoelectric acoustic
transducer of the present invention will be described below with reference to the drawings. 1 (a)
and 1 (b) are perspective views showing an embodiment of a piezoelectric acoustic transducer
according to the present invention, and FIG. 1 (c) is a cross-sectional view of FIG. 1 (a). Here, the
perspective view of FIG. 1A shows the structure of the piezoelectric acoustic transducer 10, and
the perspective view of FIG. 1B separately shows the piezoelectric element 11 and the substrate
12 used for the piezoelectric acoustic transducer 10. It is shown. In addition, although the
peripheral part of the board ¦ substrate 12 is hold ¦ maintained by case, in each figure of FIG. 1,
this case is abbreviate ¦ omitted.
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[0011]
The piezoelectric acoustic transducer 10 has a structure in which a piezoelectric element 11 is
attached to a substrate 12, and the piezoelectric element 11 has a structure in which electrodes
16a and 16b are formed on both sides of a thin plate-like piezoelectric body 15. The substrate 12
has a structure in which a metal foil 18 is bonded to a sheet-like insulator 17. Further, lead wires
19 a are attached to the electrodes 16 a and lead wires 19 b are attached to the metal foil 18,
respectively, so that a predetermined voltage can be applied to the piezoelectric element 11.
Although the piezoelectric element 11 is attached to the substrate 12 using an adhesive, since
the adhesive layer formed by the adhesive is thin, the conduction between the electrode 16 b and
the metal foil 18 is secured, The lead 19b is electrically connected to the electrode 16b.
[0012]
As the piezoelectric body 15, various piezoelectric materials such as piezoelectric ceramics and
piezoelectric polymers can be used. Among the piezoelectric materials, the piezoelectric ceramics
are suitably used in the present invention because they have excellent piezoelectric
characteristics. When using piezoelectric ceramics as the piezoelectric body 15, the electrodes
16a and 16b can be formed by printing silver paste or the like on the front and back surfaces of
the piezoelectric body 15 by screen printing, treating at a predetermined temperature, and
printing. it can. The shapes of the front and back surfaces of the piezoelectric element 11 are not
limited to the circles shown in FIGS. 1 (a) and 1 (b). That is, the piezoelectric body 15 is not
limited to the disk shape.
[0013]
Various types of resin materials (including rubber materials) are suitably used as the insulator 17
constituting the substrate 12, and examples thereof include liquid crystal polymer resins and
polyimide resins. Although copper foil excellent in conductivity is suitably used as the metal foil
18, it is also possible to use various metal foils such as aluminum foil and nickel foil. The
adhesion between the insulator 17 and the metal foil 18 may be performed using an adhesive or
may be performed by heat fusion.
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[0014]
A predetermined pattern is formed on the metal foil 18, and the elastic modulus of the substrate
12 has an in-plane distribution so as to be in a non-uniform state. This makes it possible to
generate a plurality of vibration modes on the substrate 12 and obtain a flat sound pressure level
in a wide frequency band. The substrate 12 may be easily formed in a short time since the
pattern may be formed by etching on a printed wiring board or the like in which the insulator 17
and the metal foil 18 are bonded to each other. Therefore, the manufacturing cost is not
increased. In addition, the pattern of the metal foil 18 shown in FIG.1 (b) is an example, It is not
limited to such a pattern. The pattern may be point-symmetrical or line-symmetrical, or may be
asymmetric.
[0015]
Hereinafter, in the same manner as the piezoelectric acoustic transducer 10, another
piezoelectric acoustic transducer capable of generating a plurality of vibration modes on the
substrate by making the elastic modulus of the substrate uneven and obtaining a flat sound
pressure level in a wide frequency band. Embodiments will be described.
[0016]
FIG. 2 is a cross-sectional view showing another embodiment of the piezoelectric acoustic
transducer of the present invention.
The piezoelectric acoustic transducer 20 has a structure in which two piezoelectric elements 21a
and 21b are attached to the front and back sides of the substrate 22, and the piezoelectric
elements 21a and 21b have electrodes (26a and 26b) on the piezoelectric members 25a and 25b
respectively. 26a '), (26b, 26b') are formed. The piezoelectric elements 21a and 21b may have
the same shape or different shapes.
[0017]
The substrate 22 has a structure in which metal foils 28a and 28b are bonded and integrated on
both sides of a sheet-like insulator 27. The metal foils 28a and 28b are similar to, for example,
the metal foil 18 A pattern is formed to provide a distribution of the modulus of elasticity of the
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substrate 22. The patterns of the metal foils 28a and 28b may be formed so as to overlap when
seen through from the thickness direction, and may be formed so as not to overlap each other.
The peripheral portion of the substrate 22 is held by a case, but this case is omitted in FIG.
[0018]
Lead wires 24a and 24b are attached to the electrodes 26a and 26b, respectively. Further, a
through hole 29 whose side surface is coated with a metal 23 is formed in the peripheral portion
of the insulator 27, and the metal foil 28 a and the metal foil 28 b are electrically connected by
the through hole 29. Therefore, it is not necessary to attach the lead wires to the metal foils 28a
and 28b, and the lead wire 24c may be attached to either one of them. Thus, in the piezoelectric
acoustic transducer 20, the piezoelectric elements 21a and 21b can be driven using the lead wire
24c as a common electrode.
[0019]
FIG. 3 is a cross-sectional view showing still another embodiment of the present invention. The
piezoelectric acoustic transducer 30 has a structure in which the piezoelectric vibration plate 33
in which the piezoelectric element 31 is attached to the substrate 32 is housed in the case 34 so
as to hold the peripheral portion of the piezoelectric vibration plate 33. The piezoelectric element
31 has a structure in which electrodes 36a and 36b are formed on a piezoelectric body 35, and a
substrate 32 is made by sticking a metal foil 38 processed into a predetermined pattern on one
surface of a sheet-like insulator 37. It has an integrated structure, and the pattern of the metal
foil 38 makes the elastic modulus of the substrate 32 nonuniform.
[0020]
A part of the substrate 32 is drawn out of the case 34, and the extended part 32a drawn out of
the case 34 is a lead part 38a which extends a part of the metal foil 38 and a lead part 38a It has
another lead portion 38b insulated. The lead portion 38b is wire-bonded to the electrode 36a of
the piezoelectric element 31 so as to be conductive, and thus the piezoelectric element 31 can be
driven by applying a predetermined voltage to the lead portions 38a and 38b. That is, the
extension portion 32a functions as a part of the wiring, and for example, the attachment of the
piezoelectric acoustic transducer 30 to the circuit board can be facilitated.
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[0021]
FIG. 4 is a perspective view showing still another embodiment of the present invention. The
piezoelectric acoustic transducer 40 has a structure in which a piezoelectric element 41 is
attached to a substrate 42. The piezoelectric element 41 has an electrode 46a formed on the
surface of the piezoelectric body 45, and an electrode (not shown) on the back side of the
piezoelectric body 45. Have a formed structure. The substrate 42 has a structure in which a
metal foil 48 is attached to the whole of one surface of a sheet-like insulator 47 to be integrated.
Lead wires 44a and 44b are attached to the electrode 46a and the metal foil 48, respectively.
Further, although the peripheral portion of the substrate 42 is held by the case, this case is
omitted in FIG.
[0022]
In the substrate 42, holes 49 penetrating in the thickness direction are formed at a plurality of
locations, and in these holes 49, a material having a modulus of elasticity different from that of
the insulator 47, for example, The same metal material as the metal foil 48 or a metal material
different from the metal foil 48, for example, a metal material with a high specific gravity such as
lead or tungsten is filled, and such a filling makes the elastic modulus distribution of the
substrate 42 uneven. It is assumed.
[0023]
In the substrate 42, the hole 49 is formed through the insulator 47 and the metal foil 48.
However, a hole penetrating only the insulator 47 is formed, and the inside thereof is filled with a
predetermined filler. It does not matter.
Although FIG. 4 shows a mode in which the hole 49 is formed in the outer peripheral portion of
the substrate 42, such a hole may be provided in the center of the substrate 42 to which the
piezoelectric element 41 is attached. Furthermore, a predetermined pattern such as the metal
foils 18 and 38 may be formed on the metal foil 48.
[0024]
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Fig.5 (a) is sectional drawing which shows another embodiment of this invention, FIG.5 (b) is a
perspective view which shows the components which comprise the piezoelectric acoustic
transducer 50 shown by FIG. 5 (a). . The piezoelectric acoustic transducer 50 has a structure in
which a piezoelectric element 51 is attached to a substrate 52, and the piezoelectric element 51
has a structure in which electrodes 56a and 56b are formed on both sides of a plate-like
piezoelectric body 55. The substrate 52 has a laminated structure in which a substrate 52a in
which a metal foil 58a and an insulator 57a are bonded and a substrate 52b in which a metal foil
58b and an insulator 57b are bonded are bonded. The lead wire 59a is attached to the electrode
56a, and the lead wire 59b is attached to the metal foil 58a. The peripheral portion of the
substrate 52 is held by the case, but this case is omitted in FIG.
[0025]
Although a pattern is not formed on the metal foil 58a, a predetermined pattern is formed on the
metal foil 58b, and the distribution of the elastic modulus in the substrate 52 is not uniform by
the pattern formed on the metal foil 58b. And A pattern may be formed on the metal foil 58a and
a pattern may not be formed on the metal foil 58b, or a predetermined pattern may be formed on
both the metal foils 58a and 58b.
[0026]
The same material may be used for the insulators 57a and 57b, or materials having different
elastic moduli may be used. For example, a liquid crystal polymer resin can be used as the
insulator 57a, and a urethane resin can be used as the insulator 57b. Furthermore, it is also
possible to use a resin material as the insulator 57a and to use a glass material or a ceramic
material as the insulator 57b. The number of laminated layers of the insulator and the metal foil
is not limited to two each, and may be a laminated structure having a larger number of layers.
[0027]
Although the embodiments of the present invention have been described above, the present
invention is not limited to the above embodiments. For example, as the substrate 52 constituting
the piezoelectric acoustic transducer 50, different materials are used for the insulators 57a and
57b, and the insulators 57a and 57b are directly attached to each other without sandwiching the
metal foil 58b between them. It is also possible to use a substrate having a structure in which a
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metal foil having a predetermined pattern formed on one main surface is bonded. In this case, it
is also possible to form a hole in the substrate and fill the hole with a predetermined filling
material. Thus, the characteristics of the piezoelectric acoustic transducers 10, 20, 30, 40, 50
shown in FIGS. 1 to 5 can be combined to realize piezoelectric acoustic transducers having
various forms.
[0028]
Further, although the case where a metal foil is used as a conductor constituting the substrate
has been described, it is also possible to use, for example, a substrate in which a conductive thin
film is formed on the surface of an insulator by a method such as sputtering. Furthermore,
although the case where the piezoelectric acoustic transducer is used for reproducing sound is
described in the above embodiment, conversely, it can also be used as an apparatus for
converting sound into an electrical signal like a microphone.
[0029]
As described above, according to the piezoelectric acoustic transducer of the present invention, a
flat sound pressure level can be maintained over a wide frequency band by making the elastic
modulus of the substrate to which the piezoelectric material is attached uneven. Thus, it can be
used as a sound generator for voice and music, or for converting these sounds into electrical
signals. Moreover, the piezoelectric acoustic transducer of the present invention is not
complicated in structure and easy to manufacture. Furthermore, it is possible to obtain desired
frequency characteristics by variously selecting the structure or material of the substrate or the
pattern of the conductors constituting the substrate.
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