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DESCRIPTION JPH0888897

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DESCRIPTION JPH0888897
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
speaker using a piezoelectric element, and more particularly to a composite piezoelectric speaker
using a diaphragm made of a composite of a piezoelectric element and a resin.
[0002]
2. Description of the Related Art Conventionally, in general, in a speaker, reproduction of sound
is performed by converting an electrical signal that was in the sound into vibration by a
permanent magnet and a voice coil and expanding it using a diaphragm or other means. It will be
done. In general use, one speaker is sufficient, but in playback of advanced audio such as audio,
in order to sufficiently capture the frequency domain, it is necessary to prepare a speaker that
was in each domain, The situation could not be compensated by this speaker. Also, the magnet
speaker needs to be large in order to increase the sound pressure, and it is also heavy in weight.
[0003]
In recent years, various products are becoming lighter, thinner and smaller, and the speaker
tends to have this tendency, and a flat type speaker and the like which are extremely thin and
light are required. As a means for answering such a demand, there is, for example, a sound
generator using a piezoelectric effect. Heretofore, a thin plate of lead zirconate titanate (PZT) -
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based piezoelectric ceramic, a sheet of an organic piezoelectric material, or the like has been used
as a sounding body utilizing the piezoelectric effect. As a sounding body made of a thin plate of
piezoelectric ceramic, there are a unimorph structure having a single metal plate and a bimorph
structure having two sides of a metal plate. However, the unimorph type and the bimorph type
are relatively thick and do not have flexibility in elastic properties, and because they are in
acoustically hard classes, they are strong in high frequencies but in low frequencies. It was weak.
On the other hand, although the sheet of the organic piezoelectric material can be easily obtained
in a large area and is flexible and has few problems in handling, the input is absorbed inside the
organic piezoelectric material and the output becomes small, so that a large acoustic power can
be obtained There was a defect that could not be done. In addition, there is also a composite
piezoelectric body that forms a shape after kneading of an organic substance and a piezoelectric
material powder, but of course there is a disadvantage that the characteristics of the ceramic
bulk body deteriorate.
[0004]
Therefore, a composite piezoelectric speaker in which electrodes are provided on both sides of a
composite piezoelectric body formed by bonding a plurality of columnar piezoelectric bodies
with an organic substance and arranging them in the entire sheet is constructed. (See Japanese
Patent Application Laid-Open No. 62-247700). The structure of the composite piezoelectric
speaker as described above will be described in detail. FIG. 1 is a simple cross-sectional view of a
composite piezoelectric speaker in which electrodes are attached to upper and lower surfaces of
a composite piezoelectric material sheet. In FIG. 1, 1 denotes a composite piezoelectric speaker, 2
denotes a composite piezoelectric body, 3 denotes a piezoelectric element, 4 denotes a resin, and
5 denotes an electrode. The electrode 5 is connected by a lead 6 to an audio signal source (not
shown). The composite piezoelectric body is held by the outer frame 7.
[0005]
As a specific mechanism of sound generation, an electrical signal emitted from an audio signal
source is led by the lead wire 6 and a voltage is applied to the piezoelectric element 3 by the
electrode 5. Therefore, the piezoelectric element 3 generates strain in the thickness direction,
and the composite piezoelectric body 2 vibrates in the thickness direction. This vibration is
transmitted as voice and works as a speaker. In the composite piezoelectric speaker having the
above configuration, the elements of the composite piezoelectric element forming the speaker
were examined for various shapes and volume ratios, and depending on the selection of the
composite piezoelectric element, the characteristics required for the speaker in the high
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frequency band It was found that there was a problem that the flatness was bad, there was a lot
of distortion, and the tone range was narrow. When a composite piezoelectric body is
manufactured, the piezoelectric plate is usually cut by grooving in a lattice shape, and resin is
embedded in the cut portion. For this reason, for example, in the case of forming a composite
piezoelectric material having a volume ratio of 45% of the piezoelectric element, it is necessary to
cut the piezoelectric material for 55%, and there is also a problem that the yield of expensive
piezoelectric material is poor.
[0006]
SUMMARY OF THE INVENTION As a result of examining the deterioration of the characteristics
in the high frequency band, the inventors of the present invention have found that the composite
piezoelectric element is not used as a composite piezoelectric speaker and the piezoelectric
element and the resin are joined. However, during use as a speaker, that is, during vibration, the
space between the piezoelectric element and the resin is opened, and the vibration of the
composite piezoelectric body as a whole is not good, so that it is known that flatness is not
particularly high in the high frequency band. The Furthermore, as a result of intensive
investigations by the present inventors, the piezoelectric element itself is so precisely machined
by a blade etc. that the surface roughness of the cut surface becomes low and the bonding
strength is not good when compounded with a resin etc. The present invention was conceived.
[0007]
That is, according to the present invention, in a composite piezoelectric speaker having
electrodes provided on upper and lower surfaces of a sheet-like composite piezoelectric body
made of a flexible resin and a piezoelectric element and having a diaphragm, the bonding surface
of the piezoelectric element with the resin At least a part of is a fracture surface. In the
piezoelectric element of the present invention, the bonding surface with the resin, that is, the side
surface portion needs to be a fracture surface. When the joint between the piezoelectric element
and the resin is not a fractured surface, the joint with the resin is not strong and appears to be
joined when no vibration occurs, but a gap is generated between the piezoelectric element and
the resin during vibration. In particular, there is no flatness in the high frequency band. In
addition, the bonding surface of the piezoelectric element does not have to be a fracture surface
on the entire surface, and may be an area that can maintain bonding strength with the resin in a
high frequency band.
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[0008]
Furthermore, the inventors of the present invention have a large difference in flexibility and
specific gravity between the flexible resin forming the composite piezoelectric body and the
piezoelectric element formed of the hard piezoelectric ceramic, so that the time of sound
generation is large. That is, it was found that something like waviness occurred during vibration,
and in particular, the flatness was bad and high distortion occurred in a high frequency band,
and the second invention of the present invention was conceived. That is, the second invention of
the present invention is to use a piezoelectric element having a thickness of 0.2 mm or less and
an electrode surface area of 4 mm 2 or less. The piezoelectric element in the above composite
piezoelectric body needs to have a thickness of 0.2 mm or less. If the thickness is greater than
0.2 mm, that is, if the composite piezoelectric body is also thicker than 0.2 mm, then the
amplitude in the thickness direction of the composite piezoelectric body becomes too large at the
time of sound generation in a high frequency region, and the followability to the applied audio
signal It is because it gets worse. In addition, the area of the electrode surface of the piezoelectric
element needs to be 4 mm 2 or less. Since this is usually used with a radius of curvature when
used as a speaker, if the area of the electrode surface of the piezoelectric element is larger than 4
mm 2, the curvature can not be successfully applied. Furthermore, even if the curvature is given,
the piezoelectric element itself is not deformed, so that it is discontinuously connected with the
resin having curvature as a whole but having easy curvature, and vibration during use causes the
resin and the piezoelectric element It is easy for the joint surface to be broken.
[0009]
EXAMPLES Example 1 The present invention will be specifically described with reference to the
following examples. FIG. 2 is a view showing one of the methods for forming a composite
piezoelectric sheet, FIG. 2 (A) is a plan view showing a ceramic green sheet, and FIG. 2 (B) is a
view shown in FIG. 2 (A). 2 (C) shows a cracked ceramic flat sheet obtained by firing the ceramic
green sheet, and FIG. 2 (D) shows a groove and a crack formed in the step shown in FIG. 2 (C). It
is a figure which shows the state which put resin. First, as shown in FIGS. 2A and 2B, a grid
formed of stainless steel on the surface of a relatively soft PZT-based ceramic green sheet 8
having a thickness of about 0.3 mm made of ceramic powder and an organic binder. A mold (not
shown) is pressed to form lattice grooves 9 on its surface. In this case, the depth of the groove 9
is a depth not reaching the bottom of the ceramic green sheet 8, leaving a non-grooved part, and
at this point, it is not separated into pieces of ceramic green sheet.
[0010]
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Next, the ceramic green sheet 8 grooved to the middle in the thickness direction is baked at
1200 ° C. and sintered, and as shown in FIG. 2C, it is made of a flexible member such as rubber.
The adhesive plate is placed on the flexible plate 10, and in this state, the flexible plate is twodimensionally stretched or a lattice-like form (a small form which is smaller than the above form
taking into consideration the shrinkage factor at the time of firing) The crack 11 is formed in the
lower part of the lattice-like groove 9 by pressure or impact force by pressing or the like, and the
ceramic green sheet 8 is divided along the groove 9 into a large number of ceramic pieces. Next,
as shown in FIG. 2D, the flexible plate 10 is flexed by bending it in an arc shape so that the
surface on which the ceramic green sheet 8 is placed is slightly convex. The groove 9 and the
crack 11 are expanded by expanding the elastic plate 10 in the lateral and longitudinal
directions, and in this state, the groove 9 and the crack 11 are filled with the organic substance
(polyurethane resin) 12 from above. Then, after solidifying this resin, the composite piezoelectric
sheet can be obtained by grinding the surface flatly.
[0011]
Here, for the purpose of comparison, when first pressing the above-mentioned grid-like form, it is
pressed to the bottom of the ceramic green sheet and the pieces of the ceramic green sheet are
broken apart in the same manner as above. A composite piezoelectric body was made. The
example of the present invention and the comparative example were formed in the shape of a
speaker, and various acoustic characteristics were measured up to a high frequency band.
Although the inventive example and the comparative example showed similar acoustic
characteristics at the beginning of the measurement, the flatness in the comparative example
became worse, particularly in the high frequency band. After completion of the above
measurement, when the junction between the piezoelectric element and the resin was observed,
no peeling was observed between the piezoelectric element and the resin in the example of the
present invention, but peeling was observed between the piezoelectric element and the resin in
some cases in the comparative example. The
[0012]
EXAMPLE 2 Various composite piezoelectric materials were produced in the same manner as in
the example of the present invention shown in Example 1 under the conditions shown in Table 1.
The volume ratio of the piezoelectric element in each composite piezoelectric body was 45% in
order to make the conditions uniform. An aluminum film was formed as an electrode on both
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sides of the composite piezoelectric body produced, a speaker of a fixed shape was produced, and
the results of measuring the acoustic characteristics are shown in Table 1. It can be seen that the
examples within the scope of the present invention show good acoustic properties.
[0013]
[Table 1]
[0014]
The composite piezoelectric speaker according to the present invention is characterized in that
electrodes are provided on the upper and lower surfaces of a sheet-like composite piezoelectric
body made of a flexible resin and a piezoelectric element to form a diaphragm, and the resin of
the piezoelectric element Since the joint surface of the above is a fractured surface, it is possible
to obtain a composite piezoelectric speaker which is excellent in flatness to a high frequency
band and in which generation of distortion is small.
[0015]
Brief description of the drawings
[0016]
1 shows a cross-sectional view of a composite piezoelectric speaker according to the present
invention.
[0017]
2 is a diagram showing a method of manufacturing a composite piezoelectric body according to
the present invention.
[0018]
Explanation of sign
[0019]
Reference Signs List 1 composite piezoelectric speaker, 2 composite piezoelectric body, 3
piezoelectric element, 4 resin, 5 electrode, 6 lead wire, 7 outer frame, 8 ceramic green sheet, 9
groove, 10 flexible plate, 11 crack, 12 organic matter.
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