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BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1A and 1B are a partially cutaway plan view and a
side sectional view of a conventional electroacoustic transducer, and FIG. 2 is a principle diagram
showing vibration modes in the device of FIG. , FIG. 3A. B is a partially cutaway plan view and a
side sectional view of the electroacoustic transducer of the present invention. 1 и и и и и и и и и и и и и и и и
и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и basic
vibration node .
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a mono-acoustic
transducer using a piezoelectric element, and in particular, an electro-acoustic transducer which
has an optimum high-pass conversion efficiency for a voice band will generally be provided. The
piezoelectric 'type speaker using this is realized by using a bimorph element as a driving source
and as a high sound speaker J. This is due to the relationship between the reproduction
frequency band and the output 41 at 2 иии caesar level. The bimorph element is a microphone or a
microphone. ????? It is used for vibrators such as buzzers and speakers, and power saving
and thinning can be achieved by using this element. The bimorph element is a combination of
two piezoelectric elements that expand and contract in the length direction, and when one is
extended, the other is shrunk, and the other is bent as a whole, so that the mechanical impedance
is lowered and large output electrons can be taken out. It is Usually, the piezoelectric element
used for the bimorph element is in the form of a thin disc, and the well frequency of the disc-like
piezoelectric element with free vibration is generally represented by the following equation.
Fr?? и tFY?3 p (1a) (j (? ? where I is radius, t is thickness, E is Young's modulus, ? is
density, ? is Poisson's ratio, ? is a constant. As is apparent from this equation, ?, ?, ? are
intrinsic characteristics determined by the material, and bimorphs and ? need to have a high
dielectric constant and a high electromechanical coupling coefficient. Piezoelectric ceramic and
ceramic are mainly used as the material of the element, but there is a limit to changing the
material and composition of the ceramic for use. Therefore, the fundamental resonant frequency
of the bimorph element is determined by the size and shape. 1 shows a conventional bimorph
element having the above-mentioned structure, FIG. 1A is a partially cutaway plan view, and FIG.
1B is a sectional view taken along the line C-C of FIG. Show. Electrodes 3 are formed on both
sides, and a piezoelectric ceramic having a predetermined diameter and thickness, which has
been polarized, is mechanically and electrically coupled to the intermediate electrode plate 2
through the electrodes 3. In order to use a bimorph element having such a structure as a
bimorph element for a voice band, a fundamental resonance frequency lower than the
reproduction frequency band is required, and the method and element for reducing the thickness
from the above equation It is conceivable to increase the diameter. As described above, ceramics
are mainly used for piezoelectric elements in terms of characteristics, but it is necessary to sinter
ceramics and cups at high temperatures, which makes production more difficult as they become
thinner. . Also, it is equally difficult to make the diameter large with the same thickness.
In Japanese Patent Publication No. 46-2716, it is stated that the basic resonance frequency is
lowered by providing eight slots in the radial direction, but this is achieved by making a cut from
the outer periphery toward the center Although the elastic compliance of the element is lowered,
this method lowers the fundamental resonance frequency but also reduces the electromechanical coupling coefficient which indicates the conversion efficiency. The electromechanical coupling coefficient is given by the following equation, where fr is the fundamental
resonance frequency and fa is the antiresonance frequency. It is also conceivable to make the
dimensions of the 1.69X convex ? piezoelectric elements equal to it and to increase the size of
the intermediate electrode plate, but this also reduces the electro-mechanical coupling
coefficient. When used together with a drive source of an acoustic conversion element such as a
speaker, high conversion efficiency and high force coefficient are required, and all of the
conventional examples described above have not been ideal as drive elements in any way . The
present invention solves these problems, and provides an electroacoustic transducer which has a
high conversion efficiency and lowers the left main resonance frequency. As shown in FIG. 2, as
shown in FIG. 1, the bimorph element vibrates concentrically on the basis of b ', which is a basic
vibration node when free vibrating. This node is present in the vicinity of about 0.6 to 0.7 of the
diameter a of the bimorph element as the flexural vibration of the disc. In the present invention,
by partially providing an air gap at an intermediate electrode plate position corresponding to the
basic vibration node, the elastic compliance of the vibration node can be locally increased
without lowering the force coefficient, and the basic resonance frequency can be obtained. To
lower Fig. 3 shows the structure of the electroacoustic transducer according to the present
invention. Fig. 3A is a partially cutaway plan view thereof, and Fig. 3B is a plan view of Fig. 3D.
Show the map. In the figure, parts having the same functions as in FIG. 1 are assigned the same
reference numerals. Here, what is different from FIG. 1 is that an intermittent gap 4 is provided
in the radial direction of the basic vibration node 5 in the 6-intermediate electrode plate 2. It is
necessary that the air gap portion 4 be provided in the radial direction and not reach the outer
peripheral portion. The gap 4 provided at the vibration node is not limited to a circle as shown in
the drawing, and the effect is the same even if it is another shape, and the concentrically
symmetrical arrangement is designed to an optimum size while adjusting to the characteristics.
The resonant frequency can be lowered even when the intermediate electrode plate is processed
into the shape and the same ((1) in the case where the piezoelectric ceramic in one place and the
void penetrating in the sheet are provided, but the processing into a ceramic or sheet becomes
problematic. There is a drawback that the electrical characteristics appear as an increase in
The following is a detailed description of the basic composition and the main concept pear in the
examples. EXAMPLE 1 A piezoelectric ceramic sheet having a diameter of 100 ?m and a
diameter of 3881 was aligned in the polarization direction and adhered to an intermediate
electrode plate. In the middle electrode plate, holes of diameter 4111+, и и are provided under the
conditions of the gods shown in Table 1 so as to be symmetrical at a distance of 1471 J from the
central point corresponding to the fundamental vibration node. The piezoelectric properties of
the bimorph element of the above are shown in Table 1. From this result, it is desirable for the
acoustic conversion element such as a speaker to have characteristics of high capacitance,
coupling coefficient, high admittance and low resonance frequency. Taking these into
consideration, it was found that when the eight holes are provided, the lowest resonance
frequency is obtained and the other characteristics are not degraded. In the case of providing 12
pieces, the admittance characteristic becomes worse due to the division vibration. Table 1
admittance, US fr (l [(z) Y (fr)-Y (fa intermediate electrode 500,000 pF 65% 159045 dB holes
processed 4 places 490,000 pF 64% L 450 46 dB 6 ? 500,000 I) F 62% ilo 45 dB 8 # 500,000
pF 63 1 1230 47 dB 12 ? 500,000 pF 61% 14 0038 dB peak-169 h ?. O1 (Example 2)-The
same piezoelectric ceramic as that used in Example 1 and Soxsi 8 are used as an intermediate
electrode plate with a thickness of 100 ?m and a diameter of 40 entangled brass, and the
polarization direction of the piezoelectric ceramic sort on both sides Were bonded together to
form a bimorph element. The intermediate electrode plate was provided with eight holes that are
most effective in Example 1 under various conditions as shown in Table 2. The piezoelectric
characteristics under each condition are shown in Table 2: As apparent from Table 2, the
resonant frequency can be lowered by about 20% with almost no deterioration of the
piezoelectric characteristics if the element of the J device is used. In this example, the resonant
frequency can be lowered when the slit is inserted and the piezoelectric element is also provided
with holes, or when the slit is inserted to the outer peripheral part, but both the coupling
coefficient, the admittance, and the inductance characteristics are increased. And a sufficient
conversion efficiency can be obtained. Also, even when a hole is provided in the piezoelectric
element, there is a drawback that the capacitance is lowered and the atom characteristic is
lowered, and the capacitance characteristic is lowered. (Fa) Intermediate electrode plate, Ten
thousand pF6. Involvement 1. ,. A 4 u? hole processed at 45 dB: 49,000 ?, F63% + 2 oo 47 dB
From the outer peripheral part to the center, a fundamental node 49,000 pF 40% 120030 dB
part In the above two embodiments, a disk-shaped piezoelectric element is used in the above two
embodiments, but the present invention is not limited to this shape, and other shapes such as
ovals are used. Needless to say, the same effect can be obtained even if it is present.
As apparent from the above description of V, the electricity 20) acoustic transducer of the
present invention corresponds to the basic vibration node of the bimorph element in the bimorph
element in which two piezoelectric elements are sandwiched by the electrode plate 710 of one
plate. The practical effect is great because an electro-acoustic transducer having a low resonance
frequency can be obtained without partially degrading the piezoelectric characteristics and
providing a gap at the electrode plate position. .
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