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■ Piezoelectric type microphone 特 願 Japanese Patent Application No. 45-117060 [phase]
Application No. 45 (1970) December 22 @ inventor essential point-Kadoma city Bold Kadoshin
1006 Matsushita Electric Industrial Co. Industry Co., Ltd. Kadoma City Bold Kamon 1006 [Phase]
Agent Attorney Yoshihiro Morimoto
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a conventional piezoelectric
microphone, FIG. 2 is a sectional view of a piezoelectric microphone showing an embodiment of
the present invention, and FIG. 3 is a perspective view of the main part thereof The figure is a
cross-sectional view of the same piezoelectric microphone.
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a piezoelectric
microphone having improved frequency characteristics using a plurality of piezoelectric elements
having different resonance frequencies. As shown in FIG. 1, a conventional piezoelectric
microphone using a piezoelectric element as an electroacoustic transformer transmits vibrations
of one flexural vibration type piezoelectric element 1, a cone-shaped diaphragm 2 and a
diaphragm 2 to the piezoelectric element 1. The connecting rod 3 and the case 4 are provided.
An elongated rectangular bimorph piezoelectric element made of lead zirconate titanate ceramic
is generally used as the piezoelectric element 1, and as shown in the figure, a cantilever structure
having one end fixed and one end driven is taken, and a microphone is There was an extremely
simple structure. However, when it is connected to a t-transistor type audio amplifier which
shows pure capacitive impedance and has a sound pressure desensitization characteristic of 6 db
per octave in the low frequency region, it has a high input impedance in front of the MOSFET
type. There is a need for an amplifier or a matching network that effectively lowers the sound
pressure sensitivity of high frequency characteristics to obtain flat frequency characteristics. In
this case, the former system is expensive in price, and the latter system causes a significant
reduction in sound pressure sensitivity, resulting in disadvantages such as being difficult to use
as it is. For this reason, various attempts have been made to improve the characteristics of the
microphone itself. For example, the ceramic plate used for the piezoelectric element is thinned to
make it a plate having a large area and a large capacity as a parallel connection bimorph
structure to lower the internal impedance. The way is taken. However, in order to compensate for
the above-mentioned 16 db / octave characteristic, it is very difficult to improve by about 20 db
or more at 50 to 100 Hz based on IKHz sensitivity. Therefore, the present invention provides a
piezoelectric microphone in which a plurality of piezoelectric elements are incorporated under
the same shape and size as those of a conventional piezoelectric microphone and the abovementioned defects are eliminated. One embodiment of the present invention will be described in
detail with reference to the drawings. γ is a plate type bimorph piezoelectric element having
different dimensions such as length t1 to t3, width W1 to W3, thickness tI-tz, etc., and these
piezoelectric elements 5 and 6.7 overlap each other in FIG. Although this is shown in order to
clarify the difference in size, it is assumed that they are arranged on one horizontal plane as
shown in the sectional view of FIG. Reference numerals 8, 9 and 10 are diaphragms stretched so
that their side cross sections become V-shaped. Each piezoelectric element 5, 6, 7 is attached at
one end to the outer container 14 via a suitable damping material piece L12, 13 and the other
end is attached to the lower top of the respective diaphragm 8, 9, 10 Is attached through.
Also, as can be seen from FIG. 2, each of the diaphragms 8, 9 and 10 operates as an independent
sound collection body so that one side of the deformed V-shaped diaphragm is mainly subjected
to the sound pressure. (Arranged and mounted on the case 14). Therefore, the piezoelectric
element 5 and the diaphragm 8 EndPage: 1 operate as an independent piezoelectric microphone.
The same applies to the piezoelectric element 6 and the diaphragm 9, and the piezoelectric
element 7 and the diaphragm 10. 15, 16, 17 ° 18 are partition walls provided on the back of
each diaphragm 8, 9, 10 and integrated with the case 14 to constitute a back air chamber. The
frequency at which the sound pressure sensitivity of the piezoelectric microphone unit consisting
of one diaphragm and one bimorph piezoelectric element is maximum can be obtained at the
resonance point of each acoustic vibration system, but the resonance point of each microphone
unit is approximately the piezoelectric elements 5, 6 , 7 length and thickness can vary. For
example, when the width and thickness of each piezoelectric element are the same, the resonance
frequency of each piezoelectric element decreases at a ratio of approximately 1:%: 3/9, based on
the resonance point of the piezoelectric element 5. If the thickness is further changed, this ratio
can be changed, and the overall characteristics of these microphone units constitute frequency
characteristic microphones having resonance taste at both ends and the center of the frequency
band in the range of approximately 3 to 4 octaves. be able to. Moreover, the piezoelectric
element 7 exhibiting resonance taste characteristics at low frequency broadens about three times
the width of the piezoelectric element 5 even in the capacity characteristic, and increases the
capacity by three times or more if the thickness is reduced. Can be improved. The resonance
taste characteristic of the same high pressure sensitivity can be obtained by squeezing the
deformation V-shaped apex angle of the side surface of each of the diaphragms 8, 9, 10, and the
material [111111] of each of the braking flavor pieces 11, 12, 13 can be flattened. As described
above, in the present invention, it is possible to set resonance taste characteristics that can
appropriately increase the sound pressure sensitivity in the frequency range of 3 to 4 octaves,
and the sensitivity of 1 dB per octave in the low frequency range of the piezoelectric microphone
It is possible to obtain a piezoelectric microphone that can significantly improve the frequency to
be reduced. Further, even if the conventional piezoelectric microphone having only one
piezoelectric element has the same receiving area as that of the conventional piezoelectric
microphone, one of the plurality of piezoelectric elements of the piezoelectric microphone
according to the present invention can be Since it can be made to correspond to a piezoelectric
element, the parallel capacitance of each piezoelectric element is significantly increased, which is
effective in improving the low frequency characteristics by lowering the internal impedance of
the piezoelectric microphone.
In addition, the diaphragm can use plastic moldings of the same shape, the case is extremely easy
to integrate, and the wiring is simplified if each piezoelectric element is electrically connected, for
example, to be common electrode outside the case. It is very convenient in terms of assembly and
fabrication than making a large thin plate-like piezoelectric element as in the prior art.
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