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JPS5329329

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DESCRIPTION JPS5329329
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a microphone according
to an embodiment of the present invention, FIG. 2 is a sectional view taken along the line AA 'of
FIG. 1, FIG. 3 is a perspective view of the metal frame of the same microphone, and FIG. 4 is a
diagram showing the relationship between the low frequency cutoff frequency of the microphone
and the capacitance. 1 .... - vibration film, 2 ...... metal housing case, 3 ... metal frame, 4 ......
transistor emitter follower circuit, 5 ...... Output terminal .
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a microphone
using a vibrating membrane in which electrodes are provided on both sides of a piezoelectric
polymer material, and a small, inexpensive microphone having good characteristics is provided.
In conventional microphones of this type, FET north follower circuits have been used. However,
because the dielectric constant of the polymer piezoelectric material is high, the capacitance is
relatively large as a microphone, and the FET has a manual impedance or 100 to 200 MΩ or so
and a small S knee-or 92 which is large. The sensitivity was high up to the low range of the
microphone, and when used as an actual microphone, wind noise and vibration noise entered a
lot and it was not acceptable for use. Therefore, the low-pass cut was provided separately and
used. The present invention provides a microphone that eliminates the above drawbacks. One
embodiment of the present invention is shown in FIGS. 1 and 2. FIG. FIG. 1 is a perspective view
of this embodiment. FIG. 2 is a cross-sectional view taken along the line A-A of FIG. FIG. In FIG. 2,
reference numeral 1 denotes a vibrating film obtained by vapor deposition on both surfaces of a
piezoelectric polymer film to form an electrode, and a portion of this electrode is taken out. The
polymer film (vibration film) 1 has a curvature so as to keep a constant curvature or a
predetermined vibration film surface, and the high resonance frequency and sensitivity can be
determined by selecting the curvature. 2 is a storage case, 3 is a metal frame provided at the
opening of the storage case 2 and this metal frame 3 has a function of maintaining a constant
curvature in the polymer film 1, 1 and deposition of the polymer film 1 It has a function to touch
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the surface and to take out a line from the deposition direction. 4〕。 No. 3 is an output circuit
incorporating an emitter follower circuit of a transistor. 5 is an output terminal. Further, FIG. 3a
is a view showing a method of taking out the reelt, in which the polymer film 1 is disposed on the
front surface of the frame-shaped metal frame 3 shown in FIG. And contact both sides of the
polymer film 1 between the metal frame 3 and the metal storage case 2 and contact the metal
deposition case on the surface of the polymer film 1 with the metal storage case 2 It is possible
to take out the output voltage from the metal frame 3 and the storage case 2. The vibrating film
1 is a piezoelectric polymer film having a thickness of about 6 μm to 20 μm and a dielectric
constant of 1o to 15 × 8.85 × 1 o-12 F / m. Assuming that the electrostatic capacitance of the
vibrating film 1 is such that the thickness of the film 13 is d: 9 μm, the dielectric constant t: 1
sxs, as x 10 '12 F / m, and the area S of the vibrating film is 1-1, the electrostatic capacitance is
εSQ = (F)) 4. Since it is given, the capacitance is 1200 PF.
The relationship between the low cutoff frequency of the piezoelectric microphone, the
capacitance, and the load innoance is shown in FIG. Now, when the capacitance or 1200 PF is
received by the FET (joOMΩ), the low frequency cutoff frequency is 1. It becomes around sHz,
and it becomes low noise as a microphone, so it becomes noise when it hits the wind or vibrating
film, and 1 there are many problems if noise is generated if mechanical vibration is added1, so it
is low In order to cut the area or need a bypass filter, there was a problem with the price or the
cost. In a microphone that is generally used, it is desirable to set the low cutoff frequency to
around 100 Hz, and in a microphone with a capacitance of around 1000 PF, it is better to receive
the manual impedance of its output circuit at around 500 Ω to 2 MΩ, As described in the
microphone of the present invention, the reception can be directly connected by the trano / star
emitter follower circuit so that the above-mentioned drawbacks can be eliminated. In the case of
a capacitive electroacoustic transducer, the influence of noise on the extraction of electric
terminals 1 to 5 is affected. In particular, there are stray capacitances while conducting the
electric terminals taken out of the vibrating membrane to the electric circuit, and also there are
many noises (S / N ratio can not be taken because inductive ha etc. are generated). In the present
invention, as shown in FIG. 3, the deposition surface on the outer side of the diaphragm is
crimped to the metal storage case 2 to take out the electrode, and the impedance conversion
output circuit 4 is provided in the storage case 2 for electrical connection. The induction is
carried out on the deposition surface of the vibrating film and the metal case. Further, by
providing the impedance conversion output circuit 4 in the metal case, it is possible to reduce
stray capacitance because the contact between the electric output terminal of the @ moving film
and the output circuit is shortened.
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