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BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a conventional ultrasonic
microphone, FIG. 2 is a perspective view of an ultrasonic microphone in one embodiment of the
present invention, FIG. 3 is the same sectional view, FIG. 5 is a sensitivity characteristic diagram
of the same ultrasonic microphone, FIG. 5 is a sensitivity characteristic diagram of the ultrasonic
microphone of the present invention and the conventional example, and FIGS. 6a and 6b are a
perspective view and a sectional view of another embodiment of the present invention, FIG. 7 ayb
is a perspective view and a cross-sectional view of still another embodiment of the present
invention. 5 иииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииии Piezoelectric polymer film,
9 ..... recessed part.
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic
microphone having a piezoelectric polymer film as a vibrating film, and an object thereof is to
broaden the frequency characteristics without lowering the sensitivity. FIG. 1 shows a
conventional ultrasonic microphone. In FIG. 1, 1 is a piezoelectric polymer film 1 ..... @lit: 5 h-cv =
и tiMtl + L * и и и, both sides of this piezoelectric polymer film 1 are deposited. L-, j + ",! The
piezoelectric polymer film 1 is adhered to one side of the frame 2. A grid plate 3 is disposed on
the front surface of the piezoelectric polymer film 1 at a distance q, and a plurality of holes 4 are
formed in the grid plate 3. In the above-mentioned conventional ultrasonic microphone, in order
to widen the frequency characteristics, a sound absorbing material is added, a slit, a thin fluid
layer is formed to add an acoustic resistance, and the size of the microphone 1 is controlled. Was.
However, in the case of adding acoustic resistance, there is a drawback that the sensitivity is
lowered. The present invention eliminates the above-mentioned conventional drawbacks, and
aims at broadening the bandwidth without lowering the sensitivity, and an embodiment of the
present invention will be described below. In FIGS. 2 and 3, reference numeral 6 denotes a
curved grid plate, and a plurality of holes 6 are formed in the grid plate 6. 7, 7'H The recesses
formed in the back of the grid plate 6 are different in depth 9 ++ 'J2 of the recesses 7, 7'. a,
jHHI3 ? ? molecular films, electrodes are formed on both sides of each pressed polymer 3y film
8, 8 ?. The piezoelectric polymer film 8.8 'is adhered to the outer peripheral portion of the rear
portion 7.7' of the grid plate 6. As described above, in the present embodiment, two piezoelectric
polymer films 8.8 'are adhered to the grid plate 6 to constitute two microphone units, and the
concave portions of the two microphone units are also provided. Since the depths of 7.7 ? are
different, the coincidence frequency of each microphone unit is different as shown by the broken
lines A and B in FIG. 4. Therefore, the overall sensitivity in the case of connecting two
microphone units in series is It is as shown by a solid line C in FIG. FIG. 6 shows the present
embodiment ((1+ to q2) A and 9.b. = (When J2 is used, the sensitivity of B is shown, and
according to this embodiment, a wide band can be achieved without lowering the sensitivity.
FIGS. 6a, 6b and 7a, 7b show other embodiments of the present invention, respectively, and FIGS.
6a, 6b show the depth of the four portions 9 on the back of the plate 6. Is continuously changed
to -7/4, the bottom surface of the recess 9 is inclined, and many different resonance frequencies
are present as in the above-described embodiment to reduce the sensitivity. There is no need to
broaden the bandwidth.
In the embodiment shown in FIGS. 7a and 7b, the depth of the recess 9 'of the grid plate 6 is
changed stepwise, and the bottom surface of the recess 9' is stepped. It is intended to broaden
the bandwidth without lowering it. The present invention is configured as described above, and
according to the present invention, the frequency characteristics can be broadened without
lowering the sensitivity.
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jps54133026, description
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