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[Technical Field of the Invention] The present invention relates to a condenser microphone in
which the fundamental resonance frequency of the diaphragm is lowered by irradiating the
polymer with electromagnetic waves from the outside of the case of the condenser microphone
using the polymer for the diaphragm. [Technical background of the invention and its problems]
Generally, as a small microphone incorporated in a radio tape recorder, a video camera or the
like, a condenser type using an electret is used. The configuration is as shown in FIG. That is, in
FIG. 1, reference numeral 1 denotes a vibrating membrane that vibrates upon receiving a sound
wave, 2 a membrane ring for stretching the vibrating membrane 1, 3 a spacer ring, and 4 an
electret 5 on the vibrating membrane 1 side. The fixed electrode 6 attached is, 6 is a through
hole formed in the fixed electrode 4, 7 is a damper disposed in the through hole 6, 8 is a pressing
plate of the damper 7, 9 is an impedance conversion element, and 10 is a fixed electrode 4 11 is
the printed circuit board to which the impedance conversion element 9 is attached and the
through hole 12 is opened, and 13 is to store the upper 1 to 12 and the vibration Il! This is a
case in which a hole 14 is opened at the front of I 1. A capacitor type microphone configured in a
roundabout manner vibrates the diaphragm 1 by sound waves from a sound source, thereby
deriving a change in capacitance between the fixed electrodes 4 from the impedance conversion
element 9 as a change in voltage. In recent years, radio tape recorders and video cameras, etc.
have tended to be miniaturized, and microminiaturized condenser microphones with an outer
diameter of about 61 IN are also in the stage of mass production. However, as the external line of
the microphone becomes smaller, the vibrating membrane must necessarily be smaller. As the
diameter of the vibrating membrane becomes smaller, the fundamental resonance frequency of
the vibrating membrane becomes higher. As a result, in the case of an ultra-small unidirectional
condenser microphone using this, there is a disadvantage that the C sensitivity is significantly
reduced to low frequency sound. Here, the fundamental resonance frequency fo of the circular
diaphragm fixed at the periphery is expressed as to = (0, 38 2 / a> x <E ??? (where za is the
radius of the diaphragm and ? is T applied to the vibrating membrane, m и и does not represent
the mass per unit area of the vibrating membrane). From this equation, it is necessary to reduce
the tension 1 'applied to the vibrating film in order to keep the radius a of the moving film
constant and to lower the fundamental resonance frequency of the vibrating film. However, the
conventional vibrating membrane 1 constituted by the first P is stretched and attached to the
membrane ring 2 in advance and housed in the case 13.
For this reason, as a result of testing the characteristics possessed by the assembled microphone
unit itself, all products which were not within the allowable range of the predetermined
fundamental resonance frequency were defective products and were not used. The cause of this
failure is roughly vibration l! The fundamental resonance frequency according to 1 was high. In
order to lower this, it is sufficient to reduce the tension, but the variation of the product becomes
large and eventually the number of defective products will be increased. The purpose of
preventing this is the patent application filed by the applicant on December 27, 1982! No. 57226738 "Method for producing a diaphragm for a condenser type microphone", that is, by
irradiating an electromagnetic wave of wavelength i Q'-10 to l Q -16 m to a conductive
diaphragm in which a conductive metal is deposited on a polymer, It is conceivable to use a
vibrating membrane formed by means of partially cutting the molecular chain of the polymer of
the vibrating membrane and lowering the fundamental resonance frequency of the vibrating
membrane itself at the time of stretching and stretching the membrane ring. The tension applied
to the membrane ring of the vibrating film subjected to the electromagnetic wave irradiation
treatment in this way does not change with the product becoming uneven. Therefore, even with
diaphragms treated in the same manner as defective products generated with Microbon-L lira 1using imaging film not subjected to electromagnetic wave irradiation treatment, defective
products are still generated, resulting in poor step keeping. The OBJECTS OF THE INVENTION
The present invention provides a capacitor-type microphone which eliminates the abovementioned drawbacks and improves the yield. SUMMARY OF THE INVENTION In order to
achieve the above object, the present invention is configured to achieve at least the fixed
electrode and at least a fixed electrode on the fixed electrode with a gap of a3 ░ C. and
depositing a conductive metal on the polymer. A case containing the vibrating membrane is
provided, and the polymer of the vibrating membrane is irradiated with an electromagnetic wave
from the outside of the case to reduce the fundamental resonant frequency of the vibrating
membrane. [First Embodiment of the Invention] One embodiment of the present invention will be
described in detail with reference to FIG. In FIG. 2, reference numeral 15 is a condenser type
microphone with a small outer diameter, which is configured in FIG. 1, and the diaphragm 1 of
this microphone 15 has a conductive metal 17 deposited on a polymer 16 as shown in FIG.
Configured. Here, the polymer 16 used is one that partially breaks the molecular chain of the
polymer and lowers the Young's modulus when irradiated with an electromagnetic wave in the
gamma ray to ultraviolet rays in a state where a certain tension is applied. Specific examples
include polyethylene terephthalate and polybutylene terephthalate.
Therefore, a thin film C of a polymer 16 such as polyethylene terephthalate and polybutylene
terephthalate is used for the vibrating film 1 used in the present invention, and one surface
thereof is coated with a conductive metal 17 such as aluminum by vacuum evaporation.
Configured. The capacitor type microphone [] using such a vibrating membrane 1 is microbonded
at the manufacturing stage, and the vibrating membrane 1 is removed from the membrane ring 2
within the range of a predetermined resonance frequency range (= The tension relationship C
'due to Ibaraki's stress C' In this case, although it does not fall within the predetermined
fundamental resonance frequency range, the diameter of the vibrating membrane 1 is small
enough to make the fundamental resonance frequency high. In this way, from the outside of the
case 13 of the micro-bon 15 higher than a predetermined fundamental resonance frequency, as
shown in FIG. The diaphragm 18 covers the diaphragm 1 with light tA. As the lamp 18, a high
pressure mercury lamp, a metal halide lamp, a xenon lamp, an arc lamp or the like can be
considered. Incidentally, FIG. 4 shows how the fundamental resonance frequency of the vibration
changes depending on the irradiation time when the diaphragm 18 is irradiated with the lamp
18. It is understood from the experimental results shown in FIG. 4 that the fundamental
resonance frequency of the moving film becomes lower while the irradiation time is longer. That
is, although the fundamental resonance frequency one minute after irradiation was 5 kHz, it is as
low as about 2 k Hz after 10 minutes. As a result of measuring an assembled microphone from
this, if the fundamental resonance frequency is higher than a predetermined frequency, use as a
non-defective microphone by irradiating an electromagnetic wave for an irradiation time
corresponding to the higher part. Is possible. Thus, the frequency characteristics before and after
irradiating the electromagnetic wave to the microphone having a high fundamental resonance
frequency are not shown in FIG. The waveform shown by the broken line is the one when the
fundamental resonance frequency is high, and the level at the low frequency is low. The
waveform shown by the solid line is the fundamental resonance frequency after irradiation
reduced to a predetermined value by 1 L '? :: also '7) t' low ') frequency 1' (7) L // '; in / lz. Near
the level in the high region, the sensitivity in the low region is similar to that of the non-defective
cigar. Further, when the irradiation time of the electromagnetic wave is extended, the sensitivity
increases as the fundamental resonance frequency 9 of the vibrating film decreases as shown in
FIG. However, it becomes saturated after about 10 minutes. The wavelength of the
electromagnetic wave radiated to the vibrating film 1 in the case 13 is the one of 1'Q "-10 to 1.0,
-6 m so far.
[Effect of light 1] As described above, according to the condenser type microphone of the present
invention, the electromagnetic wave is irradiated to the diaphragm from the outside of the case
of the microphone 1.1 phone having a high fundamental resonance frequency of the imaging
film. 1i1 J: C1 C1 Basic co-imaging frequency is fixed, and reproducing the product that has been
disposed of until it has been disposed of until now has the effect of producing C '.
Brief description of the drawings
FIG. 1 is a cross-sectional view of a general capacitor-type micro-bon, and FIG. 2 shows an
embodiment of the present invention?
1 'is a schematic view, FIG. 3 is a cross-sectional view showing the main part of the capacitor
type micro-bon used in the present invention, FIG. 4 is a characteristic view showing the
fundamental resonance frequency with respect to the irradiation time, FIG. . '1
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jps59176999, description
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