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JPH05145996

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DESCRIPTION JPH05145996
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
transducer for converting sound into an electrical signal or to an electric signal, and more
particularly to a diaphragm or fixed electrode of an electrostatic (condenser type) acoustic
transducer.
[0002]
2. Description of the Related Art Conventionally, an electrostatic acoustic transducer of this type
has, for example, the structure shown in FIG. That is, the fixed electrode 5 is provided opposite to
the back side of the diaphragm 1 with a certain gap 3 interposed therebetween. A bias voltage is
applied in advance between the diaphragm 1 and the fixed electrode 5. Then, when the
diaphragm 1 vibrates by sound, the capacitance formed between the two changes, and the fixed
electrode takes out an electromotive voltage proportional to this change as an electric signal to
act as a microphone. Or, in the case of a speaker, conversely, the electromotive voltage between
the two is changed by the electric signal applied to the fixed electrode 5, and the diaphragm
vibrates to generate a ground.
[0003]
The diaphragm 1 is generally light in weight and preferably has a high Young's modulus. For
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example, FEP film 7 (copolymer of 4-footer ethylene and 6-footer propylene) is used to store
electric charges by corona discharge, electron beam, etc. and hold semipermanently Let As a
result, since there is always a potential on the surface, it is not necessary to apply a bias voltage
from the outside, and miniaturization and measurement can be performed.
[0004]
Alternatively, as shown in FIGS. 6 and 7, a polyester film or metal foil (titanium alloy foil, nickel
alloy foil, etc.) is used for the diaphragm 1, and the FEP film 7 is thermally welded to the fixed
electrode 5 side to Turn
[0005]
By electretizing in this manner, sound can be converted into electricity or electricity can be
converted into sound without the need to apply a bias voltage from the outside.
[0006]
However, in the above-mentioned conventional electrostatic acoustic transducer, (1) the electret
potential of the charge stored in the FEP degrades under a high temperature environment (about
90.degree. C. or more). It can not be used for equipment used in high temperature environments.
[0007]
(2) The thickness of the FEP film can not be reduced to 10 μm or less because of its nature, so
stray loss (compared to the external bias system where a bias voltage is externally applied when
measuring the miniaturization of the converter and the increase in S / N) The rate of floating loss
is increased, which is a problem of the electret-applied electrostatic acoustic transducer in which
the diaphragm 1 or the fixed electrode 5 is electretized.
[0008]
The present invention solves such conventional problems, and enables use even in a high
temperature environment of 90 ° C. or higher, and is excellent in that the ratio of stray loss can
be reduced at the time of miniaturization and high S / N. An object of the present invention is to
provide an electrostatic acoustic transducer.
[0009]
SUMMARY OF THE INVENTION In order to achieve the above object of the present invention, in
the electrostatic acoustic transducer according to the present invention, the invention according
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to claim 1 comprises a silicon oxide (SiO2) thin film on a metal foil. The diaphragm is configured
to be electretized by forming 1 μm or more and 5 μm or less, and a fixed electrode facing the
diaphragm and provided with a predetermined gap.
[0010]
The invention according to claim 2 is configured by forming a diaphragm and a silicon oxide
(SiO2) thin film of 1 μm or more and 5 μm or less on the surface, facing the diaphragm and
having a predetermined space therebetween. And a fixed electrode diaphragm.
[0011]
Therefore, according to the present invention, (1) By using a silicon oxide thin film instead of a
conventional FEP film, silicon oxide has heat resistance even at high temperatures (90 ° C. or
higher), and thus the surface The potential, that is, the electret potential does not deteriorate, and
the bias voltage by the electret potential can be kept constant without applying an external bias
voltage, enabling use in a high temperature environment.
In addition, (2) the silicon oxide thin film can be reduced to 5 μm or less by various vapor
deposition methods, and the stray loss can be suppressed also in the miniaturization and the
increase in S / N.
[0012]
Next, an embodiment of the present invention will be described with reference to the drawings.
[0013]
FIG. 1 shows the configuration of the first embodiment of the present invention, which
corresponds to FIG. 6 of the prior art.
In FIG. 1, a hole 11 for transmitting sound is formed on the front side of the case 9.
A diaphragm ring 13 is provided on the side of the hole 11 in the inside of the case 9 to support
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and fix the diaphragm 1 with a predetermined tension, and further, the fixed electrode 5 is
opposed to the fixed electrode 5 with a spacer 15 by a spacer 15. Let
The fixed electrode 5 is held by the insulator 16 with respect to the case 9 to integrate the whole.
[0014]
A silicon oxide (SiO 2) thin film 17 is formed on the surface of the fixed electrode 5 by PVD
method C or CVD method to a thickness of 1 μm to 5 μm (FIG. 2).
The thin film 17 is subjected to corona discharge and electron beam irradiation to accumulate
charges and semipermanently store them, thereby forming an electret and setting the surface
potential to 150V to 250V.
The diaphragm 1 can be a polyester film or a metal foil (for example, a titanium alloy foil or a
nickel alloy foil) as in the prior art.
[0015]
Next, the operation of the first embodiment will be described.
When the acoustic transducer of this embodiment is used as a microphone, when the diaphragm
1 vibrates, the thickness of the slit 3 changes, and the capacitance formed between the
diaphragm 1 and the fixed electrode 5 Changes, and an electromotive voltage proportional to this
change can be taken out as an electrical signal.
The bias voltage that is the source of this electrostatic capacitance is given by the surface
potential (electret potential) obtained by electretizing the fixed electrode 5. Therefore, even if a
bias voltage is not externally supplied, a high bias voltage can be maintained and a highly
sensitive electrical signal can be obtained. In addition, since silicon oxide has high heat
resistance, the electret potential of the silicon oxide thin film 17 does not deteriorate even under
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a higher temperature environment (about 90 ° C. or more and 150 ° C. or less) than the
conventional one and maintains high sensitivity. it can. Furthermore, the silicon oxide thin film
17 can be made extremely thin (5 μm or less) by PVD or CVD, so the ratio of the effective
capacitance of the capacitance formed between the diaphragm 1 and the fixed electrode 5 is It
can be high, thus reducing the percentage of stray capacity. For this reason, it has the effect of
realizing miniaturization, high sensitivity, and high S / N.
[0016]
FIG. 3 shows the configuration of the second embodiment of the present invention, and
corresponds to FIG. 5 of the prior art. In FIG. 2, the diaphragm 1 forms a silicon oxide thin film
17 on the metal foil 19 by PVD or CVD by 1 μm or more and 5 μm or less. The thin film 17 is
electretized by corona discharge, electron beam or the like in the same manner as in the first
embodiment to set the surface potential to 150V to 250V. As described above, while the above
embodiment is for electretizing the fixed electrode 5, the diaphragm 1 is electretized for this
embodiment. Even in this case, substantially the same effect as the above embodiment can be
obtained.
[0017]
In the above embodiments, the electrostatic acoustic device has been described as a microphone
that converts sound into an electrical signal, but in other embodiments, it can be implemented as
a speaker that converts an electrical signal into sound, in which case Also, it can be used under
high temperature environment, has high miniaturization, high S / N, high sensitivity etc.
[0018]
According to the present invention, as is apparent from the above embodiments, a silicon oxide
thin film is formed on a vibrating plate or a fixed electrode and electretized, so that the electret
potential is not deteriorated even in a high temperature environment, and a high temperature
environment is obtained. Allows the use of electrostatic acoustic transducers below.
Furthermore, since the silicon oxide thin film can be formed very thin (5 μm or less),
miniaturization, high sensitivity, and high S / N can be realized.
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