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JPS60217800

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DESCRIPTION JPS60217800
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
electret condenser microphone (hereinafter abbreviated as rEcMJ) excellent in radiation
resistance performance. [Technical background of the invention and its problems] As is known,
<ECM> applies a high voltage to a dielectric, for example, a polymer film, and then removes the
voltage and then removes the voltage, resulting in a semipermanent charge on the surface of the
dielectric. Using the electret phenomenon of remaining The basic configuration of this ECM is
shown in FIG. That is, the ECM is configured such that an air layer P having a predetermined
thickness is formed between the disc-shaped electret diaphragm 1 and the disc-shaped back
electrode plate 2 by interposing the both through the annular insulating spacer 3. It is fixed and
configured. The electret diaphragm 1 fixes the vibrating body 6 in which a certain tension is
applied to the vibrating body 6 in which an electrode layer 5 such as aluminum is formed by
vacuum evaporation or the like on one surface of the polymer film 4. The vibrating body
stretching frame 7 is fixed by a conductive adhesive 8. Further, to the back electrode plate 2, a
lead wire 9 for leading a signal generated by a change in the induced charge on the surface of
the back electrode plate 2 to an amplifier (not shown) is connected. In the ECM configured in this
manner, the homocharge accumulated on the surface of the vibrator 6 causes a positive charge
on the surface of the back electrode plate 2. The amount of induced charge depends on the
thickness of the air layer P. Therefore, when sound pressure is applied to the vibrating body 6,
the vibrating body 6 vibrates to change the thickness of the air layer P, which enables sound
detection. By the way, recently, an attempt has been made to detect damage of equipment inside
the nuclear reactor J7i, for example, a reactor containment vessel by acoustic detection. In such a
case, an ECM that is compact and does not require a high voltage DC power supply is
advantageous. However, when ECM is used in a place where the possibility of radiation exposure
is high, when radiation is irradiated to the electret diaphragm 1, a large number of carriers are
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generated inside the vibrator 6 due to the influence of the radiation, There is a problem that the
charges accumulated in the vibrator 6 recombine with these carriers and disappear. Therefore,
when the ECM is irradiated with radiation, the acoustic detection sensitivity of the ECM is
lowered, and there is a problem that a desired function can not be exhibited. [Object of the
Invention] The present invention has been made based on the above-mentioned circumstances,
and an object of the present invention is to improve the radiation resistance performance of the
ECM, and thereby to optimize the ECM as an acoustic detection element such as a nuclear facility.
To provide.
SUMMARY OF THE INVENTION The present invention is characterized in that a dielectric film
constituting an electret diaphragm is covered with a shielding member containing lead as a main
component. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of
the present invention will be described below with reference to the drawings. FIG. 2 is a view
showing the overall configuration of the ECM according to the present embodiment, and 11 is a
case formed, for example, of aluminum and having a bottomed cylindrical shape. In the case 11,
the entire outer surface is covered with a lead shield 12, and a sound pressure introduction hole
13 for sound detection is provided on the bottom wall of the case 11. The sound pressure
introducing hole 13 is closed by a dustproof cloth 14 to prevent dust from entering the inside of
the case. Further, the opening of the case 13 is closed by a closing plate 15 formed of an
insulator such as resin, for example. Inside the case 11, an electret diaphragm 21, a back
electrode plate 22, and a resin support frame 23 for supporting the back electrode plate 22 are
accommodated. The electret diaphragm 21 is formed by forming an electrode layer 27 of a twolayer structure consisting of a lead layer 25 and an electrode layer 26 such as aluminum on one
surface of a polymer film 24 such as fluorocarbon resin, polyacrylonitrile or polycarbonate. The
vibrating body 28 is fixed by applying a predetermined tension to the annular conductive
vibration-body stretching frame 29. A conductive adhesive 30 is used to fix the both. The electret
diaphragm 21 is fixed in a state where the vibrating body stretching frame 29 is electrically
connected to the inner surface of the bottom wall of the case 11. The back electrode plate 22 is
connected via an annular insulating spacer 31 so that an air layer P having a predetermined
thickness is formed between it and the surface on the polymer film side of the electret diaphragm
21. The back electrode plate 22 is supported by the support frame 23. The support frame 23 is
formed by integrally connecting the cylindrical body 32 and the partition wall 33 which divides
the inside of the cylindrical body 32 in the axial direction into one, and the hole 34 is provided at
the center position of the partition wall 33 Be done. The peripheral portion of the back electrode
plate 22 is supported on one end side of the support frame 23. The other end side of the support
frame 23 is fixed to the peripheral edge portion of the closing plate 15. The closing plate 15
includes a resin plate 35, a lead shield 36 attached to the surface of the resin plate 35 on the
support frame 23, and an electrode plate 37 embedded in the other surface of the resin plate 35.
It comprises with the hole 38 provided in the predetermined position. The electrode plate 37 and
the back electrode plate 22 are electrically connected by connecting both ends of the lead 39
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passing through the holes 34 and 38 with a solder 40 ░ 41.
In the ECM according to the present embodiment configured as described above, the radiation
irradiated toward the inside of the case 11 from the circumferential direction of the case 11 is
blocked by the shield 12 attached to the outer periphery of the case 11, and the sound pressure
Radiation from the introduction hole 13 side is blocked by the shield 12 attached to the outer
surface of the bottom wall of the case 11 and the lead layer 26 provided on the surface of the
polymer film 24 on the sound pressure introduction hole 13 side. Radiation from the side of the
opening surface 11 is blocked by the shield 36 attached to the blocking plate 15. As described
above, in the ECM according to the present embodiment, even if radiation is irradiated from any
direction, the radiation is directly irradiated to the polymer film 24 by the presence of the shield
12, 3t3 and the lead layer 2G. Can be prevented. Therefore, it is possible to solve the
conventional problem that the charge existing in the vibrator 28 disappears by radiation. The
present invention is not limited to the above embodiment. For example, as shown in FIG. 3, lead
layers 51. 52 may be formed on both sides of the polymer film 24. In this way, radiation can be
shielded without particularly attaching a shield to a case or the like. Further, the shielding
member is not limited to lead, and an alloy containing lead as a main component may be used.
[Effects of the Invention] As described above, according to the present invention, since the
dielectric film is not directly exposed to radiation, the conventional defects that the charges
present in the dielectric film disappear due to the radiation are eliminated. can do. Therefore,
according to the present invention, it is possible to provide an ECM capable of highly reliable
acoustic detection in a nuclear facility or the like.
[0002]
Brief description of the drawings
[0003]
FIG. 1 is a longitudinal sectional view showing a basic configuration of a conventional ECM, FIG.
2 is a longitudinal sectional view of the ECM according to one embodiment of the present
invention, and FIG. 3 is a basic of ECM according to another embodiment of the present invention
It is a longitudinal cross-sectional view which shows a structure.
1.21 ... electret diaphragm, 2, 22 ... back electrode plate, 3.31 ... insulating spacer, 4.24 ...
polymer film, 5, 26 ... electrode layer, 6. 28 иии Vibrator, 7, 29 иии Vibrator stretch frame, 12.36 и и и
Shield, 25. . 51.52: Lead layer, P: Air layer. Applicant agent Patent attorney Takehiko Suzue Fig. 1
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Fig. 2 Fig. 2 15413 '/ ????
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