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PROBLEM TO BE SOLVED: To realize an electret condenser microphone which does not
deteriorate in function and performance in an environment such as water and water vapor and
the like. Is a solid electrolyte membrane of hydrogen ion conductivity, porous electrodes are
provided on both sides thereof, and the voltage obtained from the power supply side of the
preamplifier for the electret microphone via a low pass filter consisting of a resistor and a
capacitor is this porous Connect to the resistive electrode 【Selection view】 Fig. 2
Moisture resistant electret condenser microphone
The present invention relates to the structure of a moisture resistant electret condenser
microphone containing water droplets
Published patent publication 2002-33241 Published patent publication 2001-148897 Journal of
the Acoustical Society of Japan, Vol. 28, pp 460 1972
A capacitor microphone that takes out, as an electrical signal, a change in electrostatic
capacitance between a conductive vibrating film that vibrates due to a pressure wave of incoming
sound and a fixed electrode installed in parallel to this, as is apparent in Non-Patent Document 1
etc. The electrical impedance between the electrode and the pre-amplifier is very high compared
to general electronic circuits, even a few megohms low and a few tens gigaohms high (non-patent
document 1). When the part is affected by moisture or moisture infiltrating through a capillary
slit etc. for static pressure balance, it often suffers from inconveniences in use such as
deterioration of characteristics, increase of noise, etc. Especially frequently used in recent years
In the case of the electret type, the charge that is charged to the electret layer and constitutes the
polarization voltage is discharged and extinguished by moisture, and the function of the
microphone is There is a problem that the width is lost, and solving the problem has been a longstanding issue. Therefore, although measures such as patent documents 1 and 2 have been
devised, these are effective for water droplets. However, there is a need for measures to prevent
the inflow of moisture as gas, which penetrates as gas and condenses inside, and there has been
a demand for measures to prevent the infiltration of moisture as gas. Since the charge
annihilation of the electret is not recoverable and is particularly serious, in the present
application, it is focused on the electret type, but even in a general condenser microphone, the
water is a great enemy as described above, so It is an effect
In order to reinforce the weakness of such electret condenser microphones, the present invention
solves this problem by attaching a waterproof windshield to the front of the microphone and
providing a function of constantly discharging the water vapor component inside the microphone
housing out of the bag. Describe the contents below
FIG. 1 shows a typical structure of an electret condenser microphone as a cross-sectional view. In
FIG. 1, 10 is a protective surface cloth for preventing intrusion of wind, dust, etc., 11 is a
vibrating film and at least one surface is conductive. Reference numeral 12 denotes a fixed
electrode, which has a damping adjustment hole 17 for adjusting the damping action on the
vibrating membrane by the air layer present between the fixed electrode and the vibrating
membrane to an appropriate value. Also, the opposite surface to the vibrating membrane In the
figure, the electret layer 24 electrodeposited on a fluoroethylene propylene film etc. is installed
13 is an insulator, which electrically insulates the vibrating membrane and the fixed electrode
and properly maintain the mutual positional relationship. A combination of functions 14 is a preamplifier, and the capacitance formed by the vibrating membrane and the fixed electrode is
changed by the vibration of the vibrating membrane, and this changes to the charge of the
electret. Has the function of amplifying the signal generated as a change in surface potential and
converting the impedance to connect to the outside. 15 is a housing that mechanically holds and
holds the whole mechanically and electrically shields it. In this case, a static pressure balancing
groove 18 is provided on the outside to make atmospheric pressure fluctuation parallel to the
inside. 19 is an output and power supply terminal, 20 is a housing bottom plate, the terminal, the
preamplifier, etc. As described above, the condenser microphone is provided with a clearance for
static pressure adjustment for the purpose of preventing the performance deterioration due to
the pressure fluctuation during storage or use. Enters inside
An embodiment of the present invention is shown in FIG. 2. In FIG. 2, 10-20 and 24 in FIG. 2 are
the same as in FIG. 1. A protective surface cloth 10 is newly coated with a water repellent
material 9 composed mainly of PTFE. And 21 are provided separately with a dehumidifying
element 21 that is a solid electrolyte membrane having hydrogen ion conductivity, such as
Nafion manufactured by DuPont, and porous electrodes 23 are mounted on both sides thereof.
H2O → 2H <+> + (1/2) depending on the DC voltage obtained by connecting one of its electrodes
to the ground and the other from the power supply of the preamplifier via the low pass filter 22
consisting of a resistor and a capacitor. A low-pass filter, for example, a simple circuit as shown
in FIG. 4, is sufficient to generate a reaction of O 2 + 2e <-> and discharge the moisture inside the
housing. Here, 31 is a power supply portion of the preamplifier. , For example 32 is a ground
wire, 34 is a resistor such as 1 MΩ, 35 is a capacitor such as 1 μF, and signals of about 0.15 Hz
or more are cut off. At this time, the volume inside the housing is about 0.3 cubic centimeter at
most, and the corresponding power is very small. It is characterized that there is no need to
prepare specially. By using these two means together, it is possible to cope with vaporized water
as well as water droplets.
By carrying out the present invention, electret condenser microphones conventionally considered
to be vulnerable to humidity can be used safely under severe use conditions such as in the rain,
for example, thereby expanding the use, increasing the convenience of use, etc. The static
pressure balance function of the electret condenser microphone is required to secure the
frequency characteristics of the microphone down to the low frequency range, and the time
constant determined by the extremely thin air passage, that is, the inflow resistance and the
internal volume is It is about 1 second or more, and even if the water itself flows in, its inflow
rate is slow and can be sufficiently dealt with by the method according to the present invention
Although the embodiment is already shown in FIG. 2, the other embodiments are shown in FIG. 3
and all reference numerals in FIG. 3 are the same as in FIG. 2. In this embodiment, the fixed
electrode 12 in FIG. The adjustment hole 17 does not exist, and the electret layer is disposed on
the inside of the front surface of the housing, and the diaphragm is electrically isolated from the
housing. The sound hole 16 also serves as a braking adjustment hole. Same as previous
The present invention is intended mainly for use in microphones for voice communication such
as mobile phones, but it is of course possible to be applied to measurement, control, for example,
outdoor robots etc.
FIG. 1 is a cross-sectional view showing a typical example of a conventional structure of a
condenser microphone to which the present invention is to be applied.
FIG. 2 shows the conventional example of FIG. 1 to which the present invention is applied, and
reference numerals 11 to 20 are common to FIG.
FIG. 3 shows another embodiment in which a part of the housing is also used as a fixed electrode
to provide the installation side, and the diaphragm is insulated as the signal side.
[0012] FIG. 4 is a configuration example of a low pass filter used in the present invention.
Explanation of sign
9: water repellent coating mainly composed of PTFE 10: microphone protective surface cloth 11:
vibrating membrane 12: fixed electrode 13: insulator 14: pre-amplifier 15: housing 15: sound
hole 17: damping adjustment hole 18: static Pressure balancing groove 19: Output and power
terminal 20: Housing bottom plate 21: Dehumidifying element 22: Power supply separation
circuit 23: Porous electrode 24: Electret layer
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jp2007037069, description
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