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JPS5714292

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DESCRIPTION JPS5714292
Description 1, title of the invention
Electret device
3. Detailed Description of the Invention The present invention relates to an electret apparatus
and, more particularly, to an electret apparatus joined as shown in FIG. 9 as equalization of
electret surface charge density table etc. as induction. As is well known, electrets have the
property that a charged electric charge lasts semipermanently, and are widely used in the field of
industry as electrostatic transducers and the like. FIG. 1 shows the principle configuration of a
conventional condenser microphone using such an electret, in which an electret material 12 of a
polymer film is applied to a back electrode 11 made of a conductive metal substrate to be
electretized. The electret structure 1B is used as a solid electrode. Since the diaphragms 16 made
of metal thin film and the like stretched on the holding ring 15 on the solid foot made of the
electret structure L1 via the spacer 14 made of insulating material can be paired as a 0 J working
electrode, Power unit is configured. Thus, when the diaphragm 16 of such an electrostatic unit is
displaced by the external sound, the rice bowl C between the two electrodes changes so that Q =
CV. When the load q (this-combined electret bridge 13r (provided by)) is-the voltage, the voltage
(t) between both electrodes will be changed. Therefore, the sound pressure is electrostatically
converted into an electric signal by converting the change voltage (t) into an impedance by
converting the impedance through a field effect transistor (FBT) or the like as EndPage: 1 low
impedance. A condenser microphone is realized. Fig. 2 HFJl; <showing the case where it is
applied to a condenser headphone unit, and in principle, the electric signal is converted into
sound pressure electrostatically by conducting the opposite operation to the case of the
condenser microphone described above It is possible to Further, in this case, the diaphragm 16
as a movable body, which is structurally stretched on the holding ring 15 ', is placed on the both
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sides of the spacer J4. By connecting seven pairs of electret structures 13.13 as a fixed pole 25
through J4, a so-called nine-piece sieve type condenser headphone unit is realized. In addition, an
electric signal is given via each electrode KU (1st source (E, Q) lance (sigma)) and high resistance
(R1)-(Rt) of this headphone unit. By the way, the electrostatic transducer using the electret
structure as the fixed pole as described above is different from the usual one and no direct
current power source for polarization or deflection is required, so the structure is simplified and
as small as possible. In addition, it has the advantage of being able to reduce the cost accordingly.
However, the electret structure, which is the most important one, has a serious lack of tendency
to give sharp marks to various physical properties as a transducer in that the variation of the
surface charge density, that is, the unevenness of the charge distribution is large. It was FIG. 3
shows an example of measurement of the surface charge distribution of such a conventional
electret structure, in which the electret material 12 is deposited on the back electrode 11 made
of an aluminum plate having an outer diameter of 60 關 φ to form an electret However, as can
be seen from the figure, it can be known that it is incredibly large within several hundred volts.
In the figure, the central flat portion 12b excluding the undulations s12m in the periphery is the
non-electretized portion provided for manufacturing reasons, but the surface charge density of
the non-electretized portion 12b is the variation of that in the periphery There is a problem in
that the problem is extremely much lower than in the prior art, and the effective area for
electrostatic action is reduced accordingly. In this case, various conversions including conversion
efficiency as a 形 type transducer ! f will be further degraded. In addition, since the surface of the
electret material 12 of the conventional electret structure 7 is exposed to the surface so as to
come into contact with the air, it has poor moisture resistance and there is a problem in terms of
temporal stability. It had the serious drawback of becoming Therefore, the present invention has
been made in view of the above-described points, and in particular, as uniformity (E) of electret
surface charge distribution as induction (N) i is well illustrated,% t # foot property is significantly
improved. It is an object of the present invention to provide an electret mounting that is joined in
a manner to obtain. First, the electret structure used in the present invention will be described in
detail. That is, as shown in FIG. 4, an electret formed of a polymer film such as (PP), (TFI!), (FIltP)
or the like on the back electrode 21 made of a conductive metal substrate having the same
potential as the ground, as shown in FIG. On the electret element 23 formed by depositing the
material 22 and electretizing it, a vjt body 2 body sound made of a conductive metal material or
an organic material equal to or smaller than the area shape thereof If the same sign charge of the
electret element 23 appears in the surface direction of the dielectric 240 by placing it in an
insulating state with the source <I! The formed electret housing 25 is a complete collection. Here,
the dielectric 24 is usually (generally referred to as an insulator only, and different from the
insulator 24), as described above, generally refers to those rich in conductive metal materials and
organic materials (this will be described later).
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Here, the organic material is a thermoplastic and thermosetting resin material, a composite
material obtained by combining these with a different material, and a dielectric material such as
glass, and the volume resistance is 101 "Ω -1 or more. So-called 飴 EndPage: 2 edge material
shall be generically referred to. 1) If the charge of the electret element 23 has the negative sign
Q, the electret structure 25 which is formed as described above has the charge on the Ik surface
side positive and negative signs of the dielectric 24 mounted on the element 23 and the surface
Negative sign which is the same sign charge as the element 23 on the side The phenomenon of
the electric charge of 4) is caused as it is caused. In this case, the presence of the dielectric 24
not only merely causes the above-described dielectric function, but as described later, the
uniformity of the surface charge density as the electret structure 25 is well achieved, and its
safety is improved. The point secured is N 蒙. In the above description, when the surface
potential of the electret element 23 alone is [E0] and the surface potential induced by the
dielectric 24 mounted thereon is [E,], Ji, = α · n. Here, (α) is also referred to as an induction
coefficient if it is expressed, and it is approximately within the range of α = 0.6 to 0.99 when the
dielectric 2 is a metal. That was confirmed. FIG. 5 shows a specific example of a case for
obtaining the electret structure shown in the above manner. First, with the switch (8 W)
connected to the dielectric 24 closed, the dielectric 24 is grounded. After making it the same
electric potential or a small zero charge state, open the switch (SW) and make it isolated from the
ground. Then, for example, if the printing dielectric 24 is placed on the surface of the electret
element 23 while maintaining the zero to load state by using insulating tweezers or the like, the
dielectric action occurs as described above. In this case, when the dielectric 24 is a conductive
metal material, charges are induced at W4. However, in the case of the insulating material, it
takes a certain time for the induced charges to reach the one-leg voltage. (Fl, J E takes about 30
minutes). Also, assuming that the switch (8w) is closed again from such an induced state, the
charge disappears as if the dielectric 24 is a metal so that the potential becomes zero
immediately, but in the case of an insulating material (but in the case of a fluorine resin system).
In the case of metal, as in the case of metal), it is possible to have a number of times when it is
related to the movement of charge as it gradually decreases and disappears. Fig. 6 shows the
case where glass is used as the dielectric 24 as another specific example, and even with the glass
dielectric 24a, the induction coefficient α is about 0.83 (the electret collector single charge of
700 V On the other hand, it was confirmed that the dielectric charge of the glass dielectric is
induced at about 580 V) and at the same time as the metal lift table.
In the glass dielectric 24a, the surface potential is adjusted because the decrease time when the
switch (SW) is closed again from the a-state is relatively faster than the insulating material such
as AB8 resin and slower than the metal material. It is advantageous if necessary. FIG. 7 shows the
time-dependent change of the charge induced on the surface of the dielectric 24 as described
above (leakage% +! t) This indicates one indicator of stability, and (a) is the case of a metal
material (but the same applies in the case of a fluorine resin system), and good stability is
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obtained with almost no change from the initial state. It is done. Further, in the case of (b) Fi, for
example, an insulating material such as AB8 resin, a leak is settled about 5 minutes after the
initial state, and good stability is obtained thereafter. By the way, since such a stability protects
the surface of the element 23 by mounting the dielectric 24 on the surface of the electret
element 23, the electret surface L is different from the conventional case in that the electret
surface is tk [It is encouraged by the fact that it is done not to be exposed to the air. Tsukushi, by
protecting the surface of the electret element 23 with the dielectric 24, it is possible to improve
the moisture resistance and thus the stability over time, so that the life can be improved. Stability
can be secured. As shown in FIGS. 8 (a) and 8 (b), the surface of the electret element 23 is
provided with wavelike irregularities, so that the area directly in contact with the dielectric 24
mounted thereon is reduced. From the handling, EndPage: 3 will be able to enrich the stability.
FIG. 9 shows an example of measurement of the surface charge distribution of the electret
structure U as described above. An electret element in which the electret material 22 is rapidly
deposited on the back electrode 21a made of an aluminum plate having an outer diameter
601IIφ. A dielectric 24b having the same area and shape as that of t is placed on the surface
23a, and a distribution of charges which are induced on the surface of the dielectric 24b is
obtained. That is, as can be seen from this figure, it is known that the surface charge density is
uniform and hardly dispersed in all parts unlike the conventional case. In addition, it is based on
the precision of a footstep that it is falling slightly in the vicinity of the both ends in a figure, and
it is not essential. Then, in FIG. 9, the flat portion 22c at the center excluding the wavelike
unevenness $ 22 b on the same side is a non-electretized portion provided for manufacturing
reasons as in the conventional case, but corresponds to the non-electretized portion. In the
central portion of the surface of the dielectric 24b, the same uniform charge density as that of
the peripheral portion can be obtained without any reduction.
In contrast to the prior art, the non-electretized portion does not substantially reduce the
effective area for electrostatic action, and in this respect it can be used as an electrostatic
transducer. It is possible to significantly improve the conversion characteristics of the soot
containing the conversion rate. That is, the electret structure H formed by mounting the
dielectric 24 on the electret element 23 by the above, not only exhibits the phenomenon that the
predetermined charge based on the electret charge is fermented on the surface of the dielectric
24; Electret by X.24) The superior effect of the protection effect of X child 23 and the excellent
advantage of as uniform as possible of the surface charge density provided by the surface charge
equalization effect As soon as it became clear. Next, a junction structure considered in order to
demonstrate the excellent performance of the electret structure L1 as described above will be
described. -That is, as shown in FIGS. 10 (a) and 10 (b), the dielectric 24 is laminated on the
electret material 22 side of the electret element 23 as described above, and the side surface
substantially U-shaped joint member The electret apparatus is formed by taking a joint structure
in which both are held by 201.202. Thus, according to the joint structure of the electret integral
body 25 as described above, it is possible to surely achieve stabilization by protection of the
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surface of the electret element 23 as described above and equalization of the surface potential, as
well as @ surface abbreviation. Since the sheavetlet element 23 and the dielectric 24 can be
joined by the U-shaped joining member 201 ° 202, there is an advantage that the structure can
be simplified. In addition, since the electret element 23 and the dielectric 24 are bonded once,
there is an advantage that the stability can be further promoted since the mechanical positional
relationship between them is not changed. Furthermore, since the electret assembly L "joined in
storage, transport, assembly, etc. can be handled as a single unit, it is convenient in terms of
parts management. The number of joining members is limited to two. It is preferable that the
material is made of an elastic material, and it should be capable of further bonding to the surface.
By the way, although the electret apparatus as described above has an individual application as
an electrostatic transducer, in particular for audio equipment, in addition to the above-mentioned
microphone and headphones, a pickup cartridge and a speaker are used. When applied to these
audio devices, there are the following advantages.
That is, first, low noise and high efficiency due to increase of effective capacity, low strain rate
due to uniform voltage distribution, high damage reliability due to improvement of stability, and
overall reduction of brightness, yield Improve the accuracy, and reduce the cost by simplifying
the structure. In particular, in the case of a microphone, by increasing its capacity EndPage: 4 to
lower the noise level by lowering the input impedance to the field effect transistor for impedance
conversion, to further reduce noise be able to. In addition, in the case of headphones and
speakers, it is also possible to achieve so-called transformerless operation that can eliminate the
need for a signal supply transformer by increasing the efficiency. The following fields can be
considered as applications other than acoustic equipment. For example, switches, sensors, etc.
can be applied to various electronic devices and measuring devices (including radiation fa lid
gauges) in substantially the same manner as the electrostatic transducers described above, and
digital as a memory It is applicable also to apparatus. The present invention is also applicable to
various electrostatic devices (electrostatic printing machine, electrostatic generator, dust removal
apparatus, etc.), and also applicable to medical devices and high impedance high voltage power
supplies. . Of course, other applications as well as modifications of the above-described
embodiments and examples are possible without departing from the scope of the present
invention. Therefore, as detailed above, according to the present invention, an electret device
joined so as to obtain a good uniformity of the electret surface charge density particularly as a
induced substitution as shown in FIG. 9 and greatly improve the stability is provided. can do.
4. Brief description of the drawings FIGS. 1 and 2 are diagrams for explaining the basic
configuration of a conventional condenser microphone and condenser headphone unit, and FIG.
3 is a diagram used for FIGS. 1 and 2 Fig. 5 is a measurement diagram showing the surface 1
packing density of the electret structure, Fig. 4 shows an example of the electret structure used
in the present invention, Fig. 5 and Fig. 6-Fig. 6 show concrete example 1 of Fig. 4; FIG. 7 is a
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measurement diagram showing time-dependent change characteristics of charge induced in one
high body in FIG. 4, FIG. 8 is a view showing another specific example of m4 in FIG. 9, and FIG. 9
is the electret structure of FIG. FIG. 10 is an exploded perspective view and a sectional view
showing an embodiment of the present invention using an electret structure of m4 section,
showing a surface charge of 1 degree. 21 · · · · · · · · · · · · · · · · · · · · · · · · · · · 21 back electrode, 22 · · ·
electret material, 23 · · · electret element, 24 · · · dielectric, L "· · · 1 assembly structure 201. 202 ·
· · · · · · · Outsourcing-Attorney Attorney Takehiko Suzue EndPage: 5 □ To δ, Tf! i ('o N mouth
castle EndPage: 7 Warning: Page discontinuity
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