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Description 1, title of the invention
Electret device
3. The invention of "the invention with the detailed description of the invention" relates to an
electret apparatus, and more particularly to an induction ring-shaped apparatus capable of
increasing the surface potential of the lefttret and leveling the charge density. As is well known,
electrets have the property that a charged electric charge lasts semipermanently, and are widely
used in various fields as electrostatic type transducers and the like. FIG. 1 shows the principle
configuration of a conventional condenser microphone using such an electret, wherein an
electret material 12 such as a polymer film is adhered to a back electrode 11 made of a
conductive metal substrate to be electretized The electret structure 1-3 is used as a fixed
electrode. Then, a diaphragm 16 such as a metal thin film stretched over the holding ring 15 on
the fixed electrode formed of the electret structure 1-3 via a spacer 14 such as an insulating
material is paired as a movable electrode, A unit is configured. Therefore, when the diaphragm
16 of such an electrostatic unit is displaced by the external sound pressure, the electrostatic
capacitance C between the both electrodes is changed, but the charge Q (this Q) is obtained from
Q = Cv. In the case where the electret tank body 13 is constant, the voltage V between the two
electrodes will be changed. Therefore, a capacitor microphone which converts sound pressure
into an electric signal electrostatically by converting the change voltage V into impedance by
converting the voltage V through the field effect transistor EndPage: 1 FET etc and extracting it
as a low impedance To be realized. Fig. 2 i1 [L, <shows the case where it is applied to the
condenser headphone unit, and in principle, the electric signal is electrostatically converted to
the sound pressure by conducting the operation opposite to the case of the condenser micro ho
and / described above. Can be converted to And, in this case, a pair of electret structures 13, 13
is constructed via the sensor 14 and 14 on both sides with the diaphragm 16 as the movable
pole stretched in the holding ring 15 'at the center. Are arranged as the fixed pole 25 so as to
realize a so-called butch-shaped condenser headphone unit. An electric signal is given to each
electrode of the headphone unit from the signal source E @ via the transformer T and the high
resistance R1 + R. By the way, the electrostatic transducer using the electret structure as the
fixed electrode as described above is different from the usual one and no direct current power
source for polarization or bias is required, so the structure is simplified and as small as possible.
It is possible to make it possible, and the court has the advantage of being able to reduce the
price accordingly.
However, the electret structure, which is the most important, has an adverse effect on various
characteristics as a transducer in that the surface potential can not be so high and the variation
in surface charge density, that is, the unevenness in charge distribution is large. It had a serious
drawback that it tended to give The third M 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 1) made of an aluminum plate having an outer diameter of 60 φ
to form an electret However, as can be seen from the figure, it can be known that it varies in a
very large range of several hundred volts. In the figure, the flat portion 12b at the center
excluding the wavelike uneven portion 12a in the periphery is a non-electretized portion
provided for manufacturing reasons etc., but the surface charge density of the non-electretized
portion 12b is that of the periphery. There is a problem that the variation is much larger than the
variation, and the effective area for the electrostatic action is reduced accordingly. In this case,
various conversion characteristics including the conversion efficiency as an electrostatic
transducer Will be further degraded. In addition, the conventional electret structure is exposed so
that the surface portion of the electret material 12 is exposed to air directly, so that it has poor
moisture resistance and has problems in terms of stability over time, and the life is shortened. It
had serious drawbacks. Therefore, the present invention has been made in view of the abovedescribed points, and in particular, it is possible to favorably increase the electret surface
potential as the induced (N) form and to make the charge density uniform, and significantly
improve the stability. An object of the present invention is to provide an electret device which
can be improved. An embodiment of the present invention will now be described in detail with
reference to the drawings. That is, as shown in FIG. 4a, electret materials 221 to 22m made of
polymer films such as PP, TFE, FICP, etc. are applied to the back electrodes 211 to 21n made of a
conductive metal substrate to make them electret. A plurality of electret elements 231 to jJn
formed are stacked in the same direction. When a conductor such as a conductive metal plate 24
or metal foil having an area shape equal to or less than that of the conductor is laminated to the
electret material 221 side of the lowermost electret element 231 at the same potential as the
earth, the top electret An electret device ξ5 is realized on the surface of the back electrode 21n
of the element 23n so as to expose a charge of the same sign as that of each of the electret
elements 231 to 23n and equal to the potential approximately totaling each single element
Then, in the electret device 2-5 configured as described above, when the charge of each of the
electret elements 231 to 23 nEndPage: 2 has the negative sign e, the charge of the plus sign ■ is
on the surface of the back electrode 21ys of the uppermost element 23n. A phenomenon such as
induced at a potential substantially equal to the potential obtained by summing the potentials of
single elements or dielectric (polarization) action is provided. In this case, laminating a plurality
of electret elements 231 to 23m in the same direction with each other, and electret material 22
of the lowermost element thereof. Laminating the conductive metal plate 24 on the side not only
causes the above-described dielectric effect, but as described later, the surface charge density as
the electret device 2-5 is well homogenized. , It is important that its stability is ensured. In the
above, the surface potential of each of the electret elements 231 to 23 n alone stacked in the
same direction is CEI) to (En), which are placed on the conductive metal plate 24 and the back
surface of the uppermost element Assuming that the surface potential induced to the electrode
21m is [Es:], Em =-. Alpha. ((Et..alpha.) + E1-En), where .alpha. It was confirmed that the value was
approximately in the range of 0.7 to 1.0. Incidentally, even in the case of using the one of the
positive sign n charging as the lowermost element 231 'as shown in FIG. FIG. 5 shows a specific
example in the case of obtaining the electret device 2-5 realized as described above. First, the
contacts of the switch SW connected to the back electrodes 211 to 21 n of the respective electret
elements 231 to 23 n Are sequentially closed so that the respective back electrodes 21 to 21 n
are set to the same potential as the ground and a zero charge state, and then the switch SW is
opened to provide an insulation state by opening the switch SW. Then, for example, while
maintaining a zero charge state tube using an insulation bottle set or the like, each of the electret
elements 23 □ to 23n is electret material 221 on the conductive metal plate 24 which is at the
same potential as the earth in this case. When the layers are stacked with the .about.22n side
facing, the dielectric action is generated substantially at one time as described above. When the
switch SW is closed again from the induced state, the potential immediately becomes zero. FIG. 6
shows an index of time-dependent change (leakage characteristic) of the charge induced on the
surface of the back electrode 210 of the top element as described above, and stability from the
initial state. Good stability is obtained with almost no change.
By the way, such stability is the electret device ILi! Are stacked on the conductive metal plate 24
with the electret materials 221 to JJn facing each other, q q! Since the surfaces of the r elements
231 to 23a are maintained, this is promoted by the fact that the electret surface is not exposed
so as to be exposed to air directly unlike the conventional case. In other words, each of the back
electrodes 211 to JJn and fc maintains the surface of each of the electret confectionery 231 to
JJn by the conductive metal plate 24, thereby making it a measure that is rich in moisture
resistance and advantageous in terms of temporal stability. As a result, it is possible to maintain
stability t-a as much as possible so as to achieve long life. As shown in FIGS. 7a and 7b, if the
surface of each of the electret elements 231 to 23 is provided with a corrugated unevenness, the
element surfaces directly contact with each other's back electrode and the conductive metal
plate. As the area is reduced, the handling can be further enhanced in stability. FIG. 8 shows an
example of measurement of the surface charge distribution of the electret apparatus 25 as
described above, wherein the electret material 221 ° 222 is deposited on the back gI electrodes
211 and 212 made of aluminum plates having an outer diameter of 60 mm. Electretized electret
elements 231 and 23. Are stacked together in the same direction as their electret material 221.
The top shape of the electret element 23 is obtained by placing the area shape on the conductive
metal plate 24b of the same root with 22x @ facing downward! The distribution of charge that is
dielectric on the surface of the back electrode 212 of FIG. That is, as can be seen from this figure,
it can be known that the surface charge density is uniform and hardly dispersed at all portions
EndPage: 3 unlike the conventional case. It is to be noted that a slight decrease near both ends in
the figure is due to the accuracy of the measuring instrument and is not essential. The flat
portion 22e at the center excluding the undulations 22b in the periphery in FIG. 8 is a nonelectretized portion provided for the reason of Production-E as in the conventional case, but
corresponds to the non-electretized portion. In the central portion of the surface of the back
electrode 212, no decrease is observed, and uniform charge density equivalent to that of the
peripheral portion can be obtained. That is, unlike the conventional case, even if there is a nonelectretized portion, the effective area for electrostatic action is not substantially reduced at all,
and in this respect the conversion efficiency as an electrostatic transducer is It is possible to
greatly improve various conversion characteristics including the above.
That is, the electret device 2-5 formed by stacking a plurality of electret elements 231 ° 23 n
stacked in the same direction as above with the electret material side on the conductive metal
plate 24 is simply Each electret element 23 is not limited to the phenomenon of inducing a
predetermined charge based on the electret charge of each element on the surface of the back
electrode 21m of the upper element. It became clear that it has an extremely excellent advantage
of the improvement of the stability brought about by the protective effect of ~ 23n and the
possible equalization of the surface charge density brought about by the surface charge
equalizing effect. It is next time. By the way, although the electret device 25 as described above
has various response surfaces as an electrostatic transducer, in particular for acoustic equipment,
in addition to the above-mentioned microphone and headphones, a pickup cartridge and a
speaker are provided. When applied to these audio devices, there are the following advantages.
That is, first of all, the effective capacity is reduced, the sound efficiency and efficiency are
increased, the voltage distribution is reduced, the distortion is reduced, and the stability is
improved. And the simplification of the structure to improve the accuracy and reduce the cost. In
particular, in the case of a microphone, the capacity is increased, and the noise level is lowered
by lowering the input impedance to the field effect type transistor for impedance conversion, and
the noise is further reduced. Can be implemented. 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, in principle, substantially
the same as the above-described electrostatic transducer can be used to switch on and off one
kind of electronic machine! −? Besides being applicable to I11 constant instruments (including
dosimeters), it is also applicable to digital instruments as a memory. In addition, it is applicable to
various electrostatic support devices (electrostatic printing machine, electrostatic generator,
electrostatic dust removal attachment, etc., and also applicable to medical equipment and high
impedance high voltage power supply) . And, it is needless to say that other applications as well
as the modification of the above-mentioned embodiment and the specific example are possible
without departing from the scope of the present invention. Therefore, according to the present
invention as described in detail above In particular, it is possible to provide an electret device
capable of improving the electret surface potential as well as the induction (N) form, as well as
making the charge density uniform, and greatly improving the stability.
4. Brief description of the drawings FIG. 1 and FIG. 2 are the principle structural explanatory
views of the conventional condenser microphone and condenser headphone unit, and FIG. 3 is
the surface charge of the conventional electret structure used in FIGS. Fig. 4 is an explanatory
view showing the density, Fig. 4 is an explanatory view showing an embodiment of the electret
apparatus according to the present invention, Fig. 5 is a view showing a concrete example of Fig.
4 and Fig. 6 is an electret fK shown in Fig. EndPage of the induced charge: A measurement chart
illustrating four time-dependent change characteristics, FIG. 7 shows another specific example of
FIG. 4, and FIG. 8 illustrates the surface charge density of the electret device of FIG. It is a
measurement figure. 211 to 21 n: back electrode, 221 to 223: electret material, 231 to jJn:
electret element, 24: conductive metal plate, 2-5: electret device. Applicants Attorney Attorney
Takehiko Suzue EndPage: 5
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