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Description 1, title of the invention
Electret device
3. Detailed Description of the Invention The present invention relates to an electret device, and in
particular, to an electret 11IL form so that the electret surface charge density uniform-north can
be obtained. As is well known, Electret) has a property that H-charged electric charge lasts
semipermanently, and is widely used in various fields as an electrostatic transducer 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 assembly U is used as a fixed
electrode. Then, a diaphragm 16 made of metal thin film or the like stretched on the holding ring
15 via a spacer 14 such as an insulating material is provided as a movable electrode on the fixed
electrode made of the electret structure Yl. An electrostatic unit is configured. Thus, when the
diaphragm 16 of such an electrostatic unit is displaced by the external sound pressure, the
capacitance C) between the two electrodes & is changed, but from Q = (1: V The charge Q (given
in this case by the electret structure 13) will be-in the case of the foot, the voltage C% M between
the electrodes-changed. Therefore, by converting the change voltage (7) by impedance
conversion through a field effect transistor (FET) or the like and extracting it as a low impedance,
EndPage: 1 sound pressure is electrostatically converted into an electric signal. A condenser
microphone is realized. FIG. 2 also shows the case where the present invention is applied to a
condenser headphone unit, and in principle, an electric signal can be electrostatically converted
to sound pressure by performing the operation opposite to that of the above-mentioned
condenser microphone. It becomes possible. In this case, the diaphragm 16 as a movable pole
stretched in the holding ring 15 'is placed in the center, and the pair of electret structures 1.13 is
fixed on both sides via the spacers 14.14 on both sides of the diaphragm 16. By pairing as the
pole 25, a so-called push-pull type condenser headphone unit is realized. An electric signal is
given to each electrode of the headphone unit from the signal source (E,) through the
transformer σ) and the high resistances (R1) and (R 鵞). By the way, the electrostatic transducer
using the electret structure as the solid and rectangular poles 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 miniaturized as much as possible. In addition, it has the
advantage of being able to reduce the price accordingly.
However, the electret structure that is most important does not have the serious drawback that it
tends to adversely affect various characteristics as a transducer in that the surface charge density
is uneven, that is, the unevenness of the charge distribution is large. 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 酩 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 $ 12b at the center excluding the undulations 12 龜 at the periphery is a nonelectretized portion provided for manufacturing reasons etc., but the surface charge density of
the non-electretized portion 12b is the same as that at the periphery. There is also a problem that
the variation of the capacitance is greatly reduced significantly and the effective area for
electrostatic action is reduced accordingly, and in this case various factors including the
conversion efficiency as an electrostatic transducer The conversion characteristics of will be
further degraded. In addition, the conventional electret structure is exposed so that the surface
portion of the electret material 12 is exposed directly to the air, so that it has poor moisture
resistance and not only has problems in terms of economic stability, it also shortens its life Had a
serious drawback of Therefore, the present invention is in view of the above-described points,
and in particular, as an induction button type, electret surface charge density can be well
uniformed and stability can be greatly improved. It is an object of the present invention to
provide a bonded electret device. First, the electret structure used in the present invention will be
described in detail. That is, as shown in FIG. 4, the electret material 22 made of a polymer film
such as (PP), (TFg), (FFfP) or the like is applied to the back electrode 21 made of a conductive
metal base at the same potential as the ground. A conductive metal material or an organic
material having an area equal to or smaller than that of the electret element 23 formed by
mounting and electretizing is placed on the electret element 23 in an insulated state with the
earth. By placing it, an electret structure L ′ ′ configured so that the same sign charge as the
electret element 23 appears on the surface of the dielectric 24 is realized. Here, the dielectric 24
is generally different from that which only refers to an insulator, and as described above, a
generic term includes those including conductive metal materials and organic materials R (which
will be described later). Here, the organic material is a thermoplastic and thermosetting resin
material, a composite material combining these with another material, and a dielectric material
such as glass, and so-called insulation having a volume resistance of 10 13 Ω-1 or more. We
shall refer to materials generically.
EndPage: 2 Then, when the charge of the electret element 23 is the load code θ, the electret
structure 1j configured as described above is placed on the element 23 and the charge of the
positive / negative code Φ is on the back side of the nine dielectrics 24. Further, a phenomenon
of induction of a charge of negative sign e having the same sign charge as that of the element 23
is induced on the surface side, thus providing a dielectric (polarization) action. In this case, the
presence of the dielectric 24 not only merely causes the above-described dielectric effect, but as
described later, the uniformity of the surface charge density as the electret structure Lj is well
achieved, and the stability thereof is The point secured is 1i. In the above, when the surface
potential of the electret element 23 alone is [E0] and the table rkJt position induced on the
dielectric 24 mounted thereon is [E], the relation E = α · Eo is established. Ashi, here @) is also
called an induction coefficient, and it is confirmed that when the dielectric 24 is a metal, it is
approximately in the range of α = 0.6 to 0.99. The FIG. 5 shows a specific example of the
electret structure realized as described above in the case of i. First, with the switch (SW)
connected to the dielectric 24 closed, the dielectric 24 is grounded. After making the same
potential zero charge state, open the switch (SW) and put it in an isolated state. Then, for
example, when the dielectric 24 is placed on the surface of the electret element 23 while
maintaining the zero charge state using an insulating pin set or the like, the dielectric action
occurs as described above. In this case, when the dielectric 24 is a conductive metal material,
charges are instantaneously induced, but when it is an insulating material, it takes a certain time
(f ! + + Requires 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 has a time constant that is related to
the movement of electric charge as it gradually declines and disappears. FIG. 6 shows the case
where glass is used as the dielectric 24 as another specific example, and even if it is the glass
dielectric 24a, the induction coefficient α is about 0.83 (selector charge of the electret stack
about 700 v). On the other hand, it was confirmed that the dielectric charge of the glass dielectric
is approximately equal to that of the metal at about 580 V). In the glass dielectric 24a, the fall
time when the switch (8 W) is closed again from the dielectric state is relatively fast for
insulating materials such as kBB resin and slower for metallic materials, so the surface potential
is adjusted. It is advantageous if you need to
FIG. 7 shows one indicator of stability over time (leakage characteristics) of the electrical
property induced on the surface of the dielectric 24 as described above (leakage characteristic).
The same applies to resin systems, and good stability is obtained with almost no change from the
initial state. Further, in the case of an insulating material such as AB8 fat, for example, after
about 5 minutes from the initial state, the leakage is absorbed and good stability is obtained
thereafter. By the way, since such a stability holds the surface of the element 23 by placing the
dielectric 24 on the surface of the electret element 23, the stability of the electret surface is
different from the conventional case. It is promoted that it is done so that it will not be exposed if
exposed directly to the air. When the surface of the electret element 23 is protected by the p1
dielectric 24, it is possible to improve the moisture resistance and the stability over time, which
is advantageous in terms of stability over time, and thus prolong the life. Stability can be secured.
As shown in FIGS. 8 (a) and 8 (b), if the surface of the electret element 23 is provided with
wavelike irregularities, the area directly contacting and touching the dielectric 24 mounted
thereon is reduced. Therefore, it becomes possible to further enhance the stability from the
handling. EndPage: 3 FIG. 9 shows an example of measurement of the surface charge distribution
of the electret structure U as described above, in which the electret material 22a is deposited on
the back electrode 21a made of an aluminum plate having an outer diameter of 60 mm. On the
electret element 23a, a dielectric 24b having the same size and shape as the name and shape is
placed, and it is a distribution state of charges which are induced on the surface of the dielectric
24b. That is, as can be seen from this figure, it can be known that the surface charge density is
uniform and hardly scattered 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. Further, in FIG. 9, the central flat @ 22 e excluding the wavy unevenness s 12 b
in the periphery is a non-electretized portion provided for manufacturing reasons as in the
conventional case, but the dielectric corresponding to the non-electretized portion There is no
reduction in the central portion of the surface of the body 24b, and the same uniform charge
density as that of the surrounding portion can be obtained. In contrast to conventional cases, the
effective area for electrostatics is not substantially reduced at all even if there are nonelectretized parts), and, in this respect, as an electrostatic transducer It is possible to significantly
improve various conversion characteristics including the conversion efficiency of.
That is, the electret structure L1 formed by mounting the dielectric 24 on the electret element 23
according to the above does not only exhibit the phenomenon of inducing a predetermined
charge based on the electret charge on the surface of the dielectric 24; Improvement in the
stability provided by the protective effect of electret compound 23 by having the extremely
excellent advantage of as much as possible equalization of the surface charge density provided
by the surface charge uniforming effect. As soon as it became clear. Next, the junction structure
considered for the electret structure L1 as described above to fully exhibit its excellent
performance will be described. That is, FIG. 10 (a), (b) or FIG. a). As shown in (b), when the
electret element 23 is formed, the recessed portion 20 is formed on the electret material 22 side,
and the electret device is formed by adopting a bonding structure in which the dielectric 24 is
press-fitted into the 1 recessed portion 20. It is Thus, according to the joint structure of the
electret structure 25 as described above, the stabilization by the protection of the surface of the
electret element 23 as described above and the homogenization of the surface thereof can be
coupled to the frame. Since the electret element 23 itself can hold the junction with the dielectric
24 itself, it has an advantage that its structure can be simplified. In addition, once the electret
element 23 and the dielectric 24 are joined, there is an advantage that the stability can be further
promoted since the mechanical thermal positional relationship between them is not changed. In
addition, since the electret-structure joined in storage, transport, assembly, etc. can be handled as
a single unit, it is convenient in terms of parts management. In addition, the electret apparatus as
described above has various applications as an electrostatic transducer, but in particular for
audio equipment, the pickup cartridge is used in addition to the above-mentioned microphone
and headphone. When the speaker and the speaker are applied to these audio devices, there are
the following advantages. That is, first, low noise and high efficiency by increasing the effective
capacity, low distortion by uniform voltage distribution, high reliability by improving the stability,
and, as a whole, reduction of variation and yield The point is to improve the accuracy and
improve the cost by improving the structure and simplifying the structure. In particular, in the
case of a microphone, noise can be further reduced by increasing the capacitance and lowering
the noise level by lowering the input impedance to the field effect transistor for impedance
conversion. Also, in the case of headphones and speakers, it is possible to achieve so-called
transformerless conversion in which EndPage: 4 can be made unnecessary by increasing the
efficiency to increase the need for a transformer for feeding a cord.
The following fields can be considered as applications other than acoustic equipment. For
example, it can be applied to various electronic devices and footing devices (including radiation
dosimeters) as switches and sensors in substantially the same manner as the electrostatic
transducers described above in principle, and to digital devices as memories It is. In addition, it
can be applied to various electrostatic devices (electrostatic printing machine, electrostatic
generator, electrostatic dust removing device, scissors), and can also be applied 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 described above in detail, according to the
present invention, the electret structure joined so that the uniformity of the electret surface
charge density can be well illustrated and the stability can be significantly improved, particularly
as the a-conduction type Can be provided.
4. Brief description of the drawings. FIG. 1 and FIG. 2 are diagrams for explaining the basic
configuration of a conventional condenser 1 microphone and condenser headphone unit, and
FIG. 3 is a conventional electret assembly used in FIG. 1 and FIG. A measurement drawing
showing surface charge density, FIG. 4 is an explanatory view showing an example of an electret
structure used in the present invention, FIG. 5 is a drawing showing a specific example of FIG. 4
and FIG. The figure which shows the time-dependent change characteristic of the electric charge
induced in the dielectric by a figure, FIG. 8 is a figure which shows the other specific example of
FIG. 4, The surface charge of the electret structure of FIG. It is the disassembled perspective view
and sectional drawing which show one Example and another Example of this invention which
joins the measurement rod structure which illustrates a density. 21: back surface t11k, 22:
electret material wedge 23: electret element, 24: dielectric, L ": electret structure, 20: recess.
Outgoing agent Attorney Takeshi Suzue EndPage: 5 □> (a) Fig. (A) 10 (b) + III (b) End Page: 6
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