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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or
financial decisions, should not be based on machine-translation output.
The present invention relates to an electret apparatus, and in particular, a derivative (N) type of
an electret apparatus joined in such a way that equalization of electret surface charge density etc.
can be performed. About. As is well known, electrets have the property that a charged electric
charge lasts semipermanently, and are widely used in various fields as electrostatic 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
13 is used as a fixed electrode. Then, a diaphragm, such as a metal thin film, stretched on the
holding ring 15 over the fixed electrode made of the electret structure Ll via the spacer 14 such
as an insulating material is opposed as a movable element, thereby causing electrostatic A unit is
configured. Thus, when the diaphragm 16 of such an electrostatic unit is displaced by the
external sound pressure, the electrostatic WtC between the two electrodes is changed, but the
charge Q (in this case, the electret from Q = CV) If the structure 13) is fixed, the overpressure 11
between the two electrodes will be changed. Therefore, by converting the impedance through the
change voltage vt-field effect transistor FET or the like and extracting it as a low impedance, a
ConEndPage: 1 denser microphone is realized which converts the sound pressure into an electric
signal electrostatically. Ru. 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 at the center in this case, and a pair of sweepers V, I)
and V ') L'y) i 413 are provided on both sides of the sweeper 14.14. , Yoka, Oka 2. By arranging
them in opposite directions, the radphone unit is realized as a so-called gush-shaped capacitor.
An electric signal is supplied to each electrode of the headphone unit through the signal source E,
the transformer T, and the high resistance R1 ° R2. By the way, since the electrostatic
transducer using the electret structure as the fixed pole as described above is different from that
of the usual one, it requires a DC power source for polarization or biasing, so the structure is
simplified and the size is reduced as much as possible. It has the advantage that it is possible and,
in turn, can be made less expensive.
However, the electret structure, which is the least stable, has a serious disadvantage that it tends
to adversely affect various characteristics as a transducer in that the variation of the surface
charge distribution, that is, the unevenness of the charge distribution is large. FIG. 3 shows an
example of measurement of the surface charge distribution of the conventional electret structure,
in which the electret material 12 is deposited on the back electrode 1 made of an aluminum plate
with an outer diameter of 60 mm and electretized. As you can see from the figure, it is well
known that there is a very large variation of several hundred. In the same figure, the undulations
12 m around the periphery. There is a non-electretized portion provided for manufacturing
reasons etc. in the central Chigaki portion 12b except for the above, but the surface charge
density of the non-electretized portion 12b is extremely lowered much larger than that of the
periphery. The problem is that the effective area given to the static action is reduced accordingly,
and in this case, various conversion characteristics including the conversion efficiency as an
electrostatic transducer will be further degraded as K. In addition, the conventional electret
structure is exposed so that the surface portion of the electret material 12 is exposed to air
directly, so it has poor moisture resistance and not only has problems in terms of temporal
stability, but the life is shortened. It had a serious drawback of Therefore, the present invention
has been made in view of the above points, and in particular, it is possible to achieve good
uniformity of electret surface charge density as a derivative (N) type, and to achieve a significant
improvement in stability. It is an object of the present invention to provide an 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, TFE, FEP, etc. is
adhered to the back electrode 21 made of a conductive metal base at the same potential as the
earth to make it electretized. By placing a dielectric 24 made of a conductive metal material or an
organic material equal in area or smaller than that of the electret element 23 formed by This is
an implementation of an electret structure L1 configured such that charge of the same sign as
that of the electret element 23 appears on the surface of the dielectric 24. Here, the term
"derivative 24" as used herein generally refers to a material that includes a conductive metal
material and an organic material (which will be described later), as described above.
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 socalled insulation having a volume resistance of 10 120 -α or more. We shall refer to materials
generically. And, the electret configured as described above. EndPage: When the charge of the
electret element 23 has the negative sign e, the structure of the end page 25 has the charge of
the positive sign e on the back side of the dielectric 24 mounted on the element 23 and the same
as the element 23 on the front side. The tb dielectric (polarization) effect is brought about as a
phenomenon in which the charge of the negative sign θ, which is the sign charge, is induced. In
this case, the presence of the dielectric 24 not only causes the dielectric effect as described
above, but as will be described later, the surface charge density as the electret structure 25 is
well homogenized, and its stability is good. It is important that it is secured. In the above
description, when the surface potential of the electret element 23 alone is [Eo] and the surface
potential Th [: E, induced on the dielectric 24 mounted thereon is E, = E · Eo In the relationship, it
is confirmed that (in) is an induction coefficient, and it is approximately within the range of α =
0.6 to 0.99 when the dielectric 24 is metal. It was done. FIG. 5 shows a specific example in the
case of obtaining the electret structures realized as described above. First, the switch SW
connected to the dielectric 24 is closed and the dielectric 24 has the same potential as the
ground. That is, after the zero charge state is established, the switch SW is opened to provide an
insulation state from the ground. Then, if the dielectric 24 is placed on the surface of the electret
element 23 while keeping zero charge state by using, for example, 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 instantaneously, but when the dielectric 24 is an
insulating material, it takes a certain time (for example, until the induced charge reaches a
certain voltage) It takes about 30 minutes). Also, assuming that the switch SW is closed again
from such an induced state, the charge disappears so that the dielectric 24 immediately becomes
zero and becomes a potential when the dielectric 24 is a metal, but in the case of an insulating
material (but in the case of a fluorine resin system) Is equivalent to the case of metal) with a time
constant which is related to the movement of charge so as to gradually decrease and disappear.
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 (for electret element
charge of about 700 V). It has been confirmed that the d electric charge of the glass dielectric is
approximately equal to that of the metal at about 580 v).
It is necessary to adjust the surface potential because the decrease time of the glass dielectric
24a when the switch SW is closed again from the dielectric state is relatively quicker than Ag3
[insulation material such as oil, etc. and slower than metal material. It is advantageous when
there is. FIG. 7 shows one indicator of the time-dependent change (leakage characteristic) of the
charge induced on the surface of the dielectric 24 as described above. In the same case, good
stability is obtained with almost no change from the initial state. Further, b is, for example, an
insulating material such as an ABS resin, and after about 5 minutes from the initial state, the leak
is settled and good stability is obtained thereafter. By the way, since such a stability protects the
surface of the element 23 by placing the acid acid body 24 on the surface of the electret element
23, the electret surface is different from the conventional case. They are encouraged by the fact
that they are not exposed to direct exposure to the air. Tsushi, it is possible to protect the surface
of the electret g-core 23 by the dielectric 24 and to be excellent in moisture resistance and
therefore more advantageous in terms of temporal stability, and thus to extend 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 wavy irregularities, the area directly in contact with the dielectric 24 mounted
thereon is reduced. , You will be able to further enrich the stability from the handling. FIG. 9
shows an example of measurement of the surface charge distribution of the above-mentioned
more electret, structure UEndPage: 3, in which an electret material 22m is deposited on a back
electrode 21h made of an aluminum plate having an outer diameter of 60 mm. A dielectric 24b
having the same area and shape as that of the electret element 23a is placed on the electret
element 23a, and the charge is distributed 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
dispersed in all parts unlike the conventional case. The slight decrease near both ends in the
figure is due to the accuracy of the measuring instrument and is not essential. The flat portion
22c at the center excluding the undulations 22b'z at the periphery in FIG. 9 is a non-electretized
portion provided for the reason of manufacturing t- as in the conventional case, There is no
reduction in the central portion of the surface of the dielectric 24b corresponding to the portion,
and uniform charge density can be obtained at the same sign as that of the peripheral portion.
In contrast to the conventional combination, the effective area for electrostatics is not
substantially reduced by a small amount of dust even if there are non-electretized parts, and in
this respect, as an electrostatic transducer It is possible to greatly improve various conversion
characteristics including conversion efficiency. That is, the electret and U-structure formed by
placing the dielectric 2.4t on the electret element 23 by 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 alone. , Having an extremely excellent advantage of improving f-type property
brought about by the storage effect of the electret element 23 by the dielectric 24 and as much
as possible equalization of the surface charge density brought about by the surface charge
equalizing effect It is up to one to become clear. Next, the electret assembly L as described above!
Describes the junction structure considered to fully demonstrate its superior performance. That
is, as shown in FIGS. 10A and 10B, when the electret element 23 is formed, integral or separate
projections 201 and 202 are formed on the peripheral side of the electret material 22, and the
projections 201 ° 202 are formed. On the other hand, the electret device is formed by adopting
a bonding structure in which a through hole 241.242 formed in the peripheral portion of the
dielectric 24 is inserted and the head is crushed and fixed. The electret structure L as described
above! According to the joint structure of the present invention, it is possible to surely achieve
stabilization as well as equalization of the surface potential by holding the surface of the electret
element 23 as described above, and the projections 201 and 202 are integrally formed. In this
case, since the electret element 23 itself can hold the entire junction with the dielectric 24, it has
an advantage that the structure can be simplified. In addition, once the electret element 23 and
the dielectric 24 are joined, the mechanical positional relationship between the electret element
23 and the dielectric 24 is not changed, which further promotes stability. Furthermore, since the
electret assembly L "joined in storage, transportation 9 assembly, etc. can be treated as a single
item, it is convenient in terms of parts management. As shown in FIGS. 11 (a) and 11 (b), the
same effect as described above can be obtained by using a joint structure in which screws 208
and 204 are used instead of the above projections 201 and 202 to fix them. Can play. In this
case, 243 and 244 are countersunk holes, and 231 and 232 are screw holes.
By the way, although the electret apparatus as described above has various application surfaces
tM as an electrostatic transducer, in particular for acoustic equipment, in addition to the abovementioned microphone and headphones, a picker, an f cartridge, a di and a speaker When
applied to these audio devices, there are the following advantages. That is, first, low noise and
high efficiency by the increase of effective capacity, low distortion by uniform voltage
distribution, high reliability by the improvement of stability, and overall reduction of variation 9
improvement of yield, The point is to improve the accuracy by simplifying the structure and to
reduce the EndPage: 4 strike. In particular, in the case of a microphone, noise can be further
reduced by increasing the capacitance and lowering the input impedance to the impedance
converting field effect transistor to lower the noise level. 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, the electrostatic form
described above. It can be applied to switches, sensors, and various ladder devices (including
radiation dosimeters) in a substantially similar manner to Lance Nose in principle, and to digital
devices as memories i. In addition, it is applicable to various electrostatic devices (electrostatic
printer, electrostatic generator, electrostatic dust remover, etc.) as well as oJNd, and it is also
applicable to consumer equipment and high impedance high voltage power supply . And, it goes
without saying that other applications and modifications of the above-described embodiment and
specific examples are possible without departing from the scope of the present invention.
Therefore, as described above, according to the present invention, it is possible to particularly
show good uniformity of the surface charge density of the electret (in the form of the N2 type, as
well as an electret device joined so as to greatly improve the stability Can be provided.
4. Brief description of the drawings. FIG. 1 and FIG. 2 illustrate the basic configuration of a
conventional condenser lycrophone and condenser headphone unit, and FIG. 3 is a conventional
electret structure used in FIG. 1 and FIG. Fig. 4 is a diagram showing an example of the electret
structure used in the present invention, Fig. 5 is a diagram showing a specific example of Fig. 4
and Fig. 7 is a diagram showing a specific example of Fig. The measurement chart showing the
time-dependent change characteristics of the charge induced in the dielectric in FIG. 4, FIG. 8
shows another specific example of FIG. 4, and FIG. 9 shows the surface charge density of the
electret structure of FIG. FIG. 10 and FIG. 11 are an exploded perspective view and a cross
sectional view showing an embodiment and another embodiment of the present invention formed
by joining the electret structure of FIG. 21: back electrode, 22: electret material, 23: electret
element, 24: nfr, body, 25: panelette structure: 201, 202: projection, 203, 204 Screw. Applicant
Agent Attorney Takeshi Suzue EndPage: 5-1 (a) W (b) 11 Figure (b) EndPage: 7 Warning:
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