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Description 1, title of the invention
Electret condenser type transducer
The present invention relates to an electret condenser type transducer, and more particularly, to
an improvement in its sl and distortion characteristics. In general, transducers used in
headphones, etc. in microphones for acoustic equipment are transducers that convert electricity
(acoustic dielectricity) into machinery using changes in capacitance between a movable electrode
(a vibrating membrane) and a fixed electrode. It is Therefore, in the case of such a capacitor type
transducer like Kinki, an electret having the property that the electric charge previously charged
under a predetermined condition is semipermanently sustained is used in either the movable
electrode or the fixed electrode. So-called electret condenser type transducers have been
developed. By using an electret, it is possible to eliminate the need for a bias power supply, which
is advantageous for downsizing and cost reduction. As such an electret, a corona electret, a 'heat
electret, etc. are realized depending on the difference in the manufacturing method. However, it
is difficult to arbitrarily form the electret charge distribution on the surface, regardless of which
manufacturing method is used. As described later, the sensitivity as a transducer and 114? The
improvement of the property can not be easily illustrated, which means that the movable pole is
absorbed by the fixed pole and it can no longer operate normally as a transducer. EndPage: 1
fatality Social problems were apt to be The M1 diagram shows one rational configuration when
the electret condenser type transducer as described above is applied to a microphone. That is,
this is the case of a so-called back electret system using electrets on the fixed pole 11 side, and
the end E as shown in FIG. 2 shows the electret surface charge (voltage) distribution of the fixed
pole 11. IC! From the center to the center portion M, it has substantially flat characteristics
although it has unevenness. On the electret fixed pole II such as a coin, a movable pole 14 having
a predetermined gap by the spacer 12 and stretched over the support ring IS is paired, and the
mosquito movable pole 14 receives an external sound pressure. As the gap between the fixed
pole 11 and the fixed pole 11 is changed, the capacitance between the two poles changes. Then,
this JRization of the capacitance causes the field effect transistor FET1. If it is extracted from the
output end OUT as a good electric signal corresponding to the above sound pressure without
converting it through the impedance conversion circuit having the above, it becomes K.
However, in this case, the movable pole 14 is attracted to the electret fixed pole 11 @ by an
attractive force according to the Coulomb's law rather than shown in a broken state in a static
state where there is no sound pressure from the outside. The electrical signal extracted from the
power supply terminal OUT is always distorted on the half wave side, and the effective capacity is
limited due to the problem of adsorption, so that the effective capacity is limited and high
sensitivity can not be avoided. I can not do it. (T #), because the surface charge distribution of the
electret fixed 4ii 11 is uniform and the center portion of the movable pole 14 is largely bent
toward the electret fixed pole 11 from the point of support structure of the movable pole 14 This
is because the so-called static balance is in a state 11 that can not be avoided. In view of the
above, this point III has been developed to make the surface charge of the electret used for either
the fixed pole or the movable pole a center part is the peripheral part #) distribution. Therefore,
it is an object of the present invention to provide a very good null electret capacitor type
transducer in which the static balance can be made as correct as possible, and thus the distortion
characteristics and sensitivity can be improved. There is. An embodiment of the present invention
will now be described in detail with reference to the drawings. That is, FIG. 3 shows the case of
application to a back electret type microphone, in which movable poles 24 stretched on a
support ring 23 with a predetermined gap by a spacer 22 are provided on the electret fixed pole
21 in pairs. The back electrode portion of the electret solid phase pole 21 is connected to the
output end OUT through a field effect transistor FIT, and an impedance conversion circuit having
a ridge. Here, the electret fixed pole 21 has the electret surface charge distribution as shown in
FIG. . For example, as shown in the tis diagram to 1liT diagram, radial or lattice irregularities (but
the coarse portion is a small charge and the band portion is a large charge) are formed so as to
be smaller than the charge of. As above, 1. Since the electret condenser type transducer
configured is formed such that the surface charge distribution of the electret fixed pole 21 makes
the charge in the central portion smaller than the charge in the both ends, the movable in the
static state where there is no external sound pressure. The pole 24 is in a state where correct
static balance can be obtained without being attracted to the electret fixed pole 21 side.
As a result, even when external sound pressure is applied, the electric signal extracted at the
output terminal 0UTIC does not cause distortion on either half wave side, and has low distortion
and high fidelity. In addition, since the nine problems can be solved as much as possible when
the town moving pole 24 is adsorbed to the electret fixing 121, the effective capacity is not
limited as much as possible, EndPage: 2 can also contribute to the improvement of sensitivity.
The present invention is not limited to the above-described and illustrated nine actual travel
examples, and various modifications and applications can be made without departing from the
scope of the present invention. Therefore, as described above in detail, according to the present
invention, the static charge can be increased by making the surface charge of the electret used
for either the fixed pole or the movable pole a distribution in which the central portion is weaker
than the peripheral portion. It is possible to provide a very good electret capacitor type
transducer which can be correctly corrected and thereby improved in distortion characteristics
and sensitivity as shown in FIG.
4. Brief description of the drawings Fig. 1 is a principle block diagram showing a conventional
electret condenser type microphone, Fig. 2 is a curve showing the surface charge distribution of
electret fixed pole used in Fig. 1, Fig. 3 is this invention Fig. 4 is a curve diagram showing the
surface electric field distribution of the electret fixed pole used in Fig. 3, Fig. 5 to Fig. 7 showing
the case where the present invention is applied to a microphone as one embodiment of the
electret condenser type transducer according to The figure is a plan view and a sectional view
showing a specific example of the electret fixed pole used in FIG. 21 ... electret fixed pole, 22 ...
spacer, 23 ... support ring, 24 ... movable pole. Applicants Attorney Attorneys Suzue Takehiko 1
m 311 b 4 E E + ME 2 t s o 6 Figure off Figure = コ End 21EndPage: 3