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JPS5928799

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DESCRIPTION JPS5928799
[0001]
The present invention relates to electrostatic transducers, such as capacitor micro-bons, which
have a vibrating membrane and a back-end. In this type of condenser microphone, the back
electrode provided after the diaphragm at a distance of 30 μm L to 50 μm forms a stationary
and stationary electrode of the condenser microphone, which is usually a flat, conductive disc It
consists of If this disc is provided with a large number of perforations or slits, is it possible to
couple a very low profile, small air chamber between the vibrating membrane and the back pole
to other acoustically acting members in the microphone casing? Or connected to an external
sound field via a coupled acoustically acting member as required by a directional microphone.
Such a back electrode is described, for example, in German Patent Application Publication No. 14
37 420 and German Patent Application Publication No. 2430068. In an electrostatic converter,
for example a condenser microphone, the capacitance of the capacitor is substantially
determined by the back electrode and the face of the conductive diaphragm in front of the back
electrode, and their mutual distance. When sound is applied to the vibrating membrane of the
capacitor microbon, only a part of the total capacity is effective for the transmission of the signal;
the so-called parasitic capacitance remaining for the full capacity, effective capacitance is
substantially It is caused by fixed parts that are structurally limited, causing deterioration of
transmission rate, S / N ratio and nonlinear distortion. Therefore, it can be seen that it is
necessary to keep the ratio of the effective working capacity to the parasitic capacity as high as
possible. The conventionally known back electrodes make it possible to keep the aforementioned
proportions large enough when the diameter is larger than 15 、, so that the deterioration of
transmission degree, s / N ratio and nonlinear distortion Effects remain within the tolerable
limits. The small size ratio of 1 to 7 in the hundennan icloson causes the problem that the
diameter of the vibrating membrane and the back electrode is too large for the parasitic
capacitance relative to the working capacitance. Accordingly, in the case of the back electrode of
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the conventional structure, for example, the electrode diameter is 5.8. If m and the distance
between the vibrating membrane and the back electrode is 40 μm, the parasitic capacitance is
3.4 PF and the effective capacitance is only 3 PF. The object of the present invention is to
propose a form of back electrode in which the active working capacity is about 70% of the total
capacity and the living capacity is about 30% of the total capacity. This object is solved according
to the invention by providing notches around the sheet-like back electrode. The back electrode
thus formed has a total diameter of 5.8. During vm, it has a parasitic capacitance of 1.3 PF for an
effective working capacitance of 3 PF.
The ratio of effective working capacity to parasitic capacity is thereby again advantageous. With
an overall diameter smaller than 11 shm 1 n, the new back pole shape increases the sensitivity of
the condenser microphone, in particular, by about 30% over the conventional shape. The notch #
around the back electrode forms a back passage for air in the small air chamber with a low
height, between the mediation membrane and the back and heel. The function of the perforations
and slits in a conventional electrode is relayed by means of a notch which cooperates with the
spacer ring between the back electrode and the vibrating membrane, and thus an acoustic such
as, for example, an acoustic friction part, a spring device or a mass. As a result, the coupling of
the components acting as a function and the connection to the sound field, which is necessary for
the directional microphone, through the slit consisting of the spacer ring and the notch, occur. A
sheet-like back electrode according to the invention, for example a star-shaped back electrode,
according to the invention, having notches in the periphery, can be manufactured particularly
advantageously in a simple manner compared to the production of the back electrode of
conventional construction methods by punching out the material. . If the diameter of the back
pole is smaller than 77 cm, the problem arises that, in the known case, the diameter of the hole
suitable for the drilling is determined in accordance with the thickness of the material of the
sheet. It is necessary to avoid etching methods which are substantially more expensive than
punching. For example, difficult punching of holes or slits in a synthetic resin such as Teflon for
backplate that can be electretized can easily punch out the notch provided on the periphery of
the thin plate, so a new kind of It is no longer necessary depending on the shape of the electrode.
Since the parasitic capacitance only acts in the area of the periphery of the electrode, the size of
the notch is chosen so that the parasitic capacitance is significantly reduced by the notched
surface. As a result, the ratio of effective capacity to parasitic capacity is actually required to
realize a high-value capacitor microphone that results in high sensitivity, good transmission,
good s / N ratio, and low nonlinear distortion. It can take a value. In another embodiment of the
present invention, the ridges of the back electrode formed by the notches may not only be in the
form of a circle, but may be polygonal, oval or elliptical as required. However, for practical
reasons, it is generally round when manufacturing condenser microphones. However, special
forms such as, for example, the use of hearing aids for deaf people (other forms are also
advantageous for heavy use cases and therefore polygons, oval shapes as the form of the back of
condenser microphones and thus of the diaphragm). ! You can think of a circular thing.
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For the embodiments known today of a variety of electrostatic transducers, the polarization
voltage supplied to the converter from the outside still has the polarization voltage generated by
the electret in the converter itself. Synthetic resin with metal, metallized bite in a manner known
per se! ン’ji’:1. A back electrode is provided which is made of a material which acts on
the electret. Description of Embodiments Embodiments of the present invention will be described
in detail below with reference to the drawings. 1a to 1c show plan views of the back pole 1, 2.3
with perforations according to the prior art. The perforations 4 are arranged in accordance with
a certain number of turns, whereas the slits 5 are arranged in a circle. The perforated rod is
connected by a slit to the lower air chamber between the imaging element and the back
electrode. A surface which is in the region of the periphery of the back pole and which serves to
form parasitic capacitances is shown as a dotted area 6. An annular capacitor formed by this
annular surface and the vibrating membrane acting as an electrode facing this surface has a
capacitance value larger than half of the total capacity generated by the vibrating membrane and
the back electrode. . FIG. 2 shows a cross-sectional view of a condenser microphone with a back
pole according to the invention. The inside of the microphone casing 7 having the sound incident
amount lower a on the front surface, the moving film 9 stretched on the vibrating film holder 8
together with the spacer ring 10 and the back electrode 11 which are electrically insulated In
this case, the holding spring 12 is supported on the bottom plate 13 by being pressed against the
scrap-like protrusion 7b of the casing. The thin plate-like back electrode 11 is provided with a
notch 11a in the bath around it, and this notch is to the acoustical member of the air chamber 14
after the back electrode 14 through the slit 14a. Allow for the combination of FIG. 6 shows an
advantageous embodiment of a circular back electrode 15 according to the invention with a starshaped projection 16 which is formed by a notch 17 around the electrode. It is done. The
electrode surfaces which serve to form parasitic capacitances are shown as dotted areas 18 on
the protrusions 16. This region is very small with respect to the entire surface of the electrode,
and the parasitic capacitance is in the order of IA of the total capacitance, whereby an optimum
relationship of effective capacitance to the "parasitic capacitance" is obtained. . In FIGS. 4a to 4d,
other forms of laminated back electrodes according to the invention are shown. The edges 19, 20
of the embodiment according to FIGS. 4a and 4b show a circle and a polygon, while the
embodiment according to measure 4C is an oval edge and the embodiment according to FIG. 4d
is an oval edge. It is configured.
The notch formed cleanly on the periphery of the electrode is 1! 3a。 20a, 21a and 22a.
[0002]
Brief description of the drawings
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[0003]
1a to 1c are plan views of conventional electrodes, FIG. 2 is a cross-sectional view of a condenser
microphone having a back pole according to the present invention, and FIG. 6 is a plan view of a
round back pole according to the present invention and FIG. Force et al. 4d shows a plan view of
various back poles according to the invention.
1.2.3.1.15 · · · · · · · · · · · · · · · · · 5 · · Slit · 7 · · · microphone Cased, 7a · · · sound incident opening, 7b
· · · scrap 8: vibrating membrane holder 9: vibrating membrane 10: spacer ring 12: holding spring
13: base plate 14: air chamber 11a, 17 . 19a, 20a, 21a. 22a ... notched part, 16 ... protruding
part.
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