JPS5928799A - Static converter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrostatic transducer having a vibrating membrane and a backrest, such as a capacitor microbon.

In this type of condenser microphone, the back electrode, which is provided after the diaphragm at a distance of 30 μm rL to 50 μm, forms a fixed and immovable electrode of the condenser microphone, and this electrode is usually a flat conductive disc. Consists of. This disk is provided with a number of perforations or slits to connect a small air chamber of very low height between the diaphragm and the back electrode to other acoustically active elements in the microphone casing. , or connected to an external sound field via a coupled acoustically active member, as required by a directional microphone. Such back electrodes are described, for example, in German Patent Application No. 1437420 and German Patent Application No. 2430068.

In an electrostatic transducer, for example a capacitor microphone, the capacitor capacity is essentially determined by the back electrode and the surface of the conductive diaphragm in front of the back electrode and their mutual distance. When sound is applied to the diaphragm of a capacitor microbond, only a part of the total capacitance is effective for signal transmission; the so-called parasitic capacitance that remains with respect to the total effective capacitance is practically This is caused by fixed parts that are structurally limited and causes deterioration of transmission rate, signal-to-noise ratio and non-linear distortion. Therefore, it is understood that it is necessary to keep the ratio of effective working capacitance to parasitic capacitance as large as possible.

The conventionally known back electrodes make it possible to keep the aforementioned ratios sufficiently large for diameters larger than 15 mm, thereby avoiding disadvantages such as deterioration of transmission, signal-to-noise ratio and non-linear distortion. effects remain within tolerable limits.

Even in the case of the Fundenaan microphone, the small size ratio of 1.0 mm causes the problem that the parasitic capacitance is too large compared to the working capacitance since the diameter of the diaphragm and the back electrode are 7.0 mm. Therefore, in the case of a back electrode with a conventional structure, for example, the electrode diameter is 5.8. m,
When the distance between the vibrating membrane and the back electrode is 40 μm, the parasitic capacitance is 3.
With 4 PF, the effective capacity is only 3 PF.

The object of the present invention is to have an effective working capacity of approximately 70 times the total capacity;
The purpose is to propose a back electrode shape whose viable capacity is approximately 30% of the total capacity. This object is achieved according to the invention by providing a notch around the periphery of the thin plate-like back electrode. The back electrode formed in this way has a total diameter of 5.8 mm due to the remaining star-shaped flange around the back electrode. vm
In this case, it has a parasitic capacitance of 1.3PF with respect to an effective working capacitance of 3PF. The ratio of effective working capacitance to parasitic capacitance is thereby again advantageous.

With a total diameter smaller than 11 schiff m1n, this new backplate shape increases the sensitivity of the condenser microphone by approximately 30% compared to the conventional shape.

A notch around the back electrode forms a rear passage for air in a small, low-height air chamber between the diaphragm and the back. The function of the perforations and slits in conventional electrodes is taken over by a cut-out part cooperating with a spacer ring between the back electrode and the diaphragm, and thus an acoustic friction part, a spring device or a mass body, for example. The combination of components that act in a directional manner, and the
A connection to the sound field occurs via a slit consisting of a spacer ring and a cutout.

A thin plate-shaped back electrode according to the present invention having a notch on the periphery;
For example, a star-shaped back electrode can be produced by punching the material, which is particularly simple and advantageous compared to the production of back electrodes using conventional construction methods. If the diameter of the back electrode is smaller than 77 hams, the problem arises in the known case of determining the diameter of the holes suitable for punching them in accordance with the thickness of the material of the sheet. In practice, expensive etching methods should be avoided, even if they are simply punching.

For example, the difficult punching of holes or slits in synthetic resins such as Teflon for back electrodes that can be processed with electrets can be easily punched out with cutouts provided around the thin plate, making it possible to create new types of Due to the shape of the electrodes, it is no longer necessary.

Since the parasitic capacitance acts only in the region of the periphery of the electrode, the size of the notch is selected so that the parasitic capacitance is completely reduced by the notched surface. This shows that the ratio of effective capacitance to parasitic capacitance is actually required to achieve high value condenser microphones with high sensitivity, good transmission, good signal-to-noise ratio and low non-linear distortion. Can take a value.

In other embodiments of the present invention, the back electrode formed by the notch may not only have a circular shape, but may also have a polygonal, oval or elliptical shape if necessary. However, for practical reasons, condenser microphones are generally manufactured in a circular shape.

However, for special cases of use, such as hearing aids for the hearing impaired, other shapes may also be advantageous. ! , or (゛＾Circular one can be considered.An electrostatic type transducer has a polarization voltage supplied to the transducer from the outside or a polarization voltage generated by the electret in the conversion process itself. For various embodiments which are known today, synthetic resins with metals and metallization in a manner known per se.
i':1. A back electrode is provided consisting of a material that acts as an electret.

DESCRIPTION OF EMBODIMENTS Examples of the present invention will be described in detail below with reference to the drawings.

1a to 1c show plan views of back plates 1, 2.3 with perforations according to the prior art. The perforations 4 are arranged according to a continuous circular pattern, whereas the slits 5 are arranged in a circular pattern. Through the perforations or slits, other acoustically active elements provided after the back electrode are connected to the low air chamber between the imaging element and the back electrode. The surface in the area of the periphery of the back electrode, which serves to form a parasitic capacitance, is shown as a dotted region 6. The annular capacitor formed by this annular surface and the diaphragm facing this surface and acting as an electrode has a capacitance value greater than half of the total capacitance generated from the diaphragm and the back electrode. .

FIG. 2 shows a cross-sectional view of a condenser microphone with a back electrode according to the invention. Inside a microphone caning 7 having a lower acoustic incidence amount a on the front surface, a photographic film 9 stretched on a diaphragm holder 8 is provided with a holding spring 12 along with an electrically insulating spacer ring 10 and a back electrode 11. The retaining spring 12 is supported by the bottom plate 13 when it is pressed against the scrap-like protrusion 7b of the casing.

The thin plate-like back electrode 11 is provided with a notch 11a around its periphery, and this notch is connected to the acoustically acting member of the air chamber 14 after the back electrode 14 through the slit 14a. allows for the combination of

FIG. 6 shows an advantageous embodiment of a circular back electrode 15 according to the invention with a star-shaped projection 16, which star-shaped projection is formed by a cutout 17 on the periphery of the electrode. has been done. The electrode surface which acts to create a parasitic capacitance is shown as a dotted area 18 on the protrusion 16.

This area is very small relative to the entire surface of the electrode, and the parasitic capacitance is larger than the total capacitance IA, thereby providing an optimal relationship between the effective and working capacitance. .

In Figures 4a to 4d, another form of a laminar back electrode according to the invention is shown. The peripheries 19, 20 of the embodiment according to FIGS. 4a and 4b exhibit circular and polygonal shapes, whereas the embodiment according to FIG. 4C has an oval periphery and the fourth
The embodiment according to figure d is constructed with an oval periphery. The notch portion clearly formed on the periphery of the electrode is 1!3a.

20a, 21a and 22a.

[Brief explanation of the drawing]

1a to 1C are plan views of conventional electrodes, FIG. 2 is a sectional view of a condenser microphone having a back electrode according to the present invention, FIG. 6 is a plan view of a circular back electrode according to the present invention, and FIG. 4a is a top view of a conventional electrode. Figure 4d shows a plan view of various back electrodes according to the invention. 1.2.3.11.15... Back electrode, 4... Perforation, 5
...Slit, 7...Microphone case song, 7
a...Acoustic incidence aperture, 7b...Scrap-like protrusion, 8...
- Vibration membrane holder, 9... Vibration membrane, 10... Spacer ring, 12... Holding spring, 13... Bottom plate, 14.
...Air chamber, 11a, 17, . 19a,
20a, 21a. 22a...Notch portion, 16...Protrusion portion.

Claims (1)

[Claims] 1. In an electrostatic transducer having a vibrating membrane and a back electrode,
A thin plate-like back electrode (11) has cutouts (11a, 17) around it.
, 19a, 20a, 21a. 22a). 2. The electrostatic transducer according to claim 1, wherein the cutout surface is 70 inches or less of the remaining electrode portion. 6. The surface of the back electrode formed by the notches (11a, 17, 19a, 20a, 21a, 22a) substantially takes the shape of a circle, an oval, an ellipse, or a regular polygon (no. 3 and 4) An electrostatic transducer according to claim 1. 4. The static electrode according to claim 1, wherein the back electrode (11) is made of a metal, a conductive synthetic resin with a metalized coating, an electret-processable material, or a metal coated with an electret-processable material. Electrical converter.