Electrostatic transducer

Abstract

An electrostatic transducer comprises a back plate electrode having a plurality of apertures therein and a diaphragm disposed on the back plate electrode. Each aperture has a counterbore tapering at its top portion which faces the diaphragm, and the top surface of the back plate electrode is formed with roughness.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an electrostatic transducer and particularly to an electrostatic transducer to transduce an ultrasonic wave to an electric signal or an electric signal to an ultrasonic wave.

2. Description of the Prior Art

Recently, ultrasonic waves have been used for a television receiver for controlling its ON/OFF switch of the power source, channel selection, sound volume control, etc., often referred to as the "remote control system." A transmitter to produce ultrasonic waves for use with such remote control systems is required to provide a broad band width, a flat frequency characteristic and a small consumption of power from the battery. Further, the frequency range of the transmitter may be selected, for example, between 30 KHz and 50 KHz. In the art, a ceramic type transducer has been used as a transmitter and a receiver mounted on the TV set for transducing into electric signals the ultrasonic waves. However, such ceramic type transducers do not provide the above requirements, satisfactorily. For example, the band width is not sufficiently broad, large power for driving the transmitter is required, and also the output level of the ultrasonic wave is not large enough to perform its required function.

Assume that an electrostatic transducer is used instead of the ceramic type transducer. As is well known, a conventional electrostatic transducer comprises a back plate and a diaphragm, which is spaced a predetermined distance from the back plate. However, since ultrasonic waves are very high frequency, for example 30 KHz to 50 KHz, if the area of the diaphragm is large, it is not possible to produce a sufficiently high frequency wave. Therefore, the area of the diaphragm is selected to be small. Generally, it will be considered that the diaphragm is firmly secured to the back plate in which there is provided a plurality of apertures. In this case, the effective area of the diaphragm corresponds to the total area of the apertures. Since each aperture is small, it is possible to produce high frequency waves. However, there is no conductive layer or conductive material in the aperture, so that a condenser is not formed between the diaphragm and the aperture. Therefore, large output is not obtained. Further, a ceramic or static receiver (microphone) mounted on the TV set has the above shortcoming.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a novel electrostatic transducer.

It is another object of this invention to provide a novel electrostatic transducer which will transduce an electric signal to an ultrasonic wave or vice versa in a novel manner.

It is another object of this invention to provide an electrostatic transducer in which a back plate provides a plurality of apertures each having a tapering counterbore at its end facing the diaphragm, in order to produce a large level output.

It is another object of this invention to provide an electrostatic transducer on which a back plate is provided with a roughened surface to obtain a relatively flat frequency characteristic.

Another object is to provide a transducer in which the power consumption is minimized, because it is an electrostatic type, by making the back plate from a resin and providing tapering openings which are easily constructed.

Another object is to provide a novel transducer which has a relatively low cost for assembling.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an electrostatic transducer embodying this invention;

FIG. 2 is a cross-sectional view, on a greatly enlarged scale, of a portion of the diaphragm assembly illustrated in FIG. 1;

FIG. 3 is a top plan view of the back plate assembly illustrated in FIG. 1;

FIG. 4 is a sectional view on line IV--IV in FIG. 3;

FIG. 5 is an isometric view partly in section, on a greatly enlarged scale, of a portion of the back plate assembly illustrated in FIGS. 1 and 4;

FIG. 5A is a fragmentary diagrammatic view of a portion of the diaphragm and the upper end of one aperture; and

FIG. 6 is a graph of the frequency characteristic of an electrostatic transducer in accordance with this invention.

DESCRIPTION OF A PREFERRED EMBODIMENT

Referring now to the drawings, FIG. 1 shows, in section, an electrostatic transducer in accordance with the invention. It comprises a back plate assembly 25, a support member 6 of insulating material, for example, resin, a diaphragm assembly 23 disposed on the back plate assembly 25, a metal housing 2 having an opening 2a, and an externally threaded annulus 7 to secure the diaphragm assembly 23, back plate assembly 25 and support member 6 in the housing 2.

As shown in FIG. 2, the diaphragm assembly 23 mainly comprises a flexible film 8 of polymer plastic material, for example, polyethylene terephthalate (Teflon), and a conductive layer 9 coated on the flexible film 8 by any suitable method, such, for example, as by a vacuum evaporation, so that a diaphragm 3 is constructed by the flexible film 8 and the conductive layer 9. The diaphragm assembly 23 further includes a metal ring 4 in order to confine the marginal edge of the diaphragm 3, so that a conductive adhesive material 10 may be provided between the ring 4 and the conductive layer 9. It is understood that the conductive layer 9 is electrically connected to the ring 4 through the adhesive material 10, and the diaphragm 3 is rigidly supported by the ring 4.

The disc like back plate assembly 25 as shown in FIG. 4 comprises an insulating member 5 and a conductive layer 12 coated on the member 5. The insulating member 5 is made of polymer plastic material, for example, acrylic acid resin, or polyphenyl oxide resin. As shown in FIGS. 1, 3 and 4, a plurality of apertures 11 in the insulating member 5 provide a sufficient air volume to establish a desirable resonant frequency. It will be noted that each aperture 11 provides a smooth counterbored tapering opening 11a at its top end, as shown in FIG. 5, to provide a large area which opposes the diaphragm 3. The angle .theta. of the taper of the counterbore 11a is selected between 10.degree. and 40.degree.. In practice, it is preferably selected at 30.degree.. The insulating member 5 is further provided as shown in FIG. 5 with a plurality of small irregularities 5a and 5b, or roughness surface on its top surface. The uneven or roughened surface is formed by a sandblast technique, or by grinding with an abrasive.

Then, the conductive layer 12, for example, aluminum, is coated on the entire top surface of the insulating member 5 including the surfaces of the counterbore openings 11a by a suitable technique, for example, by vacuum evaporation.

The support member 6 is made from a resin. A metallic member 13 is threaded on its outer surface to mate with the internally threaded central bore of the insulating member 5, and its top surface engages with the conductive layer 12. (FIG. 4).

An electric signal is applied between the housing 2 and the metallic member 13, when the transducer is used as a speaker. In this case, the diaphragm 3 is vibrated, and the produced sound wave (ultrasonic wave) originates from the opening 2a. Further, when the ultrasonic wave is applied to the diaphragm 3 through the opening 2a, an electric signal is created between the metallic member 13 and the member 2. In this case, the transducer is used as a microphone.

Now, according to this invention, the apertures 11 of the member 5 are provided with tapering openings 11a, each of which effective areas construct a condenser that causes the output level to increase. This will be understood from an inspection of FIG. 5A, where the condenser is indicated at 26, the condenser being formed by the conductive layers of the diaphragm and the back plate.

Further, since the back plate assembly provides a roughened surface, a flat frequency characteristic is established, because there are numerous spaces formed between the projections of the roughened surface and the diaphragm, and since acoustic resistance formed there, the output level is reduced, but the frequency characteristic is flat (that is to say "Q damped"). The reduction of the output level is compensated for by the large effective area of the condenser as described above.

As shown in FIG. 6, according to this invention, the level increases, and a flat response is established as indicated on curve 14. The curve 15 illustrates a frequency characteristic of a ceramic type transducer.

The embodiment of the back plate assembly 25 comprises the insulating member 5 and the conductive layer 12, but if a metallic material is employed instead of an insulating material for the member 5, it is not necessary to provide a conductive layer. It will be noted that the metal back plate is expensive.

If member 5 is made from a resin, the tapered opening 11a is easily made and roughened surface is also easily made.

It will be apparent to those skilled in the art that many modifications and variations may be effected without departing from the spirit and scope of the novel concepts of the present invention.

Claims

We claim:

1. An electrostatic transducer comprising:

a housing,

a planar base having a plurality of apertures therethrough, said apertures having smooth counterbores tapered between 10.degree. to 40.degree. providing outwardly flaring openings on one side and the remaining portions of said one side formed with numerous bumps,

an electrical conductive surface formed on said base in said smooth counterbores and said remaining portions, and

an electrically conductive diaphragm mounted in said housing in closely spaced position above said one side.

2. An electrostatic transducer according to claim 1 wherein said openings are flared at an angle of 30.degree. relative to said diaphragm.

3. An electrostatic transducer according to claim 1, in which a central metal stud extends through said planar base and in electrical contact with said electrical conductive surface and provides the electrical connection to said surface.

4. An electrostatic transducer comprising:

a housing,

a flexible diaphragm of a conductive material supported by said housing,

a planar back plate assembly mounted in said housing adjacent said diaphragm,

said back plate assembly having a plurality of apertures therein which apertures have smooth counterbored tapered openings on the side facing said diaphragm and the tapered openings are tapered at an angle between 10.degree. to 40.degree. relative to said diaphragm,

said back plate assembly provided with a roughened surface thereon facing said diaphragm; and

said back plate assembly comprises an insulating member of a resin and a conductive layer coated on said roughened surface and the smooth tapered surfaces of said counterbored openings to provide a sensitive transducer having a flat frequency response up to 50,000 hertz.

5. An electrostatic transducer according to claim 4 wherein said tapered openings are tapered at an angle of 30.degree. relative to said flexible diaphragm.