Electrical transmission or interconnection systems – Electrets
Patent
1996-03-11
1998-05-26
Shoop, Jr., William M.
Electrical transmission or interconnection systems
Electrets
295921, 29886, 367170, 381191, G11C 1302
Patent
active
057570906
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a folded dielectric film element acting as an energy converter and to a procedure for manufacturing such a film element. This type of film can be used for the generation, measurement and damping of sound. Broadly speaking, the invention is concerned with the conversion of electric energy into mechanical energy or conversion of mechanical energy into electric energy. A film like this is presented e.g. in U.S. Pat. No. 4,654,546.
To permit an electric field to be utilized in this type of energy converter, the air gaps used must be very small to achieve a sufficient field strength. However, this means that the play of the converter is reduced.
SUMMARY OF THE INVENTION
The object of the present invention is to produce a new solution for increasing the amount of air or medium replaced by the converter by using a folded dielectric film and placing electrodes in the folds.
The solution of the invention makes it possible to utilize increased air motion amounts while simultaneously producing large air pressures, e.g. sound pressures in acoustic applications.
The invention also concerns a procedure for the manufacture of converter elements, in which a folded element is first compressed into a tight pack, causing the corners of the folds to be pressed into sharp edges. After this, by stretching the element, the folds assume their natural curvature, resembling a low-gradient letter S, which keeps the folds in a stable position when subjected to the forces of the electric field.
Elements manufactured according to the invention allow a high acoustic power to be reached. In noise damping applications, the elements function in a multi-effect manner, damping the noise passively while the air is flowing in the gaps between the folds. The electric energy generated by the sound waves is converted into heat in the resistances of the electrodes. A measured signal corresponding to the sound pressure can be fed in opposite phase to another element. The two first-mentioned priniciples damp sound waves of any frequency coming from any direction, and in the case of low frequencies, also those incident at an oblique angle. The sound damping capacity of the element is 20 dB at best.
BRIEF DESCRIPTION OF THE DRAWINGS
In the following, the invention is described by the aid of an example by referring to the attached drawings, in which
FIGS. 1a and 1b present a folded dielectric film according to the invention.
FIGS. 2a-2c show another folded dielectric film according to the invention.
FIGS. 3a-3c show a third folded dielectric film according to the invention.
FIG. 4a presents a variable-gain amplifier circuit and FIG. 4b a curved film.
FIGS. 5a-5c illustrate a wall structure and its damping capacity.
FIGS. 6 and 7 present applications of circuits connected according to the invention.
FIG. 8 illustrates an electret film with a metal plating on one side.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1a presents an embodiment of the invention, showing a densely folded (folds L) dielectric film element comprised of two film layers 1, 2 placed one upon the other. In FIG. 1, the electric field is alternately strengthened and weakened in successive folds L by means of a control voltage (signal). In the folded element, the film, which is charged to charge Q, is coated in the successive folds with electrode layers K such that control electrodes of opposite polarity are placed on opposite sides of the fold L. Such a film element can be manufactured e.g. from a permanently charged electret film or a three-layer film in which the middle layer consists of semiconducting material connected to a d.c. potential producing a charge Q. A control signal .DELTA. (for example, an a.c. voltage) is applied on one side of the layer K and a control signal -.DELTA. (for example an a.c. voltage) is applied in opposite phase on the opposite side of the layer K. FIG. 1b illustrates the structure of the control electrodes K, which is comprised, for example, of an AC voltage electrode (.DELTA.) and an
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Kaplan Jonathan S.
Shoop Jr. William M.
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