1983-07-07
1985-08-06
Rubinson, Gene Z.
29 2535, H04R 718
Patent
active
045337950
ABSTRACT:
An electroacoustic transducer, primarily in the form of a capacitive microphone, for incorporation into a semiconductor substrate. The vibrating element comprises a largely nontensioned diaphragm, such as an epitaxial layer formed on the semiconductor substrate, so as to greatly reduce its mechanical stiffness. The substrate is etched away in the desired area to define the diaphragm and form an acoustic cavity. A continuous array of microscopic holes is formed in the backplate to cut down the lateral flow of air in the gap between capacitor electrodes. Narrow gaps made possible by the hole array allow low voltage diaphragm biasing. In at least one embodiment, the acoustic input can be provided through the air hole array. An acoustic port may be added to alter the frequency response of the device, and a back closure provided to act as a rear acoustic cavity and an EMI shield.
REFERENCES:
patent: 3118022 (1964-01-01), Sessler et al.
patent: 4225755 (1980-09-01), Block
patent: 4321432 (1982-03-01), Matsutani
"On the Acoustical Resistance Due to Viscous Losses in the Air Gap of Electrostatic Transducers", Z. Skvor, Acustica, vol. 19, pp. 295-299, (1967/1968).
"Optimization of a Ridge Backplate for Electret Microphones", H. S. Madsen, Journal of the Acoustical Society of America, vol. 53, No. 6, pp. 1616-1619, (1973).
Baumhauer, Jr. John C.
Hershey Harold J.
Poteat Tommy L.
American Telephone and Telegraph
AT&T Bell Laboratories
Birnbaum Lester H.
Rubinson Gene Z.
Schroeder L. C.
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