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Miniature Self-Powered Microphone

IP.com Disclosure Number: IPCOM000120102D
Original Publication Date: 1991-Mar-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 2 page(s) / 51K

Publishing Venue

IBM

Related People

Hodgson, RT: AUTHOR

Abstract

Disclosed is a microphone requiring no electrical connections nor power at the microphone end of a fiber-optic cable.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 73% of the total text.

Miniature Self-Powered Microphone

      Disclosed is a microphone requiring no electrical
connections nor power at the microphone end of a fiber-optic cable.

      Strong, thin membranes can be formed using anisotropic etching
of silicon which stops at either < 111 > planes or at a heavily boron
doped surface.  We use such a membrane 1, supported like a drumhead
by the surrounding unetched silicon 2 which has been protected by
normal lithographic techniques, to form the microphone shown in Fig.
1.  A single mode laser 3 injects power into one end 4 of a single
mode optical fiber 5.  The other end 6 of the fiber is coated to give
the same reflectivity as the membrane 1, (which, due to the
interference between the light reflected from each surface of the
membrane, can be made to have a reflectivity from 0% to 65% depending
on the thickness) the reflectivity from the interferometer formed by
the end of the fiber 6 and the membrane 1 will vary from 0 to
93% as the membrane vibrates under the influence of an impinging
sound wave.

      The distance of the membrane from the end of the fiber can be
precisely determined by the lithography which produces the mask for
the anisotropic etching of the silicon.  The fiber diameter is
usually accurate to within 1 micron and the lithography can be
designed to within 1 micron and is reproducible to great accuracy
once the lithographic mask is made.  Silicon wafers are flat to
within 1 micron over the entire surface, and t...