Update on Model of Hearing

The researchers, Reichenbach and Hudspeth, that hypothesized a mechanism for sound amplification of the inner ear that I reported on in this blog from last September, have now put their theory in practice in design of a microphone that eliminates feedback and provides a capacity for tremendous sensitivity.

Unidirectional mechanical amplification as a design principle for an active microphone

Tobias Reichenbach, A. J. Hudspeth

(Submitted on 14 Apr 2011)

Amplification underlies the operation of many biological and engineering systems. Simple electrical, optical, and mechanical amplifiers are reciprocal: the backward coupling of the output to the input equals the forward coupling of the input to the output. Unidirectional amplifiers that occur often in electrical and optical systems are special non-reciprocal devices in which the output does not couple back to the input even though the forward coupling persists. Here we propose a scheme for unidirectional mechanical amplification that we utilize to construct an active microphone. We show that amplification improves the microphone's threshold for detecting weak signals and that unidirectionality prevents distortion.