Design and Characterization of an Optical Feedback-Controlled Microphone for Aeroacoustics Research

An optical feedback-controlled microphone was designed and tested for potential use in phased ``beam-forming'' arrays used in aeroacoustics research. Optical sensing was employed as a means for measuring center displacement of a stretched thin membrane due to incident acoustic pressure. The membrane was constructed of PVDF which exhibits piezoelectric properties allowing actuation of the membrane in a feedback system. The latter was used to actively modify sensor parameters, most notably membrane stiffness, resonant frequency, and damping. Testing of a prototype microphone was performed using a plane wave tube calibrator. The results demonstrate that feedback control is an effective method for improving the microphone's transient response, as well as for ``self-tuning'' and matching of microphone parameters in sensing arrays.