Field-effect transistor-based transduction and acoustic receiving transducers

Abstract

Microphones and hydrophones are representative acoustic receiving transducers. To properly receive sound waves, a receiver must be smaller than the wavelength of the target sound. The target wave characteristics do not impose any lower limits on the size of microphones. When the performance of a smaller microphone or hydrophone will be satisfactory, users generally choose a smaller device since smaller receivers are easier to install and use. However, miniaturized microphones are less sensitive at low frequencies and conventional infrasound detectors are considerably larger than those for higher frequency sounds. These trends in receiver size can be explained by considering the transduction characteristics of microphones and hydrophones. We describe two transduction mechanisms based on field-effect transistors (FET) and use them to develop new microphones and hydrophones. We used theoretical analysis and experiments to show that the sensitivity and frequency response functions of FET-based microphones and hydrophones are size-independent. These results suggest that more sensitive micro-machined microphones and hydrophones, with better frequency response functions, may be available for use in the near future. [Work supported by the Institute of Civil Military Technology Cooperation Center (16-CM-SS-18).]