High sensitivity Polyvinylidene Fluoride (PVDF) microphone based on area ratio amplification and minimal capacitance

Abstract

This paper presents an inexpensive high-sensitivity microphone based on polyvinylidene fluoride (PVDF) film. High sensitivity is achieved through pressure amplification created by the area ratio between the rigid surface exposed to acoustic waves and a crosshair-shaped PVDF film, in combination with the reduced capacitance created by a similarly shaped top electrode. The crosshair shape is obtained through simple chemical etching from commercial PVDF film. Finite-element simulations including static structure analysis, modal analysis, and harmonic response are performed to design the microphone. Peak coalescence of the first three adjacent natural frequencies caused by the structure damping ratio is observed. Static and dynamic stress analyses ensure that the design meets the mechanical constraints imposed by PVDF. A plane wave tube experiment and signal conditioning electronics are developed. Measurements include benchmarking against a commercial microphone and show that the PVDF microphone exhibits a linear response up to a sound pressure level of 140 dB and overall fluctuations of less than ±4 dB over the frequency range of 10 to 20000 Hz. The sensitivity of the microphone alone, without a conditioning circuit, is measured as 27.8 μV/Pa, which is 3.01 times the sensitivity of commercial PVDF film operating in 3-3 mode. This sensitivity gain is close to the physical area ratio of 3.2. We experimentally characterize the directivity of the sensor and measure a decay of -10.5 dB at ±90° from the microphone's axis.