In this study, we propose a bionic auditory membrane (BAM) which realizes the wide-range frequency selectivity by non-uniform thick structure. BAM developed here is an acoustic sensor consisting of flexible bridges that vibrate by applying acoustic wave. BAM works as frequency analyzer via resonance of vibration; the eigen frequencies of bridges are changed by varying the dimensions such as the length and the thickness. To overcome difficulties in fabricating three-dimensional structures by conventional microfabrication, a novel method was developed using a grayscale lithography and a negative photoresist. The thicknesses of bridges are varied by different tones of grayscale patterns in a photomask. BAM consisting of 64 bridges with various thicknesses from 6.6 μm to 49 μm is successfully fabricated and integrated in 2.0 mm × 30 mm area by single photolithography process. The eigen frequencies of the vibration were measured in air. The results revealed that the range of the frequency selectivity is from 16.7 kHz to 502 kHz, which is drastically widened by the non-uniform thick bridges compared with the uniform ones.

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