Influence of mechanical coupling by SiO₂ membrane on the frequency selectivity of microfabricated beam arrays for artificial basilar membranes

Two types of microfabricated acoustic transducers—the resonator array of isolated beams (RAIB) and the resonator array of coupled beams (RACB)—were built using MEMS technology. The frequency selectivity of the two types of transducers was qualitatively compared using the transfer functions measured with a scanning laser Doppler vibrometer (SLDV). Each RAIB beam operated as a band-pass filter in the proximity to the corresponding resonance frequency, thereby showing the frequency-selective feature of the basilar membrane (BM). However, the frequency selectivity of RACB was poor because the SiO₂ membrane, which mechanically coupled the neighboring beams, suppressed the independent response of each beam. The influence of the mechanical coupling of the SiO₂ membrane was simulated using lumped parametric models. Simulation results showed that the coupling stiffness of the SiO₂ membrane may significantly undermine the frequency selectivity of the resonator array. The comparison of the frequency-selective performance revealed that RAIB is a better option than RACB for mimicking the tonotopy of BM.