Viscous flow sensing using micro-beam arrays

Abstract

Thin, compliant fibers have been shown to provide a remarkably accurate means of detecting sound [Zhou et al., “Sensing fluctuating airflow with spider silk,” Proc. Natil. Acad. Sci., 201710559 (2017) ]. The present study extends these results by examining the forces due to air-borne sound on a periodic array of infinitely long and thin micro-beams having rectangular cross section. Results obtained using both the Finite Element Method and analytical solutions to Stokes’ equations are shown to be in excellent agreement. It is found that viscous forces are dominant when the width of the beams is less than 10 μm. Unlike typical MEMS resonators, which perform best in the absence of air, the dominance of viscous damping forces is desirable in directional acoustic flow sensors using these micro-beams. Furthermore, the frequency independent characteristic of these forces promises a flat response across a wide range of frequencies. It is predicted that smaller beams with wider gaps provide better sensitivity. For beams that are sufficiently thin, their thickness is found to have minimal influence on their performance.