Micromechanical Bistable Flow Sensors

Bistable microstructures demonstrate enhanced responsiveness to external stimuli in the vicinity of the critical configurations that separate stable and unstable states. This makes these devices attractive candidates for implementation in sensors. Here, after a short review of existing bistability-based sensing approaches, we explore the applicability of electrostatically and electro thermally actuated micro beams as flow sensors. Double clamped curved ≈ 1000 μ m long, ≈ 2.8μ m wide and ≈50 μ m thick beams, deep reactive ion etched (DRIE) from a silicon on insulator (SOI) wafer were subject to an air flow in the direction perpendicular to the beam. We show theoretically and experimentally that both the flow-induced cooling of the Joule's heated structure and the drag force reduce the critical snap-through (ST) voltages. The absolute and relative measured sensitivities of the ST voltage of ≈ 1.9 Vsm ^-1 and ≈ 2.6 % sm ^-1 , respectively, are consistent with the Reduced Order (RO) Galerkin model predictions.