A tunable threshold pressure sensor based on para- metric resonance of a microbeam subjected to electrostatic levitation is proposed. Parametric excitation can trigger a large amplitude vibration at twice the natural frequency if the mag- nitude of the driving force is large enough to overcome energy loss mechanisms in the system such as squeeze film damping. This causes a temporarily unstable response with a significant gain in oscillation amplitude over time until it is eventually capped by nonlinearities in the force or material or geometric properties. The instability divides the frequency region into two regions: distinct responses bounded by the system nonlinearity, and trivial responses with very low oscillation amplitudes. It is shown experimentally that the appearance of parametric resonance depends on the pressure, which influences the amount of energy loss from squeeze film damping. Therefore, the distinct difference in the vibration amplitude can be used to detect when the pressure passes a threshold level. The activation of parametric resonance also depends on the amplitude of the driving force (Vac). This voltage amplitude can be set to trigger parametric resonance when the pressure drops below a predetermined threshold. A reduced-order model is developed using the Euler- Bernoulli beam theory to elucidate the nonlinear dynamics of the system. The simulation results from the mathematical model are in good agreement with the experimental data. The advantages of the proposed sensor over pull-in based sensors are its reliability and improved resolution from a large signal-to-noise ratio
