DSMC investigation of the unsteady dynamics of a squeeze film beneath a microstructure undergoing large oscillations

Abstract

This dissertation investigates the behavior of a gas film in the vicinity of a micro RF switch. A two and three dimensional numerical study of the flow field is performed around a micro-cantilever beam that oscillates harmonically between an equilibrium position and the fixed substrate underneath. Unlike previous work in literature, the micro-structures undergo large displacements throughout the film gap thickness and the behavior of the gas film along with its impact on the moving micro-structure (ie. force exerted by gas on the micro-structure) are discussed. Since the gas film thickness is of the order of few microns (i.e. 0.01Kn1), the rarefied gas exists in the non-continuum regime and, as such, the Direct Simulation Monte Carlo (DSMC) method is used to simulate the fluid behavior. The impact of the squeeze film on the beam is investigated over a range of frequencies, velocity amplitudes, micro-structure dimensions, and for different film gases, corresponding to ranges of dimensionless flow parameters such as the Reynolds (Re), Strouhal (St) and Mach (Ma) numbers. Moreover, the behavior of compressibility pressure waves as a function of these dimensionless groups is discussed for different simulation case studies. A new model for the force exerted by the gas on the oscillating micro-structure is presented to capture various significant effects related to the fluid's inertia, compressibility, stiffness and damping.