Damping in resonating MEMS mirrors has a profound effect on the dynamical behavior. The validity of the existing theories is investigated in this work by theoretical and experimental means. The squeeze-film model with artificial viscosity and the molecular dynamics model are adapted for the case of a torsion mirror under a wide range of vacuum levels. The considered ambient pressure varies from atmospheric to a pressure under which structural damping prevails. High resolution experiments have been conducted on dedicated devices. Two independent experimental damping extraction methods have been employed for substantiating the validity of the measured parameters. Although the theoretical models agree favorably with the experimental data, it appears they provide slightly different predictions under different operating regimes.

An analytical and numerical study on the levitation force induced by pressure radiation in gas squeeze films is investigated. The levitation phenomenon is known to occur when a planar object is placed at close proximity to a vibrating piston. The existing analytical approaches are based on either conventional acoustic radiation, where the fluid is assumed inviscid or on a variant of the Reynolds equation that incorporates viscous effects. Alas, these solutions are often in poor agreement with accurate numerical results and, at best, describe appropriately cases that include a limited range of object weights and vibration frequencies. In this work, two cases are addressed: the flow induced by vibrations perpendicular to a flat surface and that by flexural wave propagation parallel to the surface. For the first case, numerical and second-order analytical perturbation solutions are obtained and compared, proving them to be in good agreement. In addition, a novel, analytical expression for the levitation force is also suggested that proves to be valid for a wider physical range of squeeze numbers and vibration amplitudes. For the second and more complex case ͑recently used in noncontacting transportation systems where the driving surface exhibited flexural traveling waves͒, the skin-friction force exerted on the flat surface is derived analytically based on a first-order perturbation solution, and the levitation force is analyzed numerically. Some insights on the physical behavior are then highlighted and discussed.

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