Modeling of fluid damping in resonant micro-mirrors with out-of-plane comb-drive actuation

Comb-drive micromirrors are becoming of interest for a broad range of light manipulation applications. Due to technical reasons, some of these applications require packaging of the micromirror’s optical module in ambient air. Furthermore, micromirrors for picoprojectors application are required to function at high frequencies in order to achieve high resolution images. Accordingly, a study of the energy dissipated due to the interaction between the moving parts of the micromirror and the surrounding air, leading to fluid damping, is an important issue. Even if air damping has been thoroughly studied, an extension to large air domain distortion linked to large tilting angles of torsional micromirrors is still partially missing. In such situations, the flow formation turns out to be far more complex than that assumed in analytical models. This task is here accomplished by adopting three-dimensional computational fluid dynamics models; specifically, two models, holding at different length scales, are adopted to attack the problem through an automated dynamic remeshing method. The time evolution of the torque required to compensate for the fluid damping term is computed for a-specific micromirror geometry.