Air damping characteristics of a 2D MEMS electromagnetically driven micro-mirror

Two-dimensional micromirror works as a resonant actuator applied in light detection and ranging (LiDAR) devices. The reflected mirror rotates regularly around two axes under controllable Lorentz force. It is expensive to manufacture a vacuum cave to provide high enough space in perpendicular for swing and meet the requirement for optical transmission in the motion. Air damping takes a dominant role when the structure operates in atmosphere, and affects dynamic performance of micromirror. The paper estabishes the air damping model which is helpful to describe the motion of the micromirror. Firstly, the paper presents three degrees of freedom (DOF) dynamic model of two dimensional micromirror driven by electromagnetically forces. Optimized structure was obtained according to the established model and the resonant modes were in good agreement with the finite-element simulations. Q-factor corresponding to each resonant modes of the micromirror operating in the atmosphere was derived through viscous damping theory. In the process, the fluid–solid-interaction (FSI) method was used to address the flow filed distributions. The simulation illustrates that the damping in slow scanning mode is much bigger than the value in fast scanning mode, which means the influence of structure size on damping is greater than that of rotation frequency. The frequency dependent response experiments were carried out to measure the Q-factor of the micromirror. The experimental results are in good agreement with simulation, verifying the viscous damping model is suitable for the case.