Dual actuation micro-mirrors

This paper investigates the performance of cantilever-type micro-mirrors under electromagnetic, electrostatic and dual actuation. We developed and validated a two-DOFs model of the coupled bending-torsion motions of the mirror and used it in conjunction with experiments in air and in vacuum to compare all three actuation methods. We found that electromagnetic actuation is the most effective delivering a scanning range of ±3.63° out of a geometrically allowable range of ±4° at a current amplitude i = 3 mA and a magnetic field of B = 30 mT. Electrostatic actuation, whether alone or in conjunction with electromagnetic actuation, limited the stable angular range to smaller values (as small as 0.019°) due to the presence of spurious piston motions. This is an innate characteristic of micro-scale electrostatic actuation, the electrostatic force and the undesirable piston motion grow faster than the electrostatic torque and the desired angular displacement as the voltage is increased and they limit the stable angular range. Finally, we found that the dual actuation can be used to design two-DOF mirrors where electromagnetic actuation drives angular motion for optical beam steering and electrostatic actuation drives piston motion to control the mirror focus.