b Abbasnejad - Mechanical Engineering Department, Urmia University, Urmia, Iran
r Shabani - Mechanical Engineering Department, Urmia University, Urmia, Iran
g Rezazadeh - Mechanical Engineering Department, Urmia University, Urmia, Iran

This paper addresses the static and dynamic stabilities of a parametrically excited torsional microactuator.The system is composed of a rectangular micro-mirror symmetrically suspended between twoelectrodes and acted upon by a steady (dc) while simultaneously superimposed to an (ac) voltage. First,the stability of the system subjected to a quasi-statically applied (dc) voltage is investigated, where the pull-in instability, equilibrium positions, and bifurcation points of the system are determined. Then by superimposing an (ac) voltage and extracting a Mathieu type governing equation the effects of (ac)component on the stability of the system is investigated. By varying excitation parameters (steady (dc) voltage and time-dependent amplitude of (ac) excitation), transition curves and the stability margins of the micro-mirror are demonstrated. Theoretically obtained margins are checked by means of numericalsimulations. The results show that superimposing the harmonic (ac) component could have a stabilizing effect and allow an increase of the steady (dc) component beyond the pull-in value. These results could be used in design of micro-actuators.

MEMS,Micro-mirror,Electrostatic Actuation,Parametric Oscillation,Perturbation Method