Modeling the influence of surface effect and molecular force on pull-in voltage of rotational nano-micro mirror using 2-DOF model

Herein, the torsion-bending coupled pull-in instability of rotational electromechanical nano-micro mirror is investigated using a two-degree-of-freedom (2-DOF) model. Two nano-scale phenomena (i.e., surface effect and molecular van der Waals attraction) are incorporated in the model. None of the previous 2-DOF models have taken these nano-scale effects into account. Results reveal that the influences of surface effects and intermolecular force on the coupled pull-in voltage of the nano-micro mirror highly depend on the geometrical characteristics of the system. It is found that if the mirror dimensions are of the order of the material length scale parameters, the pull-in characteristics computed via the present 2-DOF model will highly differ from those predicted by previous one-degree-of-freedom (1-DOF) models. Interestingly, the influence of surface effects on pull-in voltage of the system highly depends on the bending/torsion coupling ratio. Moreover, results show that the van der Waals force can reduce the pull-in voltage of the mirror. This deteriorating effect is more highlighted in the torsional mode than the bending mode.