Instability analysis of torsional MEMS/NEMS actuators under capillary force

The static and dynamic instabilities of a torsional MEMS/NEMS actuator caused by capillary effects are studied, respectively. An instability number, η  , is defined, and the critical gap distance, gcrgcr, between the mainplate and the substrate is derived. According to the values of η and g, the instability criteria of the actuator are presented. The dimensionless motion equation of the MEMS/NEMS torsional actuator is derived when it makes nonlinear oscillation under capillary force. The qualitative analysis of the nonlinear equation is made, and the phase portraits are presented on the phase plane. In addition, the bifurcation phenomena in the system are also analyzed.

Graphical abstractThe phase orbits connecting three equilibrium points on the phase plane, which include the periodic, heteroclinic and homoclinic orbits.Figure optionsDownload full-size imageDownload as PowerPoint slide