Electric and fluid field analysis of side-drive micromotors

Motive torque, axial force, and viscous drag torque in variable-capacitance side-drive micromotors are analyzed by finite-element modeling of electric and fluid fields. For electric field modeling, the focus is on surface-micromachined salient-pole polysilicon micromotors with 12 stator poles and eight rotor poles, and their three-dimensional geometry is considered. Comparison with results of two-dimensional in-plane and axial-plane analysis of the same motors indicates that 3-D finite-element analysis (FEA) of the electric field is required to accurately calculate the motive torque and axial force acting on the rotor. The 3-D results are in good agreement with available experimental data. For fluid field modeling, a simple axisymmetric model geometry that consists of a thin flat disk is used, and the bushing, stator, and bearing are added incrementally. The viscous drag coefficient from steady-state FEA is within 30% of the value estimated from experimental measurement.<>