Abstract: We derived the equation of motion and corresponding boundary conditions for a simply supported microbeam with vonKarman nonlinearity by using the modified couple stress theory and the variational principle, and analyzed the influences of the width, height, length of the beam and the initial gap between the microbeam and the stationary electrode on the pullin voltage and the change rule of corresponding scale effects.

Key words:  modified couple stress theory, characteristic scale parameter, pullin voltage, scale effect, microelectromechanical system (MEMS)