Independent tuning of linear and nonlinear stiffness coefficients [actuators]

Using a combination of electrostatic actuators, we present a method to independently tune the linear and nonlinear stiffness coefficients of a uniaxial micromechanical device. To demonstrate the method's capability, we investigated the tuning of an oscillator with linear and cubic restoring forces. We successfully tuned the cubic stiffness from 0.31/spl times/10/sup 11/ to -5.1/spl times/10/sup 11/ N/m/sup 3/ without affecting the resonant frequency or the linear stiffness. Numerical results are presented which characterize the actuators and indicate important design parameters. Finally, issues such as actuator design, quadratic stiffness, and stability are discussed.