A gap-closing electrostatic actuator with a linear extended range

We present a gap-closing electrostatic actuator with a linear extended range. We achieve this by designing a nonlinear spring that exactly counteracts the nonlinear effects of electrostatic attraction forces in gap-closing actuators. We demonstrate this on parallel-plates actuators with a nominal gap of g = 21 μm. The initial response up to a deflection of g/4 is stable and is inevitably nonlinear, but beyond this point we demonstrate good linearity up to a displacement of 85% of the nominal gap. By introducing the nonlinear spring, we also avoid the pull-in instability, which would have occurred at a voltage of 31 V. Instead, the system is stable and the driving voltage may be increased up to 130 V where the maximal displacement is achieved.