Electrostatic actuators with parallel plates can only be controlled over a range equal to one-third of their initial gap sizego. This limitation can be circumvented by putting a capacitor into series with the actuator. The figure shows such a configuration, where Co is the initial (at rest) capacitance of the actuator, and C1 is the capacitor in series. Determine the range of capacitances for C1 that would prevent the pull-in effect. Which value within this range would you choose for the actuator design?

Spring constant K Movable electrode + + Initial air Co Vo gap, go C1 Va Series C1 Vo= Co + C1 capacitor