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Parallel-plates based micro-tunable capacitors are known to have low travel range, which worsen as going even lower in terms of their initials gap sizes. Such conditions have put strict requirements on the operation of such designs and hence hindering their use in numerous practical applications requiring high tunability. This work is proposed to examine the possibility to implement a closed-loop control strategy to increase the maximum capacitance and therefore tunability of micro tunable capacitors. The suggested control strategy is implemented on an electrostatically actuated parallel-plates (one stationary and one movable) based micro-capacitor and had an objective to stabilize the movable electrode when it is close to the fixed one for the sake of maximizing its maximum capacitance and possibly improving its overall tunability. Robustness of the micro-capacitor to the so-called pull-in phenomenon (short-circuit instability) when using the closed loop control scheme is studied. Indeed, an adaptive sliding mode controller is designed to compensate the effects of uncertainty, disturbance and eliminate any possibility for chattering phenomenon. The controller proficiencies in terms of stabilizing the micro-capacitor and its robustness to uncertainty as well as disturbance have been thoroughly examined. Furthermore, the effects of the control parameters on the behavior of micro-capacitor, such as overshoot, settling time, steady state error, robustness to uncertainty, external disturbances and to the chattering phenomenon, have been completely inspected. The obtained results indicated satisfactory proficiency and trustworthiness of the proposed control strategy to achieve high level of tunability and maximum capacitance.

In this paper, a novel RF MEMS variable capacitor has been presented. The applied techniques for increasing the tunability of the capacitor are the increasing of the maximum capacitance and decreasing of the minimum capacitance. The proposed structure is a simple cantilever Euler–Bernoulli micro-beam suspended between two conductive plates, in which the lower plate is considered as stationary reference electrode. In this structure, two pedestals are located in both tips of the cantilever beam. In the capacitive micro-structures, increasing the applied voltage decreases the equivalent stiffness of the structure and leads the system to an unstable condition (pull-in phenomenon). By deflecting the beam toward the upper (lower) plate the minimum (maximum) capacitance decreases (increases) and tunability increases consequently. The located pedestals increase and decrease the maximum and minimum capacitance respectively. The results show that the proposed structure increases the tunability of cantilever beam significantly. Furthermore, bifurcation behavior of movable electrode has been investigated.

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