Electrostatically driving actuators

Motion is generated by electrostatic attraction force between electrically charged surfaces. Examples of electrostatic MEMS actuators are in-plane comb drives (Fig. la) and out-of-plane parallel plate actuators (Fig. lb) [4]. Both types of actuators require large driving voltages... 

Microactuators, Fig. 1 Diagrams of (a) in-plane electrostatic comb-drive actuator and actuation force and (b) out-ofplane parallel plate electrostatic actuator... 

Egawa, S., Niino, T. and Higuchi, T. (1991) Film Actuators Planar, Electrostatic Surface-Drive Actuators , Proceedings... 

Electrostatic actuators are commonly used in MEMS devices because they scale well in the micro domain, use very little power, and are straightforward to fabricate in a number of different processes. Two common forms are parallel plate actuators and comb-drive actuators. The parallel plate actuator is a parallel plate capacitor with one of the plates released so that it is able to move, as shown in Figure 3.1. The relationship between the capacitance C, voltage V, and charge Q for a parallel plate capacitor is given by... 

Show that the electrostatic force Fe of a pull-pull comb-drive actuator, as shown schematically in Figure 3.11, can be linearized in voltage by applying Vl= Vi,ias - v to the left set of fixed comb-drive fingers and = V ias + v to the right set of fixed comb-drive fingers. 

R. R. A. Syms, B. M. Hardcastle, and R. A. Lawes, Bulk micromachined silicon comb-drive electrostatic actuators with diode isolation, Sensors Actuators A 63, 61, 1997. 

Usually, artificial muscle based on electrostrictive, piezoelectric, electrostatic, or ferroelectric materials have been manufactured as a film of the dry polymer, both sides coated with a thin metallic film required to apply the electric field. Electrokinetic artificial muscles [5,6] are constituted by films of polymeric gel (polymer, solvent, and salt) and two electrodes, located as close as possible to the material or coating both on sides, which are required to apply the electric field that drives the electroosmotic process. Any of the actuators described in this paragraph has a triple layer structure metal-electroactive polymer-metal (Figure 16.2). 

The comb-drive resonator shown in Figure 3.7 is a common device in surface micromachining processes [4]. We will estimate the resonance frequency by calculating the spring constant of the folded spring and the mass of the released elements that are driven into resonance by electrostatic actuation. 

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