Controller design for nonlinear micromachined parallel plate actuators
Nikapanah Mohammad Hossein
Date of Issue2009
School of Electrical and Electronic Engineering
4G Research Lab
The use of electrostatic actuation for microelectromechanical systems (MEMS) is attractive because of the high energy densities and large forces available in microscale devices. Nonlinear micromachined electrostatic parallel plate microactuators which work by electrostatic actuation, play an important role in MEMS. Compared with other types of microactuators, these microactuators are the more common and easy to use and it’s because of the fact that they generate lower force and consume relatively no electrical power. Low power applications are ideal candidates for electrostatic actuation because electrostatic force is generated by charge distribution not current fellow. Electrostatic parallel plate microactuators have many applications such as pressure sensors, accelerometers or comb-drive actuators, RF communication components, transmission line switches, reflective diffraction grating, laser cavities, stepper positioners, microrelays, micro shutters, optical routers, tunable capacitors, wavelength division multiplexing (WDM) filters, tunable LED’s and tuned laser. Electrostatic parallel plate microactuators are normally driven by DC voltage source scheme which is called static open-loop voltage control scheme. A major problem in this control strategy is that the voltage source causes a positive feedback in the electrostatic actuation. There is a well-known instability, inherent in the use of electrostatically actuated MEMS device called “snap-through” or “Pull-In”. “Pull-In” instability comes from positive feedback which causes the actuator top plate position becomes unstable and collapses at a distance of two-thirds of the zero- bias capacitive gap and it snaps the bottom plate. This prevents application of open loop voltage control scheme for devices that require an analog control of stable position within the entire gap.
DRNTU::Engineering::Electrical and electronic engineering::Microelectromechanical systems