Abstract

Micro Electro Mechanical Systems (MEMS) such as microsensors and microactuators that use the electrostatic force between electrodes for sensing and actuation, have numerous advantages over other actuation mechanisms due to their ease of operation, simplicity and favourable scaling laws in the micro domain. One of the main considerations while using electrostatic actuations is that the devices must be operated in the safe working range as there exists the phenomenon of pull-in instability which leads to the failure of the system. In the present work, the non linear analysis of electrostatically actuated MEMS structures is carried out to predict the pull-in voltages and frequencies in order to determine the range of operation for the system throughout the life-cycle without damage. An analogy between the electrostatic phenomenon in MEMS structures and the aeroelastic phenomenon in aircraft wing structures has been inferred in this work. Initially, a linear analysis is adopted to understand the phenomenon in both these fields and their instabilities such as pull-in, divergence and flutter have been explained. Different active and passive control methods adopted so far by various researchers to avoid the instabilities in both the cases are presented. New terminologies have been proposed for MEMS based on their similarity with the aeroelastic phenomenon. The feasibility of microfabrication of the electrostatic MEMS structures based on MicraGeM process is presented in this work. The conversion of a continuous cantilever system into an equivalent lumped mass-spring model based on their energy has been formulated and the equivalent stiffness, mass and electrostatic areas are found to perform the nonlinear analysis of the system. The phase portrait techniques are adopted to find the pull-in voltage and the natural frequency of the mass-spring system, and the significance of the conservative energy value on the system behaviour are discussed. Hence a comparison of this nonlinear approach with the linear case has been done and their respective results are discussed. A non-contact optical Laser Doppler Velocimetry (LDV) set-up is used for the dynamic testing of micro cantilevers. Testing procedures along with the safe operating measures have been presented in order to avoid the pull-in condition. The frequency plots have been drawn for different DC and AC voltages based on the spectral analyzer frequency responses. Finally, the comparison of these frequency plots against the voltages from both the experimental testing and the nonlinear theoretical prediction is carried out and the percentage of accuracy of the prediction value has been found