Dynamic Behavior of Microelectromechanical Systems (MEMS) in Liquid Environments

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The objective of this project is to investigate the motion of simple microelectromechanical systems (MEMS) structures immersed in homogeneous liquids and solid/liquid suspensions. The structures will include beams designed to move normal to solid substrates and 'shuttle' plates designed to slide parallel with the substrates. The influence of geometry, gap height, surface characteristics, and fluid properties on device performance will be examined. 'Start-up' motion will be investigated by quantifying 'spring-back' behavior in beams and shuttles initially deflected by electrical forces. Normal oscillatory motion will be quantified using laser vibrometry. Start-up and oscillatory sliding motion will be observed and quantified by imaging shuttles with a high-frame-rate digital camera. The mechanical quality factor Q and frequency shift will be calculated for the two forms of oscillatory motion. Details of fluid motion will be investigated by visualization and image processing techniques. The experimental results will be compared with existing physical models on friction and lubrication, liquid/solid surface adhesion, and liquid damping forces to elucidate the dominant physical factors responsible for device performance. The results will also be used to test and determine limits in parametric relationships and to suggest design rules for the fabrication of reliable and optimal microscale mechanical devices. This study represents a pioneer investigation of fluid/structure interactions for MEMS devices in liquids. Since such devices are desirable in a variety of industries, the experimental data and analysis will be useful to engineers in many applications. The parametric relationships and design rules will ultimately allow engineers to optimize manufacturing methods and system performance while minimizing costly trial-and-error procedures.