Field-Based Microsensor and Electrostatic Microactuator

In the rapidly growing field of microelectromechanical systems, many transduction alternatives (electrostatics, electromagnetics, piezoelectricity, piezoresistivity, etc.) are being investigated by universities, government laboratories, and private companies. The Center for Engineering Design (CED) at the University of Utah is developing novel microsensors and microactuators. These devices use the advantages of electrostatics at small scales. The intuition and the experience of designing these microsensors and microactuators do not exist at present. The cause for this inexperience is that electrostatics has proved ill-suited for conventional macroscopic sensors and actuators. The goal of this research was to develop an understanding of electric field-based microsensors and microactuators. Because of the inexperience (of contemporary engineers) designing these devices, this research has made a significant contribution to the emerging area of microelectromechanical systems. Closed -form analytical methods and finite element methods (FEM) were the analysis techniques used to model the microsensors and microactuators. The analysis was aimed at verifying experiments and improving prototypes that eventually lead to products. A very simple and successful sensor consisted of a single emitter on a grounded substrate above two open -gated FETs on a grounded substrate. The emitter position can be determined from the difference of the FET output currents. A simple model of this sensor compared very well with experimental results. The next generation of sensors used more complex combinations of materials and geometry; therefore, the simple analytical model was no longer applicable. A two-dimensional FEM model was necessary and successful at understanding this next generation of sensors. Three-dimensional FEM models were used successfully to examine misalignment between the emitter and detector and the detector geometry. The Wobble motor (WM) was modelled using a closed -form solution and a realistic FEM model. Both models produced similar information about the output rotor torque. Both show that the torque is increased by decreasing the rotor insulation thickness and by better matching the rotor and stator diameters. The stator electrode width (related to the number of electrodes) and a grounded rotor core are other parameters that contribute to improved torque. The analysis showed a complex interplay between the geometric parameters.