2007 NSTI Nanotechnology Conference and Trade Show - Nanotech 2007 - 10th Annual

A Novel Topology Optimization Scheme for Micro Electro-Thermo-Mechanical Domains

M. Motiee, A. Khajepour and R.R. Mansour
University of Waterloo, CA

topology optimization, MEMS, coupled domain modeling

Developing a systematic approach to design optimum Micro-Electro-Mechanical Systems MEMS, recently has received a numerous attention among researchers. Duo to the lack of a systematic design method, typical MEMS devices design procedures encompass trial and errors and are based on designer intuition. Obviously such structures cannot be optimum and until now no methods have been able to predict better designs for MEMS. In this paper, a new topology optimization method is developed for the systematic design of electro-thermo-mechanical devices with embedded actuation scheme. The topology optimization method distributes finite number of elements in a design domain, such that some output performance is optimized. Topology optimization techniques enable systematic design directly from the behavioral specification. That is, the size, number and connectivity of elements in the structure and its entire shape are obtained as an original new solution such that the performance criterion called objective function is maximized, without relying upon human intuition. The topology optimization method was originally developed for large scale structural design problems with sole mechanical boundaries and is an iterative numerical method. This paper improves the classical topology optimization of structures with mechanical boundaries to MEMS devices in which a combined mechanical, electrical, and thermal boundaries co-exit. The optimized solution depends on objective function and lower limits on design variables. Here a new objective function is introduced to incorporate mixed boundary effects. The MEMS fabrication process limits are included in optimization constraints as lower and upper bounds on design variables. Also a new algorithmic approach to deal with multi-disciplinary domains is presented. Furthermore, the current method in the optimization of mechanical compliant mechanisms has been improved by the application of beam elements and implementation of the genetic algorithm. A graphical user interface, GUI is designed to facilitate the user interface, to control and trace the optimization procedure and to visualize the optimized solution. Several examples of optimized designs are included. The optimum structures are presented and compared with the examples from literature. We also show how the topology-dependent modeling such as heat transfer can be dealt with in a topology design technique where the number and size of elements are varied freely. The presented topology optimization method is a powerful tool to design optimized MEMS structures with on-chip actuation to deliver a specified task in their domain.

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