Technical Papers and Presentations

Introduction: Design of a thermally driven actuator used in Micro Electro Mechanical Systems (MEMS) with two different metal materials is discussed. To achieve best performance of the thermally driven actuator in this work, it is desired to use a metal material with both high coefficient of thermal expansion and Young’s modulus. However, most of the material with high Young’s modulus has relatively small coefficient of thermal expansion, or vice versa. Therefore, it is hard to find the ideal material for the design.

Here we consider two materials, one has high coefficient of thermal expansion but small Young’s modulus, the other has high Young’s modulus but small coefficient of thermal expansion. By optimizing the distribution of two materials at the same time, it is possible to obtain superior performance by assigning the materials to the right places to utilize each materials’ strong point.

To achieve the multiphysics multi-material optimization, density method with consideration of handling different materials was used for topology optimization of the device. Therefore, distribution of two materials in the design space was considered and density of the materials were used as design variables for the optimization problem. Effective material properties such as Young’s modulus and thermal conductivity were determined using interpolation scheme which based on power-law method. A Helmholtz equation based regularization was used as a filter for the design variables. Projection method was also investigated for reducing the grayscale in the optimization results.

Use of COMSOL Multiphysics^® simulation software : In this work, Solid Mechanics interface, Heat Transfer in Solids interface and Density Model in the Optimization Module of COMSOL Multiphysics V5.4 are used to set up the multiphysics, multi-material topology optimization model.

Results and Conclusions: The optimal configuration of a two material thermal actuator was designed. The material distribution, the stress and strain, temperature and heat flux path were visualized. Results shows that COMSOL Multiphysics^® simulation software is a convenient tool for setting up a multi-physics, multi-material optimization model and helps to provide non-intuitive design idea for innovative micro devices.