Design of multiphysics actuators using topology optimization – Part II: Two-material structures

This is the second part of a two-paper description of the topology optimization method applied to the design of multiphysics actuators and electrothermomechanical systems in particular. The first paper is focussed on one-material structures, the second on two-material structures. The extensions of the topology optimization method in this part include design descriptions for two-material structures, constitutive modelling of elements with mixtures of two materials, formulation of optimization problems with multiple constraints and multiple materials and a mesh-independency scheme for two-material structures. The application in mind is the design of thermally and electrothermally driven micro actuators for use in MicroElectroMechanical Systems (MEMS). MEMS are microscopic mechanical systems coupled with electrical circuits. MEMS are fabricated using techniques known from the semi-conductor industry. Several of the examples from Part I are repeated, allowing for the introduction of a second material in the design domain. The second material can differ in mechanical properties such as Young's modulus or electrical and thermal conductivity. In some cases there are significant gains in introducing a second material. However, the gains depend on boundary conditions and relations between the material properties and are in many cases insignificant.