Topology optimization of a passive thermal actuator

This paper presents a topology-optimized passive thermal micro actuator with large thermal deflection. The actuator relies on different coefficients of thermal expansion of an active material as well as the substrate and temperature changes of the surrounding environment. COMSOL Multiphysics is used for the topology optimization algorithm. The resulting shape is approximated by straight beams for a simpler fabrication. Two such shapes are arranged facing each other and coupled to a lever beam for a further increase of the temperature dependent deflection. The final design is manufactured using electroplated Ni on a Si substrate and state-of-the-art micro fabrication processes. The structures are characterized in a temperature range from -30°C up to +40°C with a measurement setup comprising a sealable chamber, a thermoelectric stage, and an optical microscope. The actuator exhibits a measured linear temperature deflection of 1 μm/K and a simulated force of 9.5 μN/K. The occupied area is 1.7×2.4 mm² while the area-specific work is 2.34 μJ/K²/m².