Highly Efficient Passive Thermal Micro-Actuator

Abstract

A passive thermal micro-actuator with large area specific work and large displacement, fabricated of electroplated nickel on a silicon substrate is presented. The actuation relies on the thermal expansion of beams in a V-shaped geometry. Two V-shaped beam stacks are aligned opposite to each other and are coupled to a lever transmission. The actuator exhibits low energy losses due to the deformation of the structure and can efficiently convert the thermally induced elastic energy into mechanical work. An analytical model considers these thermally induced mechanical energies and the energy losses caused by the deformation of the material. The calculated deflections are compared with the measured ones and results of finite-element method simulations. The presented actuator operates completely passive, relies only on temperature changes of the surrounding environment, and exhibits a measured temperature-dependent linear deflection coefficient of $1.48~\mu \text{m}$ /K with a simulated blocking force of $57~\mu \text{N}$ /K. The structure occupies an area of $2135 \,\, \times \,\, 1831~\mu \text{m}^{2}$ and the area specific work is calculated to be $21.7~\mu \text{J}/\text{K}^{2}/\text{m}^{2}\vphantom {\sum ^{R^{R}}}$ , beating state of the art thermal actuators. As proof-of-concept, a passive micro-electro-mechanical systems temperature threshold sensor is fabricated, featuring the actuator and a bistable beam that switches between two stable positions when a specific threshold temperature is exceeded. [2014-0317]