In Proceedings of SEM X International Congress & Exposition, Costa Mesa, CA, June 2006

Ti MEMS Heat Engine

Z. Wang, S. R. Kirkpatrick, T. M. Adams, and A. Siahmakoun

Preliminary models have been developed to estimate the heat transfer and structural mechanics characteristics of a proposed shape memory alloy (SMA) MEMS heat engine consisting of a temperature gradient driven oscillating titanium/nickel (TiNi) cantilever beam. The heat transfer model predicts the expected frequency of cantilever oscillations by assuming onedimensional axial conduction within the cantilever while incorporating variable property information to account for the austenite/martensite transformation within the TiNi. The structural mechanics model predicts cantilever tip deflection by assuming that any strain above the proportional limit is recoverable and can therefore be assigned a second modulus of elasticity. Standard assumptions for beams undergoing small deflection are otherwise employed. For a 100 μm long cantilever 10 μm wide and 2 μm thick, the model predicts a cycling time of 3-6 ms, corresponding to a frequency of 100-300 Hz for hot and cold temperature reservoirs of 200°C and 25°C, respectively. The model further predicts that a 0.10 mN point load applied to the tip of the cantilever will result in a deflection of nearly 15 μm. These values compare well with the existing literature on SMA-MEMS actuators and suggest the feasibility of producing such an SMA MEMS heat engine. Furthermore, co-evaporation of titanium and nickel on a silicon substrate was performed and resulted in regions of shape memory alloy thin films, providing experimental evidence for the feasibility of such a heat engine.

©2004 Society for Experimental Mechanics.

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