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14 February 1997 Modeling and measuring the response times of thin film TiNi
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The response time of TiNi has been the subject of several experimental and theoretical investigations over the past decade. One of the principal concerns with this material is the relatively low cycle speeds or operational bandwidth caused by the considerable length of time required to cool the material. In this paper a finite difference model of heat transfer including the latent heat dissipated during the phase transformation is used to predict the bandwidth of thin film TiNi. The film is modeled as a plate subjected to either forced or free convection along the exposed surfaces and clamped to a large thermal mass representative of silicon wafer at the ends of the specimens. Results indicate that both latent heat as well as the relative ratios of the transformation temperatures to ambient temperature strongly influence the bandwidth of the material. Good correlation between the analytical model and test data obtained on a 38 micron wire indicate the model contains the correct assumptions to predict bandwidths. The bandwidth of TiNi thin film are predicted to be on the order of 100 Hz necessary assuming that the transformation temperatures for the film are the same as the bulk material.
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Ken K. Ho, Peter Jardine, Gregory Paul Carman, and Chang-Jin Kim "Modeling and measuring the response times of thin film TiNi", Proc. SPIE 3040, Smart Structures and Materials 1997: Smart Materials Technologies, (14 February 1997);

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