Shear Stress Sensor Using Shape Memory Films

There is a need for a low profile, simple, accurate, localized, responsive sensor to measure shear stress in fluid flow. The unusual properties of shape memory alloys, and of Ni2MnGa in particular, suggest they could be sensing elements for shear. In recent years, single crystal films of Ni2MnGa have been grown by Molecular Beam Epitaxy (MBE). Once released from their substrate, these films have exhibited shape memory behavior. We pursue a concept based on the expectation that, when sheared, the martensite in an unconstrained single-crystal Ni2MnGa thin film will respond in a way that induces a measurable change in its electrical resistance. In Phase I we fabricated sensor prototypes and tested them in an air flow. There appeared to be a shear-induced change in electrical resistance. In Phase 2 we will continue development of this sensor, using theory to improve the designs, altering the MBE process in pursuit of the modulated martensites that have higher phase-boundary mobility, improving the fabrication process for the prototypes, testing prototypes in a wind tunnel, and considering other shape memory alloys as well.