SMA microactuators for microvalve applications

This paper presents a study of the mechanical and thermal properties of SMA microvalves, which are driven by a microactuator of a NiTi foil or a Ni2MnGa thin film. By coupled finite element simulations, von Mises stress profiles and resulting actuation forces are determined, which are compared with experimental force-displacement characteristics. The relatively high phase transformation temperatures of the used Ni2MnGa specimens M-f / A(f) of 92 / 125 degreesC, give rise to cooling times of about 25 ms compared to 90 ms for NiTi. Thus, Ni2MnGa microvalves show a superior switching performance. However, due to brittleness and buckling instability, Ni2MnGa microvalves only allow a maximum controllable pressure difference of 70 kPa, which is more than a factor of 7 smaller compared to NiTi microvalves.