A bistable SMA microvalve for 3/2-way control

In this paper the layout, fabrication, and characterization of a first-of-its-kind bistable 3/2-way shape memory microvalve are presented. A symmetric arrangement of two counteracting shape memory alloy (SMA) microbridges is used for switching. The stable states in power-off condition are realized by magnetostatic contact forces between a movable hard-magnetic cylinder and two soft-magnetic layers. A detailed design study of the magnetic retaining system is performed to meet the requirements of a large pressure range and identical flow rates in the open valve state and a low leakage in the closed valve state in both outlet ports. The overall dimensions of first demonstrators are 11 mm × 6 mm × 4 mm. The 3/2-way bistable microvalve performance is demonstrated, showing identical flow rates in both outlet ports for a pressure difference up to 200 kPa for gas (N2) and up to 100 kPa for liquid (water) with flow rates of 1250 sccm and 11 ml/min, respectively.