STRESS-OPTIMIZED SHAPE-MEMORY DEVICES FOR THE USE IN MICROVALVES

A gas valve of 6x6x2 mm(3) size has been developed for high pressure a pplications. Stress-optimised shape memory microbeams of 100 mu m thic kness are used to control the deflection of a membrane above a valve c hamber. The shape memory thin sheets have been fabricated by melting a nd rolling, which creates specific textures. Investigations by X-ray d iffraction revealed major orientations of [111] and [011] in rolling d irection. The corresponding maximum anisotropy of transformation strai n was 20%. The microbeams have been fabricated by laser cutting. For s tress-optimisation, the lateral widths of the beams are designed for h omogeneous stress distributions along the beam surfaces allowing an op timised use of the shape memory effect and a minimisation of fatigue e ffects. For actuation, a rhombohedral phase transformation is used. Th is allows operation below pressure differences of 1200 hPa in designs with one valve chamber and below 4500 hPa in pressure-compensated desi gns with a second valve chamber above the membrane. Maximum gas flows of 1600 seem (seem = cm(2) at standart conditions ! minute) and work o utputs of 35 mu Nm are achieved for a driving power of 210 mW. The res ponse times for closing the valves vary between 0.5 and 1.2 s and for opening between 1 and 2 s depending on the applied pressure difference .