Development of Microactuators Based on the Shape Memory Effect

¹ Forschungszentrum Karlsruhe, Postfach 3640, 76021 Karlsruhe, Germany
² Cranfield University, Cranfield, Bedford MK43 OAL, U.K.

Abstract

The mechanical and electrical properties of beam-cantilever microdevices fabricated from cold-rolled NiTi sheets and sputter-deposited NiTi thin films have been investigated by beam-bending experiments and electrical resistance measurements, respectively. In order to study possible size effects on the martensitic transformation, different device thicknesses have been realized down to grain dimensions of the NiTi sheets of about 20 μm, revealing enhanced transformation hystereses. For actuation control by resistive heating, the achievable displacements and work outputs were determined by the cross-section-dependent heat transfer to the device regions of maximum strain. Optimum heating/cooling performance and hysteresis control have been achieved for NiTi thin film devices with R-phase transformation above room-temperature. In order to demonstrate the potential of the microdevices for actuator applications, prototypes of membrane microvalves have been realised and tested.