A bistable magnetically enhanced shape memory microactuator with high blocking forces

Abstract

A novel approach of combining nonmagnetic shape memory alloy (SMA) microactuators with electroplated magnetic layers (ML) is presented, which enables the use of two intrinsic actuation principles in a single SMA-ML component allowing considerable gain in functionality. In the present work, we demonstrate local electroplating of Ni-81.75at.%Fe discs onto the surface of Ti-49at.%Ni microbridge structures. Antagonistic SMA-ML microactuators are fabricated by mechanically coupling two SMA-ML microbridges in their center by a spacer and prestraining them with respect to each other. The SMA-ML microactuators show bistable performance in the presence of an inhomogenous magnetic field generated by permanent magnets near the magnetic discs. Compared to antagonistic SMA microactuators fabricated without electroplated discs, a considerable improvement of mechanical performance is achieved. Magnetically enhanced SMA-ML microactuators of 7×7×4mm3 overall size show a blocking force and bistable stroke of about 33 mN and 84μm, respectively, while corresponding conventional SMA microactuators show no blocking force and a considerably smaller bistable stroke of 15μm.