Investigations on laser actuation and life cycle characteristics of NiTi shape memory alloy bimorph for non-contact functional applications

Abstract

A laser source was used as non-contact mode of heating to actuate NiTi/kapton polyimide shape memory alloy (SMA) bimorph. The bimorph was fabricated by depositing NiTi thin film over Kapton polyimide sheet of dimension 5 × 2 cm2 using thermal evaporation. The laser parameters such as laser power, scanning speed and number of passes were optimized to ensure actuation without damaging the bimorph. The actuation was carried out at laser powers and scanning speeds of 14 to 16 W and 13–16 mm/s respectively. The displacement of SMA bimorph was found to increase with increase in laser power whereas it decreases with increase in scanning speeds. At lower laser power, the scanning speeds have influenced the actuation behavior to larger extent. Notably at the laser power of 14 W, the influence of scanning speed was significant and registered 53 % reduction in displacement with increase in scanning speeds from 13 mm/s to 16 mm/s. A minimum and maximum displacement of 0.35 mm and 3.8 mm was obtained during laser actuation of bimorph. The temperature experienced during laser actuation has been simulated using COMSOL Multiphysics and corroborated with the actuation behavior of the SMA bimorph. The displacement range and the actuation speed of laser actuation were found to be higher than the conventional electrical actuation. Furthermore, the life cycle analysis has been performed up to 100 laser passes and the phenomenon for reduction in displacement has been discussed in detail. Laser actuation of SMA bimorph could be utilized in thermal switches, adaptive optics and remote actuation of SMA elements etc.