Tailoring the actuation characteristics of Ni-Ti shape memory alloy/ polyimide thin film composites

A modified approach was adopted to fabricate two configurations of shape memory alloy/polyimide thin film composites. Nickel-Titanium thin films, 2 mu m thick, were deposited onto a 50 mu m thick flexible Kapton polyimide substrate. The bimorph and sandwich configurations of developed composites were successfully investigated for two-way actuation. Investigations were carried out using a custom-made actuation setup equipped with Ohmic heating. The sandwich configuration of thin film composite substantially enhanced the actuation characteristics at lower actuation frequencies compared to its bimorph configuration. It has shown a significant increase in maximum stroke length and maximum displacement by 47 % and 67 % respectively at an actuation frequency of 0.125 Hz. Further, the actuation study was conducted on both the composites at varying input voltages and actuation frequencies. The sandwich structure displayed less efficiency with increasing frequencies. The austenite finish temperature of SMA thin film was found to be 125 degrees C beyond which composites ceased to display any additional actuation. These findings offer a promising outlook for the advancement of soft robotic actuators.