Modelling the steady state response of CuAlNi/polyimide bimorph actuator

Microactuators developed from shape memory alloy (SMA) thin films on flexible substrates find good applications in MEMS design. This article presents the models of the actuation behaviour of a thin film SMA bimorph, developed by depositing CuAlNi SMA on a curved Kapton polyimide sheet substrate through a physical evaporation technique. The thermo-mechanical behaviour of the bimorph is analyzed by actuating it through Joule heating, for various inputs. During heating, the CuAlNi SMA film produces a forward displacement and in the cooling cycle, the curved flexible substrate substantiates for a bias force to recover the bimorph to its original shape, thus revealing the shape memory effect. Modelling and simulation are essential for decision making and control to involve the SMA bimorph in applications since the model help to understand the input-output performances. The article briefs about the models developed from mathematical analysis and simulation based on the physics involved in the bimorph SMA structures; analytical models of the bimorph are developed for the thermal and mechanical responses and, a simulation model is developed to obtain its actuation. The results of the models developed coincide with the experimental outputs in the actuation voltage range of 1-2.5 V.