This paper presents the electrodynamic characterization of Nitinol wire and investigates its potential as a servo-actuator that can be utilized to recreate complex low-power muscle movements, such as those in facial muscle groups. Nitinol (NiTi) is a type of shape memory alloy (SMA) which recovers its original length after experiencing large deformation when heated above an austenite finish temperature. This shape memory effect is associated with the phase transformation between the martensite phase and austenite phase. By varying a current through the Nitinol wire, its temperature can be accurately controlled and by extension so can its internal strain or stress. The purpose of this work is twofold: 1) to examine the causal relationships between current, temperature, strain and stress in the Nitinol wire, and 2) to demonstrate the feasibility of a simple closed-loop control system such that this type of wire can be used as a servo-actuator in both position control and force control applications. Experimental results show a basic level of servo-control, achieving successful position and force tracking of a command signal. These results demonstrate the feasibility of creating networks of Nitinol wires which can mimic complex motion patterns of certain facial muscle groups.

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