Modelling and Simulation of Shape Memory Alloy Microactuator for Bionic Flexion Support in Older Adults: An Experimental Study

Introduction: Mobility challenges among elderly people have become a concern in the healthcare and engineering sectors. One common impairment in older age is the inability to perform forward bending movements. This difficulty affects essential daily activities such as dressing and removing wearable devices, leading to reduced independence and a lower quality of life. Nitinol (NiTiNOL) is an alloy composed of approximately 45% nickel (Ni) and 45% titanium (Ti). By manipulating the thermal environment, temperature variations occur in Shape Memory Alloy (SMA) wires. SMAs are widely utilised in industry, medicine, and robotics due to their flexibility, light weight, and the ability to undergo phase transformations when subjected to thermal changes in the environment. Aim: This research aims to model and simulate a micro SMA actuator for bionic applications. Materials and Methods: In this experimental study, COSMOL Multiphysics software analysed the behaviour of SMA wires. Electrical excitation was used to attain the deformation temperature of the SMA wire. The modelled SMA wire, with a diameter of 0.375 mm and length of 50 mm, was simulated at the Centre for Sensors and Control Systems Laboratory, Hindustan Institute of Technology and Science, Chennai. Results: The SMA microactuator exhibits notable thermal behaviour linked to phase transformations and mechanical properties. The modelled SMA spring features three turns, a diameter of 0.375 mm, and a length of 50 mm. It operates between 40°C and 65°C, with the austenite temperature at 65°C. These parameters yield an actuation force of 9.31 N and a displacement of 20.3 mm. Conclusion: The simulation results have been used to develop a soft robot for clinical purposes and bionic applications. To address such biomechanical deficits, an SMA-based actuator offers compact, quiet, and flexible motion in wearable or embedded assistive systems.