Inertia-Controlled Twinning in Ni–Mn–Ga Actuators: A Discrete Twin-Boundary Dynamics Study

A discrete twin-boundary modeling approach is applied for simulating the dynamic magnetomechanical response of a Ni–Mn–Ga actuator over a wide frequency range. The model is based on experimentally measured kinetic relation of individual twin boundaries and takes into account inertial forces due to acceleration of the actuator’s mass. The calculated results show good agreement with experimental measurements performed on a specially designed Ni–Mn–Ga linear spring-mass actuator. In addition, the simulation reveals several new effects that have not been considered before and can be applied to the design of improved actuators. It is identified that the demagnetization effect plays a role of an “effective spring” and results in a resonance-type response. The effects of the actuator’s mass and the twin-boundary density on the resonance response and the actuator performance are explored numerically. In particular, it is shown that mass–inertia poses an inherent upper limit over the actuator’s bandwidth, which is approximately constant and equals to about 200 Hz.