Electromotive Force Generation using the Dynamic Response of Ni50Mn28.5Ga21.5 Magnetic Shape Memory Alloy

Magnetic Shape Memory Alloys (MSMAs) are materials that respond to a change in either compressive stress or magnetic field, and can be used for applications such as actuation, sensing, and power harvesting. MSMA prismatic specimens are usually loaded magneto-mechanically by a compressive stress applied along the longest side of the specimen and by a magnetic field applied normal to the direction of the compressive stress. Karaman et al. proved the viability of using MSMAs, specifically NiMnGa single crystals, for energy harvesting applications using up to 5 Hz of cyclic stress. The group proposed a simple mathematical model to predict electrical voltage output generated by the material during the shape recovery process. The voltage output predicted by the model matched well with experimental results recorded at low frequencies(1). The magnetization reversal responsible for the voltage output has been approximated by Karaman et al. does not use the constitutive relations for the magneto-mechanical behavior of the material, such as that proposed by Kiefer and Lagoudas(2,3). This work presents simulated and experimental results describing the electromotive force (EMF) producing capabilities of a NiMnGa magnetic shape memory alloy (MSMA) at frequencies of up to 10 Hz. Unlike previous work, the current paper uses the constitutive model developed by Kiefer and Lagoudas(2-4) and the corresponding magnetization relations to theoretically predict the voltage output of the material. COMSOL Multiphysics 3.5a and Simulink were used to generate the simulated results for different constant bias magnetic fields and frequencies of excitation, partial reorientation strains and stress amplitudes. Simulated results are compared to experimental data and the reasons for data match/mismatch are discussed.