"Efficiency of Energy Harvesting in Ni–Mn–Ga Shape Memory Alloys" by Paul Lindquist, Tony Hobza et al.
Many researchers have reported on the voltage and power generated while energy harvesting using Ni–Mn–Ga shape memory alloys; few researchers report on the power conversion efficiency of energy harvesting. We measured the magneto-mechanical behavior and energy harvesting of Ni–Mn–Ga shape memory alloys to quantify the efficiency of energy harvesting using the inverse magneto-plastic effect. At low frequencies, less than 150 Hz, the power conversion efficiency is less than 0.1%. Power conversion efficiency increases with (i) increasing actuation frequency, (ii) increasing actuation stroke, and (iii) decreasing twinning stress. Extrapolating the results of low-frequency experiments to the kHz actuation regime yields a power conversion factor of about 20% for 3 kHz actuation frequency, 7% actuation strain, and 0.05 MPa twinning stress.
Lindquist, Paul; Hobza, Tony; Patrick, Charles; and Müllner, Peter. (2018). "Efficiency of Energy Harvesting in Ni–Mn–Ga Shape Memory Alloys". Shape Memory and Superelasticity, 4(1), 93-101.