Frequency Response of Acoustic-Assisted Ni–Mn–Ga Ferromagnetic- Shape-Memory-Alloy Actuator

Abstract

A prototype of Ni–Mn–Ga based ferromagnetic-shape-memory-alloy (FSMA) actuator was designed and built; an acoustic-assist technique was applied to the actuator to enhance its performance. A piezoelectric stack actuator was attached to the Ni–Mn–Ga sample to generate acoustic energy to enhance twin-boundary mobility and, hence, reduce the magnetic threshold field required for activating twin-boundary motion. The dynamic response of the acoustic-assist FSMA actuator was measured up to 1 kHz actuation. The acoustic assistance improves the actuator performance by increasing the reversible magnetic-field-induced strain (MFIS) by up to 100% (increase from 0.017 to 0.03 at 10 Hz) for drive frequencies below 150 Hz. For frequencies above 150 Hz, the acoustic-assist effect becomes negligible and the resonant characteristic of the actuator takes over the actuator response. Even though the acoustic assist does not improve the actuation at high frequencies, the MFIS output of 5% can be obtained at the resonant frequency of 450 Hz without acoustic assistance. The FSMA actuator is shown to be ideal for applications that require large strain at a specific high frequency.