Electrical stiffness tuning in ferromagnetic shape memory Ni-Mn-Ga

This paper is focused on the dynamic characterization of field-induced mechanical stiffness changes under varied bias magnetic fields in commercial-quality, single-crystal ferromagnetic shape memory Ni-Mn-Ga. Prior to the dynamic measurements, a specified variant configuration is created in a prismatic Ni-Mn-Ga sample through the application and subsequent removal of collinear or transverse bias magnetic fields. Base excitation is used to measure the acceleration transmissibility across the sample, from where the resonance frequency is directly identified. These measurements are repeated for various collinear and transverse bias magnetic fields ranging from 0 to 575 kA/m, which are applied by a solenoid and an electromagnet, respectively. A 1-DOF model for the Ni-Mn-Ga sample is used to calculate the mechanical stiffness from resonance frequency measurements. A resonance frequency increase of 21% and a stiffness increase of 52% are observed in the collinear field tests. In the transverse field tests, a resonance frequency decrease of -36% is observed along with a stiffness decrease of -61%. The damping exhibited by this material is low in all cases (approximate to 0.03). The measured dynamic behaviors make Ni-Mn-Ga well suited for vibration absorbers with electrically-tunable stiffness.