The recent developments with magnetic shape memory alloys have made FSMAs interesting option for producing mechanical actuation up to 2 kHz frequencies. It has been shown that Ni-Mn-Ga crystals can respond to external magnetic field pulses rapidly and response times of less than 0.25 ms have been recorded [1]. The short response time combined with high energy density of FSMA make these actuators an interesting candidate for applications where compact actuators are needed for producing larger strains than piezoelectric or magnetostrictive devices can typically produce.

However, to understand better the behavior of this material at different excitation frequencies, the AC properties of this material should be studied more closely. The understanding of the frequency dependent behavior of this material could be used to facilitate the design of efficient actuators. This paper will concentrate on developing a dynamical model for Ni-Mn-Ga actuator and the model will be validated with experiments in both static and dynamic cases.

The modeling of the actuators will be started from the equation describing the dependence between magnetic anisotropy of the Ni-Mn-Ga and the MFI stress. The result will be validated by static measurements to get the maximum magnetic field induced force and strain. To measure the dynamical behavior of the FSMA, a test device based on a tunable resonator has been developed and it has been be used to estimate the frequency dependent parameters. The dynamical behavior of damped harmonic oscillator is described by well known differential equation and the characteristics of the FSMA actuator will be extracted from the frequency responses by comparing the measurements with the theoretical model.

[1] Pulsed magnetic field actuation of single-crystalline ferromagnetic shape memory alloy Ni-Mn-Ga, Miguel A. Marioni et.al. Proc. SPIE Int. Soc. Opt. Eng. 4699, 191 (2002)

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1. Selected fundamental and technical advances in magnetic shape memory alloys
2. Acoustic-Assisted, Magnetic-Field-Induced Strain and Stress Output of Ni-Mn-Ga
3. Magnetic and structural properties of non-stoichiometric Ni-Mn-Ga Ferromagnetic Shape Memory Alloys