KEYWORDS: Magnetism, Shape memory alloys, Mathematical modeling, Calibration, Data modeling, Simulink, Energy harvesting, Finite element methods, Anisotropy, Magnetic sensors
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 frequencies1. 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 Lagoudas2,3. 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 Lagoudas2-4 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.
This paper presents simulated and experimental results on the flow induced in a closed channel by a magnetic fluid (i.e.
magnetorheological (MR) fluid and a ferrofluid) plunger. The results are used to assess the feasibility of using such
fluids for development of milli-micro-scale pumps. The magnetic fluid plunger acts as a piston that is moved along the
channel by an array of drive coils (or by a permanent magnet) to displace an immiscible fluid. The excited drive coils
produce a traveling magnetic field wave inside the channel which in turn produces magnetic dipoles in the magnetic
fluid. The dipoles react with the traveling wave leading to a Kelvin force that drags the magnetic fluid plunger through
the channel. The flow rates achievable in this approach are a function of channel geometry, magnetic fluid properties,
plug size, frequency of the current passing through the drive coils, and the location of the drive coils along the channel.
Representative results of the analysis of the effect of these parameters on the flow rates are presented here. While the
simulations indicate that both, MR and ferrofluids may be used for fluid actuation in the selected geometry, the experiments validated only the MR fluid option.
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