By introducing smart materials in micro systems technologies, novel smart microactuators and sensors are currently being developed, e.g., for mobile, wearable, and implantable MEMS (Micro-electro-mechanical-system) devices. Magnetic shape memory alloys (MSMAs) are a promising material system as they show multiple coupling effects as well as large, abrupt changes in their physical properties, e.g., of strain and magnetization, due to a first order phase transformation. For the development of MSMA microactuators, considerable efforts are undertaken to fabricate MSMA foils and films showing similar and just as strong effects compared to their bulk counterparts. Novel MEMS-compatible technologies are being developed to enable their micromachining and integration. This review gives an overview of material properties, engineering issues and fabrication technologies. Selected demonstrators are presented illustrating the wide application potential.

This paper presents experimental and simulation results on the performance of a novel linear actuator that uses the magnetic shape memory (MSM) effect in a Ni-Mn-Ga foil device loaded by a mechanical spring. The linear MSM actuator shows reversible actuation cycles with maximum magnetic field induced strain change of 5.6% for optimized spring constant and prestress. The experimental results are compared with simulations based on a thermodynamics-based Gibbs free energy model. The model has been implemented in a finite element program, which uses beam elements and an integral magnetic solver. The simulations qualitatively describe the observed tensile stress dependence of the magnetostrain of the MSM foil actuator. We demonstrate that the effects of material inhomogeneity need to be taken into account to further improve the agreement with the experiment.

This paper presents a miniature energy harvesting device that makes use of stress-induced cyclic martensite variant reorientation in a Ni-Mn-Ga single crystal of 0.3x2x2 mm³ size. The stress- and magnetic field-induced reorientation is investigated for single crystalline Ni50.2Mn28.4Ga21.4 specimens of 0.3 mm thickness that are cut along the (100) direction and subjected to uniaxial compressive loading. A demonstrator is presented consisting of a FSMA specimen placed in the gap of a magnetic circuit to guide and enhance the field of biasing permanent magnets. The cyclic motion of a piezoelectric bimorph actuator is used to mechanically load the FSMA specimen. The corresponding change of magnetic flux induces an electrical voltage in a pick-up coil (N=2000 turns). The effects of biasing magnetic field, strain amplitude and strain velocity are investigated. An optimum magnetic field of 0.4 T exists, where the output voltage reaches 120 mV at a strain velocity of 0.006 ms-1.

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