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Micropositioning

Novel linear actuators have been developed for positioning applications using the magnetic shape memory (MSM) effect in single crystalline Ni-Mn-Ga foils. In order to generate reversible actuation cycles, a reset mechanism has been implemented. In general, resetting could be achieved by applying a second magnetic field in perpendicular direction with respect to the initial field or by applying a mechanical biasing load. In a practical device, mechanical biasing can be easily implemented by a suitable tensile spring, see Figure 1 Main actuator components are a Ni-Mn-Ga stripe specimen, a non-magnetic reset spring, an interconnection between these components and a supporting frame (a). First, the MSMA stripe and tensile spring are preloaded by shifting one end of the supporting frame initially, the MSMA stripe is in a single variant state with the long a-axis being aligned along the tensile loading direction. When the external magnetic field B is applied in tensile direction, the c axis aligns along B through variant reorientation causing the stripe specimen to contract. After switching the magnetic field off, the initial state is restored by the spring. The graph in Figure 1(b) shows the deformation of the MSM actuator for different levels of prestress.
(Magnetic Reorientation Model)

MSM actuation involves a change in length and cross-sectional area. Assuming a simple dependency of the material’s electrical resistance on the geometric dimensions, it can be shown that the deformation directly correlates with the electrical resistance change providing a route for intrinsic position sensing. For more information see ref [1].

 

Figure 1(a): MSMA linear actuator consisting of a NiMnGa specimen and a tensile reset spring. (b) The graph shows the deformation of the linear actuator for different levels of prestress generated by the spring [1]

Further information:

  1. R. Yin, F. Wendler, B. Krevet, M. Kohl, A magnetic shape memory microactuator with intrinsic position sensing, Sensors and Actuators A 246 (2016) 48–57.
  2. M. Kohl, M. Gueltig, V. Pinneker, R. Yin, F. Wendler, and B. Krevet, Magnetic Shape Memory Microactuators, Micromachines 5, (2014), 1135-1160
  3. V. Pinneker, M. Gueltig, A. Sozinov and M. Kohl, Single phase boundary actuation of a ferromagnetic shape memory foil, Acta Materialia 64 (2014) 179–187.
  4. V. Pinneker, R.Yin, C. Eberl, A. Sozinov, Y. Ezer and M. Kohl, Evolution of local strain bands of different orientation in single crystalline Ni–Mn–Ga foils under tension, Journal of Alloys and Compounds 577 (2013) 358–361.
  5. B. Krevet, V. Pinneker and M. Kohl, A magnetic shape memory foil actuator loaded by a spring, Smart Mater. Struct. 21 (2012) 094013 (7pp).