A novel foil actuator using the magnetic shape memory effect

Abstract

A novel foil actuator of 15 × 3 mm 2 lateral dimensions is presented making use of the magnetic shape memory (MSM) effect. The actuation material is a Ni-Mn-Ga foil of 200 μm thickness that has been fabricated by cutting of a bulk Ni-Mn-Ga(100) single crystal consisting of 10 M martensite variants at room temperature. Stress-strain experiments on tensile test structures demonstrate that the stress needed for reorientation of martensite variants is about 1.2 MPa. The low twinning stress allows magnetic-field-induced variant switching, the basic mechanism of MSM actuation. A Ni-Mn-Ga foil actuator is fabricated by lithography and hybrid integration. The actuator shows a maximum magneto-strain of 4.9%, which is limited by the constraints of fixation and loading. Upon tensile loading at 1.5 MPa, linear actuation cycles are generated with an actuation stroke of 2.2%. The foil actuator is used as a benchmark system for modeling the coupled magneto-mechanical behavior of MSM actuation. We present finite element simulations based on a thermodynamic Gibbs free-energy model that qualitatively describes the observed tensile stress-dependence of magneto-strain.

Ferromagnetic shape memory flapper for remotely actuated propulsion systems

“…This process, known as martensitic reorientation, occurs through the motion of twin boundaries and is accompanied with large strains comparable to the best ordinary SMAs. Several recent works have demonstrated the potential of NiMnGa micro-actuators [17,18].…”

Magnetic Shape Memory Microactuators

“…Novel MSM linear actuators have been developed using the MIR effect in single crystalline 10M Ni-Mn-Ga foils [45,54]. Typical foil thicknesses have been in the range of 100-200 μm.…”

“…In this case, uniaxial tensile loading is used to adjust the initial state as compression loading would cause buckling perpendicular to the foil plane. In contrast to compression loading, however, two coexisting martensite variants with c-axes perpendicular to the tensile direction can be formed, which may reduce the maximum achievable shape change of 6% [45]. Based on theoretical considerations, the critical magnetic field for MIR is expected to decrease for decreasing foil thickness [10].…”

“…Based on theoretical considerations, the critical magnetic field for MIR is expected to decrease for decreasing foil thickness [10]. However, in real foil specimens, the critical magnetic field and maximum magnetostrain are affected by material inhomogeneity and surface defects depending on the technology of foil fabrication as well as by the constraints of fixation and tensile loading [34,45]. The influence of defects on the mobility of twin boundaries can be reduced by training of the MSMA material.…”

Tracking Twin Boundary Jerky Motion at Nanometer and Microsecond Scales

“…[ 7 ] Twinning reorientation in ferroelectric materials, shape memory alloys (SMA) and ferromagnetic SMA (FSMA) facilitates significant straining, [ 8 ] thus providing the fundamental mechanisms for transformation between electric/magnetic/thermal energy and mechanical energy, which are used in a variety of advanced actuation, sensing and energy harvesting applications. [ 9–12 ]…”