Ferromagnetic shape memory flapper for remotely actuated propulsion systems

Abstract

Generating propulsion with small-scale devices is a major challenge due to both the domination of viscous forces at low Reynolds numbers as well as the small relative stroke length of traditional actuators. Ferromagnetic shape memory materials are good candidates for such devices as they exhibit a unique combination of large strains and fast responses, and can be remotely activated by magnetic fields. This paper presents the design, analysis, and realization of a novel NiMnGa shear actuation method, which is especially suitable for small-scale fluid propulsion. A fluid mechanics analysis shows that the two key parameters for powerful propulsion are the engineering shear strain and twin boundary velocity. Using high-speed photography, we directly measure both parameters under an alternating magnetic field. Reynolds numbers in the inertial flow regime (>700) are evaluated. Measurements of the transient thrust show values up to 40 mN, significantly higher than biological equivalents. This work paves the way for new remotely activated and controlled propulsion for untethered micro-scale robots.

Magnetic-field-induced bending and straining of Ni–Mn–Ga single crystal beams with high aspect ratios

“…Thus, in one quarter of the beam volume, the crystallographic c-axis is perpendicular to the beam axis (hence parallel to the current magnetic field) and in the rest of the sample volume, the c-axis is parallel to the beam axis (hence perpendicular to the magnetic field). The smooth curvature of the beam implies that many twin boundaries are present because an isolated twin boundary would cause a distinct kink [15,16]. At field angles slightly below and slightly above 90°, the torque is strong and causes bending strain which competes with axial strain.…”

“…Most literature of magnetic-field-induced deformation addresses linear, uniaxial magnetic-field-induced strain (MFIS). In contrast, Ganor et al [15] and Kanner et al [16] proposed propulsion mechanisms for remotely activated micro-robots in water and fluids. They suggested mechanisms based on shearing and kinking associated with twinning.…”

Highly mobile interfaces in shape memory alloys

“…In particular, there have been a lot of development in the smart applications of Ni-Mn-Ga single crystals in the past few years (e.g. [52][53][54]). Also the works concerned with appearance of Type 1 and Type 2 interfaces in Ni-Mn-Ga thin films (e.g.…”

Microstructure and Machine Properties of Co37+xNi34-xAl29(x=0,1,2,3) Ferromagnetic Shape Memory Alloys

“…In the ternary phase diagram of Co-Ni-Al, the equilibrium phase is consist by β phase and γ phase. Thereinto, the β phase can be transform into twin martensite undergo martensitic phase transition when temperature cool down below martensitic phase transformation point [11,12]. The γ phase, which has excellent ductility, exist at the grain boundary can be greatly improved the brittleness of alloy [13,14].…”