Investigation of Micro Bending Actuator using Iron-Gallium Alloy (Galfenol)

A micro bending actuator based on bimorph, lamination of Galfenol (iron-gallium alloy) and Nickel (Ni) is investigated. Galfenol is an iron-based magnetostrictive material with magnetostrictions greater than 200 ppm, a high relative permeability mu_r > 70 and a Young´s modulus of ~70 GPa. This material is machinable by conventional cutting techniques, and can operate under tensile, bending, and impact loads without degradation in performance. The bending actuator is the Galfenol of C-shape yoke bonded with Ni (lamination) wound coils, composing close magnetic loop with connected an iron plate. The magnetostrictions (positive: Galfenol and negative: Ni) in longitude direction are constrained at bonding surface, thus, the laminations yield bending deformation with a magnetic field applied. The advantage of the actuator is simple, compact and ease of assembling including winding coil, and high tolerance against bending, tensile and impact. We machined the yoke from a plate of 1mm thickness of polycrystalline Galfenol (Fe_81.6Ga_18.4 research grade) using ultra high precision cutting technique. We measured the performance of two types using lamination using Galfenol and SUS (previous) or Galfenol with internal mechanical stress by stress annealing and Ni (improved). The displacement of the latter was observed 22 mum compared with former one of 13 mum, 70% increased due to pre-stress effect and negative magnetostriction of Ni. The actuator was verified high bending (tensile) tolerance withstanding suspended weight of 500 g and can be operated with weight of 200 g under resonant frequency.