Metal-bonded Co-ferrite composites for magnetostrictive torque sensor applications

A new class of magnetomechanical sensor materials, Co-ferrite (CoO·Fe₂O₃) and metal-bonded (Ag, Ni, Co) Co-ferrite composites, has been investigated. These materials exhibited magnetostriction in excess of 200 ppm and high d₃₃ (∂λ/∂H)_σ coefficient, 1.3×10^-9 A^-1 m, at low applied field (<100 kA/m). Selected compositions were formed into test samples in the form of rings brazed to stainless steel through-shafts. Changes of surface axial magnetic field in response to applied torque as high as 64 AN^-1 m^-2 were observed for a demonstration sample of dimensions 25 mm OD, 12.5 mm ID, and 8 mm high. A hysteresis of ±0.5 N·m was observed. These materials appear to be promising candidates for torque sensors, and other magnetostrictive sensor and actuator applications