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 d(33) (partial derivative lambda/partial derivative H)(sigma) coefficient, 1.3X10(-9) A(-1)m, at low applied field (<100kA/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.