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

A new class of magnetomechanical sensor materials, Co-ferrite (CoO/spl middot/Fe/sub 2/O/sub 3/) and metal-bonded (Ag, Ni, Co) Co-ferrite composites, has been investigated. These materials exhibited magnetostriction in excess of 200 ppm and high d/sub 33/ (/spl part//spl lambda///spl part/H)/sub /spl sigma// coefficient, 1.3/spl times/10/sup -9/ A/sup -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/sup -1/ m/sup -2/ were observed for a demonstration sample of dimensions 25 mm OD, 12.5 mm ID, and 8 mm high. A hysteresis of /spl plusmn/0.5 N/spl middot/m was observed. These materials appear to be promising candidates for torque sensors, and other magnetostrictive sensor and actuator applications.