A magnetoelastic torque transducer utilizing a ring divided into two oppositely polarized circumferential regions

Abstract

Significant improvements in both transducer performance and constructional simplicity is achieved by dividing a single ring into two equal width regions having oppositely directed circumferential magnetizations. The square hysteresis loop associated with the uniaxial anisotropy in the ring enables this magnetization arrangement to be readily instilled by rotating the shaft/ring assembly in the dipole fields of a set of axially separated permanent magnets having opposing polarizations. Following the removal of the magnets, each such region effectively becomes a single domain separated from the other only by a centrally located 180° domain wall. Unchanging performance of the transducer throughout nearly 10⁷ torque cycles, severe overloads, and a wide range of thermal environments attest to the stability of both the remanent magnetizations in each region and the position of the domain wall.