A torque transducer utilizing a circularly polarized ring

A novel type of magnetoelastic torque transducer is described. It consists of two elements: a circumferentially magnetized magnetostrictive ring, rigidly attached to a shaft carrying the torque to be measured, and a Hall effect or similar magnetic field intensity sensor mounted in proximity to the ring. Stresses in the ring, associated with the torque being transmitted, alter the effective anisotropy orientation from circular to more or less steeply helical. Discontinuity of the axial component of magnetization at the ring ends creates a magnetic field in the space around the ring. A simple analysis predicts both a linear range in the relationship between field intensity and torque and a polarity which depends on the sense of the torque. The electrical output of the field sensor is thus a linear analog of the torque. Experimental transducers exhibit these expected features as well as a small, notably negative, hysteresis. The stability of the circular magnetization is both theoretically supportable and experimentally verified