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.

Abstraci -A new type of magnetoelastic torque transducer is described. It consists of just two elements: a circumferentially magnetized, magnetostrictive ring, rigidly attached to ashaft 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 ofthe axialcomponent ofmagnetization 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 ofthe 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.

A simple construction for “polarized ring”-type torque transducers is described. Instead of residing within a separate magnetoelastically active ring, bands of circumferential remanent magnetization are established in the shaft itself. Coercivity, crystal anisotropy, and the closed circumferential configuration combine to stabilize the polarization. Symmetry precludes the appearance of magnetic fields from an untorqued shaft. Stress anisotropy associated with applied torque tilts the average easy axis into a helical orientation with chirality and helix angle proportional to torque direction and amplitude. Fields, associated with the divergence of the axial component of this magnetization, then arise in the space around each such band. Suitable shaft materials have high enough anisotropy and coercivity, and low enough magnetostriction to prevent these fields from significantly magnetizing proximate shaft regions. Experimental transducers, using heat treated alloy steel shafts, perform adequately for many industrial applications.

An alternative measurement regime for magnetoelastic force transducers, based on variations in coercive field, is described. Hc is shown to be more directly related to the primary magnetic influence of stress, namely, the orientation of effective anisotropy, than conventionally used magnetization related parameters. The stress dependence of Hc is shown to generally reflect opposing factors associated with rotational and wall displacement magnetization reversal processes. In materials wherein Hc≪K/Ms wall motion dominates and if the product of λs/K and yield stress is high enough, large monotonic reductions of Hc with positive (tensile) stress are shown to be possible. A more complex variation of Hc with increasing compression is similarly expected. Experimental results from a transducer having an 18% Ni maraging steel core support these expectations.

The increase in hysteresis loss associated with the altered microstructure and residual stress fields in regions near the cut edges of electrical steels is investigated by means of drag force measurements. Measurements are made using relatively narrow magnets on samples of two grades of nonoriented steels cut by laser or mechanical processes. Largest drag forces, hence losses, are consistently found in slow laser cut samples, smallest drag forces with fast laser cut samples, and moderately higher losses in mechanically cut samples. These results are consistent with other measurement methods.