A torque transducer based on local bands of naturally stabilized remanent circumferential magnetization

A simple construction for "polarized ring"-type torque transducers is descr ibed. Instead of residing within a separate magnetoelastically active ring, bands of circumferential remanent magnetization are established in the sha ft itself. Coercivity, crystal anisotropy, and the closed circumferential c onfiguration combine to stabilize the polarization. Symmetry precludes the appearance of magnetic fields from an untorqued shaft. Stress anisotropy as sociated with applied torque tilts the average easy axis into a helical ori entation with chirality and helix angle proportional to torque direction an d amplitude. Fields, associated with the divergence of the axial component of this magnetization, then arise in the space around each such band. Suita ble shaft materials have high enough anisotropy and coercivity, and low eno ugh magnetostriction to prevent these fields from significantly magnetizing proximate shaft regions. Experimental transducers, using heat treated allo y steel shafts, perform adequately for many industrial applications. (C) 19 99 American Institute of Physics. [S0021-8979(99)31308-6].