Torque sensor

A torque sensor for a cylindrical shaft subject to torque employs an electrically conductive loop on the shaft, which loop exhibits changing electrical impedance with changing stress and strain as the shaft is torqued. In another embodiment, a pair of loops exhibit oppositely changing electrical impedance as the shaft is torqued. In another embodiment, a magneto-elastic electrically conductive loop on the shaft exhibits changing magnetic permeability and changing electrical impedance with changing stress and strain as the shaft is torqued. In another embodiment, a pair of magneto-elastic electrically conductive loops on the shaft each have accordion-like corrugations and the loops exhibit oppositely changing magnetic permeabilities and oppositely changing electrical impedances with changing stress and strain as the shaft is torqued, wherein the corrugations of one loop stretch while the corrugations of the other loop contrast in response to one direction of shaft torque, and vice versa for the other direction of shaft torque. In another embodiment, magneto-elastic strips are placed on electrically conducting strips on the shaft. In another embodiment, magneto-elastic strips on the shaft are circumscribed by electrically conductive loops on the shaft.