Abstract
A method of imaging the permeability and anisotropic permeability on the surfaces of steel shafts is presented. This kind of method is important in evaluating steel shafts used for magnetostrictive torque sensors. We have developed a magnetic probe that can detect the average permeability and anisotropic permeability at the same time. The probe has primary coil and two sets of secondary coils for measuring the permeability and magnetic anisotropy, respectively. We found that the average permeability had a clear helical pattern, possibly introduced during the final process of manufacturing, in which rollers are used to make the steel bars straight. We also observed anisotropic permeability patterns induced on a shaft excited by the pickup head of a torque sensor. The relationship between the zero-level fluctuation of the torque sensor and the anisotropic permeability pattern is shown.
