Eddy current measurements have been performed to determine the near-surface magnetic and electrical properties of case hardened steel rods. The measurements have been carried out over a range of frequencies using a coaxial encircling coil and the alternating current potential drop technique. A small excitation current used in the eddy current measurements ensures that the response is representative of linear material properties allowing the field in the rods to be determined using a linear theoretical model. In the linear regime, the steel is characterized by its initial permeability and electrical conductivity. Complementary measurements of alternating current potential drop provide information on the conductivity and permeability of the specimens. The measurements are used to estimate the linear material properties and the case depth with the aid of linear measurement models.
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