Magnetic and transport eddy-current anomalies in cylinders with core-and-shell regions

For a conducting magnetic cylinder of radius r(0), conductivity sigma, and regionally uniform DC permeabilities mu(c), mu(s), and mu(b) in the core, the shell, and the core-shell border at r = r(b) < r(0), the complex AC permeability mu and impedance Z are calculated analytically from the Maxwell equations and the Ohm law. Compared with the results of the classical models with uniform local DC permeability, the low-frequency eddy-current anomaly factors and the high-frequency anomaly behaviors are quantitatively and conceptually explained with respect to different magnetic structures of the cylinder. The results can be used for quantitative studies of domain structures in ferromagnetic wires through AC permeability and impedance measurements and analyses. (C) 1999 Elsevier Science B.V. All rights reserved.