Transfer impedance measurements are performed on several Ni&sngbnd;Fe tubes over the frequency range of 10 to3.2 × 107hertz. The influence of axial dc magnetic fields is studied. A limiting nonlinear model is devised to explain and predict the behavior of soft magnetic material used to shield against current in coaxial configurations. The new model relates to the basic dc magnetic and electrical properties of the material, saturation induction, initial permeability, electrical conductivity and the magnitude of the applied magnetic field.