Hi HDLI, thanks for your quick response. The help, about impedance (SIBC in 2D-3D eddy-current solver) says that an effective equivalent curve (the first method a) in my question) is used, and is calculated only once before the iterative process. There are other techniques to solve the problem of non-linear ferromagnetic conductor material (e.g. mild steel of structural power transformer parts) using the impedance boundary with nonlinear permeability. My question is if the latest version of Ansys Maxwell is still using the procedure described in the help for NLSIBC problem.