Investigation of Dimensional Effect on Constant Material Parameters of Magnetic Toroidal Cores

Reliable extraction of magnetic material parameters is critical for accurate high-frequency modeling of inductive components, such as common-mode chokes in power electronic systems. Conventional techniques, including the short-circuit line (SCL) method, often assume a direct relationship between the measured inductance and the material’s relative permeability. In this study, we show, via analytical simulations, that this assumption fails in the presence of internal spatial resonances, even when the complex relative permittivity and permeability are constant. Specifically, the magnetic flux distribution within the toroidal core becomes highly nonuniform, with localized regions of opposing flux direction. This leads to a reduced net flux and results in an equivalent permeability that diverges from the intrinsic material value. Furthermore, we demonstrate that the SCL method yields different permeability values for identical materials with differing sample geometries, underscoring its sensitivity to structural effects. In contrast, the proposed methodology accurately reconstructs consistent intrinsic parameters across varying geometries. These findings reveal fundamental limitations of classical extraction techniques and lay the groundwork for developing refined methods capable of isolating true material properties from geometry- and resonance-related distortions.