2-D Axisymmetric FEM-Based Approach for Identifying Dimension- and Frequency-Independent Material Parameters of Mn-Zn Ferrites

A 2-D axisymmetric finite element (FE) method based approach is presented for identifying intrinsic, dimension- and frequency-independent, electromagnetic material parameters of Mn-Zn ferrite cores. The parameters include the DC conductivity, complex permittivity and complex permeability both for the grains and the grain-boundaries. The FE model is utilized for solving the full-wave electromagnetic field problem in a cross-section of a ferrite core placed in a dielectric setting while accounting for the grain-scale microstructure. Dielectric impedance measurements are carried out for ferrite cores over a frequency range of 1 kHz - 10 MHz. The intrinsic material parameters are identified by fitting the FE model parameters such that the modeled impedances match with the measured ones. A model with dimension- and frequency-independent electromagnetic material parameters is able to reproduce only the low frequency behaviour before the occurrence of dimensional resonance. In order to model the resonance behaviour as well, a frequency-dependent term is introduced to the imaginary part of the reluctivity to account for “excess” magnetic losses.