Material modeling of DC-biased SMT ferrite beads for EMI filters

Circuit models of ferrite beads used for electromagnetic (EM) noise filtering are important for prediction and effective reduction of EM noise on power or signal lines. A methodology for impedance characterization and modeling of surface-mount ferrite beads is proposed in this article. The presented methodology combines series and shunt characterization methods to extract the equivalent circuit model of ferrite beads. The extracted models consist of frequency-independent elements and they are valid up to 1 GHz, to cover the bandwidth required by the EM compatibility standards for measurements of EM emissions. The values of the lumped elements of the extracted model are optimized to fit the measured impedance characteristics for each ferrite bead at bias current levels up to 5 A. Finally, the values of the lumped elements are parametrized with respect to the bias current from 0 to 5 A and the normalized error of the model compared to the measurements is calculated and found to be less than 10