RF equivalent circuit modeling of ferrite-core inductors and characterization of core materials

Ferrite-core inductors play an important role in electromagnetic noise suppression. The radio-frequency (RF) equivalent circuit modeling of the inductor is very useful for characterizing the inductor and for noise filtering studies. A technique is proposed for extracting the equivalent circuit parameters of the inductor and determining the frequency-dependent effective rod permeability as well as the intrinsic permeability of the ferrite-core material. The equivalent series resistance, inductance, and the lumped shunt parasitic capacitance have been calculated versus frequency for a slug-type inductor and a toroidal-type inductor. The effective rod permeability of the ferrite rod used in the slug-type inductor and the intrinsic permeability of the ferrite core used in the toroidal-type inductor have also been estimated as a function of frequency. The calculated intrinsic permeability of the toroidal core agrees very well with that measured by the HP4291A RF Material Analyzer. The proposed method is simple and accurate. In addition, it provides an alternative way for characterizing ferrite cores at radio frequencies.