Extraction of rf permeability of ferrite materials using direct measurement of inductors on ferrite cores

Ferrite materials are widely used as chokes to minimize common-mode currents in antenna feeds, in the design of artificial magnetic conductors, and in the filtering of noise at radio frequencies (RF). Miniature inductors, consisting of a thin-wire coil around a high-permeability soft ferrite core, find wide application in RF and microwave circuits. An understanding of the high-frequency parasitic and packaging effects, such as stray capacitance, magnetic losses, resonant characteristics, etc., useful in the design of these components, can be gained from an equivalent circuit characterization of the inductor. In this paper, we present a rigorous experimental method to fully characterize the frequency dependent RF behavior of ferrite inductors. The equivalent circuit parameters of the inductor, as well as the complex effective permeability of the core, are extracted in closed form from an accurate measurement of the RF impedance, without recourse to cumbersome optimization procedures.