A rigorous experimental characterization of ferrite inductors for RF noise suppression

Miniature inductors consisting of a coil wound on a high-permeability soft ferrite core material, find useful application in the suppression of EMI at RF and microwave frequencies. These inductors can be installed as either surface-mount devices (SMD) or as discrete chokes on slugs or beads. An understanding of the high-frequency parasitic and packaging effects, such as stray capacitance, magnetic losses, resonant characteristics, etc., can be gained from an equivalent circuit description of the inductor. We present a rigorous experimental method to fully characterize the behavior of wideband SMD ferrite inductors designed for maximum noise suppression at RF. The equivalent circuit parameters of the inductor, as well as the effective permeability, are extracted in closed form from an accurate measurement of the RF impedance.