Effective medium at finite frequency: Theory and experiment

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Abstract
Besides their technological importance in electromagnetic applications, composites materials made of magnetic metal inclusions in an insulating matrix provide a stringent test of effective medium theories. While there exists numerous experimental and theoretical studies in the long wavelength approximation, that is, when induced currents can be neglected, much less information is available on the effects of, e.g., eddy currents on the effective permeability of composites, especially when it comes to a systematic comparison between experimental data and the various theoretical formulations. We intend to throw some light on this rather intricate problem by comparing experimental data with an extension of Bruggeman effective medium theory.