Measurement of Magnetism in Composite Materials

This paper focuses on the measurement of the effective magnetic permeability $\mu_{\rm eff}$ in composite structures built from nonmagnetic materials. Starting from recent studies of magnetism in microstructures, we present the results of a new theoretical and experimental analysis performed at frequencies below the medium frequencies. Mainly, we focus on how “spatial averaging” can affect the estimation of the parameter $\mu_{\rm eff}$ and show how expressions of $\mu_{\rm eff}$ derived for a single “unit-cell” configuration find analogy with that relevant to composite structured arrays. Finally, we show how to obtain negative values of $\mu_{\rm eff}$ for composite materials in the industrial frequency range and make some remarks on how future technologies can impact on the measurement of magnetism in composite materials.