Published online by Cambridge University Press: 28 February 2011
Permittivity and permeability have been studied at microwave frequencies (1 to 20 GHz) on artificial dielectrics of metal particles randomly loaded in a polymer up to 40 vol%. Ni-Cr alloy powder (∼1 to 37 μm) in various size fractions was prepared by gas-water atomization, providing an oxide coating for interparticle isolation. The alloy is ferromagnetic below 165 K, enabling a magnetic measure of volume loading. The complex permeability results are in very good agreement with calculations of induced magnetic dipole effects as functions of frequency and particle diameter. Permittivity results are independent of particle size and essentially constant with frequency. When compared with a highly successful effective spherical cluster model and a well-founded empirical curve, the present alloy powder exhibits a residual upward deviation attributed to nonspherical morphology. In sum, the microwave electromagnetic behavior of such non-percolating composites is rather well understood.