Electromagnetic properties of metal granular composite materials for EMC applications

Electromagnetic properties of copper and Fe₅₅Ni₄₅ alloy (Permalloy) composite materials have been studied by measuring the relative complex permeability (μ_r = μ_r´- jμ_r”), and permittivity (ε_r = ε_r´- jε_r”) spectra over the microwave range, as well as the a.c. electrical conductivity σ_ac spectra. The variation of σ_ac and ε_r with particle content shows the insulator-metal transition due to the percolation effect. The effective cluster model can be applied to the percolation effect in permittivity. The permeability spectra in Permalloy composites, which contain the percolated particles, can be affected by the eddy current effect. The permeability relaxation frequency of Permalloy composites shifts to the higher frequencies by the oxidation of embedded particle surfaces.