Electromagnetic properties of metal granular composite materials for EMC applications

Electromagnetic properties of copper and Fe
₅₅
Ni
₄₅
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.