Evaluation of composite electromagnetic wave absorber made of isolated Ni-Zn ferrite or permalloy

It has been found that if a composite material consists of a magnetic material isolated in a dielectric medium, the relative complex permeability of the composite material does not obey Lichtenecker's law, which is well known to explain the relative complex permeability and permittivity of composite materials. This characteristic leads to the absorption of electromagnetic wave power at frequencies above 1 GHz. We proposed an isolation model to simulate the frequency dependence of the relative complex permeability and developed a composite electromagnetic wave absorber made of ferrite-SiO₂ or a permalloy-polystyrene system in which magnetic materials are isolated. The mechanical milling method was employed to isolate the magnetic material in the dielectric medium. Ni-Zn ferrite particles could be isolated in the SiO ₂ medium and the measured values of the relative complex permeability were close to those calculated from the isolation model. Consequently, this absorber could absorb electromagnetic wave power in the frequency range from 1 to 3 GHz. Permalloy particles were also isolated in a polystyrene resin medium. The absorber made of permalloy and polystyrene resin exhibited good absorption characteristics in the frequency range between 3 and 8 GHz.