Magnetic, dielectric, and microwave absorbing properties of iron particles dispersed in rubber matrix in gigahertz frequencies

This study investigates high-frequency magnetic, dielectric, and microwave absorbing properties of iron particles dispersed in rubber matrix for the aim of thin microwave absorbers in gigahertz frequencies. High value of magnetic permeability and dielectric constant can be obtained in the composites containing thin flake iron particles which were prepared by mechanical forging of spherical iron powders using an attrition mill. The results are attributed to the reduction of eddy current loss (increase of permeability) and enhancement of space-charge polarization (increase of permittivity). However, if the initial particle size is too small (approaching to skin depth), milling effect for the increase of permeability is not observed and a low dielectric constant is predicted. If the particle size is too large, the permeability value is too small due to strong eddy current loss. With the iron particles controlled in size and shape (flakes) as the absorbent fillers, the thickness can be reduced as low as 1 mm with respect to -5 dB reflection loss in 1-2 GHz. (c) 2005 American Institute of Physics.