Complex permeability and permittivity variation of carbonyl iron rubber in the frequency range of 2 to 18 GHz

The complex dielectric permittivity (e) and magnetic permeability (m) of Radar Absorbing Materials (RAM) based on metallic magnetic particles (carbonyl iron particles) embedded in a dielectric matrix (silicon rubber) have been studied in the frequency range of 2 to 18 GHz. The relative permeability and permittivity of carbonyl iron-silicon composites for various mass fractions are measured by the transmission/reflection method using a vector network analyzer. The concentration dependence of permittivity and permeability on the frequency is analyzed. In a general way, the results show that eparameter shows a more significant variation among the evaluated parameters (e", m", m'). The comparison of dielectric and magnetic loss tangents (e"/e" and m"/m', respectively) shows more clearly the variation of both parameters (e and m) according to the frequency. It is also observed that higher carbonyl iron content fractions favor both dielectric and magnetic loss tangents.