Conductive carbon black/magnetite hybrid fillers in microwave absorbing composites based on natural rubber

The study presents the microwave properties of natural rubber based composites in the 1-12 GHz frequency range as determined by the conductive carbon black/magnetite hybrid fillers obtained by impregnation at different ratios between carbon and magnetite phase. It has been established that, the changes in the investigated properties exhibit a resonance character in the 3-9 GHz range and are caused by alternations both of frequency and the ratio between the hybrid phases. The real and imaginary parts of permittivity and permeability, dielectric and magnetic loss angle tangent and conductivity have been also determined. The composite comprising a hybrid filler whose carbon:magnetite phase ratio is 90:10 has turned to be the most successful. The good microwave characteristics of the composite are related to the dielectric and magnetic losses, as well as to the achieved optimal permittivity of the composite at the given ratio of the carbon and magnetite phase. The percent content of the conductive filler has a significant impact upon EMI SE of the composites. The introduction of Fe3O4 into the hybrid filler has a crucial role for decreasing the reflection by the composites surface.