Influence of SiO2 fillers on microwave absorption properties of carbonyl iron/carbon black double-layer coatings

Epoxy resin (ER) based double-layer composite coatings were prepared with the thickness of 1.2 mm, employing carbonyl iron (CI) and carbon black (CB) as absorbents in the matching layer and absorption layer respectively. Especially, SiO2 was introduced into the matching layer as wave-transmission material to improve the matching impendence. The complex permittivity, complex permeability and absorption properties were investigated in 2–18 GHz. With increasing SiO2 content in the matching layer, the reflection loss (RL) was enhanced in the range 2–18 GHz. When the coating with the optimized SiO2 and CI weight concentration (SiO2:CI:ER) of 2:5:1, the optimal RL got to −17.3 dB and the effective absorption band (RL better than −4 dB) reached 5.7 GHz. In comparison, the minimum RL value was only −5.9 dB and the bandwidth (RL better than −4 dB) was just 4.1 GHz for the SiO2-free composite coating.