Research On The Absorbing Properties Of Epoxy Resin Based Composite Absorbing Coatings

In this paper, the structures and performances of carbonyl iron powder (CIP), carbonyl iron fibers (CIF), Fe-Si powders and carbon black (CB) were characterized by Scanning Electron Microscope, Transmission Electron Microscope and Vector Network Analyzer etc. ER based absorbing coatings were prepared with these absorbents.The findings showed that CIP and CIF were not only magnetic loss materials but also dielectric loss materials. The aspect ratio of CIF reached 30～100, which could enhance the scattering of electromagnetic (EM) wave in the absorbers and improve the absorption properties. Fe-Si could reduce the reflection of EM on the surface of the absorber with the low permittivity. The CB powders considered as dipoles in the process of damped vibration attenuated the electromagnetic wave effectively. But the impendence matching of CB was not very good.ER based absorbing coatings were prepared with CIP, CIF, Fe-Si, and CB, respectively. The absorption peaks of the coatings moved toward the low-frequency region with the increase of absorbents weight concentrations. The impedance matching became poor when the mass fraction of the absorbents exceeded the threshold value. The absorption properties of the coatings could be improved through mixing different absorbents. When the weight concentration (CIP:CIF:ER) was 4:0.05:1, the RL of the coating reached-22.6 dB at 2.3 GHz. The good absorption properties of the CIP/Fe-Si/ER appeared not only in low frequency region but also in high frequency region. When the weight concentration (CIP:CB:ER) was 1:0.3:1, the bandwidth (RL<-4 dB) of the CIP/CB/ER coating reached 6 GHz.On the base of monolayer composites, double-layer absorbing coatings with resistance gradual changing structure (absorbing layer + matching layer) were prepared. The electromagnetic parameter was controlled by the amount of the absorbent and SiO2 which was transparent to EM in the matching layer to achieve the impendence matching between the surface of the double-layer coating and the air. The good impendence matching reduced the reflection of EM wave at the coating surface and enhanced the absorption properties. The SiO2 could improve the matching impendence and had great influence on the absorbing performance of the composite coating. With increasing SiO2 content in the matching layer, the wave loss was enhanced. When the SiO2 weight concentration (CI:SiO2:ER) got to 2:5:1, the optimal RL reached-17.3 dB and the effectual absorption band (better than -4 dB) was 5.7 GHz.