Evolution of double magnetic resonance behavior and electromagnetic properties of flake carbonyl iron and multi-walled carbon nanotubes filled epoxy-silicone

The complex permittivity and permeability, reflection loss of the flake carbonyl iron (FCI) particles and multi-walled carbon nanotubes (MWCNTs) filled epoxy-silicone resin were investigated in the frequency range of 2-18 GHz. Both the values of complex permittivity and permeability were enhanced with increasing FCI content. The magnetic resonance behavior of such composites was mainly depended on the content of FCI particles, and the μ″-f spectra changed from no visible peak to double resonance as the FCI content increased from 10 to 50 wt%. Single-layer and multi-layer microwave absorbing coatings were also designed based on the transmission line theory and electromagnetic properties of the absorber. By changing the filler content and/or optimizing the absorber structure, the measured reflection loss below -10 dB can be obtained in the frequency range of 2-16.9 GHz for FCI particles and MWCNTs filled four-layer absorber.