Epoxy-silicone filled with multi-walled carbon nanotubes and carbonyl iron particles as a microwave absorber

Microwave absorbing composites with epoxy-silicone as matrix and both multi-walled carbon nanotubes (MWCNTs) and carbonyl iron (CI) particles as absorbers were prepared, and their electromagnetic and microwave absorbing properties were investigated in the frequency range of 2-18 GHz. The microstructures of the composites show a uniform dispersion of the MWCNTs and CI particles in the matrix. The complex permittivity of the composites increased with increasing MWCNT content. A double resonance behavior of the complex permeability has been observed. One is due to the domain wall motion at about 7.5 GHz and the other is due to spin rotation at about 13.5 GHz. Reflection loss values exceeding -5 dB can be obtained in the frequency range of 10.4-18, 4.4-18 and 2-18 GHz, when the composite thickness is 0.5, 1 and 1.5 mm, respectively. A minimum reflection loss of -16.9 dB at 10.5 GHz and a bandwidth over the frequency range of 3.4-18 GHz with reflection loss below -10 dB can obtained for a composite filled with 0.5 vol% MWCNT and 50 vol% CI particles.