Broadband radar absorbing structures of carbon nanocomposites

In this paper, we present double-layer radar absorbing structures composed of E-glass fabric/epoxy composite laminates that are optimally designed to have a broad bandwidth in the X-band. The first layer is a pure E-glass fabric/epoxy composite laminate and the second layer is a carbon nanocomposite laminate. Composite prepregs of carbon nanomaterials containing carbon black (CB), carbon nanotubes (CNT), and carbon nanofibers (CNF) were used. Numerical models of the complex permittivity of carbon nanocomposites were incorporated into the design process to determine the optimal thicknesses of both the first and the second layers and the optimal filler content of the second layer. By changing the locations of the two peaks in the frequency domain, various radar absorbing structures with different absorbing performances were designed. At the same time, the influence of the electromagnetic characteristics of each carbon nanomaterial on the thickness and the absorbing performance was investigated. The thickness and 10-dB bandwidth were 4.680mm and 7.5 GHz for CB-composites, 4.090mm and 7.7 GHz for CNF-composites, and 4.277mm and 7.4 GHz for CNT-composites, respectively. The broad bandwidth of the CNF-composite as compared to its thickness was attributed to its high dielectric constant as compared to the lossy term of its complex permittivity.