Design of Radar Absorbing Structures Utilizing Carbon-Based Polymer Composites

Radar absorbing structure (RAS) is a composite laminate with a low reflection coefficient for the electromagnetic illumination in microwave frequency range, and thereby can be used in the stealth technology and electromagnetic compatibility (EMC). In this study, microwave absorbing properties of a two-layer composite laminate (carbon black impregnated rubber sheet attached to the carbon fiber–epoxy composite panel) has been investigated. Complex permittivity and permeability of the composite materials were measured in C- and X-band frequencies (4–12 GHz) by reflection/transmission technique using a coaxial waveguide and network analyzer. Complex permittivity can be controlled with the amount of carbon black in the rubber composite. High values of dielectric constant and dielectric loss are observed in the carbon fiber composite. Optimization of microwave absorption is conducted for the two-layer RAS on the basis of transmission line theory. It is found that microwave absorption is strongly sensitive to carbon black content in the rubber composite and its layer thickness. For the rubber sheet containing 10% carbon black (with dielectric constant ≍5), the maximum microwave absorption (30 dB) is predicted at 10 GHz.