Structure-Property Evaluation of the Dielectric Properties of Radar Absorbing Materials in Free Space

Since WWII, radar absorbing materials (RAMs) have been extensively used in asset protection by militaries around the world. By manipulating the dielectric properties, i.e. permittivity, e, and permeability, m, of materials through the incorporation of highly conductive additives, RAMs reduce the amount of electromagnetic radiation (EM) that is returned to a given sensor. For military applications, the EM radiation is often radar, namely X-band. In order to understand the behavior of a composite material in X-band, several measurement techniques can be employed to evaluate dielectric properties. The use of Free Space and anechoic chamber instrumentation are two such ways to achieve information on samples that are lossy, i.e. materials that have the ability to quickly dissipate EM radiation. For this work, several commercial polymer matrices were used with 4 additives, i.e., graphite flake (GF), graphite powder (GP), iron powder (CIP), and carbon black (CB), at varying loading levels to understand the structure-property relationships that affect dielectric properties in Free Space and anechoic chamber measurements. We hypothesized that the implementation of shaping of the composite would result in selective/total absorption in the X-band. We observed that commercially-available CB-loaded poly (lactic acid) (PLA) possessed the highest permittivity and power absorption, which led to lower X-band return as observed in anechoic chamber measurements. This result was confirmed through numerical modeling of the shaped part