The absorption of electromagnetic waves at microwave frequencies by synthetic chiral and racemic materials

Physical principles are discussed which may improve the absorption of electromagnetic waves, especially in the microwave regime, by synthetic chiral and racemic materials. These principles are used to design a chiral composite for enhanced electromagnetic wave absorption at about 14 GHz. The chiral absorber consists of single‐turn copper helices, each wound on a ferrite core and randomly dispersed in a dielectric absorber made of tiny spheres of graphite‐coated expanded polystyrene. Its constitutive parameters, and those of some related dielectric, chiral, non‐chiral (bihelix) and racemic absorbing composites, are studied in the 10 to 18 GHz band. The materials are analyzed as third‐order Dällenbach layers to compare their ability to reduce normal incidence specular reflection by a flat metal plate. The presence of half‐wave resonant helices moderately increases the absorption bandwidth of the dielectric host. A chiral composite and its racemic counterpart have essentially identical properties as absorbers of specular reflection.