RCS of targets with plasmonic coatings: Computation, additive manufacturing and measurement

Under certain circumstances, plasmonic coatings could be a solution to the design of stealthy targets over the microwave range. In this communication, Perfectly Electrically Conducting (PEC) spheres with plasmonic coatings are studied in the microwave spectrum. Two main issues are raised. The first one is related to the fact that the exact computation of the Radar Cross Section (RCS) of finely textured targets with overall dimensions greater than the wavelength of interest often leads to problems of hundreds of thousands of unknowns, resulting in high CPU time consumption. The question then arises with respect to the most appropriate effective medium approximation one should use in order to correctly describe the electromagnetic behaviour of the coating. In this context, a relevant diamagnetic homogenization model is proposed. The resulting approximated RCS computations are in good agreement with the exact full wave solution over a broad range of microwave frequencies. Next to this purely numerical approach, the second issue was to design and to manufacture a textured spherical metallic target so as to bring sound experimental evidence to the calculated theoretical microwave response. Relying on computer-aided additive manufacturing, a periodically grooved metallic sphere has been realized successfully. Eventually, as we shall see, experimental RCS measurements of a periodically grooved metal sphere and the corresponding theoretical computations compare fairly well.