Complex Permittivity Extraction Method of a Thin Coating: EM Properties of a Graphene- Based Film on a Composite Layer

In the design of innovative nanomaterials for electromagnetic (EM) field absorption and shielding a crucial issue is the experimental characterization of the complex effective permittivity of non-uniform layered materials or electrically thin lossy layers. This paper proposes a technique to retrieve the complex relative permittivity of a thin lossy coating supported by a dielectric substrate through transmission/reflection measurements in a rectangular waveguide. A 2-port network de-embedding method is applied to remove the EM contribution of the substrate, and the so obtained scattering parameters of the film are used in the modified Nicolson- Ross-Weir algorithm to extract the complex permittivity. The method, validated by simulations, is applied to characterize a glass-fiber reinforced composite coated with a thin coating made of graphene nanoplatelets (GNPs)-polymer composite. Finally, the reflection properties of radar absorbing panels, constituted by several bilayers of GNP-coated GFRC are investigated in the range 12.4-18 GHz.