Analytical thickness optimization for microwave graphene-based textile absorbers under oblique incidence

The absorber consists of a textile substrate sandwiched between a metallic layer, acting as a perfectly conductive ground plane, and a surface composed of polyvinylidene fluoride (PVDF) filled with graphene nanoplatelets (GNPs), which exhibits a frequency-dependent complex permittivity. Novel analytical expressions are derived to determine the optimal thicknesses of both the graphene-based surface and the textile spacer as functions of the incidence angle. The proposed model is validated through numerical simulations, leveraging both the developed analytical framework and full-wave simulations using CST Microwave Studio. The reflection coefficients for TM and TE polarizations are analysed over the 6 GHz to 18 GHZ frequency range, considering incidence angles up to 30°.