Closed-form analytical design of optically transparent wideband absorbers for 5G technology

The design of new transparent absorbers for the upcoming fifth-generation (5G) technology is investigated. The absorbers consist of a matching layer, a lossy sheet, a spacer, and a back conducting layer (BCL). Both the matching layer and the spacer are one-quarter-wavelength thick and made of polyethylene terephthalate (PET). The lossy sheet and the BCL consist of indium tin oxide (ITO) thin films or graphene-PET laminates in order to avoid the use of any metal and to guarantee the optical transmittance. An innovative closed-form formulation is developed with the aim of evaluating the optimal values of sheet resistances of the lossy layers through analytical expressions. The absorption performances are investigated considering impinging plane waves with an incidence angle between 0° and 30°. The computed absorption coefficients in transverse magnetic (TM) or transverse electric (TE) modes are greater than 0.8, and the transmission coefficient is lower than 0.1 in the 5G frequency range from 25 up to 47 GHz, assuming that the matching layer and the spacer are 1.3 mm thick. The optical transmittance of the absorbers is evaluated in the wavelength range from 400 up to 700 nm by means of an accurate matrix simulation model, considering both optical polarizations, S (i.e., TE) and P (i.e., TM) for different incidence angles. The computed average optical transmittances of the designed absorbers are greater than 80% at 550 nm, i.e., at the wavelength corresponding to the maximum eye sensitivity