High near-field electromagnetic wave attenuation at 5G millimeter-wave bands in graphene films printed by jet dispensing

Since traditional magnetic noise suppression sheets (NSS) are hard to address recent trend toward higher frequencies in the 5G mobile communication system, nonmagnetic NSS based on graphene has been developed in this study by jet dispensing (JD) on flexible polyimide sheets using a water ink composed of physically exfoliated graphene flakes and sulfate ester modified cellulose nanofiber (S-CNF). Graphene in the films was found to have c-axis alignment perpendicular to the film plane with a wide degree of dispersion from X-ray diffraction. Raman spectrometry showed an integral intensity ratio of D to G bands I _D /I _G less than 0.9 and an asymmetrical G'(2D) band, which implies few-layers graphene less than ten atomic layers. Evaluation of transmission attenuation power ratio R _tp , which is degree of near-field electromagnetic wave attenuation on a microstripline, up to 40 GHz revealed that the graphene film has a maximum R _tp of 72.4 dB at 26.8 GHz and an extremely wide bandwidth of 26.1 GHz (13.9 - 40 GHz) in which R _tp exceeds 20 dB. R _tp is found to significantly depend on sheet resistance R _S . R _tp 's in the 5G frequencies of 3.7, 28 and 39 GHz have maxima at R _S of 0.49 Ω, 10.5 Ω and 35.1 Ω, respectively. Flat press process increases packing density and conductive paths between graphene flakes in the films, leading to reduction of their resistivity ρ and R _S . The graphene JD sheets are quite promising as an advanced NSS for the 5G networks due to their high R _tp , wide bandwidth of R _tp >20dB, lightweight, high heat resistance and high radiation resistance of graphene.