  We report on the synthesis of the epoxy-based composites with graphene
fillers and testing their electromagnetic shielding efficiency by the
quasi-optic free-space method in the extremely high frequency (EHF) band (220 -
325 GHz). The curing adhesive composites were produced by a scalable technique
with a mixture of single-layer and few-layer graphene layers of a few-micron
lateral dimensions. It was found that the electromagnetic transmission, T, is
low even at small concentrations of graphene fillers: T<1% at frequency of 300
GHz for a composite with only 1 wt% of graphene. The main shielding mechanism
in composites with the low graphene loading is absorption. The composites of 1
mm thickness and graphene loading of 8 wt% provide excellent electromagnetic
shielding of 70 dB in the sub-terahertz EHF frequency with negligible energy
reflection to the environment. The developed lightweight adhesive composites
with graphene fillers can be used as electromagnetic absorbers in the
high-frequency microwave radio relays, microwave remote sensors, millimeter
wave scanners, and wireless local area networks.
