Optically transparent and flexible graphene planar microwave structures

The sheet resistance of graphene has been recently reduced below the level of previous optically transparent conductive materials. With its additional advantage of mechanical flexibility and low cost, graphene is one of the best candidates for future transparent electronics. We investigate here the possibility of using graphene for transparent and flexible microwave structures. Specifically, we study the waveguiding and nonreciprocal properties of various planar microwave transmission lines, using the 2D finite difference frequency domain (FDFD) technique. It is shown that reciprocal graphene based structures of acceptably low loss levels are achievable using graphene sheets of the lowest available resistivity, on the other hand graphene based nonreciprocal structures are accompanied by prohibitive loss due to a fundamental tradeoff between nonreciprocity and carrier density in graphene.