Weakly negative permittivity and low frequency dispersive behavior in graphene/epoxy metacomposites

As a promising substitute for periodical metamaterials, random composites with tunable negative electromagnetic parameters, which are termed as metacomposites, have drawn extensive attention owing to their unique properties and great potential applications. It is significant to decrease the values of negative permittivity and attain weakly negative permittivity with low frequency dispersive behavior, when searching for substitutable metacomposites. In this paper, the absolute value of negative permittivity in graphene/epoxy resin composites was dramatically decreased to approximately 6 by controlling the content of graphene and the microstructure of the resultant composites. Meanwhile, the permittivity spectrum showed low frequency dispersive behavior, which kept steady in a wide scope of frequency. It is indicated that the independence of negative permittivity on frequency results from the outstanding electron mobility of graphene. Moreover, it is demonstrated that the positive permittivity is ascribed to capacitive character, and the inductive character results in negative permittivity.