Researchers from the University of Pennsylvania have published a theoretical paper that proposed the possibility of two-dimensional metamaterials that could be achieved by controlling the conductivity of sheets of graphene.
The research shows that transformation optics (manipulating electromagnetic, or acoustic waves) can be achieved using a single sheet of graphene. This could lead to applications in a lot of fields such as telecommunication and image or signal processing.
Applying direct voltage to a sheet of graphene, by way of ground plate running parallel to the sheet, changes how conductive the graphene is to EM waves. Varying the voltage or the distance between the ground plate and the graphene alters the conductivity. You can actually change the conductivity of different segments of a single sheet of graphene differently from each other. This means that you could 'navigate' a wave with those segments - which basically means that you can achieve transformation optics.
More info: http://www.physorg.com/news/2011-06-two-dimensional-graphene-metamaterials-one-atom-thick-optical.html