2. Fields of application

As far as applications are concerned, we need to distinguish between the contribution of metamaterials to existing fields of application, and the new prospects suggested by the possibility of engineering permeability and permittivity down to near-zero or even negative values. In the first category, in addition to filters and phase shifters, which are not developed here as they fall within the domain of long wavelengths (from submillimetre to radio frequency), we can also include focusing devices, radiating elements and sensors. The second category is historically organized around two key applications: the superlens and the invisibility cloak.