Next-generation metamaterials for unprecedented microwave systems

This paper presents what, in the vision of the author, will be next-generation metamaterials for microwave systems. For this purpose, it first introduces some fundamentals on metamaterials and describes the different types of currently existing metamaterial structures, called micro-scale metamate-rials, in reference with their typical smallest dimension. Upon this basis, it presents a few micro-scale metamaterial properties, structures and principles, from the popular negative index of refraction, via various dispersion-engineered devices, to a very recent non-reciprocal magnet-less metamaterial. After pointing out the limitations of micro-scale metamaterial, the paper introduces next generation metamaterials, namely multi-scale metamaterials, which incorporate nano-scale and atomic-scale structures and substances. For the nano-scales, it presents the example of ferromagnetic nanowire metamaterials and their applications, while for the atomic scale it describes recent innovations in ferrite based structures, including a uniform waveguide CRLH leaky-wave antenna and a perfect electromagnetic conductor wall, as well as most recent graphene-based structures and devices. Finally, a tri-scale structure, incorporating a graphene atomic-scale, ferromagnetic wire nano-scale and a metasurface micro-scale is discussed. In conclusion, the paper suggests that, although technology is eminently unpredictable, the wealth of novel properties of metamaterials augurs a long and lasting impact of this area.