Metasurfaces 3.0: a Key Enabling Technology for the Development of beyond-5G Communication Systems

In the last two decades, the concept of metasurfaces has evolved, leading, nowadays, to unprecedented possibilities. The first generation of metasurfaces was based on regular homogeneous periodic structures. This 2D version of volumetric metamaterials had a dramatic impact in many application fields, ranging from radio up to optical frequencies. Following the evolution path of the metasurface concept, the second generation of metasurfaces was based on inhomogeneous structures characterized by quasi-periodical or gradient-like arrangements. The spatial modulation of the metasurface properties allowed enhancing the capabilities, thanks to the higher number of degrees of freedom available. Finally, the third generation of metasurfaces consists of thin patterned structures whose properties can be controlled in both space and time. This possibility, enabled by different control mechanisms (e.g. electronic, optical, thermal, chemical, liquid crystal based, etc.) and boosted by the recent advances in integration and micro/nano-fabrication technologies, allows conceiving tunable, reconfigurable, and programmable structures that can be used in a variety of applications. In this contribution, after a review of the three generations of metasurfaces and a detailed focus on the current third generation, the potential impact of these structures as a key enabling technology for beyond 5G communication systems will be discussed.