ABSTRACT
This chapter is devoted to designs of metasurface hardware, not only about metamaterial devices themselves, but also the control units usually integrated with reconfigurable intelligent surface (RIS) panels. The chapter begins with the basic design principles of metasurface devices for reflective and transmissive RIS by considering different structures of RIS elements and characteristics of component devices such as PIN diodes or varactors. The discussion is accompanied by a number of simulations and measurements of RIS devices operating in various frequency bands. Then, the control mechanisms of tunable metasurfaces are discussed, which can significantly affect the power consumption of the entire RIS hardware and the capability of an RIS. The codebook designs of an RIS focus on specific methods to accommodate unique properties of RIS hardware. In addition, two other closely related aspects are discussed. One is near-field communications, that has become quite “hot” recently in academia to provide potentially another spatial dimension. The other is metasurface-based beamforming at a base station, which may significantly reduce the energy consumption of millimeter wave base stations.
