*2.1. Electronic Approaches*

Active electronic components, such as diodes and varactors, have been widely utilized in microwave and millimeter-wave regimes for reconfigurable metasurface control [30,37–39,48–51]. However, they are incompatible with 6G applications in the THz spectrum due to the restricted cutoff frequency and dramatically increased loss [52]. To overcome this obstacle and implement reconfigurable metasurfaces in the THz spectrum using electronic approaches, CMOS transistors have to be embedded in meta-atoms with specially designed structures for local resonances [52]. Alternative solutions include integrating metasurface meta-atoms with layered semiconductor structures or graphene with electrical tunability.
