5G and 6G communication networks aim to ensure fast data rates, wide bandwidth, improved coverage and minimal latency; operating in mm-wave and sub-THz frequency bands, however, presents remarkable challenges including free-space loss, building penetration loss and strong interactions with obstacles, possibly leading to coverage gaps. Integrating active and passive devices into the environment has been widely proposed as a means of enhancing coverage without expanding the number of base stations. Among the others, Smart Electromagnetic Skins (SESs) offer a passive, thin-surface solution for redirecting incident fields in desired directions; depending on specific applications, SESs may serve as either reflective or transmitting devices, contributing to the creation of a Smart Radio Environment (SRE).