Abstract
The 6G era comes with the challenge of offering highly energy-efficient and autonomous communications securely. In this direction, we report energy efficiency (EE), energy harvesting (EH), and secure performance by employing power-collecting metasurface-coated devices capable of supporting ultralow-power (ULP) transmissions. In contrast to what are called reconfigurable intelligent surfaces ( RISs ), where the reflected signal can be combined at the receiver by being treated as transmitted from a relay, the proposed metasurface claddings can be deployed at either the transmitter or receiver or at both. The passive metasurface-coated devices can achieve ultrahigh EE and EH in addition to signal detection, combined with an enhanced secrecy rate at the legitimate user or, if used from the other side of the link, spying capabilities of eavesdroppers under ULP transmission. To quantify their efficiency, we provide a holistic model for the utilization of the metasurface shells. Building upon this model, we present preliminary results that reveal the unprecedented superiority of the proposed concept compared to the RIS paradigm. Additionally, we enumerate the main advantages of the new concept and define its role in the 6G era. Finally, possible research directions are discussed.