Nonlinear, Active, and Time-Varying Metasurfaces for Wireless Communications: A perspective and opportunities

The requirements of next-generation wireless communications have been growing exponentially in recent years, not only in terms of data rates, but also of reliability, latency, and massiveness. These demands have been inspiring new paradigms for hardware and for underlying communication protocols. In this context, metasurfaces have been enabling a range of functionalities and enhanced control over the electromagnetic wavefront, of direct relevance to wireless communications. A concerted effort between electromagnetic and system engineers may leverage these advances, with wireless systems taking advantage of metasurfaces, and metasurfaces adapting to address the needs of wireless communications. While this is already happening in the area of Reconfigurable Intelligent Surfaces (RIS), here we outline possibilities for new wireless communication modes that arise when metasurfaces are integrated with active, nonlinear, programmable and time-varying elements. We envision metasurfaces that can control the communication spectrum, channel properties and scattering features with flexibility, self-adapting to changes in the environment and users, and maximize relevant metrics of interest. Programmable multifunctional surfaces and underlying communication protocols hold the promise for opportunities in a new generation of wireless systems, changing the way we think about the propagation space and the frequency spectrum.