Theory and Design of Multifunctional Space-Time Metasurfaces

Integrating multiple functionalities into a single metasurface is becoming of great interest for future intelligent communication systems. While such devices have been extensively explored for reciprocal functionalities, in this work, we integrate a wide variety of nonreciprocal applications into a single platform. The proposed structure is based on spatiotemporally modulated impedance sheets supported by a grounded dielectric substrate. We show that, by engineering the excitation of evanescent modes, nonreciprocal interactions with impinging waves can be configured at will. We demonstrate a plethora of nonreciprocal components, such as wave isolators, phase shifters, and circulators, on the same metasurface. This platform allows switching between different functionalities by modifying only the pumping signals (harmonic or nonharmonic), without changing the main body of the metasurface structure. This solution opens the door for future real-time reconfigurable and environment-adaptive nonreciprocal wave controllers.