Microwave Space-Time-Modulated Metasurfaces
Sajjad Taravati, George V. Eleftheriades
Abstract
<p>Over the past decade, static metasurfaces have proved to be low-profile and efficient apparatuses for transformation of electromagnetic waves. However, such metasurfaces are restricted by their reciprocal and time- and frequency-invariant responses. To overcome these restrictions, space-time-modulated metasurfaces have recently been introduced for versatile, reciprocal/nonreciprocal, and frequency translation of electromagnetic waves. These are capable of changing both the momentum and energy of the incident wave and provide functionalities that are far beyond the capabilities of conventional static and reciprocal metasurfaces. This Perspective provides a discussion on the unique functionalities of a microwave space-time-modulated metasurface. In particular, we review various techniques that have been recently used for the realization of metasurfaces introducing spatiotemporal decomposition, scattering and diffraction, digital coding, nonreciprocal transmission, serrodyne frequency translation, pure frequency conversion, parametric wave amplification, and multifunctional operations. Although the paper focuses on microwave space-time metasurfaces, the described concepts can inspire realization of their optical counterparts. </p>