Dynamic Control of Waves With Reconfigurable, Time and Space-Time Modulated Metasurfaces

Abstract

Metasurfaces are two-dimensional arrays of closely-spaced, subwavelength scatterers. These surfaces can impart local changes to the amplitude, phase and polarization state of electromagnetic waves, allowing tailored control of electromagnetic wavefronts. Metasurfaces have enabled unprecedented control over electromagnetic waves, providing new opportunities in areas such as wireless communications, energy harvesting, imaging, and scattering reduction. Despite significant progress in this area, most metasurface designs provide static functionalities.

This thesis focuses on integrating electronic components with tunable properties into metasurfaces, to achieve dynamic control over electromagnetic wavefronts. We first propose a varactor-based metasurface that demonstrates advanced, tunable field control over a subwavelength thickness. The transparent metasurface is capable of rotating the polarization of an arbitrarily polarized transmitted wavefront, over a continuous range of $144.4^circ$. Next, we analyze wave propagation in temporally modulated media, and develop an analogous temporally modulated metasurface that exhibits Doppler-like frequency translation. The designed metasurface is transparent, with an overall subwavelength thickness of $0.3lambda$. Further, we propose a dual-polarized, metasurface that provides spatio-temporal control of its reflection phase. It demonstrates the large-scale integration of tunable electronic components into a metasurface design. The metasurface supports beamsteering, polarization control and frequency conversion. In addition, we are the first to study the effect of the unit cell size on a spatio-temporal system. A modified Floquet analysis is proposed to separate the scattered field into its macroscopic and microscopic variations. Notably, the spatial discretization enables unique metasurface capabilities such as subharmonic frequency translation, where Doppler-like frequency translation is demonstrated at integer multiples of the modulation frequency.