UC San Diego

Metasurfaces, constructed with periodic subwavelength meta-atoms, have aroused wide attention since it exhibits extraordinary electromagnetic behaviours in wave manipulation from microwave regime to optical ranges. Meanwhile the low-cost, ease of fabrication and compact features make it more appealing for various applications. Researchers have shown that conventional linear-time-invariant (LTI) metasurfaces are capable of energy absorption, beam formation, radiation control and polarization conversion. However, their abilities are limited since the electromagnetic (EM) response is unchangeable regardless of input power and phase.

This dissertation discusses how to empower classic LTI metasurfaces with unconventional abilities by integrating nonlinear electronic devices. The integration of nonlinear device offers more degrees of freedom to metasurfaces, enabling versatile abilities to meet complex growing demands in EM protection, isolation and wave manipulation. This dissertation theoretically and experimentally demonstrates four novel non-LTI or reconfigurable metasurfaces designs with promising application value. First, we propose a broadband absorber beyond the Bode-Fano limit by creating an energy trap using time-modulated switch/diodes. The second design realizes power-dependent reflection, instead of absorption, to realize EM protection. The triggering of the integrated diodes directly transforms the structure from a surface wave supportive state to a self-induced bandgap topology if exposed to high power RF illumination. The third concept proposes an all-passive and magnetic-free structure integrated with diodes to achieve nonreciprocity, which is a promising candidate for EM protecting layers and EM isolators/circulators. The last proposed varactor-based reconfigurable metasurface focuses on multifunctional wave manipulation, including beam steering, polarization conversion and phase offset. All these proposed structures expand the capability of wave manipulation and their applications compared to traditional LTI metasurfaces.