Time-Varying Non-Hermitian Metamaterials:
Probing and Challenging the Fundamental Limits of Electromagnetics and Photonics
Time-varying systems present unique opportunities for developing advanced electromagnetic and photonic devices. While research in this area originated more than fifty years ago, it is only in recent years that there has been a significant surge of research interest and momentum towards developing time-varying electromagnetic systems for various applications. This resurgence is driven partly by the realization that such systems may outperform traditional devices and overcome established performance limitations, such as the Bode–Fano limit for impedance matching, the Rozanov limit for electromagnetic absorption, the Chu-Harrington limit for small antennas, the delay-bandwidth limit, and various constraints due to reciprocity. In this talk, I will discuss our recent research efforts exploring both the potential and limitations of this emerging field. I will show how time-varying systems, combined with concepts from metamaterials and non-Hermitian physics, can unveil unique phenomena and achieve unique capabilities surpassing those of time-invariant systems. Furthermore, I will show how the unique properties of the temporal dimension, particularly in terms of causality and energy conservation, introduce distinct challenges and physical limitations specific to time-varying systems, despite the often-invoked space-time duality in wave physics.