ESE Ph.D. Thesis Defense: “Wave Interaction with Nonreciprocal Swift-Electron Platforms and Reconfigurable Metasurfaces”

The study of electromagnetic wave interactions with various media is of fundamental significance in both theoretical and applied sciences. Understanding how electromagnetic waves propagate, reflect, refract, and scatter when encountering different materials is essential for the design of advanced technologies in telecommunications, imaging, sensing, and computation. Furthermore, the ability to manipulate wave behavior within diverse media presents new possibilities for developing high-performance devices, such as antennas, sensors, and optical systems, with applications ranging from wireless communications to medical diagnostics.

Nonreciprocal devices, which enable unidirectional signal propagation, are critical for protecting systems from interference and enhancing the performance of telecommunications and photonic technologies. Achieving a robust nonreciprocal response is vital for ensuring signal integrity and efficiency in these systems. In this study, I present theoretical models that explore the strong and tunable nonreciprocal response of swift electrons interacting with various structures, including those in vacuum and graphene-based media. My analytical and numerical analysis demonstrates that guided modes in metallic and dielectric waveguides can be effectively manipulated by fast-moving electrons, resulting in unidirectional propagation regimes and significant nonreciprocity in light-matter interactions. Additionally, I introduce a beam-steering structure based on the interaction between antenna radiation and an electron sheet comprising swift moving electrons at constant velocity. The nonreciprocal strength of these interactions is further modulated through space-time variation of electron velocity and density, demonstrating extra degree of freedom in controlling wave propagation. The strong nonreciprocal response achieved using this method is highlighted through comparative analysis with existing approaches. I also investigate nonreciprocity in graphene-coated optical fibers, where electrically biased electrons moving along the fiber axis interact with the guided modes of the dielectric fiber. Moreover, I explore the impact of electrical bias on the absorption rate and resonance frequency of nano-patterned graphene based metasurface. This study opens new avenues for controlling and manipulating electromagnetic wave propagation in THz systems, where the nonreciprocity strength is not inherently limited by material properties.

Further, I explore the integration of memristors into conventional electromagnetic devices, which represents advancement in information storage and processing. The convergence of memristive properties with electromagnetic wave propagation offers promising opportunities for new computing paradigms, including neuromorphic computing, data storage, and communication systems. I demonstrate theoretically the design and functionality of a metastructure composed of an array of memristors (mem-cells), illustrating how this configuration can effectively capture both the amplitude and phase characteristics of incident electromagnetic waves.