ECE PhD Dissertation Defense: Arjun Singh

PhD Dissertation Defense: Design, Modeling, and Operation of Plasmonic Devices for Smart Communication Systems in the Terahertz Band

Arjun Singh

Location: 332 ISEC or Teams Link

Abstract: The terahertz (THz) band is an attractive spectral resource for realizing future communication systems, with the potential of supporting very high-speed data rates and increasingly dense networks. However, the lack of a well-developed technology that operates at these frequencies has remained a challenge for the scientific community. The very high propagation losses at THz frequencies and the decimating impact of everyday objects on THz wave propagation necessitate an up-haul of the conventional communication link, with smart control over the radiation, propagation, and detection of THz signals. Additionally, device physics at THz frequencies, among them the very high gain requirement and large electrical size, may render the often-held assumptions of the propagation model invalid. An interdisciplinary approach spanning device design and operation, and wireless propagation and signal processing is required.
To this end, the proposed research herein addresses the facilitation of an end-to-end communication link with graphene plasmonics as the cornerstone of the fundamental device physics. The devices designed can be utilized to effectively overcome the limited communication distance –The grand challenge of the THz band. Different from other undertakings, every attempt is made to ac-knowledge and accommodate the complex trade-offs in the design process. First, a novel graphene based plasmonic array architecture is proposed, explained, and modeled. The fundamental radiating element of the array architecture, called the plasmonic front-end, consists of a self-sufficient plasmonic source, a plasmonic modulator that acts as a phase controller, and a plasmonic nano-antenna for effective radiation. The designed array is compact and provides complete beamsteering support, with a new tailored algorithm developed for beamforming weight selection. Numerical evaluations and full-wave finite difference frequency domain (FDFD) simulations with COMSOL Multi-physics are utilized to verify array operation. Exploiting these properties, a multi-beam array design is presented next, where orthogonal spatial filters are utilized to provide support for spatial multiplexing towards the realization of ultra-massive MIMO (UM-MIMO). Taking this further, the design considerations of an interleaved plasmonic array are presented, in which the beamsteering capability is utilized to simultaneously achieve radio frequency interference (RFI) mitigation with channel capacity maximization for multi-user scenarios. Additionally, to realize the vision of a smart communication system with a programmable wireless environment, a hybrid reflectarray is presented. The fundamental element is modeled as a jointly designed and integrated metal-graphene patch. Numerical and simulation results are utilized to demonstrate the attractive properties of the reflectarray as compared to other proposed counterparts, including an independence from the incoming angle of the impinging wave, dynamic phase control capability, and strong reflection efficiency. The requirements of a THz communication link and their impact on the common communication protocols are considered next. It is shown that certain scenarios may render regular array operation invalid, motivating codebook designs that function in the massive near-field Fresnel zone of electrically large THz devices. Numerical simulations and theoretical analysis are presented to highlight their potential in improving system performance and capacity while reducing the system complexity. Finally, the significant milestones in the fabrication process of these devices are also presented.