Breaking the challenge of signal integrity using time-domain spoof surface plasmon polaritons

In modern integrated circuits and wireless communication systems/devices, three key features need to be solved simultaneously to reach higher performance and more compact size: signal integrity, interference suppression, and miniaturization. However, the above-mentioned requests are almost contradictory using the traditional techniques. To overcome this challenge, here we propose time-domain spoof surface plasmon polaritons (SPPs) as the carrier of signals. By designing a special plasmonic waveguide constructed by printing two narrow corrugated metallic strips on the top and bottom surfaces of a dielectric substrate with mirror symmetry, we show that spoof SPPs are supported from very low frequency to the cutoff frequency with strong subwavelength effects, which can be converted to the time-domain SPPs. When two such plasmonic waveguides are tightly packed with deep-subwavelength separation, which commonly happens in the integrated circuits and wireless communications due to limited space, we demonstrate theoretically and experimentally that SPP signals on such two plasmonic waveguides have better propagation performance and much less mutual coupling than the conventional signals on two traditional microstrip lines with the same size and separation. Hence the proposed method can achieve significant interference suppression in very compact space, providing a potential solution to break the challenge of signal integrity

Joint Community Detection and Rotational Synchronization via Semidefinite Programming

In the presence of heterogeneous data, where randomly rotated objects fall into multiple underlying categories, it is challenging to simultaneously classify them into clusters and synchronize them based on pairwise relations. This gives rise to the joint problem of community detection and synchronization. We propose a series of semidefinite relaxations, and prove their exact recovery when extending the celebrated stochastic block model to this new setting where both rotations and cluster identities are to be determined. Numerical experiments demonstrate the efficacy of our proposed algorithms and confirm our theoretical result which indicates a sharp phase transition for exact recovery

Analysis of power variation in a CANDU-6 with a loss of moderator

Moderator level -- Simulation algorithm -- Static calculations -- Kinetic calculations

Research and design of non-Foster active metamaterials

PhDDuring this PhD study, metamaterials incorporating active devices such as varactors and non-Foster circuits, were researched and designed. Starting from the research on tuneable metamaterials, an electronically controlled leaky-wave (LW) antenna based on composite right/left handed (CRLH) transmission line (TL) structure was proposed which could perform a broadband beam-fixing function with the frequency range from 1 to 4 GHz. In addition, scanning from forward to backward at a fixed frequency can be achieved by manipulating the biasing voltage applied to the varactors. Most of this study has been devoted to the non-Foster active metamaterials. First, the characterization of active magnetic metamaterials with non-Foster loads was presented. Based on the equivalent circuit model, stability of an actively-loaded loop array was examined through different analysis techniques, further to give the design specifications to achieve the broadband non-dispersive negative-Re(μ) (MNG) or μ-near-zero (MNZ) magnetic properties. Moreover, the wave propagation in the actively-loaded medium was investigated. By relating the dispersion characteristics and the effective medium properties, we henceforth proposed the design of zero-loss and broadband metamaterials. This thesis also has covered the study of active high impedance surfaces (HIS) with non-Foster loads. As a two-dimensional metamaterial structure, HIS have been widely used in the microwave and antenna engineering. However it can be easily seen that the performance of a general passive HIS is always limited by the narrow bandwidth, thus making a broadband HIS desirable. In this work, an analytical solution to achieving a stable broadband HIS structure is given by incorporating appropriate negative impedance converter (NIC) circuits. Simulation results have verified the design approach. Finally, the design of NIC circuits was presented as the key part of the realization of active metamaterials. Two schemes have been adopted to realize the design of NICs, one is the operational amplifier (op-amp) based NIC, and another is based on discrete transistors. Both types of NICs were introduced and studied in this thesis

Joint clustering and group synchronization: fundamental limits and efficient algorithms

The explosion of data in recent decades poses a formidable obstacle in data analysis due to its extensive volume and the low signal-to-noise ratio (SNR). Specifically, clustering and synchronization emerge as two fundamental problems that find applications across various scientific disciplines. In this thesis, we delve into a scenario where these two problems converge such that in the presence of heterogeneous data, each sample not only falls onto an underlying category or cluster but also associates with an unknown group element, giving rise to a joint problem that aims to recover the cluster structures and the group elements simultaneously. A motivating example is the 2D class averaging problem for cryo-electron microscopy single particle analysis, whose objective revolves around aligning and averaging projection images of a single particle that share similar viewing angles, thereby amplifying their SNR. Our study on the joint problem is based on a statistical model that integrates the stochastic block model for clustering and the random rewiring model for synchronization. In essence, the model generates a random data networks with community structures, where nodes within the same community are densely connected, as apposed to nodes across different communities that are sparsely connected. Furthermore, group transformations are observed on edges, resulting in clear observations for edges within the same cluster, while the transformations for connections across clusters are completely noisy. The first half of this thesis focuses on the development of efficient algorithms to solve the joint problem within the proposed model. Initially, we derive the maximum likelihood estimator (MLE) for recovery in the model. However, due to the non-convex nature and computational complexity of the MLE, we introduce an alternative formulation that allows for convex relaxations. This formulation serves as the foundation for the development of two efficient algorithms based on semidefinite relaxation and spectral relaxation, respectively. Remarkably, both methods achieve exact recovery of the cluster structures and the group elements, subject to mild conditions on the model parameters. In addition, we establish a performance guarantee for each algorithm, which sharply characterizes the empirical phase transition threshold for achieving exact recovery. The second part centers on the fundamental limits for creating an algorithm that achieves the exact recovery on the proposed model. In particular, we investigate the performance of the MLE, which represents the optimal estimator in terms of the recovery accuracy under a uniform prior. Through our analysis, we establish a sharp phase transition threshold for exact recovery by the MLE. Above the threshold, the exact recovery is achieved with high probability, while the MLE fails to recover with high probability below the threshold, indicating that no algorithms can succeed in such regime. Moreover, by comparing these limits with the performance of the proposed algorithms, we demonstrate a significant performance gap between the MLE and those efficient algorithms, suggesting that there is substantial room for improving the existing algorithms.Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2024-03-01 without embargo termsThe student, Yifeng Fan, accepted the attached license on 2023-08-28 at 00:01.The student, Yifeng Fan, submitted this Dissertation for approval on 2023-08-28 at 00:11.This Dissertation was approved for publication on 2023-09-05 at 15:46.DSpace SAF Submission Ingestion Package generated from Vireo submission #19818 on 2024-03-01 at 13:13:2