Magneto-inductive Passive Relaying in Arbitrarily Arranged Networks

We consider a wireless sensor network that uses inductive near-field coupling for wireless powering or communication, or for both. The severely limited range of an inductively coupled source-destination pair can be improved using resonant relay devices, which are purely passive in nature. Utilization of such magneto-inductive relays has only been studied for regular network topologies, allowing simplified assumptions on the mutual antenna couplings. In this work we present an analysis of magneto-inductive passive relaying in arbitrarily arranged networks. We find that the resulting channel has characteristics similar to multipath fading: the channel power gain is governed by a non-coherent sum of phasors, resulting in increased frequency selectivity. We propose and study two strategies to increase the channel power gain of random relay networks: i) deactivation of individual relays by open-circuit switching and ii) frequency tuning. The presented results show that both methods improve the utilization of available passive relays, leading to reliable and significant performance gains.Comment: 6 pages, 9 figures. To be presented at the IEEE International Conference on Communications (ICC), Paris, France, May 201

Four-Coil Wireless Power Transfer Using Resonant Inductive Coupling

With the developments of mobile and implantable devices, wireless power transfer (WPT) has become increasingly attractive to free a variety of electronic systems from power cords and batteries. Resonant inductive coupling is the leading technology of WPT, offering high efficiencies (\u3e75%) with power levels from microwatts to hundreds of watts. This thesis focuses on a resonant four-coil inductive WPT technology. It develops numerical models of the four-coil WPT system (incorporated into a Matlab simulator) and validates them by experiment. It then develops numerical tools using Matlab for computing self- and mutual inductances for inductors of arbitrary shape and orientations using the method of magnetic vector potential and validates these tools by experiment. Inductance-calculation tools are designed to be user-friendly and are intended to be employed as a substitute for FEA (Finite Element Analysis). Effects of high magnetic permeability materials like ferrite sheets on the self- and mutual inductance of coils are studied, and Matlab-based numerical tools are developed to analyze such effects. These tools were validated by experimental work. A proposed design methodology employing the method of reflected impedances in loosely-coupled inductors is applied to the design of a four-coil WPT presented in this thesis. This method reflects impedances sequentially through the inductors from the system load to the driving source and is incorporated in a spreadsheet calculator. A design derived from this method is subjected to experimental validation and efficiencies exceeding 76% are noted with various spacings between the transmitting and receiving coil pairs. The method is shown to be useful for first-pass design, but significant effects are noted due to mutual inductances neglected in the design procedure. The full model is necessary for accurate simulation results. Conclusions and suggestions for future work are presented

Symmetry-Related Electromagnetic Properties of Resonator-Loaded Transmission Lines and Applications

This paper reviews the recent progress in the analysis and applications of the symmetry-related electromagnetic properties of transmission lines loaded with symmetric configurations of resonant elements. It will be shown that the transmission characteristics of these reactively loaded lines can be controlled by the relative orientation between the line and the resonant elements. Two main types of loaded lines are considered: (i) resonance-based structures; and (ii) frequency-splitting structures. In resonance-based transmission lines, a line is loaded with a single resonant (and symmetric) element. For a perfectly symmetric structure, the line is transparent if the line and resonator exhibit symmetry planes of different electromagnetic nature (electric or magnetic wall), whereas the line exhibits a notch (resonance) in the transmission coefficient if the symmetry planes behave as either electric or magnetic walls (symmetric configuration), or if symmetry is broken. In frequency-splitting lines, paired resonators are typically loaded to the transmission line; the structure exhibits a single notch for the symmetric configuration, whereas generally two split notches appear when symmetry is disrupted. Applications of these structures include microwave sensors (e.g., contactless sensors of spatial variables), selective mode suppressors (of application in common-mode suppressed differential lines, for instance) and spectral signature barcodes, among others

Numerical analysis of wireless power transfer in near-field UHF-RFID systems

A preliminary numerical analysis of the power transfer efficiency (PTE) for the forward link of near-field (NF) ultra high frequency (UHF)-radio frequency identification (RFID) systems is addressed in this paper, by resorting to an impedance matrix approach where the matrix entries are determined through full-wave simulations. The paper is aimed to quantify the NF-coupling effects on the PTE, as a function of the distance between the reader and tag antennas. To allow for a PTE comparison between different reader and tag antenna pairs, a benchmarking tag-loading condition has been assumed, where the tag antenna is loaded with the impedance that maximizes the PTE. In a more realistic loading condition, the load impedance is assumed as equal to the conjugate of the tag antenna input impedance. Full-wave simulations use accurate antenna models of commercial UHF-RFID passive tags and reader antennas. Finally, a “shape-matched antenna” configuration has been selected, where the reader antenna is assumed as identical to the tag antenna. It is shown that the above configuration could be a valuable compact solution, at least for those systems where the relative orientation/position between the tag and reader antennas can be controlled, and their separation is of the order of a few centimeters or less

Mutual Coupling Reduction between Closely Spaced U-slot Patch Antennas by Optimizing Array Configuration and its Applications in MIMO

Multiple-input, multiple-output (MIMO) systems have received considerable attention over the last decade. There are some limitations when obtaining the most from MIMO,such as mutual coupling between antenna elements in an array. Mutual coupling and therefore inter-element spacing have important effects on the channel capacity of a MIMO communication system, its error rate, and ambiguity ofMIMO radar system. There is a huge amount of research that focuses on reducing the mutual coupling in an antenna array to improve MIMO performance. In this research, we focus on the antenna section of the system.Antenna design affects the performance of Multiple-Input-Multiple-output (MIMO) systems. Two aspects of an antenna‟s role in MIMO performance have been investigated in this thesis. Employing suitable an antenna or antenna array can have a significant impact on the performance of a MIMO system. In addition to antenna design, another antenna related issue that helps to optimize the system performance is to reduce mutual coupling between antenna elements in an array. Much research has focused on the reduction of mutual coupling. In this research, the effect of the antenna configuration in array on mutual coupling has been studied and the main purpose is to find the array configuration that providesthe minimum mutual coupling between elements. The U-slot patch antenna is versatile antennas that because of its features like wide bandwidth,multi-band resonance and the ease of achieving different polarizations. This research first investigated the u-slot patch antenna, its features and capabilities. Seconda CAD optimization to design a low profile, dual band U-slot patch antenna is provided. Designed antenna is a dual band antenna that is intended to work at 3.5 and 5 GHz and have sufficient gain of at least 3dB. The effect of mutual coupling on MIMO systems is studied and then different array configurations were considered for two closely spaced U-slot patch antennas. Different configurations show different mutual coupling behavior. After modeling and simulation, the array was designed, implemented and finally tested in an anechoic chamber. These results are compared to both simulation and theoretical results and the configuration with minimum amount of mutual coupling was found. Some radar experiments also have been done to prove the effect of mutual coupling on radar performanc