2,733 research outputs found
Multi-resolution time-domain modelling technique and its applications in electromagnetic band gap enhanced antennas
PhDNewly emerged Electromagnetic Band Gap (EBG) structures possess multiple frequency
bands that prohibit wave propagation and such stop bands are basically determined by
the periodicity of the structure. Such desirable features make EBG hybrid antenna an
interesting topic. Traditional full-wave techniques lack the efficiency to fully cope with
the complexity of these hybrid structures, since the periodical elements are often much
smaller in size than the accompanying antenna components.
The Haar wavelet based Multi-Resolution Time Domain (MRTD) technique provides
improved numerical resolution over the conventional Finite-Difference Time-Domain
(FDTD) method, as well as simplicity in formulation. One-dimensional, two-dimensional
and three-dimensional level-one codes are developed to assist the numerical modelling
of the hybrid EBG antennas. An explicit form of Perfectly Matched Layer (PML) configuration
is proposed, proved and presented. As a generic approach, its extensions suit
every single level of Haar wavelet functions. A source expansion scheme is proposed
thereafter.
The concept of a multi-band multi-layer EBG hybrid antenna is presented. The theoretical
prediction of antenna resonances is achieved through an effective medium model.
It has been verified via numerical simulations and measurements. The 3D MRTD code is
later applied to simulate such a structure.
In addition, EBG enhanced circularly polarized photonic patch antennas have been
studied. It is demonstrated that split-resonant rings (SRRs) and the like in EBG antennas
can lead to antenna gain enhancement, backward radiation reduction and harmonic
suppression.
Furthermore, a circularly polarized two-by-two antenna array with spiral EBG elements
is presented. The spiral element with ground via is more compact in size than
the traditional mushroom structure, which is proven very efficient in blocking unwanted
surface wave. Hence it reduces the mutual coupling of the array antenna significantly
Optimal Quality-of-Service Scheduling for Energy-Harvesting Powered Wireless Communications
XiaojingChen, Wei Ni, Xin Wang, YichuangSun, “Optimal Quality-of-Service Scheduling for Energy-Harvesting Powered Wireless Communications”, IEEE Transactions on Wireless Communications, Vol. 15 (5): 3269-3280, January 2016. © 2016 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.In this paper, a new dynamic string tautening algorithm is proposed to generate the most energy-efficient off-line schedule for delay-limited traffic of transmitters with non-negligible circuit power. The algorithm is based on two key findings that we derive through judicious convex formulation and resultant optimality conditions, specifies a set of simple but optimal rules, and generates the optimal schedule with a low complexity of O(N2) in the worst case. The proposed algorithm is also extended to on-line scenarios, where the transmit schedule is generated on-the-fly. Simulation shows that the proposed algorithm requires substantially lower average complexity by almost two orders of magnitude to retain optimality than general convex solvers. The effective transmit region, specified by the tradeoff of the data arrival rate and the energy harvesting rate, is substantially larger using our algorithm than using other existing alternatives. Significantly more data or less energy can be supported in the proposed algorithm.Peer reviewedFinal Accepted Versio
Periodic boundary value problems for nonlinear impulsive fractional differential equation
In this paper, we investigate the existence and uniqueness of solution of the periodic boundary value problem for nonlinear impulsive fractional differential equation involving Riemann-Liouville fractional derivative by using Banach contraction principle
Limbs and Cospectral Vertices in Trees
We generalize Schwenk's result that almost all trees contain any given limb
to trees with positive integer vertex weights. The concept of characteristic
polynomial is extended to such weighted trees and we prove almost all weighted
trees have a cospectral mate. We also prove almost all trees contain
cospectral vertices for any integer
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