5,548 research outputs found
Constant beamwidth generalised sidelobe canceller
In this paper, we proposed a constant beamwidth discrete Fourier transform (DFT) beamformer based on the generalised sidelobe canceller (GSC). Broadband signals are decomposed into frequency bins which are grouped into octaves and tapered individually. The resulting beampattern possesses constant beamwidth across the entire operating spectrum, thus ensuring uniform spatial resolution. Further incorporation of the GSC allows adaptive nulling of interference to coincide with uniform resolution, enhancing the beamformerâs performance. However, modification to the constraint equation of the standard GSC is required to account for the frequency-dependent weighting of sensors
Adaptive transient solution of nonuniform multiconductor transmission lines using wavelets
AbstractâThis paper presents a highly adaptive algorithm for the transient simulation of nonuniform interconnects loaded with arbitrary nonlinear and dynamic terminations. The discretization of the governing equations is obtained through a weak formula-tion using biorthogonal wavelet bases as trial and test functions. It is shown how the multiresolution properties of wavelets lead to very sparse approximations of the voltages and currents in typical transient analyzes. A simple yet effective timeâspace adaptive al-gorithm capable of selecting the minimal number of unknowns at each time iteration is described. Numerical results show the high degree of adaptivity of the proposed scheme. Index TermsâElectromagnetic (EM) transient analysis, multi-conductor transmission lines (TLs), wavelet transforms. I
Multiobjective optimization of electromagnetic structures based on self-organizing migration
PrĂĄce se zabĂœvĂĄ popisem novĂ©ho stochastickĂ©ho vĂcekriteriĂĄlnĂho optimalizaÄnĂho algoritmu MOSOMA (Multiobjective Self-Organizing Migrating Algorithm). Je zde ukĂĄzĂĄno, ĆŸe algoritmus je schopen ĆeĆĄit nejrĆŻznÄjĆĄĂ typy optimalizaÄnĂch Ășloh (s jakĂœmkoli poÄtem kritĂ©riĂ, s i bez omezujĂcĂch podmĂnek, se spojitĂœm i diskrĂ©tnĂm stavovĂœm prostorem). VĂœsledky algoritmu jsou srovnĂĄny s dalĆĄĂmi bÄĆŸnÄ pouĆŸĂvanĂœmi metodami pro vĂcekriteriĂĄlnĂ optimalizaci na velkĂ© sadÄ testovacĂch Ășloh. Uvedli jsme novou techniku pro vĂœpoÄet metriky rozprostĆenĂ (spread) zaloĆŸenĂ© na hledĂĄnĂ minimĂĄlnĂ kostry grafu (Minimum Spanning Tree) pro problĂ©my majĂcĂ vĂce neĆŸ dvÄ kritĂ©ria. DoporuÄenĂ© hodnoty pro parametry ĆĂdĂcĂ bÄh algoritmu byly urÄeny na zĂĄkladÄ vĂœsledkĆŻ jejich citlivostnĂ analĂœzy. Algoritmus MOSOMA je dĂĄle ĂșspÄĆĄnÄ pouĆŸit pro ĆeĆĄenĂ rĆŻznĂœch nĂĄvrhovĂœch Ășloh z oblasti elektromagnetismu (nĂĄvrh Yagi-Uda antĂ©ny a dielektrickĂœch filtrĆŻ, adaptivnĂ ĆĂzenĂ vyzaĆovanĂ©ho svazku v ÄasovĂ© oblastiâŠ).This thesis describes a novel stochastic multi-objective optimization algorithm called MOSOMA (Multi-Objective Self-Organizing Migrating Algorithm). It is shown that MOSOMA is able to solve various types of multi-objective optimization problems (with any number of objectives, unconstrained or constrained problems, with continuous or discrete decision space). The efficiency of MOSOMA is compared with other commonly used optimization techniques on a large suite of test problems. The new procedure based on finding of minimum spanning tree for computing the spread metric for problems with more than two objectives is proposed. Recommended values of parameters controlling the run of MOSOMA are derived according to their sensitivity analysis. The ability of MOSOMA to solve real-life problems from electromagnetics is shown in a few examples (Yagi-Uda and dielectric filters design, adaptive beam forming in time domainâŠ).
An adaptive disturbance rejection control scheme for voltage regulation in DC micro-grids
© 2019 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.Uncertain generation by renewable sources and load variations have resulted in adding energy storage systems in the grid to maintain grid parameters (voltage, frequency) within prescribed limits. The disturbances being non-deterministic in nature, the voltage regulation control by the storage systems relies mostly on dual loop architecture with an outer voltage and inner current loop. Improvement in controller dynamics can be achieved through feed forward of disturbance profile but at expense of additional sensors and communication in the grid. This work explores the application of an adaptive disturbance rejection control scheme for disturbance estimation (without using additional sensors) employing an extended state and proportional integral observer (PI+ESO). The proposed observer aim to achieve robust disturbance estimation under grid parameter uncertainty. The effectiveness of the proposed scheme over the conventional one will be put forward through H8 and H2 norm analysis of the system. The design and simulation results of the proposed scheme will be presented in this work.Peer ReviewedPostprint (author's final draft
Hamiltonian description and traveling waves of the spatial Dysthe equations
The spatial version of the fourth-order Dysthe equations describe the
evolution of weakly nonlinear narrowband wave trains in deep waters. For
unidirectional waves, the hidden Hamiltonian structure and new invariants are
unveiled by means of a gauge transformation to a new canonical form of the
evolution equations. A highly accurate Fourier-type spectral scheme is
developed to solve for the equations and validate the new conservation laws,
which are satisfied up to machine precision. Further, traveling waves are
numerically investigated using the Petviashvili method. It is found that their
collision appears inelastic, suggesting the non-integrability of the Dysthe
equations.Comment: Research report. 17 pages, 7 figures, 38 references. Other author's
papers can be downloaded at http://www.lama.univ-savoie.fr/~dutykh/ . arXiv
admin note: substantial text overlap with arXiv:1110.408
Flexible lensless endoscope with a conformationally invariant multi-core fiber
The lensless endoscope represents the ultimate limit in miniaturization of
imaging tools: an image can be transmitted through a (multi-mode or multi-core)
fiber by numerical or physical inversion of the fiber's pre-measured
transmission matrix. However, the transmission matrix changes completely with
only minute conformational changes of the fiber, which has so far limited
lensless endoscopes to fibers that must be kept static. In this letter we
report for the first time a lensless endoscope which is exempt from the
requirement of static fiber by designing and employing a custom-designed
conformationally invariant fiber. We give experimental and theoretical
validations and determine the parameter space over which the invariance is
maintained
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