Browsing by Author "Wang, Lixin"
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Item Open Access Comparison of 3-dimensional datasets by using the generalized n-dimensional (n-D) Feature Selective Validation (FSV) technique(IEEE, 2016-09-28) Zhang, Gang; Orlandi, A.; Duffy, A. P.; Wang, LixinAutomatic methods to evaluate the validity of computational electromagnetics computer modeling and simulations have widespread applications. The Feature Selective Validation method is a heuristic technique which has been shown to give broad agreement with visual assessment for 1-dimensional data. As a heuristic technique, extending the dimensionality is an important target for the improvement and development of FSV. One of the major challenges in the development of n-dimensional FSV is the difficulty of obtaining visual assessment results, since the visual comparison of three and higher dimensional data is difficult or even impossible. This paper formulates the comparison of 3-dimensional data based on an established generalized n-dimensional FSV approach. The performance of the approach is investigated by means of the LIVE Video Quality Database which provides subjective scores of 150 distorted videos. A statistical evaluation of the relative performance of FSV and other publicly available full-reference Video Quality Assessment algorithms is presented. Further, parameter tuning is performed to improve the agreement of 3-dimensional FSV results and subjective scores. The proposed approach is finally applied to the self-referenced validation of an electromagnetic simulation model to identify and locate the continuous variation of electric field within a region of space.Item Open Access Comparison of Data with Multiple Degrees of Freedom Utilizing the Feature Selective Validation (FSV) Method(IEEE, 2016-04-27) Zhang, Gang; Duffy, A. P.; Orlandi, A.; Di Febo, D.; Wang, Lixin; Sasse, Hugh G.The feature selective validation method has been shown to provide results that are in broad agreement with the visual assessment of a group of engineers for line, 1-D, data. An implementation using 2-D Fourier transforms and derivatives have been available for some years, but verification of the performance has been difficult to obtain. Further, that approach does not naturally scale well for 3-D and higher degrees of freedom, particularly if there are sizable differences in the number of points in the different directions. This paper describes an approach based on repeated 1-D FSV analyses that overcomes those challenges. The ability of the 2-D case to mirror user perceptions is demonstrated using the LIVE database. Its extension to n-dimensions is also described and includes a suggestion for weighting the algorithm based on the number of data points in a given “direction.”Item Open Access A Dimension-reduced Sparse Grid Strategy for Stochastic Collocation Method in EMC Software(IEEE, 2017-05-17) Bai, Jinjun; Zhang, Gang; Duffy, A. P.; Wang, LixinStochastic Collocation Method (SCM), a prevailing uncertainty analysis method, has been successfully implemented in Electromagnetic Compatibility (EMC) simulation, especially in EMC commercial software. However, the “curse of dimensionality” problem (dimensionality means the number of uncertain variables) limits the application of the SCM. This paper proposes a novel sparse grid strategy in order to improve the computational efficiency of the SCM, especially in high dimensionality case. In the proposed strategy, it is revealed that the number of the collocation points is in proportion to the dimensionality. By simulating two shielding effectiveness analysis examples in CST software, the feasibility of the proposed method can be presented clearly, with the help of the Feature Selective Validation method.Item Open Access Down-sampled and Under-sampled Data sets in Feature Selective Validation (FSV)(IEEE, 2014-06-09) Zhang, Gang; Wang, Lixin; Duffy, A. P.; Sasse, Hugh G.; Di Febo, D.; Orlandi, A.; Aniserowicz, KarolFeature Selective Validation (FSV) is a heuristic method for quantifying the (dis)similarity of two data sets. The computational burden of obtaining the FSV values might be unnecessarily high if data sets with large numbers of points are used. While this may not be an important issue per se it is an important issue for future developments in FSV such as real-time processing or where multi-dimensional FSV is needed. Coupled with the issue of data set size, is the issue of data sets having ‘missing’ values. This may come about because of a practical difficulty or because of noise or other confounding factors making some data points unreliable. These issues relate to the question “what is the effect on FSV quantification of reducing or removing data points from a comparison – i.e. down- or under-sampling data?” This paper uses three strategies to achieve this from known data sets. This paper demonstrates, through a representative sample of 16 pairs of data sets, that FSV is robust to changes providing a minimum data set size of approximately 200 points is maintained. It is robust also for up to approximately 10% ‘missing’ data, providing this does not result in a continuous region of missed data.Item Open Access Objective selection of minimum acceptable mesh refinement for electromagnetic simulation(IEEE, 2015-04-29) Duffy, A. P.; Zhang, Gang; Koziel, Slawomir; Wang, LixinOptimization of computational electromagnetics (EM) simulation models can be costly in both time and computing resource. Mesh refinement is a key parameter in determining the number of unknowns to be processed, which, in turn, controls the time and memory required. Hence, it is important to use only a mesh that is good enough for the objectives of the simulation. This might be for direct handling of high-fidelity EM models or, even more importantly, for setting up low-fidelity models in variable-fidelity optimization. On the other hand, in the early stages of an optimization process, a relatively coarse mesh can show whether the governing parameters of the simulation are being appropriately modeled. As the simulation geometry approaches its target, then so to can the mesh definition become more refined. This paper presents an approach to identify the minimum acceptable mesh coarseness based on the projected evolution of FSV’s Global Difference Measure as a model is refined from a very crude representation. Our approach is demonstrated using two examples of antenna structures.Item Open Access Performance Comparison of the SGM and the SCM in EMC Simulation(IEEE, 2016-09-23) Bai, Jinjun; Zhang, Gang; Wang, Di; Duffy, A. P.; Wang, LixinUncertainty analysis methods are widely used in today’s Electromagnetic Compatibility (EMC) simulations in order to take account of the non-ideality and unpredictability in reality and improve the reliability of simulation results. The Stochastic Galerkin Method (SGM) and the Stochastic Collocation Method (SCM), both based on the generalized Polynomial Chaos (gPC) expansion theory, have become two prevailing types of uncertainty analysis methods thanks to their high accuracy and high computational efficiency. This paper, by using the Feature Selective Validation (FSV) method, presents the quantitative accuracy comparison between the foregoing two methods, with the commonly used Monte Carlo Method (MCM) used as the comparison reference. This paper also introduces SCM into the CST software simulation as an example of performing uncertainty analysis. The advantages and limitations of SGM and SCM are discussed in detail in this paper. Finally, the strategy of how to choose between SGM, SCM, and MCM under different situations is proposed in the conclusion section.Item Open Access Step Frequency TR-MUSIC for Soft Fault Detection and Location in Coaxial Cable(IEEE, 2023-03-27) He, Xin; Wang, Lixin; Yang, Dazhi; Chang, Kaixing; Duffy, A. P.; Zhang, GangSoft faults in cables may trigger short circuits and open circuits in time, in that, they ought to be detected and thus eliminated at an earliest possible stage, as to ensure safe and stable operation of the cables. A method called the time-reversal multiple signal classification (TR-MUSIC) had been proposed in the literature, which has been demonstrated to be an effective technique for locating soft faults in cables, owing to its high resolution and excellent noise robustness. However, traditional TR-MUSIC relies on a vector network analyzer for measuring the scattering matrix of cables, which adds cost and complexity to its implementation. In this regard, a new way of acquiring the desired scattering parameters is herein proposed. An arbitrary function generator is used to inject incident signals into the cable under test, and an oscilloscope is used to collect the reflected signals. After post-processing, the phase of scattering parameters can be obtained. There's another key issue in the image of the detection results, ghost traces caused by the periodicity of Green's function severely impact the vision saliency of the actual fault location, which limits the performance of the fault location. A step frequency variant of TR-MUSIC has been proposed, therefore, to mitigate ghost traces. Experimental results show that the fault location error of the proposed approach is smaller than 0.33% for a 51-m long coaxial cable. Moreover, in the case of introducing noise, the proposed approach can operate in situations with signal-to-noise ratios as low as dB.Item Open Access Thermal Effects on Crosstalk of Multiconductor PVC Cables and Estimation of Thermal Accelerating Ratios(IEEE, 2022) Zhang, Gang; Chen, Xiao; Yang, Dazhi; Duffy, A. P.; Li, Ming; Wang, LixinThis paper is concerned with how crosstalk amplitudes of multi-conductor PVC cables vary with heating temperatures and time to determine thermal effects on the cables in realistic conditions, and thus proposes a method to estimate aging rates and acceler-ating ratios with respect to the variation of crosstalk amplitudes. First, the mechanism of thermal effects on crosstalk of multicon-ductor cables is analyzed: high temperatures accelerate chemical reactions in insulating materials to change their microstructures as well as their permittivity. The resulting variation of permittivi-ty leads to changes in crosstalk amplitude. Then, experiments are conducted to measure crosstalk amplitudes of cables in a thermal chamber. Finally, based on measured results, time-based varia-tions of crosstalk amplitudes at different temperatures are demonstrated and the equivalent chemical reaction rates calculat-ed. By fitting the rates with the Arrhenius equation, accelerating ratios between different temperatures are obtained.