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111 results on '"Zhang, Wenxun"'

17. Electromagnetic scattering from a chiral cylinder - general case

Author

Chen, ZhiNing, Hong, Wei, and Zhang, WenXun

Subjects
Electromagnetic waves -- Scattering, Chirality -- Analysis, Wave equation -- Numerical solutions, Business, Computers, Electronics, Electronics and electrical industries
Abstract

In this paper, a generalized finite-difference (FD) scheme combined with the measured equation of invariance (MEI) is presented for the analysis of electromagnetic scattering from an inhomogeneous and lossy chiral cylinder with electrically large, arbitrarily shaped cross section. A new FD mesh in both chiral and achiral regions is formed, and the FD equations in a chiral medium are derived; then a large sparse matrix is formulated. The numerical results of bistatic scattering width (two-dimensional radar cross section) are given for the chiral cylinders of rectangular, elliptical, and complex cross section, respectively. Some results are compared with available data.

Published
1996

27. Statistical Distributions of Dayside ECH Waves Observed by MMS

Author

Lou, Yuequn, primary, Gu, Xudong, additional, Summers, Danny, additional, Ni, Binbin, additional, Liu, Kaijun, additional, Fu, Song, additional, Xiang, Zheng, additional, Zou, Zhengyang, additional, Cao, Xing, additional, Zhang, Wenxun, additional, Huang, He, additional, and He, Ying, additional

Published
2018
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33. A novel broadband and high-gain microstrip reflectarray antenna with variable polarization

Author

Zhang Wenxun, Liu Zhen-guo, Shen Wei, and WU Zhihang

Subjects
Patch antenna, Coaxial antenna, business.industry, Computer science, Antenna measurement, Antenna aperture, Antenna factor, Electronic, Optical and Magnetic Materials, Microstrip antenna, Optics, Electronic engineering, Antenna noise temperature, Electrical and Electronic Engineering, Antenna gain, business
Abstract

This article proposes a new kind of microstrip reflectarray antenna, of which the polarization could be reconfigured among all the polarization states instead of some fixed states in a dual-or multi-polarized antenna. The mechanism for polarized variability is so simple that only mechanical rotation is needed. Theoretical analysis shows that the reflected polarization covers all states and that the dual-or multi-layered unit structure sandwiched with air-gaps can broaden the bandwidth efficiently. Moreover, it is demonstrated that adopting more elements can enhance antenna gain. With these advantageous features, this kind of antenna has the potential significance for engineering applications in radar, communication, etc. In this article, a complete theoretical analysis as well as a specific design sample is given to verify this method.

Published
2008

35. Interactions between H+ band EMIC waves and radiation belt relativistic electrons: Comparisons of test particle simulations with quasi-linear calculations.

Author

Fu, Song, Ni, Binbin, Tao, Xin, Ge, Yasong, Liu, Jiang, Lou, Yuequn, Gu, Xudong, Cao, Xing, Xiang, Zheng, Zhang, Wenxun, and Zhang, Yang

Subjects
RADIATION belts, RELATIVISTIC electrons, OCEAN wave power, ELECTRON scattering, RELATIVISTIC particles, DIFFUSION processes
Abstract

We develop a general 3-D relativistic test particle (TP) simulation code to examine the trajectories and pitch angle variations of test electrons. We investigate the conditions when the electrons transit broadband, parallel propagating H+ band electromagnetic ion cyclotron (EMIC) waves to find whether the classical quasilinear theory (QLT) can be applied to interactions between H+ band EMIC waves and radiation belt relativistic (and ultra-relativistic) electrons. We find that to reach good consistency between TP scattering coefficients and QLT calculations, the wave-particle resonant interaction time (which indicates the time of particles traveling in the wave fields and being resonant with the wave fields) must be carefully calculated to ensure the validity of the linear diffusion process. This wave-particle resonant interaction time depends largely on the wave amplitude, the bandwidth, and the initial parameters of electrons for TP simulations; once the time of electrons traveling in the wave fields becomes large enough when the pitch angles of electrons scattered by wave fields reach the maximal value limited by the resonance condition and cannot be diffused any longer, the linear diffusion process of particles defined by QLT will not be valid any longer. When the resonant electrons start to travel through the wave field, they undergo the linear diffusion process resulting from the pitch angle scattering by the H+ band EMIC wave field. As the time of traveling in the wave fields increases, the test electrons will suffer effective pitch angle scattering and the pitch angles of these electrons will reach the maximum value limited by the resonance condition, which is determined by the wave and electron parameters. These electrons are then reflected by the wave fields and the linear wave-particle interactions defined by QLT will not be valid anymore. This kind of wave-particle interaction subsequently introduces considerable deviation of TP diffusion coefficients from those predicted by QLT calculations. Our results demonstrate that the general validity of QLT in describing how broadband EMIC waves affect radiation belt relativistic electrons is highly related to the time of electron traveling in the wave fields, which tends to increase for smaller wave power and broader wave frequency spectra. [ABSTRACT FROM AUTHOR]

Published
2019
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36. New approach to electromagnetic scattering from a conductive disc-ring structure

Author

Ye Chunfei and Zhang Wenxun

Subjects
Physics, Radar cross-section, Classical mechanics, Dimension (vector space), Scattering, Simple (abstract algebra), Charge density, Electrical and Electronic Engineering, Electrical conductor, Fourier series, Integral equation, Computational physics
Abstract

A one-dimensional modified integral equation for electromagnetic scattering from a metallic concentric disc-ring structure is derived by using Fourier expansion and separating the contribution of charge density from conventional EFIE. In the case of normal incidence, the derived equation is very simple and easy to be solved numerically regardless of the electric dimension of the structure. The comparison between the data of RCS of a disc by using this method and analytical method shows the effectiveness of this approach. Numerical results are also given for current distributions and the scattered fields for a disc-ring structure.

Published
1995

37. On convergence of collocation technique

Author

Zhang Wenxun and Hong Wei

Subjects
Mathematical optimization, Collocation, Rate of convergence, Normal convergence, Convergence (routing), Orthogonal collocation, Applied mathematics, Convergence tests, Electrical and Electronic Engineering, Galerkin method, Compact convergence, Mathematics
Abstract

In this paper, the convergence rate at matching points of collocation technique is shown to beO(h 2), that is just the same as the global convergence rate of Galerkin’s method with triangular pulses as basis and weighting functions. A numerical example to verify the conclusion is given.

Published
1991

38. Solution of arbitrary cross-section waveguide using method of eigen weighted boundary integral equation

Author

Zhu Lei and Zhang Wenxun

Subjects
Mathematical analysis, Free boundary problem, Boundary value problem, Mixed boundary condition, Electrical and Electronic Engineering, Boundary knot method, Singular boundary method, Boundary element method, Integral equation, Robin boundary condition, Mathematics
Abstract

Based on the second kind of Green’s identity, a boundary integral equation for arbitrary cross-section waveguide is transformed to a system of linear homogeneous algebraic equations by means of expansion of boundary bases and by using the eigen functions of a fictitious regular boundary as weighting functions, which corresponds to less algebraic equations than BEM and simpler coefficients than the modified BEM. The numerical results for some typical metallic waveguides are given by using the method of eigen-weighted boundary integral equation, and they are accurate enough with fast convergence.

Published
1990

39. Analysis of dipole and dipole array by a collocation technique with multipoint weighting

Author

Zhang Wenxun and Hong Wei

Subjects
Collocation, Computation, Mathematical analysis, Superconvergence, Computer Science::Numerical Analysis, Mathematics::Numerical Analysis, Weighting, Dipole, Computer Science::Computational Engineering, Finance, and Science, Collocation method, Orthogonal collocation, Electrical and Electronic Engineering, Galerkin method, Mathematics
Abstract

A collocation method with multipoint weighting is presented in this paper. It converges as rapidly as the Galerkin method but needs less computation effort. By means of the technique with Gauss points (superconvergence points) as the collocating points, dipole and dipole array are analyzed, and the numerical results are in good agreement with those given in relative references.

Published
1990

42. On the superconvergence of the method of moments (EM field problems)

Author

Zhang Wenxun, Yang Xiehua, and Hong Wei

Subjects
Polynomial, Rate of convergence, Degree (graph theory), Mathematical analysis, Piecewise, Boundary value problem, Method of moments (statistics), Superconvergence, Mathematics, Weighting
Abstract

The global convergence rate of the method of moments for EM boundary value problems with piecewise polynomial basis functions of degree k and piecewise polynomial weighting functions of degree n(n >

Published
2003

43. Importance of electron distribution profiles to chorus wave driven evolution of Jovian radiation belt electrons

Author

Huang, Jing, Gu, XuDong, Ni, BinBin, Luo, Qiong, Fu, Song, Xiang, Zheng, and Zhang, WenXun

Abstract

Wave‐particle interactions triggered by whistler‐mode chorus waves are an important contributor to the Jovian radiation belt electron dynamics. While the sensitivity of chorus‐driven electron scattering to the ambient magnetospheric and wave parameters has been investigated, there is rather limited understanding regarding the extent to which the dynamic evolution of Jovian radiation belt electrons, under the impact of chorus wave scattering, depends on the electron distribution profiles. We adopt a group of reasonable initial conditions based upon the available observations and models for quantitative analyses. We find that inclusion of pitch angle variation in initial conditions can result in increased electron losses at lower pitch angles and substantially modify the pitch angle evolution profiles of > ~500 keV electrons, while variations of electron energy spectrum tend to modify the evolution primarily of 1 MeV and 5 MeV electrons. Our results explicitly demonstrate the importance to the radiation belt electron dynamics in the Jovian magnetosphere of the initial shape of the electron phase space density, and indicate the extent to which variations in electron energy spectrum and pitch angle distribution can contribute to the evolution of Jovian radiation belt electrons caused by chorus wave scattering.

Published
2018
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