A hybrid technique is developed for the evaluation of two dimensional electromagnetic scattering from electrically large conducting bodies with cracks on their surfaces (TE case). The edge based finite element metho...A hybrid technique is developed for the evaluation of two dimensional electromagnetic scattering from electrically large conducting bodies with cracks on their surfaces (TE case). The edge based finite element method (FEM) is employed to compute the scattering from the cracks. Physical optics (PO) and physical theory of diffraction (PTD) are utilized to evaluate the scattering from the large bodies with the cracks filled with perfect conductors. These two methods are combined by an efficient coupling scheme. Some of numerical results are presented. It is shown that the hybrid technique has some advantages over other methods in regard to saving computer memory units and CPU time.展开更多
More stable and accurate recursive formulas and a computing procedure for scat-tering coefficient calculation of a multilayered sphere are proposed, This procedure involves threelogarithmic derivatives of Ricatti-Bess...More stable and accurate recursive formulas and a computing procedure for scat-tering coefficient calculation of a multilayered sphere are proposed, This procedure involves threelogarithmic derivatives of Ricatti-Bessel function ψ_n~＇(z)/ ψ_n(z), X_n~＇(z)/X_n(z),ξ_n~＇(z)/ ξ_n(z), as wellas the ratioψ_n(z)/X_n(z). The asymptotic behavior, stability, and accuracy of the procedureand scattering coefficients a_n and b_n are discussed for various complex refractive indices. Thisprocedure can be applied to large and small inhomogeneous spherical particles.展开更多
The multi-grid method has been known as an efficient iterative method for the linear systems and nonlinear systems that arise from finite difference approximations for partial differential equations. In this paper, th...The multi-grid method has been known as an efficient iterative method for the linear systems and nonlinear systems that arise from finite difference approximations for partial differential equations. In this paper, the multigrid method is extended to the application of solving integral equations which appear in electromagnetic scattering problems. The diakoptic theory is used for this purpose. Compared with other methods, the numerical results show that the multigrid method is powerful to solve electromagnetic scattering problems and can be used to compute electromagnetic scattering problems with electrically large bodies and complex structures.展开更多
Microwave remote sensing has become the primary means for sea-ice research, and has been supported by a great deal of field experiments and theoretical studies regarding sea-ice microwave scattering. However, these st...Microwave remote sensing has become the primary means for sea-ice research, and has been supported by a great deal of field experiments and theoretical studies regarding sea-ice microwave scattering. However, these studies have been barely carried in the Bohai Sea. The sea-ice microwave scattering mechanism was first developed for the thin sea ice with slight roughness in the Bohai Sea in the winter of 2012, and included the backscattering coefficients which were measured on the different conditions of three bands（L, C and X）, two polarizations（HH and VV）, and incident angles of 20° to 60°, using a ground-based scatterometer and the synchronous physical parameters of the sea-ice temperature, density, thickness, salinity, and so on. The theoretical model of the sea-ice electromagnetic scattering is obtained based on these physical parameters. The research regarding the sea-ice microwave scattering mechanism is carried out through two means, which includes the comparison between the field microwave scattering data and the simulation results of the theoretical model, as well as the feature analysis of the four components of the sea-ice electromagnetic scattering. It is revealed that the sea-ice microwave scattering data and the theoretical simulation results vary in the same trend with the incident angles. Also, there is a visible variant in the sensitivity of every component to the different bands.For example, the C and X bands are sensitive to the top surface, the X band is sensitive to the scatterers, and the L and C bands are sensitive to the bottom surface, and so on. It is suggested that the features of the sea-ice surfaces and scatterers can be retrieved by the further research in the future. This experiment can provide an experimental and theoretical foundation for research regarding the sea-ice microwave scattering characteristics in the Bohai Sea.展开更多
Starting from the basic integral equation for multiple scattered fields,a set of coupledlinear equations for the expansion coefficients of elastic multiple scattered fields by randomlydistributed spherical scatterers ...Starting from the basic integral equation for multiple scattered fields,a set of coupledlinear equations for the expansion coefficients of elastic multiple scattered fields by randomlydistributed spherical scatterers has been derived by using the expansions of the fields and thetranslational addition theorems of vector spherical wave functions.Thus,a new theory for thiskind of problems is developed.Different from the others,this theory gives the multiple elasticallyscattered fields in all space regions.展开更多
The scattering characteristics of electromagnetic waves from buildings are presented. The uniform geometric theory of diffraction (UTD) is employed to approximate the near field-far field distribution. The numerical r...The scattering characteristics of electromagnetic waves from buildings are presented. The uniform geometric theory of diffraction (UTD) is employed to approximate the near field-far field distribution. The numerical results presented demonstrate that the UTD solution can be conveniently and efficiently applied to many practical problems. As such results are of importance to the mobile communication field.展开更多
电离层中释放的金属蒸气产生人工等离子体云团,其可显著改变无线电波传播。本文利用几何绕射理论(geometrical theory of diffraction, GTD)和有限元法(finite element method, FEM)相结合的方法,给出了经由天线、人工等离子云团和无人...电离层中释放的金属蒸气产生人工等离子体云团,其可显著改变无线电波传播。本文利用几何绕射理论(geometrical theory of diffraction, GTD)和有限元法(finite element method, FEM)相结合的方法,给出了经由天线、人工等离子云团和无人机(unmanned aerial vehicle, UAV)群组成的传播链路中信号强度计算方法。利用30~70 MHz甚高频(very high frequency, VHF)信号研究人工等离子体云团与UAV群的复合散射特性,得出如下结论:接收功率随着信号频率增加呈下降趋势;当机群由N架UAV构成时,阵因子迭加使机群雷达散射截面(radar cross section, RCS)出现一定的起伏,同相迭加时,接收功率可比单个UAV高约20lg N dB;利用人工等离子体云团散射可实现VHF频段用于对米级尺度RCS目标进行超视距探测,有助于解决紧急情况下电离层扰动对高频探测的不利影响。展开更多
户外冲击放电试验导致附近建筑内通话中断、网络重启等问题时有发生,近年来带有智能组件的变压器进行冲击耐压试验时智能组件故障率高达50%,迫切需要开展冲击试验过程的电磁骚扰研究。为此进行了冲击试验的骚扰源特性分析,分析结果表明...户外冲击放电试验导致附近建筑内通话中断、网络重启等问题时有发生,近年来带有智能组件的变压器进行冲击耐压试验时智能组件故障率高达50%,迫切需要开展冲击试验过程的电磁骚扰研究。为此进行了冲击试验的骚扰源特性分析,分析结果表明冲击电流幅值可超过10 k A,频率主要在10 MHz以下。基于骚扰耦合路径分析,提出了将电缆屏蔽层与接地网导体联合建模的直接耦合法,该方法可以同时考虑电缆屏蔽层的散射效应和电缆内部瞬态的波动效应,误差分析表明该方法比国际大电网会议(CIGRE)推荐的解耦法计算结果更加精确。在武汉特高压交流试验基地开展的典型冲击放电试验表明:直接耦合法计算结果与测量结果基本一致,验证了直接耦合法的准确性;冲击试验情况下电缆屏蔽层双端接地比单端接地降低骚扰电压水平效果更好。展开更多
几何绕射理论(Geometrical Theory of Diffraction,GTD)模型能够精确描述高频区雷达目标的电磁散射机理。该文在分析雷达回波稀疏特性的基础上,将参数估计问题转化为压缩感知理论中的稀疏信号重构问题,据此提出了一种基于压缩感知的2维...几何绕射理论(Geometrical Theory of Diffraction,GTD)模型能够精确描述高频区雷达目标的电磁散射机理。该文在分析雷达回波稀疏特性的基础上,将参数估计问题转化为压缩感知理论中的稀疏信号重构问题,据此提出了一种基于压缩感知的2维GTD模型参数估计方法。该方法首先利用2维傅里叶变换成像确定目标散射中心的支撑区域,然后在支撑区域内对散射中心的GTD参数进行估计,最后利用聚类方法和最小二乘方法对估计结果进行修正。仿真和暗室测量数据实验结果表明,与现有方法相比,所提方法能有效改善模型参数的估计性能,且对提高散射中心类型参数的估计精度更为明显。展开更多
文摘A hybrid technique is developed for the evaluation of two dimensional electromagnetic scattering from electrically large conducting bodies with cracks on their surfaces (TE case). The edge based finite element method (FEM) is employed to compute the scattering from the cracks. Physical optics (PO) and physical theory of diffraction (PTD) are utilized to evaluate the scattering from the large bodies with the cracks filled with perfect conductors. These two methods are combined by an efficient coupling scheme. Some of numerical results are presented. It is shown that the hybrid technique has some advantages over other methods in regard to saving computer memory units and CPU time.
基金Supported by the National Natural Science Foundation of China
文摘More stable and accurate recursive formulas and a computing procedure for scat-tering coefficient calculation of a multilayered sphere are proposed, This procedure involves threelogarithmic derivatives of Ricatti-Bessel function ψ_n~＇(z)/ ψ_n(z), X_n~＇(z)/X_n(z),ξ_n~＇(z)/ ξ_n(z), as wellas the ratioψ_n(z)/X_n(z). The asymptotic behavior, stability, and accuracy of the procedureand scattering coefficients a_n and b_n are discussed for various complex refractive indices. Thisprocedure can be applied to large and small inhomogeneous spherical particles.
文摘The multi-grid method has been known as an efficient iterative method for the linear systems and nonlinear systems that arise from finite difference approximations for partial differential equations. In this paper, the multigrid method is extended to the application of solving integral equations which appear in electromagnetic scattering problems. The diakoptic theory is used for this purpose. Compared with other methods, the numerical results show that the multigrid method is powerful to solve electromagnetic scattering problems and can be used to compute electromagnetic scattering problems with electrically large bodies and complex structures.
基金The National Science Foundation for Young Scientists of China under contract No.41306193the National Special Research Fund for Non-Profit Marine Sector under of China under contract No.201105016the European Space Agency-Ministry of Science and Technology of the People’s Republic of China(ESA-MOST)Dragon 3 Cooperation Programme under contract No.10501
文摘Microwave remote sensing has become the primary means for sea-ice research, and has been supported by a great deal of field experiments and theoretical studies regarding sea-ice microwave scattering. However, these studies have been barely carried in the Bohai Sea. The sea-ice microwave scattering mechanism was first developed for the thin sea ice with slight roughness in the Bohai Sea in the winter of 2012, and included the backscattering coefficients which were measured on the different conditions of three bands（L, C and X）, two polarizations（HH and VV）, and incident angles of 20° to 60°, using a ground-based scatterometer and the synchronous physical parameters of the sea-ice temperature, density, thickness, salinity, and so on. The theoretical model of the sea-ice electromagnetic scattering is obtained based on these physical parameters. The research regarding the sea-ice microwave scattering mechanism is carried out through two means, which includes the comparison between the field microwave scattering data and the simulation results of the theoretical model, as well as the feature analysis of the four components of the sea-ice electromagnetic scattering. It is revealed that the sea-ice microwave scattering data and the theoretical simulation results vary in the same trend with the incident angles. Also, there is a visible variant in the sensitivity of every component to the different bands.For example, the C and X bands are sensitive to the top surface, the X band is sensitive to the scatterers, and the L and C bands are sensitive to the bottom surface, and so on. It is suggested that the features of the sea-ice surfaces and scatterers can be retrieved by the further research in the future. This experiment can provide an experimental and theoretical foundation for research regarding the sea-ice microwave scattering characteristics in the Bohai Sea.
文摘Starting from the basic integral equation for multiple scattered fields,a set of coupledlinear equations for the expansion coefficients of elastic multiple scattered fields by randomlydistributed spherical scatterers has been derived by using the expansions of the fields and thetranslational addition theorems of vector spherical wave functions.Thus,a new theory for thiskind of problems is developed.Different from the others,this theory gives the multiple elasticallyscattered fields in all space regions.
文摘The scattering characteristics of electromagnetic waves from buildings are presented. The uniform geometric theory of diffraction (UTD) is employed to approximate the near field-far field distribution. The numerical results presented demonstrate that the UTD solution can be conveniently and efficiently applied to many practical problems. As such results are of importance to the mobile communication field.
文摘电离层中释放的金属蒸气产生人工等离子体云团,其可显著改变无线电波传播。本文利用几何绕射理论(geometrical theory of diffraction, GTD)和有限元法(finite element method, FEM)相结合的方法,给出了经由天线、人工等离子云团和无人机(unmanned aerial vehicle, UAV)群组成的传播链路中信号强度计算方法。利用30~70 MHz甚高频(very high frequency, VHF)信号研究人工等离子体云团与UAV群的复合散射特性,得出如下结论:接收功率随着信号频率增加呈下降趋势;当机群由N架UAV构成时,阵因子迭加使机群雷达散射截面(radar cross section, RCS)出现一定的起伏,同相迭加时,接收功率可比单个UAV高约20lg N dB;利用人工等离子体云团散射可实现VHF频段用于对米级尺度RCS目标进行超视距探测,有助于解决紧急情况下电离层扰动对高频探测的不利影响。
文摘户外冲击放电试验导致附近建筑内通话中断、网络重启等问题时有发生,近年来带有智能组件的变压器进行冲击耐压试验时智能组件故障率高达50%,迫切需要开展冲击试验过程的电磁骚扰研究。为此进行了冲击试验的骚扰源特性分析,分析结果表明冲击电流幅值可超过10 k A,频率主要在10 MHz以下。基于骚扰耦合路径分析,提出了将电缆屏蔽层与接地网导体联合建模的直接耦合法,该方法可以同时考虑电缆屏蔽层的散射效应和电缆内部瞬态的波动效应,误差分析表明该方法比国际大电网会议(CIGRE)推荐的解耦法计算结果更加精确。在武汉特高压交流试验基地开展的典型冲击放电试验表明:直接耦合法计算结果与测量结果基本一致,验证了直接耦合法的准确性;冲击试验情况下电缆屏蔽层双端接地比单端接地降低骚扰电压水平效果更好。
文摘几何绕射理论(Geometrical Theory of Diffraction,GTD)模型能够精确描述高频区雷达目标的电磁散射机理。该文在分析雷达回波稀疏特性的基础上,将参数估计问题转化为压缩感知理论中的稀疏信号重构问题,据此提出了一种基于压缩感知的2维GTD模型参数估计方法。该方法首先利用2维傅里叶变换成像确定目标散射中心的支撑区域,然后在支撑区域内对散射中心的GTD参数进行估计,最后利用聚类方法和最小二乘方法对估计结果进行修正。仿真和暗室测量数据实验结果表明,与现有方法相比,所提方法能有效改善模型参数的估计性能,且对提高散射中心类型参数的估计精度更为明显。
