Electromagnetic Scattering From Multilayer Rough Surfaces With Arbitrary Dielectric Profiles for Remote Sensing of Subsurface Soil Moisture

Radar remote sensing of soil moisture content at low frequencies requires an accurate scattering model of realistic soils, which often involves multilayer rough surfaces and dielectric profiles. In this paper, a hybrid analytical/numerical solution to two-dimensional scattering from multilayer rough surfaces separated by arbitrary dielectric profiles based on the extended boundary condition method (EBCM) and scattering matrix technique is presented. The reflection and transmission matrices of rough interfaces are constructed using EBCM. The dielectric profiles are modeled as stacks of piecewise homogeneous dielectric thin layers, whose scattering matrices are computed by recursively cascading reflection and transmission matrices of individual dielectric interfaces. The interactions between the rough interfaces and stratified dielectric profiles are taken into account by applying the generalized scattering matrix technique. The scattering coefficients are obtained by combining the powers computed from the resulting Floquet modes of the overall system. The bistatic scattering coefficients are validated against existing analytical and numerical solutions. Field-collected soil moisture data are then used for numerical simulations to investigate the penetration capability at different frequencies and to address the potential of low-frequency radar systems in estimating deep soil moisture. In particular, soil moisture profiles during dry ground, wet ground, and wet subsurface layer conditions are examined. The results show that both backscattering coefficients and copolarized phase difference at low frequencies are sensitive to the roughness of subsurface interfaces and deep soil moisture. Also, much larger depth sensitivity can be achieved using copolarized phase difference than scattering coefficients     

平板与正弦型组合粗糙面的电磁波复合散射

分别用正弦型组合粗糙面和正弦型二维粗糙面模拟海洋表面，建立了海上目标电磁散射的简化模型，用物理光的双次反弹来表示目标与组合粗糙面之间的电磁波相互作用。     

损耗介质周期加载圆柱波导场分析

本文利用傅立叶级数将损耗介质周期加载圆柱波导结构的场展开,通过分界面上场匹配的模式分析方法得出了TMOn模的色散曲线、电磁场分布以及品质冈数等特性参量.编写了程序DDET-TM并计算TM01模的各特性参量,得到的结果与HFSS的仿真结果吻合较好,验证了本方法的适用性.     

粗糙表面电磁散射系数数字方法分析与比较

回顾了随机粗糙表面电磁散射特性计算方法的特点,分析对比了各类积分方程法和微分方程法的核心算法,着重讨论了矩阵分裂算法的计算效率,以及时域有限差分法求解色散粗糙面宽带散射特性的有关问题,指出了粗糙表面散射系数的计算和选择方法。     

粗糙海面上三维金属目标的电磁散射特性分析

该文采用矩量法(MoM)计算粗糙海面上三维金属目标的电磁散射特性。计算了位于半空间媒质中的电偶极子和磁偶极子的矢量位并矢格林函数和标量位格林函数,并将其应用于矩量法中。把海水视为下半空间媒质,粗糙海面为位于上半空间中的介质表面。通过建立介质和金属混合目标的积分方程,并采用迭代方法求解矩阵方程以得到该模型的散射特性,数值结果验证了本文方法的有效性。     

一维粗糙介质分形海面电磁散射的扩展边界条件法

在采用经典扩展边界条件法处理导体分形粗糙面散射的基础上,将此方法推广到了一维粗糙介质分形海面的电磁散射.通过与传统的基尔霍夫近似法计算结果进行比较,验证了本文所给的方法,分析了不同入射角,不同分维和空间波数时海面双站散射振幅角分布的特点.     

太赫兹低频段随机粗糙金属板散射特性研究

该文提出了一种高效混合近似算法计算太赫兹频段无限薄金属板的电磁散射特性。在太赫兹低频段,金属目标可以被视为具有微粗糙表面的理想导体,散射场可以分为相干场和非相干场。该文采用物理光学法结合截断劈增量长度绕射系数法和微扰法来计算金属板的电磁散射分布。基于蒙特卡洛方法,分别利用多层快速多极子和提出的混合算法计算太赫兹低频段金属板的雷达散射截面,仿真结果表明该文提出的混合算法能够高效快速地给出太赫兹低频段金属板的电磁散射特性。      

Scattering of Electromagnetic Waves by a Coated Nihility Cylinder

An analytical solution for the scattering of electromagnetic plane waves from an infinitely long nihility cylinder, coated with a double positive (DPS), double negative (DNG), epsilon negative (ENG), or mu negative (MNG) layer of uniform thickness is presented. The solution is determined by solving the scalar wave equation in the cylindrical coordinates, for different regions and applying the appropriate boundary conditions at the interfaces. Both TM and TE polarizations as incident plane have been considered in the analysis. Comparison of behaviors of a coated nihility cylinder with a coated PEC cylinder has been made. It is noted that two situations are more closer for DNG coating as compared to DPS coating.     

Scattering of Electromagnetic Waves by a Semi-Infinite Carbon Nanotube

Scattering of electromagnetic cylindrical waves by an isolated, semi-infinite, open-ended, single-shell, zigzag carbon nanotube (CN) is considered in the optical regime. The CN is modeled as a smooth homogeneous cylindrical surface with impedance boundary conditions known from quantum-mechanical transport theory. An exact solution of the diffraction problem is obtained by the Wiener-Hopf technique. The differences between the scattering responses of metallic and semiconducting CNs are discussed.     

Minimizing Electromagnetic Scattering by Varying Height of Metallic Surfaces

This letter determines the dimensional profile of a periodic metallic surface that minimizes the electromagnetic energy scattering of an incident plane-wave back in the incident direction, irrespective of the plane-wave incidence angle. Simple Fourier series is used to describe the surface height variation and it is shown that a small number of design parameters are required to obtain the optimal profile of the surface. Experimental validations are presented and a very good agreement with electromagnetic simulation results is achieved.     

Analysis of Electromagnetic Waves Scattering by a Finite Size Dielectric and Metal Cylinder in a Rectangular Waveguide

The paper presents a rigorous solution of the scattering problem by a circular dielectric and perfectly conducting cylinders of any radius and any height in the rectangular waveguide oriented perpendicularly to a wall. The method is based on the representation of fields in waveguide and dielectric medium by cylindrical eigenfunctions and application of boundary conditions on surfaces of the cylinder to evaluate the fields inside and outside the cylinder. The reflection and transmission coefficients are expressed through the fields. As an example the reflection and transmission coefficients versus frequency for various dielectric and metallic cylinders are computed. The comparison of numerical with experimental data is presented.     

Scattering Analysis of Dielectric Periodic Structures by an Oblique Incidence

The scattering of dielectric periodic structures by a plane wave incident in the direction oblique to the periodic grooves is analyzed by a method which combines the multimode network theory with the rigorous mode matching method. Combining the TE and TM characteristic mode functions determined in the corresponding 2-D scattering problem resulting from a TE or TM wave incident along the principal-plane of the same structure, and using a simple mathematical transformation, the 3-D scattering problem by an oblique incidence is rigorously solved.     

The Diffraction of Electromagnetic Waves by Dielectric Steps in Waveguides

The problem of determining the scattered electromagnetic fields when a dielectric step discontinuity is placed in a waveguide is considered. Although an exact method of solution is not presently known, the recently introduced modified residue-calculus technique (MRCT) can be successfully extended to obtain a very accurate and numerically efficient approximate solution of the semi-infinite dielectric step. A still further extension of the modified residue-calculus method yields the approximate solution for the case of a finite dielectric step. A unique advantage of the present methods is that the degree of accuracy obtained is independent of the relative permittivity of the dielectric material and of the frequency. Thus very high permittivities or frequencies can be considered without an attendant increase in computational complexity. Numerical data are presented which confirm the accuracy of the method.     

Fast Solution of Electromagnetic Scattering From Thin Dielectric Coated PEC by MLFMA and Successive Overrelaxation Iterative Technique

To speed up solution of electromagnetic scattering from 3-D conducting structures coated by thin dielectric material, the multilevel fast multipole algorithm and successive overrelaxation iterative technique are applied into the thin dielectric sheet (TDS) model. Based on the TDS model, only the induced current density on the surface of the conducting structure is required. By adding unitary operator for unknown current on both sides of the electric field integral equation, a successive overrelaxation iteration is constructed. The total computational expense is reduced greatly while reasonable accuracy is maintained. Numerical results demonstrate the validity and efficiency of the present method.      

分层粗糙面电磁散射的矩量法研究

本文主要采用矩量法(method of moment MOM)研究了分层粗糙面的电磁散射特性,首先给出了该散射问题的积分方程和矩阵方程,然后通过与时域有限差分(finite difference time domain FDTD)计算结果的对比说明了本文所提算法的有效性,最后讨论了分层粗糙面的均方根高度、相关长度以及两层粗糙面之间的距离对双站散射系数的影响。     

Scattering of Electromagnetic Waves by a Cylinder Moving Along its Axis

The scattering of a time-harmonic, linearly polarized plane electromagnetic wave by a cylinder uniformly moving along its axis is discussed. The formalism is relativistically exact, and explicit forms are provided for first-order velocity effects. Consideration is given to both a cylinder moving in free space, using the procedure suggested by Einstein, and two refractive media; it is veritied that the first case is a special case of the second one. Thin scatterers are considered and it is shown that no first-order velocity effects are present. For a moving medium, having in its rest frame the same constitutive parameters as the surrounding medium, it is shown that the velocity-independent part vanishes, but scattered fields of the first order in the velocity are still present. Moreover, these waves appear with the opposite polarization (compared to the incident wave).     

Broadband Müller-MLFMA for Electromagnetic Scattering by Dielectric Objects

The multilevel fast multipole algorithm (MLFMA) is very efficient for solving large-scale electromagnetic scattering problems. However, at low frequencies, or when the discretization is small compared with the wavelength, both the MLFMA and the underlying integral equation formulation typically suffer from a subwavelength breakdown. For the electromagnetic scattering from a homogeneous dielectric object, we obtain a stable and well-conditioned surface integral formulation using a variant of the classical Muumlller formulation and linear basis functions. To overcome the subwavelength breakdown of the MLFMA, we use both propagating and evanescent plane waves to represent the fields. The implementation is based on a combination of the spectral representation of the Green's function and Rokhlin's translation formula. We also present a new interpolation scheme for the evanescent part, which significantly improves the error-controllability of the MLFMA-implementation. Several numerical results verify both the error-controllability and scalability of the proposed algorithm     

Scattering of Electromagnetic Waves by Arrays of Conducting Cylinders Interspaced by Inhomogeneous Dielectrics

The scattering and transmission properties of arrays of rectangular conducting cylinders interspaced by homogeneous and inhomogeneous dielectric materials are studied by a fimite-difference coupling method for an E-polarized incident wave. Computed numerical results are presented which reveal interesting physical phenomena.     

A Source-Model Technique for the Analysis of Transient Electromagnetic Scattering by a Periodic Array of Cylinders

The source-model technique is applied to the solution of the problem of electromagnetic scattering by a periodic array of perfectly conducting cylinders illuminated by a transient plane wave. Special attention is given to the non-causality problem arising in the case of oblique incidence. This problem is alleviated by utilizing a transformation specifically tailored to the source-model formulation in a manner that significantly reduces the number of unknown future values that are required at each time step. Using this transformation, together with a band-limited extrapolator, it is possible to obtain a relatively stable solution that provides a satisfactory degree of accuracy for a wide range of incidence angles. To exemplify the use of this technique, we apply it to the case of circular cylinders.     

用场量迭代法分析三维介质目标的电磁散射

本文用场量迭代方法对三维电场积分方程进行数值求解,得到了给定电磁波照射下介质体内的场分布,并由此求得介质体外的散射场.从本文给出的几个算例看出,得到的解能较快收敛,并且避免了矩阵求逆运算,具有运算简便与速度快等优点。本文给出的薄板形介质的计算结果与现有文献的实验结果和计算结果进行了比较.证实了本文方法的正确性。