三维有耗生物体局部逆散射的矩阵摄动理论

本文提出任意形状三维有耗生物体局部逆散射的矩阵摄动理论，当一个正常生物体物体的内部介质特性发生局部变化时，本文获得了变化散射场与介质特性的关系，进而导出了逆散的问题的各阶矩阵摄动解。具体的重建实例验证了上述理论的有效性。     

电磁点理论在有耗介质涂层导体薄片上TE波散射中的应用

在ＴＥ波入射下，对于计算二维封闭导体柱散射问题所常用的磁场积分方程法，当用于导体薄片时将会失效。本文采用电磁格点理论和电场方法研究这个问题。结合二维介质柱的电磁格点方程，解决了有耗介质涂层导体薄片的ＴＥ波散射。文中给出计算实例。     

电磁格点理论在有耗介质涂层导体薄片上TE波散射中的应用

在ＴＥ波入射下，对于计算二维封闭导体柱散射问题所常用的磁场积分方程法，当用于导体薄片时将会失效．本文采用电磁格点理论和电场方法研究这个问题．结合二维介质柱的电磁格点方程，解决了有耗介质涂层导体薄片的ＴＥ波散射．文中给出计算实例．     

二维有耗介质体电磁反演的时域玻恩迭代方法

本文利用时域非线性优化方法求解二维有耗介质的体的逆散射问题获得了很好的结果。并对正散射的求解精度做了改进。     

时域玻恩迭代的改进方法

本文提出了一种能够加速收敛的助推法，把助推法应用于时域非线性优化方法求解二维有耗介质体的逆散射问题，获得了很好的结果。     

T矩阵递推算法用于二维混合目标RCS计算

利用递推算法计算任意形状二维导体加介质体目标的电磁散射。建立导体部分单独存在时的T矩阵，对于内谐振频率点上生成的病态矩阵用奇异值分解方法解决，用广义递推算法求出有耗介质单体T矩阵。然后采用二体散射的方法求得总散射场。计算结果表明了该方法的正确性。     

二维有耗介质目标重建的Newton迭代方法

本文给出了一种由已知的散射场数据重建二维非均匀有耗目标的复介电常数的迭代算法。由积分方程出发，利用点匹配技术导出了依赖于未知参数的解析逆散射公式。由此可以以解析的形式计算场量对未知参数的导数（Jacobian和Hessian矩阵）。本文采用Newton优化方法迭代求解逆散射问题，具有二次收敛特性。为了克服逆散射中解的不适定性，连续采用多个方向的TM波照射目标，并采集目标区域外的散射场数据，以及采用共轭梯度法（CGM）求解逆问题，数值结果表明了本文所提方法的可行性和灵活性。     

直接反演非均匀介质柱的一种新方法

以往对介质柱的反演基本上都是采用这代优化方法,非常耗时。本文从电磁散射的积分方程出发结合矩量法提出一种直接反演二维非均匀介质柱的方法,即由散射场的测量值,无需迭代或优化而直接反演出介质柱的介电特性参数分布。通过引入正则化方法来改善解的稳定性。理论分析和模拟计算都表明,本文提出的方法计算量小且一般情况下有较高的精度和稳定性。     

双层介质柱损耗正切的逆散射法研究

本文导出了双层复介电常数圆柱体散射场的矩阵解公式,并用所模拟的散射场定量研究了用滤波-反投影技术计算出的介质柱内部介电常数分布特性。文中给出了介质圆柱的二维径向分布曲线以及由重构图象矩阵中统计回收计算出的介电常数损耗。     

电磁格点理论在有耗介质涂层导体柱TE和TM波散射中的应用

本文采用格点理论，建立了求解有耗介质涂层导体柱电磁散射（包括ＴＭ和ＴＥ两种情况）的基本方法。涂有有耗介质层的导体柱可以看成是一群由面格点和线格点组成的混合格点，分析它们的自作用和互作用，可以方便地解决散射问题。文中还给出了若干计算实例。     

High-frequency scattering by a conducting circular cylinder coatedwith a lossy dielectric of nonuniform thickness

A closed-form expression for the field produced by a plane wave incident on an infinitely long conducting cylinder, coated with a lossy dielectric of nonuniform thickness, is obtained using perturbation theory. This approximate series solution is later evaluated asymptotically for electrically large cylinder sizes. The scattered fields are interpreted using geometric optics and creeping waves. The fields are calculated using the exact series, the approximate perturbation series, and the high-frequency asymptotic solutions, and compared for different angles of incidence     

Application of a point-matching MoM reduced scheme to scatteringfrom finite cylinders

One of the most common methods for the solution of three-dimensional (3-D) scattering problems is the electric-field volume integral equation numerically solved by the application of the method of moments (MoM)-usually the point-matching version. Although simple to formulate, it shows inherent difficulty and complexity because of the 3-D integrals appearing in the interaction matrix elements and of the singularity of the dyadic Green's function (DGF) present in the computation of the self-cell elements. In this paper, a transformation method is presented, which in the case of the point-matching MoM, both reduces the 3-D integrals to two-dimensional (2-D) ones, and also eliminates the need of separate treatment of the singularity while maintaining the same degree of approximation. Comparison to published results is made for the case of scattering by a finite dielectric cylinder. Further examples are presented for scattering by layered dielectric cylinders and lossy cylindrical shells excited by uniform plane waves     

Scattering by arbitrarily cross-sectioned layered, lossy dielectric cylinders

The scattering properties of TM or TE illuminated lossy dielectric cylinders of arbitrary cross section are analyzed by the surface integral equation techniques. The surface integral equations are formulated via Maxwell's equations, Green's theorem, and the boundary conditions. The unknown surface fields on the boundaries are then calculated by flat-pulse expansion and point matching. Once the surface fields are found, scattered field in the far-zone and radar cross section (RCS) are readily determined. RCS thus obtained for circular homogeneous dielectric cylinders and dielectric coated conducting cylinders are found to have excellent agreements with the exact eigenfunction expansion results. Extension to arbitrary cross-sectioned cylinders are also obtained for homogeneous lossy elliptical cylinders and wedge-semicircle cross-sectioned cylinders, with and without a conducting cylinder in its center. RCS dependences on frequency and conductivity as well as the matrix stability problem of this surface integral equation method are also examined.     

Numerical analysis of electromagnetic fields in biological issues

The feasibility of using integral equation techniques to predict EM fields in biological tissues is demonstrated by analyzing the scattering from arbitrary cylinders composed of lossy dielectric materials. For the circular cylinder case, good agreement is obtained between moment method solutions and exact solutions. To show the applicability to arbitrary geometries, an elliptical cylinder is also considered.     

用BP神经网络技术重构介质圆柱体电磁参数

将BP神经网络技术应用于介质圆柱体电磁逆散射问题研究,通过BP神经网络将原逆散射问题转化为一个回归估计问题.设置多个目标散射场观测点,分别以目标不同的电磁参数及其响应下的散射电场的幅值作为BP网络的输出与输入,采用L-M训练算法,经过适当的训练,建立起逆散射模型,再以新的散射电场作为输入,实时重构了自由空间及半空间介质圆柱体的相对介电常数和电导率.数值结果显示了该方法的有效性及准确性,为目标的实时逆散射研究提供了一种高效的方法.     

High-frequency scattering by objects buried in lossy media

The uniform geometrical theory of diffraction (UTD) is extended so that it can be used to calculate the scattering from an object buried in a lossy medium. First, the accuracy of this high frequency method is examined by comparing numerical results for the scattering by a polygonal cylinder in a lossy medium of infinite extent with calculations based on a method of moments (MoM) solution. Next, the more difficult scattering problem of a polygonal cylinder in a lossy half space is treated. The UTD solution for the unbounded region is employed together with the fields of rays introduced by the interface between air and the lossy medium to obtain expressions for the scattered field in air and in the lossy medium     

TM scattering by an impedance sheet extension of a paraboliccylinder

An integral equation and method of moments (MM) solution are presented for the two-dimensional (2-D) problem of transverse magnetic (TM) scattering by an impedance-sheet extension of a perfectly conducting parabolic cylinder. An integral equation is formulated for a dielectric cylinder of general cross section in the presence of a perfectly conducting parabolic cylinder. It is then shown that the solution for a general dielectric cylinder considerably simplifies for the special case of TM scattering by a thin multilayered dielectric strip that can be represented as an impedance sheet. The solution is termed an MM/Green's function solution, where the unknowns in the integral equation are the electric surface currents flowing in the impedance sheet; the presence of the parabolic cylinder is accounted for by including its Green's function in the kernel of the integral equation. The MM solution is briefly reviewed, and expressions for the elements in the matrix equation and the scattered fields are given. Sample numerical results are provided