有耗媒质中3D目标体散射特性的TSNU-PSTD模拟

结合PML边界条件的傅立叶时域伪谱(PSTD)算法已广泛用于模拟电磁波传播和目标散射,但传统的PSTD方法在每个坐标方向上需要均匀分布的空间坐标网格点,从而不能够很好地模拟曲面目标和与网格空间尺寸不一致的目标,基于变空间的PSTD方法可以很好地克服这些不足。文中将CFS-PML边界条件在PSTD算法中实现并将它与TSNU-PSTD方法结合模拟了大范围有耗媒质中2D\3D曲面介质体目标的电磁散射,部分结果与FDTD计算结果进行了比较。仿真结果表明,基于变空间的PSTD只需平均每波长分成3个网格就可以达到较好的精度,可高效模拟电大尺寸空间曲面形状目标体的电磁散射。     

MRTD算法在一维PBG结构中的应用

将基于Daubechies紧支集尺度函数的时域多分辨分析(MRTD)算法用于光子带隙结构(PBG)的时域分析中,实现了MRTD算法的连接边界和PML吸收边界条件,并对带隙结构的反射系数进行了数值模拟和验证,所得结果与解析解一致.与传统FDTD 算法相比,MRTD算法在较大的网格散尺寸下,仍保证了精度,从而节省了内存并提高了计算效率.     

Z 变换法改进PML-FDTD 吸收边界条件

时域有限差分（FDTD）方法是计算时域电磁散射和辐射的一种简单有效的方法,被广泛应用于求解电磁场问题中,但由于计算机容量的限制,FDTD 计算只能在有限区域进行,为了能模拟开域电磁过程,在计算区域的截断边界处必须给出吸收边界条件,完全匹配层(PML)是一种行之有效的吸收边界条件。在PML 中应用Z 变换,和传统的引入PML 的方法相比,得到的迭代公式的程序更方便、更简单;考虑到要模拟的FDTD 计算区域的虚拟物质属性,采用了特殊的处理方法;数值实验验证了这种方法的有效性和吸收边界的吸收效果。     

一种新的PML构造及其在FDTD方法中的应用

完全匹配层(PML)吸收边界在处理开域问题的时域有限差分(FDTD)方法中已得到广泛应用.本文从PML中分裂场特性出发,提出一种新的PML构造,该构造中仅有八个子区且无角区.另外,采用降维方法对PML中分裂场进行存储,有效地节省计算内存.三维数值测试结果表明,构造的八层PML反射本地误差约为-160dB.另外,金属球散射截面模拟计算结果证实了新PML构造的实用性.     

平面光集成器件的时域伪谱法分析

将时域伪谱（PSTD）方法应用于平面光集成器件的分析，推导并实现了可用于PSTD方法的单轴各向异性完全匹配层（UPML）吸收边界条件，讨论了专用于导波结构仿真的一种紧凑的PSTD激励源。并对分布式反馈（DFB）光栅进行了数值模拟，其仿真结果与传统时域有限差分（FDTD）方法相当吻合，但PSTD无论在计算时间还是内存需求方面都大大优于FDTD方法。     

并行时域平面波在电大目标瞬态散射中的应用

基于电磁场时域积分方程数值技术计算复杂目标的瞬态散射特性,其计算量和内存需求大,应用经典的单元分组算法-时域平面波算法,降低了时域积分方程的计算规模.文中在研究时域平面波算法并行算法的基础上,开发了基于.NET Remoting 的电磁场分布式数值计算方案.数值结果表明,该分布式并行方案显著提高了时域平面波算法的计算效率,为解决电大目标瞬态电磁散射问题提供了一条有效途径.     

一种改进的Mur吸收边界条件

吸收边界条件是时域有限差分(FDTD)算法解决电磁问题的重要条件。提出一种改进的吸收边界条件。将惠更斯面推广到二维的时域有限差分算法中,并利用惠更斯面来改进Mur吸收边界。惠更斯面具有理论基础成熟、编程简单、占用的计算内存少等优点,可以方便地插入到FDTD计算域中。FDTD数值仿真证明,惠更斯面在增加少量计算量的同时大幅度提高了Mur边界的吸收性能。而在应用的截断边界元胞数目相同的情况下,改进的Mur吸收边界能达到比PML吸收边界更好的吸收效果。     

三维大尺寸介质目标散射问题的总场边界PSTD技术

传统的伪谱时域差分(PSTD)方法中不存在硬连接边界条件,基于Gao 等人的思想,在PSTD计算区域内设置8～10个网格层的连接区.通过引入加权窗函数,使得整个计算区域被有效地划分为总场区、连接区和散射场区.总场边界PSTD技术在成功地把入射波引入到PSTD计算区域内的同时,更便于复杂目标离散建模.以时域高斯脉冲为宽频带平面入射波,通过数值算例,验证了总场边界PSTD技术应用于三维大尺寸介质目标散射问题的有效性和实用性.     

基于.NET Remoting分布式计算电大目标瞬态散射特性

电磁场时域积分方程方法(TDIE)在解决瞬态电磁问题和宽带电磁问题等方面显示出独特的优势,然而TDIE的数值计算方法--时间步进算法(MOT)的计算规模较大,严重阻碍了TDIE方法在求解电大目标瞬态电磁特性中的应用.文章在研究MOT并行算法的基础上,开发了基于.NET Remoting的电磁场分布式数值计算方案.数值结果表明,该分布式并行方案显著提高了TDIE的计算效率,为解决电大目标瞬态电磁散射问题提供了一条有效途径.     

基于MPI实现粗糙地面电磁散射并行FDTD计算

提出了在由微机互连构成的机群(COW)并行计算系统上应用信息传递的方式实现粗糙地面散射并行FDTD算法.综合考虑了区域分割和负载平衡因素,并详细分析了子区域在普通网格和吸收边界处与相邻子区域的场值的数据传递,提高了二维粗糙地面FDTD并行计算效率.解决了在计算电大尺寸粗糙地面散射时产生的内存不足和计算耗时长等瓶颈问题.理论分析和数值计算结果验证了该算法的正确性;当计算电大尺寸的粗糙地面散射时,并行效率提升明显,即当参与计算的处理器数量达到6个时,并行效率仍然可以保持在90%以上.     

The 3-D multidomain pseudospectral time-domain algorithm for inhomogeneous conductive media

A three-dimensional (3-D) multidomain pseudospectral time-domain (PSTD) method with a strongly well-posed perfectly matched layer (PML) is developed as an accurate and flexible tool for the simulation of electromagnetic wave propagation and scattering in inhomogeneous and conductive media. This approach allows for an accurate treatment of curved geometries by multidomain decomposition and curvilinear coordinate transformation. Numerical experiments show the results agree excellently with analytical solutions and results of other well-known algorithms, and demonstrate a remarkable improvement in accuracy and efficiency over the FDTD method. The 3-D multidomain PSTD algorithm is then applied to calculate radar cross sections (RCS).     

Multidomain pseudospectral time-domain simulations of scattering by objects buried in lossy media

A multidomain pseudospectral time-domain (PSTD) method with a newly developed well-posed PML is introduced as an accurate and flexible tool for the modeling of electromagnetic scattering by 2-D objects buried in an inhomogeneous lossy medium. Compared with the previous single-domain Fourier PSTD method, this approach allows for an accurate treatment of curved geometries with subdomains, curvilinear mapping, and high-order Chebyshev polynomials. The effectiveness of the algorithm is confirmed by an excellent agreement between the numerical results and analytical solutions for perfectly conducting as well as permeable dielectric cylinders. The algorithm has been applied to model various ground-penetrating radar (GPR) applications involving curved objects in a lossy half space with an undulating surface. This multidomain PSTD algorithm is potentially a very useful tool for simulating antennas near complex objects and inhomogeneous media.     

A FDTD-based modal PML

The finite-difference time-domain (FDTD) method is one of the most popular numerical methods for solving electromagnetic problems because of its algorithmic simplicity and flexibility. For an open waveguide structure, modal perfectly matched layer (PML) schemes have been developed as efficient absorbing terminations. However, since these PML schemes are not derived directly from the FDTD algorithm, they do not perform as well as the original three-dimensional (3-D) PMLs. In this letter, a FDTD-based one-dimensional modal PML is proposed. Because it is derived directly from the FDTD formulation, its numerical dispersion characteristics are very close to the original FDTD method. Relative differences between results obtained with the proposed method and the original 3-D PML are found to be less than -220dB, and the proposed modal PML is shown to perform at least the same as the original PML if not better.     

A new anisotropic perfectly matched layer medium for mesh truncation in finite difference time domain analysis

In this paper an unsplit anisotropic perfectly matched layer (PML) medium, previously utilized in the context of finite element analysis, is implemented in the finite difference time domain (FDTD) algorithm. The FDTD anisotropic PML is easy to implement in the existing FDTD codes, and is well suited for truncating inhomogeneous and layered media without special treatment required in the conventional PML approach. A further advantage of the present approach is improved performance at lower frequencies. The applications of the unsplit anisotropic PML/FDTD method are illustrated by considering the problems of a plane wave propagation and an open microstrip line.     

Complex Envelope Six-Stages Split-Step PML Algorithm for Open Region Electromagnetic Problems

An implicit complex envelope split-step perfectly matched layer algorithm is presented for modeling open region finite difference time domain (FDTD) problems. The algorithm is based on splitting the FDTD time-step into six stages with an equal time increment of $Delta_{t}/6$ and it is suitable for band-limited electromagnetic applications. Numerical examples carried out in two dimensions show that the proposed algorithm presents a significant improvement over the other existing six-stages split-step FDTD algorithm for different Courant–Friedrichs–Lewy numbers and for different cell sizes per wavelength.      

An efficient PSTD algorithm for cylindrical coordinates

A pseudospectral time-domain (PSTD) algorithm is developed to overcome limitations in the conventional solution methods for Maxwell's equations in cylindrical coordinates. It is based on the fast Fourier transform (FFT) representation of spatial derivatives and a centered grid. The main contributions of this algorithm are to eliminate the singularity problem at the axis and to allow a larger time step. It uses a coarse grid close to the Nyquist sampling density provided that the geometrical modeling does not require fine cells. It reduces the required number of unknowns and the number of time steps in the finite-difference time-domain (FDTD) method and is efficient for large-scale problems     

Perfectly matched layer implementation using bilinear transform for microwave device applications

This paper presents an extensive study on the perfectly matched layer (PML) implementation using bilinear transform in the finite-difference time-domain (FDTD) simulation. The bilinear transform is used to implement both the stretched coordinate PML (SC-PML) and the uniaxial PML (UPML) with the complex frequency-shifted (CFS) equations. It is shown that with the CFS factor, the implemented SC-PML and UPML attain significantly lower relative reflection error over wide frequency range with both superior in performance to the split-field PML. The FDTD algorithm incorporating these PMLs is applied to analyze wide-band responses of some complex microwave devices, including RF microelectromechanical systems switch and coplanar waveguide crossover junction.     

Z-transform implementation of the perfectly matched layer for truncating FDTD domains

A simple algorithm for implementing the perfectly matched layer (PML) is presented for truncating finite difference time domain (FDTD) computational domains. The algorithm is based on incorporating the Z-transform method into the PML FDTD implementation. The main advantage of the algorithm is its simplicity as it allows direct FDTD implementation of Maxwell's equations in the PML region. In addition, the formulations are independent of the material properties of the FDTD computational domain. Numerical examples are included to demonstrate the effectiveness of these formulations.