时域有限差分中各向异性完全匹配层的实现方法

本文讨论了如何在给定边界层数的条件下,通过调整各介质层吸收层的介质参数来实现入射波的最佳吸收,并利用自适应遗传算法对算法中的边界参数进行优化。     

FDTD方法吸收边界条件的研究及应用

用时域有限差分法(FDTD)求解电磁散射问题中,吸收边界条件的设置起着关键性作用.通过时间和空间上的递推算法对时域有限差分法中的两种吸收边界条件:Mur吸收边界条件和完全匹配层(PML)的吸收效果进行了比较和分析.同时,引入参数对PML的差分方程进行了优化,避免了将电磁场分裂为两个分量进行计算,进而降低了计算内存开销.实验结果证明PML具有更优越的吸收性能.最后,在FDTD算法中应用PML吸收层对一圆柱形导体的雷达散射截面积(RCS)进行数值仿真,验证了FDTD算法在计算雷达散射截面积(RCS)上的有效性.     

泄漏同轴电缆在隧道中的辐射特性研究

为了考察泄漏同轴电缆在矩形隧道中的辐射特性,根据泄漏同轴电缆的辐射理论,用时域有限差分方法计算了泄漏同轴电缆开槽口处的电磁场分布,再用射线追踪法分析了在矩形隧道中从泄漏同轴电缆槽口处漏泄出的电波经直射、反射之后所形成的辐射场,结果表明:泄漏同轴电缆辐射出的电磁波可以布满隧道空间,能够弥补传统天线在闭域或半闭域空间中存在...     

基于FDTD的机载短波天线辐射特性分析

机载天线辐射特性的研究对于机载天线的设计与布局具有重要的意义。机载天线在机身的影响下会改变其原有辐射特性,针对上述问题采用时域有限差分法(FDTD)对机载短波天线的辐射特性进行了分析,并应用FDTD对某型号机载短波天线进行了仿真:使用软件建立整机模型,应用自适应网格对其进行了剖分,设置了PML吸收边界,添加激励并计算得出增益方向图,最后将仿真结果与实测结果进行了比较,二者在天线工作频带内吻合,验证了FDTD对机载天线辐射特性进行分析的有效性与实用性。     

TTI介质井间地震波场紧致交错网格高阶有限差分模拟及边界条件

研究井间地震波场的形成过程以及波场的传播机理、规律,对于指导实际井间地震勘探有着重要的意义．从具有倾斜对称轴的横向各向同性介质（TTI）的二维三分量一阶速度-应力弹性波方程出发,采用高阶紧致交错网格差分算子对方程进行差分离散,得到了TTI介质中井间地震波场正演的高阶有限差分格式．并推导了TTI介质完全匹配层吸收边界条件公式和相应的紧致交错网格高阶差分格式,在此基础上实现了二维三分量TTI介质中井间地震波场模拟．数值算例表明：紧致交错网格高阶有限差分方法模拟的记录精度高,数值频散小,该方法能够精确的模拟复杂各向异性介质中的地震波传播过程,可以得到高精度的正演记录．完全匹配层吸收边界能有效地解决人工边界问题,是一种高效的边界吸收算法．     

三维集成转接板互连电磁传播仿真中吸收边界条件的选取及其验证

为了完成三维集成转接板互连结构中电磁场分布的建模与数值计算,采用时域有限差分法(Finite DifferenceTime Domain, FDTD)仿真二维横电波(Transverse Electric, TE)的传播,观察在添加Mur吸收边界条件和完全匹配层(Perfectly Matched Layer, PML)吸收边界条件时边界处磁场的变化,绘制误差曲线与等相位线来检验这两种边界条件的吸收性能。结果表明,将PML边界条件作为二维TE波的吸收边界可以确保仿真结果更符合工程实际。     

FDTD结合SPICE对微波有源电路的分析

时域有限差分(FDTD)方法由于其强大的功能,已经成为电磁场数值模拟的重要方法之一,本文主要讨论了时域有限差分法对微波源电路建模的理论和方法:模拟子电路的SPICE软件结合FDTD法的建模方法。根据传统的FDTD加入集总元件的建模方法的不足,提出用SPICE软件结合FDTD法进行包含集总元件的微波电路的建模,通过此种方法可以方便的对任意端口数、任意复杂度的微波子电路进行建模。     

基于FDTD的平面波入射介质的仿真

在二维时域有限差分法的基础上,以MATLAB为环境,进行电磁场数值仿真计算以及设置入射波与介质圆柱边界条件.用完美匹配层、矢量亥姆霍兹方程解决了吸收边界和平面波入射有损介质的问题.将平面电磁波入射到介质圆柱上的状态很好地模拟出来.     

超宽带信号地面回波仿真方法研究

研究地面的超宽带回波特性,能够为超宽带无线电系统设计提供仿真支持。为保证计算结果的可信性,需要考虑土壤的色散特性和地面起伏对回波的影响。目前在超宽带地面回波计算中所使用的FDTD（时域有限差分）算法计算量较大或者存在较大误差。使用卷积完全匹配层（CPML）作为吸收边界,多极点Debye模型描述土壤介质特性,在FDTD算法基础上推导出了多极点Debye介质的CPML-FDTD算法。对不同条件地面的回波进行了仿真计算,与未使用PML（完全匹配层）的FDTD算法计算结果进行比较分析,表明文中使用的算法结果正确且效率较高。     

基于OpenCL的GPU加速三维时域有限差分电磁场仿真算法研究

提出了一种基于开放运算语言（OpenCL）的GPU加速三维时域有限差分（FDTD）电磁场仿真计算的方法．该方法利用图形处理单元（GPU）的并行处理特性并结合OpenCL接口标准实现了时域卷积完全匹配层（CPML）吸收边界条件的三维FDTD的高性能加速计算．首先设置FDTD仿真参数并动态申请内存空间,然后初始化OpenCL的计算参数,对三维电磁模型基于OpenCL进行FDTD加速仿真．本方法显著提升了FDTD电磁场仿真速度,与利用CPU计算相比速度提升可达5-8倍,且具有CPML吸收边界条件,可以模拟电磁波在自由空间的传播;基于OpenCL编译的语言程序可以运行在CPU或GPU硬件上,并可充分发挥多核CPU的并行计算能力,使得FDTD电磁场仿真具有更广泛的实际应用．     

修正共形FDTD技术在声散射中的应用

传统时域有限差分法(UFDTD)将曲面目标边界作为台阶近似来处理,当网格划分不很精细时,计算结果会有很大的误差.共形技术可以解决这一问题,但它要满足一定的共形条件,实现起来比较困难.针对刚性目标的声散射问题,提出一种修正共形技术,它不需要满足任何共形条件就能达到很好的稳定性.文中给出了此共形技术的基本原理和稳定性证明,并针对声散射问题进行数值模拟.仿真结果表明:在同样计算量的情况下,此方法的计算精度明显高于传统方法;在同样计算精度的情况下,此方法的计算量大约比传统方法节省50%.     

基于三角面元的FDTD网格生成与可视化实现

针对三维复杂目标利用时域有限差分法(FDTD)进行电磁数值计算中遇到的Yee元胞建模的难题,提出了一种将三维三角面元模型转换为Yee元胞模型的方法,方法的实质是判断Yee元胞的中心点是否在目标模型的内部或是表面,根据判断后输出的结果进行了FDTD数值计算,计算结果证明了方法可以正确且快速的实现时域有限差分法的自动网格剖分,实现了FDTD网格的自动剖分.并利用OpenGL技术编程实现了剖分模型的可视化,有效的提高了时域有限差分法的电磁仿真系统预处理的能力.     

On optimization of finite-difference time-domain (FDTD) computation on heterogeneous and GPU clusters

A model for the computational cost of the finite-difference time-domain (FDTD) method irrespective of implementation details or the application domain is given. The model is used to formalize the problem of optimal distribution of computational load to an arbitrary set of resources across a heterogeneous cluster. We show that the problem can be formulated as a minimax optimization problem and derive analytic lower bounds for the computational cost. The work provides insight into optimal design of FDTD parallel software. Our formulation of the load distribution problem takes simultaneously into account the computational and communication costs. We demonstrate that significant performance gains, as much as 75%, can be achieved by proper load distribution.     

A new parallel meshing technique integrated into the conformal FDTD method for solving complex electromagnetic problems

A new efficient parallel finite-difference time-domain （FDTD） meshing algorithm, based on the ray tracing technique, is proposed in this paper. This algorithm can be applied to construct various FDTD meshes, such as regular and conformal ones. The Microsoft F# language is used for the algorithm coding, where all variables are unchangeable with its parallelization advantage being fully exploited. An improved conformal FDTD algorithm, also integrated with an improved surface current algorithm, is presented to simulate some complex 3D models, such as a sphere ball made of eight different materials, a tank, a J-10 aircraft, and an aircraft carrier with 20 aircrafts. Both efficiency and capability of the developed parallel FDTD algorithm are validated. The algorithm is applied to characterize the induced surface current distribution on an aircraft or a warship.     

电磁波传输时域有限差分方法及仿真

针对电磁散射特性研究问题,根据拉普拉斯变换原理,为提高电磁波传输效率,提出了一种新的分析磁等离子电磁波传输的时域有限差分(FDTD)方法.将磁等离子的电流密度本构方程进行拉普拉斯变换到s域,结合电流密度卷积方法将其逆拉普拉斯变换到时域,得到电流密度关于时间的本构方程.利用上述方法计算出一维磁化等离子体板电磁波的反射系数及其相位.实验证明,计算结果与解析值结果一致.并证明方法的准确性及高效性.     

Microwave tomography for breast cancer detection on Cell broadband engine processors

Microwave tomography (MT) is a safe screening modality that can be used for breast cancer detection. The technique uses the dielectric property contrasts between different breast tissues at microwave frequencies to determine the existence of abnormalities. Our proposed MT approach is an iterative process that involves two algorithms: Finite-Difference Time-Domain (FDTD) and Genetic Algorithm (GA). It is a compute intensive problem: (i) the number of iterations can be quite large to detect small tumors; (ii) many fine-grained computations and discretizations of the object under screening are required for accuracy. In our earlier work, we developed a parallel algorithm for microwave tomography on CPU-based homogeneous, multi-core, distributed memory machines. The performance improvement was limited due to communication and synchronization latencies inherent in the algorithm. In this paper, we exploit the parallelism of microwave tomography on the Cell BE processor. Since FDTD is a numerical technique with regular memory accesses, intensive floating point operations and SIMD type operations, the algorithm can be efficiently mapped on the Cell processor achieving significant performance. The initial implementation of FDTD on Cell BE with 8 SPEs is 2.9 times faster than an eight node shared memory machine and 1.45 times faster than an eight node distributed memory machine. In this work, we modify the FDTD algorithm by overlapping computations with communications during asynchronous DMA transfers. The modified algorithm also orchestrates the computations to fully use data between DMA transfers to increase the computation-to-communication ratio. We see 54% improvement on 8 SPEs (27.9% on 1 SPE) for the modified FDTD in comparison to our original FDTD algorithm on Cell BE. We further reduce the synchronization latency between GA and FDTD by using mechanisms such as double buffering. We also propose a performance prediction model based on DMA transfers, number of instructions and operations, the processor frequency and DMA bandwidth. We show that the execution time from our prediction model is comparable (within 0.5 s difference) with the execution time of the experimental results on one SPE.     

A novel hybrid algorithm based on FDTD and WCS‐FDTD methods

In this article, a hybrid algorithm based on traditional finite‐difference time‐domain (FDTD) and weakly conditionally stable finite‐difference time‐domain (WCS‐FDTD) algorithm is proposed. In this algorithm, the calculation domain is divided into fine‐grid region and coarse‐grid region. The traditional FDTD method is used to calculate the field value in the coarse‐grid region, while the WCS‐FDTD method is used in the fine‐grid region. The spatial interpolation scheme is applied to the interface of the coarse grid region and fine grid region to insure the stability and precision of the presented hybrid algorithm. As a result, a relatively large time step size, which is only determined by the spatial cell sizes in the coarse grid region, is applied to the entire calculation domain. This scheme yields a significant reduction both of computation time and memory requirement in comparison with the conventional FDTD method and WCS‐FDTD method, which are validated by using numerical results.     

Pentadiagonal alternating-direction-implicit finite-difference time-domain method for two-dimensional Schrödinger equation

In this paper, we have proposed a pentadiagonal alternating-direction-implicit (Penta-ADI) finite-difference time-domain (FDTD) method for the two-dimensional Schrödinger equation. Through the separation of complex wave function into real and imaginary parts, a pentadiagonal system of equations for the ADI method is obtained, which results in our Penta-ADI method. The Penta-ADI method is further simplified into pentadiagonal fundamental ADI (Penta-FADI) method, which has matrix-operator-free right-hand-sides (RHS), leading to the simplest and most concise update equations. As the Penta-FADI method involves five stencils in the left-hand-sides (LHS) of the pentadiagonal update equations, special treatments that are required for the implementation of the Dirichlet’s boundary conditions will be discussed. Using the Penta-FADI method, a significantly higher efficiency gain can be achieved over the conventional Tri-ADI method, which involves a tridiagonal system of equations.     

Rotationally symmetric FDTD for wideband performance prediction of TM01 DR filters

The generalized perfectly matched layer (GPML) coupled with rotationally symmetric (RS)‐FDTD method has been utilized to extract the S‐parameters for several probe‐coupled TM₀₁ dielectric resonator (DR) filters to directly obtain the theoretical wideband spurious performance. The computationally efficient (RS)‐FDTD method has also been used to obtain accurate filter parameters for TE₀₁ and TM₀₁ dielectric resonators loaded in cylindrical cavities. The RS‐FDTD method combined with digital filtering and the Matrix Pencil technique are used to analyze the resonant frequencies, inter‐resonator coupling, and external Q values. When perturbation theory is used with RS‐FDTD, accurate values of unloaded Q are obtained. © 2002 Wiley Periodicals, Inc. Int J RF and Microwave CAE 12: 259–271, 2002.