粒子模拟中的时偏FDTD算法

给出一种能自动对高频噪声进行过滤的时域有限差分(FDTD)算法,称为时偏FDTD算法.在中心差分FDTD算法的基础上,引入时间偏置和松弛迭代处理,得到该算法的计算公式,并进行稳定性与收敛性分析.通过对相对论磁控管的计算,与中心差分FDTD算法比较,验证了该算法的滤波特性.     

Numerical simulation of resonance structures with FDTD algorithms based on GPU B-CALM and CPU Meep

Simulation time is one of the bottlenecks of finite-difference-time-domain (FDTD) method. There are several ways of reducing the simulation time, one of which is the usage of graphical processing unit (GPU). Thus in this paper we present comparison between two free FDTD software packages. One is based on central processing unit and other is based on GPU. The 3D test structures we analyzed were metallic rectangular cavity resonator and microring resonator based refractive index sensor. The comparison between two FDTD software packages is made with regard to simulation time and numerical accuracy. It is shown that both packages agree in numerical results and that GPU based FDTD implementation performs same simulation up to 18 times faster.     

基于目标三角面元模型生成FDTD共形网格的方法

 提出了一种基于目标三角面元数据的FDTD共形网格生成方法,该方法通过投影求交计算得到目标表面各三角面元与网格线的交点,将每条网格线与三角面元的交点按坐标进行排序,根据交点的坐标及其编号的奇偶性确定FDTD共形网格的位置,并生成相应的共形FDTD计算所需的元段长度。结合处理理想导体曲面的CFDTD方法修正共形网格上的磁场递推式。数值结果证实了共形网格生成方法的正确性和在提高FDTD方法计算精度方面的有效性。     

含时Schrödinger方程的高阶辛FDTD算法研究

提出了一种新的算法——高阶辛时域有限差分法(SFDTD(3, 4): symplectic finite-difference time-domain)求解含时薛定谔方程.在时间上采用三阶辛积分格式离散, 空间上采用四阶精度的同位差分格式离散, 建立了求解含时薛定谔方程的高阶离散辛框架;探讨了高阶辛算法的稳定性及数值色散性.通过理论上的分析及数值算例表明:当空间采用高阶同位差分格式时, 辛积分可提高算法的稳定度;SFDTD(3, 4)法和FDTD(2, 4)法较传统的FDTD(2, 2)法数值色散性明显改善.对二维量子阱和谐振子的仿真结果表明: SFDTD(3, 4)法较传统的FDTD(2, 2)法及高阶FDTD(2, 4)法有着更好的计算精度和收敛性, 且SFDTD(3, 4)法能够保持量子系统的能量守恒, 适用于长时间仿真.     

Plasma Induced Wiggler Magnetic Field in a Cavity: II-FDTD Method for a Switched Lossy Plasma

The transformation of an elliptically polarized standing source wave in a cavity by a lossy plasma created with arbitrary space and time profiles is numerically computed using the Finite-Difference Time-Domain (FDTD) method. The FDTD equations derived are shown to be very robust and results are presented for several practical scenarios.     

Sound field of thermoacoustic tomography based on a modified finite-difference time-domain method

A modified finite-difference time-domain （FDTD） method is proposed for the sound field simulation of the thermoacoustic tomography （TAT） in the acoustic speed inhomogeneous medium. First, the basic equations of the TAT are discretized to difference ones by the FDTD. Then the electromagnetic pulse, the excitation source of the TAT, is modified twice to eliminate the error introduced by high frequency electromagnetic waves. Computer simulations are carried out to validate this method. It is shown that the FDTD method has a better accuracy than the commonly used time-of-flight （TOF） method in the TAT with the inhomogeneous acoustic speed. The error of the FDTD is ten times smaller than that of the TOF in the simulation for the acoustic speed difference larger than 50%. So this FDTD method is an efficient one for the sound field simulation of the TAT and can provide the theoretical basis for the study of reconstruction algorithms of the TAT in the acoustic heterogeneous medium.     

粒子模拟中的一种高频噪声抑制算法

对粒子模拟中的高频噪声的产生机理进行分析,并给出一种既能对高频数值噪声进行过滤又能满足Q值较高的相对论型微波器件计算要求的时域有限差分(FDTD)算法——High_Q FDTD算法.在中心差分FDTD算法和时偏FDTD算法的基础上,给出High_Q算法的计算公式,并着重分析算法的稳定性与收敛性.通过对相对论返波管(RBWO)的计算,将计算结果与中心差分和时偏FDTD算法的计算结果比较,验证算法有较好的滤波特性和计算精度.     

High-order FDTD methods for transverse electromagnetic systems in dispersive inhomogeneous media

This Letter introduces a novel finite-difference time-domain (FDTD) formulation for solving transverse electromagnetic systems in dispersive media. Based on the auxiliary differential equation approach, the Debye dispersion model is coupled with Maxwell's equations to derive a supplementary ordinary differential equation for describing the regularity changes in electromagnetic fields at the dispersive interface. The resulting time-dependent jump conditions are rigorously enforced in the FDTD discretization by means of the matched interface and boundary scheme. High-order convergences are numerically achieved for the first time in the literature in the FDTD simulations of dispersive inhomogeneous media.     

Modeling and simulation of multiple resonant Lorentz dispersive materials for integrated optics

Complex materials are of increasing interest in Finite-Difference Time-Domain (FDTD) modeling. For example, when the particle density becomes large, collisional fluid models of plasmas are an attractive alternative to particle in cell methods. Further, frequency dispersive meta-materials are of increasing interest. Thus, Finite-Difference Time-Domain (FDTD) models are derived for magnetized plasmas and for the Lorentz and Drude material models. This paper models the Lorentz material using the FDTD tool. The modal analysis and various types of simulation results are also presented for these materials.     

移动坐标系FDTD方法在脉冲波传播中的应用

通过在时域有限差分(FDTD)方法中引入移动坐标系,解决了一般FDTD方法处理脉冲长距离传播时面临的困难。推导了移动坐标系下的场方程和FDTD差分格式,并将该方法应用于模拟波导中电磁脉冲的传播。计算结果表明,在传播过程中,脉冲波包沿传播方向逐渐展宽,脉冲的峰值场强变小,同时出现了色散现象,脉冲中传播较慢的成分逐渐移向尾部,产生带尾态,这与一般FDTD方法得到的计算结果接近。多个频率的计算结果表明,该方法与一般FDTD方法得到的数据的相对误差小于0.1%,验证了方法的可行性和正确性。     

细缝算法在细缝结构屏蔽效能计算中的应用

通过比较不同细缝算法(TSF)计算误差随细缝宽度相对网格步长占比和频率的变化,以及各TSF算法计算获得的孔缝处及远离孔缝位置场分布的差异,给出了时域有限差分（FDTD）计算中不同TSF算法的适用性。在此基础上,将TSF算法用于分析工程中搭接缝结构的屏蔽效能问题,结果表明:将工程搭接缝等效模型与TSF算法结合,能够使用FDTD快速地计算其屏蔽效能,有效解决了基于FDTD的含细缝复杂结构的屏蔽效能评估问题。     

Ultrasonic pulse waves in cancellous bone analyzed by finite-difference time-domain methods

The trabecular frame of cancellous bone has a high degree of porosity, anisotropy and inhomogeneity. The propagation of ultrasonic waves in cancellous bone is significantly affected by the trabecular structure. In this paper, two two-dimensional finite-difference time-domain (FDTD) methods, which were the popular viscoelastic FDTD method for a viscoelastic medium and Biot's FDTD method for a fluid-saturated porous medium, have been applied to numerically analyze the ultrasonic pulse waves propagating through bovine cancellous bone in the directions parallel and perpendicular to the trabecular alignment. The Biot's fast and slow longitudinal waves, which were identified in previous experiments for the propagation parallel to the trabecular orientation, could be analyzed using Biot's FDTD method rather than the viscoelastic FDTD method. For the single wave propagation in the perpendicular direction, on the other hand, the viscoelastic FDTD result was found to be in more good agreement with the experimental result.     

LED光学传播的有限元研究

有限时域差分(FDTD)广泛应用于提高发光二极管(LED)芯片外量子效率.这种方法是针对波导结构的一种分析计算,对于激光器是有效的,但是对LED很难模拟其有源层多种模式出射的情况.应用有限元电磁场分析方法对LED进行光学建模并对光子晶体结构的外量子效率进行了计算.特别在对光源的处理上,使用了点光源球面波来进行分析并且考...     

A Locally Conformal Algorithm for Handling Curved Metallic Surfaces and Its Application

This paper describes a modified locally conformal algorithm for finite-difference time-domain (FDTD) method. Fields in the entire computational domain are computed by a regular FDTD algorithm except those near curved metallic surfaces, where special techniques proposed in this paper are applied. The computation efficiency of a regular FDTD method is maintained while a high space-resolution is obtained by this new algorithm. To validate the reliability of the algorithm, coaxial continuous transverse stub arrays at millimeter wave Ka-band and microwave X-band are tested, and the simulated results show good agreement with the experimental results from an HP-8510B Network Analyzer and the simulation results from software package HFSS.     

一种可用于分析任意介电常数张量的各向异性波导导模的二维时域有限差分模型

为分析具有任意介电常数张量的各向异性波导的导模，本文通过把简化的二维时域有限差分（２－ＤＦＤＴＤ）法扩展至任意各向异性介质，提出了一种以Ｄ、Ｅ和Ｈ场为基础的统一的简化２－ＤＦＤＴＤ模型．利用该模型，研究了简化的复数２－ＤＦＤＴＤ方法与实变数２－ＤＦＤＴＤ方法之间的关系．文中还讨论了复变数方法和实变数方法的激励技术．     

高斯波束在双负媒质中的传播特性分析

 提出了一种基于Drude色散媒质模型的2维TM模时域有限差分法,数值模拟了高斯波束从自由空间垂直入射和斜入射到双负媒质(介电常数和磁导率同时为负)平板后的折射现象,并给出了平板内外的电场强度分布。模拟结果显示：垂直入射时,双负媒质平板对高斯波束具有汇聚作用,通过改变媒质的折射率,可以控制高斯波束通过组合平板的传播时间而不发生衰减;斜入射时,折射波束与入射波束均位于法线的同一侧,高斯波束在双负媒质与空气交界面处发生了负折射。     

大规模集成光波导时域有限元差分法仿真的子域合成法

用时域有限元差分的子域合成法(Synthetic subdomain method of FDTD)对大规模的光波导模拟,把仿真的光波导划分成两个或多个区域,在不影响仿真精度的条件下,删除对仿真对象影响不大的区域,并相应改变吸收边界条件进行时域有限元差分法数值模拟,考查光的传播和损耗状况,并与常规方法的运算结果相比较,结果一致且不影响计算精度。与常规方法相比,两段子域合成法所占内存约为前者的55%,时间约为前者的60%,三段子域合成法所占内存约为前者的31%,时间约为前者的28%,可见子域合成法比常规方法更有利于应用于大规模集成光波导的数值模拟仿真,对节省硬件及时间资源具有实际意义,提高工作效率。     

阻尼受击板的时域建模及声音合成

为满足声源辨识中对合成冲击声的迫切需求,建立了球-板撞击的时域模型,提出一种时域快速求解方法,并进行了实验验证.首先给出一种将时域有限差分法(FDTD)和模态展开法(MEM)相结合的时域混合方法,求解板的振动方程,并解决了混合方法中MEM的模态截断和初值问题,及两种方法中阻尼的一致性问题;随后,给出了简支矩形板的冲击声计算结果,通过与FDTD方法的运算量进行对比,验证了混合方法的高效性;最后,针对自由边界下的L形板进行了实验验证.结果表明,与传统FDTD方法相比,时域混合方法在保证合成冲击声精度的前提下可将计算效率提高100至1200倍。      

Z变换在磁化等离子体电磁脉冲传播时域分析中的应用

 通过Z变换的方法,将与频率有关的磁化等离子体的介电常数由频域变换到Z域,推导了Z变换形式的时域有限差分法计算式,模拟了电磁脉冲在磁化等离子体中的传播。经过离散傅里叶变换,给出了电磁波通过磁化等离子体后的反射系数和透射系数与频率的关系。还给出了模拟结果和理论值的对比。结果表明,Z变换算法的模拟结果比卷积分更接近理论值。     

基于半解析递归卷积的通用色散介质FDTD方法

基于数字信号处理中的半解析递归卷积（SARC）算法,提出了一种用于色散介质电磁特性分析的半解析递归卷积时域有限差分方法（SARC FDTD）. 该方法既保持了FDTD方法处理复杂目标的灵活性,又吸取了线性系统SARC算法的绝对稳定性和高精度、低内存、高效率等优点,只需给出色散介质模型的极点和对应系数,即可运用SARC FDTD递推公式和通用程序进行计算,具有较好的通用性. 通过Debye,Drude和Lorentz三种常用色散介质模型对算法进行了验证. 关键词： 时域有限差分 色散介质 半解析递归卷积