基于Split-Field FDTD法的近埋地无限长散射体二维算法

提出了一种基于周期结构split-field FDTD法的近埋地无限长散射体二维算法.该方法根据散射体轴向均匀性将三维split-field FDTD法转化为二维算法,减少了内存和计算量,可分析斜入射脉冲波照射下近地、埋地无限长散射体散射问题.为了进一步减小计算量,连接边界上的入射波(地上为原始入射波和反射波的叠加,地下为透射波)采用一维FDTD法引入.吸收边界采用了UPML匹配层,导出了适用于split-field FDTD算法与有耗介质匹配的UPML方程.通过数值算例,验证了此二维算法应用于近埋地无限长散射体问题的有效性和实用性.     

三维FDTD方法中高效平面波源的引入

应用分裂平面波时域有限差分（Splitting Plane wave Finite Difference Time Domain,SP-FDTD）方法到三维时域有限差分（Finite Difference Time Domain,DFDTD）中引入高效平面波源.该方法基于分裂场思想,在一维FDTD上构造了新的迭代公式,使得一维FDTD和三维FDTD离散网格之间的数值相速度一致,消除了由于相速不一致而在总场区引起的泄漏误差以及插值带来的数值误差.通过数值算例验证了SP-FDTD方法对不同波源在任意角度（斜入射）下的平面波入射都是有效的,且泄露误差均在-300dB水平.     

单层和多层有缝金属板电磁波透射的FDTD分析

采用在入射波一侧的总场边界处同时引进入射波和反射波作为激励源的FDTD方法来分析斜入射时单层和多层有缝金属板电磁波透射问题.通过计算金属板缝隙附近的散射场,提取缝隙口径面上的等效面磁流,进而得到透射截面.计算机仿真结果证实了算法的有效性.数值计算结果表明,两金属板上所开缝隙的相对偏移以及两板间插入介质板将会改变屏蔽效应.该方法可以有效分析平面波斜入射时多层金属板上任意形状缝隙的散射和透射,包括缝隙内或金属板之间填充有介质情形.     

加权总场法在PSTD算法中的应用

伪谱时域(PSTD)方法可以处理电大尺寸目标电磁散射问题。本文介绍了一种能够把入射波有效引入PSTD计算区域的新方法——加权总场法。该方法通过引入类似于FDTD中连接边界的连接层，将计算区域划分为总场区、连接区和散射场区。为了总场区和散射场区的连续，在连接区引入窗函数．通过设置8—10层连接区就可以将入射波有效地引入到PSTD总场区。这样使入射波和目标分离，实现了复杂目标的单独建模，从而使PSTD便于模拟复杂目标的电磁散射。文中以高斯脉冲为入射波，通过二维情况下目标散射宽度的数值结果，验证了加权总场法应用于PSTD算法时的有效性和计算精度。     

垂直人射HEMP近地面电磁环境特性研究

高空核爆电磁脉冲(HEMP)具有覆盖范围广、峰值场强高等特点,对电子设备构成严重威胁.针对有关HEMP标准中主要涉及自由空间HEMP波形描述的情况,研究了双指数HEMP平面波垂直入射地面时,地面附近的电磁脉冲环境特性.基于时域有限差分(FDTD)法提出使用一维合成平面波解决总场空间激励源的引入问题.通过设置不同的入射波状态和环境因素,仿真计算了HEMP在地面附近的电磁脉冲环境参数,并对HEMP在地面附近的传播特点与规律进行了总结和归纳.结果表明,较低位置处反射场削弱了部分入射场,使总场幅度降低;较高位置处经历较为完整的入射场和反射场的冲击;地表介质的电气参数对总场也有影响,其中电导率的影响较大.这些结论有利于指导地面附近电子设备的防护设计.     

垂直人射HEMP近地面电磁环境特性研究

高空核爆电磁脉冲(HEMP)具有覆盖范围广、峰值场强高等特点,对电子设备构成严重威胁.针对有关HEMP标准中主要涉及自由空间HEMP波形描述的情况,研究了双指数HEMP平面波垂直入射地面时,地面附近的电磁脉冲环境特性.基于时域有限差分(FDTD)法提出使用一维合成平面波解决总场空间激励源的引入问题.通过设置不同的入射波...     

BOR-FDTD斜入射脉冲平面波一维时域算法

针对斜入射脉冲波不能直接引入BOR-FDTD计算的问题,根据柱坐标系统中入射波在对称轴方向只有时间延迟的特性,结合平面波的柱面波展开,提出了一种行之有效的计算BOR-FDTD中斜入射脉冲平面波的一维时域算法,从而避免了大量快速傅里叶变换运算,节省了计算时间.计算结果表明该算法运行速度比基于完全傅里叶变换的算法快50倍.就整个程序运行时间而言,一维时域算法可以节省约20%的计算时间.为了验证该算法的有效性,计算了高斯脉冲斜入射时有限长金属圆柱体的散射问题,提取出某一频率下圆柱体母线电流密度分布并与MoM计算结果比较,二者吻合较好.然后计算了金属球的单站RCS随频率的变化,所得结果与理论值一致性也很好.     

单脉冲平面波以不同方向入射时开孔屏蔽室内的耦合场研究

采用时域有限差分(FDTD)法计算了开孔屏蔽室对单脉冲平面波的耦合,取得了与实测波形一致的结果.计算结果表明:若入射波传播方向垂直于开孔面,则屏蔽室内的耦合场仅取决于屏蔽腔体的谐振特性;若入射波传播方向平行于开孔面,则屏蔽室内的耦合场为具有源特征的低频分量与屏蔽室内的高频谐振波分量组成.     

碰撞等离子体的高阶FDTD算法

给出了电磁波在均匀、碰撞等离子体中传播的四阶时间和四阶空间FDTD算法.该算法比Yee氏FDTD算法每一个网格每一维增加一个存储单元,与常规的二阶等离子体FDTD算法相同.由于采用四阶时间和四阶空间近似,因此该算法能有效地减小数字色散误差,其频带宽度比二阶算法的频带宽度更宽.为了验证该高阶算法的正确性,对均匀、碰撞等离子体平板的电磁波反射系数进行了计算,并与解析结果、二阶FDTD计算结果进行了比较,证明了该算法的高效和精确.     

有耗平面和三维目标复合散射的FDTD分析

采用FDTD方法计算了有耗地面与三维目标的复合散射,对吸收边界条件,连接边界条件和近远场变换作了细致讨论.吸收边界使用了广义PML吸收层,它对电磁波有较好的吸收效果.连接边界处则利用解析入射波和三波迭加技术,上半平面用入射波和反射波、下半平面用透射波作为对目标的外加场进行计算.得到近场数据后,为避免出现复杂的Sommerfeld积分,用互易原理简化了外推过程.FDTD算法与矩量法和快速多层多极子相比,具有节省内存,计算时间短等优点.通过地上物体和地下物体的计算验证了FDTD方法的精确性,讨论了散射体离地高度对后向RCS的影响.     

计算电大尺寸建筑物内电波场强的PSTD方法

本文采用一种新的时域数值方法－伪谱时域（ＰＳＴＤ）法来计算电大尺寸建筑物内电波场强。提出了由初始条件技术和一维ＰＳＴＤ方程对入射平面波脉冲进行模拟,并利用纯散射场法和线性插值把平面波引入求解问题空间,有效地解决了ＰＳＴＤ方法中入射波设置问题。数值结果表明这种新方法用于模拟电大尺寸建筑物内电波场强的精度和有效性。     

FDTD simulation of TE and TM plane waves at nonzero incidence in arbitrary Layered media

Plane wave scattering is an important class of electromagnetic problems that is surprisingly difficult to model with the two-dimensional finite-difference time-domain (FDTD) method if the direction of propagation is not parallel to one of the grid axes. In particular, infinite plane wave interaction with dispersive half-spaces or layers must include careful modeling of the incident field. By using the plane wave solutions of Maxwell's equations to eliminate the transverse field dependence, a modified set of curl equations is derived which can model a "slice" of an oblique plane wave along grid axes. The resulting equations may be used as edge conditions on an FDTD grid. These edge conditions represent the only known way to accurately propagate plane wave pulses into a frequency dependent medium. An examination of grid dispersion between the plane wave and the modeled slice reveals good agreement. Application to arbitrary dispersive media is straightforward for the transverse magnetic (TM) case, but requires the use of an auxiliary equation for the transverse electric case, which increases complexity. In the latter case, a simplified approach, based on formulating the dual of the TM equations, is shown to be quite effective. The strength of the developed approach is illustrated with a comparison with the conventional simulation based on an analytic incident wave specification with half-space, single frequency reflection and transmission for the edges. Finally, an example of a possible biomedical application is given and the implementation of the method in the perfectly matched layer region is discussed.     

FDTD中微带线激励源设置的新方法

ＦＤＴＤ已广泛应用于微带问题的计算中,本文提出了一种新的微带线馈电激励设置方式,同以往的激励设置方法不同,它不仅能计算Ｇａｕｓｓｉａｎ脉冲激励也能计算正弦波激励,计算过程中,源平面无需切换成吸收边界,场区的划分使反射场自然从总场区分离出来。     

An efficient and accurate technique for the incident-waveexcitations in the FDTD method

An efficient technique to improve the accuracy of the finite-difference time-domain (FDTD) solutions employing incident-wave excitations is developed. In the separate-field formulation of the FDTD method, any incident wave may be efficiently introduced to the three-dimensional (3-D) computational domain by interpolating from a one-dimensional (1-D) incident-field array (IFA), which is a 1-D FDTD grid simulating the propagation of the incident wave. By considering the FDTD computational domain as a sampled system and the interpolation operation as a decimation process, signal-processing techniques are used to identify and ameliorate the errors due to aliasing. The reduction in the error is demonstrated for various cases. This technique can be used for the excitation of the FDTD grid by any incident wave. A fast technique is used to extract the amplitude and the phase of a sampled sinusoidal signal     

FDTD modeling of scatterers in stratified media

The FDTD technique is well suited for calculating the fields scattered by buried objects when the sources are close enough to the air/ground interface so that they can be incorporated into the solution space. Difficulties arise, however, when the sources are far from the interface since the total fields in the solution space are not all outgoing waves. Using well-known formulas for the fields transmitted and reflected by stratified media, this paper discusses a method whereby the fields scattered by a buried object can be easily calculated by the FDTD technique when the incident field is a plane wave     

E-polarized scattering from a conducting rectangularcylinder with an infinite axial slot filled by a resistively coateddielectric strip

The potential use of resistive films for damping the resonance spikes observed in the radar cross section (RCS) spectrum of a partially open rectangular cavity is investigated using a recently developed finite-difference-time-domain (FDTD) method that utilizes the resistive-sheet boundary condition for the modeling of resistive films. Backscattering data obtained in the first resonant region for an E -polarized plane wave normally incident into the slotted side of the cavity are presented. It is shown that resonance behaviors can be eliminated completely with a low-resistance film that attenuates significantly the impinging wave. Poorer resonance damping performance is observed as the film resistance increases because more of the field is allowed to penetrate into the cavity. For the latter case, the presence of the resistive film lowers the Q-factor of the slotted cavity such that the resultant resonance spectrum is lower in strength and broader in bandwidth     

Modeling of rough-surface effects in an optical turning mirrorusing the finite-difference time-domain method

A finite-difference time-domain (FDTD) method is applied to calculate the forward-reflected and back-reflected powers of a guided mode from a rough turning mirror in a bent waveguide of a high-power laser array. By segmenting this large problem into a number of smaller problems, the simulation region can be shrunk to a small area containing only the details of the rough-surface mirror. By launching the incident wave judiciously, the computation time grows linearly with the length of the mirror. A farfield transformation of the calculated time-domain scattered field yields forward-reflected and back-reflected powers. The computer time needed to analyze this large turning-mirror system is reduced to about 3 min of CRAY time, compared to several hours for a brute-force approach using a full mesh     

Plane waves in FDTD simulations and a nearly perfect total-field/scattered-field boundary

The total-field/scattered-field (TFSF) boundary has been successfully used for a number of years to introduce energy into finite-difference time-domain (FDTD) grids. If the propagation of the incident field is grid-aligned, a perfect TFSF implementation can be realized by using an auxiliary one-dimensional FDTD simulation which models propagation of the incident field. Here "perfect" implies the incident field propagation exactly matches the way in which the field propagates in the FDTD grid. However, for propagation which is not grid-aligned, no similarly perfect implementation has previously been presented. This work provides a framework for a perfect TFSF boundary for pulsed plane waves which do not propagate in a grid-aligned fashion. To achieve this, homogeneous plane-wave propagation is rigorously quantified. Using this knowledge and a specification of the desired incident field, the dispersion relation is used to ascertain the incident field at any point in the grid. It is required to account for, unlike in the continuous world, the electric field, the magnetic field, and the wavenumber vector not forming a mutually orthogonal set. Group velocity is also considered because of its relevance to the implementation.     

A novel finite-difference time-domain wave propagator

A novel time-domain wave propagator is introduced. A two-dimensional (2-D) finite-difference time-domain (FDTD) algorithm is used to analyze ground wave propagation characteristics. Assuming an azimuthal symmetry, surface, and/or elevated ducts are represented via transverse and/or longitudinal refractivity and boundary perturbations in 2-D space. The 2-D FDTD space extends from x=0 (bottom) to x→∞ (top), vertically and from z→-∞ (left) to z→∞ (right), horizontally. Perfectly matched layer (PML) blocks on the left, right, and top terminate the FDTD computation space to simulate a semi-open propagation region. The ground at the bottom is simulated either as a perfectly electrical conductor (PEC) or as a lossy second medium. A desired, initial vertical field profile, which has a pulse character in time, is injected into the FDTD computation space. The PML blocks absorb field components that propagate towards left and top. The ground wave components (i.e., the direct, ground-reflected and surface waves) are traced longitudinally toward the right. The longitudinal propagation region is covered by a finite-sized FDTD computation space as if the space slides from left to right until the pulse propagates to a desired range. Transverse or longitudinal field profiles are obtained by accumulating the time-domain response at each altitude of range and by applying the discrete Fourier transformation (DFT) at various frequencies     

An FDTD/ray-tracing analysis method for wave penetration through inhomogeneous walls

A novel method of studying wave penetration through inhomogeneous walls using the hybrid technique based on combining finite-difference time-domain (FDTD) and ray tracing methods is presented . The FDTD method is used to analyze the transmission characteristics of inhomogeneous walls. Using the knowledge of the tangential electric and magnetic field distributions along the borders of the FDTD computation domain, rays are sent out to cover the rest of the environment so that prediction of signal coverage can be made more efficiently without compromising the accuracy. Numerical results of the method have been compared and shown to agree very well with those of measurement and those of full wave analysis. Examples have shown the inadequacy of the traditional ray tracing method in the presence of walls made of concrete blocks. However, the proposed method can accurately predict signal coverage by taking into account the scattered fields by the inhomogeneity inside the walls. The method does not add much to computational complexity. Reduction in computation time is even more significant when the incident waves can be approximated to be plane waves and the wall structure is periodic.