基于FDTD的雷电脉冲对飞机介质舱体内干扰作用的研究

该文提出一种利用时域有限差分计算雷电磁脉冲对飞机碳纤维介质舱体内的干扰作用的分析方法。将雷电通道等效为垂直于无限大导体地面的线天线,利用天线场区划分的概念将雷电电磁场划分为近区场和远区场。在远场情况下,通过在舱体侧设置平面波源来分析雷电脉冲对舱内的干扰;在近场情况下,通过在舱体一侧设置延伸至完全匹配层(PML),并与PML外金属边界相接的线电流来模拟一段雷电通道,有效避免了传统设置线电流时的静电积累效应,并分析近距离雷电对舱体的干扰。计算结果与解析结果吻合较好。分析解决了雷电脉冲的近场和远场情况下飞机碳纤维舱体内的电场分布及变化情况,为飞机介质舱体的电磁加固提供依据。     

Analysis of the CDF biorthogonal MRTD method with application to PEC targets

We consider the biorthogonal Cohen-Daubechies- Feauveau (CDF) wavelet family in the context of a biorthogonal multiresolution time-domain (bi-MRTD) analysis. A disadvantage of previous bi-MRTD analyses is an inability to handle abrupt changes in material properties, particularly for a perfect electric conductor (PEC). A multiregion method is proposed to address PEC targets. The proposed method is based on the fact that the CDF bi-MRTD may be viewed as a linear combination of several conventional finite-difference time-domain (FDTD) solutions. The implementation of the connecting surface is also simplified. Several numerical results are presented, with comparison to analytic and FDTD results.     

渐近波形估计技术应用于导体柱RCS方向图的快速获取

本文基于渐近波形估计(AWE)技术和矩量法(MOM)快速预测任意形状导电柱体(PEC)的单站RCS方向图.首先采用矩量法求解导体柱的电场积分方程,得到导体柱在某一给定方向入射波照射下的表面电流的低阶矩量,然后利用AWE技术求出在任意方向入射波照射下用有理分式函数表示的表面电流,进而计算出RCS方向图.计算结果表明AWE完全能逼近MOM精确计算的曲线,同时在计算速度上可加快几十倍.     

A novel FDTD formulation for dispersive media

A novel FDTD formulation for dispersive media called piecewise linear JE recursive convolution (PLJERC) finite-different time-domain (FDTD) method is derived using the piecewise linear approximation and the recursive convolution relationship between the current density J and the electric field E. The high accuracy and efficiency of the PLJERC method is confirmed by computing the reflection coefficients of an electromagnetic wave through a collision plasma slab in one dimension.     

Novel FDTD simulation method using multiple-analysis-space for electromagnetic far field

Wide-band undesired electromagnetic noise near electronic systems, which includes small noise source like the printed circuit board (PCB), is a current problem in the field of electromagnetic interference. However, the estimation method for the electromagnetic noise near a system under test has not been established. This paper proposes a newly developed estimation method of the electromagnetic noise for a wide area, from near to far field, using the finite difference time-domain (FDTD) method. The proposed FDTD simulation method is an estimation technique for near to far field with multiple analysis spaces (MAS). The MAS has an internal analysis space (IAS) and an external analysis space (EAS). The analysis near a radiation source can be calculated in the IAS. The EAS is the outside space from IAS, which is for calculation of the far field. It is expected that the proposed FDTD method by MAS (FDTD-MAS) decrease in the calculation cost in terms of computational time and memory costs, especially for estimation of radiation from PCB. The principle procedure of the FDTD-MAS method is described in the first part of this paper. As example of advantages of the calculation and confirmation of the calculation accuracy, the electric field distributions radiated from a 1-GHz half-wavelength dipole antenna in an IAS of 0.3/spl times/0.3 m/sup 2/ area and an EAS of 7/spl times/7 m/sup 2/ area are used as examples. When the cell size ratio of IAS to EAS is changed from 6 to 20, the FDTD and theoretical values show good agreement. It is indicated that the FDTD-MAS simulation method is one of the most powerful tools for the estimation of electromagnetic noise from near field to far field from small and thin source.     

An E-J Collocated 3-D FDTD Model of Electromagnetic Wave Propagation in Magnetized Cold Plasma

A new three-dimensional finite-difference time-domain (FDTD) numerical model is proposed herein to simulate electromagnetic wave propagation in an anisotropic magnetized cold plasma medium. Plasma effects contributed by electrons, positive, and negative ions are considered in this model. The current density vectors are collocated at the positions of the electric field vectors, and the complete FDTD algorithm consists of three regular updating equations for the magnetic field intensity components, as well as 12 tightly coupled differential equations for updating the electric field components and current densities. This model has the capability to simulate wave behavior in magnetized cold plasma for an applied magnetic field with arbitrary direction and magnitude. We validate the FDTD algorithm by calculating Faraday rotation of a linearly polarized plane wave. Additional numerical examples of electromagnetic wave propagation in plasma are also provided, all of which demonstrate very good agreement with plasma theory.      

An algorithm for computations of the power deposition in humantissue

The finite-difference time-domain (FDTD) is the most often used method for evaluation of electromagnetic fields in human tissue. This is of particular importance for compliance testing of portable telephones. The specific absorption rate (SAR) averaged over 1 or 10 g tissue mass is required by regulations not to exceed a prescribed value. A computer algorithm is developed for post-processing the FDTD data. This algorithm can be used for uniform as well as graded meshes, while the required cubical shape is maintained. Extensive investigations are shown of the resultant SAR due to the number of electric field components used in field averaging, and the volume of air within the cube. The latter is easily controlled in the algorithm, but the regulations on the permissible SAR do not specify it at the present time     

Z-transform theory and the FDTD method

In implementing the finite-difference time-domain (FDTD) method on materials which are dispersive or nonlinear, the relationship between the flux density and the electric field can be the most complicated part of the problem. Because the FDTD method is a sampled time-domain method, this relationship can be can be looked upon as a digital filtering problem. The Z transform is typically used in digital filtering and signal processing problems. The paper illustrates the use of the Z transform in implementing the FDTD method where complicated dispersive or nonlinear materials are involved     

直角坐标系下非均匀FDTD网格生成系统

基于非均匀FDTD网格的电磁场模拟是一种解决诸多实际电磁场问题的通用、有效方法.本文介绍了在直角坐标系下非均匀FDTD网格图形生成系统,可以快速、高效地产生1D、2D、3D FDTD网格,展现物体的几何图形,还可以动态地、可视化地得到检查、调节和修改.作为检验,本文以一实际结构为例,产生并显示了其网格图形.     

Fast RCS computation over a frequency band using method of momentsin conjunction with asymptotic waveform evaluation technique

The method of moments (MoM) in conjunction with the asymptotic waveform evaluation (AWE) technique is applied to obtain the radar cross section (RCS) of an arbitrarily shaped three-dimensional (3-D) perfect electric conductor (PEC) body over a frequency band. The electric field integral equation (EFIE) is solved using the MoM to obtain the equivalent surface current on the PEC body. In the AWE technique, the equivalent surface current is expanded in a Taylor's series around a frequency in the desired frequency band. The Taylor series coefficients are then matched via the Pade approximation to a rational function. Using the rational function, the surface current is obtained at any frequency within the frequency range, which is in turn used to calculate the RCS of the 3-D PEC body. A rational function approximation is also obtained using the model-based parameter estimation (MBPE) method and compared with the Pade approximation. Numerical results for a square plate, a cube, and a sphere are presented over a frequency bandwidth. Good agreement between the AWE and the exact solution over the bandwidth is observed     

High-Order Discrete Helmholtz Decompositions for the Electric Field Integral Equation

We develop a differential form based formalism to address the problem of low-frequency breakdown of the electric field integral equation (EFIE). Note, in this formalism we approximate the surface magnetic field, not the surface current as is conventionally the case. A discrete Helmholtz decomposition is achieved for both triangular and quadrilateral curvilinear meshes based on a star-cotree decomposition. These decompositions are based upon the construction of a canonical basis which ab-initio possess the required separation into irrotational and nonirrotational spaces. This makes the process of construction clear and generally applicable. The construction of appropriate bases is demonstrated for a range of interpolation orders. The effects of these constructions is demonstrated on a simple flat PEC plate problem     

Three-dimensional CAD-based mesh Generator for the Dey-Mittra conformal FDTD algorithm

It is well-known that the finite-difference time-domain (FDTD) method is subject to significant errors due to the staircasing of surfaces that are not precisely aligned with major grid planes. Dey and Mittra introduced a locally conformal method (D-FDTD) that has shown substantial gains in the accuracy of modeling arbitrary surfaces in the FDTD grid. A mesh generator for this purpose was reported by Yu and Mittra. In this paper, we present the formulation and validation of an alternative CAD-based mesh generator for D-FDTD that has improved capabilities for arbitrary three-dimensional (3-D) perfect electric conductor (PEC) geometries. This mesh generator is capable of importing AutoCad and ProE files of 3-D PEC scatterers and resonators. It can reduce the required FDTD grid resolution by up to 4:1 in each Cartesian direction in 3-D relative to conventional staircased FDTD models when modeling cavity resonances of complex PEC structures such as twisted waveguides.     

Calculation methods of electromagnetic fields very close to lightning

In this short paper, we present two methods: Quasi-images formula and finite-difference time-domain (FDTD) method to evaluate the electromagnetic fields very close to lightning channel, which are applicable for poorly conducting ground case, and the numerical results are consistent with each other. Moreover, the vertical electric fields at 15 m obtained by the two proposed methods is in good agreement with the measured result, and the horizontal electric field at a distance of 100 m above finely conducting ground obtained by the FDTD method is identical to the field obtained by accurate Cooray-Rubinstein approximation. With the proposed quasi-images formula, the effects of electrical dispersion of the ground on the lightning generated electromagnetic fields are analyzed and some significant results are obtained.     

Improvements to the finite-difference time-domain method forcalculating the radar cross section of a perfectly conductingtarget

Several improvements to the finite-difference time-domain (FDTD) method for calculating the radar cross section (RCS) of a perfectly conducting target are presented. Sinusoidal and pulsed FDTD excitations are compared to determine an efficient method of finding the frequency response of targets. The maximum cell size, the minimum number of external cells, and a method to eliminate field storage in the shielded internal volume of perfect conductors to reduce the computer storage requirements of FDTD are discussed. The magnetic-field DC offset induced by surface currents on perfectly conducting objects is observed, and its effects are removed by postprocessing to achieve convergence of the RCS calculations. RCS calculations using the FDTD method in two dimensions are presented for both square and circular infinite cylinders illuminated by both transverse electric and transverse magnetic polarized plane waves. The RCS of a metal cube in three dimensions is also presented. Good agreement between FDTD calculations and theoretical values was achieved for all cases, and parameters necessary to achieve this agreement are examined     

Microwave modeling and validation in food thawing applications

Developing temperature fields in frozen cheese sauce undergoing microwave heating were simulated and measured. Two scenarios were investigated: a centric and offset placement on the rotating turntable. Numerical modeling was performed using a dedicated electromagnetic Finite Difference Time Domain (FDTD) module that was two-way coupled to the PHYSICA multiphysics package. Two meshes were used: the food material and container were meshed for the heat transfer and the microwave oven cavity and waveguide were meshed for the microwave field. Power densities obtained on the structured FDTD mesh were mapped onto the unstructured finite volume method mesh for each time-step/turntable position. On heating for each specified time-step the temperature field was mapped back onto the FDTD mesh and the electromagnetic properties were updated accordingly. Changes in thermal/electric properties associated with the phase transition were fully accounted for as well as heat losses from product to cavity. Detailed comparisons were carried out for the centric and offset placements, comparing experimental temperature profiles during microwave thawing with those obtained by numerical simulation.     

On the electromagnetic field in a cavity fed by a tangentialelectric field in an aperture in its wall

Heretofore, the electromagnetic field produced by a specified tangential electric field in an aperture in the wall of an arbitrarily shaped cavity has most often been expanded in terms of cavity modes. An alternative approach, that of the electric field integral equation is presented. In this approach, the cavity field is expressed as the field of a surface density of tangential electric current, or a surface density of tangential magnetic current, or a combination of surface densities of tangential electric and magnetic currents on the boundary of the cavity. Each surface density is characterized by a single tangential vector function which is determined by the integral equation requiring that the part of the electric field tangent to the boundary of the cavity must reduce to the specified tangential electric field in the aperture and zero elsewhere on the boundary of the cavity. The electric field integral equation method is specialized to more easily determine the field inside an arbitrary cylindrical cavity excited by a tangential electric field in an aperture in its lateral wall. The method is further specialized to a circular cavity     

Hybrid finite-difference/finite-volume time-domain analysis formicrowave integrated circuits with curved PEC surfaces using anonuniform rectangular grid

In this paper, we present a hybrid algorithm that combines the finite-difference time-domain (FDTD) and finite-volume time-domain (FVTD) methods to analyze microwave integrated-circuit structures that may contain curved perfect electric conductor (PEC) surfaces. We employ the conventional nonuniform FDTD in regions where the objects are describable with a rectangular mesh, while applying the FVTD method elsewhere where we need to deal with curved PEC configurations. Both the FDTD and FVTD quantities are defined in the mutually overlapping regions, and these fields from the respective regions are interpolated by using their nearest neighbors. We validate this algorithm by analyzing the scattering parameters of a stripline with one or more adjacent cylindrical vias, whose geometries are frequently encountered in printed-circuit-board designs. It is found that the hybrid FDTD-FVTD approach requires little increase in central processing unit time and memory in comparison to the conventional FDTD, while its computational accuracy is significantly improved over a wide range of frequencies. Specifically, this accuracy is found to be comparable to that achieved by doubling the mesh density of the staircased FDTD     

Approximate Crank-Nicolson schemes for the 2-D finite-difference time-domain method for TE/sub z/ waves

Two implicit finite-difference time-domain (FDTD) methods are presented in this paper for a two-dimensional TE/sub z/ wave, which are based on the unconditionally-stable Crank-Nicolson scheme. To treat PEC boundaries efficiently, the methods deal with the electric field components rather than the magnetic field. The "approximate-decoupling method" solves two tridiagonal matrices and computes only one explicit equation for a full update cycle. It has the same numerical dispersion relation as the ADI-FDTD method. The "cycle-sweep method" solves two tridiagonal matrices, and computes two equations explicitly for a full update cycle. It has the same numerical dispersion relation as the previously-reported Crank-Nicolson-Douglas-Gunn algorithm, which solves for the magnetic field. The cycle-sweep method has much smaller numerical anisotropy than the approximate-decoupling method, though the dispersion error is the same along the axes as, and larger along the 45/spl deg/ diagonal than ADI-FDTD. With different formulations, two algorithms for the approximate-decoupling method and four algorithms for the cycle-sweep method are presented. All the six algorithms are strictly nondissipative, unconditionally stable, and are tested by numerical computation in this paper. The numerical dispersion relations are validated by numerical experiments, and very good agreement between the experiments and the theoretical predication is obtained.     

任意截面导体柱电磁散射特性的时域分析

本文采用共形网格的ＦＤＴＤ法对任意截面导体柱的电磁散射特性进行了分析。首先采用广义环路积分法导出共形网格上的时域有限差分方程,然后针对共形网格导出其一阶和二阶吸收边界条件。这种吸收边界条件在曲率半径趋于无穷大时分别退化为一阶和二阶Ｍｕｒ 吸收边界条件。由于采用共形网格,网格节点数远少于普通ＦＤＴＤ法中的节点数,从而大大节省了计算时间和存储空间。在时谐平面波和高斯脉冲激励下,首先计算了导体柱表面的时域感应电流,然后运用Ｆｏｕｒｉｅｒ变换计算导体柱的ＲＣＳ,其结果与其它文献结果一致。     

辅助方程-双向隐式差分法的电磁散射研究

在辅助差分方程(ADEs)的基础上结合交替隐式时域有限差分方法(ADI-FDTD),提出ADEs-ADI-FDTD方法用以计算色散媒质的电磁散射问题。由于三维ADI-FDTD方法的复杂性,在此采用了全分裂场形式的场量以简化完全匹配层(PML)吸收边界的处理及在连接边界处入射场的加入。针对Debye型色散媒质,利用极化强度辅助差分系列方程推导了ADEs-ADI-FDTD方法中电、磁场的迭代方程及其相关参数表达式,最后通过对色散媒质和各向同性等离子体等物体进行仿真计算,计算结果显示了本文算法在时间上的高效性和精确性。