Finite element analysis of electromagnetic scattering from periodic cylindrical structures at oblique incidence

A hybrid technique which combines the finite element method (FEM) and an expansion of the field in terms of Floquet modes is presented for the analysis of the scattering from, and the transmission through, penetrable periodic cylindrical structures, at skew incidence. The method is very flexible and allows the analysis of practical cylindrical configurations with arbitrary cross-section and material properties.<>     

Boundary element method for electromagnetic scattering from cylinders

The computation of low frequency scattering of electromagnetic fields by solid/hollow dielectric or conducting cylinders using the boundary element method (BEM) is considered. A general computer program has been developed for both transverse electric and magnetic cases. Numerical examples are given for conducting circular cylinders, and solid and hollow dielectric cylinders. The computational accuracy is checked by comparing the results with the analytic solution or computing an error defined from the optical theorem. In addition some problems at an interior resonance of the scatterer are discussed. The method can be directly applied to more complicated geometries.     

Finite element analysis of electromagnetic interaction with uniform moving medium

A finite element vector formulation for studying the electromagnetic interaction with infinitely long cylinders of arbitrary cross-section moving along their axes is presented. The problem is solved in the laboratory reference frame by using the Minkowski transformed constitutive equation to take into account body motion. The formulation is verified by analysing simple structures for which an analytical solution is known     

FINITE DIFFERENCE METHOD FOR ELECTROMAGNETIC SCATTERING FROM PERFECTLY CONDUCTING CYLINDER

A numerical method of solving electromagnetic wave scattering problem is described.Radiation boundary condition(RBC)is applied to confine EM scattering problem in unboundedregion into problem in finite region.Combined with RBC and scatterer surface boundary condi-tion,Helmholtz equation in the finite region is solved numerically by the finite difference method.Thus the distribution of induced surface current on conducting cylinder and near field can beobtained.Computational results for both polarizations for circular,elliptic and square cylindersare presented.These results are in excellent agreement with those obtained by the eigenfunctionexpansion method or moment method and much better then the results of OSRC method.     

Analysis of electromagnetic scattering from a cavity with a complextermination by means of a hybrid ray-FDTD method

The electromagnetic modeling of engine cavities is a very difficult task because the electrical size of the cavity is very large, while the engine termination is geometrically complex. High-frequency techniques can adequately model the cavity, but perform poorly when applied to the termination. Low-frequency techniques are currently infeasible for such large geometries because of the large memory and computation time requirements. The authors present a hybrid method which combines the most attractive features of the lowand high-frequency techniques. The finite-difference time-domain (FDTD) method is applied to the small region surrounding the termination. The remainder of the cavity is modeled with ray methods. To validate this method, they consider two-dimensional cavities with complex terminations. Their results are compared against those found from a hybrid combination of the modal method and the method of moments     

Finite element computation of electromagnetic fields [hyperthermiatreatment]

A three dimensional finite element solution scheme is developed for numerically computing electromagnetically induced power depositions. The solution method is applicable to those problems for which it can be reasonably assumed that the magnetic permeability is homogeneous. The method employs an incident field/scattered field approach where the incident field is precalculated and used as the forcing function for the computation of the scattered field. A physically logical condition is used for the numerical boundary conditions to overcome the fact that electromagnetic problems are generally unbounded (i.e., the boundary condition is applied at infinity) but numerical models must have a boundary condition applied to some finite location. At that numerical boundary, an outgoing spherical wave is simulated. Finally, an alternate to a direct solution scheme is described. This alternate method, a preconditioned conjugate gradient solver, provides both a storage and CPU time advantage over direct solution methods. For example, a one-thousand fold decrease in CPU time was achieved for simple test cases. Unlike most iterative methods, the preconditioned conjugate gradient technique used has the important property of guaranteed convergence. Solutions obtained from this finite element method are compared to analytic solutions demonstrating that the solution method is second-order accurate     

CAVERN: a prediction code for cavity electromagnetic analysis

The authors describe an application of the fast Fourier Bessel transform to speed up their jet-engine scattering-analysis code, CAVERN. Because of the engine termination, it is typically necessary to break up the computational domain into that of the inlet and engine regions. In the inlet region, the fields are modeled using ray techniques, whereas the complex engine must be modeled using a different and more-rigorous formulation. A need then arises for interfacing the two computational domains, in a manner that maintains field continuity. Since the engine is always housed in a cylindrical or near-cylindrical inlet section, one way for interfacing the two computational regions is to represent the ray and engine fields using a cylindrical-modal expansion. The engine can then be characterized, via the modal-scattering matrix, in a manner independent of the excitation. Ray fields can be readily turned into modes, and vice versa, and continuity of the fields at the interface of the two regions is maintained, since both use the same modal representation. However, for inlets whose diameter spans 50λ or so, the task of transforming rays into modes and vice versa can become a bottleneck, because of the large number of propagating modes present in the cavity. Use of the fast Fourier Bessel transform can alleviate this difficulty, as described     

求解电大口径含腔目标电磁散射内问题的新途径

含腔目标,尤其是含电大尺寸口径面腔体目标的电磁散射是目标散射问题中极其重要和极具挑战的问题.现有的精确求解含腔目标散射问题的方法由于计算机内存的限制都不能很好地应用于电大尺寸口径面含腔目标的散射求解.对此,提出了用电场积分方程结合局部耦合原理求解含腔目标电磁散射的问题,即求解腔体口径面上的等效磁流.该方法在保证较高精度的同时打破了现有方法中计算机内存对腔体口径尺寸的制约.为提高求解效率,文中采用多层快速多极子方法加速内域电流的求解,同时用其扩展形式加速口径面近区场的计算.另外,高阶方法的采用进一步扩大了求解问题的规模.数值结果表明了该方法的有效性.     

Highly storage-efficient hybrid finite element/boundary element method for electromagnetic scattering

By properly choosing boundary surfaces and meshes of the hybrid finite element/boundary element method, one can reduce storage requirements of the boundary element matrices to the order of M for M boundary nodes.<>     

Three-dimensional electromagnetic scattering from inhomogeneousobjects by the hybrid moment and finite element method

The hybrid moment and finite element methods are used to obtain 3-D scattering and/or absorption from inhomogeneous, arbitrarily shaped objects. The surface of the object is approximated by triangles and the volume of the object is approximated by tetrahedrons. The electrical parameters are assumed constant in each tetrahedron. The Galerkin testing procedure is used. To avoid contaminations of spurious mode, a divergenceless vector basis function is used in finite elements. The calculated internal field and scattered field for a homogeneous sphere, a layered sphere, and a lossy prolate spheroid are compared with Mie series solutions and other numerical techniques. The accuracy and rate of convergence of the solution are discussed     

Non-uniform wavelets in electromagnetic scattering analysis

Non-uniform wavelets are constructed to benefit from both adaptively refined grids for modelling edge singularities and compression of moment matrices with wavelet bases. They are applied to the analysis of electromagnetic scattering problems     

Finite element analysis of axisymmetric radomes

A two-step technique for the analysis of axisymmetric radomes is presented. Initially, an axisymmetric finite-element approach is employed, together with an absorbing boundary condition for mesh truncation, to determine the near fields scattered by an empty radome illuminated by a distant source. Next, the reciprocity theorem is invoked to determine the far-field pattern of an antenna encased by the radome, by computing the interaction between the current distribution on the antenna and the near-field data determined in the first step. The details of the formulation are presented along with numerical results for two different arrays enclosed by radomes of varying permittivities     

相控阵雷达天线的有限元分析

应用有限元分析软件MSC／NASTAN对某相控阵雷达天线进行分析计算,给出其静力及动力特性,确保设计的产品满足使用要求。     

Point-matched time domain finite element methods for electromagnetic radiation and scattering

Direct time domain computation of Maxwell's differential equations will soon become a practical technique because of the availability of supercomputers. The principal methods used in time domain computations and the supporting theories are presented. The point-matched finite element method is chosen as the main feature of this presentation, which includes the discretization of equations, conforming mesh generation, dielectric and metallic interfaces, numerical stability and simulation of radiation conditions. Numerical results of scattering of Gaussian pulses are presented in time sequences.     

Analyses of electromagnetic scattering from wire-mesh structures

Various analytical and numerical methods have been developed recently to calculate the interaction of wire-mesh structures with electromagnetic waves. An intercomparison of these methods is reported for the two cases where the wire junctions are bonded and unbonded. In particular, it is found that the average boundary condition method of Kontorovich and Astrakhan appears to give valid results only if the interwire spacing of the mesh is small compared with a wavelength. However, we may safely conclude from both their work and ours that bonding the wire junctions may degrade the shielding performance of such meshes.     

Finite element analysis extends its domain

Finite element analysis (FEA), traditionally used to predict stress and dynamic response in mechanical systems, is finding its way into a wider realm of electrical engineering applications. These tasks range from finding the temperature distribution in IC packages, to analyzing mechanical and electrical faults in disk drives. This article addresses the capabilities of such programs to solve critical engineering problems by presenting an overview of current and potential uses for FEA in electrical engineering     

NEW APPROACH TO ELECTROMAGNETIC SCATTERING FROM A CONDUCTIVE DISC-RING STRUCTURE

A one-dimensional modified integral equation for electromagnetic scattering from a metallic concentric disc-ring structure is derived by using Fourier expansion and separating the contribution of charge density from conventional EFIE. In the case of normal incidence, the derived equation is very simple and easy to be solved numerically regardless of the electric dimension of the structure. The comparison between the data of RCS of a disc by using this method and analytical method shows the effectiveness of this approach. Numerical results are also given for current distributions and the scattered fields for a disc-ring structure.     

Finite element analysis of cardiac defibrillation currentdistributions

We have developed a two-dimensional finite element model of the canine heart and thorax to examine different aspects of the distribution of current through cardiac tissue during defibrillation. This model allows us to compare various electrode configurations for the implantable cardioverter/defibrillator. Since we do not yet know the electrical criteria to apply for predicting defibrillation thresholds, such as the minimum current density required for defibrillation or the critical mass if indeed such quantities are applicable, we measured defibrillation energy in dogs to determine the voltages to apply to the model for calculating current distributions. By analyzing isopotential contours, current lines, power distributions, current density histograms, and cumulative current distributions, we estimated the critical fraction and threshold current density for defibrillation, compared various electrode configurations, and assessed the sensitivity of the defibrillation threshold to electrode position, patch size, and tissue conductivity. We found that blood can shunt defibrillation current away from the myocardium, particularly in configurations using a two-electrode catheter, that myocardial tissue conductivity strongly affects the current distributions, and that epicardial patch size is more important that subcutaneous patch size. Our results are consistent with successful defibrillation requiring that 80 +/- 5% of the heart must be rendered inexcitable by a current density of 35 +/- 5 mA/cm2 or greater. This two-dimensional, isotropic model has allowed us to analyze some of the determinants of defibrillation, but more detailed interpretation of experimental data may require the extension of the model to three dimensions.     

Finite element analysis of lossy dielectric waveguides

This paper presents a full-wave analysis of lossy dielectric waveguides using a hybrid vector finite element method. To avoid the occurrences of spurious modes in the formulation, edge elements and first-order nodal finite element basis functions are used to span the transverse and the z components of the electric field, respectively. Furthermore, the direct matrix solution technique with minimum degree of reordering has been combined with the modified Lanczos algorithm to solve for the resultant sparse generalized eigenmatrix equation efficiently     

双层弯曲热执行器的有限元分析

研究了一种由多晶硅电阻、硅和金属层构成的双层弯曲热执行器。利用有限元方法计算了该执行器的纵向偏转和温度分布。为了提高精度,本文提出了一种三层结构的有限元模型,当用厚度为1μm的硅和0郾5μm厚的铝薄膜构成执行器时,在5V电压的驱动下可以获得最大位移为25郾62μm。由有限元分析还可以得到温度分布,最后和实验结果进行了比较,并讨论了误差产生的原因。