Application of Impedance Loading to Geometric Transition Radar Absorbent Material

This paper describes a novel, lightweight technique for significantly improving the low-frequency reflectivity performance of conventional geometric transition radar absorbent materials as used typically in anechoic chamber facilities for electromagnetic compatibility testing. The improvement is achieved by the inclusion of impedance-loading elements within the base region of the absorber, and these are implemented in the form of one or more frequency-selective surfaces (FSS). The discussion covers the design of the FSS using computer simulation technology microwave studio, its predicted effect on absorber performance at both normal and oblique incidence, the effect of manufacturing tolerances, and the fabrication and characterization of a prototype-loaded absorber panel.     

Finite-difference approach to the solution of time-domain integralequations for layered structures

A numerical algorithm for the analysis of transient electromagnetic fields in planar structures is proposed based on the time-domain magnetic-field integral equation (MFIE), electric-field integral equation (EFIE), and the marching-on-in-time approach. The field vectors are represented in terms of vector potential functions which are calculated either by integration or by the three-dimensional (3-D) wave equation according to the geometry of the structure. Thus, the algorithm combines the advantages of integral equation techniques and finite-difference schemes. While this approach is applicable to any geometries, it is especially suitable for multilayered planar structures and is competitive to the finite-difference time-domain (FDTD) method in the case of open and radiating problems. Theoretical results are verified by the analysis of a pulse propagation in a homogeneous open-end microstrip line     

E-P-AMCBFM分析介质与PEC混合体的电磁散射

使用基于表面积分方程的矩量法来分析介质与理想导体混合体的电磁散射是计算电磁学的一大热点。对理想导体目标体表面建立电场积分方程,在介质目标体表面建立PMCHW方程组,与基于矩阵分块技术的自适应修正特征基函数法结合,对介质涂敷理想导体目标体的电磁散射进行分析,将其称之为EFIE-PMCHW-AMCBFM(E-P-AMCBFM)。并讨论不同参数如基函数阶数,矩阵块间重叠区域等对计算效率的影响,数值结果表明E-P-AMCBFM对于处理介质-理想导体混合体的电磁散射问题具有较高的精度和效率。     

High-frequency electromagnetic field coupling to long terminatedlines

We present a theory for the EMC problem of electromagnetic field coupling to a long line with arbitrary terminations. The theory is applicable for the high-frequency plane wave electromagnetic field excitations, when the transmission line approximation is no longer valid. Analytical expressions are derived for the induced current along the line, and at the two-line terminals. The coefficients of these expressions are determined using a procedure based on the exact solutions of the integral equation for two similar line configurations, but having a significantly shorter length. The method is, therefore, particularly efficient when considering the electromagnetic field coupling to very long lines. The advantage of the proposed approach is that, in contrast with transmission line approximation, it takes into account high-frequency radiation effects. Furthermore, it allows a considerable reduction in computation time and storage requirements with respect to conventional numerical solutions based on the thin-wire approximation     

埋地三维复杂介质目标电磁散射特性分析

采用混合位积分方程（MPIE）和基于四面体元基函数的矩量法分析计算了埋地三维介质目标电磁散射问题,利用二级离散复镜像（DCIM）和广义函数束（GPOF）相结合的方法求解近场Sommerfeld积分,很好地解决了多层媒质中复杂目标电磁散射计算中的棘手问题,其方法简练、精确、高效,数值分析结果与有关文献吻合很好,证实了该方法的正确性和通用性。此外,该文还通过计算比较了不同观察点、不同目标埋地深度及介质参数的电磁散射特性。     

基于积分方程区域分解算法的研究进展

介绍了近年来用于电磁建模的积分方程区域分解算法（domain decomposition method,DDM）.DDM是一种基于"分而治之"策略的框架性算法,为复杂电磁问题的求解提供了一种灵活的技术途径.结合国内外研究动态详细介绍了三类积分方程DDM,即重叠型积分方程DDM,非共形、非重叠型积分方程DDM以及基于等效原理的积分方程DDM,并通过数值算例说明了这些算法的优缺点.最后总结了积分方程DDM的主要挑战以及展望.     

Electromagnetic wave absorber with wide-band frequencycharacteristics using exponentially tapered ferrite

As a countermeasure of EMI or EMC, various types of electromagnetic wave absorbers are used. A wide-band design method of an electromagnetic wave absorber with using exponentially tapered ferrite, which has very wide-band frequency characteristics, is proposed and discussed. The wide-band electromagnetic wave absorber can be designed under some approximations by the theoretical model using the equivalent material constants (equivalent complex permittivity and permeability) method for the regions varying spatially in the shape of ferrite. Based on the model, wide-band electromagnetic wave absorbers with taper, which have not only excellent reflectivity frequency characteristics but also a bandwidth of 30 MHz to 2150 MHz or 2430 MHz under the tolerance limits of -20 dB reflectivity, were designed     

A Low‐Cost Method to Evaluate Absorber Reflectivity Using an Antenna with a Small Radiating Aperture and Frequency‐Domain Instrument

We propose a way to measure the absorber reflectivity at a low cost. Only one simple antenna with a small radiating aperture and a frequency‐domain instrument are utilized. The previously used equation for calculating the reflectivity of an absorber is inaccurate, and, therefore, a new equation is derived based on multiple reflection analysis and three test models. Notably, the reflection coefficient of the antenna is included in the derived equation. The accuracy of the proposed method is proven through simulation and measurements. It can be easily applied to a product examination by absorber manufacturers and customers owing to its advantages of simplicity, cost effectiveness, and non‐cutting examination.     

Analysis of lightning-radiated electromagnetic fields in the vicinity of lossy ground

An antenna theory (AT) approach in the frequency domain is presented to compute electromagnetic fields radiated by a lightning return stroke. The lightning channel is modeled as a lossy-wire monopole antenna (a wire antenna with distributed resistance) energized by a current source at its base, and the ground is modeled as a lossy half-space. The method of moments is used for solving the governing electric field integral equation (EFIE) in the frequency domain. The resultant current distribution along the channel is used to calculate electromagnetic fields at different distances from the channel. All field components are evaluated using a rapid but accurate procedure based on a new approximation of Sommerfeld integrals. In contrast with the previous models, the approach proposed here is characterized by a self-consistent treatment of different field components in air or on the surface of a lossy half-space. It is shown that the omission of surface wave terms in the general field equations, as done in the perfect-ground approximation, can strongly affect model-predicted field components.     

Solving Low-Frequency EM-CKT Problems Using the PEEC Method

The partial element equivalent circuit (PEEC) formulation is an integral equation based approach for the solution of combined electromagnetic and circuit (EM-CKT) problems. In this paper, the low-frequency behavior of the PEEC matrix is investigated. Traditional EM solution methods, like the method of moments, suffer from singularity of the system matrix due to the decoupling of the charge and currents at low frequencies. Remedial techniques for this problem, like loop-star decomposition, require detection of loops and therefore present a complicated problem with nonlinear time scaling for practical geometries with holes and handles. Furthermore, for an adaptive mesh of an electrically large structure, the low-frequency problem may still occur at certain finely meshed regions. A widespread application of loop-star basis functions for the entire mesh is counterproductive to the matrix conditioning. Therefore, it is necessary to preidentify regions of low-frequency ill conditioning, which in itself represents a complex problem. In contrast, the charge and current basis functions are separated in the PEEC formulation and the system matrix is formulated accordingly. The incorporation of the resistive loss (R) for conductors and dielectric loss (G) for the surrounding medium leads to better system matrix conditioning throughout the entire frequency spectrum, and it also leads to a clean dc solution. We demonstrate that the system matrix is well behaved from a full-wave solution at high frequencies to a pure resistive circuit solution at dc, thereby enabling dc-to-daylight simulations. Finally, these techniques are applied to remedy the low-frequency conditioning of the electric field integral equation matrix     

A higher order parallelized multilevel fast multipole algorithm for3-D scattering

A higher order multilevel fast multipole algorithm (MLFMA) is presented for solving integral equations of electromagnetic wave scattering by three-dimensional (3-D) conducting objects. This method employs higher order parametric elements to provide accurate modeling of the scatterer's geometry and higher order interpolatory vector basis functions for an accurate representation of the electric current density on the scatterer's surface. This higher order scheme leads to a significant reduction in the mesh density, thus the number of unknowns, without compromising the accuracy of geometry modeling. It is applied to the electric field integral equation (EFIE), the magnetic field integral equation (MFIE), and the combined field integral equation (CFIE), using Galerkin's testing approach. The resultant numerical system of equations is then solved using the MLFMA. Appropriate preconditioning techniques are employed to speedup the MLFMA solution. The proposed method is further implemented on distributed-memory parallel computers to harness the maximum power from presently available machines. Numerical examples are given to demonstrate the accuracy and efficiency of the method as well as the convergence of the higher order scheme     

A closer look at reverberation Chambers - 3-D Simulation and experimental verification

This paper presents three-dimensional (3-D) full-wave simulations of the electromagnetic field inside a medium-sized reverberation chamber. A frequency-domain method-of-moments approach based on the electric field integral equation is used. A synopsis of the computational challenges particular for reverberation chambers is described and a detailed overview on the chamber modeling procedure is given. The electric field inside the chamber is computed and the influence of small geometric details and asymmetries is investigated as well as the effect of different excitations and stirrers. It is demonstrated that a statistics-based validation of reverberation chamber simulations is insufficient. To validate simulation results, therefore extensive near-field measurements inside the prototype reverberation chamber are performed. The complete 3-D reverberation chamber simulation, considering stirrers, door, and various practical excitations, accurately predicts the fields within the chamber in the important lower-to-medium frequency range and thus represents a reliable tool facilitating reverberation chamber optimization.     

Loop-tree implementation of the adaptive integral method (AIM) for numerically-stable, broadband, fast electromagnetic modeling

The adaptive integral method (AIM) is implemented in conjunction with the loop-tree (LT) decomposition of the electric current density in the method of moments approximation of the electric field integral equation. The representation of the unknown currents in terms of its solenoidal and irrotational components allows for accurate, broadband electromagnetic (EM) simulation without low-frequency numerical instability problems, while scaling of computational complexity and memory storage with the size of the problem are of the same order as in the conventional AIM algorithm. The proposed algorithm is built as an extension to the conventional AIM formulation that utilizes roof-top expansion functions, thus providing direct and easy way for the development of the new stable formulation when the roof-top based AIM is available. A new preconditioning strategy utilizing near interactions in the system which are typically available in the implementation of fast solvers is proposed and tested. The discussed preconditioner can be used with both roof-top and LT formulations of AIM and other fast algorithms. The resulting AIM implementation is validated through its application to the broadband, EM analysis of large microstrip antennas and planar interconnect structures.     

高速电路电源/地层间阻抗参数计算与分析

为了快速准确地计算高速电路地层与电源层之间的阻抗参数,基于边界积分方程提出了有效的计算方法.该方法充分利用了实际电源层/地层的结构特征,将三维电磁场问题转化为二维问题,减少了计算时间.由于在计算中不需要考虑整个 电源层/地层结构的格林函数,故该方法可以用于任意边界形状的电路板.基于提出的积分方程法,分析了介质相对电介质...     

Radiation and low-frequency scattering of EM waves in a generalanisotropic homogeneous medium

This paper focuses on a boundless homogeneous medium with general anisotropy of electromagnetic properties. The explicit exact form of the four spectral Green's dyads Gˆ_νξ(k) is obtained and a coordinate-free representation of the four spatial Green's functions Gˆ_νξ(x-x') in terms of one scalar potential W(x-x') is developed. On this basis, asymptotic expressions for the radiation field due to arbitrary sources are derived that show that the associated modes and the eigenmodes determine radiation along a singular optic axis and in all other directions, respectively. Using an integral equation approach and the theory of Newtonian potential, the problem of low-frequency scattering by a small anisotropic ellipsoidal body immersed into an anisotropic medium is solved analytically     

Fast numerical modeling of multitransmitter electromagnetic data using multigrid quasi-linear approximation

Multitransmitter electromagnetic (EM) surveys are widely used in remote-sensing and geophysical exploration. The interpretation of the multitransmitter geophysical data requires numerous three-dimensional (3-D) modelings of the responses of the receivers for different geoelectrical models of complex geological formations. In this paper, we introduce a fast method for 3-D modeling of EM data, based on a modified version of quasilinear approximation, which uses a multigrid approach. This method significantly speeds up the modeling of multitransmitter-multireceiver surveys. The developed algorithm has been applied for the interpretation of marine controlled-source electromagnetic (MCSEM) data. We have tested our new method using synthetic problems and for the simulation of MCSEM data for a geoelectrical model of a Gemini salt body.     

Improved Electric Field Integral Equation (IEFIE) for Analysis of Scattering From 3-D Conducting Structures

In this paper, a novel improved electric field integral equation (IEFIE) is developed to achieve fast and accurate solution of electromagnetic scattering from 3-D conducting structures. By adding the principle value term of the magnetic field integral equation (MFIE) operator into the EFIE operator, a well-conditioned improved EFIE operator is constructed. To achieve a reasonable accuracy, several update steps for the current vector are required. A multilevel fast multipole algorithm (MLFMA) is also applied to accelerate the computation of matrix-vector multiplications in the iteration. The present method attains much faster convergence of iterations than traditional EFIE and much better accuracy of the solution than the traditional combined field integral equation, particularly for 3-D structures with open or sharp surfaces. Numerical results show the validity and efficiency of the present method.     

Microwave imaging within the second-order Born approximation:stochastic optimization by a genetic algorithm

This paper addresses the problem of reconstructing the location, shape, and dielectric permittivity distribution of an inhomogeneous dielectric object from measurements of the field scattered by the object. The object is an inhomogeneous infinite cylinder of arbitrary cross section illuminated by a transverse magnetic incident electric field. The approach is based on the Lippmann-Schuringer integral equation for the electromagnetic inverse scattering problem, approximated by applying the second-order Born approximation, which allows an extension of the range of contrast values that can be accurately imaged. The numerical approach is developed in the spatial domain and makes use of a multi-illumination multiview processing. In particular, the inverse problem is recast in a global nonlinear optimization problem (including a penalty function), solved by a stochastic method based on a genetic algorithm. In this paper, the mathematical formulation of the approach is described and the results of several dielectric reconstructions are reported, including comparisons with analogous reconstructions performed within the linearized (first-order) Born approximation     

Comparison of electromagnetic absorber used in anechoic andsemi-anechoic chambers for emissions and immunity testing of digitaldevices

The absorber used in anechoic and semi-anechoic chambers employed for emissions and immunity testing of digital devices is examined. Using reflectivities obtained by the method of homogenization, the advantages and disadvantages of urethane pyramids, twisted-pyramids, wedges, as well as ferrite tiles, ferrite grids, and “hybrid” combinations of urethanes and ferrites, are determined. General reflectivity guidelines are also presented for comparing absorber used for the electromagnetic compatibility (EMC) testing of digital devices from 30 to 1000 MHz     

A representation theorem based analysis of two-dimensionalelectromagnetic scattering from materials and resistive cards

Representation-theorem-based surface integral operators are presented and used to predict electromagnetic scattering from a material body with an embedded resistive card. The integral operators are obtained from a representation theorem for the 2-D Helmholtz equation in a region with constant electrical properties characterized by complex permittivity and permeability. A resistive card embedded in the region is introduced by enforcing a resistive boundary condition on the representation theorem integrals as the thickness of a geometrically thin region surrounding an embedded card approaches zero. Surface integral operators are obtained by letting the field point in the representation theorem equations approach material boundaries and resistive cards. Multiple regions with constant electrical properties (including perfect conductors) are allowed by enforcing boundary conditions between regions. Two polarizations of normally incident plane wave radiation are considered. Prediction and experiment are in good agreement for a resistive card embedded in a bulk material