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

investigation of nonplanar perfectly matched absorbers for finite element mesh truncation we present a detailed theoretical and numerical investigation of the perfectly matched layer pml concept as applied to the problem of mesh truncation in the finite element method fem we show that it is possible to extend the cartesian pml concepts involving half spaces to cylindrical and spherical geometries appropriate for closed boundaries in two and three dimensions by defining lossy anisotropic layers in the relevant coordinate systems by using the method of separation of variables it is possible to solve the boundary value problems in these geometries the analytical solutions demonstrate that under certain conditions outgoing waves are absorbed with negligible reflection and the transmitted wave is attenuated within the pml to reduce the white space in radiation or scattering problems conformal pmls are constructed via parametric mappings it is also verified that the pml concept which was originally introduced for problems governed by maxwell s equations can be extended to cases governed by the scalar helmholtz equation finally numerical results are presented to demonstrate the use of the pml in fem mesh truncation

a 3 d hybrid finite element boundary element method for the unified radiation and scattering analysis of general infinite periodic arrays we present a rigorous frequency domain variational 3 d electromagnetic formulation for the general nonself adjoint infinite periodic array problem the hybrid method described combines the vector finite element and floquet boundary element techniques it is general in the sense that it is applicable to infinite periodic arrays of the open or aperture types it is thus effective for modeling both the scattering and radiation performance of diverse fss absorber and phased array structures the technique accurately handles arbitrarily complicated 3 d geometries lossy inhomogeneous media and internal as well as external excitations these analyses can be applied to general skewed grids under arbitrary scan and polarization conditions

relative index theorems and supersymmetric scattering theory we discuss supersymmetric scattering theory and employ krein s theory of spectral shift functions to investigate supersymmetric scattering systems this is the basis for the derivation of relative index theorems on some classes of open manifolds as an example we discuss the de rham complex for obstacles in n and asymptotically flat manifolds it is shown that the absolute or relative euler characteristic of an obstacle in n may be obtained from scattering data for the laplace operator on forms with absolute or relative boundary conditions respectively in the case of asymptotically flat manifolds we obtain the chern gauss bonnet theorem for thel2 euler characteristic

adjustment for non differential misclassification error in the generalized linear model it is well known that estimates of association between an outcome variable and a set of categorical covariates some of which are measured with misclassification tend to be biased upon application of the usual methods of estimation that ignore the classification error we propose a method to adjust for misclassification in covariates when one applies the generalized linear model in the case where one can observe some true covariates only through surrogates we combine a latent class analysis with the approach to incorporate multiple surrogates into the model we include discussion on the efficacy of repeated measurements which one can view as a special case of multiple surrogates with identical distribution we provide two examples to demonstrate the applicability of the method and the efficacy of multiple replicates for a covariate subject to misclassification in a regression framework

time domain finite difference and finite element methods for maxwell equations in complex media extensions of finite difference time domain fdtd and finite element time domain fetd algorithms are reviewed for solving transient maxwell equations in complex media also provided are a few representative examples to illustrate the modeling capabilities of fdtd and fetd for complex media the term complex media refers here to media with dispersive bi anisotropic inhomogeneous and or nonlinear properties present in the constitutive tensors

3 d numerical mode matching nmm method for resistivity well logging tools a three dimensional 3 d numerical mode matching nmm method is presented for poisson s equation in general inhomogeneons media it reduces the original 3 d problem into a series of two dimensional 2 d eigenvalue problems plus a one dimensional 1 d layered medium problem which can be modeled efficiently by a recursion procedure the algorithm is tested for several 3 d inhomogeneous media and an excellent agreement between the nmm and analytical solutions is obtained for all test cases we demonstrate some typical applications of the 3 d nmm algorithm in resistivity well logging including invasion zones of noncircular shape vertical and horizontal fractures and horizontal wells the solution procedure proposed is directly applicable to wave propagation in 3 d inhomogeneous media

perfectly matched layer in three dimensions for the time domain finite element method applied to radiation problems a new perfectly matched layer pml formulation for the time domain finite element method is described and tested for problems in three dimensional space an integral part of this pml algorithm is a novel time integration scheme based on galerkin s method with a piecewise linear temporal expansion of the electric field our time integration procedure is constructed by forming a linear combination of exact and trapezoidal integration applied to the temporal weak form which reduces to the well known newmark scheme in the case where the pml is not present this technique allows for a consistent time discretization of the electric field vector wave equation augmented with the pml which includes terms that involve the electric field itself time derivatives thereof and exponential functions temporally convolved with the electric field the auxiliary variables that are associated with such convolutions are efficiently updated in an explicit manner by matrix vector products the new pml formulation is successfully tested on canonical problems the pml can very efficiently absorb propagating electromagnetic waves which is demonstrated by reflections coefficients as low as 100 db the pml formulation is capable of giving highly accurate results for very broad frequency bands which is confirmed by tests that show an error smaller than 2 over more than six octaves in frequency finally we apply the pml formulation to a bow tie antenna and comparisons with measurements show good agreement

using replicate observations in observer agreement studies with binary assessments by introducing replicate observations into observer agreement studies one can obtain better measures of observer agreement than heretofore possible new methodology based on the analysis of latent variables allows a separation of within and between observer variation for binary measures of assessment among pairs of observers maximum likelihood estimation and hypothesis testing are discussed the methodology is illustrated using data on the assessment of dysplasia by pathologists

a non overlapping domain decomposition method with non matching grids for modeling large finite antenna arrays a non overlapping domain decomposition method ddm is proposed herein to solve maxwell equations in r 3 in this work the maxwell equations are discretized using a vector finite element method with hierarchical h curl vector basis functions there are two major ingredients in the proposed non overlapping ddm a a proper 1st order transmission condition to enforce field continuity across domain boundaries and b a cement technique to allow non matching grids for neighboring domains moreover a detail fourier analysis of the transmission condition for a canonical half space example is presented the analysis provides significant insights into the convergence behavior of the proposed non overlapping ddm for solving electromagnetic radiation problems such as the large finite antenna arrays particularly for the antenna arrays the proposed non overlapping ddm is extremely efficient since the formulation can easily incorporate geometrical repetitions exponentially tapered notch vivaldi antenna arrays with size up to 100x100 elements are solved on a common pc to validate the proposed non overlapping ddm

continuously inhomogeneous higher order finite elements for 3 d electromagnetic analysis a novel higher order entire domain finite element technique is presented for accurate and efficient full wave three dimensional 3d analysis of electromagnetic structures with continuously inhomogeneous material regions using large generalized curved hierarchical curl conforming hexahedral vector finite elements that allow continuous change of medium parameters throughout their volumes this is the first general 3d implementation and numerical demonstration of the inherent theoretical ability of the finite element method fem to directly treat arbitrarily continuously inhomogeneous materials the results demonstrate considerable reductions in both number of unknowns and computation time of the entire domain fem modeling of continuously inhomogeneous materials over piecewise homogeneous models they indicate that in addition to theoretical relevance and interest large curved higher order continuous fem elements also have great potential for practical applications that include structures with pronounced material inhomogeneities and complexities

perfectly matched layer for the time domain finite element method a new perfectly matched layer pml formulation for the time domain finite element method is described and tested for maxwell s equations in particular we focus on the time integration scheme which is based on galerkin s method with a temporally piecewise linear expansion of the electric field the time stepping scheme is constructed by forming a linear combination of exact and trapezoidal integration applied to the temporal weak form which reduces to the well known newmark scheme in the case without pml extensive numerical tests on scattering from infinitely long metal cylinders in two dimensions show good accuracy and no signs of instabilities for a circular cylinder the proposed scheme indicates the expected second order convergence toward the analytic solution and gives less than 2 root mean square error in the bistatic radar cross section rcs for resolutions with more than 10 points per wavelength an ogival cylinder which has sharp corners supporting field singularities shows similar accuracy in the monostatic rcs

fast and efficient analysis of radome enclosed antennas in receiving mode by an iterative based hybrid integral equation modified surface integration method an iterative based hybrid method which combines the volume surface integral equation vsie and the modified surface integration msi method is presented to analyze the radome enclosed antennas in receiving mode compared with the previously published hybrid approaches this method improves computational accuracy by including the effects of shaded wall of the radome and the mutual interactions between antennas and radome during the numerical solution of the vsie in an iterative manner by embedding different parts of the antenna radome structure ars into three distinct oct trees the multilevel fast multipole algorithm mlfma is used to accelerate both the vsie solution and the surface volume integrations in the msi stage the new method obtains more accurate results than its original version within less cpu time and keeps good accuracy with much less memory usage and computational time when compared with the mlfma accelerated full wave vsie solution for the entire ars

on the azimuthal fourier components of the green s function for the helmholtz equation in three dimensions many algorithms that compute acoustic or electromagnetic fields scattered by surfaces of revolution require fast evaluation of the azimuthal fourier components gm of the green s function for the helmholtz equation in three dimensions in this article we derive a recurrence relation for the functions gm and obtain explicit formulas for their partial derivatives these observations significantly reduce the complexity of the computation of the scattered fields generated by axisymmetric scatterers

scattering from complex bodies of revolution using a high order mixed finite element method and locally conformal perfectly matched layer an efficient finite element method fem is presented to analyze the scattering from complex bodies of revolution bor made of perfectly electric conductors and or dielectrics in the proposed method high order edge based vector basis functions are used to expand the transverse field components and high order node based scalar basis functions are used to expand the angular component the fem mesh is truncated using a locally conformal perfectly matched layer pml by the complex coordinate stretching such a kind of pml is very easy to implement in the numerical process and is able to enclose an arbitrarily shaped convex object in the spatial domain numerical examples are presented to demonstrate the accuracy and efficiency of the presented method

a perfectly matched layer for fluid solid problems application to ocean acoustics simulations with solid ocean bottoms a time domain legendre spectral element method is described for full wave simulation of ocean acoustics models i e coupled fluid solid problems in unbounded or semi infinite domains taking into account shear wave propagation in the ocean bottom the technique can accommodate range dependent and depth dependent wave speed and density as well as steep ocean floor topography for truncation of the infinite domain to efficiently absorb outgoing waves a fluid solid complex frequency shifted unsplit perfectly matched layer is introduced based on the complex coordinate stretching technique the complex stretching is rigorously taken into account in the derivation of the fluid solid matching condition inside the absorbing layer which has never been done before in the time domain two implementations are designed a convolutional formulation and an auxiliary differential equation formulation because the latter allows for implementation of high order time schemes leading to reduced numerical dispersion and dissipation a topic of importance in particular in long range ocean acoustics simulations the method is validated for a two dimensional fluid solid pekeris waveguide and for a three dimensional seamount model which shows that the technique is accurate and numerically long time stable compared with widely used paraxial absorbing boundary conditions the perfectly matched layer is significantly more efficient at absorbing both body waves and interface waves

a spectral integral method for smooth multilayered bodies of revolution a spectral integral method sim is developed to solve the scattering problem from smooth multilayered bodies of revolution bors this sim is a spectral method to improve the accuracy and efficiency of the sim by the fast fourier transform fft algorithm this method can achieve high accuracy and greatly reduce the computational time consumption in our bor sim the bor generatrix current is expanded by the truncated fourier series then the impedance matrix is generated in the spectral domain to solve the scattering problem unlike the conventional methods that need eight to ten segments per wavelength in the bor sim two points per wavelength are adequate to achieve high accuracy according to the nyquist theorem being accelerated by fft this method shows a significant efficiency advantage over the conventional bor method numerical results demonstrate the accuracy and efficiency of our new method by combining with the poggio miller chang harrington wu tsai surface integral equations this method can be used to solve many practical scattering problems

nystrom type method in three dimensional electromagnetic diffraction by a finite pec rotationally symmetric surface time harmonic electromagnetic wave diffraction by a perfectly electrically conducting pec finite rotationally symmetric surface located in free space is investigated the problem is split to independent azimuth orders and reduced to the sets of coupled hypersingular and singular integral equations ies for the surface current components these ies are discretized by the nystrom type method of discrete singularities using the interpolation type quadrature formulas from the solutions of corresponding matrix equations the near and the far field patterns are obtained the presented method has guaranteed convergence for arbitrary not axially symmetric primary field

a fast higher order time domain finite element boundary integral method for 3 d electromagnetic scattering analysis a novel hybrid time domain finite element boundary integral method for analyzing three dimensional 3 d electromagnetic scattering phenomena is presented the method couples finite element and boundary integral field representations in a way that results in a sparse system matrix and solutions that are devoid of spurious modes to accurately represent the unknown fields the scheme employs higher order vector basis functions defined on curvilinear tetrahedral elements to handle problems involving electrically large objects the multilevel plane wave time domain algorithm is used to accelerate the evaluation of the boundary integrals numerical results demonstrate the accuracy and versatility of the proposed scheme

misclassification in more than one factor in a case control study a combination of mantel haenszel and maximum likelihood approaches misclassification can arise in the case control setting in both the risk factor of interest and in a potential confounder if true status is not ascertainable but an independent replicated sample is available adjusted maximum likelihood estimates of the individual binomial proportions can be obtained and hence a relative risk estimate of the mantel haenszel type constructed an interval estimate on the latter can be calculated using the asymptotic properties of the likelihood function the method is illustrated by application to a case control study of breast cancer risk and such lifestyle attributes as diet smoking and alcohol consumption in which misclassification was anticipated and consequently repeatability data were collected

a highly robust and versatile finite element boundary integral hybrid code for scattering by bor objects a hybrid technique is presented that combines the finite element and boundary integral methods for simulating electromagnetic scattering from body of revolution bor objects this technique correctly models the boundary conditions along the axis of revolution in both the finite element and boundary integral formulations and yields highly accurate solutions because of the decoupled computations for the finite element and boundary integral equations the technique is highly efficient as compared to the method of moments especially for bors comprising layered or inhomogeneous materials it is applicable to a variety of complex large size bor objects consisting of perfect conductors anisotropic impedance surfaces anisotropic resistive surfaces and anisotropic inhomogeneous materials

application of stable fem fdtd hybrid to scattering problems a recently developed stable finite element method fem finite difference time domain fdtd hybrid that eliminates the staircase approximation of complex geometries is tested by convergence studies for radar cross sections for a conducting sphere 1 db accuracy in all directions is obtained with nine cells per wavelength whereas the nasa almond requires a higher resolution of about 15 cells per wavelength for scatterers with a smooth boundary the results converge quadratically with the mesh size but for a horizontally polarized wave incident on the nasa almond the order of convergence is lower because of singular fields at the tip

an iteration free domain decomposition method for the fast finite element analysis of electromagnetic problems an iteration free finite element domain decomposition method ddm is proposed for the simulation of 3 d electromagnetic problems the finite element tearing and interconnecting feti with robin type transmission condition is introduced to construct a domain decomposition framework based on hierarchical mathcal h matrix algorithm the numerical green s function of each subdomain can be represented by a data sparse matrix form subsequently the original 3 d problem is reduced to a 2 d problem on the skeleton derived from the finite element discretization of pseudo differential operator the skeleton matrix can also be efficiently approximated with an mathcal h matrix by assembling all the numerical green s functions of subdomains based on mathcal h lu factorization algorithm the computational complexity and memory requirement for the direct solution of the skeleton equation can be reduced to be logarithmic linear the resulting direct feti d feti method completely depends on direct method without any iterative process hence it does not suffer from the issue of convergence rate and avoids redundant computations for multiple right hand side problems numerical examples demonstrate the effectiveness of the proposed method

integral equation analysis of radiating structures of revolution a methods for solving radiation problems involving structures of revolution is presented that is based on the direct solutions of one dimensional integral equations for the currents the kernels of these equations are derived explicitly and their singularities are studied efficient methods for their computation are presented the numerical solution is obtained by a method of moments technique using sinusoidal basis functions applications include the determination of the current densities reflection coefficient and far field patterns for several waveguide fed structures numerical checks and comparisons with experiment demonstrate the accuracy of the method

a highly effective preconditioner for solving the finite element boundary integral matrix equation of 3 d scattering a highly effective preconditioner is presented for solving the system of equations obtained from the application of the hybrid finite element boundary integral fe bi method to three dimensional 3 d electromagnetic scattering problems different from widely used algebraic preconditioners the proposed one is based on a physical approximation and is constructed from the finite element method fem using an absorbing boundary condition abc on the truncation boundary it is shown that the large eigenvalues of the finite element fe abc system are similar to those of the fe bi system hence the preconditioned system has a spectrum distribution clustered around 1 in the complex plane consequently when a krylov subspace based method is employed to solve the preconditioned system the convergence can be greatly accelerated numerical results show that the proposed preconditioner can improve the convergence of an iterative solution by approximately two orders of magnitude for large problems

full wave analysis and optimization of a tara like shield assisted paraboloidal reflector antenna using a nystrom type method using the recently developed method based on the rigorous theory of singular and hypersingular integral equations ies and nystrom type discretization a paraboloidal reflector assisted with a conical shield is investigated to decrease the computation time we propose a new method of calculation of the modal green s functions in the quasi optical range the far and near fields of the studied reflector are analyzed in the transmission and reception cases and reveal fine features that escape asymptotic analysis elementary numerical optimization of the shield assisted paraboloidal antenna is performed

diffraction of axisymmetric waves in a borehole by bed boundary discontinuities this paper presents the calculation of the diffraction of axisymmetric borehole waves by bed boundary discontinuities the bed boundary is assumed to be horizontal and the inhomogeneities to be axially symmetric in such a geometry an axially symmetric source will produce only axially symmetric waves since the borehole is an open structure the mode spectrum consists of a discrete part as well as a continuum the scattering of a continuum of waves by bed boundaries is difficult to treat the approach used in the past in treating this class of problem has been approximate in nature or highly numerical such as the finite element method we present here a systematic way to approximate the continuum of modes by discrete modes after discretization the scattering problem can be treated simply since the approach is systematic it allows derivation of the solution to any desired degree of accuracy in theory but in practice it is limited by the computational resources available we also show that our appr

connection between type a and e factorizations and construction of satellite algebras recently we introduced a new class of symmetry algebras called satellite algebras which connect with one another wavefunctions belonging to different potentials of a given family and corresponding to different energy eigenvalues here the role of the factorization method in the construction of such algebras is investigated a general procedure for determining an so 2 2 or so 2 1 satellite algebra for all the hamiltonians that admit a type e factorization is proposed such a procedure is based on the known relationship between type a and e factorizations combined with an algebraization similar to that used in the construction of potential algebras it is illustrated with examples of the generalized morse potential the rosen morse potential and the kepler problem in a space of constant negative curvature and in each case the conserved quantity is identified it should be stressed that the method proposed is fairly general since the other factorization types may be considered as limiting cases of type a or e factorizations

analysis of periodic structures via a time domain finite element formulation with a floquet abc an accurate absorbing boundary condition abc is presented for three dimensional time domain finite element fem td analysis of infinitely periodic structures the proposed abc serves to truncate the computational domain in the nonperiodic directions and it is highly effective to absorb both the fundamental and the higher order floquet modes the formulation is applicable both for scattering and radiation analysis validation results are presented that demonstrate the ability of the fem td to obtain highly accurate results over a broad frequency band that includes frequencies where a higher order floquet mode is propagating nonevanescent

a hybrid finite element method for axisymmetric waveguide fed horns a new method for finding radiation patterns and the reflection coefficients associated with an axisymmetric waveguide fed horn is presented the approach is based on a hybrid finite element method fem wherein the electromagnetic fields in the fem region are coupled to the fields outside by two surface integral equations because of the local nature of the fem this formalism allows for the presence of inhomogeneities to be included in the problem domain the matrix equation which results from the application of this method is shown to be complex symmetric comparisons of calculated and measured data for two different horns show good agreement

on the formulation of hybrid finite element and boundary integral methods for 3 d scattering this paper studies in detail a variety of formulations for the hybrid finite element and boundary integral fe bi method for three dimensional 3 d electromagnetic scattering by inhomogeneous objects it is shown that the efficiency and accuracy of the fe bi method depends highly on the formulation and discretization of the boundary integral equation bie used a simple analysis of the matrix condition number identifies the efficiency of the different fe bi formulations and an analysis of weighting functions shows that the traditional fe bi formulations cannot produce accurate solutions a new formulation is then proposed and numerical results show that the resulting solution has a good efficiency and accuracy and is completely immune to the problem of interior resonance finally the multilevel fast multipole algorithm mlfma is employed to significantly reduce the memory requirement and computational complexity of the proposed fe bi method

modeling conformal antennas on metallic prolate spheroid surfaces using a hybrid finite element method in this paper the hybrid finite element boundary integral fe bi method appropriate for modeling conformal antennas on doubly curved surfaces is developed the fe bi method is extended to model doubly curved convex surfaces by means of a specially formulated asymptotic dyadic green s function the fe bi method will then be used to examine the effect of curvature variation on the resonant input impedance of a cavity backed conformal slot antenna and a conformal patch antenna recessed in a perfectly conducting electrically large prolate spheroid surface the prolate spheroid shape provides a canonical representation of a doubly curved mounting surface the numerical results for conformal slot and patch antennas on the prolate spheroid are compared as a function of curvature and orientation

electromagnetic scattering by an inhomogeneous gyroelectric sphere using volume integral equation and orthogonal dini type basis functions the electromagnetic scattering by an inhomogeneous gyroelectric sphere is studied in this work the solution is constructed using the well known electric field volume integral equation efvie the kernel that incorporates the green s function is expanded in spherical vector wave functions and the unknown electric field and electric displacement is expanded in spherical vector wave functions using fully orthogonal dini type basis functions the permittivity tensor of the spherical object supports a continuously varying radial inhomogeneity while its permeability is that of free space this approach allows a fully analytical computation of the unknown matrix coefficients in special cases of homogeneous permittivity tensors the validation of our method is performed by comparisons with published results in the literature new numerical results are given for various continuously varying permittivity tensors

a finite element boundary integral formulation for scattering by three dimensional cavity backed apertures a novel numerical technique is proposed for the electromagnetic characterization of the scattering by a three dimensional cavity backed aperture in an infinite ground plane the technique combines the finite element and boundary integral methods to formulate a system of equations for the solution of the aperture fields and those inside the cavity specifically the finite element method is used to formulate the fields in the cavity region and the boundary integral approach is used in conjunction with the equivalence principle to represent the fields above the ground plane unlike traditional approaches the proposed technique does not require a knowledge of the cavity s green s function and is therefore applicable to arbitrary shape depressions and material fillings furthermore the proposed formulation leads to a system having a partly full and partly sparse as well as symmetric and banded matrix which can be solved efficiently using special algorithms

array decomposition method for the accurate analysis of finite arrays presented in this paper is a fast method to accurately model finite arrays of arbitrary three dimensional elements the proposed technique referred to as the array decomposition method adm exploits the repeating features of finite arrays and the free space green s function to assemble a nonsymmetric block toeplitz matrix system the toeplitz property is used to significantly reduce storage requirements and allows the fast fourier transform fft to be applied in accelerating the matrix vector product operations of the iterative solution process each element of the array is modeled using the finite element boundary integral fe bi technique for rigorous analysis consequently we demonstrate that the complete lu decomposition of the matrix system from a single array element can be used as a highly effective block diagonal preconditioner on the larger array matrix system this rigorous method is compared to the standard fe bi technique for several tapered slot antenna tsa arrays and is demonstrated to generate the same accuracy with a fraction of the storage and solution time

numerical simulation of bor scattering and radiation using a higher order fem numerical simulations of body of revolution geometries for scattering and radiation problems are presented the formulation consists of a finite element boundary integral fe bi method which is based on a finite element method that uses higher order nodal based scalar basis functions for the azimuthal field component and higher order edge based vector basis functions for the transverse field this formulation when combined with a symmetric fe bi hybridization scheme yields a final system of equations that is more accurate than earlier first order formulations numerical examples are given to demonstrate the accuracy and capabilities of the higher order solution

domain decomposition method based on generalized scattering matrix for installed performance of antennas on aircraft we describe the factorization factopo domain decomposition method based on the boundary element method bem and the finite element method fem applied to the analysis of antenna performance on aircraft the benefits of the subdomain method are mainly the ability to deal with collaborative studies involving several companies and the reduction of the computation costs by one or more orders of magnitude especially in the context of parametric studies furthermore this paper proposes global functions defined on fictitious surfaces surrounding radiating elements to deal with the computation of antenna far field patterns in a multidomain mode by masking the complexity of the antenna wires thin surfaces materials feeding network the external domain of the aircraft can be closed so that the combined field integral equation can be used which is better conditioned than the electric field integral equation and converges much faster the accuracy and efficiency of this technique is assessed by directivity computations of vhf monopole antennas mounted on fokker 100 and atr42 scaled mock up domain decomposition results obtained by combining two sets of subdomains are compared with measurements and the feko commercial method of moments code

a single boundary implicit and fft accelerated time domain finite element boundary integral solver a novel time domain finite element boundary integral fe bi solver for analyzing broadband scattering and radiation from free standing electromagnetically large and perfect electrically conducting platforms supporting inhomogeneous and geometrically intricate structures is presented the solver has three distinctive features that render it especially attractive for broadband analysis of installed antennas i the fe and bi solver components are hybridized using a single surface interface ii the hybrid equations are solved by an implicit time marching scheme accelerated by an outer jacobi iterative solver that leverages inner direct fe and iterative bi solvers iii the bi solver component is accelerated by a distributed memory parallel implementation of the time domain adaptive integral method based on the message passing interface the accuracy late time stability and performance of the proposed time domain fe bi solver are demonstrated via its application to various scattering and radiation problems moreover the solver is used to characterize conformally mounted antennas on several platforms including an aircraft

a new dual primal domain decomposition approach for finite element simulation of 3 d large scale electromagnetic problems a novel dual primal non overlapping domain decomposition method ddm for the finite element solution of three dimensional 3d large scale electromagnetic problems is proposed this method reduces the computational complexity from solving the original 3d problem to an equivalent interface problem by utilizing the idea of the dual primal finite element tearing and interconnecting feti dpem method the new method which is referred to as the feti dpem2 combines the dual primal idea with two lagrange multipliers and implements robin type transmission condition at the subdomain interfaces to significantly improve the convergence of the interface solution in the high frequency region similar to the original version a global coarse problem related to the degrees of freedom at the subdomain corner edges is designed to propagate the residual error to the whole computational domain at each iteration which further increases the convergence numerical examples are presented to demonstrate the validity and the capability of this method the results show that the proposed method produces fast solutions to large scale problems in any frequency band

generalized scattering matrix analysis of a class of finite arrays of coupled antennas by using 3 d fem and spherical mode expansion a rigorous method for characterizing in terms of a multimode scattering matrix a finite array of antennas where each antenna can be described by means of spherical waves is presented in this paper the procedure provides the impedance coupling and radiating characteristics of the arrays and comprises two steps first the generalized scattering matrix gsm of each single antenna is numerically calculated over a wide band of frequencies for this purpose we use a previously developed methodology that combines the domain segmentation technique the three dimensional finite element method 3d fem spherical mode expansion and a reduced order model obtained using a symmetric matrix pade spl acute via lanczos sympvl algorithm second the overall gsm of the finite array is calculated starting from the gsm of each antenna and using rotation and translation of spherical waves a closed form expression for the overall gsm is given and different examples are shown in order to validate the proposed method

the singular integral problem in surfaces the calculation of surface current distribution given the geometry and source description is a fundamental problem in antenna theory in extending the harmonic analysis integral equation method from one dimensional to two dimensional problems a new way to deal with the singularity in the source field relation is needed some results are given for surface current integrals which convert them to a convergent form

a novel dual field time domain finite element domain decomposition method for computational electromagnetics a novel dual field time domain finite element domain decomposition method is presented for numerical simulation of electromagnetic phenomena the method divides the computation domain into several non overlapping subdomains and computes both the electric and magnetic fields in each subdomain by solving second order vector wave equations a leapfrog like scheme is employed in the time marching to update the alternating electric and magnetic fields adjacent subdomains are related to each other by the equivalent surface currents on the subdomain interfaces which are also updated in a similar fashion the method requires minimum communications between the subdomains thus is highly suitable for parallel computations the proposed domain decomposition method is particularly attractive for the numerical simulation of finite arrays and large scale electromagnetic problems numerical stability and dispersion error analyses are conducted and several radiation examples are presented to demonstrate the accuracy and efficiency of the method

stability of explicit implicit hybrid time stepping schemes for maxwell s equations an improved version of the stable fem fdtd hybrid method t rylander and a bondeson comput phys commun 125 75 2000 for maxwell s equations is presented the new formulation has a modified time stepping scheme and is rigorously proven to be stable for time steps up to the stability limit for the fdtd the new scheme gives less reflection at the boundary between the structured and unstructured grids than the original formulation the hybrid method is compared to the fdtd with staircasing for scattering from a conducting sphere the discretization errors of the hybrid show quadratic dependence on mesh size while the scaling is less clear for the fdtd the fdtd gives errors that are 5 60 times higher than that of the hybrid depending on resolution and staircasing strategy

modeling radiation with an efficient hybrid finite element integral equation waveguide mode matching technique a method is presented to model electromagnetic radiation combining the finite element technique in the penetrating portion of a three dimensional 3 d radiating structure with an integral equation on the outer surface of the computational domain and with a waveguide mode matching technique on a cross section of the feeding waveguide the antenna can be of general shape provided a portion of the surrounding medium up to a surface of revolution is chosen as part of the computational domain this truncation scheme and the accurate source representation are more general than those existing in the literature for radiation modeling an open ended waveguide and a waveguide with a choke ring are analyzed and their radiation patterns are obtained and compared with available measurements

em field induced in inhomogeneous dielectric spheres by external sources the electromagnetic field induced in the interior of inhomogeneous dielectric bodies by external sources can be evaluated by solving the well known electric field integrodifferential equation efide for spheres with constant magnetic permeability but variable dielectric constant a direct mainly analytical solution can be used even in case when the inhomogeneity in renders separation of variables inapplicable this approach constitutes a generalization of the hybrid analytical numerical scalar method developed by the authors in two recent papers for the corresponding acoustic scalar field induced in spheres with variable density and or compressibility this extension by no means trivial owing to the vector and integrodifferential nature of the equation is based on field vector expansions using the set of three harmonic surface vectors orthogonal and complete over the surface of the sphere for their angular dependence and dini s expansions of a general type for their radial functions the use of the latter has been shown to be superior to other possible sets of orthogonal expansions and as far as its convergence is concerned it may further be improved by properly choosing a crucial parameter in their eigenvalue equation the restriction to the spherical shape is imposed here to allow use of the well known expansion of green s dyadic in spherical eigenvectors of the vector wave equation

a dual field domain decomposition method for the time domain finite element analysis of large finite arrays a novel dual field time domain finite element domain decomposition method is presented for an efficient and broadband numerical simulation of electromagnetic properties of large finite arrays instead of treating the entire array as a single computation domain the method considers each array element as a smaller subdomain and computes both the electric and magnetic fields inside each subdomain adjacent subdomains are related to each other by the equivalent surface currents on the subdomain interfaces in an explicit manner furthermore the method exploits the identical geometry of the array elements and further reduces the memory requirement and cpu time the proposed method is highly efficient for the simulation of large finite arrays numerical stability and computational performance of the method are discussed several radiation examples are presented to demonstrate the accuracy and efficiency of the method

time domain finite element methods various time domain finite element methods for the simulation of transient electromagnetic wave phenomena are discussed detailed descriptions of test trial spaces explicit and implicit formulations nodal and edge facet element basis functions are given along with the numerical stability properties of the different methods the advantages and disadvantages of mass lumping are examined finally the various formulations are compared on the basis of their numerical dispersion performance

mam a multipurpose admittance matrix for antenna design via the finite element method further exploitation of matrix valued transfer functions describing electromagnetic phenomena is proposed in addition to traditional modal port inclusion in finite element analysis new computational domain ports are allowed as field expansion in terms of piecewise basis functions is considered an admittance type matrix arises and as a result a multiport network manages all electromagnetic complexity circuit handling of this network efficiently outperforms full wave analyses for different modifications of the actual structure thus making it possible to use this methodology for design purposes a model order reduction process is also used for fast frequency sweeping and special emphasis is placed on its accuracy finally numerical examples demonstrate the robustness capability and versatility of the proposed technique

finite element method for unbounded field problems and application to two dimensional taper treatment of the finite element method for an unbounded field problem was proposed by mcdonald and wexler in 1972 their method is superior to others because it can exclude the singularities of green s functions this paper explains the treatment of the method in our 1979 letter which had some revisions of mcdonald and wexler s and calculated the time harmonic field problems examples presented are electromagnetic fields of two dimensional tapers which are open ended electromagnetic waves propagate in the taper and radiate from the taper to free space in this case the exact solutions for radiation from tapers are not available because of the complicated shape and so the finite element method is useful in solving these problems electromagnetic fields of tapers involving dielectric slabs are also calculated as examples of inhomogeneous problems

electric and magnetic losses modeled by a stable hybrid with explicit implicit time stepping for maxwell s equations a stable hybridization of the finite element method fem and the finite difference time domain fdtd scheme for maxwell s equations with electric and magnetic losses is presented for two dimensional problems the hybrid method combines the flexibility of the fem with the efficiency of the fdtd scheme and it is based directly on ampere s and faraday s law the electric and magnetic losses can be treated implicitly by the fem on an unstructured mesh which allows for local mesh refinement in order to resolve rapid variations in the material parameters and or the electromagnetic field it is also feasible to handle larger homogeneous regions with losses by the explicit fdtd scheme connected to an implicitly time stepped and lossy fem region the hybrid method shows second order convergence for smooth scatterers the bistatic radar cross section rcs for a circular metal cylinder with a lossy coating converges to the analytical solution and an accuracy of 2 is achieved for about 20 points per wavelength the monostatic rcs for an airfoil that features sharp corners yields a lower order of convergence and it is found to agree well with what can be expected for singular fields at the sharp corners a careful convergence study with resolutions from 20 to 140 points per wavelength provides accurate extrapolated results for this non trivial test case which makes it possible to use as a reference problem for scattering codes that model both electric and magnetic losses

fast simulation of triaxial borehole induction measurements acquired in axially symmetrical and transversely isotropic media we introduce and successfully test an efficient method to simulate triaxial borehole electromagnetic em induction measurements acquired in axially symmetrical and transversely isotropic ti media the method uses a fourier series expansion to express the azimuthal dependence of em fields and the source term whereby the essentially 3d problem collapses to a series of independent 2d problems each 2d problem is solved with a semianalytic method that uses normalized bessel functions and normalized hankel functions to express the radial dependence of em fields thereby improving numerical stability in addition use is made of amplitude and slope basis functions to describe the longitudinal dependence of em fields to avoid grid refinement in the vicinity of horizontal formation boundaries for validation we compare the new simulation method to two 1d analytic methods in horizontally and radially layered formations and to one 3d finite difference method 3dfd in multilayered formations that include borehole and invasion zones numerical results indicate that the method is accurate in formations with high conductivity contrasts compared to 1d methods and is more than ten times more efficient than the 3dfd method in multilayer formations

on the development of a higher order pml a higher order perfectly matched layer pml is proposed based on stretched coordinates to effectively attenuate both propagating and evanescent waves the new pml has multiple poles in contrast to the regular pml with a single pole the implementation is also derived and results are shown to be better than those of the regular pml and the recently proposed complex frequency shifted cfs pml with an insignificant increase in the computational cost

fem bem formulation for the analysis of cavity backed patch antennas on chiral substrates an extended variational formulation to study cavity backed microstrip patch antennas with chiral materials is presented a finite element boundary integral numerical approach is applied to satisfy the stationary condition associated with the variational formulation and some features of chiral media for patch antenna applications are investigated specifically an appreciable reduction of the antenna dimensions with respect to the isotropic case and an undesirable increase in the cross polarization levels are observed

a vector dual primal finite element tearing and interconnecting method for solving 3 d large scale electromagnetic problems a lagrange multiplier based non overlapping domain decomposition method referred to as the dual primal finite element tearing and interconnecting feti dp is formulated for the finite element simulation of large three dimensional 3 d electromagnetic problems this formulation extends the feti dp for solving the scalar helmholtz equation to the solution of the vector curl curl wave equation using edge based finite elements it enforces the field continuity explicitly along the edges shared by more than two subdomains and implicitly at the interfaces between two subdomains through the use of lagrange multipliers with the aid of a direct sparse solver for each subdomain system the large global problem is reduced to a much smaller interface problem from which a neumann boundary condition is obtained at the interfaces between all the subdomains this neumann boundary condition is then used to calculate the field within each subdomain it is shown that the resulting feti dpem method is scalable with respect to the size of finite elements and the number of subdomains it is also scalable with respect to the size of the subdomains when the subdomains with its surfaces enclosed by perfect magnetic conductors cannot support any resonant modes the feti dpem method is applied to the electromagnetic simulation of array type structures where the geometrical redundancy is fully exploited to speedup the simulation and reduce the memory requirement numerical results for the simulation of finite antenna arrays and photonic bandgap devices are presented to demonstrate the application accuracy efficiency and capability of the feti dpem method

phased array antenna analysis with the hybrid finite element method a new analysis technique for infinite phased array antennas was developed and demonstrated it consists of the finite element method fem in combination with integral equation radiation conditions and a novel periodic boundary condition for 3 d fem grids accurate modeling of rectangular circular and circular coaxial feeds is accomplished by enforcing continuity between the fem solution and several waveguide modes across an aperture in the array s ground plane the radiation condition above the array is enforced by a periodic integral equation in the form of a floquet mode summation thus reducing the solution to that of a single array unit cell the periodic boundary condition at unit cell side walls is enforced through a matrix transformation that mathematically folds opposing side walls onto each other with a phase shift appropriate to the array lattice and scan angle the unit cell electric field is expanded in vector finite elements galerkin s method is used to cast the problem as a matrix equation which is solved by the conjugate gradient method a general purpose computer code was developed and validated for cases of open ended waveguides microstrip patches clad monopoles and printed flared notches showing that the analysis method is accurate and versatile

a linear nonconforming finite element method for maxwell s equations in two dimensions part i frequency domain we suggest a linear nonconforming triangular element for maxwell s equations and test it in the context of the vector helmholtz equation the element uses discontinuous normal fields and tangential fields with continuity at the midpoint of the element sides an approximation related to the crouzeix raviart element for stokes the element is stabilized using the jump of the tangential fields giving us a free parameter to decide we give dispersion relations for different stability parameters and give some numerical examples where the results converge quadratically with the mesh size for problems with smooth boundaries the proposed element is free from spurious solutions and for cavity eigenvalue problems the eigenfrequencies that correspond to well resolved eigenmodes are reproduced with the correct multiplicity

two dimensional induction log modeling using a coupled mode multiple reflection series method in induction logging both vertical and radial conductivity variations exist in the logged medium elementary separation of variables cannot be applied directly to the partial differential equation describing the electromagnetic field in such a medium a modal expansion method of solution can be designed using modes defined with respect to the vertical coordinate this method breaks the original two dimensional 2 d problem into a set of independent one dimensional 1 d problems the receiver signal is decomposed into a direct signal traveling within the borehole and a reflection signal bearing information about the conductivity distribution outside the borehole the solution is obtained as a coupled mode multiple reflection series accounting for repeated mode reflections at the vertical boundaries in the medium each term in the series represents the next higher order reflection in a sequence of multiple reflections results show two terms are sufficient to reach accuracy acceptable for log modeling

an unconditionally stable subcell model for arbitrarily oriented thin wires in the fetd method a computational subcell model for thin wires is developed for electromagnetic simulations the maxwell equations are discretized by a finite element approximation on a tetrahedral grid the wires are described by a second order equation for the current the geometry of the wires can be chosen independent of the volume grid a symmetric coupling between field and wires yields a stable semi discrete field wire system and an unconditionally stable fully discrete field wire system the system of equations is in each time step solved by a preconditioned conjugate gradient method the accuracy of the subcell model is demonstrated for dipole and loop antennas with comparisons with the method of moments and experimental data

a parallel finite element tearing and interconnecting algorithm for solution of the vector wave equation with pml absorbing medium a domain decomposition method based on the finite element tearing and interconnecting feti algorithm is presented for the solution of the large sparse matrices associated with the finite element method fem solution of the vector wave equation the feti algorithm is based on the method of lagrange multipliers and leads to a reduced order system which is solved using the biconjugate gradient method bicgm it is shown that this method is highly scalable and is more efficient on parallel platforms when solving large matrices than traditional iterative methods such as a preconditioned conjugate gradient algorithm this is especially true when a perfectly matched layer pml absorbing medium is used to terminate the problem domain

remarks on the equivalence between the shape invariance condition and the factorisation condition it is shown that the shape invariance condition for supersymmetric potentials and the factorisation condition for sturm liouville eigenvalue problems are equivalent the roots of this self consistency condition in supersymmetric quantum mechanics and the factorisation method are found in the theory of riccati equations

calculating expected mortality the widely used person years method of calculating expected mortality has been discussed recently by several authors in studies where mortality is either lower or higher than the standard mortality of some reference population the use of exposure to death as an estimator of the expected number of deaths will generally lead to bias always exaggerating the difference between study and standard mortality this bias is examined in a proportional hazards model the recent suggestion by hartz et al of calculating the mortalities of individuals during their potential follow up time is claimed to be only rarely feasible in practice excerpt

using test retest reliability data to improve estimates of relative risk an application of latent class analysis the paper discusses the problem of interval estimation for the relative risk when some test retest data are available on random subsamples drawn from case control studies it is shown that although the upper portion of the interval may be very wide indeed the lower bound of the interval estimate may be improved considerably by the collection of even modest amounts of repeat measurements

rigorous analysis of three dimensional structures incorporating dielectrics the paper presents the sr3d software 3d radiating structures which calculates the electromagnetic characteristics of arbitrarily shaped structures incorporating dielectric material the rigorous analysis method is based on the integral equation formulation the authors included a variational approach using the reaction concept of rumsey the problem is numerically solved with a surface finite elements method a guided mode excitation has been introduced in order to compute the reflection coefficient at the transmit port and the transmission coefficient between the different parts fed by guided modes this software is validated by excellent agreement between simulated and measured radioelectric performances patterns and swr

analysis of exponential time differencing for fdtd in lossy dielectrics we determine the stability condition and analyze the accuracy of the exponential and centered time differencing schemes for finite difference time domain fdtd in an isotropic homogeneous lossy dielectric with electric and magnetic conductivities spl sigma and spl sigma respectively we show that these schemes are equivalent and determine that for accuracy both schemes must be used with a time step that finely resolves the electric and magnetic conduction current relaxation time scales the implications of these results for perfectly matched layer pml type absorbing boundary conditions are discussed

on the variational formulation of hybrid finite element boundary integral techniques for electromagnetic analysis this paper addresses the time harmonic electromagnetic analysis of a three dimensional inhomogeneous radiator scatterer in free space such analysis can be carried out by combining the finite element method fem with the method of moments mom which yields finite element boundary integral fe bi formulations a general framework is presented within which stationary fe bi formulations can be established variational boundary value problems which relate to equivalent underlying variational principles stationary functionals the formulations are shown to be accurate robust and computationally efficient they avoid the problem of interior resonances without resorting to the combined field integral equation and they result in symmetric system matrices which preserve reciprocity explicitly thus the stationary fe bi framework combines the fem and mom on the continuous level as opposed to the usual approach of hybridization after discretization which generally leads to asymmetric matrices the stationary fe bi framework allows one to solve either for the electric and magnetic fields on the volume of the problem domain or for one volume and one exterior surface field quantity with only marginal differences in computational cost the volume surface formulations have the same storage requirements as previous fe bi formulations and can be more efficiently solved the volume volume formulations provide simultaneous solutions of the electric and magnetic fields which could for instance be used to construct error estimators directly based on maxwell s equations

a novel hybridization of higher order finite element and boundary integral methods for electromagnetic scattering and radiation problems a novel hybridization of the finite element fe and boundary integral methods is presented for an efficient and accurate numerical analysis of electromagnetic scattering and radiation problems the proposed method derives an adaptive numerical absorbing boundary condition abc for the finite element solution based on boundary integral equations unlike the standard finite element boundary integral approach the proposed method is free of interior resonance and produces a purely sparse system matrix which can be solved very efficiently unlike the traditional finite element absorbing boundary condition approach the proposed method uses an arbitrarily shaped truncation boundary placed very close to the scatterer radiator to minimize the computational domain and more importantly the method produces a solution that converges to the true solution of the problem to demonstrate its great potential the proposed method is implemented using higher order curvilinear vector elements a mixed functional is designed to yield both electric and magnetic fields on an integration surface without numerical differentiation to be used in the calculation of the adaptive abc the required evaluation of boundary integrals is carried out using the multilevel fast multipole algorithm which greatly reduces both the memory requirement and cpu time the finite element equations are solved efficiently using the multifrontal algorithm a mathematical analysis is conducted to study the convergence of the method finally a number of numerical examples are given to illustrate its accuracy and efficiency

finite element analysis of complex axisymmetric radiating structures a finite element method fem is developed for the analysis of complex axisymmetric radiating structures the method is based on the electric field formulation with the transverse field expanded in terms of edge based vector basis functions and the azimuth component expanded using nodal based scalar basis functions this mixed representation of the electric field eliminates spurious solutions and permits an easy treatment of boundary conditions on conducting surfaces as well as across material interfaces the fem mesh is truncated using a previously developed cylindrical perfectly matched layer pml the method has been successfully applied to three radiating structures a corrugated horn antenna a spherical luneburg lens and a half maxwell fish eye numerical results are presented to show the validity accuracy and efficiency of the method

a domain decomposition method with nonconformal meshes for finite periodic and semi periodic structures we present a domain decomposition method as a preconditioner for krylov type solvers to model complex electromagnetic problems containing periodicities the method reduces memory requirements by decomposing the original problem into several nonoverlapping sub domains the 1st order transmission condition is employed on interfaces between adjacent sub domains to enforce continuity of electromagnetic fields and to ensure the sub domain problems are well posed by following the spirit of duality paring a symmetric system is obtained to reduce the computational burdens of the present method the finite element tearing and interconnecting like algorithm is adopted this algorithm results in the computation of the so called numerical green s function which can be compressed efficiently via a rank revealing matrix factorization algorithm the final system matrix is solved by krylov solvers instead of classical stationary solvers to improve the convergence of iterative solvers several robust implementation details are discussed and the choice of some popular krylov subspace solvers is studied through numerical examples

main reflector shaping of omnidirectional dual reflectors using local conic sections this work presents an alternative method for go synthesis of dual reflector antennas suited for omnidirectional coverage both reflectors are bodies of revolution where a single conic section generates the sub reflector while a concatenation of local conic sections represent the main reflector generatrix which is shaped to provide an arbitrary radiation pattern in the antenna s elevation plane to illustrate the method omnidirectional axis displaced ellipse oade configurations are synthesized to provide a cosecant squared radiation pattern in the elevation plane two different ray structures are considered with real or virtual main reflector caustics the go shaping results are validated by method of moments simulations

efficient computation of electromagnetic waves in anisotropic orthogonal plano cylindrically layered media using the improved numerical mode matching nmm method an orthogonal plano cylindrically layered opcl medium consists of materials stratified planarly and layered concentrically in the orthogonal directions the numerical mode matching nmm method has previously been shown to be a fast and robust semianalytical solver to investigate the propagation of electromagnetic em waves in such a complex but isotropic or transversely isotropic medium in this paper several important improvements have been made to extend applications of this efficient solver to the anisotropic ocpl medium the formulas for anisotropic media with three different diagonal elements in the cylindrical coordinate system are deduced to expand its application the perfectly matched layer pml is incorporated along the radial direction as an absorbing boundary condition abc to make the nmm method more accurate and efficient for unbounded low conductivity media and applicable to lossless media we manipulate the weak form of maxwell s equations and impose the correct boundary conditions at the cylindrical axis to solve the singularity problem finally we also offer formulas for computing em fields excited by a magnetic dipole located at any position with an arbitrary orientation numerical results have demonstrated the efficiency and accuracy of this method

a novel efficient algorithm for scattering from a complex bor using mixed finite elements and cylindrical pml an efficient finite element method fem is developed to compute scattering from a complex body of revolution bor the bor is composed of a perfect conductor and impedance surfaces and arbitrary inhomogeneous materials the method uses edge based vector basis functions to expand the transverse field components and node based scalar basis functions to expand the angular component the use of vector basis functions eliminates the problem of spurious solutions suffered by other three component fem formulations the fem mesh is truncated with a perfectly matched layer pml in cylindrical coordinates the use of pml in cylindrical coordinates avoids the wasted computation which results from a spherical mesh boundary with an elongated scatterer the fem equations are solved by ordering the unknowns with a reverse cuthill mckee algorithm and applying a banded matrix solution algorithm the method is capable of handling large realistic radar targets and good agreement with measured results is achieved for benchmark targets

hybridizing semianalytical and conventional finite element schemes for simulations of electromagnetic borehole resistivity measurement abstracta semianalytical finite element method fem has been developed to simulate electromagnetic borehole resistivity measurements in a layered underground formation a piecewise homogeneous structure is divided into several layers each layer is uniform in the longitudinal direction and the distributions of geometry and material can be arbitrary on the transverse plane or cross section of the layer to develop this semianalytical finite element scheme the standard functional corresponding to the vector wave equation is cast to a new form in the hamiltonian system based on dual variables that are the transverse components of electric and magnetic fields on the cross section of the layer the 2d finite elements are used to discretize the cross section and a high precision integration scheme based on the riccati equations is used to exploit the longitudinal homogeneity in the layer by transforming a 3d layered problem into a series of 2d problems this semianalytical fem can save a great amount of

scattering and radiation analysis of three dimensional cavity arrays via a hybrid finite element method a hybrid numerical technique is presented for a characterization of the scattering and radiation properties of three dimensional cavity arrays recessed in a ground plane the technique combines the finite element and boundary integral methods and invokes floquet s representation to formulate a system of equations for the fields at the apertures and those inside the cavities the system is solved via the conjugate gradient method in conjunction with the fast fourier transform thus achieving an o n storage requirement by virtue of the finite element method the proposed technique is applicable to periodic arrays comprised of cavities having arbitrary shape and filled with inhomogeneous dielectrics several numerical results are presented along with new measured data which demonstrate the validity efficiency and capability of the technique

finite element analysis of complex antennas and arrays various technical issues are addressed in the frequency and time domain finite element analysis of complex antennas and arrays that may consist of fine structures and composite materials the paper starts with the finite element formulation of a generic antenna problem formulation for the modeling of general electrically and magnetically dispersive lossy and anisotropic materials in the time domain finite element analysis is presented for the first time this is followed by discussion of three typical techniques for truncation of the finite element computational domain via the use of absorbing boundary conditions perfectly matched layers and boundary integral equations it then describes the modeling of antenna feeds using a current probe including an improved model a voltage gap and a waveguide port boundary condition after that numerical approaches to modeling infinite phased arrays large finite arrays and antenna platform interaction are presented including two novel domain decomposition algorithms in both the frequency and time domains numerical examples are given to demonstrate the capability and application of the finite element analysis of a variety of complex antennas and arrays

novel and stable formulations for the response of horizontal coil eccentric antennas in a cylindrically multilayered medium in this paper we present a set of novel and stable formulations to calculate the response of logging tools with horizontal coil antennas in an eccentric borehole straddling cylindrically multilayered formations it can be applied in fast forward computation and the inverse problem for electromagnetic em well logging in deviated and horizontal wells where eccentric scenarios are often encountered our formulations are different from previous ones in following aspects first the tool mandrel can be cylindrically multilayered and the electrical parameters of each layer are arbitrary namely it is not limited to being perfectly metallic second the em propagation in inhomogeneous medium is considered by the generalized reflection and transmission method in place of the transfer matrices the associated generalized reflection and transmission coefficients are expressed by the ratios of bessel or hankel functions that obviate the notorious overflow problem for numerical computation finally a set of linear matrix functions are constructed to solve for the em waves in a borehole based on the concept of the generalized reflection rather than that of the fictitious boundary numerical results in comparison with those from other approaches have demonstrated the validity and stability of our new formulations