The use of the FFT for the efficient solution of the problem ofelectromagnetic scattering by a body of revolution

The enhancement of the computational efficiency of the body of revolution scattering problem is discussed with a view of making it practical for solving large body problems. The problem of the electromagnetic scattering by a perfectly conducting body is considered, although the methods provided can be extended to multilayered dielectric bodies as well. Typically, the generation of the elements of the moment method matrix consumes a major portion of the computational time. It is shown how this time can be significantly reduced by manipulating the expression for the matrix elements in a manner that allows one to compute them efficiently by using the fast Fourier transform (FFT). A technique for extracting the singularity of the Green's function that appears within the integrands of the matrix diagonal is also presented, further enhancing the usefulness of the FFT. It is shown that, with the use of the method discussed here, the computational time can be improved by at least an order of magnitude for large bodies in comparison to that for previous algorithms     

A parallel finite-element tearing and interconnecting algorithm forsolution 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     

An Efficient Application of the Discrete Complex Image Method for Quasi-3-D Microwave Circuits in Layered Media

An efficient means of evaluating reactions arising from the mixed-potential integral equation for layered media for quasi-3D microwave circuits is presented. Analytical formulations for the z-integration in the spectral domain are derived, thus avoiding expensive 2D evaluation and interpolation of the layered Green's function. In this paper, closed-form formulations for the resultant Sommerfeld integrals are evaluated via the robust two-step discrete complex image method. The overall computational time can consequently be greatly reduced when analyzing quasi-3D circuits in layered media using the proposed method.     

On the long-time behavior of unsplit perfectly matched layers

This paper shows how to eliminate an undesirable long-time linear growth of the electromagnetic field in a class of unsplit perfectly matched layers (PML) typically used as absorbing boundary conditions in computational electromagnetics codes. For the new PML equations, we give energy arguments that show the fields in the layer are bounded by a time-independent constant, hence they are long-time stable. Numerical experiments confirm the elimination of the linear growth, and the long-time boundedness of the fields.     

On the performance of tubular surface coils in nuclear magneticresonance imaging and spectroscopy

Surface coils are important devices in the clinical application of nuclear magnetic resonance imaging and spectroscopy (NMRIS) because they have higher signal-to-noise ratios than body or head coils in superficial regions. This paper describes our theoretical and experimental study of the performances of tubular surface coils, aiding the effective application of such coils to NMRIS. We present formulas for the RF magnetic (H₁) fields produced by tabular surface coils placed over layered media, and for the self- and loaded-impedances of these coils. The calculated results show the dependence of the coil performances on the coil design parameters and the characteristics of the sample under test. We include the calculated results for the H₁ field phase shifts in conductive samples     

Finite-difference time-domain analysis of microwave circuit deviceson high performance vector/parallel computers

In this paper, an efficient finite-difference time-domain algorithm for high performance distributed memory vector/parallel computers is presented. The algorithm is developed in a manner which requires only one interprocessor communication per time step. Illustrated examples based on the analysis of microwave circuit devices are presented demonstrating the efficiency and scalability of the finite-difference time-domain algorithm     

Finite-difference, time-domain analysis of lossy transmission lines

An active and efficient method of including frequency-dependent conductor losses into the time-domain solution of the multiconductor transmission line equations is presented. It is shown that the usual A+B√s representation of these frequency-dependent losses is not valid for some practical geometries. The reason for this the representation of the internal inductance the at lower frequencies. A computationally efficient method for improving this representation in the finite-difference time-domain (FDTD) solution method is given and is verified using the conventional time-domain to frequency-domain (TDFD) solution technique     

Time-domain analysis of periodic structures at oblique incidence:orthogonal and nonorthogonal FDTD implementations

A novel implementation of periodic boundary conditions incorporated into the finite-difference time-domain (FDTD) technique in both orthogonal and nonorthogonal grids is presented in this paper. The method applied is a field-splitting approach to the discretization of the Floquet-transformed Maxwell equations. As a result, the computational burden is reduced and the stability criterion is relaxed. The results of the two methods are compared to experimental data     

Study of mixed-order basis functions for the locally corrected Nystro/spl uml/m method

A high-order locally corrected Nystro/spl uml/m (LCN) method employing the mixed-order basis functions proposed by C$80al/spl iota/s$80kan and Peterson is presented for the electromagnetic scattering by targets composed of both dielectric and conducting bodies. An integral operator based on a combined field formulation for conducting surfaces and a Mu/spl uml/ller formulation for dielectric surfaces is used. It is found that for general scattering objects, mixed-order basis functions accelerate the convergence of the LCN solution, can eliminate spurious charges, and can significantly reduce the condition number of the impedance matrix.