Search

A robust and accurate iterative algorithm is proposed for the solution of electromagnetic wave scattering from 1-D layered rough surfaces. The forward–backward method (FBM) has been applied extensively for solving electromagnetic scattering from single-layer rough surfaces due to its rapid convergence rate. Nevertheless, the performance of the FBM deteriorates, as it is applied to layered random rough surface problems. The proposed method greatly improves the convergence rate of the FBM by applying a residual minimization step. The computational cost of the minimization step and the forward–backward sweeps is expedited by using the spectral acceleration. In this communication, the proposed algorithm is applied as a solution to the problem of electromagnetic wave scattering from layered rough surfaces. Numerical results are presented to demonstrate the better convergence properties of the proposed method as compared with the standard FBM. In addition, the proposed method is shown to be more robust than the FBM, especially as the distance between interfaces decreases. The computational complexity of the proposed algorithm is also presented and discussed.

An efficient and accurate iterative method is proposed for computing electromagnetic (EM) scattering from 1-D dielectric rough surfaces. The communication improves the convergence of forward backward method, applying it to the problem of 2D wave scattering from random lossy rough surfaces using a coupled surface integral equation formulation. A matrix splitting technique is introduced to reduce the number of matrix-vector multiplications required by the correction step and Spectral Acceleration (SA) is applied to reduce the computational complexity of each matrix-vector product from O(N2) to O(N). The proposed method is called the improved forward backward method with spectral acceleration (IFBM-SA). The numerical analysis demonstrates that IFBM-SA has a higher convergence rate than FBM-SA and a recent technique which is used as a reference method. Moreover, IFBM-SA is more robust than the reference method and has smaller storage requirements meaning that it can readily scale to larger problems. In addition an eigenvalue based analysis is provided illustrating how the improvement step works.

This communication presents an improved forward backward technique for the solution of electromagnetic wave scattering problems. The forward backward method displays rapid convergence when the eigenvalues of the associated iteration matrix are small. Conversely when the eigenvalues are large it displays poorer convergence. The hybridized method presented in this communication helps to circumvent the poor convergence of the forward backward method in the latter case by introducing an optimally sized correction in the approximate direction of the eigenvector associated with the iteration matrix's dominant eigenvalue. Numerical results are presented in order to demonstrate the convergence of the improved forward backward method.

The paper describes a reduced forward operator for solving electromagnetic scattering problems using a volume integral equation in conjunction with a conjugate gradient fast Fourier transform scheme. The reduction is obtained by decoupling of the interaction between the locations in the spatial computational domain at which there is non-zero contrast and those positions at which there is zero contrast. The decoupling is achieved by multiplication of the kernel by a diagonal matrix whose entries reflect the presence or absence of contrast at the associated point. Analysis supported by numerical experiments shows that the conjugate gradient algorithm applied to the reduced system converges more rapidly than when it is applied to the original system.

A novel technique is proposed to greatly enhance the convergence property of stationary iterative solvers applied for the solution of scattering from two-dimensional random rough surfaces. The proposed method extends the standard improvement step to enable the use of multiple correction vectors, leading to a significantly improved convergence rate of stationary iterative methods with negligible increases in computational complexity. Spectral acceleration technique is also applied to reduce a computational burden and storage requirements. Numerical results are shown to demonstrate the advantages of the proposed technique.

A new iterative technique is proposed for the computation of electromagnetic scattering from randomly rough lossy surfaces. The proposed method is an extension of the improved forward backward method (IFBM), introduced by Brennan et al. The improvement step of the IFBM is modified for the use of multiple correction vectors instead of a single correction vector in the original technique. Spectral acceleration (SA) is applied in combination with a matrix splitting technique for a reduction of computational complexity from O(N2) to O(N). Numerical experiments are presented to compare to those techniques proposed in recent studies to demonstrate the efficiency of the proposed method. The modified improvement step significantly enhances the convergence rate of the forward backward method with negligible increases in storage requirements and computational complexity.

A hybridised asymptotic waveform evaluation (AWE) technique is presented for the efficient solution of EM scattering problems over a wide frequency band. The technique involves extracting high-frequency phase information from the surface current to generate a residual problem. This residual problem is solved over the frequency band using a low-order expansion AWE. The phase information can then be reinserted to get estimates for the surface current at all frequencies along the band. Numerical results are presented showing the application of the techniques presented to several scattering problems.

As a step towards the realization of wireless nanosensor networks in agricultural monitoring applications, a theoretical path-loss model is proposed. This model can predict the average attenuation of THz radiation in a channel composed of air and plant leaves, given the composition of air as well as attributes of leaves such as their permitivity. In addition, a Monte Carlo-based log-distance path-loss model in the vicinity of a plant is proposed, which takes the shadow fading nature of such a channel into account. The latter model, which is based on the transmission distance, can approximate variations of THz path-loss from its mean value. Through simulation results, it is shown that the proposed log-distance/Monte Carlo- based model is in good agreement with the theoretical model.

The availability of fast numerical methods has rendered the integral-equation approach suitable for practical application to radio planning and site optimization for UHF mobile radio systems. In this paper, we describe a conceptually simple scheme for the efficient computation of UHF radial propagation loss over irregular terrain, which is based on the fast far-field approximation. The method is substantially faster than conventional integral-equation (IE) solution techniques. The technique is improved by incorporating the Green's function perturbation method and we outline a way in which the formulation can be made more exact. Computational issues such as terrain profile truncation and the effect of small-scale roughness are addressed. The method has been applied to gently undulating terrain and compared to published experimental results in the 900-MHz band. It has also been successfully applied to more hilly terrain and to surfaces with buildings added.

A novel accelerated algorithm is proposed, which suggests a solution for arbitrarily shaped, three-dimensional (3D) perfecly conducting scattering objects. The method is an innovative combination of a stationary iterative solver, the Forward-Backward Method (FBM), and a renowned accelerated scheme, the Multilevel Fast Multipole Algorithm (MLFMA). The accuracy and computational efficiency is then carefully investigated in a comparison with conventional methods to demonstrate the advantages of the proposed technique.

The Improved Forward Backward Method and Symmetric Successive over Relaxation (SSOR) method are proposed to compute electromagnetic (EM) scattering from 1-D dielectric rough surfaces. In addition the Spectral Acceleration (SA) technique is applied to reduce the computational complexity of each matrix-vector product from O(N 2 ) to O(N). The proposed methods are referred as IFBM-SA and SSOR-SA. They are compared with the FBM-SA which is a well-known and effective method in computing the scattering from randomly rough lossy surfaces in terms of convergence rate and run time. FBM-SA is shown to be a special case of SSOR-SA where the relaxation parameter is unity. The numerical analysis demonstrates that IFBM-SA has a higher convergence rate than the SSOR-SA and FBM-SA.

This paper presents an efficient and precise iterative method for computing the electromagnetic (EM) wave scattering from dielectric rough surfaces described by exponential correlation functions. The proposed method is based on improving the convergence rate of the Forward Backward Method (FBM) [1]. Moreover, a matrix splitting technique is introduced to reduce the number of matrix-vector multiplications required by the correction step and Spectral Acceleration (SA) [2], [3] is applied to reduce the computational complexity of each matrix-vector product from O(N2) to O(N). The proposed method is called the Improved Forward Backward Method with Spectral Acceleration (IFBM-SA) and is compared to FBM-SA in terms of convergence rate and the run time required to achieve a desired relative error norm. The numerical analysis demonstrates that IFBM-SA has a much higher convergence rate than FBM-SA. Therefore, IFBM-SA can be efficiently used to compute the electromagnetic scattering from randomly rough surfaces.

In this paper an efficient method is proposed for computing electromagnetic wave propagation over terrain profiles. The paper extends the Tabulated Interaction Method (TIM) [1], applying it to the problem of 2D wave scattering from lossy surfaces using a coupled surface integral equation formulation. The proposed method is compared with the recently proposed Chacracteristic Basis Function Method (CBFM) [2], [3] with which it shares several features. The numerical analysis demonstrates that TIM has a dramatically lower computational complexity and storage than CBFM.

This communication is concerned with the development of a model-order reduction (MOR) approach for the acceleration of a source-sweep analysis using the volume electric field integral equation (EFIE) formulation. In particular, we address the prohibitive computational burden associated with the repeated solution of the two-dimensional electromagnetic wave scattering problem for source-sweep analysis. The method described within is a variant of the Krylov subspace approach to MOR, that captures at an early stage of the iteration the essential features of the original system. As such these approaches are capable of creating very accurate low-order models. Numerical examples are provided that demonstrate the speed-up achieved by utilizing these MOR approaches when compared against a method of moments (MoM) solution accelerated by use of the fast Fourier transform (FFT).

This paper extends the method developed in [1] to the problem of 2D wave scattering from lossy dielectric randomly rough surfaces using a coupled surface integral equation formulation. Moreover, a similar implementation to BMIA/CAG [2] is used to split the impedance matrix into a sparse strong interaction matrix and a dense weak interaction matrix. Taylor series expansions and FFTs are applied to compute matrix vector products involving the weak interaction matrix. By doing this the complexity of the optimisation step is reduced from order of O(N2) to order of O(N logN).

Approximations are introduced into a magnetic field integral equation (MFIE) formulation of a two-dimensional (2-D) terrain scattering problem, which allow most of the integrals inherent in the MFIE to be performed analytically. The implementation of the method is discussed and an example is given comparing its performance against a reference solution and measured data. The new formulation applies to both TM/sup z/ and TE/sup z/ polarizations and is an improvement over the electric field integral equation (EFIE) formulation of the tabulated interaction method (TIM) in that far-field patterns can be calculated analytically leading to increased flexibility of the method.

This paper presents an improved buffered block forward backward (BBFB) technique for the solution of 3D wave scattering problems. The BBFB method displays rapid convergence when the eigenvalues of the associated iteration matrix are small. Conversely when the eigenvalues are large it displays poorer convergence. The optimised step presented in this paper helps to circumvent the poor convergence of the forward backward method in the latter case by introducing an optimally sized correction in the approximate direction of the eigenvector associated with the iteration matrix's dominant eigenvalue. Numerical results are presented in order to demonstrate the convergence of the improved BBFB method.

This paper presents a model order reduction algorithm for the surface electric field integral equation (EFIE) formulation of the electromagnetic wave scattering problem. The method allows fast and accurate frequency sweep calculations of electromagnetic wave scattering from a perfectly conducting (PEC) three-dimensional object. We apply the well-conditioned asymptotic waveform evaluation (WCAWE) method to circumvent the computational complexity associated with the numerical solution of such formulations. Practical implementation issues are addressed with numerical examples given to illustrate the accuracy and robustness of the proposed methods.

The buffered block forward backward method is described and applied to the problem of scattering from dielectric cylinders. Numerical results suggest that the method converges in the case of scattering from bodies closed at infinity while it produces divergent results in the case of scattering from closed bodies.

In this paper the convergence properties of the buffered block forward Backward (BBFB) method are investigated and shown to be independent of source position. The BBFB method is applied to the electric field integral equation (EFIE) for the case of a three-dimensional flat plate and wedge scatterer, at varying source locations. The convergence of the solution for the two problems, at each source location, is obtained and the corresponding iteration matrices for each scatterer computed. The numerical data provided in this paper illustrates and supports the conclusion that the source position does not affect the ability of the BBFB method to converge. Rather the convergence of the method is based on the geometry of the problem itself and the specific application of the BBFB algorithm to the problem.

A method for speeding up integral calculations occurring in iterative solutions of electromagnetic wave scattering problems is described. Present methods suffer from having to perform time consuming integral calculations at many points. The method involves enumerating the full integral only at certain points and approximating the integral at neighbouring points by making localised phase and amplitude adjustments to the calculated integrals. This is shown to speed up the process tremendously. An example of scattered field calculation over the terrain is given and compared with a regular forward scattering approach.

This study presents a model order reduction algorithm for the volume integral equation formulation of electromagnetic wave scattering. The authors apply the Arnoldi algorithm to circumvent the computational complexity associated with the repeated solution of the forward electromagnetic scattering problem for varying material parameters. The authors discuss practical implementation issues regarding procedures for the implementation and termination of the Arnoldi iteration. An approximate extension of the Arnoldi algorithm to the problem of wave scattering from an inhomogeneous body is introduced and implemented. This approximation is shown to be exact in the limit as the level of reduction approaches zero. Numerical examples are presented which demonstrate the accuracy and efficiency of their approximate extension.

The implementation of a multilevel algorithm for the accurate method-of-moments (MoM) solution of the electric-field integral-equation (EFIE) formulation of electromagnetic-wave scattering by arbitrarily shaped objects is described. The technique makes use of the fast far-field algorithm. The Rao–Wilton–Glisson basis set is employed to represent the surface current induced on the scatterer. Numerical results are presented to demonstrate the accuracy which can be achieved with the technique. Despite the use of the far-field approximation, the method presented is a general one and, because of its simplicity, possesses advantages over currently available accelerated numerical iterative solvers for the EFIE.