The Experts below are selected from a list of 297 Experts worldwide ranked by ideXlab platform
Conor Brennan - One of the best experts on this subject based on the ideXlab platform.
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VTC Spring - Incorporation of Backscattering Into FAFFA Analysis of UHF Wave Propagation Over Irregular Terrain
2007 IEEE 65th Vehicular Technology Conference - VTC2007-Spring, 2007Co-Authors: Conor BrennanAbstract:An efficient fast Far-Field Approximation based algorithm for computing the electric Fields propagating over irregular terrain in two dimensions is described. Symmetric successive over-relaxation, or forward-backward, is used to compute the surface current in an efficient manner. The results suggest that under the magnetic Field integral equation formulation the backscattered Field is negligible and strongly support the use of the forward scattering assumption.
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Application of the fast Far-Field Approximation to the computation of UHF pathloss over irregular terrain
IEEE Transactions on Antennas and Propagation, 1998Co-Authors: Conor Brennan, P.j. CullenAbstract: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.
P.j. Cullen - One of the best experts on this subject based on the ideXlab platform.
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Application of the fast Far-Field Approximation to the computation of UHF pathloss over irregular terrain
IEEE Transactions on Antennas and Propagation, 1998Co-Authors: Conor Brennan, P.j. CullenAbstract: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.
Weng Cho Chew - One of the best experts on this subject based on the ideXlab platform.
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A Groundwave Propagation Model Using a Fast Far-Field Approximation
IEEE Antennas and Wireless Propagation Letters, 2017Co-Authors: Gokhan Apaydin, Levent Sevgi, Weng Cho ChewAbstract:A fast Far-Field Approximation (FAFFA), which is simple to use, is applied to groundwave propagation modeling from a nonpenetrable surface with both soft and hard boundaries. The results are validated against available reference models as well as compared to other numerical methods such as split step parabolic equation model and the method of moments.
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Fast Far‐Field Approximation for calculating the RCS of large objects
Microwave and Optical Technology Letters, 1995Co-Authors: Weng Cho ChewAbstract:A fast Far-Field Approximation (FAFFA) is developed to estimate the RCS of conducting scatterers. This method accounts for the interaction between subscatterers in two ways, depending on the electrical distance between the subscatterers. The interactions of subscatterers separated by a large electrical distance are computed in three stages: (1) aggregation, which computes the total Field at a group center due to the subscatterers of the group; (2) translation, which translates the Field from one group center to another; and (3) disaggregation, which distributes the Field in a group center to each subscatterer in the group. Two strategies are employed to accelerate the computation in the above three stages. One is the use of Far-Field Approximation to simplify the computation in the translation stage; the other is the use of interpolation and smoothing techniques, which reduces the complexity of aggregation and disaggregation. The overall computational complexity for a matrix-vector multiplication is of the order of N1.33, and the memory requirement is of order N. Numerical results show that this method can predict a RCS that is very close to exact solution, and that the method can be applied to objects with very large electrical sizes. © 1995 John Wiley & Sons. Inc.
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fast Far Field Approximation for calculating the rcs of large objects
Microwave and Optical Technology Letters, 1995Co-Authors: Weng Cho ChewAbstract:A fast Far-Field Approximation (FAFFA) is developed to estimate the RCS of conducting scatterers. This method accounts for the interaction between subscatterers in two ways, depending on the electrical distance between the subscatterers. The interactions of subscatterers separated by a large electrical distance are computed in three stages: (1) aggregation, which computes the total Field at a group center due to the subscatterers of the group; (2) translation, which translates the Field from one group center to another; and (3) disaggregation, which distributes the Field in a group center to each subscatterer in the group. Two strategies are employed to accelerate the computation in the above three stages. One is the use of Far-Field Approximation to simplify the computation in the translation stage; the other is the use of interpolation and smoothing techniques, which reduces the complexity of aggregation and disaggregation. The overall computational complexity for a matrix-vector multiplication is of the order of N1.33, and the memory requirement is of order N. Numerical results show that this method can predict a RCS that is very close to exact solution, and that the method can be applied to objects with very large electrical sizes. © 1995 John Wiley & Sons. Inc.
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Fast Far Field Approximation for calculating the RCS of large objects
IEEE Antennas and Propagation Society International Symposium. 1995 Digest, 1Co-Authors: Cai-cheng Liu, Weng Cho ChewAbstract:Provides an RCS estimation technique called the fast Far Field Approximation (FAFFA). The idea of the method is to compute the interactions between elements using different methods depending on the electrical distance between the elements. When the distance is small, the exact interaction is calculated; When the distance is large, the Far Field Approximation is used. The Field interactions are calculated iteratively using the conjugate gradient (CG) method. The iteration process takes into account the higher order terms in GO, PO or PTD Approximations. The algorithm has a computational complexity of O(N/sup 1.33/) and memory requirement of O(N) for N unknown problems. The authors first present the formulation using a two dimensional electrical Field integral equation (EFIE) for the TM wave incident case. Then they give numerical simulations for both two dimensional and three dimensional targets.
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The application of Far-Field Approximation to accelerate the fast multipole method
IEEE Antennas and Propagation Society International Symposium. 1996 Digest, 1Co-Authors: Jiming Song, Weng Cho Chew, Eric MichielssenAbstract:The fast multipole method (FMM) is an efficient method in the iterative solution of the matrix equation that is associated with the integral equation of wave scattering. The key idea of the FMM is to divide the interactions between groups of scatterers into near-Field interactions and non-near-Field interactions, and perform the non-near-Field interactions efficiently with the aid of the multipole expansion of the Fields. The Far-Field Approximation is introduced in FMM to calculate the wave interactions between groups that are separated by a very large distance. The advantage of this approach is that it automatically switches back to the original FMM for small problems. Under the Far-Field Approximation, the translation operator is much simpler than that used in the FMM. Numerical results show speed up of the modified FMM over the original FMM for problems as small as several thousands.
Michael I. Mishchenko - One of the best experts on this subject based on the ideXlab platform.
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Electromagnetic scattering by a fixed finite object embedded in an absorbing medium
Optics express, 2007Co-Authors: Michael I. MishchenkoAbstract:This paper presents a general and systematic analysis of the problem of electromagnetic scattering by an arbitrary finite fixed object embedded in an absorbing, homogeneous, isotropic, and unbounded medium. The volume integral equation is used to derive generalized formulas of the Far-Field Approximation. The latter serve to introduce direct optical observables such as the phase and extinction matrices. The differences between the generalized equations and their counterparts describing electromagnetic scattering by an object embedded in a non-absorbing medium are discussed.
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Far-Field Approximation in electromagnetic scattering
Journal of Quantitative Spectroscopy & Radiative Transfer, 2005Co-Authors: Michael I. MishchenkoAbstract:The volume integral equation formalism is used to derive and analyze specific criteria of applicability of the Far-Field Approximation in electromagnetic scattering by a finite three-dimensional object. In the case of wavelength-sized and larger objects, this analysis leads to a natural subdivision of the entire external space into a near-Field zone, a transition zone, and a Far-Field zone. It is demonstrated that the general criteria of Far-Field scattering are consistent with the theory and practice of T-matrix computations.
Bernhard Roth - One of the best experts on this subject based on the ideXlab platform.
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Detection, numerical simulation and approximate inversion of optoacoustic signals generated in multi-layered PVA hydrogel based tissue phantoms.
Photoacoustics, 2016Co-Authors: Elias Blumenröther, O. Melchert, M. Wollweber, Bernhard RothAbstract:Abstract Optoacoustic (OA) measurements can not only be used for imaging purposes but as a more general tool to “sense” physical characteristics of biological tissue, such as geometric features and intrinsic optical properties. In order to pave the way for a systematic model-guided analysis of complex objects we devised numerical simulations in accordance with the experimental measurements. We validate our computational approach with experimental results observed for layered polyvinyl alcohol hydrogel samples, using melanin as the absorbing agent. Experimentally, we characterize the acoustic signal observed by a piezoelectric detector in the acoustic Far-Field in backward mode and we discuss the implication of acoustic diffraction on our measurements. We further attempt an inversion of an OA signal in the Far-Field Approximation.
