An advanced numerical model in solving thin-wire integral equations by using semi-orthogonal compactly supported spline wavelets

In this paper, shielding effectiveness (SE) of a perforated enclosure with imperfectly conducting walls is evaluated. To this end, first, an accurate numerical technique based on method of Moments (MoM) is presented. In this method, lossy metallic walls of the enclosure are replaced by equivalent electric surface current sources. Then, the impedance boundary condition on the imperfectly conducting surfaces is applied and an electric field integral equation is extracted. At the end, the integral equation is solved numerically by Galerkin method. In addition to the mentioned numerical method, an extremely fast analytical technique based on transmission line model(TLM) is proposed which is able to predict the SE with high level of accuracy over a large frequency bandwidth just in a few seconds. For validation of both methods, other commercial softwares (FEKO and CST) are employed and several enclosures with different conductivities are studied. Lossy MoM method shows accurate results for conductivities down to 10S/m, while efficient TLM method proves its accuracy for conductivities down to 250S/m.

The use of a dyadic layered-medium Green's function as the kernel in a method of moments (MoM) modeling problem greatly reduces the complexity of modeling a stratified medium. Compared to the free-space Green's function, there is an additional cost of having to compute a semi-infinite Sommerfeld integral for each call to calculate the dyadic layered-medium Green's function. This letter discusses a method to tabulate and interpolate the Green's function as a method of reducing the impedance matrix filling time. This method can be used in conjunction with existing methods for increasing the computational speed of the Green's functions.

Theory and experiment of a spherical probe-fed conformal antenna with a parasitic element mounted on a spherical multilayer structure are presented in this paper. Rigorous mathematical Method of Moments (MoMs) for analyzing various radiating spherical structures is presented in this paper by using Dyadic Green's Functions (DGFs) in conjunction with Mixed Potential Integral Equation (MPIE) formulation. Linear Rao-Wilton-Glisson (RWG) triangular basis functions are applied in MPIE formulation. Current distributions on coaxial probe and conformal radiating elements are computed by using spatial domain Dyadic Green's Function (DGF) and its asymptotic approximation. A prototype of such an antenna is fabricated and tested. The effect of the parasitic element on the input impedance and radiation patterns of the antenna is investigated. It is shown that the antenna characteristics are improved significantly with the presence of the conducting parasitic element. Good agreement is achieved between the results obtained from the proposed methods and the measurement results.

The incomplete Hankel functions (IHFs) are employed to evaluate the scattered field from thin truncated cylinders excited by uniform plane waves or by arbitrarily oriented elemental current sources. Metallic and dielectric lossy structures are modeled by means of impedance boundary conditions (IBCs) including surface curvature effects. The scattering currents, expanded in triangular basis functions, are determined upon solving electrical field integral equations (EFIEs) by means of the point-matching method of moments (MoM). The scattered field is then expressed in closed analytical form in terms of IHFs, thus yielding highly accurate numerical results. Furthermore, accurate IHFs approximants are also derived to reduce the computational burden in the analysis of large electrical structures. The proposed approach is demonstrated in practical applications involving cylindrical dielectric structures used in planar lenses, lossy dielectric cylinders suitable to model cane-like vegetation, as well as polarization rotators featuring multiple stages composed of thin metallic wire arrays.

The analysis of transient scattering for TMz (horizontally) polarization from a cylindrical perfectly conducting (PEC) object buried in a lossy medium is considered. The possible paths travelled by the reflected waves and the multiple reflections are identified by using timing analysis. The dielectric half-space is considered to be flat. The surface equivalence principle and a decomposition method are utilized to form a set of electric field integral equations (EFIEs) for the currents on the object and the portion of the surface most strongly interacting with the object. To obtain the scattered electric field, the EFIEs are solved in the frequency domain using the Method of Moments (MoM). Then, inverse Fourier transform is utilized to get the time domain signals. The short-pulse scattering results are used to investigate the effects of multipath.

Numerical computations of electromagnetic radiation and scattering problems for arbitrarily shaped and electrically large objects in the same environment are preferably performed by combining the method of moments (MoM) with the uniform geometrical theory of diffraction (UTD). Composite metallic/dielectric objects with arbitrary shape are handled efficiently with the finite element boundary integral (FEBI) method. For large scale problems, the MoM solution is accelerated by the multilevel level fast multipole method (MLFMM). On the other hand, electrically large objects with relatively simple shape are treated sufficiently with ray-based high-frequency methods, like geometrical optics (GO) and UTD. However, until now MoM-UTD hybrid approaches have been restricted to conventional MoM formulations with only the electric field integral equation (EFIE), resulting in limited modeling capabilities. The same restrictions also exist in the hybrid FEBI-UTD method. The paper presents MLFMM-UTD hybridization for the combined field integral equation (CFIE), in order to extend further the applicability of the FEBI-UTD method. The resulting modeling technique is referred to as the FEBI-MLFMM-UTD method. The MLFMM-UTD hybridization is performed in the translation procedure on the various MLFMM levels, by taking into account additional contributions received at the testing groups due to UTD objects. Due to different ray directions for outgoing and incoming waves, appropriate interpolation and anterpolation procedures must be applied to consider the UTD contributions.

The method of moments (MOM) is applied to the problem of electromagnetic scattering from general three‐dimensional dielectric targets in an arbitrary multilayered environment. The dyadic multilayered Green's function is computed via the method of complex images, and the Galerkin MOM solution is effected by employing triangular patch basis functions. Several example frequency and time domain results are presented, with application to radar‐based sensing of plastic land mines.

In this paper, radiation patterns of a thin circular conducting loop embedded in a two-layered spherical chiral medium but illuminated by a plane wave are obtained. The method of moments is employed in this work to formulate the current distribution along the circular loop enclosed by the spherical chiral radome shell. The dyadic Green's functions defining electromagnetic fields due to sources in both the outer and inner regions are applied. In the Galerkin's procedure for the method of moments, basis functions used in the work are sine and cosine functions which form a Fourier series. The formulation itself here is quite compact, straightforward, and easy-to-use. Effects of various geometrical and dielectric parameters of the chiral radome shell are discussed. As expected, the role of the spherical chiral radome is again realized as a polarization transformer. Associated with these parameters, waves and fields in such an electromagnetic system are characterized. It should pointed that there existed some ...

A parallelized version of multilevel Characteristic Basis Function method (ML-CBFM) is applied in this paper to the problem of electromagnetic scattering in the VHF and UHF bands from trees in large forest areas that are modeled as three dimensional, finite-length, dielectric cylinders. The use of this method enables us to achieve a significant reduction in terms of computing time and memory consumption, as compared to the conventional Method of Moments (MoM), and this, in turn, enables us to handle very large forest areas, well beyond the reach of conventional MoM. Furthermore, we take advantage of the fact that the ML-CBFM algorithm is naturally parallelizable, which provides us an added advantage over the conventional MoM. The ML-CBFM results are shown to be in good agreement with those obtained via the conventional MoM, which confirms the fact that the proposed method is not only computationally efficient, but is accurate as well.

Electromagnetic (EM) problems with conducting objects can be described by electric field integral equation (EFIE). The EFIE has a well-known low-frequency-breakdown (LFB) problem due to the serious imbalance between the vector potential and scalar potential at low frequencies. The problem was overcome by using loop-tree and loop-star basis functions in the method of moments (MoM) solution, but it is inconvenient to implement in complicated structures. Later on, one proposed an augmentation method to remodel the equations based on the traditional Rao-Wilton-Glisson (RWG) basis function in the MoM. In this paper, we propose a novel augmentation method to remedy the LFB issue based on the Nyström method. The Nyström has some unique merits compared with the MoM and using it can greatly simplify the augmentation process. A numerical example is provided to demonstrate the proposed approach and its robustness can be verified.

This work investigates numerically two different methods of moments applied to Hermite derived probability distribution model and variations of Weibull distribution fitted to the short-term time series peaks sample of stochastic response parameters of a simplified jack-up platform model which represents a source of high non-Gaussian responses. The main focus of the work is to compare the results of short-term extreme response statistics obtained by the so-called linear method of moments (L-moments) and the conventional method of moments using either Hermite or Weibull models as the distribution model for the peaks. A simplified mass-spring system representing a three-legged jack-up platform is initially employed in order to observe directly impacts of the linear method of moments (L-moments) in extreme analysis results. Afterward, the stochastic response of the three-legged jack-up platform is analyzed by means of 3D finite element model. Bias and statistical uncertainty in the estimated extreme statistics parameters are computed considering as the “theoretical” estimates those evaluated by fitting a Gumbel to a sample of episodical extreme values obtained from distinct short-term realizations (or simulations). Results show that the variability of the extreme results, as a function of the simulation length, determined by the linear method of moments (L-moments) is smaller than their corresponding ones derived from the conventional method of moments and the biases are more or less the same.

The electromagnetic radiation and scattering from a body of revolution (BOR) of arbitrary shape have been widely discussed during several decades. The objects can contain perfect electric conductor (PEC), homogeneous dielectric bodies, coated conducting bodies and combined dielectric and conducting bodies [1][2]. The traditional method used to solve BOR with integral equations is the Method of Moments (MoM). And the computational time consumed in solving the integral equation of the BOR problem depends on the evaluation of modal Green's function (MGF), which is a time consuming process. Some research has been done to reduce this computational complexity. For example, Abdelmageed used spherical Bessel function to expansion to evaluate the MGF [3]. In this work, we extend the fast inhomogeneous plane wave algorithm (FIPWA) [4][5] to accelerate the computation of the MoM for composite homogeneous dielectric and conducting bodies of revolution. PMCHW [6] (Poggio-Miller-Chang-Harrington-Wu) equations and electric field integral equation are used for solving the homogeneous dielectric and conducting objects, respectively. Both the memory requirement and CPU time are reduced for large-scale BOR problems. Numerical results are given to demonstrate the validity and efficiency of the FIPWA.

The discretization in Method of Moments (MoM) of the Electric-Field Integral Equation (EFIE) is traditionally carried out with divergence-conforming sets of basis functions, like the RWG set. This enforces the normal continuity of the current across the edges arising from the discretization and makes the quasi-singular Kernel contributions numerically manageable. However, these MoM-implementations of the EFIE show little flexibility when handling nonconformal meshes, normally arising from from the juxtaposition or interconnection of independent meshes in the modular design of composite objects. A nonconforming discretization of the EFIE is possible if the testing procedure is carried out over volumetric elements attached to the surface triangulation, inside the body. In this paper, we present a new nonconforming discretization of the EFIE, where wedges attached to the source triangles are used as testing volumetric elements.

A new numerical solution method is summarized for the problem of electromagnetic scattering from a cylindrical object of arbitrary cross-section buried in a lossy dielectric half-space that is considered to be flat. The surface equivalence principle and a decomposition method are employed to form a set of electric field integral equations (EFIEs) for the currents on the object and the portion of the surface most strongly interacting with the object. The Method of Moment (MoM) is used to solve the EFIEs in the frequency domain to obtain the scattered electric field.

A solution to electromagnetic scattering from a cylindrical object of arbitrary cross-section buried in a lossy-grounded dielectric medium with flat interfaces based on surface equivalence principle and a decomposition technique is developed. A set of electric field integral equations (EFIEs) for the currents on the object and the portion of the surfaces most strongly interacting with the object are obtained, and then the method of moment is used to solve these EFIEs in the frequency domain to obtain the scattered electric field.