The quasi-linear Maxwell equations describing electromagnetic wave propagation in nonlinear media permit several weak solutions, which may be discontinuous (shock waves). It is often conjectured that the solutions are unique if they satisfy an additional entropy condition. The entropy condition states that the energy contained in the electromagnetic fields is irreversibly dissipated to other energy forms, which are not described by the Maxwell equations. We use the method employed by Krûzkov to scalar conservation laws to analyze the implications of this additional condition in the electromagnetic case, i.e., systems of equations in three dimensions. It is shown that if a cubic term can be ignored, the solutions are unique and depend continuously on given data.
A rigorous solution in L2 to the EFIE for 2-D screens is developed and proposed as a reference solution for testing the convergence rate and scattering amplitude error of any MoM algorithm in L2. The proposed reference solution permits to choose judiciously an appropriate mesh density for a MoM algorithm instead of using the ten-points-rule in all cases. Additionally, using the reference solution it is demonstrated that the discrepancy should not be used as a performance value of the scattering amplitude error while solving the EFIE with the MoM in L2. Both the E- and H-cases are considered.
A ring source of arbitrary current backed by a perfectly conducting sphere is analyzed through Green's function formulation. The infinite double sum of the Green's function is written in terms of a single series by performing a transformation of the coordinate system. The resulting form is used for the numerical evaluation of the scattering integral. The operation of the coupled loop-sphere structure is understood via the discussion of several numerical results.
Astudy is presented of the light wave propagation in a new type of dielectric optical waveguide with hyperbolic kind of crosssection. Further, the waveguide is assumed to have a conducting helical winding. The analysis essentially requires the use of elliptical coordinate system, which finally results into Mathieu and modified Mathieu functions as the representatives of the electromagnetic fields within the lightguide. Field components in the different sections of the guide are deduced, and the characteristic dispersion equation for the system is derived. The preliminary investigation on such type of waveguide throws the idea that the presence of helix pitch angle (which serves the purpose of additional controlling parameter for the guide) in the dispersion relation would greatly affect the propagation characteristics of the guide, and this can be of great practical importance.
An algorithm focusing on the occlusions between rays and NURBS surfaces is presented in this paper,where simple geometrical principle which makes the algorithm adequate in possible cases is used. When the ray starts from or ends on the surface,the self-shadowing is also taken into account. The algorithm given can be applied to optical methods like PO GTD or UTD in electromagnetic calculation where shadowing is of key problem and especially when the NURBS modeling is introduced.
High frequency field expressions are derived around feed point of a two dimensional cassegrain system using the Maslov's method. Maslov's method is a systematic procedure for predicting the field in the caustic region combining the simplicity of ray theory and generality of the transform method. Numerical computations are made for the analysis of field pattern around the caustic of a cassegrain system.
In this paper, wide band transmitting and receiving antennas; each composed of a bowtie partially covered by an open conducting box; are proposed for ground-penetrating-radar (GPR) system. The inner walls of the conducting box are covered by a lossy coating which is composed of a number of layers with a conductivity profile designed to achieve better characteristics of the bowtie antenna. The Finite-Difference Time-Domain (FDTD) method is applied to simulate the radiating and receiving antennas, the buried target and the wave propagation in the lossy ground soil over the frequency band of operation. The performance of the proposed system is examined as regards the antenna characteristics and the buried target detectability. The impedance and voltage standing wave ratio (VSWR) of the partially covered bowtie antenna are presented over a wide frequency range. The capability of the proposed GPR system to detect targets buried in a ground soil is examined by investigating the change of the coupling between the transmitting and receiving antennas due to the presence of a buried target. The effect of the ground soil on the antenna characteristics is studied for some common types of real soils when the GPR system is placed at different heights above the ground surface.
In this paper, the bistatic polarimetric signature of a perfectly conducting faceted octahedron with high dimensions with respect to the wavelength, is considered and a closed form solution for its fast computation is developed. This particular object, composed by eight triangularly shaped trihedral corner reflectors, should exhibit a large bistatic and monostatic Radar Cross Section (RCS) over a wide angular range. Scattering from a Trihedral Corner Reflector (TCR) is dominated by single, double and triple reflections. First, shadowed areas in excitation and observation are evaluated with the help of Geometrical Optics (GO). A Physical Optics (PO) integration is performed on each plate for the computation of scattered fields, taking into account the shadowed surfaces. GO is used to take into account the lighting of each face for initial reflections of double and triple reflections. First-order diffractions, which are based on the fringe current expressions for the exterior edges of the TCR are also included in the analysis with the help of Method of Equivalent Currents / Incremental Length Diffraction Coefficients (MEC/ILDC). This permit us to calculate fast the bistatic signature of a TCR for arbitrary incidence and observation angles. The polarimetric bistatic signature of an octahedral reflector is then obtained, and results are discussed. Finally, several prospects are explained
Abstract-In this paper, ray propagation in stratified semi-infinite percolation lattices consisting of a succession of uniform density layers is considered. Two different mathematical approaches for analytically evaluating the penetration depth are presented. In order to compare performances and to assess the range of validity of the two approaches, an exhaustive set of numerical Monte-Carlo-like experiments is presented.
In this paper, a miniaturized printed dipole antenna with the V-shaped ground is proposed for radio frequency identification (RFID) readers operating at the frequency of 2.45 GHz. The principles of the microstrip balun and the printed dipole are analyzed and design considerations are formulated. Through extending and shaping the ground to reduce the coupling between the balun and the dipole, the antenna's impedance bandwidth is broadened and the antenna's radiation pattern is improved. The 3D finite difference time domain (FDTD) Electromagnetic simulations are carried out to evaluate the antenna's performance. The effects of the extending angle and the position of the ground are investigated to obtain the optimized parameters. The antenna was fabricated and measured in a microwave anechoic chamber. The results show that the proposed antenna achieves a broader impedance bandwidth, a higher forward radiation gain and a stronger suppression to backward radiation compared with the one without such a ground.
This article deals with an approach to the design of planar antennas that use metamaterial-loaded substrates based on the effective medium approximations. Metamaterials are structured composite materials with unique electromagnetic properties due to the interaction of electromagnetic waves with the finer scale periodicity of conventional materials. They may be used to modify the effective electromagnetic parameters of planar antenna substrates and to design antennas with the improved coupling to the feed, increased impedance matching bandwidths, miniaturized dimensions, and narrower beamwidths compared to those that use conventional dielectric materials for the same purposes. The electromagnetic analysis and optimization based on the effective medium approximations of metamaterials is very convenient since it deals with only a few bulk medium parameters instead of a large number of parameters describing a discrete structure. At the same time, the most common way of obtaining these effective medium parameters is transmission/reflection simulations or measurements in free space or in a homogeneous background medium. For a host medium which is not homogeneous, as for a grounded substrate, the effective medium parameters are different from the free space ones. The scattering losses in a metamaterial medium need to be accurately taken into account and included as parameters in full-wave bulk medium models. For this reason, in the effective medium approach for antenna substrates, one needs to use the appropriate effective medium approximations that take the coupling between inclusions into account and also to evaluate the effects of the scattering losses. In practice, this is done by finding the effective medium parameters inside an arbitrary substrate medium, and not in a homogeneous host medium or in free space. This paper presents the methodology and the results of FDTD analysis of planar antennas that have substrates with various metamaterial inclusion densities. The effective bulk medium approach presented in the article is analyzed by comparing the antenna return losses and radiation patterns to the ones computed for a discrete structure. The Green's function of the host medium (antenna substrate) is used to calculate the approximate bulk effective medium parameters of the MTM-loaded substrate.
In this paper, signal descriptions and formulations for the radio frequency (RF) front-end of a passive backscatter radio frequency identification (RFID) reader working at ultra high frequencies (UHF) are discussed in detail, and a set of design considerations aiming to improve the read range are outlined. The reader's architecture is proposed and the design details of its RF frond-end are presented. The read range is formulated through calculating the time-averaging power absorbed by the tag and the signal-noise-ratio (SNR) of the demodulation, and accordingly RFID systems can be classified into tag-determining and reader-determining ones. It is concluded that the gain of the reader antenna, the phase noise of the local oscillation (LO) and the receive-transmit isolation coefficient dominate the demodulation output noise of the reader, and consequently the readerdetermining maximum operational distance. A prototype reader working at the frequency of 915MHz was built with off-the-shelf components and was evaluated with a commercial tag in an indoor environment. The measured results show that this RFID system is of tag-determining and has a read range of 8.4 meters, which are in good agreement with the calculated results.
A new method is introduced to analyze arbitrary nonuniform transmission lines.In this method, the equations of nonuniform transmission lines are converted to the equations of uniform transmission lines, which have been excited by distributed equivalent sources.Then, the voltage and current distributions are obtained using an iterative method.The validity of the method is verified using a comprehensive example.
Using fractional curl operator, impedance of the surface which may be regarded as intermediate step between the perfect electromagnetic conductor (PEMC) and dual to the perfect electromagnetic conductor (DPEMC) has been determined. The results are compared with the situation which is intermediate step ofp erfect electric conductor (PEC) and perfect magnetic conductor (PMC).
The metamaterial slab with low refractive index exhibits directive properties which make it suitable to work as antenna. The characteristics of such a device are affected under the presence of a conducting rod of arbitrary shape placed over the slab. A qualitative and quantitative approach is presented which is possible by implementing the method of auxiliary sources. For the evaluation of the far field quantities the method of stationary phase is employed. A validation example considering a circular rod is solved rigorously with use of the method of moments. Several numerical results are shown and discussed.
Aim of this paper is to present an efficient scheme of domain decomposition to study, in the time domain, multiple scattering by separated obstacles and sources with any composition and geometry, in an homogeneous media. A method of decomposition into disjointed sub-domains is proposed, resting onto an homogeneous and adaptable approximation of coupling terms and leading to a natural parallelized and hybrid numerical schema. It permits to significantly lower the cumulative error of dissipation and/or dispersion introduced by classical scheme. It also leads to a suitable answer for a wide class of problems involving large scattering scenes limiting for classical time domain methods. Numerical examples are given to illustrate it.
This paper presents a combined Entropy Decomposition and Support Vector Machine (EDSVM) technique for Synthetic Aperture Radar (SAR) image classification with the application on rice monitoring. The objective of this paper is to assess the use of multi-temporal data for the supervised classification of rice planting area based on different schedules. Since adequate priori information is needed for this supervised classification, ground truth measurements of rice fields were conducted at Sungai Burung, Selangor, Malaysia for an entire season from the early vegetative stage of the plants to the ripening stage. The theoretical results of Radiative Transfer Theory based on the ground truth parameters are used to define training sets of the different rice planting schedules in the feature space of Entropy Decomposition. The Support Vector Machine is then applied to the feature space to perform the image classification. The effectiveness of this algorithm is demonstrated using multi-temporal RADARSAT-1 data. The results are also used for comparison with the results based on information of training sets from the image using Maximum Likelihood technique, Entropy Decomposition technique and Support Vector Machine technique. The proposed method of EDSVM has shown to be useful in retrieving polarimetric information for each class and it gives a good separation between classes. It not only gives significant results on the classification, but also extends the application of Entropy Decomposition to cover multi-temporal data. Furthermore, the proposed method offers the ability to analyze single-polarized, multi-temporal data with the advantage of the unique features from the combined method of Entropy Decomposition and Support Vector Machine which previously only applicable to multipolarized data. Classification based on theoretical modeling is also one of the key components in this proposed method where the results from the theoretical models can be applied as the input of the proposed method in order to define the training sets.
An alternative sub-domain formulation is presented, in two variants, for the analysis of thin-wire circular loops via moment methods. Curved piecewise sinusoids are used as basis functions, while both point matching and reaction matching (Galerkin's method) are examined as testing schemes. The present study is primarily focused on frill-driven loops, but some of the essential similarities and differences between them and gap-driven ones are also discussed in brief. Numerical results are presented to verify the two variants of the proposed formulation and demonstrate their capabilities for analyzing small and large loops. Special attention is drawn to the behavior of the solutions as the number of basis/testing functions grows. Finally, a complexity analysis is attempted and the potential savings in execution times that may be attained by taking advantage of certain features of the proposed numerical schemes are discussed.