This paper studies the left-handed behavior in conventional 2-port coupled line networks. The propagation parameters of 12 periodic structures, each has a different coupled line configuration, have been derived and the left-handed bands have been determined. Two structures were fabricated and measured to confirm the composite right/left handed (CRLH) characteristics. Measurements and EM simulations were in a very good agreement with the developed theory. In the light of the proposed theory, a geometrical circuit model was also proposed for split ring resonator (SRR). The model is capable to predict its performance over a wide band.
I present an algorithm to simulate low-frequency electromagnetic propagation in an anisotropic earth, described by a general (non-diagonal) conductivity tensor. I solve the electric formulation by explicitly imposing an approximate form of the condition ∇·J = 0, where J is the current density vector, which includes the source and the induced current. The numerical algorithm consists of a fully spectral explicit scheme for solving linear, periodic parabolic equations. It is based on a Chebyshev expansion of the evolution operator and the Fourier and Chebyshev pseudospectral methods to compute the spatial derivatives. The latter is used to implement the air/ocean boundary conditions. The results of the simulations are verified by comparison to analytical solutions obtained from the Green function. Examples of the electromagnetic field generated by a source located at the bottom of the ocean illustrate the practical uses of the algorithm.
The dipole impedance of an aperture in a plane conductor is obtained by modifying the general network formulation of electromagnetic apertures presented by Mautz and Harrington. The derived dipole impedances are combined in parallel to form an effective circuit description of low frequency aperture diffraction. Power transmitted into the aperture by an incident wave is determined by incorporating standard techniques for the transfer of wave power at an impedance mismatch. This transmitted power is divided into forward and backward scattered fields based upon the behavior of image currents surrounding the aperture, leading to a peak in forward scattered power above unity, consistent with known aperture behavior. The presented aperture circuit maintains an excellent correspondence with measurements of radiated power for an aperture excited by high energy electrons and with the numerically calculated impedance of a circular aperture using the finite element method.
A multilayer soil model for retrieving soil moisture content using the Integral Equation Method (IEM) is investigated in this paper. The total reflection coefficients of the natural soil are obtained using the multilayer model, and volumetric scattering is approximated by the internal reflections between layers. The surface reflection terms in IEM model are replaced by the total reflection coefficients from the multi-layer soil surface in retrieving the soil moisture content. The original IEM model includes only the surface scattering of the natural bare soil, while the multilayer soil - IEM model (MS-IEM) includes both the surface scattering and the volumetric scattering within the soil. Both the MS-IEM model and the original IEM model are compared in soil moisture retrieval using the experimental Synthetic Aperture Radar (SAR) backscattering coefficient data in the literature. It is noted that the mean square error between the measurement data and the values estimated by the modified IEM model is about 7.7%, while that between the measured and the estimated by the original IEM model is about 12%. The accuracy of estimating soil moisture by the IEM model is improved by 4.3%. In addition, the regression analysis between the measured and model-predicted soil moistures has been done.
A computationally efficient surrogate-based framework for reliable simulation-driven design optimization of microwave structures is described. The key component of our algorithm is manifold mapping, a response correction technique that aligns the coarse model (computationally cheap representation of the structure under consideration) with the accurate but CPU-intensive (fine) model of the optimized device. The parameters of the manifold mapping surrogate are explicitly calculated based on the fine model data accumulated during the optimization process. Also, manifold mapping does not use any extractable parameters, which makes it easy to implement. Robustness and excellent convergence properties of the proposed algorithm are demonstrated through the design of several microwave devices including microstrip filters and a planar antenna.
A realistic model of ground soil is developed for the electromagnetic simulation of Ground Penetrating Radar (GPR) systems. A three dimensional Finite Difference Time Domain (FDTD) algorithm is formulated to model dispersive media using N-term Debye permittivity function with static conductivity. The formulation of the algorithm is based on the concept of the Piecewise Linear Recursive Convolution (PLRC) in order to simulate the dispersion properties of soil as a two-term Debye medium. This approach of ground modeling enhances the accuracy and reliability of results obtained for GPR problems. The developed algorithm is validated when simulating practical GPR Systems used to detect different objects buried in Puerto-Rico and San Antonio clay loams. The proposed algorithm is employed to compare the impact of using two-term Debye model to simulate real soil on the coupling coefficient between transmitting and receiving antennas due to the absence and presence of buried targets to that of using non-dispersive soil model. The effect of soil moisture content on the performance of GPR system in detecting buried objects such as metallic and plastic pipes is investigated.
A method of solving the scattering problem for general multilayer anisotropic structures composed of conventional materials and metamaterial is presented. The analysis is based on calculation of the hybrid matrix of layers by means of a recursive algorithm. The method does not have the complexity and instability problems of other methods and is reliable in all cases. The zero reflection from stratified structures of conventional materials and metamaterials has then been introduced Various aspects of such a structure from the viewpoints of frequency and incident angle are presented and a rule for zero reflection from anisotropic medium is addressed. An interesting special case of total transparency is observed.
In this article a novel numerical technique, called Fitness Adaptive Differential Evolution (FiADE) for optimizing certain pre-defined antenna configuration to attain best possible radiation characteristics is presented. Differential Evolution (DE), inspired by the natural phenomenon of theory of evolution of life on earth, employs the similar computational steps as by any other Evolutionary Algorithm (EA). Scale Factor and Crossover Probability are two very important control parameter of DE .This article describes a very competitive yet very simple form of adaptation technique for tuning the scale factor, on the run, without any user intervention. The adaptation strategy is based on the fitness function value of individuals in DE population. The feasibility, efficiency and effectiveness of the proposed algorithm in the field of electromagnetism are examined over a set of well-known antenna configurations optimization problems. Comparison with the some very popular and powerful metaheuristics reflects the superiority of this simple parameter automation strategy in terms of accuracy, convergence speed, and robustness.
An important aspect of the studies undertaken in bioelectromagnetism relates to the choice of the exposure facility, the characteristics of a real electromagnetic environment are far more complex compared to the one plane wave irradiation set-up used in the majority of bioelectromagnetic studies. Moreover biological requirements should represent the starting point in the design of an in vitro exposure system. Indeed it is important to avoid altering the electromagnetic properties of the exposure system in the presence of the biological equipments. Related to these two essential points, this article contributes to show the advantages of a Mode Stirred Reverberation Chamber (MSRC) to guarantee a controlled electromagnetic environment around biological material for in vitro experimentation. An example of irradiation of in vitro human skin cells cultures will be considered to illustrate this paper. In order to show that the biological conditions and physical requirements for in vitro experiments are checked, two aspects are described. Firstly the characterization of the electromagnetic field generated around the biological system (both equipments and cultures) is achieved. Secondly the analysis of the Specific Absorption Rate (SAR) inside the biological medium is evaluated both numerically and experimentally. Initially, the statistical properties of fields inside the MSRC were checked with or without biological devices in order to verify their electromagnetic transparency with respect to the reverberating properties of the electromagnetic environment (inside MSRC) and the good agreement of the experimental electromagnetic power distribution with the theoretical one. The second part of this work corresponds to the determination of the SAR distribution. The computation of electromagnetic energy absorbed by biological medium (SAR) was based upon Finite Difference in Time Domain (FDTD) technique. A numerical analogy was achieved between MSRC behavior and a free-space finite sum of random plane waves. Simulations are able to provide both an estimation of SAR distribution inside each biological culture dish and a computation of the coupling effects between dishes. Relying on the previous conclusions, temperature measurements were led to evaluate the experimental SAR levels and its time variations inside the MSRC. Two high-frequency (900 MHz) environments were considered: a 10 minutes exposure with standard field amplitude inside the biological incubator of 7.87 V/m and 30 minutes with 41V/m (SAR ranged from 2.6 mW/kg to 73 mW/kg, mean values). Numerical and experimental results prove the ability of MSRC to provide a large and efficient tool to achieve bioelectromagnetic experiments at high frequencies.
Based on the vectorial angular spectrum representation and the method of stationary phase, internal vectorial structures of a phase-flipped Gauss (PFG) beam diffracting in the far field are derived in analytical forms. The energy flux for the TE term, TM term and the whole beam are derived and depicted by numerical examples. Influences of the f parameter on the whole energy flux distributions are analyzed. Discrepancies of the whole energy flux distributions between the paraxial and non-paraxial cases are shown in detailed manners. Furthermore, influences of the f parameter on discrepancies between two cases are also studied.
Although there is no certain known mechanism of how the electromagnetic fields (EMFs) at power frequency (50/60 Hz) can affect human health, it has been epidemiologically shown that they have many hazards on human health. Also the power frequency fields may interfere with the nearby electrical and electronic equipment. In response to the precautionary principle, it might be needed in some situations to reduce the magnetic and electric fields of a high voltage line segment when it passes in close proximity to a populated area or may interfere with sensitive equipment. In other words, new arrangements of high voltage "green lines" are needed. This paper introduces a numerical solution based on Particle Swarm Optimization (PSO) technique, to reduce both magnetic and electric fields of high voltage overhead transmission line by rearranging the conductors. The horizontal, vertical, and triangular configurations of both single circuit and double circuit transmission lines were investigated. The examples presented in this paper show that the rearranged line configurations can introduce up to 81% reduction in magnetic field and up to 84% in electric field when the effects of ice and wind are considered, and up to 97% reduction in both magnetic and electric fields when these effects are neglected. A comparison is made between the cost of reducing EMFs of a line segment in a suburban area in Amman in Jordan, and the cost of not-reducing EMFs, where it is found that the cost of reducing the fields is outweighed by the "possible health costs" otherwise.
The scattering of an oblique electromagnetic wave incident on a sub-wavelength circular pore with a finite depth on the surface of a semi-infinite perfect conductor is investigated analytically. We use the method of matched asymptotic expansion to find the multipole structure. The expansion is based on the duality property of the source-free Maxwell equations, and the resultant scattering fields are fully expressed in terms of the scalar and the conjugate vector potentials. There are two regions defined by the analytical method: the electro/magneto-static inner region and the radiation outer wave region. For both TM and TE incidences, the scattering waves are lead by leading dipoles. In the next order of the scattering waves, a mixture of the dipole, the quadrupole and the octupole is found. This is a striking finding, that the multipoles are not organized in a strictly ascending manner when the size of the pore is considered. In addition, the sophisticated three-dimensional interplay of the multipoles, the pore depth, and the incident angle is revealed. The magnitudes of the scattering dipoles are confirmed convergent smoothly to those of the back-scattering dipoles of electromagnetic waves transmitted through a hole in a perfect conducting plate with a finite thickness when the pore depth is larger than about 1, normalize to the pore radius.
The authors suggest the generalized method of induced electromotive forces (EMF) for the investigation of the characteristics of single and systems of thin impedance vibrators at their arbitrary excitation and distribution of the surface impedance on the ground of the made analysis in the pro-posed paper. The distinctive peculiarity of this method is the use of the approximating functions, re-sulted from the integral equation solution for the current by means of the asymptotic averaging me-thod, in the current distribution along the impedance vibrator.
This paper presents an improved approach for the propagation of electromagnetic (EM) fields along a helical hollow waveguide that consists of two bendings in the same direction. In this case, the objective is to develop a mode model for infrared (IR) wave propagation, in order to represent the effect of the radius of the cylinder of the helix and the step's angle on the output fields and the output power transmission. This model enables us to understand more precisely the influence of the step's angle and the radius of the cylinder of the helix on the output results of each section (bending). The output transverse components of the field, the output power transmission and the output power density for all bending are improved by increasing the step's angle or the radius of the cylinder of the helix, especially in the cases of space curved waveguides. This mode model can be a useful tool to improve the output results in all the cases of the helical hollow waveguides with two bendings for industrial and medical regimes.
Central Force Optimization (CFO) is a new multi-dimensional search metaheuristic based on the metaphor of gravitational kinematics. In this paper, for the first time, the CFO is applied to the optimal design of multilayer microwave absorbers (for normal incidence) in a specific frequency range. Several numerical examples are presented, in which the CFO results are compared with those found by other evolutionary algorithms. It is shown that the CFO results are comparable to those found by the self-adaptive differential evolution (SADE) algorithm and better than those found by particle swarm optimization (PSO) and gravitational search algorithm (GSA).
The results of an ultrawideband (UWB) measurement campaign carried out in a Hercules C-130 military cargo airplane are presented. The environment encompasses several metallic surfaces resulting in a large number of multipath components. Path-loss factor n representing the distance dependence of the channel path-loss is calculated for various frequency centers and bandwidths. A path-gain calculation model based on the concept of seperability of distance and frequency variables is proposed and comparison to measurements is given. Furthermore, time dispersion parameters, namely mean excess delay and root mean square (r.m.s.) delay spread are examined and their dependence on transmitter-receiver antennas separation is investigated. A power law is then employed to model the relation between the number of multipath components and the r.m.s delay spread. The temporal correlation between adjacent path amplitudes is found to be negligible. A modified Saleh-Valenzuela model is invoked to describe the clustering of multipaths, where a different power decay factor is used for the rays of the first cluster as opposed to subsequent clusters. Moreover, the Weibull distribution models the small scale channel fading with a lognormally distributed shape parameter. The average values of this parameter imply severe fading conditions. Finally, simulation results of the proposed statistical model are compared to measured data demonstrating reasonable agreement.
Rain attenuation is one of the most crucial factors to be considered in the link budget estimation for microwave satellite communication systems, operating at frequencies above 10 GHz. This paper presents a mathematical model for converting terrestrial rain attenuation data to be used for satellite applications at Ku-band. In the proposed technique, the ITU-R P 618-9, together with a combination of ITU-R P 530-12 and the revised Moupfouma model have been adopted for satellite and terrestrial rain attenuation predictions, respectively. The model has been used for transforming the measured rain attenuation data of some DIGI MINI-LINKS operating at 15 GHz in Malaysia, to be used for MEASAT 2 applications. It was found that the model predictions are fairly reasonable when compared with direct beacon measurements in Malaysia and similar tropical locations. The model will provide a relatively accurate method for transforming the measured terrestrial rain attenuation to be used for satellite applications; and therefore substantially reduce the cost of implementing Earth-satellite links in some tropical regions that have sufficient rain attenuation data for the terrestrial links.
Recently, we have introduced a numerical method for calculating local dispersion of arbitrary shaped optical waveguides, which is based on the Finite-Difference Time-domain and filter diagonalization technique. In this paper we present a study of photonic crystal waveguides at interfaces and double hetero-structure waveguides. We have studied the waveguide stretching effect, which is the change in lattice constant of photonic crystals along waveguiding direction. Hybrid modes at photonic crystal heterostructure interfaces are observed, which are the results of superposition of existing modes in adjacent waveguides. The dispersion at the interfaces of a double hetero-structure waveguide tends to the dispersion of outer waveguides. The effective area still holding the dispersion of the middle waveguide is shorter than the geometrical length of the middle waveguide. The results of this study present a clear picture of dispersion at interfaces and the transmission in photonic crystal hetero-structures.
Adaptive nulling algorithms that minimize the total array output power from the array require constraints on the adaptive weights, otherwise nulls would be placed in the main beam and the desired signal rejected. The concept of cancellation patterns is reviewed and extended to partial adaptive nulling. Cancellation patterns are then extracted from adaptive nulling results with a genetic algorithm and a 32 element dipole array model. The cancellation patterns provide insight into the constraints needed for the successful implementation of a power minimization adaptive algorithm.
A two-layer nondestructive method for characterizing the electric and magnetic properties of lossy conductor-backed magnetic materials using a flanged rectangular-waveguide probe is examined. The two reflection measurements necessary to determine both permittivity and permeability are made by first applying the probe to the material under test and then applying the probe to a knownmaterial layer placed on top of the material under test. The theoretical reflection coefficient is obtained using a rigorous full-wave solution, and an extrapolation scheme is used to minimize the error due to truncating the modal expansion of the waveguide fields. An error analysis is performed to compare the performance of the technique to the two-thickness method, which utilizes two different thicknesses of the material under test. The properties of the known material layer that result in the least error due to network analyzer uncertainty are determined. The sensitivity of the two-layer method is also explored and discussed.