Showing papers in "Progress in Electromagnetics Research B in 2009"
TL;DR: The model is used to evaluate energy consumption and node lifetime for a sensor network with fixed configuration and it is shown that existing energy models over-estimate life expectancy of a sensor node by 30-58% and also yield an "optimised" number of clusters which is too large.
Abstract: A comprehensive energy model for wireless sensor networks is provided by considering seven key energy consumption sources some of which are ignored by currently available models. We demonstrate the importance of using such a comprehensive model by comparing it to other existing energy models in terms of the lifetime of a sensor node. We use our model to evaluate energy consumption and node lifetime for a sensor network with fixed configuration and we validate this evaluation by simulation. We show that existing energy models over-estimate life expectancy of a sensor node by 30-58% and also yield an "optimised" number of clusters which is too large. We further make the following two observations: 1) the optimal number of clusters increases with the increase of free space fading energy, 2) for sensor networks with 100 sensors over an area of 10 4 -10 5 (m 2 ), finding the optimal number of clusters becomes less important when free space fading energy is very low (less than 1670 pJ/bit/m 2 ), while for larger networks, on the other hand, cluster optimization is still important even if free space fading energy is low. Guidelines for efficient and reliable sensor network design as well as extension to a sensor network with rotating cluster heads are provided.
220 citations
TL;DR: A comparison between difierent modern population based optimization methods applied to the design of scannable circular antenna arrays is presented and a comparative analysis of the performance of the optimized designs with the case of conventional progressive phase excitation is achieved.
Abstract: A comparison between difierent modern population based optimization methods applied to the design of scannable circular antenna arrays is presented in this paper. This design of scannable circular arrays considers the optimization of the amplitude and phase excitations across the antenna elements to operate with optimal performance in the whole azimuth plane (360 - ). Simulation results for scannable circular arrays with the amplitude and phase excitation optimized by genetic algorithms, particle swarm optimization and the difierential evolution method are provided. Furthermore, in order to set which design case could provide a better performance in terms of the side lobe level and the directivity, a comparative analysis of the performance of the optimized designs with the case of conventional progressive phase excitation is achieved. Simulation results show that
201 citations
TL;DR: ICA has better capability to remove the clutter in comparison to other applied techniques; especially it is found that ICA has a capability to distinguish the difierence between clutter and low dielectric target whereas other clutter removal techniques are not showing signiflcant result.
Abstract: Nowadays, through wall imaging (TWI) is an emerging topic of research in which one of the most important tasks is to minimize the clutter through which detection accuracy can be improved. Clutter in TWI is due to many reasons like wall coupling, antenna coupling, multiple re∞ections etc. To analyze the clutter reduction techniques, flrstly we indigenously assembled a TWI system (i.e., step frequency continuous wave radar (SFCW)) in UWB range (freq. 3.95GHz to 5.85GHz), and difierent observations have been taken. We have considered metallic plate and one more material with low dielectric constant (Te∞on) as a target and kept them behind the plywood wall. A-scan and B-scan observations have been carried out. The observed data are preprocessed for imaging and then difierent types of clutter reduction techniques like Principal Component Analysis (PCA), Independent Component Analysis (ICA), Factor Analysis (FA) and Singular Value Decomposition (SVD) have been applied, and results were analyzed. Signal to noise ratio (SNR) of the flnal images (i.e., after clutter removal with difierent techniques) has been computed to compare the results and know the efiectiveness of individual clutter removal techniques. It is observed that ICA has better capability to remove the clutter in comparison to other applied techniques; especially it is found that ICA has a capability to distinguish the difierence between clutter and low dielectric target whereas other clutter removal techniques are not showing signiflcant result.
162 citations
TL;DR: The results reveal that design of antenna arrays using the PSO method provides considerable enhancements compared with the uniform array and the synthesis obtained from other optimization techniques.
Abstract: Linear and circular arrays are optimized using the particle swarm optimization (PSO) method. Also, arrays of isotropic and cylindrical dipole elements are considered. The parameters of isotropic arrays are elements excitation amplitude, excitation phase and locations, while for dipole array the optimized parameters are elements excitation amplitude, excitation phase, location, and length. PSO is a high-performance stochastic evolutionary algorithm used to solve N-dimensional problems. The method of PSO is used to determine a set of parameters of antenna elements that provide the goal radiation pattern. The efiectiveness of PSO for the design of antenna arrays is shown by means of numerical results. Comparison with other methods is made whenever possible. The results reveal that design of antenna arrays using the PSO method provides considerable enhancements compared with the uniform array and the synthesis obtained from other optimization techniques.
140 citations
TL;DR: In this paper, a multilayer shielding structure with both absorbing and re∞ecting composite layers is considered, and frequency dependencies for an efiective permittivity are approximated by the Debye curves using a curve-fltting procedure, in particular a genetic algorithm.
Abstract: Composites containing conducting inclusions are required in many engineering applications, especially, for the design of microwave shielding enclosures to ensure electromagnetic compatibility and electromagnetic immunity. Herein, multilayer shielding structures are studied, with both absorbing and re∞ecting composite layers. In this paper, flber-fllled composites are considered. For modeling absorbing composites with low concentration of conducting cylindrical inclusions (below the percolation threshold), the Maxwell Garnett theory is used. For re∞ecting layers, when concentration of inclusions is close to or above the percolation threshold, the McLachlan formulation is used. Frequency dependencies for an efiective permittivity are approximated by the Debye curves using a curve-fltting procedure, in particular, a genetic algorithm.
102 citations
TL;DR: The design of a novel Fractal planar inverted F antenna (F-PIFA) based on the self affinity property has met the performance criteria for a mobile phone application.
Abstract: The design of a novel Fractal planar inverted F antenna (F-PIFA) based on the self affinity property is presented in this paper. The procedure for designing a Fractal Planar Inverted F Antenna is explained and three different iterations are designed for use in cellular phones. The F-PIFA has a total dimension of 27 mm × 27 mm and has been optimized to be operational at GSM (Global System for Mobile Communication), UMTS (Universal Mobile Telecommunication System) and HiperLAN (High Performance Radio LAN) with the frequencies range from 1900 MHz to 2100 MHz, 1885 to 2200 MHz and 4800 MHz to 5800 MHz respectively. The antenna achieved −6 dB return loss at the required GSM, UMTS and HiperLan frequencies with and has almost omnidirectional radiation pattern. This antenna has been tested using realistic mobile phone model and has met the performance criteria for a mobile phone application. Simple semi-empirical formulas of the operational frequency, numerical calculation and computational SAR of the antenna also has been presented and discussed.
95 citations
TL;DR: A comprehensive review of radio wave attenuation in forest environments is presented and some possible future work is proposed to improve the performance of radio links in forest environment.
Abstract: A comprehensive review of radio wave attenuation in forest environments is presented in this paper. The classic analytical methods of propagation loss modeling and prediction are described flrst. This provides information on the physical processes that the radio waves undergo while propagating through a forest. The focus of this paper is on the review and summary of the experimental work done in this area and the development of empirical propagation loss prediction models. The propagation loss variation due to external factors such as antenna height-gain, depolarization, humidity efiect etc. are examined and discussed individually. In view of current research work done in this area, some possible future work is proposed to improve the performance of radio links in forest environment.
89 citations
TL;DR: In this article, a planar µ-negative metamaterial structure called double-sided split ring resonator (DSRR) was proposed, which combines the features of a conventional SRR and a broadside-coupled SRR (BC-SRR) to obtain much better miniaturization at microwave frequencies for a given physical cell size.
Abstract: This paper introduces a planar µ-negative (MNG) metamaterial structure, called double-sided split ring resonator (DSRR), which combines the features of a conventional SRR and a broadside-coupled SRR (BC-SRR) to obtain much better miniaturization at microwave frequencies for a given physical cell size. In this study, electromagnetic transmission characteristics of DSRR, BC-SRR and conventional SRR are investigated in a comparative manner for varying values of substrate parameters which are thickness, the real part of relative permittivity and dielectric loss tangent. Simulation results have shown that magnetic resonance patterns of all these three structures are affected in a similar way from variations in permittivity and in loss tangent. However, changes in substrate thickness affect their resonance characteristics quite differently: In response to decreasing substrate thickness, resonance frequency of the SRR increases slowly while the bandwidth and the depth of its resonance curve do not change much. For the DSRR and BC- SRR structures, on the other hand, resonance frequency, half power bandwidth and the depth of resonance curve strongly decrease with decreasing substrate thickness. Among these three structures, all having the same unit cell dimensions, the newly suggested DSRR is found to reach the lowest resonance frequency, hence the smallest electrical size, which is a highly desired property not only for more effective medium approximation but also for miniaturization in RF design. The BC-SRR, on the other hand, provides the largest
86 citations
TL;DR: In this paper, a TEM horn antenna placed in a solid dielectric medium is proposed for microwave imaging of the breast, which couples the microwave energy into the tissue without being immersed itself in a coupling medium.
Abstract: A novel TEM horn antenna placed in a solid dielectric medium is proposed for microwave imaging of the breast. The major design requirement is that the antenna couples the microwave energy into the tissue without being immersed itself in a coupling medium. The antenna achieves this requirement by: 1) directing all radiated power through its front aperture, and 2) blocking external electromagnetic interference by a carefully designed enclosure consisting of copper sheets and power absorbing sheets. In the whole ultra-wide band the antenna features: 1) good impedance match, 2) uniform field distribution at the antenna aperture, and 3) good coupling efficiency.
86 citations
TL;DR: The resonant frequency results predicted by FIS models are in very good agreement with the experimental results available in the literature.
Abstract: Models based on fuzzy inference systems (FISs) for calculating the resonant frequency of rectangular microstrip antennas (MSAs) with thin and thick substrates are presented. Two types of FIS models, Mamdani FIS model and Sugeno FIS model, are used to compute the resonant frequency. The parameters of FIS models are determined by using various optimization algorithms. The resonant frequency results predicted by FIS models are in very good agreement with the experimental results available in the literature. When the performances of FIS models are compared with each other, the best result is obtained from the Sugeno FIS model trained by the least- squares algorithm.
80 citations
TL;DR: The developed EPSO is tested and compared with a standard benchmark to be validated as an e-cient optimization tool for beamforming applications and updated formulas of global best particle position and velocity are modifled to improve the convergence accuracy of classical Practical Swarm Optimization.
Abstract: In this paper, Enhanced Practical Swarm Optimization (EPSO) algorithm is proposed to be applied to pattern synthesis of linear arrays. Updating formulas of global best particle position and velocity are modifled to improve the convergence accuracy of classical Practical Swarm Optimization. The developed EPSO is tested and compared with a standard benchmark to be validated as an e-cient optimization tool for beamforming applications. Difierent numerical examples are presented to illustrate the capability of EPSO for pattern synthesis with a prescribed wide nulls locations and depths. Collective multiple deep nulls approach and direct weights perturbations approach are considered to obtain adaptive wide null steering subject to peak side lobe level and minimum main beam width constraints. Starting from initial Chebyshev pattern, single or multiple wide nulls are achieved by optimum perturbations of elements current amplitude or complex weights to have either symmetric or asymmetric nulls about the main beam. Proper formation of the cost function is presented for all case studies as a key factor to include the pattern constraints in the optimization process.
TL;DR: In this article, a new microstrip antenna with Koch shaped fractal defects on the patch surface is presented and the overall electric length of the antenna is increased largely and hence the size of antenna is reduced to 85%.
Abstract: With development of communication with integration technology, size reduction of microstrip antennas is becoming an important design consideration for practical applications. Here a new microstrip antenna with Koch shaped fractal defects on the patch surface is presented. Using this method, the overall electric length of the antenna is increased largely and hence the size of antenna is reduced to 85%, compared to an ordinary microstrip antenna with the same resonance frequency. Antenna is simulated using high frequency structure simulator (HFSS) V.10 which is based on finite element modeling (FEM). Finally antenna is fabricated on RO4003 substrate. Measurement results are in good agreement with simulated results.
TL;DR: In this paper, the scattering of an arbitrary electromagnetic wave by a thin disk located in free space is formulated rigorously in terms of coupled dual integral equations (CDIEs) for the unknown images of the jumps and average values of the normal to the disk scattered-field components.
Abstract: The scattering of an arbitrary electromagnetic wave by a thin disk located in free space is formulated rigorously in terms of coupled dual integral equations (CDIEs) for the unknown images of the jumps and average values of the normal to the disk scattered-field components. Considered are three cases of the disk: (1) zero-thickness perfectly electrically conducting (PEC) disk, (2) thin electrically resistive (ER) disk and (3) dielectric disk. Disk thickness is assumed much smaller than the disk radius and the free space wavelength, in ER and dielectric disk cases, and also much smaller than the skin-layer depth, in the ER disk case. The set of CDIEs are \decoupled" by introduction of the coupling constants. Each set of DIEs are reduced to a Fredholm second kind integral equation by using the semi-inversion of DIE integral operators. The set of \coupling" equations for finding the coupling constants is obtained additionally from the edge behavior condition. Thus, each problem is reduced to a set of coupled Fredholm second kind integral equations. It is shown that each set can be reduced to a block-type three-diagonal matrix equation, which can be effectively solved numerically by iterative inversions of the two diagonal blocks and 2 x 2 matrix.
TL;DR: In this article, a three-dimensional approach based on the Coulombian model is presented for the calculation of the magnetic field components created by ring permanent magnets. But the results presented in this paper clearly show that the two-dimensional studies dealing with the optimization of ring permanent magnet dimensions cannot be treated with the same precisions as 3D studies.
Abstract: This paper presents an improvement of the calculation of the magnetic field components created by ring permanent magnets. The three-dimensional approach taken is based on the Coulombian Model. Moreover, the magnetic field components are calculated without using the vector potential or the scalar potential. It is noted that all the expressions given in this paper take into account the magnetic pole volume density for ring permanent magnets radially magnetized. We show that this volume density must be taken into account for calculating precisely the magnetic field components in the near-field or the far-field. Then, this paper presents the component switch theorem that can be used between infinite parallelepiped magnets whose cross-section is a square. This theorem implies that the magnetic field components created by an infinite parallelepiped magnet can be deducted from the ones created by the same parallelepiped magnet with a perpendicular magnetization. Then, we discuss the validity of this theorem for axisymmetric problems (ring permanent magnets). Indeed, axisymmetric problems dealing with ring permanent magnets are often treated with a 2D approach. The results presented in this paper clearly show that the two-dimensional studies dealing with the optimization of ring permanent magnet dimensions cannot be treated with the same precisions as 3D studies.
TL;DR: In this paper, the authors extended the unified theory of near-field-far-field transformations with spiral scannings for quasi-spherical antennas to the case of nonspherical ones, i.e., antennas with two dimensions very different from the third one.
Abstract: The unified theory of near-field–far-field transformations with spiral scannings for quasi-spherical antennas is extended in this paper to the case of nonspherical ones, i.e., antennas with two dimensions very different from the third one. To this end, these antennas are no longer considered as enclosed in a sphere, but in a proper convex domain bounded by a rotational surface. The extension, heuristically derived by paralleling the rigorous procedure valid for the spherical source modelling, allows one to overcome its main and serious drawbacks. In fact, the corresponding near-field–farfield transformations use a reduced number of near-field measurements and, above all, allow one to consider measurement surfaces at a distance smaller than one half the antenna maximum size, thus remarkably reducing the error related to the truncation of the scanning zone. These are very important features, which make the spiral scannings more and more appealing from the practical viewpoint. Some examples of the application of this theory to spirals wrapping the conventional scanning surfaces employed in the near-field–far-field transformations are reported, and the accuracy and robustness of the far-field reconstructions are assessed.
TL;DR: In this article, the authors presented a class of ultra-thin metamaterial absorbers, which consists of periodic microstrip lines on top of a planar lossy substrate backed by a conducting metallic plate.
Abstract: This paper presents a class of ultra-thin metamaterial absorbers, which consists of periodic microstrip lines on top of a planar lossy substrate backed by a conducting metallic plate. A highly efficient full-wave analysis method was developed to solve the electromagnetic response of the absorbers. The influence of electromagnetic properties of the substrate and physical dimensions of the microstrip lines were analyzed. Genetic algorithm was used to optimize the absorption bandwidth of the absorbers. Effective permeability and permittivity of the absorbers were retrieved to shed a new light on the absorption mechanism of the absorbers and to explain their ultimate bandwidth limit. It was found that the ultimate bandwidth limit of the metamaterial absorbers is the same as that of normal absorbers.
TL;DR: This methodology includes a rapidly-converging iterative scheme that produces an analytical model of the behavior of the antenna structure and sensitivity and tolerance analysis can be carried out without the need for further costly electromagnetic simulations.
Abstract: We propose an optimization methodology suitable for the design of various antenna structures. This methodology includes a rapidly-converging iterative scheme. In each iteration stage, the algorithm generates a parameterized Cauchy model using the available results from previous iterations. Optimization is then applied to this Cauchy model to obtain better design parameters that are also used in enhancing the accuracy of the model. This cycle continues until the speciflcations are met. In addition, this on-the-∞y technique produces an analytical model of the behavior of the antenna structure. Sensitivity and tolerance analysis can thus be e-ciently carried out without the need for further costly electromagnetic simulations.
TL;DR: A method based on plant growth simulation algorithm (PGSA) for pattern nulling by controlling only the element amplitudes of linear antenna array is presented.
Abstract: A method based on plant growth simulation algorithm (PGSA) is presented for pattern nulling by controlling only the element amplitudes of linear antenna array. The PGSA is a new and highly e-cient random search algorithm inspired by the growth process of plant phototropism. Simulation results for Chebyshev patterns with the imposed single, multiple and broad nulls are given to show the performance of the proposed method.
TL;DR: In this article, a comprehensive review of the dielectric properties of normal and cancerous breast tissue, and the heterogeneity of normal breast tissue are examined and compared using the Finite Difierence Time Domain (FDTD) method.
Abstract: Microwave imaging is one of the most promising emerging imaging technologies for breast cancer detection. Microwave imaging exploits the dielectric contrast between normal and malignant breast tissue at microwave frequencies. Many UWB radar imaging techniques require the development of accurate numerical phantoms to model the propagation and scattering of microwave signals within the breast. The Finite Difierence Time Domain (FDTD) method is the most commonly used numerical modeling technique used to model the propagation of Electromagnetic (EM) waves in biological tissue. However, it is critical that an FDTD model accurately represents the dielectric properties of the constituent tissues and the highly correlated distribution of these tissues within the breast. This paper presents a comprehensive review of the dielectric properties of normal and cancerous breast tissue, and the heterogeneity of normal breast tissue. Furthermore, existing FDTD models of the breast are examined and compared. This paper provides a basis for the development of more geometrically and dielectrically accurate numerical breast phantoms used in the development of robust microwave imaging algorithms.
TL;DR: In this paper, the performances of thinned arrays based on Almost Difference Sets are analyzed in the presence of mutual coupling effects, where the geometry under test is composed by thin dipole elements and the arising mutual interactions are modeled by means of the induced EMF method.
Abstract: In this paper, the performances of thinned arrays based on Almost Difference Sets are analyzed in the presence of mutual coupling effects. The geometry under test is composed by thin dipole elements and the arising mutual interactions are modeled by means of the induced EMF method. To assess the robustness of the ADS-based thinning technique also in such a non-ideal case, an extensive numerical analysis is carried out by considering several test cases characterized by different aperture sizes, lattice spacings, and thinning factors. The obtained results show that the peak sidelobe estimators deduced in the ideal case still keep their validity although, as expected, a deterioration usually arises due to the mutual coupling. The final version of this article is available at the url of the journal PIERB http://www.jpier.org/PIERB/
TL;DR: This paper describes the design of the disk-loaded monopole with a parasitic array for beam switching and the reduced-size antenna namely a sector antenna array, which has allowed at least 50% of the size reduction.
Abstract: This paper describes the design of the disk-loaded monopole with a parasitic array for beam switching. Usually the radiation pattern of a single element such as a ?/4 monopole and the disk-loaded monopole provide low values of gain. The beamwidth is normally large and the coverage is wide. This may be appropriate in an on-body channel where the antenna orientation may not be easily controlled, such as when the users put the terminal in their pocket. In some non-body applications such as WLAN, it is necessary to design antennas with high gain to meet other demands such as high capacity or long range. Also, in the on-body environment it is essential to have such gain in order to minimize the path loss between the antennas, and hence increase the battery life. The antenna was excited using coaxial cable produced more gain and pattern compared to the single element top disk-loaded antenna. The reduced-size antenna namely a sector antenna array also has been discussed in detail in this paper. Such design has allowed at least 50% of the size reduction. The simulation results have shown very good agreement with the measurement for both antennas.
TL;DR: In this article, the characteristics of planar waveguides with chiral nihility meta-materials are studied theoretically and anomalous dispersion curves, electromagnetic fields, energy flow distribution and the power of several low-order guided modes in the chiral Nihility waveguide are presented.
Abstract: The characteristics of guided modes in the planar waveguides which the core or cladding consists of chiral nihility meta-materials are studied theoretically. The dispersion curves, electromagnetic fields, energy flow distribution and the power of several low-order guided modes in the chiral nihility waveguides are presented. Some novel features such as anomalous dispersion curves, the power flows opposite to the wave vector propagation direction in the chiral nihility waveguides have been found.
TL;DR: A graphics processing based version of the Finite-Difierence Frequency-Domain method, which uses a central flnite difierencing scheme for solving Maxwell's equations for electromagnetics, which shows more than 40 times speed over the CPU code.
Abstract: This paper presents a graphics processing based im- plementation of the Finite-Difierence Frequency-Domain (FDFD) method, which uses a central flnite difierencing scheme for solving Maxwell's equations for electromagnetics. The radar cross section for difierent structures in 2D and 3D has been calculated using the FDFD method. The FDFD code has been implemented for the CPU calcu- lations and the same code is implemented for the GPU calculations using the Brook+ developed by AMD. The solution obtained by using the GPU based-code showed more than 40 times speed over the CPU code.
TL;DR: Scale-changing networks as mentioned in this paper model the electromagnetic coupling between various scale levels in the studied structure and are computed separately, which allows forming a monolithic (unique) electromagnetic formulation for the global electromagnetic simulation of complex planar structures.
Abstract: The concept of Scale-Changing Network is reported for the electromagnetic modeling of complex planar structures composed of a collection of metallic patterns printed on a dielectric surface and whose size covers a large range of scale. Examples of such multi-scale structures are provided by multi-band frequency-selective surfaces, flnite-size arrays of non-identical cells and fractal planar objects. Scale-Changing Networks model the electromagnetic coupling between various scale levels in the studied structure and are computed separately. The cascade of Scale-Changing Networks bridges the gap between the smallest and the highest scale levels and allows forming a monolithic (unique) electromagnetic formulation for the global electromagnetic simulation of complex planar structures. Derivation of these networks is presented and key advantages of the electromagnetic approach are reported.
TL;DR: In this paper, the authors present a comprehensive location scheme in a rich multipath environment based on the estimation of the distance between two wireless nodes in line-of-sight (LOS) from the best statistical estimator of the round-trip time (RTT), assuming a linear regression as the model that best relates this estimator to the actual distance.
Abstract: This paper presents a comprehensive location scheme in a rich multipath environment. It is based on the estimation of the distance between two wireless nodes in line-of-sight (LOS) from the best statistical estimator of the round-trip time (RTT), assuming a linear regression as the model that best relates this statistical estimator to the actual distance. As LOS cannot be guaranteed in an indoor environment, the efiect of non-line-of-sight (NLOS) is mitigated by a two-step correction scheme. At a flrst step, the severe NLOS error is corrected from distance estimates applying the prior NLOS
TL;DR: The modified winding function method, applied to a faulted synchronous generator, is modified and is used for online diagnosis of mixed eccentricity fault and it is shown that static, dynamic and mixed eccentricities lead to the increase of the amplitude and occurrence of the distortion in the aforementioned inductances.
Abstract: In this paper, winding function method (WFM), applied to a faulted synchronous generator, is modified and is used for online diagnosis of mixed eccentricity fault. For the first time, the static and mixed eccentricities are modeled in synchronous generators. A modified winding function (MWF) method introduced here is more precise compared with previous methods. This MWF enables to compute the air gap magnetic permeance accurately. Here, two or three terms of the infinity permeance series have not been used, but a closed form equation is employed for permeance evaluation. This leads to a very precise computation of the inductances of the faulted machine. Self inductances of the stator and rotor, mutual inductance of two stator phases and the mutual inductance of rotor and stator are obtained. Meanwhile, it is shown that static, dynamic and mixed eccentricities lead to the increase of the amplitude and occurrence of the distortion in the aforementioned inductances. Since calculation of inductances is the most important step for fault diagnosis of the machine, the proposed method improves the on-line diagnosis of the fault. Meanwhile, the spectrum analysis of stator current, obtained from experimental results, is illustrated.
TL;DR: In this article, the authors investigate boundary effects and other consequences of spatial dispersion by analyzing in detail the response of a metamaterial half-space to a monochromatic plane wave normally incident from free-space.
Abstract: In this paper we investigate boundary effects and other consequences of spatial dispersion by analyzing in detail the response of a metamaterial half-space to a monochromatic plane wave normally incident from free-space. The metamaterial is composed of an orthorhombic lattice of identical particles, each of which exhibits both an electric and magnetic response. Rather than relying on the conventional boundary conditions and the Clausius-Mossotti equations, we use instead the point-dipole interaction model and an expansion of polarization in eigenmodes to determine the structure's dispersion relation and electromagnetic response. Using the nearest- neighbor approximation, we show how truncating the crystal lattice excites an "ordinary" mode and two "extraordinary" modes that are necessary to satisfy the boundary conditions at the interface. For most cases, the extraordinary modes are evanescent, and thus form a thin transition layer at the surface. However, under certain conditions, typically near particle resonances, either one or both of these modes can be propagating.
TL;DR: In this article, a design of Wide-Band Microstrip Yagi-Uda antenna with high gain and high front to back (F/B) ratio is presented, and measured return loss and radiation pattern of this antenna is presented to validate the results of simulations by two methods.
Abstract: This paper presents a design of Wide-Band Microstrip Yagi-Uda antenna with high gain and high front to back (F/B) ratio. Numerical and measured results of our design show more than 18dB front to back ratio at 5.5GHz and no backward radiation at 5.2GHz. An impedance bandwidth of 22.05% was achieved around 5.5GHz. The antenna gain (10{12.4dBi) can be varied to be suitable for various applications. Measured return loss and radiation pattern of this antenna is presented to validate the results of simulations by two methods. The flrst method based on flnite element method (FEM) and the second one based on flnite integral technique (FIT) were used to analyze antenna structure, and subsequently the Genetic Algorithm (GA) was applied by using HFSS simulator to obtain the optimized parameters. In order to flnd the best design method for this antenna, the efiect of distance between the parasitic elements of proposed antenna was studied. Finally two microstrip Yagi-Uda array antennas were combined to increase the gain of antenna. To demonstrate the major beneflts, a comparison of our initial and flnal designs of Yagi-Uda antenna is provided.
TL;DR: In this paper, a numerical model of the soil ionization phenomena that can occur when earth electrodes are injected by high pulse transient currents, as the one associated with a direct lightning stroke, is proposed.
Abstract: This paper proposes a numerical model of the soil ionization phenomena that can occur when earth electrodes are injected by high pulse transient currents, as the one associated with a direct lightning stroke. Based on finite difference time domain numerical scheme, this model ascribes the electrical breakdown in the soil to the process of discharge in the air. In fact, as soon as the local electric field overcomes the electrical strength, the air in the voids trapped among soil particles is ionized, and the current is conducted by ionized plasma paths locally grown. The dimension of these ionized air channels is strictly dependent upon the local temperature. Thus, a local heat balance is enforced in order to obtain the time variable conductivity profile of the medium. This model can be implemented both for concentrated and extended electrodes, since no hypothesis has to be enforced about the geometric shape of the ionized region. Validation of the proposed model is obtained by comparing simulation results with experimental data found in technical literature.
TL;DR: In this paper, a wide-angle bicone antenna terminated by a spherical cap is investigated and the antenna radiation patterns have been observed for various values of ka where k represents the phase constant and a represents the conical length.
Abstract: The wide-angle bicone antenna terminated by a spherical cap is investigated. The antenna radiation patterns have been observed for various values of ka where k represents the phase constant and a represents the conical length. It is seen that for large values of ka the radiation pattern is limited within an angular sector bounded by the cones of the antenna. Next the antenna is optimized for ultra- wideband (UWB) operation through the use of loading techniques. The transient wideband radiated and received responses of the antenna have been observed and the relationship between the wave shapes of the transient fleld and the input pulse have been determined.