The Debye expansion integrals obtained by application of the Modified Watson Transformation and Debye series expansion to the Mie series for the high frequency plane wave transmitted into a double negative(DNG) cylinder are solved in the geometrically lit regions of the corresponding Debye series terms. The Debye series expansion is made up to the possible maximum term after which double ray field formation is first observed. Using the steepest descent method and the geometrical optics approximation, the role of the lower ray in the double-ray field formation is pointed out. For refractive indices satisfying |n| ≥ 10, it is shown that the maximum Debye series term index up to which simple single-ray tracing can be performed is bigger for a DNG cylinder than that for a DPS cylinder and the difference between the term indices incrases as |n| increases.
This paper discusses the characterization of landmine by using the electromagnetic induction technique (EMI). The proposed approach is based on the identification of the physical and geometrical properties of a landmine, from the sensor response. But in such an identification, the inverse problem is unavoidable. At first, we begin by simulating the landmine signature by solving a direct problem using the finite element method which constitutes the direct model. After that, we determine the landmine characteristics by using an inverse model based on a cost function optimization. This model is based on an iterative process which coupling nite element analysis and Particles Swarm Optimization (PSO). In this step, we apply two PSO techniques: the Standard PSO (SPSO) and the Improved PSO (IPSO), and discuss the problem of local minima of the cost function. The proposed iterative model is applied to determine the conductivity, geometry, and depth of metallic landmine from its signature measured by EMI. The numerical solution gives good results for the identification of landmine.
This paper develops a more precise analytical model for calculating salient pole synchronous machine (SPSM) inductances in case of general eccentricity including static, dynamic and mixed eccentricities. The developed method is based on the modified winding function approach (MWFA) which accurately considers variable air gap function and leads to pure analytical expressions of inductances. Available analytical techniques, based on MWFA, approximate the air gap function and simplify the geometrical model of SPSM, whereas, in this study, the influence of the openings between the rotor salient poles has been taken into account by using an effective form of rotor pole shoes. Using this technique, flux fringing effect is considered. By taking into account machine geometry, type of windings connection and flux fringing effect, this method is able to model most of the important features of an eccentric SPSM. The developed analytical expressions can calculate time varying inductances of SPSMs with any eccentricity type and degree in the frame of a single program. Simulation results for static eccentricity are compared with experimental tests on a laboratory generator to verify accuracy of the proposed model.
A unit cell based numerical approach to model the metal powders and metal-dielectric composites at microwave frequencies is proposed. The unit cell based numerical modeling helps to compute the equivalent reflection and transmission coefficients of these materials, which are commonly used measured parameters at RF and microwave frequencies. The computation of the reflection and transmission coefficients of these artificial dielectric samples also facilitates the determination of their effective constitutive properties, defined in terms of the effective permittivity and permeability, using the reflection transmission approach. The applicability of the proposed unit cell method is first verified for some mixed dielectrics using the classical mixing formulas, and the standard waveguide approach. Once the validity of the proposed approach is ascertained, the effective constitutive properties of copper powder is determined. A detailed parametric analysis is also carried out in order to study the effect of various parameters such as the packing fraction, the grain size and the gap between adjacent spherical shaped metal particles, on the effective constitutive properties of the copper powder compact. This detailed analysis is quite helpful in order to optimize various parameters of the microwave sintering of metal powders and metal-dielectric composites before the actual start of the sintering process using microwaves.
The capability of Ground Penetrating Radar (GPR) systems of accurately reconstructing the geometrical features of buried objects, when working in critical conditions, is investigated. A customized microwave tomographic approach is used to tackle the imaging through the processing of comparative experimental and synthetic GPR data. The first ones have been gathered in laboratory controlled conditions, while the second ones have been obtained by exploiting an ad-hoc implementation of a CAD tool. Attention is paid to the significant case of `strong' scatterers having size comparable to the wavelengths of the probing signal, and possibly located close to the interface where the GPR antennas move. The results from imaging point out the potential of the proposed approach, showing in particular to which extent, in challenging operational settings, it is possible to recover also the information about the shape of metallic targets in addition to their correct location and size.
Few works on symmetric and asymmetric dielectrics have been published, specifically the case of chiral and bi-isotropic media. For this reason, and taking into account the complexity of the studied environment, this paper treats the asymmetrical effects on the resonant frequency and the bandwidth of a rectangular microstrip patch antenna in a complex bi-anisotropic substrate-superstrate configuration. This structure is studied theoretically, and the obtained results are discussed and commented. The numerical analysis used in this paper is mainly employed in order to obtain original results. The originality of this work is presented by the bianisotropic chiral asymmetry and the combined effect of the substrate and the superstrate.
It is well known that using proper signal compression techniques, the range resolution of the radar systems can be enhanced without having to increase the peak transmits power. Whereby the range resolution is inverse proportional with the frequency band of the scanning signals, in the last period of time, in radar systems literature a lot of suitable wideband signals were designed and analyzed as performance level. However, for the large majority of these signals, the compression filter response contains significant sidelobes which may cause difficulties in the target detection and range estimation process. Consequently, in the radar signal processing theory, the sidelobes reduction techniques using synthesis of some proper nonlinear FM (NLFM) laws represents a major scientific research direction. In order to assure the sidelobes suppression, the main objective of this paper is to present an adequate synthesis algorithm of some NLFM laws based on stationary phase principle. The achieved experimental results confirm a significant sidelobes reduction (i.e., more than -40 dB) without necessity to apply some weighting techniques. Finally, the analysis of the synthesized NLFM laws by ambiguity function tool was also discussed.
In this paper, an algorithm based on penalty cost function for synthesizing at-top patterns is proposed. A descent algorithm (DA) as its optimizing approach is proposed in this paper as well. Apparently, whole algorithm efficiency totally depends on the DA. Unlike traditional descent method, the DA defines step length by solving a inequality, instead of Wolf or Armijo-type search rule, stimulation results indicate that it can improve the computational efficiency. Under mild conditions, we prove that the DA has strong convergence properties. Several numerical examples are presented to illustrate the effectiveness of the proposed algorithm. The results indicate that the approach is effective in the pattern shape precisely in both mainlobe and sidelobe region for arbitrary linear arrays.
Electrical cables of all types are subject to aggressive environments that can create defects or accelerate aging. Many application domains require diagnosis methods and tools. Among many methods, reflectometry has proven to be the best candidate and can be easily applied to the detection and localization of hard defects, while only requiring one access point to the wire. But soft defects are more difficult to track and require new powerful methods. This paper presents a review of the recent state of the art in the field of wired network diagnosis and shows the evolution of future activities in this domain. It provides new perspectives and new research domains are proposed.
A problem of electromagnetic fields excitation by a system of finite-dimensional material bodies in two arbitrary electrodynamic volumes coupled by holes, cut in a common boundary of the volumes, is defined in a rigorous formulation. For the system containing two material bodies and one coupling hole, the problem is reduced to a system of two-dimensional integral equations relative to surface electric currents on the material bodies and equivalent magnetic current in the coupling hole. The resulting integral equations are correctly transformed to a system of one-dimensional equations for currents in a narrow slot and on thin impedance vibrators, which may have irregular electrophysical and geometrical parameters. The resulting equations system for a transverse slot in a broad wall of a rectangular waveguide and impedance vibrators with variable surface impedance is solved by a generalized method of induced electro-magneto-motive forces (EMMF) under assumption that interaction between the vibrators and the slot is absent. Calculated and experimental plots of electrodynamic characteristics for this vibrator-slot structure are presented.
We introduce a data-driven unsupervised classification algorithm that uses polarimetric and interferometric synthetic aperture radar (PolInSAR) data. The proposed algorithm uses a classification method that preserves scattering characteristics. Our contribution is twofold. First, the method applies adaptive model-based decomposition (AMD) to represent the scattering mechanism, which overcomes the flaws introduced by Freeman decomposition. Second, a new class initialization scheme using a histogram clustering algorithm based on a Dirichlet process mixture model is applied to automatically determine the number of clusters and effectively initialize the classes. Therefore, our algorithm is data-driven. In the first step, the Shannon entropy characteristics of the PolInSAR data are extracted and used to calculate the local histogram features. After applying AMD, pixels are divided into three canonical scattering categories according to their dominant scattering mechanism. The histogram clustering algorithm is applied to each scattering category to obtain the number of classes and initialize them. The iterative Wishart classifier is applied to refine the classification results. Our method not only can obtain promising unsupervised classification results but also can automatically assign the number of classes. Experimental results for E-SAR L-band PolInSAR images from the German Aerospace Center demonstrate the effectiveness of the proposed algorithm.
The effective coefficients for Maxwell's equations in the frequency domain are calculated for a multiscale isotropic medium by using a subgrid modeling approach. The correlated fields of conductivity and permeability are approximated by Kolmogorov's multiplicative continuous cascades with a lognormal probability distribution. The wavelength is assumed to be large as compared with the scale of heterogeneities of the medium. The permittivity ε(x) and the electric conductivity σ(x) satisfy the condition σ(x)/(ωε(x)) < 1, where ω is the cyclic frequency. The theoretical results obtained in the paper are compared with the results from direct 3D numerical simulation.
Time- and frequency-domain theory of multiwire magnetic transmission lines is presented for the first time. The familiar theory of electric multiconductor transmission lines (MTL) is based on the manipulation of two matrices, the longitudinal impedance and the transverse admittance. However, for magnetic MTLs, the key matrices are the transverse impedance and the longitudinal admittance. It is shown how the latter matrices are defined and how they should be used to determine the modal propagation constants and modal characteristic wave admittances that characterize the various travelling wave modes of magnetic MTLs. The theory is illustrated considering a three-wire system with three-fold symmetry. Simulation results, in the range 0.1 GHz to 10 GHz, are presented, showing that the magnetic MTL can exhibit superluminal phase velocity and zero attenuation dispersion.
Demand for wireless communication technologies and systems keep increasing and has reached the peak where the capacity can only be achieved by improving spectrum utilization. The spectrum allocated to TV broadcast systems can be shared by wireless data services through exploiting spatial reuse opportunities (Spatial TV white space). Path loss models are used extensively in signal prediction, coverage optimization and interference analysis. Recently, it is being used in estimating distances for safe operation of secondary users in TV white space. Peculiarities of these models give rise to high prediction errors when deployed in a different environment other than the one initially built for. It is however not very clear which model gives the best fit and what the penalties are for using the models outside the intended coverage area. In this paper, we assess the fitness of nine empirical widely used path loss models using five novel metrics to gauge their performance. In order to achieve this, field strength measurements were conducted in the VHF and UHF regions along six different routes that spanned through the urban, suburban and rural areas of Kwara State, Nigeria. A program was developed in VB 6.0 language to compute the path losses for the empirical models. The measurement results were converted to path losses and are compared with the model's prediction. The results show that no single model provides a good fit consistently. However, Hata and Davidson models provide good fitness along some selected routes with measured RMSE values of less than 10 dB. ITU-R P.1546-4, Walfisch Ikegami (WI), Egli, CCIR and FSPL perform woefully, with higher RMSE and SC-RMSE (Spread Corrected RMSE) values. Further analysis on the error spread as a function of distance along 60 km route revealed that Hata and Davidson models show symmetry up to about 30 km with slight divergence between 24 km and 30 km, after which Davidson model gives lower prediction error along the route. The prediction errors for Davidson model distributes nearly symmetrically around the mean error of 2.15 dB. It is noteworthy that the Gaussian error distribution within the window of ±5 dB dominates the frequency counts. However, the error counts for CCIR model closely follow normal distribution with a mean error of -6.37 dB but Hata, FSPL, Walfisch Ikegami and ITU-R P. 529-3 models do not follow normal distribution curve.
Near-field inductive channels created between two or more magnetically coupled coils are studied in this paper. Peer-to-peer configurations and array architectures are discussed. The array channels are used for cooperative relaying with inductive methods with potential to provide range extension and enhanced data rate access in magnetic induction communication systems. The received power shows the presence of the nearest neighbour interactions and the influences of higher order coupling from nodes two or more positions away from the receiver. This influence causes phase changes in the communication system. Four methods of exciting the antenna arrays are proposed. They are array edge excitation, center excitation, collinear array excitation and multi-array excitation. Experiments with hardware nodes show that while array edge excitation provides increased power at the array edge, it is out performed by array center excitation which results to twice the power captured at the array center node compared to the power captured at edge excited first element. We demonstrate by example that a receiver is influenced most by its neighbouring nodes on both sides and that the effects of second and third tier neighbours are relatively insignificant.
A time domain chipless RFID tag based on cascaded microstrip coupled transmission line sections (C-sections), which can operate in multi-frequency bands is presented. The group delay characteristics of the C-sections are exploited to generate the tag Identification (ID). The tag comprises cascaded commensurate group of C-sections and two cross-polarized ultra wide-band (UWB) antennas. Since the proposed tag can operate in multi-frequency, this paper proves the possibility of increasing the coding capacity compared to the existing time domain designs. A tag operating at ISM (Industrial Scientific and Medical) bands at 2.45 GHz and 5.8 GHz together with conformance of frequency and power regulations is discussed elaborately. The proposed device is designed, prototyped and experimentally verified. The time domain characteristic of the tag is also validated experimentally by interrogating with a short pulse. Furthermore, measurement results obtained using a commercial UWB (Ultra Wide Band) radar which can be used a chipless RFID reader is also incorporated. The obtained results confirm the concept and the possibility of using temporal multi-frequency in chipless RFID.
Magnetic angle sensors detect the angular position of a permanent magnet attached to a rotating shaft. The magnet is polarized diametrically to the rotation axis. No soft magnetic flux guides are present. The semiconductor die is placed on and orthogonal to the rotation axis. There are two kinds of systems: (i) perpendicular systems detect the field components perpendicular to the rotation axis, and (ii) axial systems detect the component parallel to the rotation axis. The former use magneto-resistive sensors or vertical Hall effect devices; the latter use Hall plates. This paper focuses on axial systems, derives their conceptual limitations, and compares them with perpendicular systems. An optimized system and optimum shapes of magnets are reported. Angle errors due to assembly tolerances of magnet and sensor versus shaft are explained. It is proven that assembly tolerances of optimized axial systems give three times larger errors than perpendicular systems.
A novel design of a CPW fed printed monopole antenna for dual polarization applications is proposed in this paper. The monopole is formed of a rectangular patch embedded with a hour-glass shaped slot. In a modified version of the antenna, an additional spiral shaped slot is incorporated in the ground plane. The overall dimensions of the antenna are kept at 40 x 40 mm. The impedance bandwidth achieved by the first antenna is 123% from 2.5 GHz to 10.5 GHz which is further increased to 145.5% at the center frequency of 11 GHz with the second antenna. A low polarization ratio (< 10 dB) arising from increased cross-polarization is obtained in the frequency band of 4 GHz to 10 GHz making the antenna useful for dual-polarization applications in this band.
Magnetic Resonance Imaging (MRI) technique is one of the most useful diagnostic tools for human soft tissue analysis. Moreover, the brain anatomy features and internal tissue architecture of brain tumor are a complex task in case of 3-D anatomy. The additional spatial relationship in transverse, longitudinal planes and the coronal plane information has been proved to be helpful for clinical applications. This study extends the computation of gray level co-occurrence matrix (GLCM) and Run length matrix (RLM) to a three-dimensional form for feature extraction. The sub-selection of rich optimal bank of features to model a classifier is achieved with custom Genetic Algorithm design. An improved Extreme Learning Machine (ELM) classifier algorithm is explored, for training single hidden layer artificial neural network, integrating an enhanced swarm-based method in optimization of the best parameters (input-weights, bias, norm and hidden neurons), enhancing generalization and conditioning of the algorithm. The method is modeled for automatic brain tissue and pathological tumor classification and segmentation of 3D MRI tumor images. The method proposed demonstrates good generalization capability from the best individuals obtained in the learning phase to handle sparse image data on publically available benchmark dataset and real time data sets.
A 2-D analytic based eddy-current transient model for a conducting plate is derived that is capable of accounting for continuous changes in the input conditions. Only the source field on the surface of the conducting plate needs to be known. In addition, a 2-D steady-state analytic based eddy-current model that is capable of accounting for frequency and velocity changes in two directions is derived. Both analytic based models have been validated using finite element code. The transient and steady-state models are integrated into an electromechanical system where the magnetic source is a Halbach rotor. The accuracy of both calculation methods is compared. The stiffness and damping coefficients are derived using the steady-state model.
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