In this paper, angular glint characteristics of a two-dimension (2-D) perfect electric conductor (PEC) target above a PEC rough surface are investigated. The induced surface currents on the target and on the rough surface are obtained by employing the method of moments com-bining UV matrix decomposition technique (MOM-UV). Based on electromagnetic (EM) theory and the phase-front distortion concept of angular glint, the formulae of angular glint for 2-D target are proposed, and angular glint is calculated precisely by using phase gradient method (PGM). The analysis of the result is implemented by means of numerical extraction of the coupling currents and relationship between the phase front and angular glint, thus revealing the effects of the coupling on the angular glint.
In this paper the propagation of electromagnetic waves in a medium with non zero conductivity is discussed, analyzing the dielectric properties of the sea water, in order to accurately characterize a wireless communication channel. Mathematical models for sea water dielectric constant, wavelength, propagation speed and path loss when an electromagnetic wave at 2.4 GHz propagates through sea water are presented. A Bow-Tie microstrip antenna that is required to overcome the high path loss and bandwidth requirements in sea water is studied. A dual-band antenna, with arc-shaped circular slots, operating for IEEE802.11 b/g/n standards, at 2.4 GHz and 5.1 GHz for WLAN communications, with dimensions 1.4 cm2 is implemented. Return loss, input impedance and gain have been extracted in order to characterize antennas' performance in a conductive medium.
Permanent-magnets (PMs) with tangential and parallel magnetization directions are combined in the Halbach PM (HPM) machine, which can offer high performances. However, the existing lumped parameter magnetic circuit (LPMC) model can only calculate one PM magnetization direction, namely either tangential direction or parallel direction. The key of this paper is to propose a method to divide and establish equivalent magnetic motive force (MMF) for HPM machine with both tangential and parallel magnetizations. Then, a LPMC model, using equivalent MMF, is developed to predict the electromagnetic performances for a four-phase HPM machine. In order to verify the effectiveness of the proposed LPMC model, a 6-pole/8-slot 15 kW HPM prototype is built. The comparative results of the proposed LPMC model, finite-element results and the experiments verify the effectiveness of the proposed LPMC model.
This paper evaluates and compares the reflection loss, absorption loss and electromagnetic shielding effectiveness of a diverse range of shield. A design methodology is presented to yield these three quantities and propose a new relation of equivalent impedance for multilayer conductive sheets with considering the equivalence between single and the laminated structure. Analysis is carried out for the study of three shields: i) Polyaniline/polyurethane (PANI/PU), ii) Aluminum-Polyaniline/polyurethane-Aluminum (Al-(PANI/PU)-Al), iii) Nickel-Polyaniline/polyurethane-Aluminum (Ni-(PANI/PU)-Al) in the case of oblique incidence for electrical and magnetic polarization.
Based on a proposed inexact Hodge decomposition, this paper describes a viable scheme using the second order finite elements in the T-Ω method considering multiply-connected regions for the eddy current problems. Several numerical examples have been presented to demonstrate the effectiveness of this scheme.
In this article, the mixed potential integral equation is discretized using the Rao-Wilton-Glisson basis functions in order to obtain a method of moments matrix equation for a source reconstruction problem. The weighting functions used in the setup of the moments equation are Dirac delta functions. The entries of the moments matrix are computed using a semi-analytical method which is applicable to any method of moments problem with point matching. The analytical calculation is made possible by employing a differentiation property of the scalar Green function and the properties of the mesh elements of the source plane. The semi-analytical method makes it easier to increase the accuracy of the moments matrix elements. The accuracy of the method is shown by comparing the results obtained using the semi-analytical method to those obtained by a fully numerical procedure.
Performance of a harmonic transponder strongly depends on the properties of the antenna and diode used, which makes finding a good combination of them very important. For a transponder with a fixed antenna geometry, the effect of different diodes is analyzed through electromagnetic simulations and theoretical calculations. The antenna used in the transponder is directly matched to the impedance properties of a particular diode. Effects of both detector and varactor diodes on the return loss characteristics of the antenna and the obtainable transponder response are observed. Criteria for selecting a suitable diode are given. Benefits and drawbacks of using different antenna matching techniques are discussed, and principal design steps are given both for transponders matched directly to the antenna and for transponders with external matching circuits.
Due to the inaccuracies in radar's measurement, autofocus including range alignment and phase compensation is always essential in inverse synthetic aperture radar (ISAR) imagery. Compressed sensing (CS) based ISAR imagery suggests that the image of target can be reconstructed from much fewer random pulses. Because the number of pulses is inadequate and the pulse intervals are nonuniform, conventional phase compensating algorithms can't work in CS imaging. In this paper, an iterative algorithm is proposed to compensate the phase errors and reconstruct high-resolution focused image from limited pulses. In each iteration, the image of target is reconstructed by CS method, and then the estimation of phase errors is updated based on the reconstructed image. By cycling these steps, well-focused image can be obtained. The smoothed ℓ0 algorithm is used to reconstruct the image, and the idea of minimum entropy optimization is used to estimate the phase errors. Besides, a method of extracting range bins in range profile based on amplitude information is proposed, which can reduce the computational complexity and improve the speed of convergence considerably. Both simulation and experiment results from real radar data demonstrate the effectiveness and feasibility of our method.
Two-dimensional (2D) electromagnetic scattering from a target above the sea with breaking water wave is studied by a multiregional iterative analytical-numerical method that combines the boundary integral method (BIM) and the Kirchhoff approximation (KA). Based on the ``Pierson-Moskowitz'' (PM) sea surface and the LONGTANK breaking wave, a theoretical model of a target above the rough sea surface with breaking wave is built firstly in this paper. Unlike traditional sea surface, the multipath scattering between the crest of the breaking wave and the target cannot be accurately predicted based on KA alone. To improve the algorithm precision, a multiregional hybrid analytical-numerical method is proposed. In our multiregional model, the whole sea is divided into two subregions: the breaking wave and the PM sea surface. The scattering from the breaking wave and the object is well approximated by BIM, while the PM sea surfaces can be estimated very well by KA based on Fresnel theories. Taking the interaction between KA region and BIM region into account, an iterative system is developed which gives a quick convergence. The hybrid technique presented here is highly efficient in terms of computing memory, time consumed, and versatility.
We theoretically investigate the photonic band gaps in one-dimensional photonic crystals based on nanocomposite of silver nanoparticles. The dielectric permittivity is calculated in accordance with temperature dependence of plasma frequency of silver nanoparticle. The effect of temperature on these structures by incorporating the volume expansion coefficient of nanoparticle is analysed. The behaviors of photonic band gaps with variation of nanoparticle concentration, radii of nanoparticle, thickness of the layers and temperature are observed. The evolution of these results leads to designing the desired photonic crystals.
Linear array SAR (LASAR) has been attracting more and more attention for its capability of obtaining three dimensional (3D) resolutions. However, the low resolution in cross track (CT) direction limited by the length of its linear antenna array has become the bottleneck of its practical applications. To overcome this problem, we present a novel algorithm based on sparse reconstruction (SR) to improve the resolution in CT direction. First, it establishes a 1D real-valued sparse model for LASAR, which deals with the 3D image column by column along CT direction in each equi-range slice. This enables it to handle large scenes. Second, it employs the spatially variant apodization (SVA) to filter bases of the measurement matrix. As a result, the cross coherence gets suppressed as well, and it is helpful to improve the performance of sparse reconstruction algorithms (SRAs). Third, we propose the resolution enhancement ability (REA), which provides a new idea to evaluate how many times the resolution could be improved. Experimental results validate that when the signal to noise ratio (SNR) is 30 dB, LASAR could usually obtain 2 times of resolution improvement in CT direction, while the proposed method further improves the REA by a factor about 2.5. Moreover, the 3D surface terrain simulation shows a great improvement for the digital elevation map (DEM) in resolution enhancement.
A new class of incomplete Bessel polynomials is introduced, and its application to the solution of electromagnetic problems regarding transient wave radiation phenomena in truncated spherical structures. The definition of said special functions is introduced, and the relevant analytical properties are derived. The definition is such that the interrelationships between the incomplete polynomials parallel, as far as is feasible, those for canonical Bessel polynomials.
Spatial resolution represents akey performance aspect in electrical capacitance volume tomography (ECVT). Factors affecting the resolution include the ``soft-field'' nature of ECVT, the number of capacitance channels used, the ill-conditioned nature of the imaging reconstruction problem, and the signal-to-noise ratio of the measurement apparatus. In this study, the effect of choosing different numbers of capacitance plates on the performance of ECVT is investigated. Specifically, two ECVT sensors with 12 and 24 capacitance channels but covering equal volumes of a cylinder are used to examine the resulting impact on the image resolution.
Overhead power transmission line is influenced by the resistivity of earth return path. The topic is developed in literature by considering a homogeneous and isotropic earth, or verily the soil is more represented by several layers. The scope of this paper is to provide an equivalent homogeneous soil to the two layers stratified soil. The equivalent electromagnetic properties of the soil are calculated using an accurate minimization method. Numerical results presented in this paper, show the efficiency of the proposed model.
The analytical expressions for corona discharge currents are usually represented by the mathematic models based on curve fitting method. For the complex mechanisms, none of these currently models can describe a measured corona current with arbitrary waveforms. A novel curve fitting method using BP neural network (BPNN) technique is applied to describe the mathematic model of the corona currents in time domain. The analytical expressions for the currents can be established via extracting the weights and thresholds parameters of the trained BPNN. The expressions all have the same structure which has only four types of parameters, and the structure is independent of the corona current waveforms. A curve fitting for the measured corona currents with arbitrary waveforms by different models was carried out, and the results were analyzed, which indicate that the BPNN method performs best. Compared with the current expressions fitted by the double exponential function and Gaussian function, the expressions by BPNN can fit the current waveforms with the lowest mean square error (MSE) in time domain and the highest accuracy to spectra of the currents in frequency domain. The proposed method is suitable for establishing a unified analytical expressions model for corona currents with arbitrary shapes.
In this paper, the dynamics of rain attenuation are examined, and dynamic diversity gain is evaluated for a pico-scale site diversity system. Since modern satellite communication systems operate at frequencies above 10 GHz, their efficient design requires the adoption of Propagation Impairment Mitigation techniques and so rain attenuation time series synthesizers. For rain attenuation, which is the most dominant fading mechanism, the dynamic stochastic model, proposed by Maseng-Bakken, based on the lognormal distribution is the most widely accepted and used. In this latter model, the dynamic parameter is required for the generation of slant path rain attenuation time series. In this paper, firstly, a simple expression is proposed for the calculation of the dynamic parameter in terms of the mean wind speed, elevation angle of the link, and dynamic parameter of rainfall rate. The new theoretical expression is tested with simulated data with very encouraging results. This expression is then used into a unified rain attenuation synthesizer with inputs from the rainfall rate statistics and the satellite slant path characteristics. Finally, the dynamic diversity gain is calculated for pico-scale site diversity systems for various link characteristics.
The origin of omnidirectional band gaps in one-dimensional layered photonic structures which are aligned according to the generalized Kolakoski in flation rule are studied using the transfer matrix formalism. On their basis some particular designs of cascaded aperiodic heterostructures are proposed. It is found that the proposed cascaded structures stand out by the omnidirectional reflection bands which cover whole near-infrared spectral region.
We analyze and discuss an ultra-compact metamaterial absorber (MA) by introducing meander lines into the resonant cells and covering another dielectric layer onto the MA. The size reduction procedures are presented step by step and an ultra-compact metamaterial absorber with in-plane (lateral) dimension of λ/28 and vertical thickness of λ/37 is obtained. We further present two variations of MA congurations which can reach similar ultra-compact sizes. The proposed ultra-compact MAs show near-unity absorption under a wide range of incident angles for both TE and TM radiations.
Height extraction by radar remote sensing is an attractive issue for the building detection and recognition. According to the analysis on the building geometrical properties in the SAR imagery, a novel height estimation algorithm is proposed following a model-based geometrical structure prediction and matching strategy. The range Doppler equation is introduced and simplified for the building 2D geometrical structure prediction in the slant image plane. An evaluation function implementing the ratio of exponentially weighted averages (ROEWA) is also established for the matching between the predicted structure and the observed SAR image. By incorporating the genetic algorithm (GA), the evaluation function is maximized to get the optimal height parameter. The experimental results with the simulated and real airborne and spaceborne SAR images show that the proposed method could efficiently estimate building height from single SAR imagery, and achieve better performance than two popular algorithms with the partial occlusion case.
In this paper, a 3D quasi-static numerical algorithm for computation of the magnetic field produced by power lines is presented. These power lines can be overhead power line phase conductors and shield wires or buried cable line phase conductors. The basis of the presented algorithm is the application of Biot-Savart law and the thin-wire approximation of cylindrical conductors. The catenary form of the power line conductors is approximated by a set of straight cylindrical segments. By summing up contributions of all conductor segments, magnetic field distribution is computed. On the basis of the presented theory, a FORTRAN program PFEMF for computation of the magnetic flux density distribution was developed. For each conductor catenary, it is necessary to define only global coordinates of the beginning and ending points and also the value of the longitudinal phase conductor current. Global coordinates of beginning and ending points of each catenary segment are generated automatically in PFEMF. Numerical results obtained by program PFEMF are compared with results obtained by simple 2D model and results obtained using software package CDEGS.