Effective permittivity and permeability of a medium consisting of an infinite number of ferromagnetic microwires are evaluated in this paper. Analysis is carried out with the help of local and average fields inside a unit cell. In the literature, effective permittivity of the microwire grid is obtained by assuming the grid as an impedance loaded surface. The analysis is applicable only for the case of TM_{z} polarized normally incident wave. Proposed analysis enable us to evaluate all the three diagonal components of effective permittivity and permeability for arbitrarily incident uniform plane wave having arbitrary polarization angle. Numerical results are obtained through MATLAB, and a comparison is done with the results available in the literature for validation. Numerical results have shown a DNG like behaviour of the medium for a TM_{z} polarized incident wave.
In this paper, a fast time domain imaging algorithm called bistatic forward-looking fast factorized backprojection algorithm (BF-FFBPA) based on sub-aperture and sub-image is proposed for general bistatic forward-looking synthetic aperture radar (BFSAR) with arbitrary motion. It can not only accurately dispose the large spatial variant range cell migrations and complicated motion errors, but also achieve high imaging efficiency. First, the imaging geometry and signal model are established, and the implementation of backprojection algorithm (BPA) in the BFSAR imaging is given to provide a basis for the proposed BF-FFBPA. Then, considering motion errors, the more accurate requirements of splitting sub-aperture and sub-image in the BF-FFBPA is introduced based on the range error analysis to offer the tradeoff between the imaging quality and efficiency. Finally, the implementation and computational burden of the BF-FFBPA is provided and analyzed. Simulated results and evaluations are given to prove the correctness of the theory analysis and the validity of the proposed approach.
An efficient and accurate hybrid model has been developed for the electromagnetic leakage from two apertured cascaded metallic rectangular enclosures connected by a metallic plate with an aperture covered by a non-magnetic conductive sheet excited by an electric dipole located in the enclosure. The leakage fields through the covered aperture are derived by using the dyadic Green's function and employing the approximate boundary conditions at both sides of the sheet which is regarded as an infinite conductive plate. Then, the leakage fields into the external space through the aperture regardless of its thickness at the end of the enclosure are derived based on a generalization of the method of moments (MoM). Finally, the shielding effectiveness (SE) at the target points outside the enclosure is calculated for the intermediate analysis of the leakage fields. Comparison with the full wave simulation software CST has verified the model over a wide frequency band. The hybrid model then is employed to analyze the effect of different factors including the thickness and the conductivity of the conductive sheet on the SE, and the corresponding physical mechanisms of the leakage fields are also illuminated. The hybrid model can also be extended to deal with other cases, including the whole plate made of non-magnetic conductive material without apertures, the infinite thickness of the aperture at the end of the enclosure, and the aperture at the end of the enclosure is also covered by a non-magnetic conductive sheet.
The analysis of the electromagnetic scattering from perfectly electrically conducting (PEC) objects with edges and corners performed by means of surface integral equation formulations has drawbacks due to the interior resonances and divergence of the fields on geometrical singularities. The aim of this paper is to show a fast converging method for the analysis of the scattering from PEC polygonal cross-section closed cylinders immune from the interior resonance problems. The problem, formulated as combined field integral equation (CFIE) in the spectral domain, is discretized by means of Galerkin method with expansion functions reconstructing the behaviour of the fields on the wedges with a closed-form spectral domain counterpart. Hence, the elements of the coefficients' matrix are reduced to single improper integrals of oscillating functions efficiently evaluated by means of an analytical asymptotic acceleration technique.
Electrical conductivity imaging in the human body is usually pursued by either electrical impedance tomography or magnetic induction tomography (MIT). In the latter case, multiple coils are almost always used, so that nonlinear reconstruction is preferred. Recent work has shown that single-coil, scanning MIT is feasible through an analytical 3D convolution integral that relates measured coil loss to an arbitrary conductivity distribution. Because this relationship is linear, image reconstruction may proceed by any number of linear methods. Here, a direct method is developed that combines several strategies that are particularly well suited for inverting the convolution integral. These include use of a diagonal regularization matrix that leverages kernel behavior; transformation of the minimization problem to standard form, avoiding the need for generalized singular value decomposition (SVD); centering the quadratic penalty norm on the uniform solution that best explains loss data; use of KKT multipliers to enforce non-negativity and manage the rather small active set; and, assignment of the global regularization parameter via the discrepancy principle. The entire process is efficient, requiring only one SVD, and provides ample controls to promote proper localization of structural features. Two virtual phantoms were created to test the algorithm on systems comprised of ~11,000 degrees of freedom.
A mathematical model of a large rectenna array (LRA) is presented. It is shown that matrices describing the LRA linear subsystem have a number of specific features that must be considered when the rectenna mathematical model is developed. The state equation for the LRA was obtained. It is shown that the model functioning in nonlinear mode of the infinite rectenna array can be reduced to finding the parameters of one equivalent receiver-rectifier element (RRE) at the fundamental frequency and its harmonic. The external parameters of the RRE and LRA characteristics were obtained.
In this paper the results of the estimated electric field associated with tortuous lightning paths at close distance (50 m to 500 m) are shown. Such results are compared with experimental data available in the literature and are illustrated along with a quantitative analysis of the field waveforms and their frequency spectra. The limits of the usual straight-vertical channel assumption and the influence of tortuosity at different azimuth and distances from the lightning channel base are also highlighted.
In this paper, the computation of forces and torques mutually applied between a helical toroidal magnet and a magnet shaped like an angular plane sector is illustrated. The evaluation considers the magnetostatic field hypothesis. The main aim of this study is to furnish a tool for performing fast and accurate evaluation of forces and torques based on the method of the magnetic charges with reference to helical toroidal magnetic systems. The particular geometry of the case study concerns the development of unconventional configurations of electrical machines. These configurations should reduce the magnetic flux changing during the machine operation. A small change of the magnetic flux reduces all the losses associated to the flux variation. The illustrated model for the computation of forces and moments also represents a starting point for a reliable analytical numerical evaluation of the external/internal actions applied to parts of other kinds of helical toroidal systems as stellarator and similar ones.
Magnetic anomaly detection (MAD) is to find hidden ferromagnetic objects, and a hidden object is often described as a magnetostatic dipole. Many detection methods are based on the orthonormal basis functions when the target moves along a straight line relatively to the magnetometer. A new kind of parabolic trail orthonormal basis functions (PTOBF) method is proposed to detect the magnetic target when the trajectory of the target is parabola. The simulation experiment confirms that the proposed method can detect the magnetic anomaly signals in white Gaussian noise when SNR is -15.56 dB. The proposed method is sensitive to the characteristic time and curvature. High detection probability and simple implementation of proposed method make it attractive for the real-time applications.
It is a widely held view that analytical integration is more accurate than the numerical one. In some special cases, however, numerical integration can be more advantageous than analytical integration. In our paper we show this benefit for the case of electric potential and field computation of charged triangles and rectangles applied in the boundary element method (BEM). Analytical potential and field formulas are rather complicated (even in the simplest case of constant charge densities), they have usually large computation times, and at field points far from the elements they suffer from large rounding errors. On the other hand, Gaussian cubature, which is an efficient numerical integration method, yields simple and fast potential and field formulas that are very accurate far from the elements. The simplicity of the method is demonstrated by the physical picture: the triangles and rectangles with their continuous charge distributions are replaced by discrete point charges, whose simple potential and field formulas explain the higher accuracy and speed of this method. We implemented the Gaussian cubature method for the purpose of BEM computations both with CPU and GPU, and we compare its performance with two different analytical integration methods. The ten different Gaussian cubature formulas presented in our paper can be used for arbitrary high-precision and fast integrations over triangles and rectangles.