In this paper, linear lightning diffusion into a Faraday cage is studied. The high-altitude Electromagnetic Pulse (HEMP) and nearby lightning are used as examples for a uniform field drive and the direct-strike lightning adjacent to the enclosure is used as a worst-case configuration of a line source excitation. The time-derivative of the magnetic field (HDOT) inside the enclosure for a uniform field drive with a decaying exponential waveform is analyzed and numerically determined. The physically relevant time-derivative of the magnetic field and voltage characterizations of an optimum coupling loop inside the enclosure for a decaying exponential waveform in a worst-case line source coupling configuration are numerically determined. First, the impulse and the unit step response peaks are shown to bound the decaying exponential peaks. Next, a simple fit function for a decaying exponential peak HDOT or a voltage bound for a single-turn loop inside the Faraday cage is constructed from peak responses of the unit step and impulse limiting cases. Excitations used are from (1) a uniform field drive of HEMP or nearby lightning and (2) a line source of direct-strike lightning. Comparisons of HDOT and voltage bounds of the fit function and actual numerical evaluations are given in Table 3.
We present an ω-k approach based on the use of a 1D Non-Uniform FFT (NUFFT) routine, of NER (Non-Equispaced Results) type, programmed on a GPU in CUDA language, amenable to real-time applications. A Matlab main program links, via mex files, a compiled parallel (CUDA) routine implementing the NUFFT. The approach is shown to be an extension of an already developed parallel algorithm based on standard backprojection processing to account also for near-field data. The implementation of the GPU-based, parallel NUFFT routine is detailed and the computational advantages of the developed approach are highlighted against other confronted sequential or parallel (on multi-core CPU) procedures. Furthermore, the benefits of the $\omega$-k, NUFFT-based processing are pointed out by both comparing its accuracy and computational convenience against other interpolators, and by providing numerical results. By comparing the computational performance of the algorithm against a multi-core, Matlab implementation, the speedup has been about 20 for a medium size image. The performance of the approach has been pointed out in the applicative case of vegetation imaging against experimental data of a boxtree (Buxus tree), also under a source of temporal decorrelation (wind).
A new permittivity is defined for anisotropic dielectrics with permanent polarization, which allows obtaining simple connections between the quantities of electric field. As an application, using the defined quantity, we will demonstrate advantageous forms of the refraction theorems of the two-dimensional electric field lines at the separation surface of two anisotropic dielectrics with permanent polarization, anisotropic by orthogonal directions.
This paper deals with the evaluation of the electric and magnetic field generated by a set of N periodically distributed filamentary conductors, in a circular arrangement. The results obtained lead to the computation of a continuous product of distances. In close connection with the computation of such a continuous product, the general problem of the factorization of a sum or difference of two powers, aN±bN, where a and b are positive real numbers and N a positive integer, is addressed.
Based on the magnetocaloric effect, magnetic refrigeration at room temperature has, for the past decade, been a promising and environmentally friendly technology predicted to have a significantly higher efficiency than the present conventional methods. However, to the authors' knowledge, so far no prototypes have been presented for large scale applications. This paper presents the modeling of a superconducting-based magnetic refrigeration system for large scale applications. On one hand, electromagnetic computations are undertaken to maximize magnetic field produced in order to get the best performance (temperature span and cooling power) and to limit the mechanical efforts (forces and torque). On the other hand, the thermal modeling aims to evaluate and to optimize the cooling performance.
This paper presents a new method for computing fields diffracted by a wedge for the MECA formulation, which is valid not only for perfect electric conductors but also for lossy penetrable dielectrics. The method is based on the computation of a wedge correction matrix, which establishes a mapping function between fields incident at and diffracted by the wedge. The MECA method is based, in general, upon the oblique incidence of a plane wave at the interface between free space and lossy dielectric media. MECA reduces to the well-studied physical optics (PO) formulation in case of PEC (perfect electric conductor) scatterers. In this work, we consider a scenario involving diffraction caused by a plane wavefront incident on a wedge with flat faces and straight edge. The version of the stationary phase method for three-dimensional equivalent source distributions is employed to calculate the asymptotic contribution of the integration boundary along the edge of the diffraction wedge. This contribution of the critical boundary points is compared to the GTD (geometrical theory of diffraction) diffracted field in order to obtain the correction matrix by which the incident electric field vector is multiplied in MECA. As required to accomplish this comparison, the three-dimensional incident electric field is previously resolved into an edge-fixed coordinate system. Good agreement is demonstrated between full-wave method-of-moments (MoM) results and the results obtained by modifying MECA with our diffraction correction technique. is demonstrated between full-wave method-of-moments (MoM) results and the results obtained by modifying MECA with our diffraction correction technique.
In this paper, a level set method for shape reconstruction problems is considered. By measuring the scattered field, we tried to retrieve the localisation and permittivity of buried objects. The forward problem is solved by the method of moments. For solving the inverse problem, we adopt an evolution approach. Therefore, we introduce a level set technique witch is flexible in handling complex shape changes. A conjugate gradient-based method is used in order to define iterative updates for the level set functions with the goal to minimize a given least squares data misfit functional. In particular, the proposed method is capable of creating new holes inside the design domain, which makes the final design independent of Experimental results demonstrate the feasibility and effectiveness of the proposed technique.
The focusing properties of six array configurations in the form of square, square with interlaced elements, square ring, cross (+) shape, cross (X) shape, and square ring plus diagonals shape arrays are investigated. The performance parameters, such as field distribution in the focal region, size of the focal spot, depth of field, level of field at focal point, and sidelobe structure, are compared. Computer simulations using MTALAB environment are performed in the investigations. The square ring and square ring plus diagonals configurations show favorable focusing properties. The resultant field patterns will help to find the arrays usefulness for hyperthermia and imaging applications.
Characteristics of reflected power from a planar interface of chiral and/or chiral nihility media have been investigated theoretically. Focus of the study is tunneling and rejection of power associated with these interfaces. Effect of polarization of incidence field and parametric dependence on reflected power have been noted. It is found from numerical results that power tunneling and rejection have strong dependency on the polarization of incidence field, angle of incidence, and chirality parameter.
Long data collecting time is one of the bottlenecks of the stepped-frequency continuous-wave ground penetrating radar (SFCW-GPR). We discuss the applicability of the Compressive Sensing (CS) method to three dimensional buried point-like targets imaging for SFCW-GPR. It is shown that the image of the sparse targets can be reconstructed by solving a constrained convex optimization problem based on l1norm} minimization with only a small number of data from randomly selected frequencies and antenna scan positions, which will reduce the data collecting time. Target localization ability, performance in noise, the effect of frequency bandwidth, and the effect of the wave travel velocity in the soil are demonstrated by simulated data. Numerical results show that the presented CS method can reconstruct the point-like targets in the right position even with 10% additive Gaussian white noise and some wave travel velocity estimation error. p
An efficient numerical solution is been developed to compute the impedances of rectangular transmission lines. Method of moments is applied to integral equations for the current density, where the cross section is discretized, to improve the convergence, by a nonuniform grid that obeys the skin effect. Powerfulness of this approach up to rather high frequencies is verified by comparing with asymptotic formulas and other references. Detailed discussion is given for the current density distribution and its effect to the impedance, especially for a high frequency range.
We introduce an electromagnetic investigation of the complex experimental setup used in studying the Ratchet Effect at low We introduce an electromagnetic investigation of the complex experimental setup used in studying the Ratchet Effect at low temperature. This investigation, based on intensive electromagnetic simulations, shows that a compromise has to be taken into consideration between the physical aspects, the technological and the practical restrictions as well as the electromagnetic conditions of the observed phenomenon. By improving the electromagnetic response of the whole system, the Ratchet induced photovoltage can be increased, and hence the Ratchet device can be used for practical applications in wireless communications.
An ultra-wideband microwave imaging system that employs a heterogeneous breast phantom and covers the ultra-wideband (UWB) frequency range (3.1 GHz to 10.6 GHz) is presented. The platform scanning system allows monostatic and bistatic mode of operation. In this work, developed heterogeneous phantoms are used to mimic the realistic breast tissues. A utilized tapered slot antenna array allows for a high resolution hemispherical scan, achieved by rotating the imaged object on a turntable. Full design details of the scanning system and the utilized post-processing algorithm are explained. To validate the reliability of the presented system, the results of several imaging cases, including the challenging low dielectric contrast case, are presented.
A new image reconstruction algorithm for early breast cancer detection using ultra-wideband microwave signals is proposed. In this algorithm, the backscattered electric and magnetic fields are measured and combined in a novel way; the direction of power flow with respect to a given focal point is used to localize tumors. Significant improvement in signal-to-mean raito (SMR) and signal-to-clutter ratio (SCR) are achieved when driving signals consist of waves with multiple polarizations. Numerical results demonstrate nearly 5.5 dB improvement of SMR and SCR over the traditional Confocal Microwave Imaging method when a single 8 mm breast tumor is present. Breast Cancer Facts Figures 2011-2012
Lorentz Reciprocity principle is often used to describe electrical networks and reception/radiation properties of antennas residing in a linear, time-invariant, and symmetric medium. In its reaction integral form, it is usually conceived as a mathematical tool to prove electromagnetic relations. However, reciprocity, more than a mathematical tool, can be used as a powerful alternative to convert a penetration problem into a radiation one for numerical computations and measurements. We review the reciprocity formulation and show simple steps on how to apply reciprocity to penetration problems. Numerical calculations for a wire probe (antenna) inside missile-like structure are carried out for both radiation and its reciprocity formulated penetration problems, and it is shown numerically that results from both methods are identical. One of the advantages of this indirect formulation is that the radiation properties of the structure can be easily measured contrary to the direct measurement of the penetrated signal inside the structure.
Pipelines are the most common apparatus in industries; therefore, the need for inspection during the manufacturing, construction and the operation stage is inevitable and invaluable. Magnetic Induction Tomography (MIT) is a new type of tomography technique that is sensitive to the electrical conductivity of objects.~It has been shown that the MIT technique is appropriate for imaging materials with high electrical conductivity contrasts; hence, the majority of the MIT systems were designed for detecting metallic objects. In this paper, MIT technique was proposed for pipeline inspection. Structural damages of the outer surface of the pipe were considered in this study. Nonetheless, it is challenging to use the traditional MIT pixel based reconstruction method (PBRM) as a suitable pipelines inspection tool because of the limited resolution. A narrowband pass filtering method (NPFM) of imaging pipe geometry was developed as a suitable image reconstruction method.~The proposed method can overcome the resolution limitations and produce useful information of the pipe structure.~This paper shows the comparative results from the novel NPFM and from traditional PBRM. While the PBRM fails to detect damages in outer structure of the pipe the NPFM successfully indentifies these damages. The method has been verified using experimental data from very challenging test samples. It is well known that using a coil array with an imaging region of 100 mm the PBRM based MIT can retrieve information with accuracy of about 10 mm (about 10%). With proposed NPFM the information on a resolution of 2 mm (which is about 2%) can be detected using the same measurement data.
This paper describes an original approach for determining independent loops needed for mesh-current analysis in order to solve circuit equation system arising in inductive Partial Element Equivalent Circuit (PEEC) approach. Based on the combined used of several simple algorithms, it considerably speed-up the loops search and enables the building of an associated matrix system with an improved condition number. The approach is so well-suited for large degrees of freedom problems, saving significantly memory and decreasing the time of resolution.
Recently, many numerical methods that are developed for the solution of electromagnetic problems have greatly benefited from the hardware accelerated scientific computing capability provided by graphics processing units (GPUs) and orders of magnitude speed-up factors have been reported. Among these methods, the finite-difference frequency-domain (FDFD) method as well can be accelerated substantially by utilizing an efficient algorithm customized for GPU computing. In this contribution, an algorithm is presented that treats iterative solution of the FDFD linear equation system similar to solution of three-dimensional Finite-Difference Time-Domain (FDTD) method, which inherently yields itself to high level parallelization. The presented algorithm uses BICGSTAB iterative solver. Integrated with BICGSTAB, an efficient method of performing matrix-vector products for the linear system of FDFD equations is adapted and implemented in Compute Unified Device Architecture (CUDA). It is shown that FDFD can be solved with a speed-up factor of more than 20 on a GPU compared with the solution on a central processing unit (CPU), while memory usage as well can be reduced substantially with the presented algorithm.
The frequency difference between signal-under-test and reference signal in phase demodulation will affect the result of the actual phase noise measurement. In order to eliminate the effect, an algorithm for both eliminating the frequency difference and extracting the phase noise of the signal-under-test is presented. Simulation and experiment results show that this algorithm is effective. By using the algorithm in our experiment, the noise floor of the measurement system is improved by 10.1 dB and 9.3 dB, respectively, and the measurement precision is improved from 90.03% to 96.31%. In addition, the use of this algorithm can lower the requirement on the frequency precision of reference source and reduce the cost of measurement system.
Stability and dispersion analysis for the three-dimensional (3-D) leapfrog alternate direction implicit finite difference time domain (ADI-FDTD) method is presented in this paper. The leapfrog ADI-FDTD method is reformulated in the form similar to conventional explicit FDTD method by introducing two auxiliary variables. The auxiliary variables serve as perturbations of the main fields variables. The stability of the leapfrog ADI-FDTD method is analyzed using the Fourier method and the eigenvalues of the Fourier amplification matrix are obtained analytically to prove the unconditional stability of the leapfrog ADI-FDTD method. The dispersion relation of the leapfrog ADI-FDTD method is also presented.