This paper is the third part of a series dealing with permanent magnet passive magnetic bearings. It presents analytical expressions of the axial force and stiffness in radial passive magnetic bearings made of ring permanent magnets with perpendicular polarizations: the inner ring polarization is perpendicular to the outer ring one. The main goal of this paper is to present a simple analytical model which can be easily implemented in Matlab or Mathematica so as to carry out parametric studies. This paper first compares the axial force and stiffness in bearings with axial, radial and perpendicular polarizations. Then, bearings made of stacked ring magnets with alternate polarizations are studied for the three kinds of polarizations, axial, radial and perpendicular. The latter correspond to Halbach structures. These calculations are useful for identifying the structures required for having great axial forces and the ones allowing to get great axial stiffnesses.
The paper deals with the analysis of the magnetic field distribution near the transition tower of an overhead-underground transmission line of 110 kV. The current density induced in the human body due to this field is also estimated. A hybrid numerical technique combining both the boundary element method and the charge simulation method is employed for this purpose. This technique is implemented in the author's own software package dedicated to the analysis of electromagnetic exposure in the vicinity of power objects. A simplified numerical model of the human body of dimensions recommended by the IEC/EN standards is employed in computations. Obtained numerical results are related to the appropriate regulations regarding the human exposure to the electromagnetic fields.
A generalized version of the weighted-averages method is presented for the acceleration of convergence of sequences and series over a wide range of test problems, including linearly and logarithmically convergent series as well as monotone and alternating series. This method was originally developed in a partitionextrapolation procedure for accelerating the convergence of semiinfinite range integrals with Bessel function kernels (Sommerfeld-type integrals), which arise in computational electromagnetics problems involving scattering/radiation in planar stratified media. In this paper, the generalized weighted-averages method is obtained by incorporating the optimal remainder estimates already available in the literature. Numerical results certify its comparable and in many cases superior performance against not only the traditional weighted-averages method but also against the most proven extrapolation methods often used to speed up the computation of slowly convergent series.
In this paper, we make an assumption that the inertia vibrations of the electron groups in the rock fragment of the crack tips generate EMR pulses during the fracture of rocks. Based on this assumption we develop an oscillating dipoles model to analyze and simulate the EMR phenomena induced by the rock fractures. Then we use this model to simulate the EMR pulses recorded in the Rabinovitch's compression experiments on granite and chalk. Our simulations indicate a comparable accordance with Rabinovitch's experimental results. From our simulation results, we also find that the crack width associates with the maximum EMR voltage peak value.
A semi-analytical model for the propagation of the repetition frequency high power microwave (HPM) pulses is established. The effects of different parameters of the repetition frequency HPM pulses on air breakdown are analyzed. A critical repetition frequency for the HPM pulse is presented under which the electron density does not exceed that of the air breakdown when the individual pulse arrives. The prediction for the critical repetition frequency and the threshold of the air breakdown due to the repetition frequency HPM pulses is demonstrated with several numerical simulations.
Scattering of electromagnetic (EM) waves by many small particles (bodies), embedded in a homogeneous medium, is studied. Physical properties of the particles are described by their boundary impedances. The limiting equation is obtained for the effective EM field in the limiting medium, in the limit a → 0, where a is the characteristic size of a particle and the number M(a) of the particles tends to infinity at a suitable rate. The proposed theory allows one to create a medium with a desirable spatially inhomogeneous permeability. The main new physical result is the explicit analytical formula for the permeability μ(x) of the limiting medium. While the initial medium has a constant permeability μ0, the limiting medium, obtained as a result of embedding many small particles with prescribed boundary impedances, has a non-homogeneous permeability which is expressed analytically in terms of the density of the distribution of the small particles and their boundary impedances. Therefore, a new physical phenomenon is predicted theoretically, namely, appearance of a spatially inhomogeneous permeability as a result of embedding of many small particles whose physical properties are described by their boundary impedances.
This paper presents the graphics processing unit (GPU) accelerated fundamental alternating-direction-implicit finite-difference time-domain (FADI-FDTD) with complex frequency shifted convolutional perfectly matched layer (CFS-CPML). The compact matrix form of the conventional ADI-FDTD method with CFS-CPML is formulated into FADI-FDTD with its right-hand-sides free of matrix operators, resulting in simpler and more concise update equations. Using Compute Unified Device Architecture (CUDA), the FADI-FDTD with CFS-CPML is further incorporated into the GPU to exploit data parallelism. Numerical results show that a much higher efficiency gain of up to 15 times can be achieved.
Terahertz spectroscopy brings precious complementary information in life science by probing directly low energy bindings inside matter. This property has been demonstrated on dehydrated substances, and interesting results are obtained on liquid solutions. The next step is the characterization of living cells. We have successfully integrated THz passive circuits inside Biological MicroElectroMechanical Systems (BioMEMS). They are based on metallic wires called Planar Goubau Line (PGL). We demonstrate that high THz measurement sensitivity can be reached with new design based on spirals. But we show that the principal interest of this design is its high spatial resolution below the wavelength size compatible with living cell investigation.
Excitation of electromagnetic ion-cyclotron instability in the magneto plasma in the presence of perpendicular A.C. electric field for a generalized distribution function for background cold electrons and hot ion plasma has been studied. This distribution function is reducible to anisotropic and loss-cone type for different values of spectral index j. The particle trajectories have been estimated and used to find the dispersion relation and growth rate by using the method of characteristic solutions. Temporal electromagnetic ion cyclotron instability for various plasma parameters has been studied. The role of choice of parameters, distribution function and simultaneous presence of a.c. electric field is studied for excitation of electromagnetic ion cyclotron instability. The results have been used to explain the satellite observations of AMPTE/CCE and compared with earlier work done for temperature anisotropy and other types of distribution functions using other techniques.
Several georeferenced measurements of electric field were done in a pilot area of Caracas, Venezuela, to verify that the magnitude of radio frequency electromagnetic fields is below the human exposure limits, recommended by the International Commission on Non-Ionizing Radiation Protection. The collected data were analyzed using geographical information systems, with the objective of using interpolation techniques to estimate the average electromagnetic field magnitude, to obtain a continuous dataset that could be represented over a map of the entire pilot area. This paper reviews the three methods of interpolation used: SPLINE, Inverse Distance Weighting (IDW) and KRIGING. A statistical assessment of the resultant continuous surfaces indicates that there is substantial difference between the estimating ability of the three interpolation methods and IDW performing better overall.
A novel time-domain physical optics (TDPO) is proposed to determine the transient response of electromagnetic scattering of electrically large homogeneous dielectric targets modeled with triangular facets. Formula of the novel TDPO is derived, in which a time-domain convolution product between the incident plane wave and the time-domain physical-optics (PO) integral is included. The time-domain PO integral is evaluated with a closed-form expression based on a Radon transform interpretation, which makes the novel TDPO highly efficient in speed. The wideband rador cross section (RCS) is conveniently obtained from the transient response with a fast Fourier transform (FFT). Numerical results demonstrate the efficacy of the new method.
The Epsilon-Near-Zero (ENZ) super-tunneling structure with weakly coupled cascaded ultra-narrow channels is proposed and demonstrated to have notably wider bandwidth than single stage tunneling structure. An extensive parametric study for such structures is performed to investigate the factors which can affect super-tunneling performance. It is found that the coupling between the ultra-narrow channels is required to be weak enough to ensure a continuous supertunneling band. In addition, electric field in the cascaded channels is enhanced, compared with that in the single channel structure.
A simple design of one dimensional gradual stacked photonic crystal (GSPC) structure has been proposed. The proposed structure consists of a periodic array of alternate layers of SiO2 and Si as the materials of low and high refractive indices respectively. The structure considered here has three stacks of periodic structures with five layers each. The lattice period of successive stack is increased by a certain multiple (say gradual constant, γ) of the lattice period of the just preceding stack. For numerical computation, the method of transfer matrix method (TMM) has been employed. It is found that such a structure has wider reflection bands in comparison to a conventional dielectric PC structure, and the width of the omni-directional reflection (ODR) bands can be enlarged by increasing the value of the gradual constant. Hence, a GSPC structure can be used as a broadband omnidirectional reflector, and the bandwidth of omni-directional gaps can be tuned to a desired wavelength region by choosing appropriate value of γ.
This paper presents asynchronous particle swarm optimization (APSO) applied to the time-domain inverse scattering problems of two-dimensional metallic cylinder buried in slab medium. For this study the finite-difference time-domain (FDTD) is employed for the analysis of the forward scattering part, while for the APSO is applied for the reconstruction of the two-dimensional metallic cylinder buried in slab medium, which includes of the location and shape the metallic cylinder. For the forward scattering, conceptually several electromagnetic pulses are launched to illuminate the unknown scatterers, and then the scattered electromagnetic fields around are measured. In order to efficiently describe the details of the cylinder shape, sub-gridding technique is implemented in the finite difference time domain method. Then, the measured EM fields are used for inverse scattering, in which APSO is employed to transform the inverse scattering problem into optimization problem. By comparing the measured scattered fields and the calculated scattered fields, the shape and location of the metallic cylinder are reconstructed. In addition, the effects of Gaussian noises on imaging reconstruction are also investigated.
An analysis has been presented by means of mode matching method for two microwave cavities of different sizes which are fed by TE10 waveguide and which are loaded with lossy dielectric slab type material. The accuracy of the results obtained is presented together with the comparison of the results which are obtained by HFSS numerical method. The optimization of the load location has been performed in order to maximize the electrical field on the material. The principle of this optimization is based on finding the existence of the positions in which S11 reflection coefficient is the lowest. When the feeding guide for the two different microwave cavities is entirely at the centre of the resonator, the reflection coefficient distribution change has been detected according to the different positions of the material in the oven, and then the lowest positions have been found out. The electric field changes in the detected positions have been recorded.
A fractal array is an antenna array which holds a property called "self-similarity". This means that parts of the whole structure are similar to the whole. A recursive procedure for evaluating the impedance matrix is allowed primarily by exploiting the self-similarity. However, numerous fractal arrays are extremely complicated in structure. Therefore, for these arrays, it is extremely elaborate to formulate explicitly a recursive relation. This paper proposes a simple procedure for evaluating, without formulating explicitly a recursive relation, the impedance matrix of fractal and fractile arrays; a fractile array is any array with a fractal boundary contour that tiles the plane without gaps or overlaps.
Non Destructive Testing techniques are more and more exploited in order to quickly and cheaply recognize flaws into the inspected materials, specially for carbon fiber reinforced polymers in recent years. Their production which are widely used both in civil and military applications, is an elaborate process un-free from faults and problems. Problems during the manufacturing, such as plies' overlapping, can cause flaws in the resulting material, this way compromising its integrity. Within this framework, this work aims to propose a design of ferrite core probe for eddy current non destructive evaluation, in order to investigate the presence of defects in carbon fiber epoxy composite materials. In this context, modelling is a powerful tool for inspection improvements. It helps probe-coil designers to optimize sensors for each examination requirement, providing better understanding of the involved physics, supporting operator training and increasing defect analysis reliability. Particularly, Finite Element based analyzes will be carried out into this path. After this step, in order to improve the quality of simulated measurement, a filtering technique has been exploited in order to improve the accuracy and performance of the flaw detection.
The nonlinear responses of a one-dimensional heterostructure containing two kinds of single-negative materials with an air gap are investigated. It is shown that the frequency of zero-phase gap bistable heterostructure can be tuned simply by adjusting the width of air gap. On the other hand, the optical bistability is achieved at very low values of input intensity due to the enhancement of Kerr nonlinearity near the frequency of the defect mode. It is shown that transmission of the structure is relatively insensitive to incident angle and losses.
Reconstructing high-accuracy Digital Elevation Model (DEM) is influenced by phase errors, such as phase trend, low coherence problems and phase unwrapping. These problems could result in the conversion errors from the phase to height. In this paper, a method is proposed to reconstruct the high-accuracy DEM using satellite interferometric synthetic aperture radar (InSAR). The proposed algorithm mainly aims to reduce the phase errors from the phase trend and low coherence problems. It consists of three steps. Firstly, the orbit state vectors are precisely interpolated in 3-D coordinates rather than in a separate dimension with the exploration of the orbital elements. Secondly, the relationship between external DEM and the interfermetric phase is built by the improved precise geo-location algorithm. The phase trend is estimated according to the topographic information and then removed from the unwrapped interferogram. Thirdly, the interferogram in low coherent regions are all updated with the simulated phases from actual DEM. The accuracy of the InSAR derived DEM can be significantly improved without any ground control points (GCPs), especially in those regions contaminated by masses of residues. Meanwhile, the phase trend caused by atmosphere effects or orbits uncertainty can also be eliminated by using this method. The experiment has demonstrated the proposed method can yield quite satisfactory results for producing high-accuracy DEM using Envisat data.
A radiofrequency field (RF) field exists inside body tissue during magnetic resonance imaging (MRI). If any implanted medical device is present, there can be a very intense concentration of the scattered RF field in the tissue surrounding certain parts of the implant. This causes tissue heating that can reach dangerous levels. Scattered field considerations show that it is possible to neglect the loading effect of the implant on the MR RF source. This leads to an incident field simplification. The presence of the implant in nonhomogeneous tissue increases the complexity of the scattering problem. An approach is presented that makes the computational problem considerably smaller. A method of moments (MoM) formulation of the electromagnetic model is presented. The relevant issues that arise during a finite element method (FEM) formulation are also discussed. The methods are illustrated by solving the problem for a typical implant using MoM as well as FEM.
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