Fleld Distribution Research Articles

Electric Field Calculation along the Surface of Composite Insulator Covered with Sand Grains Based on Finite Element Method

This paper aims to discuss the efiect of sand grains covered with composite insulator on the surface electric fleld distribution of insulator in sandstorm condition. Comsol Multiphysics software based on flnite element method, was used for the three-demensional modeling and simulation. Based on the calculation results, the efiects of size, charge quantity, polarity and position of sand grains on electric fleld distribution are discussed. The simulation results show sand grains with difierent sizes have difierent distortion to electric fleld. Electric fleld is severely afiected by charge quantity, polarity and position of sand grains. This study provides theoretical reference for the research of insulator ∞ashover mechanism under the dust environment.

Optimized Design of the Truncated Cone Permanent Magnet Using ANSYS

This article examines the performance characteristics of truncated cone permanent magnet. ANSYS is employed to analyse the magnetic circuit and magnetic fleld distribution of truncated cone permanent magnet. An approach for optimized design of the truncated cone permanent magnet is provided to adjust the parameters for physical dimension of truncated cone permanent magnet and keep magnetic induction density in air gap stable.

FIELD MEASUREMENTS WITHIN A LARGE RESONANT CAVITY BASED ON THE PERTURBATION THEORY

Due to the sensitivity of the fleld distribution within a resonant cavity to the presence of an object, conventional measurement techniques employing a probe sufier from a limited accuracy. Therefore we propose a new measurement technique of the electric fleld distribution that avoids the use of a probe. Based on the perturbation theory, it consists of a measure of the cavity resonant frequency variation while displacing a small perturbing object within the cavity. The choice of the perturbing object shape, dimension and material is discussed with the help of simulation and measurement results in a canonical case. The case of reverberation chamber equipped with a mode stirrer is also considered, as well as the insertion of a metallic box within the cavity. Our measurement setup is very low-cost, simple to set up and to use, and adapted to any cavity geometry.

DUAL-BAND CIRCULAR POLARIZER AND LINEAR POLARIZATION TRANSFORMER BASED ON TWISTED SPLIT-RING STRUCTURE ASYMMETRIC CHIRAL METAMATERIAL

In this paper, a bi-layer twisted split-ring structure asymmetric chiral metamaterial was proposed, which could achieve circularly polarized (giant circular dichroism efiect) wave with dual bands and linear polarization transformation (giant optical activity) with asymmetric transmission wave emissions simultaneously from linearly polarized incident wave at microwave frequencies. Experiment and simulation calculations are in good agreement, indicating that the dual-band circular polarizer features high conversion e-ciency around 5.32GHz and 6.6GHz in addition to large polarization extinction ratio of more than 16dB, while cross linear polarization transformation with asymmetric transmission is observed around 10.52GHz. The transformation behavior for both circular and linear polarizations could be further illustrated by simulated surface current and electric fleld distributions. The proposed asymmetric chiral metamaterial structure could be useful in designing novel EM or optical devices, as well as polarization control devices.

THE EFFECT OF ANTENNA INCIDENT FIELD DISTRIBUTION ON MICROWAVE TOMOGRAPHY RECONSTRUCTION

For microwave tomography applications, we show that the utilized incident fleld distribution can afiect the achievable image quantitative accuracy and resolution. In particular, for the synthetic cases considered here, it is shown that the use of a focused incident fleld distribution within the imaging domain often results in either enhanced or equivalent image reconstruction as compared to the use of an omnidirectional incident fleld distribution.

3D FIELD-CIRCUIT ANALYSIS OF MEASUREMENT PROPERTIES OF CURRENT TRANSFORMERS WITH AXIALLY AND RADIALLY CONNECTED CORES MADE OF DIFFERENT MAGNETIC MATERIALS

We report results continuing the research which looks at the in∞uence of two difierent magnetic materials in a core construction on the transformation errors of a current transformer (1). In this paper we consider the behaviour of two difierent magnetic materials in a core. They are joined in a difierent way to the previous study; not axially (one-by-one), but also radially (one inside the second). We have conducted 3D analyses of the electromagnetic fleld distribution for difierent cases of current transformers and carried out computations based on the flnite-element numerical method. We compare the results with tests of real-life models.

MAGNETIC FIELD DISTRIBUTION AND LEVITATION FORCE CALCULATION IN HTSC-PMG MAGLEV VEHICLES

This paper presents a new analytical method for predicting magnetic fleld distribution and levitation force in three conflgurations of high temperature superconducting (HTSC) maglev vehicles. The permanent magnet guideways (PMG) are composed with ferromagnetic materials and NdFeB permanent magnets. The proposed analytical model is based on the resolution in each region of Laplace's and Poisson's equations by using the technique of separation of variables. For the study, we consider the HTSC as a perfect diamagnetic material. The boundary conditions and Fourier series expansion of interfaces conditions between each region are used to flnd the solution of magnetic fleld. The developed analytical method is extended to compute the magnetic fleld distribution generated by the three types of PMGs when removing the HTSC bulk. Magnetic fleld distribution and vertical force obtained analytically are compared with those issued from the flnite element method (FEM).

A MULTI-SPHERE PARTICLE NUMERICAL MODEL FOR NON-INVASIVE INVESTIGATIONS OF NEURONAL HUMAN BRAIN ACTIVITY

In this paper, a multi-sphere particle method is built- up in order to estimate the solution of the Poisson's equation with Neumann boundary conditions describing the neuronal human brain activity. The partial difierential equations governing the relationships between neural current sources and the data produced by neuroimaging technique, are able to compute the scalp potential and magnetic fleld distributions generated by the neural activity. A numerical approach is proposed with current dipoles as current sources and going on in the computation by avoiding the mesh construction. The current dipoles are into an homogeneous spherical domain modeling the head and the computational approach is extended to multilayered conflguration with difierent conductivities. A good agreement of the numerical results is shown and, for the flrst time compared with the analytical ones.

IMPACT OF FINITE GROUND PLANE EDGE DIFFRACTIONS ON RADIATION PATTERNS OF APERTURE ANTENNAS

In this study, the impact of flnite ground plane edge difiractions on the amplitude patterns of aperture antennas is examined. The Uniform Theory of Difiraction (UTD) and the Geometrical Optics (GO) methods are utilized to calculate the amplitude patterns of a conical horn, and rectangular and circular waveguide apertures mounted on square and circular flnite ground planes. The electric fleld distribution over the antenna aperture is obtained by a modal method, and then it is employed to calculate the geometrical optics fleld using the aperture integration method. The UTD is then applied to evaluate the difiraction from the ground planes' edges. Far-zone amplitude patterns in the E and H planes are flnally obtained by the vectorial summation of the GO and UTD flelds. In this paper, to accurately predict the H-plane amplitude patterns of circular and rectangular apertures mounted on square ground planes, the E-plane edge difiractions need to be included because the E-plane edge difiractions are much more intense than those of the H-plane edge regular and slope difiractions. Validity of the analysis is established by satisfactory agreement between the predicted and measured data and those simulated by Ansoft's High Frequency Structure Simulator (HFSS). Good agreement is observed for all cases considered.

ANALYTICAL CALCULATION OF PARALLEL DOUBLE EXCITATION AND SPOKE-TYPE PERMANENT-MAGNET MOTORS; SIMPLIFIED VERSUS EXACT MODEL

This paper deals with the prediction of magnetic fleld distribution and electromagnetic performances of parallel double excitation and spoke-type permanent magnet (PM) motors using simplifled (SM) and exact (EM) analytical models. The simplifled analytical model corresponds to a simplifled geometry of the studied machines where the rotor and stator tooth-tips and the shape of polar pieces are not taken into account. A 2D analytical solution of magnetic fleld distribution is established. It involves solution of Laplace's and Poisson's equations in stator and rotor slots, airgap, buried permanent magnets into rotor slots and non magnetic region under magnets. A comparison between the results issued from the simplifled model with those from exact model (EM) (which represents a more realistic geometry with stator and rotor tooth-tips and the shape of polar pieces) is done to show the accuracy of the simplifled geometry on magnetic fleld distribution and electromagnetic performances (cogging torque, electromagnetic torque, ∞ux linkage, back-EMF, self and mutual inductances). The analytical results are verifled with those issued from flnite element method (FEM).

NEAR-FIELD FOCUSING IN ONE PLANE USING A LOADED SECTORAL HORN ANTENNA

A near-fleld focused antenna used as a feed for linear array is presented in this paper. This antenna is an H-plane sectoral horn with a biconvex dielectric lens placed in its aperture. This antenna focuses the beam in one plane (H-plane) to illuminate a linear array with a small width and provide a large aperture on the other plan to illuminate the length of the array. The simulated fleld distribution on the array is found to be in good agreement with the measurement of a prototype at 9.41GHz.

HYBRID FEM-FMM APPROACH FOR EFFICIENT CALCULATIONS OF PERIODIC PHOTONIC STRUCTURES

A hybrid approach to flnd the optical response of periodic photonic structures to incident light is presented. The approach is based on a scattering matrix combination of the Finite Element Method (FEM) and the Fourier Modal Method (FMM). Optical response calculations include: scattering in both re∞ection and transmission directions, absorption and electric and magnetic fleld distributions inside the structure. The approach is tested on a structure | composed of dielectric and metallic materials | that is periodic in one direction. An analysis of the calculation accuracy shows that the approach depends on the subdivision into FEM and FMM domains and that the optimal subdivision depends on the calculations frequency range as well as on the structure geometry. For testing, we use the commercial FEM solver contained in CST Microwave Studio and a based on C/C++ Fourier Modal Method implementation.

ELECTRIC-FIELD DISTRIBUTIONS OF DIELECTRIC SINGLE LAYERS OF SPHERES WITH DIFFERENT COMPACTNESS

The internal electric-fleld distribution from single layers of dielectric spheres with high refractive index (n = 2:65) has been analyzed for a number of difierent compactness cases by FDTD (Finite- Difierence Time-Domain) method. The fleld distributions from the transmission spectra were compared with the internal electric-fleld distribution of the Mie modes of an isolated sphere. In general, the agreement is very good in almost all cases studied. The results show that TE and TM Mie modes are the origin of the resonances in the transmission spectra of the single layers. The resonances of the monolayer attributed to TE11 and TM11 Mie modes are only excited for compactness values lower than 0.38, suggesting a dependence of periodical arrangement efiects for these modes. Moreover, the fleld distribution corresponding to some of the dips in the spectrum cannot be directly attributed to Mie modes (TE21). The result indicates these are formed by degenerated or weakly coupled Mie modes induced by the periodic structure.

A SIMPLE LOCAL APPROXIMATION FDTD MODEL OF SHORT APERTURES WITH A FINITE THICKNESS

This paper brings forward a simple local approximation flnite-difierence time-domain (FDTD) method for the analysis of short apertures with a flnite thickness. By applying the equivalence principle together with a simple local approximation, the varying fleld distribution is accurately derived. The updating equations for the slot fleld can be derived by casting the fleld distributions into the contour paths containing the apertures. The method has been applied to two problems and the results are compared with the high-resolution standard FDTD simulation results and the measurement results. The accuracy of the proposed method is verifled from the comparison of both the fleld distribution and the time-domain and frequency-domain slot coupling results. It is demonstrated that the local approximation is highly e-cient and timesaving, and the present method is stable, numerically and computationally e-cient.

INFLUENCE OF CELLULAR PROPERTIES ON THE ELECTRIC FIELD DISTRIBUTION AROUND A SINGLE CELL

Electric flelds have been widely used for the treatment of neurological diseases, using techniques such as non-invasive brain stimulation. An electric current controls cell excitability by imposing voltage changes across the cell membrane. At the same time, the presence of the cell itself causes a re-distribution of the local electric fleld. Computation of the electric fleld distribution at a single cell microscopic level is essential in understanding the mechanism of electric stimulation. In addition, the impact of the cellular biophysical properties on the fleld distribution in the vicinity of the cell should also be addressed. In this paper, we have begun by flrst computing the fleld distribution around and within a spherical model cell. The electric flelds in the three regions difiered by several orders of magnitude. The fleld intensity in the extracellular space was of the same order as that of the externally applied fleld, while in the membrane, it was calculated to be several thousand times greater than the applied fleld. In contrast, the fleld intensity inside the cell was greatly attenuated to approximately 1/133th of the applied fleld. We then performed a

INEXPENSIVE AND EASY FABRICATION OF MULTI-MODE TAPERED DIELECTRIC CIRCULAR PROBES AT MILLIMETER WAVE FREQUENCIES

Tapered dielectric flbers are widely used in the near fleld microscopy to focus the incident beam or collect near fleld signal. Single mode is always required so that the geometrical dimension of the waveguide is smaller than the wavelength. This paper proposes an inexpensive and easy fabrication of multimode tapered Te∞on probe which has bigger dimensions than the wavelength. The fleld distribution in and outside the probe is analyzed by the total internal re∞ection theorem and solid core circular dielectric waveguide theory. Simulations are carried out in Microwave Studio CST. Novel applications based on focal points in and outside the probe are discussed, especially dielectric permittivity sensing of biomolecules using a capillary tube is emphasized by the simulations and experiments.

FIELD APPROACH IN THE TRANSFORMATION OPTICS CONCEPT

An alternative, fleld-based formulation of transformation optics is proposed. Field transformations are expressed in the language of boundary conditions for the electromagnetic flelds facilitated through the introduction of generalized potential functions. It is shown that the fleld-based approach is equivalent to the conventional coordinate-transformation approach but is preferable when looking for speciflc fleld distribution. A set of example devices such as invisibility cloaks, concentrators, rotators, and transformation optics lenses capable of creating light beams with predetermined fleld distribution (e.g., Gaussian and sinusoidal) is studied to validate the efiectiveness of the fleld-based formulation. As for the boundary conditions for the cloaked region the absence of the normal component of the Poynting vector is justifled. In the frames of the fleld- based approach the physical reasons behind inflnite components (singularities) of the material parameters of transformation optics devices are straightforwardly revealed.

DESIGN AND VALIDATION OF A TEM CELL USED FOR RADIOFREQUENCY DOSIMETRIC STUDIES

A Transverse Electromagnetic Mode (TEM) cell is an interesting option for studying the biological efiects of radiofrequency radiation at reduced scale (in vitro studies). Controlled and well-characterized exposure conditions are essential for a conclusive investigation: the biological sample is exposed to a uniform incident electromagnetic wave and the dose of absorbed radiation is precisely determined and correlated with the efiect. Unfortunately, experimental dosimetry is often unavailable or inapplicable, so that a pre- characterized and validated experimental setup is most valuable. As such, the primary objective of the present work is to experimentally validate a computational model of a self-built TEM cell designed for bioelectromagnetic experiments in the 100MHz{1GHz frequency range. Validation is achieved by comparing the computed vs. measured values for three signiflcant parameters: scattering parameters, incident electric fleld distribution, and absorbed power in a set of liquid samples. Successful validation and characterization is achieved by using CST Microwave Studio's flnite integration technique (FIT), and respectively a network analyzer for the experimental setup. The secondary objective is a dosimetric study of four difierent liquid samples loaded in the cell. The absorption coe-cient (AC) is used, assimilated to the speciflc absorption rate (SAR) of energy deposition in the entire sample volume. AC is shown to converge in experiment and simulation up to 800MHz for all samples. AC doesn't depend directly on the samples' volume (despite greater volumes frequently showing higher absorption) but rather upon the internal fleld distribution, which in turn mostly depends on the frequency and on the dimensions of the liquid samples.

FIRST-PRINCIPLE ANALYSIS FOR ELECTROMAGNETIC EIGEN MODES IN AN OPTICAL METAMATERIAL SLAB

Electromagnetic (EM) eigen modes in a flshnet metamate- rial (MM) slab have been comprehensively analyzed in an experimental conflguration, based only on precise solutions of Maxwell equations. The EM eigen modes were directly detected from light-absorption peaks. Each mode was explicitly characterized by the dispersion di- agram and EM fleld distributions. It was consequently found that the modes were classifled into either inner modes inside the slab or a mode at the interface with the surrounding media. The symmetric properties of the inner modes were clarifled using group theory. The in- terface mode was found to come from surface plasmon polariton at ∞at metal/insulator interface. The present analysis procedure is generally applicable to MM slabs and enables to clarify the properties without models or assumptions, which have been usually used in MM studies.

ACCURATE CALCULATION OF THE RIGHT-OF-WAYWIDTH FOR POWER LINE MAGNETIC FIELD IMPACT ASSESSMENT

In this work, approximate formulas are presented for computing the magnetic fleld intensity near electric power transmission lines. Original expressions are given for single circuit lines of any type of arrangement and double circuit lines in both super-bundle and low-reactance conductor phasing. These expressions can be used for assessing directly the Right-of-Way width of power lines related to maximum magnetic fleld exposure levels which may be e-ciently used in environmental impact assessment. The accuracy of approximate formulas is demonstrated by comparison with exact formulas for computing the rms fleld distribution.