Rigorous Field Analysis Research Articles

Determining Ionization Threshold in Layer Insulation

This research relates to the dielectric strength of layer insulation of HV electronic transformers and similar structures. A simple method of evaluating layer insulation has been devised and validated. It requires measurement of the insulation sample voltage and current, and digitally manipulating these variables. Thus, active energy absorbed by the sample insulation, consisting of pure dielectric and ionization losses, can be derived. The first depend quadratically on the applied voltage, whereas the ionization losses are zero below a certain level [ionization threshold (IT)] but rise sharply above it. By studying the behavior of the loss curve we can determine IT. Several samples imitating layer insulation were manufactured and tested. The main construction variables were wire diameter and layer insulation parameters. Samples were tested at high frequency, 20–120 kHz, HV at different voltage shapes. Testing of unpotted samples revealed that ITs had small spread between the samples and depended only on the voltage amplitude. Above IT, ozone was copiously generated, and the sample temperature rose rapidly. An important finding was that ITs of potted samples not necessarily were higher than ITs of their unpotted counterparts. FEA of the electrostatic field in the winding has been performed. The windings’ capacitance was calculated. It became evident that a simplistic calculation using a flat electrodes’ approximation was too crude to be useful. Calculation in a “real” geometry yielded close match to the experimental results. Comparing the voltage between the wire and the insulation layer with the Paschen’s curve for air, one notes good agreement between the two sets at voltages close to the experimentally found ITs. Thus, probably the most important information that can be drawn from a rigorous field analysis is the IT value.

Multiple Dirac points by high-order photonic bands in plasmonic-dielectric superlattices.

The emergence of Dirac points (DPs) characterizes the topological phase transition and the gapless interface states in composite metal-dielectric metamaterials. In this work, we study a kind of compound plasmonic-dielectric periodic structure (PDPS) which sustains both plasmonic modes and multiple photonic modes. The structure has primitive cell consisting of four layers made from triple constituent components. Due to the generalized Su-Schrieffer-Heeger, DPs can emerge at the Brillouin zone center. More specifically, in weak plasmonic-photonic mode interaction regime, multiple DPs would emerge at the Brillouin zone center and edge due to the band folding, from the perspective of general effective medium. From the rigorous field analysis, the origin of these DPs is clearly demonstrated. These interleaved DPs behave as the intermediate transitions of the surface impedance for the PDPS and raise fully spanned topological interface states originated from 0 to 2nd-order photonic bands in the PDPS. The cases of combining our PDPS with either a plasmonic or dielectric homogenous medium are presented.

Insight of limitations of effective media theory for metal–dielectric multilayer metamaterials

Effective media theory (EMT) is usually used in the simulations and descriptions of one type of metamaterials which are composed of metal–dielectric multilayer films because of its simplicity and intuitiveness. It is consistent with the rigorous electromagnetic field analysis when the approximation conditions are strictly satisfied. However, there are several noticeable, and sometimes significant failures for the predicted properties that are caused by the approximation dealing with the finite layer of metal/dielectric multilayer structures. These inaccuracies and errors including surface plasmon polaritons (SPPs) spreading angles, reflection properties and interference patterns for SPPs lithography, originate from the differences of isofrequency contours between ideal hyperbolic multilayer structures and the actually fabricated multilayer structures with finite layer of films. Simulation results of EMT with metal/dielectric multilayer structures are analyzed and compared with the rigorous field analysis approach. Being aware of these issues can help to reduce the errors and improve the designs of the plasmonic devices for many applications.

Bandwidth Optimization of an Integrated Microstrip Circulator and Antenna Assembly: Part 2

The integration of a ferrite circulator with an arbitrary load - such as a wideband antenna - is considered by examining the conditions for perfect circulation over large bandwidths. These conditions relax the requirements of the loading impedance from being purely real (e.g., 50 ohms) to being complex, per a circulation impedance equation. The impedance equation is couched in terms of open-circuit impedance parameters, which are the natural parameters for describing an embedded microstrip circulator. By means of a rigorous field analysis, the impedance parameters are computed by modeling the microstrip ferrite circuit as a closed PEC/PMC cavity. The justification, features, and limitations of this model are discussed in detail, it is shown herein how the Z parameters can be invoked in some search algorithm to optimize the parameters of the ferrite, to achieve either superb circulator bandwidth or isolation performance. An example of a wideband circulator is given for which both simulation and experimental data are provided. The high degree of correlation between these two data sets corroborates the methodology

A comparison between the method based on a rigorous field analysis and the impedance transformation method for the intrinsic surface impedance of superconductor films

In obtaining the intrinsic surface resistance (RS) from the effective surface resistance (RS,eff) measured at microwave frequencies by using the dielectric resonator method, the impedance transformation method reported by Klein et al. [N. Klein, H. Chaloupka, G. Muller, S. Orbach, H. Piel, B. Roas, L. Schultz, U. Klein, M. Peiniger, J. Appl. Phys. 67 (1990) 6940] has been very useful. Here we compared the RS of YBa2Cu3O7−δ (YBCO) films on dielectric substrates obtained by a rigorous field analysis based on the TE-mode matching method with those by the impedance transformation method. The two methods produced almost the same RS,eff vs. RS relation in most practical cases of the substrate thickness being less than 1mm and sapphire and rutile used as the materials for the dielectric rod. However, when the resonant frequency of the dielectric resonator became close to that of the resonant structure formed by the substrates and the metallic surroundings, the RS,eff vs. RS relations appeared strikingly different between the two methods. Effects of the TE011-mode cutoff frequency inside the substrate region, which could not be considered in the impedance transformation method, on the relation between the RS,eff and RS of superconductor films are also investigated. We confirmed our arguments by demonstrating a case where existence of evanescent modes should be considered for obtaining the RS of YBCO films from the RS,eff.

A Generalized Node for Embedding Subwavelength Objects Into 3-D Transmission-Line Models

The transmission-line modeling (TLM) method is a well-established time-domain numerical algorithm for electromagnetic simulation and has been employed in a wide range of application areas. Producing accurate simulations of problems involving both physically important fine features, such as thin wires, as well as large-scale objects has proved very demanding, both in terms of computer time and memory. Clearly, such problems occur in many electromagnetic compatibility (EMC) applications. A general TLM node has been derived from rigorous field analysis that allows the embedding of almost arbitrarily shaped small objects within TLM cells. In particular, this approach allows the highly important case of short lengths of thin wires which are obliquely orientated to the cell faces to be tackled efficiently and, consequently, piece-wise linear models of arbitrarily routed curved wires to be modeled.

Field modeling of circular microresonators by film mode matching

The film mode matching method for rigorous vectorial field analysis of circular microresonators and bent optical waveguides is described in detail. Immittance formulation is used to assure high numerical stability. Problems with the evaluation of cylindrical functions of complex order in the transition region and their cross products have been satisfactorily solved, which makes the method reliable and accurate. Results of two commercial mode solvers are used for benchmarking. The importance of vectorial modeling of microresonators is demonstrated by a numerical example.

Electromagnetic Wave Propagation through an Azimuthally Asymmetric Helix Slow Wave Structure

In the fabrication of the practical helix slow wave structure (SWS), the misalignment or the dielectric constant variation in its support is not avoidable and, thus, causing azimuthal asymmetry in the structure. Therefore, the analysis of the asymmetric structure becomes an important issue. In this study, rigorous field analysis of a general asymmetric helical SWS was done by considering the structure as a helix supported by n wedge shaped dielectric supports, enclosed in a metal envelope. To consider the angular harmonic effect, the dielectric was not smoothed out. Using the present theory, the dispersion characteristics of the asymmetric helical structure were obtained. The study of the dispersion characteristics of the asymmetric structure revealed the stopband characteristics near the π-phase-shift point. This result was compared with that obtained from 3D FEM code, high frequency structure simulator (HFSS) and found to be in good agreement. It was also found that the asymmetry in the structure lowered the phase velocity and the cut-off frequency but increased the stopband width.

Field-Based Waveguide Filter Synthesis in the Time Domain

Abstract Computer modeling of components and systems has revolutionized engineering design. Yet, most computer-aided design (CAD) approaches follow the strategy employed in traditional practice: an initial model, created with empirical or approximate rules, is tested (analyzed) and modified (optimized) until it meets specifications. The key concept in this CAD approach is thus the efficient combination of numerical analysis with an optimization strategy. In this paper we explore a new approach to electromagnetic design of waveguide filters and aim at creating an alternative design methodology. The main idea consists in exploiting the intrinsic optimization capability of electromagnetic fields to minimize energy storage and losses, not by means of a variational formulation, but by exploiting the topology of three-dimensional standing wave pattern created in space. This new field synthesis approach relies on time-domain modeling of electromagnetic fields and employs the Transmission-Line Matrix (TLM) modeling method. After a theoretical introduction tothe synthesis methodology we describe a step-by-step synthesis of an iris-coupled rectangular waveguide bandpass filter and verify the result by performing a rigorous field analysis of the synthesized topology.

Sensitivity analysis of TWT's small signal gain based on the effect of rod shape and dimensions

An extensive study aiming at analyzing the effect of rod shapes and dimensions on the gain of helix traveling wave tubes (TWTs) is performed. The evaluation of tube small-signal gain is obtained by making use of a rigorous field analysis which takes into account the helix tape model and the dielectric inhomogeneous loading conditions. Computing time to perform the analysis is extremely low compared with the time required in the case of a full wave, three-dimensional (3-D) electromagnetic simulator. The accuracy of the simulation approach has been extensively verified in a previous paper. A novel expression for the attenuation constant has been introduced in the model to improve the quality of results. The proposed study allows a better understanding of tube behavior before fabrication highlighting the contribution of the shape, the mechanical tolerances and the /spl epsiv//sub r/ variation of the rods to the small-signal gain.

Aerial and grounding system analysis by the shifting complex images method

This paper introduces a novel computer method for the analysis of both aerial and grounding systems of conductors. The computer method based on an hybrid approach, allows to incorporate into a single linear system both lumped and distributed circuit parameters, evaluated by a rigorous electromagnetic field analysis. The conductor system is replaced by a suitable set of elementary current sources. These may be plain or hollow, bare or insulated, freely oriented and interconnected in the three dimensional space, which is considered formed by two half spaces each one homogeneous, linear and isotropic (e.g., air and soil). Therefore the method does not pose geometric and topological limitations and enables to compute voltages and currents at the source (boundary) elements as well as vector potentials, electric and magnetic fields anywhere in the surrounding medium. The range of application of this method is sufficiently wide including any practical electric power system application. The method may be applied for frequencies up to 1 MHz, thus covering the frequency spectrum of a typical full lightning too. Results which are derived first in the frequency domain can be converted to the time domain by Fourier transform algorithms. In this way it is also possible to analyze the response to transient signals of both aerial and grounding systems having complex geometry.

A Rigorous Two-Dimensional Field Analysis of Dfb Structures - Abstract

It is the aim of this work to develop a two-dimensional (2-D) analysis for the electromagnetic field distribution in distributed feedback (DFB) structures. This analysis is based on an equivalent network for the 2-D wave equation which must be satisfied by the components of both electric and magnetic field. The parameters of the equivalent network are determined from the physical parameters of the DFB structure in a straightforward manner. The zero-input response of this equivalent network leads to the dispersion relation for the modes guided by the DFB structure. The method has been applied to a number of optical components utilizing a DFB structure like DFB lasers, optical filters, and multi quantum well DFB lasers. A comparison with common methods of analysis shows that the network modeling yields accurate numerical results. At the same time its computational efficiency can be maintained quite high.

A Rigorous Two-Dimensional Field Analysis of DFB Structures

A Rigorous Two-Dimensional Field Analysis of DFB Structures

Field Characteristics of Axial-Field Motor and 8-pole Impulsed Magnetizing Fixture for the Rotor Magnet using 2-D Model

This paper describes a method for field analysis inside the flat-type brushless DC motor and 8-pole magnetizing fixture for the rotor magnet using 2-D field simulator. Rigorous field analysis of two-kinds entail 3-D analysis. However, this analysis is not often appropriate for system designs because of the time and cost involved. For field analysis in this study, the 3-D problem is reduced to a 2-D boundary value problem by introducing a cylindrical cutting plane at the mean radius of the magnets. Independent of sizes and shapes of systems, a reasonable 2-D field distributions can be obtained.

Design of bandpass filters using triple‐mode dielectric rod resonators

AbstractMultiply degenerate mode dielectric resonators in which several resonant modes are degenerate in one physical cavity are effective for miniaturizing the bandpass filter (BPF) in the microwave frequencies. In this paper, for a triple‐mode dielectric rod resonator at the resonant frequency of 8.5 GHz at which the TMO1δ mode is degenerate with the dual mode EH11δ, an accurate design is carried out. A three‐stage Chebyshev BPF and six‐stage elliptic function BPF are designed using these resonators. The coupling coefficient between the dielectric resonators via a coupling hole is computed by a rigorous electromagnetic field analysis. The validity of the computed results is confirmed by experiment. As a result, in comparison with the BPF using the conventional triple‐mode cylindrical cavity resonators, the filter volume is reduced to one‐fifth.

Rigorous field analysis of a spherical shield by using the multipole technique

The vector spherical multipole analysis is applied to determine the shielding effectiveness and the scattering cross sections of a homogeneous spherical shell with arbitrary thickness and material parameters. This canonical EMC-problem is formulated as a classical three-domain-problem and then solved rigorously with respect to the continuity-conditions of the tangential field components. Numerical results are presented especially for a shell material with low conductivity. In case of a well conducting thin shell an asymptotic evaluation of the multipole solution leads exactly to the results obtained byKaden, but in addition the amplitude of the shielding effectiveness at the resonance frequencies can be predicted.

Scattering from a dielectric circular cylinder partially clad by a perfect electric conductor

A rigorous field analysis of scattering from a dielectric circular cylinder partially clad by a perfect electric conductor, and excited by a magnetic or electric line current in the free space outside the dielectric cylinder, is given in this paper. The field equivalence theorem is utilised to derive, for each excitation, a system of coupled integral equations for the equivalent magnetic and induced currents on the dielectric interface and the perfectly electrical conductor, respectively. Galerkin's method is applied to determine the unknown equivalent currents, which are used to determine the scattered field outside and inside the dielectric cylinder. Numerical results for the equivalent magnetic currents, far scattered field patterns, and radar cross-section of the problem are given for TE and TM polarisations. It has been shown that the radar cross-section is reduced by increasing the dielectric constant of the dielectric cylinder, and the far field is changed by increasing the arc length of the perfect electric conductor.

A Simple Model for Anisotropic Loading of a Vane-Loaded Helix for Broad-Band Travelling-Wave Tubes

A simple model is developed for the analysis of a broadband slow-wave structure, for a travelling-wave tube, consisting of a helix supported by a dielectric in a metal envelope provided with metal vanes. Simplified models such as one in which the vanes are replaced by an axially conducting cylindrical sheath at the vane tips and the other in which the vanes are azimuthally smoothed out have been tried out, but with limited success. The combination of the results on the dispersion of the structures obtained using the first of these models with those obtained elsewhere by a rigorous field analysis, considering the angular harmonic effects of the vanes, both the results being interpreted in the framework of equivalent circuit analysis, however, proved to be fairly successful, as evidenced by the validation of the approach against the rigorous field theory.

Resonant modes in shielded uniaxial-anisotropic dielectric rod resonators

Rigorous field analysis by the mode-matching method is presented for dielectric rod resonators, including such uniaxial dielectrics as sapphire, which are placed between two parallel conducting plates or in a conducting cavity. The wave equations for E/sub Z/ and H/sub Z/ in a uniaxial anisotropic dielectric medium are derived in a cylindrical coordinate system. Based on these wave equations, the characteristic equations for the two resonator structures are derived and can be used to calculate the resonant frequencies of any resonant mode. Cutoff conditions of the resonant modes are discussed for parallel-plate-type resonators. Resonant frequencies of some lower order modes are calculated for both types of resonator. Mode charts useful for designing the resonators are presented. It is verified that the mode-matching method used commonly for the analysis of isotropic-dielectric resonators can be applied successfully to uniaxial-dielectric resonators. >

Asymptotic Scattering of Electromagnetic Waves from an Array of Dielectrically Loaded Conducting Strips

A rigorous field analysis of the electromagnetic scattering from a perfectly conducting strip loaded with a dielectric cylinder is presented. The dielectric cylinder is of circular cross-section and the dielectric medium is assumed to be linear, homogeneous, and isotropic. The strip is oriented radially with respect to the center of the cylinder and can be located inside or outside, but touching, the outer boundary of the cylinder. The structure is excited by a plane wave or a line current field and both TM and TE to z excitations are considered. The solution of the scattering from a single loaded strip is based on a boundary value approach and a high frequency asymptotic technique is also developed for the scattering from an array of loaded strips. The validity of this proposed solution is investigated by comparing the numerical results of selected cases with those based on exact and method of moments solutions. Sample numerical results for the scattering from a single loaded strip and an array of loaded strips are presented which illustrate how the far scattered field and the scattering cross-section are affected by the dielectric loading.