Full-wave Finite Element Method Research Articles

Propagation characteristics of power line harmonic radiation into the stratified anisotropic ionosphere

Power line harmonic radiation (PLHR), which specifically refers to the electromagnetic wave radiation observed in ionosphere or magnetosphere, is radiated by the transmission lines of power systems on the ground. PLHR is shown as a parallel spectrogram between 400 Hz and 5 kHz in frequency-time power spectrogram of electromagnetic field. And the frequency spacing of the parallel spectrogram is 50/100 Hz or 60/120 Hz. As an artificial pollution source in the near earth space, PLHR has attracted more and more attention. However, so far, there have been little proposed quantitative researches on the formation mechanism. This paper studies the propagation model for the electromagnetic waves generated by the electric dipole source above the non-ideal conductive ground in the stratified anisotropic ionosphere. Based on the method by Lehtinen(2008), a new full-wave finite element method is give to solve the problem. By recursively calculating reflection coefficients and mode amplitudes, the method contains no index increasing items. So it can effectively overcome the numerical overflow in programming calculations. In order to verify the correctness of the method, comparison are made between the existing analytical solutions and the solutions obtained from the proposed method, and they are in excellent agreement. Further more, using the present model, the new method and the associated parameters about practical power lines, ground and ionosphere, we have studied the effects of the frequency of dipole source, the bottom boundary height of ionosphere, the earth conductivity, and the geomagnetic field direction on PLHR propagation in the ionosphere. Results show that when the frequency of radiation source equals the cut off frequency of earth-ionosphere waveguide-guided wave modes, the strength of PLHR for penetrating into the ionosphere becomes larger. Keeping the harmonic current constant, a smaller ground conductivity would be accompanied by a larger power of PLHR. PLHR propagates along the direction of the geomagnetic field in the ionosphere. Therefore, it is much easier for a high-order harmonic radiation of transmission lines to penetrate into the ionosphere along the direction of the geomagnetic field in the areas with low ground conductivity under a certain condition. Results obtained in this paper may have important implications to explain the formation mechanism of PLHR.

ANALYSIS OF COMPLEX DISCONTINUITIES IN CIRCULAR WAVEGUIDES USING HYBRID FINITE ELEMENT METHOD AND MULTIMODAL VARIATIONAL METHOD

We propose a hybrid multimodal variational method (MVM) and finite element method (FEM) to the analysis of complex 2D discontinuities in circular waveguides. The finite element method characterizes waves in arbitrarily shaped discontinuities, and the total response of the circuit is obtained by applying the multimodal variational method. The proposed hybrid method is successfully applied to the full-wave analysis of discontinuities with great practical interest (i.e., circular, cross-shaped, off- centered, ridged, multi-aperture irises, etc.), thus improving CPU time and memory storage against several full-wave finite element method based computer aided design (CAD) tools (i.e., HFSS High Frequency Structural Simulator).

Polarization-dependent bandwidth in low-index plasmonic metamaterials.

We investigate the visible range, less-than-one index bandwidth, n(λ)<1, of an optical metamaterial structure composed of plasmonic gold nanoparticles, and show that it is highly dependent on the polarization of incident light. The full-wave finite element method is used to obtain the spectral characteristics of the structure. We have found spectral bands over which the structure shows the desired low index. Further, a possible increase of the bandwidth by as much as 270% is demonstrated by a change in the incident polarization that extends the low-index bandwidth range (503-600nm) asymmetrically into a wider range (485-750nm) covering longer wavelengths close to near infrared. This asymmetric overlap might have the potential for new optical applications.

Enhanced photoabsorption in front-tapered single-nanowire solar cells.

Vertically aligned single-nanowire is verified to be a unique building block to realize the high-efficiency solar cell beyond Schockley-Queisser limit. We proposed a front-tapered vertically aligned single-nanowire solar cell (V-SNSC) and investigated numerically the possibility of this configuration to improve the photoabsorption efficiency compared to the conventional designs, by using 2.5D full-wave finite-element method. The influences of the feature sizes of aspect ratio, bottom radius, and nanowire length on the light-trapping properties were explored; the detailed field distribution and carrier generation rate were revealed as well based on the theory of dielectric resonant antenna, in order to elucidate the underlying physical mechanism. Results showed that, compared with the cylindrical counterparts, the absorption capability of V-SNSCs could be greatly enhanced by using a front-tapered configuration with less material utilized, and that such a positive effect can be further strengthened by increasing the nanowire length. The proposed configuration provides a promising approach to engineer the photoabsorption in the photovoltaic and other optoelectronic devices.

A DESIGN OF TRIPLE-BAND SLOT LOADED CIRCULAR MICROSTRIP ANTENNA FOR C- AND X- BAND APPLICATIONS

The design and development of a triple-band slot loaded circular microstrip antenna is demonstrated in this paper for the applications of C (4.66-8 GHz) and X (8.91-9.93 GHz) bands. The proposed antenna design consists of a pair of connected square slots which are centrally inserted on the circular radiating element. The antenna resonates at three frequencies of 4.76, 7.45 and 9.27 GHz with impedance bandwidths of 3.98% (4.67-4.86 GHz), 17.40% (6.82-8.12 GHZ) and 14.48% (8.58-9.92 GHz) respectively. The antenna is excited through a simple 50-Ω microstripline feed. The proposed antenna may suitable for uplink and downlink of C-band satellite communication and of X band radar applications. The simulation results are obtained by utilizing 3-D full-wave finite element method based high frequency structural simulator (HFSS) for comparison of experimental results. Acceptable agreement is observed between the both simulation and experimental results.

Full-wave FEM simulations of electromagnetic waves in strongly magnetized non-homogeneous plasma

Electromagnetic wave propagation in anisotropic media has been widely studied over the last decades since there are several applications where anisotropy plays an important role. This paper presents a procedure to carry out three-dimensional (3D) finite element method (FEM) full-wave simulations of the electromagnetic field in inhomogeneous magnetized plasma of an electron cyclotron resonance ion source (ECRIS). We used COMSOL Multiphysics software and MATLAB to model a cold anisotropic magnetized plasma, described by full-3D non-uniform dielectric tensor, enclosed by the metallic cylindrical cavity where the plasma is formed. A proper mesh generation, exploiting FEM-based COMSOL versatility, allowed us to optimally model ECRIS cavity and microwave waveguide launching structure, with a good computational efficiency and high resolution of the solution especially around the resonance regions. Numerical simulations have been performed in the frequency domain: in the resonance regions especially, the material properties exhibit a spatial variation that leads to a large sparse ill-conditioned matrix which is solved by MUltifrontal Massively Parallel Solver (MUMPS) direct method. We implement a method to perform full-wave simulations considering a cold plasma model for the constitutive relations; the obtained results show that the presence of ECR layer, along with the cavity walls, strongly influences the shape and strength of the electromagnetic field distribution, featuring a strong non-uniformity of the main electromagnetic parameters.

Sensing Depth of Microwave Radiation for Internal Body Temperature Measurement

This paper investigates modeling of the interaction of human tissues with a probe antenna situated on the surface of the skin. The goal is to differentiate temperature changes at different depths under the skin for passive radiometric measurements of internal body temperature. An improved metric is defined in order to differentiate thermal power radiated from a specific part of the tissue relative to the total thermal power received by the probe antenna. The frequency range between 0.5 and 3 GHz is investigated due to the sensing depth that can be achieved for a given receiver sensitivity. The general approach is to validate full-wave finite element method (FEM) EM simulations with a spectral-domain analysis for layered lossy dielectrics with a dipole at the interface between two of the layers. This was successfully done for a dipole on a water half-space and a stack of three tissues (skin, fat, and muscle). A new type of multifrequency probe was designed for 1.4, 2.7, and 4.9 GHz operation, and the predicted impedance validated experimentally. To the authors' knowledge, this is the first time that the near-field received power of a dipole probe placed in contact with lossy layered media is examined as a function of frequency. This is shown to be significantly different than the plane wave case, and is necessary knowledge for the design of a portable radiometer for microwave internal body thermometry.

Broadband Absorptance High Efficiency Silicon Nanowire Fractal Arrays for Photovoltaic Applications

ABSTRACTNanowire arrays have been proposed to enhance light trapping, increase efficiencies, and reduced material cost in photovoltaic solar cells. In this work we present a new crystalline silicon nanowire array structure, inspired by fractal geometry. The array structure is assumed to be an infinite 2D array in the x and y directions, and composed of vertically aligned SiNW suspended in air. Hexagonal fractal-like geometry is adapted in arranging cylindrical SiNW in these arrays. Full-wave finite element method 3D simulation is used to compute reflectance, transmittance and absorptance of the array for a normal incidence plane wave. The proposed fractal-like distribution of SiNW arrays yield broad absorption spectrum and enhanced efficiency while using less material. The efficiency of the proposed fractal-like SiNW arrays achieve ∼100% enhancement over that of the equivalent thickness flat c-Si film, and ∼18% enhancement over an equivalent height hexagonal array. The proposed optimized structures achieved a filling ratio ∼25%, which is ∼33% less than the corresponding hexagonal array.

A Planar Lens Antenna With Circular Edge Inspired by Gaussian Optics

A novel two-dimensional fan-beam lens is presented. The principle of operation of the lens is based on Gaussian optics. The focal point of the circular interface between the dielectric and air is coincident with a focal point of a hyperbolic reflector, while the feeding source is located in the other focal point. The ray tracing method along with physical optics and full wave finite element method (Ansys HFSS) are used to simulate the structure and study the effect of the feed blockage. The two-dimensional lens is implemented in a parallel-plates waveguide and a technique for matching the feeding structure is proposed. Measurement results are presented and confirm the predicted performance.

Miniature Microstrip Antenna with and without a Superstrate at THz Frequency

This paper presents comparative study of a rectangular Microstrip patch antenna at Terahertz (THz) frequency ranging from 0.6 to 1 THz with and without superstrate. The results report ed here were obtained using Ansoft HFSS 11.0 which uses full wave finite element method for simulation. In this study the miniature antenna was simulated first and then we load it with a superstrate and varied the height of the superstrate to optimize the antenna performance. Here in this paper we have selected 4 antenna configurations to compare. First antenna is a simple rectangular patch, second antenna is having a superstrate of height 50 microns, Third antenna is with a superstrate of 75 micron height and the fourth antenna is with a superstrate of 100 micron. Best performance of antenna i.e., -10dB bandwidth of around 19% was achieved at central frequency of 0.5 THz and 75 micron superstrate height.

A NOVEL TWO-LAYER STACKED MICROSTRIP ANTENNA ARRAY USING CROSS SNOWFLAKE FRACTAL PATCHES

In this paper, a novel approach was used to design two-layer stacked high-gain microstrip antenna array with improved bandwidth and high aperture e-ciency. Cross Snow∞ake fractal microstrip patches were employed as radiation elements. Varieties of antenna arrays with difierent fractal iterations were optimized by using the Genetic Algorithm (GA) associated with 3D full-wave Finite Element Method (FEM) in order to investigate the in∞uence of the Cross Snow∞ake fractal radiators. As compared with the conventional square patches, the Cross Snow∞ake fractal conflguration provides extremely high ∞exibility to achieve a wideband performance and maintains higher aperture e-ciency at operating frequency band. A prototype antenna with 2£2 Cross Snow∞ake radiators was fabricated and measured. Both simulated and measured results show that the proposed antenna has some promising performances to be more specially, the measured impedance bandwidth is 22.9% (from 5.18GHz to 6.52GHz) when S11 < i10dB; the simulated gain is 12.0dBi and its corresponding aperture e-ciency is up to 87.4% at the working frequency 5.8GHz.

基于MEMS工艺的高增益低副瓣太赫兹波纹喇叭天线设计

本文提出了一种基于微电子机械系统(MEMS)工艺的高增益低副瓣太赫兹波纹喇叭天线设计方法。利用三维全波有限元电磁仿真软件Ansys HFSS，对角锥喇叭的波纹开槽尺寸和条数进行参数分析和优化设计，获得了在275 GHz至580 GHz的有效带宽内(回波损耗小于10 dB)增益超过8 dB和副瓣电平小于-13 dB的太赫兹波纹喇叭天线。结果表明波纹开槽可有效提高太赫兹喇叭天线增益并压低副瓣，同时也说明MEMS工艺可有效用于太赫兹功能器件设计。 A novel high gain and low side-lobe terahertz (THz) corrugated horn antenna based on Micro-electro-me- chanical-systems (MEMS) technology is proposed. Properties of the antenna for different corrugated groove sizes and numbers are investigated and optimized by using three-dimensional (3D) electromagnetic full-wave finite element method (FEM) simulation software package Ansys High Frequency Structure Simulator (HFSS). The gain and side-lobe of the THz antenna can be designed greater than 8 dB and less than -13 dB, respectively in the band wide for 10 dB return loss from 275 GHz to 580 GHz. The results show that the corrugated groove can effectively improve the gain and depress the side-lobe of the horn antenna at the THz frequency range. Meantime, the THz functional devices could be effectively fabricated using MEMS technology.

COMPLEX RECTANGULAR FILTER DESIGN USING HYBRID FINITE ELEMENT METHOD AND MODIFIED MULTIMODAL VARIATIONAL FORMULATION

We hybridize vector Finite Element Method (FEM) and a Modifled Multimodal Variational Formulation (MMVF) to the accurate and fast design of complex isotropic rectangular fllters. The MMVF is applied to the full-wave description in the rectangular waveguides while the FEM characterizes waves in the arbitrarily shaped discontinuities. The proposed hybrid method is applied to the full-wave analysis of circuits with great practical interest (i.e., cross-shaped iris and multimode fllters), thus improving CPU time and memory storage against several full-wave FEM based Computer Aided Design (CAD) tools (i.e., HFSS High Frequency Structural Simulator). The performances of the proposed hybrid method are validated with experimental results and HFSS simulations.

Use of the full-wave Finite Element Method for the numerical electromagnetic analysis of LEMP and its coupling to overhead lines

The computation of lightning-originated surges on overhead power lines due to nearby lightning return strokes requires accurate models for the calculation of both the incident lightning electromagnetic pulse (LEMP) and the coupling of this field to the line conductors. The availability of numerical algorithms for the resolution of full-wave Maxwell's equations (also called numerical electromagnetic analysis – NEA) could provide benchmark results useful to assess the uncertainties introduced by approximate models and solution methods. This paper presents and discusses the results of LEMP and lightning-induced voltages calculations obtained using a time-domain full-wave Finite Element Method (FEM) model. The results obtained by the FEM model are compared with those provided by traditional approaches based, for the LEMP calculation, on the combined use of the dipole technique and the Cooray–Rubinstein formula and, for the LEMP-to-line coupling, on the Agrawal et al. model.

Integral equation analysis and optimization of 2D layered nanolithography masks by complex images Green’s function technique in TM polarization

Analysis and optimization of diffraction effects in nanolithography through multilayered media with a fast and accurate field-theoretical approach is presented. The scattered field through an arbitrary two-dimensional (2D) mask pattern in multilayered media illuminated by a TM-polarized incident wave is determined by using an electric field integral equation formulation. In this formulation the electric field is represented in terms of complex images Green's functions. The method of moments is then employed to solve the resulting integral equation. In this way an accurate and computationally efficient approximate method is achieved. The accuracy of the proposed method is vindicated through comparison with direct numerical integration results. Moreover, the comparison is made between the results obtained by the proposed method and those obtained by the full-wave finite-element method. The ray tracing method is combined with the proposed method to describe the imaging process in the lithography. The simulated annealing algorithm is then employed to solve the inverse problem, i.e., to design an optimized mask pattern to improve the resolution. Two binary mask patterns under normal incident coherent illumination are designed by this method, where it is shown that the subresolution features improve the critical dimension significantly.

Terahertz composite right-left handed transmission-line metamaterial waveguides

We report terahertz metamaterial waveguides based on the concept of composite right/left-handed transmission-lines. The waveguides are implemented in a metal-insulator-metal geometry fabricated with spin-coated Benzocyclobutene and contact photolithography. Angle-resolved reflection spectroscopy shows strong resonant absorption features corresponding to both right-handed and left-handed (backward wave) propagating modes within the leaky-wave bandwidth. Tuning of the waveguide dispersion is achieved by varying the effective lumped element series capacitance. The experimental results are in good agreement with full-wave finite element method simulations as well as an intuitive transmission-line circuit model.

Full-wave analysis of H-plane waveguide junction loaded with metallic posts

A hybrid method that combines moment method and mode matching technique is presented to study H-Plane waveguide discontinuity loaded with metallic posts at the junction of two waveguides. By expanding Eigen modes in waveguides, applying continuity of tangential fields at the discontinuity and finally nulling the tangential electric field on the post surface, a system of algebraic equations is solved to obtain current distribution on the posts and consequently scattering parameters of the structure. Then, as an application, an in-line dual-mode rectangular waveguide bandpass filter is analyzed using the proposed method along with generalized scattering matrix method. The numerical results are in good agreement with existing full wave finite element method in high frequency structure simulator (HFSS) results and measurements. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE , 2011.

Millimeter-wave power module combiner junction for high resolution advanced radar and communications

Power combiner junctions based on hybrid waveguide structures were designed, fabricated, and characterized for advanced radar and communications millimeter-wave power modules.Various structures of the four port combiners were investigated at Ka- and V-bands. The measurement results were compared with the three-dimensional full wave finite element method solutions. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:2227–2231, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25488

Full-Wave Model of Frequency-Dispersive Media With Debye Dispersion Relation by Circuit-Oriented FEM

Dispersive materials play an important role in a wide variety of applications (e.g., waveguides, antenna structures, integrated circuits, bioelectromagnetic applications). In this paper, a full-wave finite-element method (FEM-SPICE) technique for modeling dispersive materials is proposed. A finite-element formulation employing Whitney elements capable of analyzing electromagnetic geometries with dispersive media is described, and a Norton equivalent network is developed for each element. The overall network can be analyzed using a circuit simulator based on SPICE, and is suitable for both frequency- and time-domain analysis. This approach exploits the flexibility of finite-element mesh generation and computational efficiency of modern circuit simulators. Simple test configurations are analyzed to validate the proposed formulation.

Resonance shifting and plane impedance calculations for a rectangular cavity in printed circuit board using closed form solutions

AbstractA method for arbitrarily shifting the dominant mode frequency of a rectangular cavity in printed circuit boards (PCBs) is presented. Standard closed‐form and analytic solutions are used to determine the frequency, quality factor, and impedance of the cavity. Calculations are compared with 3D full wave finite element method (FEM) solutions. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 452–455, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24080