Time domain modeling of a thin wire in a two-media configuration featuring a simplified reflection/transmission coefficient approach

The paper deals with a transient analysis of a straight thin wire in a presence of a two-media configuration using a simplified reflection coefficient approach. A direct time domain formulation is based on thin wire antenna theory and on the corresponding space–time integral equation for the wire above a dissipative half-space, or buried in a real ground. The effect of a half-space is taken into account via the simplified reflection/transmission coefficient arising from the modified image theory. The resulting space–time integral equation for the wire above and below ground, respectively, is handled via the time domain Galerkin–Bubnov variant of the indirect boundary element method (GB-IBEM) and some illustrative numerical results are presented.The transient response computed via the simplified reflection/transmission coefficient approach is compared, where possible, to the results obtained via the Fresnel coefficients approach.     

Frequency domain boundary element versus time domain finite element model for the transient analysis of horizontal grounding electrode

The paper deals with two different approaches to the assessment of the transient impedance of a horizontal grounding electrode: frequency domain boundary element analysis, based on the straight thin wire antenna model (AM) and generalized telegrapher’s equations combined with inverse Fast Fourier Transform (FFT); and time domain finite element analysis based on the transmission line model (TLM) and standard telegrapher’s equations. Extensive numerical experiments have been undertaken and some of illustrative numerical results are presented in this paper.     

Human exposure to transient electromagnetic fields using simplified body models

Analysis of the human body exposed to transient electromagnetic fields is presented in this work. The human body is represented by one or more vertical conductors. Modeling of the vertical conductors is based on the transmission line (TL) theory in the frequency domain. The related transient response is computed using the inverse Fourier transform (IFT). Per-unit-length parameters are calculated for finite heights and the physical characteristics of the human and soil are taken into account. The assessment of the space–time dependent current distribution induced in the body is carried out in the general case where the human is not directly in contact with the ground. The results, related to various transient exposures, obtained with TL body representation are compared to the direct time domain results computed using the human equivalent antenna model of the body.     

Comparison of analytical and boundary element modeling of electromagnetic field coupling to overhead and buried wires

The paper deals with various approaches for the analysis of electromagnetic field coupling to horizontal straight line of finite length in the presence of a lossy half-space based on the theory of thin wire antennas. The formulation is posed in the frequency domain and it is based on the corresponding Pocklington integro-differential equation. Throughout this work the Pocklington equation is solved numerically via the Galerkin–Bubnov scheme of the indirect boundary element method (GB-IBEM) and analytically. The obtained results are compared to NEC results and to the results obtained by applying the transmission line (TL) model, i.e. to the results obtained by solving the corresponding Telegrapher’s equations.     

Performance profile comparison of the quasi-lumped element resonator antenna

The performance profile comparison of the quasi-lumped element resonator antenna is presented. The specific advantages of this antenna are investigated by comparing it to the standard long wire antenna approach, and, in particular, also to the many available differently loaded wire antenna approaches, which are also optimized for maximal radiation efficiency and directivity for example, the capacitively loaded long wire antenna and the planar H-shaped elements loaded transmission line design. It was noted that the quasi-lumped element resonator antenna formed by small interdigital capacitors and line inductors proved to be compact in size with an aperture size of 5.8 × 5.6 mm² and better directional characteristics.     

Finite-difference time-domain model for the feeding gap of coaxial probe driven antennas

In the finite-difference time-domain (FDTD) method, a simple and realistic feed model for coaxial probe driven antennas is proposed here. The feed zone of the antenna may be considered as an equivalent source in view of the antenna theory and a load port in view of the transmission line theory. The proposed feed model is constructed by combining the infinitesimal-gap source condition of the antenna and the equivalent load condition of the feed line. It leads to perform no additional FDTD cell modelling of the line. The transient reflected voltage and the input impedance of cylindrical monopole antennas fed by coaxial lines are calculated numerically and then compared with the accurate measurement and a full fine-grid. The FDTD results of the proposed model have a good agreement with the measured data and the fine-grid results.     

Computation of transient electromagnetic fields radiated by atransmission line: An exact model

A novel time domain analytical method for predicting electromagnetic field transients resulting from power line switching operations is presented in this paper. This method, which is directly derived from electromagnetic field theory of a power transmission line, allows the field transients to be accurately and efficiently calculated. It will be shown that conventional numerical methods for computing transmission line transient electromagnetic fields are in fact degenerative approximate models for this analytical method     

Investigation of very fast transient overvoltage distribution in taper winding of tesla transformer

In order to study the very fast transient overvoltage (VFTO) distribution in the taper winding of a tesla transformer under high-frequency steep-fronted voltage surge, we built a distributed line model based on multiconductor transmission line (MTL) theory. We used a new hybrid algorithm combining finite-element-method (FEM) and interpolation formulas to quickly evaluate the induction coefficient matrix K by utilizing some characteristics of the taper structure. The turn-to-ground and interturn voltage distributions can be obtained by solving the telegraphist's equations in the frequency domain. We measured the voltage distribution inside the taper winding to find some ways to weaken the voltage oscillations. Here, we compare the results with numerical values.     

Time domain modelling of thin wire arrays in the presence of a two media configuration using the boundary element analysis

Transient response of a multiple wire configuration in the presence of a two-media configuration excited by a voltage source (antenna mode) or illuminated by an incident field is analysed using the boundary element method (BEM). The analysis is based on the solution of the corresponding set of the coupled space-time Hallen integral equation and it is carried out directly in the time domain. The influence of a two media configuration is taken into account via the space time reflection coefficient. The corresponding integral equation set is handled via the time domain variant of the Galerkin–Bubnov indirect boundary element method (GB-IBEM). Some illustrative numerical results for both antenna and scattering mode are presented in the paper.     

500 kV输电线路跳线风偏有限元分析与试验研究

为了解输电线路跳线的风偏特性,以指导跳线的合理布置,从而减少由跳线风偏引起的闪络跳闸事故的发生,对某500 kV输电线路的跳线进行有限元风振响应分析和风洞试验研究。首先,运用时域有限元分析方法对500 kV输电线路跳线的风振响应进行分析,研究了不同风速、不同风向角以及加装悬垂绝缘子串对跳线风偏特性的影响。然后,基于相似性理论制作了500 kV输电线路跳线的气弹模型,开展了风洞试验并与有限元分析结果进行对比验证。结果表明：输电线路跳线的风偏位移随风速和风向角的增大而增大,与风速呈正比例函数关系;随着风向角的增大,跳线风偏角的增大幅度减小;加装悬垂绝缘子串可有效抑制跳线风偏。分析得到的输电线路跳线风偏结果可为跳线的风致振动理论研究以及实际输电线路建设提供依据。     

Current induced along horizontal wire above an imperfectly conducting half-space

The boundary element/exponential approximation technique for calculating the loaded straight wire horizontally located above a dissipative half-space is presented. The influence of a lossy ground is taken into account via Sommerfeld integrals appearing within the kernel of the electric field integral equation for thin wire. These integrals are computed by means of the exponential approximation technique. The resulting integral equation for loaded wire above an imperfect earth is solved by the boundary element method. Numerical results are obtained for current distribution along a resistively loaded dipole antenna and along a transmission line of a finite length.     

Enhanced radiation from an electrically small radiator using an array of sub-wavelength holes

An experimental demonstration of radiation enhancement from an electrically small antenna (ESA) using an array of sub-wavelength holes engraved on a metallic plate is presented in this paper. A weakly radiating, chip inductor loaded open coplanar waveguide transmission line is used as the reference ESA. We show that an array of sub-wavelength hole loaded metallic aperture, placed near the antenna, can significantly enhance radiated power from the source. The hole array converts the high spatial reactive spectrum existing in the near-field of the antenna into a far-field propagating spectrum. The theory is validated by experiments and simulations in the microwave frequency regime. This novel radiation enhancement scheme is seen to enhance the gain of the antenna from ?8.5 to ?2.5?dBi and radiation efficiency from 13 to 33% around resonance.     

Analytical versus boundary element modelling of horizontal ground electrode

Different approaches to the analysis of horizontal ground electrode, based on the wire antenna theory have been used in this work. The spatial distribution of the induced current along the electrode is obtained by solving the homogeneous Pocklington integro-differential equation. The spatial distribution of the scattered voltage along the electrode is computed using the generalized telegrapher's equation. The assessment of current and voltage induced along the electrode is carried out using both analytical and numerical approaches. The numerical solution of integral expressions arising from the antenna theory model is numerically handled via the Galerkin–Bubnov scheme of the Indirect Boundary Element Method (GB-IBEM). Some illustrative results for the current and voltage induced along the horizontal electrode are given in the paper.     

Dual-band microstrip-to-coplanar strip balun transition and loop antenna application

A microstrip-to-coplanar strip balun transition and its applicability to a single-fed dual-band tapered loop antenna are presented. The dual-band transition consists of a simple two-section transmission-line transformer and a two-section open-ended line. Closed-form design equations based on ideal transmission lines are derived and then verified with the examples of two designs. The application of the transition to a single-fed 0.9/1.8 GHz dual-band tapered loop antenna is then demonstrated. The measured performance of the antenna proves the validity of the proposed dual-band transition network.     

SPICE model for lossy piezoceramic transducers

A transmission line equivalent circuit for piezoelectric transducers has been modified to provide modeling of lossy piezoceramic transducers. A lossy transmission line is used to model the mechanical losses. The equivalent circuit parameters are derived from analogies between electrical transmission lines and acoustic wave propagation. Implementation of the equivalent circuit model in SPICE is shown. Simulations and measurements in the time and frequency domain of a low-Q material and a multilayered ultrasonic sensor using a low-Q piezoceramic transducer are presented.     

Radiometric Evaluation of Antenna-Feed Component Losses

Low-noise antenna systems are frequently used in conjunction with measurements of atmospheric and cosmic background noise at microwave frequencies. The input transmission line losses of these receiving systems must be precisely calibrated to insure proper identification of the portion of operating noise temperature attributable to the external environment. Although most components in an antenna line can be calibrated by conventional insertion-loss measurements, many feed component losses must be evaluated by means of nonstandard techniques. This paper describes a radiometric method for calibrating the loss of multimode antenna-feed components in which the field is linearly or circularly polarized. The method consists of measuring operating noise temperature, first with the components under evaluation installed and again after substitution by a waveguide section of known loss. Calibration and error analysis equations are derived and discussed. Application of the radiometric method, for the calibration of a mode-generator and quarter-wave plate polarizing section, resulted in a loss measurement of (0.0069 ±0.0016 pe)/dB.     

Finite calculus formulation for incompressible solids using linear triangles and tetrahedra

Many finite elements exhibit the so‐called ‘volumetric locking’ in the analysis of incompressible or quasi‐incompressible problems.In this paper, a new approach is taken to overcome this undesirable effect. The starting point is a new setting of the governing differential equations using a finite calculus (FIC) formulation. The basis of the FIC method is the satisfaction of the standard equations for balance of momentum (equilibrium of forces) and mass conservation in a domain of finite size and retaining higher order terms in the Taylor expansions used to express the different terms of the differential equations over the balance domain. The modified differential equations contain additional terms which introduce the necessary stability in the equations to overcome the volumetric locking problem. The FIC approach has been successfully used for deriving stabilized finite element and meshless methods for a wide range of advective–diffusive and fluid flow problems. The same ideas are applied in this paper to derive a stabilized formulation for static and dynamic finite element analysis of incompressible solids using linear triangles and tetrahedra. Examples of application of the new stabilized formulation to linear static problems as well as to the semi‐implicit and explicit 2D and 3D non‐linear transient dynamic analysis of an impact problem and a bulk forming process are presented. Copyright © 2004 John Wiley & Sons, Ltd.     

一种新型复合左右手负阶谐振天线的设计

为了获得高增益小尺寸天线,通过在基片集成波导上引入二阶Hilbert分形缝隙,提出了一种新型复合左右手传输线.在等效电路模型的基础上,利用HFSS和Serenade软件对该传输线的电路参数进行了提取;利用MATLAB语言给出了该传输线的色散曲线;最后,由该传输线设计了终端短路的缝隙天线.实验结果表明：该天线馈电网络简单,工作在复合左右手传输线的-1阶模式上,比之前报道的复合左右手谐振天线具有更小的电尺寸和更高的增益.由于这些性能,使得该天线可以用于无线通信系统中.     

Numerical study of transient 2-D compressible flow with heat and mass transfer using the finite volume method

In this paper, we used a pressure-based finite volume method to investigate the problem of transient 2-D compressible flow with heat and mass transfer in a rectangular domain. We have used this method to solve the governing equations with given initial and wall slip boundary conditions. We implemented the SIMPLE-TS algorithm in order to compute the numerical solutions for the flow variables, viz., velocity, pressure, temperature, concentration, density. The variation of density of the fluid along the horizontal and vertical line through geometric center of the domain has been studied. The transient solutions of temperature and concentration indicate that, the transient flow though dominates initially, it finally settles down to steady states solutions after elapse of some time. Nusselt number and Sherwood numbers were used to predict the behavior of heat transfer and mass transfer, respectively, at the center line of the rectangular domain.     

智能天线移动台端实时发送系统的设计

探讨了智能天线的基本理论, 介绍了采用高速可编程逻辑器件 FPGA(Field Programmable Gate Array)的智能天线移动台端实时发送模块的设计与实现, 由于只采用 DSP 实现信号处理不能满足数据的实时生成与发送, 所以本系统采用 DSP FPGA 的硬件结构, 将一些原本由 DSP 执行得很耗时的运算用 FPGA 通过逻辑门的方式并行实现, 保证了数据的实时生成和发送.