An adjoint variable method for frequency domain TLM problems with conducting boundaries

We propose a novel adjoint variable approach to design sensitivity analysis with the frequency domain transmission line modeling (FDTLM) method. An enlarged system matrix is constructed that includes the perturbed metal sections of the structure. The adjoint system of equations is then formed and solved. The derivatives of the responses with respect to all designable parameters are estimated using two analyses of the original and the adjoint systems. Second-order terms are included by approximating the values of the incident voltage waveforms in the perturbed areas. Our novel technique is illustrated through a number of examples.     

Radiation from a short dipole or monopole near a thick conducting cylinder of resonant length

Using a theoretical-numerical technique involving the magnetic field integral equation, the radiation fields are determined for configurations comprised of a centrally located dipole and a thin quarter-wave monopole near conducting cylinders of finite lengths. Such configurations are important since they give measures of the radiation effects of fuselages of aircraft or other structures which the cylinders may model. The radiation fields are determined in the three principal planes for wavelengths passing through the resonant length of the cylinder, i.e.,L approx lambda. The radiation patterns for both the dipole and monopole sources when normalized with respect to one another are similar to within approximately 1 dB. The vertically polarized patterns in the horizontal plane (the plane orthogonal to the dipole axis and containing the cylinder axis) show small deviations from their near omnidirectional characteristics for cylinder electrical lengths of 0.5, 1.0, and1.5lambda. On the other hand, the cross polarized component (the horizontal component) in the same plane shows a substantial enhancement of the intensity of the lobe structure at resonance. The patterns are compared to those acquired experimentally in an anechoic chamber and close agreement is demonstrated.     

Bandwidth of a dipole near and parallel to a conducting plane

A theoretical method is proposed for explaining the bandwidth previously measured on flat folded dipoles near and parallel to a conducting plane. With a sinusoidal-current assumption, the symmetrical dipole short- or open-circuited is compared with a lossy transmission line. We are able to express the bandwidth by simple formulas which are in agreement with experiments.     

Fast MM-PO-based numerical modelling technique for wideband analysis of antennas near conducting objects

A highly efficient computational electromagnetics technique based upon method of moments-physical optics (MM-PO) hybrid formulation combined with the impedance matrix interpolation and a dynamic adaptive frequency sampling for wideband analysis of antennas radiating in the presence of conducting bodies is presented. Sample numerical results demonstrate the capability of the technique     

Correction factor for nonplanar incident field in monopolecalibrations

In calibrating monopole antennas, the length of the antenna can be comparable to the separation distance. In that case, there is a significant variation in both the magnitude and the phase of the incident field along the length of the antenna under test. An expression for a correction factor is presented to account for this effect. The correction factor is evaluated for some representative cases, and some guidelines are given for when this factor should be taken into account. The effect can exceed 1 dB in some practical cases     

近场纳米光纤探针腐蚀制备技术概述

纳米光纤探针是扫描近场光学显微镜的常用关键器件,化学腐蚀法制备近场光学光纤探针是基于腐蚀液弯液面的高度随光纤芯径的动态变化过程。从流体力学杨一拉普拉斯方程出发,研究了弯液面高度随光纤芯径大小的变化关系,分析了影响腐蚀法制备纳米光纤探针的相关因素,追踪了利用化学腐蚀制备纳米光纤探针的最新进展,介绍了静态腐蚀法、动态腐蚀法和选择腐蚀法等多种方法,并分析了每种方法的特点,作了比较和总结。     

Model of a dipole antenna in free-space and near a perfectly electrical conducting plate

In this paper, an accurate method is developed to model dipole antennas in free-space or near an infinite perfectly electrical conducting plate. The magnetic field integral equation is implemented and point-matching is used to construct the interaction matrix. The edges of the cylinder, which can cause numerical instabilities in the simulated current distribution, are getting a special treatment by choosing a specific set of basis functions. The excitation is modeled based on the equivalence principle and leads to the application of a magnetic surface current over the gap region. The exact kernel of the integral equation is applied and all possible current components are taken into account. When the antenna is close to a conducting plate, a strong modification of the surface current distribution is observed. It is demonstrated that for these configurations, the incorporation of the circumferential component of the surface current distribution is needed. At larger distances, the circumferential surface current can be neglected in the total distribution. The only approximation (or rather assumption) we made is that we impose a longitudinal directed electrical field over the boundary of the gap region. The results are verified experimentally.     

Transmission model for coils near flat conducting medium simulating wireless body area network at 10.8 MHz

Transmission between small antenna coils at 10.8 MHz is investigated in free space and near a flat, conducting medium for different separations between the coils and heights above the medium. Models are derived, and a physical explanation is given. Excellent agreement is obtained between the measurements and the models.     

Correction factor for determining the London penetration depth fromstrip resonators

The strip resonator technique is a popular way to measure the temperature (T)-dependent London penetration depth λ_L(T) in superconducting thin films. The temperature dependence can provide fundamental information about the superconducting energy gap and hence insight into the pairing mechanism. Since λ _L(T) characterizes the film's response to a magnetic field near the surface, it qualifies the suitability of the superconducting film for microwave device applications. There has been much controversy regarding the actual form of the temperature dependency, with some researchers reporting a weak-coupled Bardeen-Cooper-Schriefer (BCS)-like behavior and others favoring a Gorter-Casimir type fit. This paper shows that the disagreement can be at least partially attributed to a temperature sensitive term traceable to stray susceptance coupled into the resonator. The effect is inherent to the technique, but a simple procedure to compensate for it can be used and is presented here as a correction factor (1+ξ)     

An E-Field solution for a conducting surface small or comparable to the wavelength

A newE-field solution is presented for the electric current and electric charge induced on a perfectly conducting surface illuminated by an incident electromagnetic field. This solution is a moment solution to the electric field integral equation on the surface. The expansion functions consist of a set of functions suitable for expanding the magnetostatic current and a set of functions whose surface divergences are suitable for expanding the electrostatic charge. The testing functions are similar to the expansion functions. With these expansion and testing functions, the newE-field solution works well with surfaces whose maximum dimension may be as small as10^{-15}wavelengths or as large as a few wavelengths. PreviousE-field solutions begin to deteriorate when the maximum dimension of the surface falls below a few hundredths of a wavelength. The newE-field solution is applied to a conducting circular disk and a conducting sphere.     

Spectral iterative algorithm for RCS computation in electricallylarge or intermediate perfectly conducting cavities

A novel algorithm designed to compute efficiently and accurately the high-frequency electromagnetic scattering from open-ended waveguide cavities is presented. The cavity is converted into a stepped-waveguide model so that the field spectra are propagated, forward and backward, along each waveguide section. As boundary conditions for perfect electric conductors are applied via image theory, they are of local nature and take into account only the first-order interactions between each pair of waveguide sections. Accordingly, additional forward-backward iterations must be performed if multiple interactions are to be taken into account. Finally, the radar cross section due to the interior irradiation is calculated by a Kirchhoff-based aperture integral. Good agreement with method of moments and hybrid modal solutions is found, as well as with experimental data, for two-dimensional and three-dimensional cavities with rectangular cross section     

Modal characteristic equation and dispersion curves for an elliptical step-index fiber with a conducting helical winding on the core-cladding boundary - an analytical study

A special type of elliptical step-index fiber with a conducting helical winding on the core-cladding boundary is proposed and investigated theoretically. Using elliptic cylindrical coordinates, boundary conditions are derived and longitudinal field components for the even and odd modes are obtained. The characteristic equation for the waveguide to be studied is determined by solving the fourth-order determinantal equation, which also contains complex quantities. In order to study the fundamental mode, the modal index /spl nu/ is put as /spl nu/=1. The equations obtained involve modified Mathieu functions of the first order and their derivatives. Applying approximations, cutoff conditions are obtained. Numerical computations are made. Dispersion curves are obtained for different pitch angles of the helical winding.     

Correction factor for resistivity and Hall mobility measurement of two-layer structures by spreading resistance techniques

The spreading resistance of a circular disc contact located on a two-layer semiconductor structure, and its relative change due to magnetic field has been determined, with the magnetic field perpendicular to the contact face, and with the physical magnetoresistance zero in both layers. The correct value of the spreading resistance differs from the result obtained by the usual approximation, especially if the contact diameter is comparable with the thickness of the upper layer. The conditions are given when the relative change in resistance due to the magnetic field is determined by the mobility in the upper layer only. The results show the applicability of the spreading magnetoresistance technique in determining the Hall mobility in a two-layer structure.     

A method for the constructive synthesis of an antenna array of crossed orthogonal electric dipoles located near a perfectly conducting sphere

A method for the constructive synthesis of an antenna array of crossed orthogonal dipoles located over a perfectly conducting sphere is proposed. The method is based on a modification of the genetic algorithm for solving the problem of constructive synthesis of the antenna array. In implementation of this method, specific features of a known electrodynamic model are used with the radial coordinate of the radiator taken into account.     

Experiment and numerical analysis for edge and corner bonded PoP bottom package assemblies under four-point bending

This paper presents the four-point bend test results for edge and corner bonded 0.5 mm pitch lead-free package stackable very thin fine pitch ball grid arrays (PSvfBGAs) as package-on-package (PoP) bottom packages on a standard IPC/JEDEC bend test board. The tests were carried out based on the above standard with a 30 mm loading span, 90 mm support span and 7.5 mm/s crosshead speed. The daisy chain resistance, strain, crosshead displacement and load of each PSvfBGA were measured and a 20% increase in the resistance was used as the failure criterion. Materials used in this study were a UV-cured acrylic edge bond adhesive, a thermal-cured epoxy edge bond adhesive and a thermal-cured epoxy corner bond adhesive. The test results show that all of them can improve the bend performance significantly; especially the edge bond high module epoxy increased the crosshead displacement, strain and bending force when mechanical damage occurred by 33.46%, 26.74% and 3.05% respectively. Failure analysis indicated that the predominant failure site was PCB pad lift/cratering regardless of with or without adhesives. The 3D quarter finite element model was also built to further study the improvement mechanism of bend performance by these adhesives.     

Optimum Pre-Emphasis Network for Satellite Transmission of an FM TV Signal near or at Threshold

An optimun pre-emphasis network for the transmission of a FM television signal which is received at or near threshold is described. Objective and subjective measurements of video signal-to-noise ratio (SNR) versus received carrier-to-noise ratio (CNR) for an optimum and CCIR pre-emphasis network are given. The results show that there is an improvement of about 2 dB in SNR using the optimum pre-emphasis network over that achieved with the CCIR network. Subjective tests also show a preference for use of the optimum pre-emphasis network. These results are useful in the design of low cost earth terminals to receive higher quality television signals from a satellite transmitter.     

Antennas in material media near boundaries with application to communication and geophysical exploration, Part II: The terminated insulated antenna

The properties of the insulated antenna in a dissipative medium near a boundary are reviewed. The important effects on antennas of being embedded in media with different properties over a wide range of frequencies are treated specifically in terms of three examples. These are: 1) a traveling-wave antenna in the earth below air atf sim 0.1MHz for subsurface communication; 2) an antiresonant antenna on the sea floor atf sim 1kHz and 3) an electrically short antenna on the sea floor atf sim 1Hz--both for geophysical measurements. In each case the current distribution, impedance, input power, effective length, and electric field in the range of interest are determined.     

导体介质组合体电磁分析的建模与计算

为提高导体介质复合目标电磁散射分析的效率,采用一类新的表面混合场积分方程进行求解,该方程通过伽略金方法建立的阻抗矩阵具有良好的条件数.分析了多区域连接边上的电磁流分布和基函数的定义,然后根据边界条件推导了广义EFIE-CFIE-JMCFIE方程形式,最后比较了不同积分方程建立阻抗矩阵的收敛性.数值算例表明该方法能明显提高计算效率,实现导体介质复合目标电磁散射分析快速、准确的求解.     

A graphical user interface (GUI) for plane-wave scattering from a conducting, dielectric, or chiral sphere

Various numerical techniques have been developed for modeling electromagnetic field propagation in various novel complex media. The validity of these techniques is usually verified by comparison to the exact solutions of canonical problems. Recently, research has focused on chiral media, a subclass of materials known as bianisotropic materials, and numerical techniques have been developed in order to calculate the interaction of electromagnetic fields with chiral objects. One canonical problem for these techniques is plane-wave scattering from a chiral sphere. This work presents a software package that displays and saves the calculated data for the scattering from a chiral, dielectric, or perfectly conducting sphere using a friendly graphical user interface (GUI).     

A novel four-point bend test for strength measurement of opticalfibers and thin beams. I. Bending analysis

A novel four-point bend apparatus is described for strength measurement of thin compliant beams that avoids the loading and gripping problems associated with other techniques. The apparatus has proved particularly useful for strength measurement of relatively weak optical fibers. In this four-point bend system, loading pin displacement rather than applied load is the measured quantity from which failure stress is calculated, avoiding the load based instability at high deflection. A single-ended support design for the loading pins permits the specimens to be conveniently immersed in the test environment and enables several specimens to be tested simultaneously. Nonlinearities in the deflection/stress relationship are analyzed and a correction factor to the linear bending theory is presented. Friction between the specimen and support pins is found to increase local stresses at the pins. In the second part of this work, a statistical analysis is presented that determines the effective tested length in bending and the tension to bending strength ratio. The predictions of the analysis are confirmed by strength measurements on a weak silica fiber