线性动态网络混合分析法

提出了线性动态网络(时不变、时变)混合分析法,将线性时不变电容和电感的电流、电压,线性时变电容的电流、电压和电荷,线性时变电感的电流、电压和磁通都作为独立变量与节点电压一起参与分析,可以方便地形成由一组线性代数方程与一组微分方程构成的混合方程。虽然方程的规模有所扩大,但方程的建立较为容易。这一混合方程在时域离散后成为一组线性差分方程,易于用计算机进行数值求解。     

Planar near-field to far-field transformation using an equivalentmagnetic current approach

An alternative method is presented for computing far-field antenna patterns from near-field measurements. The method utilizes the near-field data to determine equivalent magnetic current sources over a fictitious planar surface that encompasses the antenna, and these currents are used to ascertain the far fields. Under certain approximations, the currents should produce the correct far fields in all regions in front of the antenna regardless of the geometry over which the near-field measurements are made. An electric field integral equation (EFIE) is developed to relate the near fields to the equivalent magnetic currents. The method of moments is used to transform the integral equation into a matrix one. The matrix equation is solved with the conjugate gradient method, and in the case of a rectangular matrix, a least-squares solution for the currents is found without explicitly computing the normal form of the equation. Near-field to far-field transformation for planar scanning may be efficiently performed under certain conditions. Numerical results are presented for several antenna configurations     

Direct tunneling at the front contact of amorphous silicon p-i-ndevices

The device physics behind hole direct tunneling currents at the front contact of a-Si:H p-i-n homojunction have been explored. In this paper, the dark I-V, the light I-V, and the QE characteristics of this structure with and without hole direct hole tunneling currents are evaluated and compared. The three differential equation systems of the Poisson's equation, the continuity equation for free electrons, and the continuity equation for free holes have been solved with allowances for direct tunneling currents. Hole direct tunneling currents at the front contact of a-Si:H p-i-n homojunctions give rise to a significant increase in the dark current level at high forward voltages and to an increase in the open-circuit voltage of the light I-V characteristic when the front electron barrier is low. The hole thermionic emission current and the hole direct tunneling current have been carefully compared to the front contact. Hole tunneling currents introduce important modifications to the carrier transport physics not only to the front contact but also in the bulk of the a-Si:H p-i-n homojunction     

Surface integral formulation for calculating conductor anddielectric losses of various transmission structures

The power-loss method, along with a surface integral formulation, has been used to compute the attenuation constant in microstrip and coplanar structures. This method can be used for the analysis of both open and closed structures. Using the surface equivalence principle, the waveguide walls are replaced by equivalent electric surface currents and dielectric surfaces are replaced by equivalent electric and magnetic surface currents. Enforcing the appropriate boundary condition, and E-field integral equation (EFIE) is developed for these currents. Method of moments with pulse expansion and point matching testing procedure is used to transform the integral equation into a matrix one. The relationship between the propagation constant and frequency is found from the minimum eigenvalue of the moment matrix. The eigenvector pertaining to the minimum eigenvalue gives the unknown electric and magnetic surface currents     

Comparison of tunneling currents in graphene nanoribbon tunnel field effect transistors calculated using Dirac-like equation and Schrodinger’s equation

The tunneling current in a graphene nanoribbon tunnel field effect transistor(GNR-TFET) has been quantum mechanically modeled. The tunneling current in the GNR-TFET was compared based on calculations of the Dirac-like equation and Schrodinger’s equation. To calculate the electron transmittance, a numerical approach-namely the transfer matrix method(TMM)-was employed and the Launder formula was used to compute the tunneling current. The results suggest that the tunneling currents that were calculated using both equations have similar characteristics for the same parameters, even though they have different values. The tunneling currents that were calculated by applying the Dirac-like equation were lower than those calculated using Schrodinger’s equation.     

异质结耗尽层基区侧复合对突变HBT重要性分析

基于热场发射.扩散载流子输运模型,在电流连续性方程中包含异质结(BB结)耗尽层基区侧复合电流的前提下,推导出了描述突变HBT电流特性的新解析方程.在此基础上,探讨了对BB结耗尽层基区侧复合电流各不同考虑情况下的HBT电流计算结果的差异程度.结果表明:在较高集电极电流密度处,E-B结耗尽层基区侧的复合电流很重要;此外,在电流连续性方程中包含E-B结耗尽层基区侧的复合电流,这在更高集电极电流密度处也是必要的.     

理想导体半圆柱TE波散射的混合法解

本文应用混合技术分析了在TE平面波激励下,理想导体半圆柱的双站散射。该混合技术是把半圆柱劈附近的电流表示为未知数,圆柱曲面上的一阶电流应用Fock理论求解,高阶绕射电流表示为含有未知系数的Fock型函数。圆柱平面上的一阶电流用物理光学近似和曲劈的一致性几何绕射理论得到。劈的二阶绕射电流表示为含有未知系数的GTD形式。然后通过磁场积分方程,运用简单矩量法求得劈附近的电流和未知的绕射系数。最后计算了理想导体半圆柱的双站散射截面,结果与矩量法的结果吻合得相当好。     

Coupling Between Two Collinear Parallel-Plate Waveguides of Unequal Widths

The problem of coupling between two collinear parallel-plate waveguides of unequal widths is investigated using the moment methods. The exciting mode of the waveguide is assumed as the incident field and an integral equation for the induced currents is expressed in terms of the reflected, the transmitted, and the evanescent currents on the walls of the waveguides. This integral equation is solved numerically and the results for the reflections and the transmission coefficients and the radiated field are obtained. The effect of varying the coupled waveguide width and the separation distance of the waveguides is investigated.     

周期性结构电磁感应电流宽带特性的快速计算

采用MOM法将周期结构的电场积分方程转化为关于感应电流的矩阵方程和频率导数矩阵方程，并根据Pade逼近理论由给定频率处的频率导数感应电流确定周期性结构在任一频率入射波照射下的感应电流，进而计算周期性结构的电磁感应电流宽带特性。计算结果表明，AWE在计算速度上比MOM可加快十几倍。     

On the Evaluation of Antenna-Mode Currents Along Transmission Lines

In this paper, we derive an integral equation describing the antenna-mode currents along a two-wire transmission line (TL). We show that when the cross-sectional dimensions of the line are electrically small, the integral equation reduces to a pair of TL-like equations with equivalent line parameters (inductance and capacitance). The derived equations make it possible to compute the antenna-mode currents using any traditional TL coupling code with appropriate parameters. The derived equations are tested against numerical results obtained using numerical electromagnetics code (NEC), and reasonably good agreement is found     

Single integral equation for electromagnetic scattering bythree-dimensional homogeneous dielectric objects

A single integral equation formulation for electromagnetic scattering by three-dimensional (3-D) homogeneous dielectric objects is developed. In this formulation, a single effective electric current on the surface S of a dielectric object is used to generate the scattered fields in the interior region. The equivalent electric and magnetic currents for the exterior region are obtained by enforcing the continuity of the tangential fields across S. A single integral equation for the effective electric current is obtained by enforcing the vanishing of the total field due to the exterior equivalent currents inside S. The single integral equation is solved by the method of moments. Numerical results for a dielectric sphere obtained with this method are in good agreement with the exact results. Furthermore, the convergence speed of the iterative solution of the matrix equation in this formulation is significantly greater than that of the coupled integral equations formulation     

Numerical solution of integral equations for dielectric objects ofprismatic shapes

A numerical method to investigate scattering from dielectric geometries of prismatic shapes has been developed. The surface integral equations are formulated by Schelkunoff's equivalence principle in terms of equivalent surface electric and magnetic currents. To solve these integral equations for the unknown currents, the object's cross-section is mapped onto a circle. In the transformed space, Fourier type entire-domain basis functions are used in the cross section and triangular subdomain basis functions are selected along the generating curve to represent the currents. A moment method is then used to reduce the integral equations to a matrix equation to compute the current coefficients. It is found that the transformation of the object's surface to a circular shape improves the convergence of the current mode in the cross-section. However, the current modes are coupled on the surface and the matrix equation includes all the modes     

Block Diagonalization of the Electromagnetic Impedance Matrix of a Symmetric Buried Body Using Group Theory

A major problem with the volume-current integral-equation technique of three-dimensional electromagnetic modeling is the computational time and-storage required to form and solve the impedance matrix equation for the scattering currents. If the horizontal cross sections of a body with vertical sides all possess a certain symmetry, the matrix contains information about the effect of the symmetry on the scattering currents. This information can be deduced easily using group representation theory independent of any numerical computation or particular incident field geometry, and the original matrix, containing redundant informnation, can be replaced by a block-diagonal matrix. A straightforward example is used to illustrate this general technique. The computer storage requirements and solution time for the block-diagonalized matrix equation are significantly smaller than those for the original matrix equation.     

Modelling current/voltage characteristics of space-charge-limitedcurrents with nonlinear velocity-field relationships

A simple empirical equation is presented to describe the current/voltage characteristic of space-charge-limited currents in semiconductor materials with a nonlinear velocity-field relationship. The equation covers the entire current/voltage characteristic and yields asymptotic behaviour in good agreement with previously published results     

Scattering by an infinite wedge with tensor impedance boundaryconditions-a moment method/physical optics solution for thecurrents

Plane wave scattering by an infinite, two-dimensional wedge whose faces are characterized by impedance tensors is discussed. A combination of the moment method (MM) and physical optics (PO) is used to obtain a solution for the equivalent electric currents. The currents near the edge on each face are expanded with a set of basis functions consisting of pulse functions, defined on a meshed region, plus a function spanning the whole face. The currents outside the meshed region are taken to be the sum of physical optics currents, taken to be known, plus the whole-face basis function current. Expressing the equivalent magnetic currents in terms of the electric currents through the impedance tensors, the expansion coefficients for the electric current expansion are determined through an MM solution of the magnetic field integral equation. Sample results for wedges with isotropic and anisotropic face impedances are presented     

The Analysis of Monopole Antennas Located on a Spherical Vehicle: Part 2, Numerical and Experimental Results

Presented are various numerical results illustrating the behavior of thin monopole antennas located on a perfectly conducting sphere. The method of analysis, described in a previous paper, uses an integral equation solution for the unknown wire currents, and a modified Green's function to limit the range of integration to over the wires only. Studies are made of the input quantities, radiated currents and induced sphere currents for various antenna geometries. A comparison of the computed input impedance of monopole on the sphere is made with experimental data and good agreement is noted.     

Analysis of cavity-backed aperture antennas with a dielectricoverlay

A full-wave analysis of cavity-backed aperture antennas with a dielectric overlay is presented. The theoretical approach uses a closed-form dyadic Green's function in the spectral domain. The aperture equivalent magnetic currents are obtained using the surface equivalence theorem and an integral equation is obtained by matching the fields across the aperture. The moment method applied in spectral domain analysis is employed to solve the integral equation for the equivalent magnetic currents with proper combination of subdomain or entire domain expansion functions. Numerical results include the aperture field distribution and antenna parameters such as input impedance, bandwidth, and efficiency. A set of measurements data is compared with results based on the theoretical work     

Electromagnetic analysis of an antenna embedded in a compositeenvironment

This paper addresses the problem of an antenna embedded in a hole dug in the ground. The composite medium configuration consists of a half-space dielectric (representing the Earth-air interface) containing a cylindrical hole filled with a different dielectric medium. The wire antenna resides within this hole, on the axis. The solution strategy is based on decomposing the problem into simpler subproblems, which are treated sequentially. First we calculate a numerical dyadic Green's function for the composite medium by solving an integral equation formulated over a background consisting of the unperturbed dielectric half space (for which the Green's functions are known in a spectral integral form). This integral equation is solved via the fictitious currents method, which is a special case of the method of moments. We then solve the integral equation for the antenna currents using this numerical Green's function and determine the input impedance and radiation pattern     

Scattering by perfectly-conducting rectangular cylinders

The problem of determining the fields scattered by a perfectly-conducting rectangular cylinder is reduced to the solution of an integral equation. This equation is then solved by digital computer methods. Data are given for surface currents, radiation patterns and scattering cross sections for bothE- andH-incident waves.     

Field emission from cadmium sulphide

A technique for etching fine field emitters of CdS single crystals has been developed. Relatively high field-emission currents at low voltages are obtained (typically 10?6 A at 2kV). The results, when plotted, agree with the Fowler?Nordheim equation, with deviations at currents above 10?7 A and below 10?9 A. Possible explanations of the deviations are discussed.