Space-charge and secondary emission effects in a computer simulation of crossed-field distributed-emission amplifiers

A generalized steady-state nonlinear electron-wave interaction theory is developed for the crossed-field distributed-emission or emitting-sole amplifier. The system equations are non-linear integro-differential equations, developed from the one-dimensional equivalent transmission-line equation, the Lorentz force equation, the continuity equation, and Poisson's equation. The effects of dc, RF and space-charge forces are taken into account, and secondary emission from the sole electrode is included in the theory. Digital computer solutions indicate a gain threshold with RF drive, and that the inclusion of space-charge forces and secondary emission enhances the gain. A linearly decreasing magnetic field near the output also increases the gain. Approximate solutions based on a hard-kernel-bunch (HKB) model are shown to give excellent agreement with the computer solutions.     

Exact principal mode field for a lossy coaxial line

Exact field equations for a lossy coaxial transmission line with an infinite outer conductor are presented. The corresponding determinantal equation is solved to obtain an exact propagation constant from which errors in the usual microwave approximation and an alternative full frequency range approximation are calculated. The calculations show that the microwave approximation, although containing a large relative error at the lower frequencies, is still useful in practical applications     

A hybrid equation approach for the solution of electromagneticscattering problems involving two-dimensional inhomogeneous dielectriccylinders

A numerical procedure for the solution of electromagnetic scattering problems involving inhomogeneous dielectric cylinders of arbitrary cross section is discussed. The cases of illumination by both transverse magnetic (TM) and transverse electric (TE) plane waves are considered. The scattering problems are modeled via a hybrid integral-equation/partial-differential-equation approach. The method of moments is applied to obtain a system of simultaneous equations that can be solved for the unknown surface current densities and the interior electric field. The interior region partial differential equation and the exterior region surface integral equation are coupled in such a manner that many existing surface integral equation computer codes for treating problems involving scattering by homogeneous dielectric cylinders can be modified easily to generate the block of the matrix corresponding to the surface current interactions. The overall system matrix obtained using the method of moments is largely sparse. Numerical results are presented and compared with exact solutions for homogeneous and inhomogeneous circular cylinders     

二维有耗介质目标重建的迭代－共轭梯度方法

本文提出了一种由已知的散射场数据重建二维非均匀有耗目标的复介电常数的迭代算法。连续采用多个方向的ＴＭ平面波照射目标，并分别采集目标区域外的散射场数据。本文利用矩量法．（ＭＯＭ）将积分方程变成矩阵方程，我们以Ｂｏｒｎ近似为初始值，通过多次迭代，实现目标特性的重建。通常，逆问题多是不适定的。为了克服解的不适定性，我们采用共轭梯度法（ＣＧＭ）求解逆问题。最后，通过计算机模拟，给出了一些数值重建结果。     

Standing spin waves in ferromagnetic thin films

A theory of spin wave resonance in ferromagnetic thin films is discussed in a manner that permits a computation of the real and imaginary parts of the circularly polarized RF fields as well as the power absorption spectrum. The case of the dc field intensity applied normal to the surface of the film is considered, and the saturation magnetization is taken as constant throughout the body of the film. Variations in dc fields near the surfaces are treated in the boundary conditions for the RF magnetization by considering the unsymmetrical nature of the exchange interaction at the surfaces. The boundary conditions are characterized by a constant for each surface that controls the degree of surface pinning in the RF magnetization. Damping is included in the formulation by means of a phenomenological constant in the spin wave equation and by simulaneous solution of this equation with Maxwell's equations for a conductor. The results of a computer program are presented showing the roles of the various parameters in determining the power absorption spectrum and RF fields. A comparison with experimental spectra is made, and an anomalous resonance at field intensities higher than that for the principal resonance is predicted.     

Pulse saturation in a traveling wave parametric amplifier

The pulse saturation on a nondispersive traveling wave parametric amplifier is solved in the slowly varying approximation with space and time by reducing the dynamic equations to a degenerate form-of the sine-Gordon equation. If the group velocity of the signal wave differs from that of the pump and idler waves, the signal wave obeys the sine-Gordon equation.     

Effect of an AC electric field on the conductance of single-wall semiconductor-type carbon nanotubes

The effect of an ac electric field on the conductance of a system of single-wall semiconductor-type carbon nanotubes placed in a dc electric field is considered. The strength vectors of dc and ac electric fields are directed along the nanotube axis. The electronic system of carbon nanotubes is considered in the context of the Boltzmann kinetic equation in the relaxation-time approximation. The dependence of the current density in the system on the characteristics of applied fields is studied. The effect of absolute negative conductance is detected.     

Study of a longitudinally nonuniform plasma layer

Transformation of the energy of surface waves in a plane plasma layer with a longitudinal irregularity of density is studied by the method of spectral decomposition. The total field is represented by an expansion in surface and pseudo-surface waves. A system of integro-differential equation for the coefficients of expansion determining the amplitudes of the transmitted, reflected, and scattered waves is obtained. It is shown that, in some special cases, this system of equations is reduced to a system of ordinary differential equations even if the plasma density rapidly changes. The fraction of the energy of surface waves that transforms into radiation at an acute angle with the layer can reach 50–60%.     

Scattering of surface magnetostatic waves by periodic slot gratings

Scattering of the magnetostatic surface waves generated in thin films by the gratings formed from slots in a metal screen is theoretically analyzed. A boundary-value problem for the Maxwell equations is formulated and solved in the static approximation. An algorithm of numerical solution of the boundary-value problem is proposed. Scattering of magnetostatic surface waves by 2D periodic slot gratings that are infinite along one coordinate and finite along the other coordinate is studied for an arbitrary orientation of slots and an arbitrary angle of incidence of the magnetostatic wave. The band structure of gratings is studied. The possibility of formation of magnonic crystals based on slot gratings is demonstrated.     

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.     

Numerical simulation of scattering from three-dimensional randomlyrough surfaces

Randomly rough surface patches in three dimensions are generated on the computer. The FD-TD method is used to compute scattering from surface patches by converting the Maxwell's equations into difference equations using a central difference approximation for the space and time derivatives. The volume of grids above the rough surface is divided into the total field and the scattered field regions. In between these two regions, obliquely incident waves are generated. To reduce computation, the volume of grids is chosen to be small, and a transformation is used to convert the scattered field into far zone fields for bistatic scattering coefficient calculations. Possible errors near the edge of the surface due to the use of a relatively small volume are suppressed by introducing a windowing function. Very good agreements are obtained between the results obtained by this method and those calculated by an integral equation method (IEM) for scattering from randomly rough perfectly conducting and dielectric surfaces     

A self-consistent field analysis of spherical-mirror Fabry-Perot resonators

The integral equation for the field distributions of the resonant modes in a spherical-mirror Fabry-Perot resonator is solved in the limit of infinite Fresnel numbers. With this approximation the electric field is described in terms of Hermite-Gaussian functions and the resonance condition is obtained. The variations of nodal surface radii and characteristic mode dimensions are examined. A new definition of incremental mode volume leads to a minimum volume at a mirror spacing to mirror radius ratio of 1.5.     

Microwave remote sensing of a two-layer random medium

A two-variable expansion technique is used to solve for the mean Green's function from the Dyson equation under the nonlinear approximation. The Bethe-Salpeter equation then gives rise to a set of modified radiative transfer (MRT) equations which accommodate coherent effects essential to bounded media. It is found that the nonlinear approximation, instead of the more popular bilocal approximation, should be used for the case of bounded media. The two approximations yield identical results for unbounded media. The MRT equations are then solved for a two-layer random medium. The MRT equations give rise to simple and useful solutions which are applicable to both active and passive microwave remote sensing.     

Coupled plasma waves in a system of two two-dimensional superlattices in the presence of a quantizing electric field

The effect of a dc electric field on coupled plasma waves in a system of two two-dimensional super-lattices is studied. In the case of high temperatures, a dispersion relation is obtained and the fundamental and resonant modes of the plasma waves are numerically studied. The calculations are performed based on the quantum theory of plasma waves in the random phase approximation taking into account umklapp processes.     

A new method of analysis for PWM switching power converters

A new method of analysis for pulse-width modulation (PWM) switching power converters is presented. It allows one to find an approximate periodic solution for the converter vector state variable. The converter is modelled by a differential equation with periodic coefficients. This equation is substituted by an equivalent system of linear differential equations with constant coefficients. Only the forced (steady-state) solutions should be found for each equation of this system. The equations are solved in sequence. The final steady-state solution of the PWM differential equation is obtained as the sum of these forced solutions. The method allows one to find the converter dc transfer function and efficiency, to evaluate their frequency dependences, and to find the critical frequency and ripple. The first three equations of the equivalent system are usually adequate for practical purposes, and these equations are obtained by an easy formal procedure. One can also obtain the dynamic equation of the state variable dc component, and calculate the converter line to output and duty cycle to output transfer functions. A boost converter is used as an example to confirm the analytical results by numerical simulation.     

The performance of a timer-controlled token passing mechanism withfinite buffers in an industrial communication network

The timer-controlled token-passing mechanism widely used in industrial communication networks is analyzed. Several real network parameters, such as finite buffers and finite token-holding time (THT), which generally determine the overall performance of a network, are considered. The approximate matrix equation between the queue length distribution and the token rotation time is derived. Based on this matrix equation, the equations for the mean waiting time and the blocking probability are also derived. These equations can be easily solved using personal computers, due to its simple matrix structure and small computation time. Using these equations, the performance of field bus or other timer-controlled token-passing networks can be more accurately evaluated, since finite size buffers and finite THT are considered. The approximation error is shown to be small by computer simulation     

On filtered binary processes

The problem of calculating the probability density function of the output of anRCfilter driven by a binary random process with intervals generated by an equilibrium renewal process is studied. New integral equations, closely related to McFadden's original integral equations, are derived and solved by a matrix approximation method and by iteration. Transformations of the integral equations into differential equations are investigated and a new closed-form solution is obtained in one special case. Some numerical results that compare the matrix and iteration solutions with both exact solutions and approximate solutions based upon the Fokker-Planck equation are presented.     

A calibrated model for the subthreshold operation of a short channel MOSFET including surface states

Describes a simple two-dimensional subthreshold model for short channel MOSFET's. The effects of surface state density are also included in the model. A regional charge density approximation was used in the solution of Poisson's equation and an analytical solution of the continuity equation in two dimensions was derived. Excessive computations are avoided in the present model; this was made possible by the use of a valid regional charge approximation. The model was experimentally verified by performing measurements on short channel devices. The model was calibrated from measurements on a long channel device which was present on the same silicon chip. Results are presented for the subthreshold leakage current as a function of substrate bias, polysilicon gate length, diffusion depth and surface state density.     

Analysis of diffraction of a plane wave and of the field of a point source by a multirow grating

A multirow grating of impedance or dielectric elements is considered. The 2D problem of scattering by such a grating is solved with the help of the modified null field method and the pattern equation method. A system of integral equations is derived and the reflection and transmission coefficients are determined as functions of various parameters of the problem. The excitation of the grating by a current filament is investigated. An asymptotic solution is obtained for the case when the periods of the grating rows and interrow distances are rather large. In the low-frequency approximation, a solution to the problem for a grating of circular cylinders is presented.     

Two-dimensional computer simulation models for MOSLSI fabrication processes

A two-dimensional process simulation program has been developed. The process models used for this program are oxidation, diffusion, ion implantation, and deposition/etching of CVD films. The numerical models are based on a finite-difference approximation to diffusion equation. A large number of equations derived from the diffusion equation are solved by Stone's method because of its excellent rate of convergence. Attention is paid primarily to lateral impurity diffusion and lateral oxidation near the edge of the oxidation mask. Oxidation enhanced diffusion of boron is also included. We have obtained good quantitative agreement between calculated and experimentally observed diffused line capacitance variation with reverse bias voltage which is strongly affected by the lateral channel stop diffusion in a locally oxidized process.