bluuebunny/crossref_metadata_2025_split huggingface dataset:
The use of orthogonal curvilinear meshes in TLM models
Authors: Meliani H. , De Cogan D. , Johns P. B. 
Published: August 2005

AbstractThe development of numerical models to describe physical problems with irregular boundaries frequently involves the use of very fine or variable Cartesian meshes when a more descriptive mesh might be appropriate. This paper describes the application of the transmission line matrix (TLM) technique to the analysis of orthogonal curvilinear mesh problems. Although very high levels of accuracy are possible, the computational efficiency may be reduced owing to the stub admittance factor, S, and the need for an accurate evaluation of the transmission line parameters.
A self‐consistent model for short‐channel mosfets
Authors: Banna M. El , Nokali M. El 
Published: August 2005

AbstractA de model for short‐channel MOSFETs is presented in this paper. Several second‐order effects associated with small‐geometry MOSFETs such as mobility degradation, carrier velocity saturation and channel length modulation are included in the model. The analysis emphasizes the modeling of the output conductance and the transconductance which are important in analogue circuit simulation. The theoretical predictions of the model are in good agreement with the experimental data available in the literature.
The 3D transmission‐line matrix method: Theory and comparison of the processes
Authors: Saguet P. 
Published: August 2005

AbstractThis paper presents an overview of the 3D transmission‐line matrix method of analysis, describing the various nodes which are available to date: expanded node, asymmetrical condensed node, symmetrical condensed node. The most general scattering matrices of these nodes are given. The various techniques used to implement irregularly graded meshes are also described. A comparison of all the processes applied to the same structure is made. Conclusions on their use are then discussed.
The discrete time domain Green's function or Johns matrix — A new powerful concept in transmission line modelling (TLM)
Authors: Hoefer Wolfgang J. R. 
Published: August 2005

AbstractA new TLM‐based concept analogous to the Green's function approach in classical electromagnetic theory is presented. It employs the procedure known as time domain diakoptics. The response of a TLM mesh to a unit impulse excitation at selected input points is interpreted as a discrete Green's function in the time domain, and the term ‘Johns matrix’ is proposed for this characteristic response. As in classical theory, the response of the mesh to an arbitrary excitation is found by convolving the excitation with its Johns matrix. This concept extends the generalized scattering parameter concept into the time dimension, opens unprecedented possibilities for partioning time domain problems at the field level, and permits large‐scale preprocessing of substructures for computer‐aided design. It also represents and elegant way of modelling broadband absorbing boundary conditions, imperfectly conducting walls and general frequency dispersive boundaries in the time domain.
The calculation of radar cross‐section (RCS) using the TLM method
Authors: German Fred J. , Gothard Griffin K. , Riggs Lloyd S. , Goggans Paul M. 
Published: August 2005

AbstractThe calculation of the radar cross‐section (RCS) of complex bodies using the symmetrical condensed TLM method is presented. The technique is based on a near‐to‐far field transformation of the TLM calculated near fields. Several two‐dimensional examples are presented which validate the method. The main advantage of utilizing techniques such as TLM for RCS computation lies in the ability to model arbitrary bodies with complex material compositions.
The modelling of networks with frequently changing topology whilst maintaining a constant system matrix
Authors: Hui S. Y. R. , Christopoulos C. 
Published: August 2005

AbstractThis paper describes a novel technique with which a system with changing topology can be modelled whilst maintaining a constant system matrix. This technique employs a new transmission‐line switch model which has a constant characteristic impedance, irrespective of its state. The method is explained, compared with the switched‐resistance method and demonstrated by two examples. It has been found that the proposed method offers substantial advantages in the formulation of the problems and in the efficiency of computation.
Analysis of acoustic radiation patterns of array transducers using the TLM method
Authors: Saleh A. H. M. , Blanchfield P. 
Published: August 2005

AbstractThe paper describes the application of the TLM numerical method for the analysis of acoustic wave propagation. It presents a general scattering algorithm for modelling homogeneous and inhomogeneous mediums where both the density and compressibility of the propagation space are varied. The method is used to obtain the acoustic radiation patterns of discrete transducer arrays. The effect of the spacing and the number of transducer elements on the radiation pattern are demonstrated by numerical results obtained using a two‐dimensional TLM mesh. The results also show the effect of array shading on the radiation pattern. Beam steering by delayed excitation of the transducer elements is also demonstrated here. In addition the paper presents two simple techniques for detecting the direction of wave propagation in the TLM mesh.
Numerical aspects of the boundary residual method
Authors: Bunch K. J. , Grow R. W. 
Published: August 2005

AbstractThe boundary residual method is a powerful technique for solving EM boundary‐value problems. This technique produces matrices difficult to solve using many of the standard numerical techniques. This paper discusses lesser‐known numerical aspects of this method, and it shows efficient and well‐conditioned methods to solve both the homogeneous and non‐homogeneous boundary residual problem.
Modelling of the generation of Ga interstitials during the diffusion of Zn into GaAs
Authors: Harrison I. 
Published: August 2005

AbstractThe diffusion of Zn into a GaAs crystal is modelled using numerical techniques similar to those of Zahari and Tuck.1 This technique does not directly solve any differential equations, the physical processes are directly modelled. The diffusion of Zn is assumed to be by the kick‐out mechanism. In this mechanism the Zn atoms diffuse into the crystal interstitially with a constant diffusion coefficient. The interstitial Zn atoms transfer to the substitutional lattice site by kicking out a Ga atom. The incorporation of the Zn atoms on to the lattice sites is assumed to take place at a rate much greater than the diffusion of the interstitial Zn. The diffusion of the generated Ga interstitial is also contained in the model. The effect on the Zn concentration profile and Ga interstitial concentration of varying both the Ga interstitial diffusivity and equilibrium concentration has been examined. Finally, the implications of these results on Zn induced disordering of GaAs/AlAs superlattices is discussed.
Modelling of electrically thick cylindrical antennas
Authors: Tan Soon Hie 
Published: August 2005

AbstractHallen's integral equation has been used as the basis for the formulation of cylindrical antenna theories for many years. Being a Fredholm integral equation of the first kind, its solution is mathematically an ill‐posed problem. The stability of the numerical methods based on this integral equation is dependent on the singularity and the non‐smoothness of the kernel function. For electrically thick cylindrical antennas, the dominance of the singular part of the kernel (logarithmic) is weakened and the kernel function becomes relatively smooth. This observation implies possible deteriorations of the stability of the numerical methods based on Hallen's integral equation. This paper describes the development of an alternative formulation for the electrically thick cylindrical antennas based on the singular integral equation of the first kind with a Cauchy‐type kernel which eliminates the potential instability problem. A numerical method based on this formulation of the antenna problem has been implemented and case studies show that it is very stable and efficient for the numerical modelling of electrically thick cylindrical antennas.
Radiation losses in microstrip antenna feed networks printed on multilayer substrates
Authors: Harokopus W. P. , Katehi P. B. 
Published: August 2005

AbstractThe effect of the substrate structure on the radiation properties of microstrip array feed networks is investigated with the space‐domain integral equation approach. Numerical and analytical techniques are employed to produce efficient computer algorithms. Results for space and surface wave losses are presented for corner discontinuities printed on substrate/superstrate, and two‐layer substrate structures. Comparisons are made with the single‐layer case.
An investigation of the numerical properties of the mode‐matching technique
Authors: Sorrentino R. , Mongiardo M. , Alessandri F. , Schiavon G. 
Published: August 2005

AbstractA new insight into the numerical properties of the mode‐matching (MM) technique is given at the example of capacitive and inductive diaphragms in rectangular waveguide. The presence of two sources of error is pointed out and the existence is demonstrated of an optimum modal ratio which produces the best compensation between the two errors. The MM technique is formulated in a generalized form as an integral equation for either the electric field on the aperture or the current on the diaphragm. This allows the edge condition to be incorporated into the basis functions in order to improve the numerical efficiency of the method. An extensive investigation of the numerical properties of the various formulations in different cases is presented, including the frequency behaviour of the numerical error.
Comprehensive MoL analysis of a class of semiconductor‐based transmission lines suitable for microwave and optoelectronic application
Authors: Wu Ke , Vahldieck Ruediger 
Published: August 2005

AbstractA comprehensive analysis procedure is presented to investigate mode propagation in a class of semiconductor‐based transmission lines suitable for application in microwave or optoelectronic circuits. The method of lines (MoL) has been used to investigate single or multiconductor planar transmission line structures printed on a combination of insulating and semiconducting substrate. Homogeneous as well as inhomogeneous doping areas in the semiconductor are included in the theoretical formulation. Numerical results are presented for III–V semiconductor travelling wave electro‐optic modulators in double‐rib, multilayer strip waveguide configuration, microslabTMtransmission lines with partial and full strip cover and slow‐wave MIS microstrip/coplanar transmission lines on thick and thin film semiconductor substrate with gradually inhomogeneous doping layer.
Improvements in the analysis of a TH0mp cavity for precise complex permittivity measurements
Authors: Marchildon Louis , Akyel Cevdet , Abdulnour Jawad , Gauthier Sylvain 
Published: August 2005

AbstractAn analysis of the relationship between complex permittivity and complex resonance frequency is proposed for a cylindrical cavity oscillating in a TM0mp mode. Effects of wall conductivity, coupling loops, and holes for the insertion of dielectric samples are fully taken into account. With dielectric samples of small radii, insertion holes produce the most important corrections. Their effect is modelled through a finite difference solution of the field equations in the neighbourhood of the holes. A computer program is described for the analysis, the use of which is illustrated with results of measurements.
An efficient velocity–space model of carrier transport in Gallium Arsenide
Authors: Dunn Douglas E. , de Araujo Carlos A. Paz 
Published: August 2005

AbstractA new GaAs carrier transport modelling methodology is presented, designed to address the competing needs of microscopic detail and of computational efficiency. The rationale for advanced semiclassical models based on the Boltzmann transport equation (BTE) are reviewed and discussed in terms of the unique properties of GaAs. A new methodology is then presented, formulated around a one‐dimensional velocity–space variable. It includes a realistic description of the GaAs band structure including multiple valleys, non‐parabolicity, and anisotropy, which is used to explicitly evaluate the scattering distributions, and rates, for different scattering mechanisms. These in turn allow a direct evaluation of the BTE scattering inegral, which is solved iteratively with the non‐scattering terms. Based on this methodology, a prototype model is shown to reproduce the GaAs velocity–field relationship in homogeneous, undoped material. Band structure and forward‐scattering effects are clearly visible in the model's solutions for the carrier velocity distribution. The model's computational simplicity, combined with a finer level of detail, makes it suitable for device simulation without invoking Monte Carlo or other computationally intensive methods.
Computational models for laminated magnetic materials
Authors: Silvester Peter P. 
Published: August 2005

AbstractThe permeability tensor of the homogeneous bulk material externally equivalent to a laminated packet of non‐linear, anisotropic, non‐hysteretic sheets is derived by symbolic computation. The composite permeability bears a surprisingly simple algebraic relationship to the local permeabilities of its component materials even in the general case. Several special cases of common interest, where the tensor permeability assumes symmetric or diagonal form, are examined. Results are presented both as algebraic expressions and as brief optimized Fortran subroutines suitable for fitting into field analysis programs.
Application of the TLM method to two‐dimensional scattering problems
Authors: Simons N. R. S. , Bridges E. 
Published: August 2005

AbstractIn this paper the application of the TLM method to electromagnetic scattering problems is investigated. To achieve the full computational benefits of using a time‐domain numerical method, pulse excitation can be applied together with Fourier transformation of an output impulse response to yield frequency‐domain results over a wide bandwidth. The configuration of the mesh is the same as that used in FD–TD scattering simulations (i.e., separation of the simulation space into total and scattered field regions). To terminate the exterior boundaries of the mesh, absorbing boundary conditions are applied to absorb the outward travelling waves. The effect of the absorbing boundaries on both time‐ and frequency‐domain results is investigated. Frequency‐domain scattered far‐field patterns are presented for perfectly conducting square and circular cylinders illuminated by an incident plane wave (TM case). Forward and back scattering cross‐section results obtained from a single TLM simulation indicate both the accuracy and efficiency of the method for calculating frequency‐domain results over a wide bandwidth.
Radiation and scattering of transient electromagnetic fields (invited paper)
Authors: Felsen Leopold B. 
Published: August 2005

AbstractUnder wideband and especially ultrawideband (short pulse) excitation, the electromagnetic fields, after encounters with a propagation or scattering environment, reveal features which range from highly resolved spikes or dips to smooth oscillations at early and late observation times, respectively. Time‐domain (TD) analytic modelling should be structured around wave objects which relate features (observables) in data to distinct features in the environment. A strategy to this end, named observable‐based parametrization (OBP), is proposed here. The rules are learned from frequency‐ and time‐domain asymptotics applies to spatial and spectral domain representations of tractable prototype problems. This leads to self‐consistent hybrid combinations OBP–TD travelling (wavefront) and oscillatory (resonant) synthesizing basis fields; the latter include novel TD leaky modes for guiding wave channels and TD Bragg modes for periodic arrays. These concepts are illustrated by examples.
Characteristics of a rectangular waveguide containing a magnetized cylindrical ferrite post
Authors: Diamandi Ioanna , Sahalos John N. , Vafiadis Elias 
Published: August 2005

AbstractA rigorous formulation of the scattering by a magnetized ferrite in a rectangular waveguide is presented. The EM field depends on the dimension, the frequency and the internal static magnetic field of the ferrite post. For some special values of the above quantitites the reflection or the transmission coefficient becomes equal to zero. These values give a family of filters and the results which follow explain their characteristics.
An investigation of the different TLM configurations used in the modelling of diffusion problems
Authors: Ait‐sadi Rachida , Naylor Phillip 
Published: August 2005

AbstractThe commonly used transmission‐line modelling (TLM) network of one‐dimensional diffusion problems often results in unwanted oscillations. Two different TLM configurations (line boundary (LB) and resistance boundary (RB)), are investigated with some techniques necessary to reduce the oscillations. Comparisons between the various LB and RB models addressed in this paper, indicate that, in general, two‐dimensional TLM models produce consistently more accurate results.
TLM modelling using an SIMD computer
Authors: Tan C. C. , Fusco V. F. 
Published: August 2005

AbstractA major limitation of the transmission‐line matrix (TLM) method used to solve Maxwell's equations is the long computation time required. The TLM scattering calculations involved can, however, be viewed as parallel in nature. This paper describes an effort to reduce computational time by using an SIMD, DAP multiprocessor computer employed to solve a two‐dimensional TLM electromagnetic field formulation. A parallel algorithm based on the TLM scattering algorithm is designed and implemented using FORTRAN‐ PLUS Enhanced on an AMT DAP 510 machine. Here the connectivity of the DAP is exploited to simulate the intrinsic scattering behaviour on which the TLM algorithm relies. The results show that parallel processing on an SIMD machine such as the DAP is advantageous, especially for higher‐order mesh sizes.
Integral equation formulation of radiation from rectangular waveguides and horns
Authors: Moheb H. , Shafai L. 
Published: August 2005

AbstractThe radiation field patterns of rectangular waveguides and horns of finite dimensions are obtained numerically. The electric field integral equation is formulated to relate their radiation patterns to the surface current distribution. These currents are determined numerically by reducing the integral equation to a matrix equation, using the moment method. The computed currents are then used to calculate the radiation patterns and cross‐polar fields of the finite wavegiudes and horns. The method is numerically efficient and can be applied to the computation and optimization of the antenna feed configurations.
Numerical simulation of two‐valley semiconductor device model based on an ENO shock capturing algorithm
Authors: Radunvić Desanka , Radunović Jovan 
Published: August 2005

AbstractSimulation results for a n+−n−n+ two‐valley semiconductor device obtained by use of a shock capturing numerical agorithm are presented. The one‐dimensional problem is modelled by two systems of Euler equations connected by their source terms, and the Poisson equation. The resulting system of seven equations is hyperbolic and non‐linear, and it is a great problem to find an adequate numerical approximation of its time‐dependent discontinuities. There are additional complications due to the stiffness of the source terms.The numerical method used in this paper is first‐order acurate in time but of high spatial order in regions of smoothness. Before the method is applied, the system has to be transformed to a characteristic form. The adopted shock capturing algorithm enables the choice of the order of the accuracy by the appropriate choice of the reconstruction polynomial. Reconstructions of the second and fourth order are tested and some numerical results are presented. Because of the stiffness of the source terms, the sixth‐order accurate scheme breaks down. The results presented, and especially the response obtained of the structure to the step and periodic applied voltage, prove the correctness of the used schemes.
On the responses of strip‐line interconnects with discontinuities excited by external fields
Authors: Sali S. 
Published: August 2005

AbstractAn algorithm is developed to evaluate the responses of discontinuous coplanar strip‐lines excited by external electromagnetic fields. The algorithm uses the cascade chain matrix method which employs the distributed circuit parameters to model the external field coupling to the line and it is applicable to most commonly encountered discontinuities in microwave integrated circuit interconnects on lossy substrates. A general CAD program is developed based on this model and it is applied to realistic coplanar strip‐line interconnections with geometric and resistive discontinuities to illustrate the capabilities of the algorithm. These interconnect models are selected from a practical microwave integrated circuit design. Simplicity and fast speed of the algorithm enable computer‐aided analysis of externally induced electromagnetic noise in integrated circuits to be carried out. The effects of dielectric losses in the integrated circuit substrates and the discontinuities in the conducting tracks on the wave coupling are investigated in isolation.
Parallel three‐dimensional finite difference beam propagation methods
Authors: Masoudi Husain M. , Arnold John M. 
Published: August 2005

AbstractIn this work, we show the implementation of two explicit three‐dimensional finite‐difference beam propagation methods (BPM) on two different parallel computers, namely a transputer array and a Connection Machine (CM). To assess the performance of using parallel computers, serial computer codes of the two methods have ben implemented and a comparison between the speed of the serial and paralledl codes has been made. Large gains in the speed of the paralled FD‐BPMs has been obtained compared to the serial implementations. In addition, a comparison between the performance of the transputer array and the CM in executing the two FD‐BPMs has been discussed. Finally, to assess and compare the two methods, three different rib waveguides and three different directional couplers have been analysed and the results compared with published results.
Adaptive finite element mesh generation program for electron gun simulation
Authors: Xia S. , Broers A. N. 
Published: August 2005

AbstractThis paper describes a computer program for generating finite element meshes for electron guns. Two new methods, the ‘projection’ and the ‘mesh density function’ methods, are used to generate the mesh. The new methods enable the mesh distribution to be set smothly and changed easily, and also enable the mesh distribution to be adjusted according to parameters associated with the gun configuration or by feedback from the electric field calculation. The new program, which can handle a large variety of complicated electron gun structures, has been used in conjunction with the SOGUN program which has been developed by Zhu and Munro for electron gun simulation.