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  • Articles  (258)
  • Electrical and Electronics Engineering  (233)
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  • Electrical Engineering, Measurement and Control Technology  (258)
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  • Articles  (258)
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  • 1
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. i 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 2
    Electronic Resource
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 75-75 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 3
    Electronic Resource
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 127-139 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: In this paper the traditional square mesh 2D-TLM algorithm is generalized for rectangular meshes of arbitrary aspect ratio. It is shown that the anisotropic rectangular TLM network can be conceived in such a way that the propagation vector remains independent of the direction of propagation in the infinitesimal approximation. A full dispersion analysis of the rectangular mesh in then performed for the general case, and results are compared to that of the traditional square mesh.
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  • 4
    Electronic Resource
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 155-166 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The 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.
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  • 5
    Electronic Resource
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 167-177 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Ray-besed methods have been previously developed for accurately predicting the electromagnetic scattering from cavity interiors that allowed for realistic modelling of complex cavities such as jet engine inlets. An analytic geometric model is developed for bifurcated cavities based on connecting sections of generalized super-ellipse functions. The electromagnetic scattering from such cavities using the ‘shooting and bouncing rays’ (SBR) method is discussed.
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  • 6
    Electronic Resource
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 209-221 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A theoretical analysis has been developed to study the crosstalk in crossed bundles of parallel lines. The model is based on the theory of the coupled transmission lines and the resulting system of differential equations has been solved by means of the finite difference, time-domain (FDTD) method. The frequency response of the network has been achieved by the discrete fourier transform (DFT) algorithm; measurements, performed with a vectorial network analyser, show a good agreement with numerical simulation.
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  • 7
    Electronic Resource
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 35-41 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The eigenmodes in electromagnetic cavities, loaded with arbitrarily shaped dielectric materials, are computed by the edge element method. The computation shows that the well known ‘spurious modes’ no longer appear. Formulae are given and verified so that the number of zero eigenvalues, which come from ∇ × H = 0, may be accurately predicted. Formulae for the order and density of the global matrices are given for a rectangular cavity regularly divided into bricks and tetrahedra, allowing an associated comparison between the contrasting edge and nodal element formulations. Comparison of the computed results with available theoretical and previously published data show the edge element approach to be a robust, accurate and effective method.
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  • 8
    Electronic Resource
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 253-265 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A numerical frequence-domain modelling of two-terminal, non-linear microwave circuits is presented. It basically relies on a process allowing the solution of the frequency-domain curcuit harmonic balance equations while accounting for the semiconductor device by means of an accurate numerical macroscopic physical model. In its present state of development, the model allows the study of a single two-terminal device circuit operating in harmonic mode. Its capabilites are illustrated by means of the results of a study devoted to the optimization of the load curcuit configuration of a millimetre-wave avalanche diode frequency multiplier. The influence of the output load impedance level on the circuit output RF performance has been investigated for different input power levels in direct frequency multiplication mode and in the presence of additional circuit tunings at low harmonic rank idler frequencies.
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  • 9
    Electronic Resource
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994) 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 10
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 309-319 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: This paper describes a rigorous and systematic procedure to derive a non-linear distributed FET model that an easily be implemented in CAD routines of simulators based on harmonic balance techniques. The new model is derived from a knowldge of the conventional linear lumped equivalent circuit, from non-linear current sources extracted with pulsed measurements, and from the physical dimensions of the FET.For fundamental and haromonic requencies, the FET is modelled by N identical cells. Each cell is made up of a non-linear two-port section inserted between two linear four-port sections that simulate the coupling and the distributed effects along the electrodes of the FET in the width direction only. This non-linear distributed scaling approach to FET modelling has been applied to the analysis of a submicrometre-gate GaAs FET at Millimetre-wave frequencies, and the results were compared to the non-linear lumped element approach. This approach can be applied to other transistors used in non-linear regions at microwave and millimetre-wave frequencies.
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  • 11
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 375-375 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 12
    Electronic Resource
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. ii 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 13
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 399-405 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Symbolic computational systems introduce some unique features in computational engineering. There have been several papers published on the solution of differential equations under given boundary conditions by symbolic systems. The finite element formalism has received prime attention in the course of development of symbolic computation in engineering. The main idea has been to develop a symbolic FEM package to reduce the burden of manual algebra, eliminate errors introduced by numerical quadrature, and improve the efficiency of element generation.This work discusses a symbolic solution to electromagnetic linear antenna problems. The solution is a method of moments that transforms Pocklington's integral equation to a matrix equation. The symbolic system is used to produce (1) analytical integration, (2) the parametric expression for the input impedance and (3) computational code for forward and reverse problem of the input impedance.
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  • 14
    Electronic Resource
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 419-432 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: This paper presents a new finite element formulation in the Laplace domain for both diffusion and wave equations with applications in the field of electrical engineering. With the aid of congruence transformation of matrices, the finite element equations in the Laplace domain are solved and time-domain results can be obtained through the inverse Laplace transform. In a test problem, good agreement between the numerical results derived with the present method and the analytical solutions has been found. For applications in which only Dirichlet and Neumann boundary conditions are involved, this new finite element approach can be applied and provide both frequency-domain and time-domain results in one run without any timestepping scheme. The limitations of using the congruence transformation in solving propagation problems are also addressed in this paper.
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  • 15
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 433-452 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A hybrid method obtained as a combination of the coupled-mode method (CMM) and the mode-matching method (MMM) is developed and applied in the analysis of multiple dielectric and magnetic discontinuities in rectangular waveguides. As both are moment methods, some kind of truncation has to be carried out in the computer implementation. It is shown that selection of a different number of modes in the two methods is not necessary, unless low-permittivity meida inside the waveguide are considered. As a consequence, the procedure for slecting the number of basis functions is only done in one of the methods. Numerical examples are presented showing the behaviour of the method and the proofs of convergence. Examples are included illustrating the power of this hybrid technique, especially in relation to non-reciprocal structures containing magnetized ferrites.
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  • 16
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994) 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 17
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 15-24 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: This paper describes the application of the boundary element method to solving two-dimensional steady slow viscous flow problems (creeping flow) in thermal silicon oxidation. The proposed method used the velocity-pressure formulation. The use of the incompressibility condition as a boundary condition and the application of the second Green's identity to transform the domain integral into a boundary integral result in a system of three boundary integral equations for velocity components and pressure. Solution of this system to be an ill-posed problem because of the presence of boundary conditions of the first kind. Two methods of regularization are employed. The numerical results for trench oxidation process are presented.
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  • 18
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994) 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 19
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 43-67 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The particle-in-cell method is coupled with boundary-fitted co-ordinates in order to model the stationary Maxwell-Lorentz problem in technical devices. New numerical algorithms describing the transition between the grid model and the mesh-free model are developed and the existing techniques of finite difference schemes for equidistant grids are extended to non-equidistant, arbitrarily shaped, convex four-point meshes. The modelling process is described, and both the numerical approximation and the algorithms are discussed. Applications in different technical devices show the flexibility of the method.
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  • 20
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 77-84 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Series function expansion algorithms of the time-domain analysis of boundary value problems are discussed. Electromagnetic fields inside a structure under investigation are expanded into series of basis functions and the expansion coefficients are found by means of the Galerkin method. The numerical cost of algorithms is discussed and a cost efficient approach is proposed for formulations using sine and cosine expansion functions. Compared with conventional time-domain methods the algorithms described show the time evolution of the expansion coefficients rather than the samples of a physical continuum at discrete nodes.
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  • 21
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. ii 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 22
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 189-199 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A rigorous technique for studying a thin wire circular loop antenna excited by a magnetic frill is developed. The exact kernel is derived and used to improve the accuracy. The scheme is applicable to small as well as large loops. Results obtained are nearly indistinguishable from those determined by the Fourier expansion method for non-resonant loops. A disagreement of 2 per cent is generally observed when the loop is close to reasonant for βb 〉 2. Compared with the conventional numerical method where a loop is represented by a polygon of straight wires, the present scheme is much faster and more accurate. Extension of this method to cover an antenna system of arbitrarily oriented loops intermingled with straight wires can be easily achieved.
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  • 23
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994) 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 24
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 239-252 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Simulation 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.
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  • 25
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 283-304 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: An 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.
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  • 26
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 329-342 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The finite element method (FEM) with local absorbing boundary conditions has been recently applied to compute electromagnetic scattering from large 3-D geometries. In this paper, we present details pertaining to code implementation and optimization. Various types of sparse matrix storage schemes are discussed and their performance is examined in terms of vectorization and net storage requirements. The system of linear equations is solved using a preconditioned biconjugate gradient (BCG) algorithm and a fairly detailed study of existing point and block preconditioners (diagonal and incomplete LU) is carried out. A modified ILU preconditioning scheme is also introducted which works better than the traditional version for our matrix systems. The parallelization of the iterative sparse solver and the matrix generation/assembly as implemented on the KSR1 multiprocessor is described and the interprocessor communication patterns are analysed in detail. Near-linear speed-up is obtained for both the iterative solver and the matrix generation/assembly phases. Results are presented for a problem having 224,476 unknowns and validated by comparison with measured data.
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  • 27
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 371-372 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 28
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 357-370 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The calculation of potentials in homogeneous and isotropic media by the boundary element method has the advantage that a harmonic solution of Laplace's equation is obtained for given approximated boundary conditions. The technique leads to the solution of linear systems with full matrices of dimension 1000-10,000 for medium- and large-sized three-dimensional problems, An efficient solution procedure of the linear systems is required.While the iterative solution of the large and sparse linear systems arising from the finite difference or the finite element method is well documented, the systems resulting from the boundary element method are typically solved by direct methods. However, in many cases an iterative solver needs far fewer operations to achieve a sufficient accuracy. Importantly, there are many alternative methods, each of them well suited for different types of problem.Here, we provide an overview of state-of-the-art iterative solvers. We will discuss the particular methods that have been successfully applied to systems arising from field calculations in the high-voltage engineering by the boundary element method. The selection of appropriate methods is discussed. We demonstrate that iterative solutions can be much faster than direct solvers with regards to the number of operations. Furthermore, these solvers are optimally suited for today's supercomputers because they can be efficiently vectorized and parallelized.
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  • 29
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 407-418 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: This paper provides details of a widely applicable technique of hybrid modelling of thermal and particle diffusion which can help to reduce computational load in explicit formulation. The undesirable effects of artificial boundaries, which are introduced when a simulation is truncated or when an expanding mesh is used, can be eliminated by the use of discrete Green's functions. The technique can also be applied to problems involving infinite or near-infinite domains or problems where a complex thermal region is embedded within a larger, more simply described domain.
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  • 30
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 179-188 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A convex hexahedral TLM mesh of arbitrary shape is presented and the transmission-line matrix method extended to any non-orthogonal configuration. The novel mesh constitutes a natural generalization of Johns' condensed node. The associated TLM process is analysed and reconstructed as a genuine finite difference time-domain algorithm. Nodal S-parameters are derived from discretized Maxwell's equations and canonical stability criteria yield the TLM timestep. Unitarity is discussed and energy conservation confirmed in the non-conductive case.A given block-diagonal representation of the S-matrix restrains processing time per node and iteration within the range of traditional methods. The shortcomings of the rigid classical grid, as the need for inaccurate staircasing approximations, are, however, ruled out.Our analysis takes advantage of the recently developed propagator integral approach.
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  • 31
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 201-207 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The existing treatment of an instantaneous endothermic change of state is extended to deal both with exothermic effects and with first order Arrhenius changes. These extended treatments are used to model complex changes of phase occurring during the firing of ball clay and china clay, both of which are constitutents of the slip used in the production of vitreous china ware. The adequacy of the treatments is investigated for both clays by comparing a TLM simulation of a DSC (differential scanning calorimetry) experiment with measurements made during the experiment.
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  • 32
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 321-328 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The paper describes and compares the wave-chain and transmission matrix approaches to the calculation of transfer-function coefficients for ladder circuits (semi-symbolic analysis). It is found that the wave-chain matrix approach can be computationally more efficient.
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  • 33
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 343-355 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: To make possible the application of the three-dimensional finite element method to electrically large problems, it is combined with the analytical solutions of arbitrary large cavity with aperture. In this paper, detailed analysis for this hybrid method is presented. The element matrices necessary for coupling the finite element method to analytical solutions are given. The proposed hybrid method significantly reduces the number of unknown since only the inhomogeneity needs to be discretized. Thus computer memory and storage demands are reduced. In addition. This hybrid method employs the edge element which is not expected to produce spurious solutions. Also, the formulation presented in this paper preserves the sparsity of the finite element matrix, and does not require any matrix inversion. This new hybrid method is used to compute the field distributions in various partially filled rectangular enclosure. The results match well with the pure edgebased finite element method and analytical solutions.
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  • 34
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 377-398 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Field computations by mathematical and numerical methods are presented in the time and frequency domain. The techniques used are discretization and modal expansion. The effects of modelling and frequency range on the accuracy and calculation requirements are investigated and discussed. By way of application, several results of RF-filter designs are presented, where these methods have been implemented in CAD programs.
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  • 35
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 453-453 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 36
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 1-14 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Variational boundary element formulations are developed. Two functionals based on the dual and complementary energy approach are considered, which provide the upper and lower bound of the solution. Calculated examples of electrostatic fields are demonstrated for their field distributions and capacitances. Validity and the solution accuracy are discussed in comparison with the conventional boundary element solution.
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  • 37
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 25-33 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The method of effective penetration depth is used to produce a novel scalar or polarized finite difference approach for the solution of optical rib waveguide field problems. The new method is quicker than previous finite difference approaches and requires less computer memory. Propagation constant values are presented for a range of semiconductor rib waveguides and are found to be indistinguishable from benchmark results produced using earlier methods of analysis. A simple polarization correction formula recently derived is confirmed by utilizing the good accuracy of these results. This enables discussion of the relationship between quasi-TE, quasi-TM and scalar modes, and a further substantial reduction of the cpu time.
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  • 38
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 69-74 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The application of multigrid techniques to the computation of the static solutions of electromagnetic field problems governed by Laplace's equation is described. This technique is compared with the conventional successive over-relaxation (SOR) method for solving finite difference problems. In contrast to SOR, the number of iterations of multigrid needed to achieve convergence is largely independent of the grid size. It is shown that the relative performance of multigrid is excellent on large grids where the number of iterations of SOR needed to achieve convergence becomes prohibitively large. The technique is illustrated by applying a parallel implementation of multigrid to find a quasistatic solution of a boxed microstrip problem.
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  • 39
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 85-97 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A new approach to efficiently compute the low-frequency eigenmodes of a time-domain model approximating a linear physical system is proposed. The method is based on principles known from digital signal processing, in particular from parametic spectrum estimation, so it is not surprising that the achievable accuracy is much higher than the accuracy of the usual non-parametric discrete Fourier transform approach. The algorithm works in the general lossy case even for a very large number of unknowns and can easily be extended to calculate steady-state solutions under sinusoidal excitations for several different frequencies simultaneously.
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  • 40
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 99-125 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: In this paper we demonstrate the use of differential equations by means of an example from network analysis and show that differential/algebraic equations (DAE), rather than explicit ordinary differential equations (ODE), are more suitable for the description of electrical systems and networks. The main ideas of numerical integration of ODEs are presented. We consider this material from the point of view of replacing the ODE by a difference equation (DE). In particular, the relationship between the ODE and the associated DE is discussed. In the last Section the application of integration methods for OEDs upon DAEs and its difficulties are discussed. The paper is intended as a review; but a few new results are also included.
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  • 41
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994) 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
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  • 42
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 141-153 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Applying the method of moments to Maxwell's equations, Yee's two-dimensional FDTD scheme with central difference approximations and the two-dimensional TLM method are dervied from first principles of field theory. By comparing the eigenvalues of the two methods, the differences between two-dimensional FDTD and TLM are illustrated.
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  • 43
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 225-238 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Transverse transmission concepts in the Fourier transmission domain for multilayer planar transmission medium are presented. This complete transverse transmission theory (TTT) is found to be a superset of different Fourier-transform-based numerical techniques widely used in guided wave analysis, namely the modematching method and the spectral-domain approach. The features of the theory are: the expansion of field quantities in longitudinal section (LSE/LSM) modes, the concept of rotation of the transverse field vectors, and a comprehnsive algorithm using recursive matrix standard form. It is shown that the mode-matching method and spectral-domain approach are generally equivalent except for the last step of imposing the final boundary conditions, and can therefore be summarized in a unified theory within the framework of TTT. In addition, a new parameter, the polarization coefficient, has been introduced to describe the field polarization of the guided wave in a quantitative manner. It is believed that the present theory will help us to gain more insight into hybrid mode propagation in multilayer planar circuits.
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  • 44
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 267-281 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: This paper considers the adaptation of drift-diffusion device simulation methodology to study Auger-recombination-induced hot electron transport characteristics in InGaAsP/InP double heterostructure laser diodes. In order to model the transport behaviour of the Auger hot electrons, we decompose the conventional electron current continuity equation into two components, with one for the Auger hot electrons and the other for the low-energy electrons. These equations, which use the energy relaxation time parameter to model the dynamics of the Auger hot electrons, are then coupled with the hole current continuity equation and the Poisson equation to obtain self-consistent solutions. Results from the case studies of one-dimensional N-p-P InGaAsP/InP double heterojunction laser diodes with material composition corresponding to 1·3 μm and 1·55 μm wavelength emissions are presented. We have observed that hot electrons generated through Auger recombination inside the active region can spread into both the N- and the P-InP cladding layers. Within the drift-diffusion framework, it is demonstrated that the hot electron concentration in the N-InP cladding layer can be five orders of magnitude higher than that in the P-InP cladding layer. Because energy transport of the hot electrons in not modelled under the drift-diffusion approximation, the simulated results are discussed to highlight some of the possible limitations in using drift-diffusion physics to study Auger hot electron transport behaviour. The importance of taking energy transport into account is emphasized.
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  • 45
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 307-307 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 46
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994) 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 47
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    Advanced Materials for Optics and Electronics 4 (1994), S. 343-347 
    ISSN: 1057-9257
    Keywords: Dimethyzinc ; Adduct ; MOVPE ; GaAs (p-doping) ; AlGaAs (p-doping) ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The adduct between dimethylzinc and triethylamine has been used as a p-dopant source in the growth of GaAs and Al0.3Ga0.7As alloys by metalorganic vapour phase epitaxy (MOVPE). The dopling efficiency of this adduct in these alloys and in InP is lower than that of dimethyl zinc.
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  • 48
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    Advanced Materials for Optics and Electronics 4 (1994), S. 401-405 
    ISSN: 1057-9257
    Keywords: MOVPE ; ZnSe ; Growth mechanism ; Surface chemistry ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: In situ optical reflection measurement was employed to study surface processes during the MOVPE growth of ZnSe films under an alternate supply of diethylzinc (DEZn) and dimethylselenide (DMSe) using H2 and/or N2 as carrier gases. We have found that the time-dependent reflection signal exhibits a unique saw-toothed pattern during the DEZn supply, which is attributed to the adsorption and structural change of the DEZn. In contrast, the influence of DMSe on the time-dependent signal appears to be rather marginal. A growth mechanism is proposed based on these experimental results, through which the important role of ambient hydrogen is discussed.
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  • 49
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    Advanced Materials for Optics and Electronics 3 (1994), S. 151-161 
    ISSN: 1057-9257
    Keywords: MOVPE ; (Hg, Cd)Te ; Decomposition products ; GC-MS ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The pyrolysis reactions of di-isopropyl telluride and dimethyl cadmium, both alone and in combination and with and without mercury, have been studied using the technique of gas chromatography-mass spectrometry (GC-MS). For example, when mercury and dimethyl cadmium are mixed in hydrogen at the growth temperature (370°C), the volatile products observed are methane, ethane and dimethyl mercury. In contrast, when di-isopropyl tellurideis substituted for the cadmium precursor in this reaction, the products observed are propane, propene and 2,3-dimethylbutane with no volatile mercury-containing compounds. Heating the two organometallic precursors together at the growth temperature in the absence of mercury gives products expected from the pyrolysis of each one alone plus a number of interaction products such as 2-methylpropane. The results of these studies will be presented, a mechanism for the reactions proposed and the implications for MOVPE growth discussed.
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    Advanced Materials for Optics and Electronics 3 (1994), S. 191-198 
    ISSN: 1057-9257
    Keywords: ZnSe ; ZnSSe ; GaAs substrate ; MOVPE ; Photoluminescence ; Quantum well ; Interface properties ; Growth interruption ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: In this work we report on ZnSxSe1 - x/ZnSe quantum wells grown by atmospheric pressure MOVPE on GaAs substrates. Diethylznc (DEZn), diethylselenium (DESe), diethylsulphur (DES) and H2S were used as source materials. Binary quantum wells with ZnSe or ZnS as barrier were usually grown in sets of 10 pairs on a 0.5 μm ZnSe or ZnS buffer, respectively. QWs with different well thicknesses (1-4 nm) show a typical shift to higher energies with decreasing well thickness and also a large decrease in PL intensity with increasing well thickness. Owing to the onset of relaxation above 5 nm well thickness, no PL emission could be observed. QWs of the same thickness but grown at different temperatures (420-520°C) show a broadened line shape with decreasing growth temperature. Growth interruption (3-50 s) also causes a broadening of the PL emission with decreasing interruption time. This is caused by interface reconstruction at higher growth temperatures and longer growth interruption. A ZnS buffer of 0.5 μm improves the PL line shape compared with a ZnSe buffer.ZnSxSe1 - x/ZnSe single and multiple QWs (Lz = 1-4 nm) were grown to reduce the strain in the structures. A typical quantum confinement energy shift of 160 meV for the 1 nm well can be observed in ZnS0.68Se0.32/ZnSe QWs. In comparison with the binary QWs, the FWHM could be reduced by about a factor of two to 34 meV. This improvement was obtained by an optimisation of the switching process to prevent the desorption of sulphur from the ZnSSe during the growth interruption.
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  • 51
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    Advanced Materials for Optics and Electronics 3 (1994), S. 73-80 
    ISSN: 1057-9257
    Keywords: MOVPE ; ZnSxSe1 - x ; MQW ; Optical properties ; Lasing Exciton ; Electron-hole plasma ; Dynamics ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Non-linear and stimulated emission of ZnSxSe1 - x/ZnSe multilayer structures grown by MOVPE on GaAs is investigated by means of high-density excitation spectroscopy using a high-resolution pulsed excimer-dye laser system as well as a picosecond titanium-sapphire laser for time-resolved measurements. Heterostructures with ZnSe layers or single and multiple quantum wells were grown in which the ZnSe layer widths were varied between 1 nm (strong quantum confinement) and 500 nm (quasi-bulk situation). The sulphur concentration in the ZnSxSe1 - x buffer, barrier and cap layers was chosen between x = 0.045 and x = 0.74 in order to find the most promising compromise with regard to maximum band offset to ZnSe for most efficient carrier confinement and suitable waveguiding properties depending on variation in the refractive index, and to highest structural quality of the actively emitting ZnSe layers. Stimulated emission is found to occur in all samples, being brightest in the sample with the lowest sulphur concentration in the cap and barrier layers. Its dynamical properties point to a probable interpretation in terms of electron-hole plasma creation, which, however, may not be the basic process in narrow-quantum wells or strongly structurally disturbed samples.
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  • 52
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    Advanced Materials for Optics and Electronics 3 (1994), S. 183-190 
    ISSN: 1057-9257
    Keywords: Scanning transmission electron microscopy (STEM) ; High-resolution ; Z-contrast ; ADF ; HAADF ; Electron energy loss spectroscopy (EELS) ; ZnSxSe1 - x/ZnSe quantum wells ; MOVPE ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Epitaxial growth techniques for ZnSxSe1 - x/ZnSe heterostructures have already achieved a high degree of development. Further improvements strongly require characterisation techniques with high compositional sensitivity and high spatial resolution. Therefore in this work high-resolution Z-contrast, which provides compositional information down to the atomic scale, has been used for the first time to characterise ZnSxSe1 - x/ZnSe quantum well structures. The influence of structural defects on Z-contrast is demonstrated by comparison of scanning transmission electron microscopy (STEM) bright field images and STEM Z-contrast micrographs of planar defects and dislocations. The compositional abruptness of ZnSxSe1 - x/ZnSe interfaces in MOVPE-grown quantum well (QW) structures is judged from high-resolution Z-contrast micrographs. Electron energy loss spectroscopy (EELS) measurements were performed for the first time in ZnSxSe1 - x/ZnSe QW structures in order to obtain quantitative compositional information with nanometre spatial resolution. From EELS line scans, which monitor the selenium concentration across ZnSe QWs, the obtainable spatial resolution is estimated to be about 1-2 nm. The problems that have prevented quantitative analysis of the selenium concentration up to now are discussed.
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    Advanced Materials for Optics and Electronics 3 (1994), S. 203-208 
    ISSN: 1057-9257
    Keywords: ZnSe ; Diallylselende ; Plasma ; MOVPE ; Nitrogen doping ; Raman spectroscopy ; Photoluminescence ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: In order to obtain high quality Znse epilayers on GaAs which can be intentionally P- and n-type doped growth at a reduced temperature is highly desirable. Therefore in this work the suitability of diallylselenide and the influrnce of plasma precracking have ben investigated. Photoluminesscence, Raman spectroscopy, scanning electron microscopy, X-ray, SIMS and Hall measurements were used to anaylse the samples. The selenium precursor was fully decomposed at temperatures above 360°C if it was precracked by a plasma. Bound excitions could be resolved with negligible donor-acceptor pair (DAP) and copper green emission in the PL spectra form films which were grown with a plasma at temperatures beyond 530°C. Clearly the hpe for reduction in the deposition temperature was not achieved. Raman spectra also revealed strong crystalline quality variations. For the doping experiments nitrogen was used as the carrier gasa instead of hydrogen. Plasma cracking of the selenium precursor was still necessary. Thye substitution of the H2 carrier gas by nitrogen reduced the growth rate by a factor of 2.6 but enhanced the crystalline properties of the samples as shown by the Raman measurements. Strong DAP emission at 2.7eV in the (PL) spectra was observed. SIMS measurements showed a nitrogend concertration of about 3 × 1017 cm-3. An additional nirtogen plasama (0-7W) had a begligible effect on the nitrogen concentration in the sample. The samples were semi-insulating, whichmight be a conswquence of the crystalline quality of ZnSe grown with DASe as selenium precursor.
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    Advanced Materials for Optics and Electronics 3 (1994), S. 239-245 
    ISSN: 1057-9257
    Keywords: Substrates ; MOVPE ; MCT ; Surface morphology ; Structural properties ; Photoconductors ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: After a review of the structural properties of (Hg,Cd)Te layers grown by MOVPE on GaAs substrates, topical questions such as out-diffusion of Ga and As from the substrate into the layers, monolithic integration of signal procesing into the substrate and the presence of pyramidal defects in (100) layers will be discussed. In order to solve the last problem, a systematic study of the influence of the (h11) GaAs substrate orientation and polarity on the structrual properties and surface morphology of CdTe layers grown by MOVPE has ben carried out. Twin-free layers are obtained on (211)A, (311)B and (511)B GaAs surface orientations as ezplained by a model taking into accountthe type of dangling bonds at the interface. The performance of photoconductors fabricated on(Hg,Cd)Te layers of various orientations confirms these results. Particularly good results have been obtained for the (311)B orientation.
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    Advanced Materials for Optics and Electronics 3 (1994), S. 261-267 
    ISSN: 1057-9257
    Keywords: ZnSe ; ZnSxSe1 - x ; MOVPE ; Photoluminescence ; Mapping ; Purified ; DESe source ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: In this paper we report new results concerning the cause of impurities responsible for the Ix, and I2-peaks in photoluminescence (PL) spectra of ZnSe grown by MOVPE. An improvement in ZnSe epilayer quality is obtained by using a metal organic selenium precursor with reduced chlorine concentration. The PL spectrum of such a layer shows typical excitonic transitions, but compared with samples grown with a more contaminated source, the intensity of the Ix, and the I2 peaks decreases relative to the free exciton transition. A Gaussian fitting of the donor-bound exciton peaks taking the background of other structures into account shows that the ratio between the Ix and I2 peaks does not differ significantly between two samples. Both the decrease in donor-bound exciton transitions and the unchangeability of the ratio Ix/I2lead to the conclusion that only chlorine impurities are responsible for Ixand Ix. In order to verify the homogeneity of impurity uptake across a 2 inch wafer, we performed PL mapping of ZnSxSe1 - x layers. Mapping of a 2 inch ZnSe wafer shows that the FWHM of Ix across a wafer does not vary significantly (1.55 ± 0.21 meV). On mapping a 2 inch ZnS0.3Se0.7 wafer fabricated with H2S as the sulphur source at TD = 480°C, we found a rotational symmetric dstribution of sulphur in the layer. The sulphur content x at the centre is nearly constant. The difference in x between the centre and the boundary of a bad surface region at the edge of the wafer is less than Δx = 0.045. The FWHM of the band edge luminescence follows the same tendency across the wafer. The dependence of homogeneity on the reactor design as well as the uptake of unintentional impurities from the precursor is discussed in detail.
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    Advanced Materials for Optics and Electronics 3 (1994), S. 51-55 
    ISSN: 1057-9257
    Keywords: MOVPE ; Quantum wells ; ZnSe/ZnSxSe1 - x heterostructures ; Gain ; Excitons ; Luminescence dynamics ; Transfer processes ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Optically pumped stimulated emission in ZnSe/ZnSxSe1 - x heterostructures grown by MOVPE has been observed up to 170 K. Gain measurements have been performed using the variable stripe length method. The underlying gain mechanism at 25 K is atributed to an excitonexciton scattering process. Photoluminescence excitation spectra and the temporal evolution of the luminescence indicate a transfer process from the ZnSxSe1 - x barrier into the ZnSe active layer.
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    Advanced Materials for Optics and Electronics 3 (1994), S. 275-282 
    ISSN: 1057-9257
    Keywords: Far-infrared spectroscopy ; Raman spectroscopy ; MOVPE ; ZnSe ; Implantation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: We discuss the optical analysis of Zn(Se,S) layers by the application of far-infrared (FIR) and Raman spectroscopy. First a summary is presented of the principles of FIR and Raman Spectroscopy with regard to the relevant epilayer properties which can be investigated by these methods. Subsequently we treat some selected results of FIR and Raman analysis of epilayers grown on GaAs(100) by metal organic vapour phase epitaxy (MOVPE). The main points of interest are crystalline quality, free carrier concentration and interface sharpness. It is shown that n-type conductivty is achieved by Ga implantation in ZnSe but the annealing process (870°C, 30 s) leads to a p-type interface layer in the GaAs due to Zn diffusion. Furthermore, the beneficial effect of growth interruptions to the sharpness of ZnS/ZnSe multiquantum-well interfaces is demonstrated.
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  • 58
    ISSN: 1573-4862
    Keywords: Beam propagation ; bimetallic weld ; Gauss-Hermite beam model ; finite element method ; ultrasonics ; anisotropic medium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract In this paper, predictions of two models for the propagation of ultrasonic beams through a two-dimensional, bimetallic weld geometry are compared. The finite element method can predict beam propagation through quite general geometry with high accuracy. This model, however, requires significant computational time. On the other hand, the approximate Gauss-Hermite model offers considerably greater computational speed, but has lower accuracy in certain regions and cannot treat the most general geometries and inhomogeneities in material properties. This paper compares the performances of the two models for the case of the two-dimensional, bimetallic weld consisting of multiple layers, some of which have anisotropic properties. It is found that the results of the two models are in good agreement in the vicinity of the central ray, and that the deviation increases as one moves away from the axis. Also, as the beam propagates through multiple interfaces, the accuracy of the Gauss-Hermite solution decreases.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 167-167 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 183-193 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: An equivalent circuit for a symmetrical condensed TLM node is presented. The basic circuit has twelve ports and consists of 24 1:1 ideal transformers. Three additional conductances model the conductivity of the medium. The circuit is extended with additional ideal transformers giving six ports for short-circuit and open-circuit stubs which model the permittivity and permeability of the inhomogeneous medium. The scattering matrix of the 18-port network is determined symbolically by solving a set of linear circuit equations. The matrix agrees with previously published results for a symmetrical condensed TLM node, obtained from Maxwell's equations.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 233-236 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: We have extended the one-dimensional transmission-line modelling (TLM) of diffusion, drift and recombination of charge carriers in semiconductors to multiple dimensions. Detailed TLM formulation of the continuity transport equation in a more general form is presented.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 29-45 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The Hilbert space representation of the TLM method for time-domain computation of electromagnetic fields and the algebraic computation of the discrete Green's function are investigated. The complete field state is represented by a Hilbert space vector. The space and time evolution of the field state vector is governed by operator equations in Hilbert space. The discrete Green's functions may be represented by a Neumann series in space- and time-shift operators. The Hilbert space representation allows the description of the geometric structures by projection operators, too. The system of difference equations governing the time evolution of the electromagnetic field in configuration space is derived from the operator equation for the field state vector in the Hilbert space.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 67-81 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The state and output equations of the overall networks are derived from the state and output equations of individual multiports and knowledge of the interconnections between them. A generalized lumped-distributed L/D multiport is described by its associated state, output and non-linear equations in the time domain. Any network can be considered as composed of a set of multiports and independent sources. These equations have been incorporated into a computer-aided procedure for the analysis of L/D networks. The procedure can be used for the simulation of any non-linear microwave circuit and offers the facility of developing a multiport equivalent circuit for any linear or non-linear device or subcircuit. Several examples are successfully analysed using the developed general program.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 109-126 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The difference equations of the scalar linear transmission-line matrix (TLM) routine as introduced by Johns for numerically solving the diffusion equation are shown to be isomorphic to Goldstein's correlated random walk model of diffusion. For the infinite homogeneous bar their exact solution is derived algebraically and given in the form of Jacobi polynomials. This puts the TLM algorithm on a sounder mathematical and physical basis. The accuracy in solving the diffusion equation is investigated in general form and thus its astonishing efficiency explained. Several other basic questions of this numerical technique are also discussed.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 161-164 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A comparative study of two alternative networks for TLM modelling of diffusion processes has been undertaken. Some of their inherent advantages and disadvantages are analysed according to the ratio between the impedance of the lossless transmission lines and the lumped resistance. Their relative accuracy and utility in controlling the timestep automatically are examined.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 237-251 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: This paper describes a rigorous and systematic procedure to derive a non-linear distributed FET model that can easily be implemented in CAD routines of simulators based on harmonic balance techniques. The new model is derived from a knowledge of the conventional linear lumped equivalent circuit, from non-linear current sources extracted from pulsed measurements, and from the physical dimensions of the FET.For fundamental and harmonic frequencies, the FET is modelled by N identical cells. Each cell is made up of a non-linear two-port section inserted between two linear four-port sections that simulate the coupling and the distributed effects along the electrodes of the FET in the width direction only. This non-linear distributed scaling approach to FET modelling has been applied to the analysis of a submicrometre-gate GaAs FET at millimetre-wave frequencies, and the results were compared with the non-linear lumped element approach. This approach can be applied to other transistors used in non-linear regions at microwave and millimetre-wave frequencies.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 283-297 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A finite element method formulation is given for solving Schrodinger's wave equation for a single electron in a crystal lattice cell subject to a known periodic potential. The formulation has been implemented for a two-dimensional lattice, with an arbitrary potential profile, modelled by quadratic isoparametric elements, The FEM solver returns a specified number of electronic energy states, En, and nodal values of the complex wavefunctionψn Input data is generated by a standard FEM mesh generator. The postprocessing, given n, for reproducing a full 2-D E-k Brillouin diagram and given k, the electronic distribution, has been implemented. Tests on a 2-D generalized Kronig-Penney energy band model showed excellent agreement; between FEM results and analysis. The solver was further satisfactorily checked against published augmented plane wave calculations for a circular potential well within a square lattice. Specimen results are presented for the same circular well but with graded potential distributions and for a rectangular potential barrier set askew in a square lattice. Two-dimensional energy band solvers have application to superlattice nanostruc- tures, whilst a general, full 3-D FEM quantum solver seems feasible.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 299-304 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A 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.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 1-1 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 19-27 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: We show the derivation of parameters in the frequency domain from time-domain data. Far-field characteristics are obtained by a convolution formula with the harmonic field amplitudes, which are obtained via a Fourier transform or by sampling. The electric field of filter ports is expanded into the discrete eigenmodes. By this method, a monochromatic exact open boundary can be formulated and the fields divided into the incident and the reflected part. For wide band operation an a posteriori error correction scheme is presented.
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    Keywords: Engineering ; Electrical and Electronics Engineering
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 99-108 
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    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A 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.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 145-159 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A finite difference method is used to design a new type of sectoral horn antenna with corner channel inserts which produces a tapered aperture amplitude distribution in the E-plane. The channel inserts, which present a simple modification to the horn aperture geometry, act as effective side-lobe suppression devices. The efficiency of the suppression technique was successfully tested on an experimental horn whose performance is compared to that of a horn with similar geometrical dimensions but with no channel sections.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 127-134 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The stress birefringence and mode coupling effects in polarization-preserving fibres are most important problems which need to be improved. For a realization of some optical devices, the dielectric waveguide with sinusoidally varying circular cross-section has been investigated. It becomes very important to analyse the electromagnetic field distribution in a dielectric waveguide with a time-dependent moving boundary. This paper shows that numerical methods can simulate the effect of the external disturbance on the dielectric waveguide from time to time. The author has discussed body fitted grid generation with moving boundary for the Poisson and Laplace equations.1,2 We have extended this technique for Maxwell's equation. The technique employs a kind of an expanded numerical grid generation. As the author adds the time component to grid generation, the time dependent co-ordinate system which coincides with a contour of moving boundary can be transformed into a fixed rectangular co-ordinate system. We could show the electric distribution in the waveguide time by time to verify the possibility of an application for an optical fibre. This technique makes it possible not only to analyse the effect of the external disturbance in a coherent optical communication system but also to fabricate optical devices.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993) 
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    Keywords: Engineering ; Electrical and Electronics Engineering
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 207-220 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A propagator integral interpretation for general TLM processes is presented and applied to discretized Maxwell's equations. The approach provides exact algebraic solutions of finite difference equations along a quite universal scheme.Specifically, Johns's process based on the symmetrical condensed node is reconstructed and generalized as a clear-cut FD algorithm. The fields computed are exact time-domain solutions of the FD equations, provided that total voltages and currents are evaluated and stub quantities are not externally excited. Losses are very naturally incorporated into the TLM algorithm.The structural similarity of the TLM process (properly operated) with the propagator integral appears just as fundamental as general and should have further applications.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 195-206 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The computer implementation of time-domain finite difference methods for the solution of Maxwell's equations is considered. As the basis of this analysis, Maxwell's equations are expressed as a system of hyperbolic conservation laws. It is shown that, in this form, all the well-known differencing schemes can be easily expressed, thus increasing the applicability of the implementation issues to be discussed. Practical issues, such as computational efficiency and memory requirements, are discussed for the implementation of the finite difference schemes. Advanced programming techniques in the C language are used to implement the finite difference schemes discussed. The example of the penetration of electromagnetic energy through a shield with a thick gap is used to check the performance of the methods. It is shown that, for cases where the disturbance remains localized in the computational mesh, these techniques result in memory and CPU time savings.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 221-231 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Photoconductive circuit elements (PCEs) are suitable for switching applications: they can be turned on and off rapidly, they can conduct a large current in the ‘on’ state when applying a laser or other optical excitation containing high energy photons exceeding the silicon band gap energy, they have a large resistance in the ‘off’ state when the light is off, and they can be fabricated using a simple process. We report the steady- state characteristics of PCEs simulated from a two-dimensional simulator called PISCES-2B. The effects of the conducting channel length, the resistivity of the intrinsic silicon, and the type of contact region on the performance of the PCE will be investigated and discussed. Based on the simulation results, optimal PCE device make-ups will also be suggested.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993) 
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    Keywords: Engineering ; Electrical and Electronics Engineering
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 269-281 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The estimation of transfer-function parameters, such as poles and zeros, is useful for characterizing and identifying electromagnetic scatterers. The conventional frequency-domain Prony's technique can estimate these parameters from sampled, frequency-domain data. However, it fails to estimate the true parameters when the sampled data contains contributions from out-of-band poles. In this paper, an extended frequency-domain Prony's technique is developed that circumvents this problem by adding polynomial terms to the standard, Prony pole series. This new technique is shown to be very effective for estimating the poles of transfer functions over very wide bandwidths, without the need for large numbers of simultaneous equations, even when the data are corrupted by noise.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993) 
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 3-17 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Ultra-wideband (UWB) pulsed plane wave scattering from a large but finite strip grating in free space is analysed in the frequency domain via decomposition into plane wave spectra, implemented numerically by the method of moments, and then inverted into the time domain (TD). To make this procedure practical under UWB conditions, closed form expressions are derived for interaction integrals involving widely separated expansion and testing functions. These closed forms are based on a judicious choice of the basis functions, and on asymptotic methods for reducing the integrals. Although large separation distances are assumed, the expressions have been found to be accurate for separations as small as 0·1 wavelengths. The TD self terms can also be evaluated efficiently. To test the frequency domain algorithm, comparisons are made with available data in the literature for surface currents and far-field scattering from multiple strips. New short pulse TD results are shown as well.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 47-65 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: In this paper a new TLM model for the two-dimensional wave equation is introduced. It is synthesized directly from a FD algorithm. The FD algorithm is second-order-accurate in both space and time, and is explicitly time-stepped. The spatial derivatives in the FD algorithm are approximated by the weighted combination of two standard central difference stencils, one oriented as usual, the other rotated by 45° with its arms extended by a factor of (2)1/2. The TLM model is realized as the weighted connection of two original models (with the same geometrical configuration as the FD algorithm). The weighting in the TLM model is accomplished by using a variable intrinsic impedance for specific elemental transmission lines. The FD and TLM methods possess identical dispersion relations if the former is operated at its upper limit of stability. Therefore, under these conditions both represent identical models for the simulation of wave propagation. The propagation characteristics of the new model are investigated and the conditions for approximate numerical isotropy are provided. The numerical implementation (scattering matrix and transfer event) is described. To validate the new model, the calculation of cutoff frequencies of various modes in rectangular waveguide is performed. Comparison with analytical results (for an unfilled waveguide) and other numerical results (for a waveguide partially filled with a dielectric) validate the implementation of the model.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 83-98 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A major limitation of the boundary element method (BEM) for the solution of electrical potential problems is the long computational time required. However, a large portion of the calculations involved can be viewed as being parallel in nature and can therefore be computed concurrently. This paper makes an effort to increase the efficiency of the BEM process using transputer-based multiprocessor computing techniques. The algorithms developed may equally well be applied to any multiprocessor system. The application selected to demonstrate the technique is the solution of an electrostatic problem governed by a two-dimensional Laplace equation.A parallel algorithm for problem setup and field extraction using BEM is designed and implemented on a transputer array. Special attention is directed to the utilization of the parallel processors to achieve maximum efficiency. The analysis in this work concentrates on the communication strategies for passing data between processors as well as a consideration of the workload attributed to each processor.The parallel algorithms were implemented using 3L Parallel Fortran; however, the choice of topology for the overall BEM implementation was limited by the fact that certain parts of the algorithm could only utilize a pipeline configuration of processors. Comprehensive results for the parallel BEM algorithm are given and they are encouraging, indicating that parallel processing has much to offer when applied to the boundary element method.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 135-144 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Redundancy in the simplest form of a two-dimensional TLM network is identified and a method of eliminating it is described. Results obtained using the non-redundant algorithm are compared with those derived from the standard, redundant algorithm. The non-redundant approach is extended to deal with non-uniform elemental capacitance; a cylindrical geometry is taken as an example of this. The scope for and benefits of rendering TLM diffusion models non-redundant are discussed.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 165-166 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 169-181 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A numerical approach to the estimation of the current density distribution and the eddy current loss in bundled multi-wire cables using the boundary element method is proposed. Under the assumption of the gradual twist of the bundled wires, the cables are modelled to be two-dimensional with respect to their cross-sections. Three-phase transmission lines of cyclic symmetrical configuration are considered for which a reduction method is utilized to provide efficient computation. Some numerical demonstrations are made for three types of three-phase transmission-line models, consisting of a single wire and three and seven bundled wires. Two cases are considered: one in which the bundled wires are electrically contacted one to another on their surfaces and one in which they are independently insulated. The equivalent resistance is also calculated to examine the skin effect. The skin effect and the effectiveness of the multi-wire configuration to reduce the skin effect are well demonstrated.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 253-268 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The 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.
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 6 (1993), S. 305-307 
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    Keywords: Engineering ; Electrical and Electronics Engineering
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    Journal of nondestructive evaluation 11 (1992), S. 9-17 
    ISSN: 1573-4862
    Keywords: Casuality ; effective medium ; ultrasonics ; polycrystalline medium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract The paper investigates the transient response of a random medium as predicted by two methods, a perturbation scheme and a causal approach. It is shown by direct computation of a pulse propagation that the perturbation scheme yields an “advanced” response inconsistent with the physical realizability of the medium. The causal model as well as a modified perturbation scheme exhibit a physically reasonable behavior.
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    Journal of nondestructive evaluation 11 (1992), S. 69-77 
    ISSN: 1573-4862
    Keywords: Welds ; flaw classification ; ultrasonics ; neural networks
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract A probabilistic neural network is used here to classify flaws in weldments from their ultrasonic scattering signatures. It is shown that such a network is both simple to construct and fast to train. Probabilistic nets are also shown to be able to exhibit the high performance of other neural networks, such as feed forward nets trained via back-propagation, while possessing important advantages of speed, explicitness of their architecture, and physical meaning of their outputs. Probabilistic nets are also demonstrated to have performance equal to common statistical approaches, such as theK-nearest neighbor method, while retaining their unique advantages.
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  • 92
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    Springer
    Journal of nondestructive evaluation 11 (1992), S. 221-226 
    ISSN: 1573-4862
    Keywords: Nonlinear viscoelastic behavior ; adhesive layers ; ultrasonics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract The purpose of this paper is to provide a theoretical framework to study the nonlinear viscoelastic behavior of adhesive layers. The stress-strain behavior of the adhesive material in shear is assumed to have a nonlinear elastic part and a linear viscoelastic part, i.e., σ yx =f(ε yx )+K mεyx. To measuref(ε yx ) andK m by an ultrasonic technique, it is proposed to prestress the adhesive layer in the nonlinear range and to superimpose a small amplitude ultrasonic signal. The reflected field is used to obtain the wave speed and hencedf(ε yx )/dε yx as a function of the pre-stress. The viscoelastic parameter is obtained from the amplitude decay. By repeating this procedure for various values of prestress and using numerical integration, the stress-strain behavior of the adhesive layer can be reconstructed.
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  • 93
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    Springer
    Journal of superconductivity 5 (1992), S. 119-125 
    ISSN: 1572-9605
    Keywords: YBa2Cu3O7 ; MOVPE ; vapor pressures ; β-diketonates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The vapor pressures of theβ-diketonates Y(THD), Ba(THD), and Cu(THD), commonly used as precursors for MOVPE of YBa2Cu3O7, and Y(MCP) were measured at different temperatures. A time-resolved static method recording the pressure vs. time at constant temperature was used, permitting us to deduce the vapor pressure even if the materials tend to decompose. The values of the constants of the Clausius-Clapeyron equation log10p(T)/p 0=A-B/T are,A=11.7, 8.7, 8.27, 16.6 andB=4359, 2654, 3602, and 6453 K for Y(THD), Y(MCP), Ba(THD), and Cu(THD), respectively withp 0= 1 Pa and temperatureT in K. The thermal stability of the sources was measured and are discussed.
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  • 94
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992), S. 67-81 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A novel spectral procedure for the numerical solution of non-linear boundary value problems is presented. The discrete spectral equations are solved by an iterative algorithm using space-domain preconditioning. The preconditioning operator is obtained by spatial weighting (or windowing) of the exact differential operator.Convergence behaviour of the iterative solution is investigated using an eigenvalue analysis. Theoretical estimates for the convergence rate and accuracy are compared with that achieved in a numerical application - a non-linear boundary value problem from semiconductor device modelling.The method combines the infinite-order exponential accuracy of spectral discretizations with the sparse structure of finite difference equations. This offers numerical advantages in comparison to previously developed Fourier-Galerkin algorithms, particularly important for physically ill-conditioned and strongly non-linear problems. The tradeoff of achievable accuracy versus computer time is easily controlled, thus making essential speed-ups possible for moderate accuracy requirements.
    Additional Material: 12 Ill.
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  • 95
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992), S. 93-110 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: In 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.
    Additional Material: 13 Ill.
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  • 96
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992), S. 129-137 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: This paper reports the results of a study of an error parameter, m, which has been proposed as a measure for determining the effects on accuracy of the basic assumptions upon which TLM modelling of diffusion and heat flow has been founded. The nature of the m parameter is studied in detail by using a two-dimensional thermal diffusion problem. The use of m in the implementation of automatic timestepping is discussed in a practical three-dimensional engineering problem.
    Additional Material: 7 Ill.
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  • 97
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992) 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Type of Medium: Electronic Resource
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  • 98
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992), S. 141-141 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 99
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992), S. 145-147 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 100
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 5 (1992), S. 163-182 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: An overview is given on the application of finite difference time-domain analysis techniques to the simulation of electromagnetic wave phenomena and the design of planar microwave integrated circuits. In particular the application to the analysis of three-dimensional discontinuities in coplanar microwave circuits is described and numerical and experimental results are presented. Finally the design of planar microwave circuits containing non-linear active components using the finite difference time-domain method in combination with a harmonic balance technique is demonstrated using an example of a LUFET circuit.
    Additional Material: 17 Ill.
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