Search

Finite-element techniques are applied to the frequency response computation of the input impedance of antennas with the eddy current losses taken into account. Both time-domain and frequency-domain approaches are discussed. Comparison to results for a dipole patch antenna with T-match obtained by assuming infinite conductivity is presented. [ABSTRACT FROM AUTHOR]

Different techniques are investigated to improve the performance of the solution process of 3-D, time-periodic, nonlinear, voltage-driven eddy current problems under the influence of dc bias by the means of the finite-element method. The underlying nonlinear iteration technique is the time-periodic fixed-point method. The benefit of a static approximation to generate an initial solution, i.e., of a static initialization is pointed out. A secant method and a Schur complement technique to carry out the static initialization are compared. The procedures developed are applied to 3-D models of one- and three-phase benchmark transformer problems with dc bias. [ABSTRACT FROM AUTHOR]

Abstract: An efficient finite element method to take account of the nonlinearity of the magnetic materials when analyzing three-dimensional eddy current problems is presented in this paper. The problem is formulated in terms of vector and scalar potentials approximated by edge and node based finite element basis functions. The application of Galerkin techniques leads to a large, nonlinear system of ordinary differential equations in the time domain. The excitations are assumed to be time-periodic and the steady-state periodic solution is of interest only. This is represented either in the frequency domain as a finite Fourier series or in the time domain as a set of discrete time values within one period for each finite element degree of freedom. The former approach is the (continuous) harmonic balance method and, in the latter one, discrete Fourier transformation will be shown to lead to a discrete harmonic balance method. Due to the nonlinearity, all harmonics, both continuous and discrete, are coupled to each other. The harmonics would be decoupled if the problem were linear, therefore, a special nonlinear iteration technique, the fixed-point method is used to linearize the equations by selecting a time-independent permeability distribution, the so-called fixed-point permeability in each nonlinear iteration step. This leads to uncoupled harmonics within these steps. As industrial applications, analyses of large power transformers are presented. The first example is the computation of the electromagnetic field of a single-phase transformer in the time domain with the results compared to those obtained by traditional time-stepping techniques. In the second application, an advanced model of the same transformer is analyzed in the frequency domain by the harmonic balance method with the effect of the presence of higher harmonics on the losses investigated. Finally a third example tackles the case of direct current (DC) bias in the coils of a single-phase transformer. [Copyright &y& Elsevier]

Solving electromagnetic wave propagation problems with the finite-element method results in a large number of unknowns due to the necessity of modeling an extensive portion of the surroundings of the conducting structures. These equation systems are often ill-conditioned because of the great material differences as well as changes in size between neighboring elements. In addition, the resulting matrices are indefinite. Common iterative methods exhibit poor convergence due to these conditions. Direct solution techniques result in high memory requirements. The aim of this article is to present an approach with smaller memory demand than the direct methods and better convergence properties than common iterative techniques. An iterative method based on domain decomposition is presented and compared to various conventional iterative and direct solution techniques. [ABSTRACT FROM AUTHOR]

A finite element method for the analysis of three-phase, three-limb power transformers under dc bias is presented. The phase voltages and the dc components of the phase currents are assumed to be given. Using parallel algorithms, the steady-state periodic solution is obtained without stepping through the transients using a fixed-point method to solve the nonlinear equations. A novel technique to obtain the starting solution for the fixed-point iterations to ensure fast convergence is introduced. The solution to a large, real world problem is presented. [ABSTRACT FROM AUTHOR]

A method is presented for obtaining the steady-state solution of three-dimensional eddy current problems with nonlinear material properties and periodic excitations using the T,\Phi-\Phi formulation. The problem is formulated in the time-domain and the application of a fixed-point approach combined with a discrete Fourier-transformation technique ensures that, during one nonlinear iteration step, there is no coupling between the time-steps within one period. The steady-state result is hence obtained by solving half as many time steps as their number in one period. Since the time steps are decoupled, their computation can be readily parallelized resulting in a fast method. Comparison with results obtained by a transient time-stepping technique is presented. [ABSTRACT FROM PUBLISHER]

A method is presented for the optimal choice of the fixed-point reluctivity in nonlinear eddy current problems solved for steady-state in the frequency and the time domain. The optimal selection is shown to ensure a minimal contraction number for the fixed-point method. The proposed technique is compared to earlier approaches using a 2-D example. [ABSTRACT FROM AUTHOR]

Abstract: Two different techniques for the analysis of nonlinear, periodic eddy‐current problems are compared using a three‐dimensional benchmark problem. The methods are the parallel time periodic finite element method and the time periodic fixed‐point technique. [ABSTRACT FROM AUTHOR]

In ultra-high-frequency radio-frequency-identification (UHF-RFID) the conjugate complex matching of the packaged UHF-RFID transponder IC and the tag antenna structure is important to increase the reading range of the transponder tag. Quite often half-wavelength dipole-like antenna structures are used. Due to the fact that the impedances of the packaged IC and the dipole antenna structure are in different domains, a matching structure is needed to accomplish the conjugate complex matching. A common technique to carry out the matching is the so called T-match. Since the nominal input impedance of the IC depends on the applied antenna voltage (and in a strongly non-linear way), the backscatter abilities of the tag are also functions of the applied voltage. In the present work those dependencies are investigated in terms of full-wave finite element simulations and measurements. [ABSTRACT FROM PUBLISHER]

In radio frequency identification (RFID), the design and investigation of ultra-high-frequency (UHF) circular loop antennas used as reader antennas as well as tag antennas is of growing importance. Since these antennas are electrically short, a 2-D finite-element method (FEM) analysis using a single-component magnetic vector potential together with perfectly matched layers (PMLs) at the boundary is proposed in this paper in order to perform very fast and accurate axisymmetric simulations compared to very time-consuming 3-D calculations. In addition, the capacitances of the tag loops have been calculated using a 3-D quasi-static electric approach taking the gap of the loops into account. [ABSTRACT FROM AUTHOR]