A. Konrad

A nonlinear adaptive method of elimination of power line interference in ECG signals

A new method of elimination of power line noise in electrocardiogram signals is presented. The proposed method employs, as its main building block, a recently developed signal processing algorithm capable of extracting a specified component of a signal and tracking its variations over time. Design considerations and performance of the proposed method are presented with the aid of computer simulations. Superior performance is observed in terms of effective elimination of noise under conditions of varying powerline interference frequency. The proposed method presents a simple and robust structure which complies with practical constraints involved in the problem such as low computational resource availability and low sampling frequency.

A review of finite element open boundary techniques for static and quasi-static electromagnetic field problems

This paper presents a review of finite element open boundary techniques for the computation of static and quasistatic electromagnetic fields. The underlying assumptions and ideas behind these techniques are outlined and explained. The advantages and shortcomings of each technique are discussed. The goal of this review is to aid those working on numerical solutions of open boundary problems using the finite element method to gain perspectives on the variety of techniques presently available or being developed. This review is also intended to facilitate the communication of numerical techniques between the low-frequency field computation community and those in the high-frequency community.

Coupled field-circuit problems: trends and accomplishments

The formulations and numerical methods for two-dimensional eddy-current problems in which conductors with eddy currents are connected by external circuits are reviewed. A general formulation valid for arbitrary circuit connections is obtained using the loop-current method. >

A method of extraction of nonstationary sinusoids

A novel method of extraction of nonstationary sinusoidal signals and estimation of their parameters, namely amplitude, phase and frequency is presented. A set of nonlinear differential equations governs the dynamics of the algorithm. Mathematical proofs of the existence, uniqueness and stability of a periodic orbit of such a dynamical system are given. Performance of the proposed algorithm is demonstrated with the aid of computer simulations and the laboratory verification of its functionality is presented. The proposed algorithm exhibits a high degree of noise immunity and robustness and is shown to have a very simple structure which renders it suitable for both software and hardware implementation.

Three-dimensional vector potential analysis for machine field problems

Modern electrical plant and machinery have to be designed to operate at high power densities at minimum cost and optimal efficiency with a high degree of reliability during operation. These stringent requirements necessitate accurate performance prediction at the design stage. As a first and important step in this process, the magnetic field distribution must be evaluated taking full account of the geometrical complexity of the field region, magnetic saturation of the iron parts, and circulating currents in conducting media. The advent of digital computers has spurred the development of sophisticated numerical techniques to accomplish this task with a high degree of precision. In this paper, three-dimensional vector potential solution methods for linear and nonlinear diffusion and magnetostatic field problems are presented. The methods are illustrated by numerical examples where feasible. This research has been partially funded by the Electric Power Research Institute, Palo Alto, California under EPRI contract RP 1288-1.

A method for circuit connections in time-dependent eddy current problems

The authors consider eddy current diffusion problems in which the electromagnetic field is computed in 2-D but external circuit connections, between the conductors with eddy currents are taken into account. The approach combines conventional circuit analysis techniques with the integro-differential finite element formulation of the transient eddy current problem. Conductors with eddy currents are treated as circuit elements with terminal voltages implicitly defined by the field equations. A numerical example is presented to illustrate the proposed formulation. >

A survey of numerical methods for transient eddy current problems

The efficiencies of different time-stepping schemes and associated algebraic system solvers for transient eddy current computations are assessed. For 2-D problems, the direct methods nested dissection (ND) and quotient minimum degree (QMD) are shown to be preferable to the incomplete Cholesky conjugate-gradient (ICCG) method, provided enough memory is available. The multilevel preconditions (MP) method is highly efficient for magnetically homogeneous problems both in 2-D and 3-D. The efficiency of multilevel methods for inhomogeneous problems, although proven theoretically, needs further practical investigation. >

Comparison of three formulations for eddy-current and skin effect problems

Three finite-element formulations based on different definitions of current density are compared. Formulations I and II are based on incomplete equations for total and source current densities, respectively. Formulation III is based on a complete equation for source current density. To validate the third formulation, a one-dimensional test problem is solved analytically for the magnetic field intensity. The formulations are applied to a nondestructive testing example and a three-phase bus-bar example. Results show that errors due to the use of incomplete equations for current densities increase with frequency and conductor dimensions.

Improved finite element method for EMAT analysis and design

Electromagnetic acoustic transducers (EMATs) operating in transmitting mode are examined. Two different finite element formulations, derived for two different definitions of source current density, are compared in order to show the importance of skin and proximity effects. An EMAT consisting of six source conductors is modeled as an example. Results obtained with an earlier method are compared with new FEM results at two different frequencies. The effect of lift-off and distance between conductors is investigated.

Lossy transmission line transient analysis by the finite element method

A time-domain finite-element (TDFE) method applied to the analysis of electrical transients on lossy transmission lines is presented. The general telegraph equations are solved numerically at discrete time steps. Examples of voltage waveform on lossy single-phase lines are shown. Preliminary results indicate that the TDFE method works well for single-phase lossy transmission line transient analysis. >