Abstracts

 
1 Comparison of three formulations for eddy-current and skin effect problems
Jafari-Shapoorabadi, R.; Konrad, A.; Sinclair, A.N.

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.

3 Galerkin's method and the variational procedure
Ziarani, A.K.; Konrad, A.
Galerkin's method and the variational procedure, when applied to most practical problems in electromagnetics, lead to matrix equations of the same form. Variational procedures for self-adjoint and nonself-adjoint operators also result in the same form of matrix equations for a large subclass of problems. However, the three cases may yield different matrix equations in general. This paper examines the subclass of problems for which these methods result in the same matrix equation and provides systematic ways for classification of problems for which two or all three of the cases lead to the same matrix equation. It also describes properties of the coefficient matrix in the matrix equation.

4  A method of elimination of interferences of quasi-periodic nature
Ziarani, A.K.; Konrad, A.; Rogers, E.S., Sr.

A nonlinear adaptive method for the elimination of quasiperiodic interferences of time-varying nature having frequency characteristics within the frequency range of the signal of interest is presented. The methodology is exemplified by its application in removing power line interference from electrocardiogram signals.

5  An adaptive noise reduction technique
Ziarani, A.K.; Konrad, A.

An adaptive method of reduction of noise of stochastically unknown composition is presented. The signal of interest may be composed of time-varying components. The signal processing algorithm used as the functional core of the proposed noise reduction technique is a nonlinear adaptive filter which, while offering efficient time-tracking capability, has a very simple and robust structure.

6  Improved finite element method for EMAT analysis and design
Jafari-Shapoorabadi, R.; Konrad, A.; Sinclair, A.N.

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.

7  Finite element determination of the absolute magnitude of an ultrasonic pulse produced by an EMAT
Jafari-Shapoorabadi, R.; Sinclair, A.N.; Konrad, A.

Electromagnetic acoustic transducers or EMATs for short, are investigated in transmitting mode for nonferromagnetic conducting materials. Two different finite element (FE) formulations, derived from different definitions of source current density, are compared. A differential equation based on an incomplete equation for the source current density is solved analytically for the magnetic vector potential (MVP). To validate the FE results, one-dimensional (1D) analytical solutions are used. An EMAT example containing six source conductors is also modeled. The FE results are compared with results obtained from existing methods for two EMAT meander coil conductor sizes. The results show the importance of using the complete equation for the source current density in the modeling of EMATs, in order to properly account for skin and proximity effects.

8  Efficient modeling of apertures in thin conducting screens by the TLM method
Argus, P.; Fischer, P.; Konrad, A.; Schwab, A.J.

The shielding effectiveness of enclosures used in EMC is often determined by apertures. Mostly these apertures are small compared to the wavelength and the enclosure's dimensions. The modeling with numerical field calculation methods can therefore be difficult. This paper presents the extension of the transmission line matrix (TLM) method by special subcellular structures leading to an efficient modeling of apertures in the time domain.

 

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