Showing papers by "Dragan Poljak published in 2012"

Time-Domain Generalized Telegrapher's Equations for the Electromagnetic Field Coupling to Finite Length Wires Above a Lossy Ground

Abstract: In this paper, a time-domain variant of the generalized telegrapher's equations for transient electromagnetic field coupling to a finite-length wire above a lossy half-space is derived. The approach is fully based on the thin-wire antenna theory. The lossy ground effects are taken into account by means of the reflection coefficient approximation. The obtained equations are handled numerically via the Galerkin-Bubnov indirect boundary element method. Computational examples are presented for the case of a single-wire line excited by an electromagnetic pulse excitation source. The obtained results for the induced current along the line are compared with those obtained using 1) the method of moments solution of the electric field integral equation implemented in the numerical electromagnetics code (NEC-4), and 2) the transmission line (TL) theory. It is shown that the results obtained by the proposed method are in excellent agreement with those of NEC-4. It is also shown that the TL approximation yields in general results which are in reasonably good agreement with the full-wave results, especially for the early time response and even beyond the limits of the accuracy of the TL theory. The TL theory can, however, give accurate results only for times before the arrival of the first reflection from the TL terminations and it fails to reproduce accurately the dispersion effects occurring after the first reflection.

Analytical Model for Electromagnetic Radiation by Bare-Wire Structures

Abstract: This paper presents a simple analytical model to estimate the radiated fleld for broadband Power line communication (PLC) or metallic wire structures. In our approach, we avoid to discretize the line and compute the current for each segment (dipole). We consider only near and far end currents and their derivatives (voltages) to express analytically the radiated electromagnetic fleld. The case of multiple conductor power line is considered with simplifled hypothesis: cables are not insulated and the surrounding media is homogenous. The basic electromagnetic equations are formulated and applied to the line to provide analytical expressions able to compute flelds in near and far zones which is not usually treated. The main purpose of this paper is to provide an analytical model applied to bare wires corresponding to classical outdoor transmission lines. The advantage of this method is that we do not need to know the current along the line to calculate the radiated flelds; therefore, in our study we use only the currents and voltages at the terminations. The calculation time is strongly reduced compared to dipoles conventional method. Results obtained from the proposed closed-form formulation agree with Feko simulation. For indoor conflgurations, cables are usually insulated and the surrounding media is no more homogeneous; this case is treated with a generalized approach and will be proposed in future paper.

Electromagnetic Field Coupling to Overhead Wire Configurations: Antenna Model versus Transmission Line Approach

Abstract: The paper deals with two different approaches for the analysis of electromagnetic field coupling to finite length overhead wire: the wire antenna theory (AT) and the transmission line (TL) method The analysis is carried out in the frequency and time domain, respectively Within the frequency domain analysis the wire antenna formulation deals with the corresponding set of Pocklington integrodifferential equation, while the transmission line model uses the telegrapher's equations The set of Pocklington equations is solved via the Galerkin-Bubnov scheme of the Indirect Boundary Element Method (GB-IBEM), while the telegrapher’s equations are treated using the chain matrix method and the modal equation to derive per-unit-length parameters For the case of the time domain analysis AT model uses the space-time Hallen integral equation set, while TL approach deals with the time domain version of the telegrapher’s equations Hallen equations are handled via time domain version of GB-IBEM, while time domain telegrapher’s equations are solved by using Finite Difference Time Domain (FDTD) method Many illustrative computational examples for the frequency and time domain response, respectively, for several configurations of overhead wires, obtained via different approaches, are given in this paper

Some computational aspects of using current and voltage sources in electromagnetic models of lightning return strokes

Abstract: The paper deals with some computational aspects of modeling the lightning return strokes using the full wave model. The electromagnetic model of lightning return stroke is based on the thin wire antenna theory and the related Pocklington integro-differential equation in the frequency domain while the corresponding transient response is obtained by means of hybrid (analytical and numerical) version of the Inverse Fourier Transform. The Pocklington equation is solved by the Galerkin-Bubnov Indirect Boundary Element Method (GB-IBEM). Special attention is given to the computational differences arising from the usage of current and voltage source, respectively.

Antenna Models for Electromagnetic Compatibility Applications

Abstract: In recent decades there have been a number of significant advances in EMC modeling which can be carried out within a significantly shorter time than it would be necessary for building and testing the appropriate prototype via experimental procedures. Moreover EMC simulation can predict the system behaviour for a rather wide variety of parameters including different initial and boundary conditions, excitation types, and different configuration of the system itself. EMC-computational models are often classified as

Assessment of SAR in the human body exposed to an RFID loop antenna

Abstract: In this paper, the human exposure to electromagnetic field radiated from the RFID anti-theft gate system is analyzed. Anti-theft gate system is based on two parallel coaxial square loop antennas. Simplified parallelepiped human body model is used for the SAR calculation. The obtained results were analyzed according to ICNIRP guidelines and were found to be below appropriate limits, regarding both occupational and public exposure.

Computation of SAR in Human Eye and Pregnant Woman Using Different Simulation Tools

Abstract: Electromagnetic modeling of large scale problems arising from complex geometries, such as the human body or the specific organ, is generally undertaken by numerical methods implemented in simulation software packages. The structures involving high discretization density (mainly based on Magnetic Resonance Imaging and handled by Finite Difference Time Domain method) consume tremendously high computational cost. On the other hand, oversimplified numerical models may result in significantly less accuracy. The aim of this work was to investigate how detailed numerical model could be created using standard personal computer. Two rather complex cases of exposure were analyzed: human eye and pregnant woman exposed to radiofrequency electromagnetic radiation. The SAR distribution, peak localized 10g-averaged SAR and volume-averaged SAR in these models were determined using two software packages based on different numerical methods: FEKO software based on Finite Element Method and SEMCAD X software based on Finite Difference Time Domain method. The obtained results were compared to the results arising from other scientific studies which included the models of different complexity solved by different numerical methods.

On the analysis of vertical straight thin wire above a lossy ground: Analytical versus numerical solution

Abstract: The paper deals with analytical and numerical modeling of vertical straight thin wire above a lossy ground. The analysis is based on the solution of the corresponding Pocklington integro-differential equation. The numerical solution is carried out via the Galerkin-Bubnov Indirect Boundary Element Method (GB-IBEM). Some illustrative computational examples are presented in the paper. Obtained numerical results are compared to NEC results.

Some Numerical Methods Of Thermal DosimetryFor Applications In Bioelectromagnetics

Abstract: Some thermal dosimetry methods for the analysis of human exposure to high frequency (HF) electromagnetic radiation are reviewed in this work The formulation is based on the bio-heat transfer equation Calculating the distribution of specific absorption rate (SAR) inside the biological body provides an assessment of a related thermal response to HF electromagnetic fields The temperature increase is obtained by solving the bio-heat transfer equation for different exposure scenarios via Boundary Element Method (BEM) and Finite Element Method (FEM), respectively Some illustrative computational examples are presented in the paper

Influence of the grounding electrode conductivity on the induced transient current

Abstract: The paper deals with the assessment of the influence of finite conductivity of the horizontal electrode to related transient response. Transient response of the grounding electrode buried in a lossy half-space is determined via analytical solution of the corresponding Pocklington equation in the frequency domain. Time domain response is obtained by means of Inverse Fast Fourier Transform (IFFT). The electrode is excited via an equivalent current source representing the lightning strike current. Presence of the earth-air interface is taken into account via a simplified reflection coefficient arising from the Modified Image Theory (MIT). The transient current at the center of the electrode is calculated for the case of perfectly conducting (PEC) electrode and for the electrodes made of copper and aluminum. Comparison of the results shows no discrepancy between these electrodes, justifying the use of a PEC electrode approximation.

Antenna model of wind turbine struck by lightning

Abstract: The paper deals with an analysis of direct lightning strike to the wind turbine using thin wire antenna theory. Wind turbine is represented by a simple wire structure, while the lightning channel is represented by an equivalent lossy vertical wire attached to the wind turbine. The entire structure is energized by an ideal voltage source at the junction point. The analysis is based on the solution of the set of Pocklington integro-differential equations for arbitrary wires above the ground in the frequency domain. The corresponding transient response is obtained by means of Inverse Fourier transform. The set of Pocklington integro-differential equations is solved by the Galerkin-Bubnov Indirect Boundary Element Method.