Showing papers by "Dragan Poljak published in 2002"

The boundary element modelling of the human body exposed to the ELF electromagnetic fields

Abstract: In this paper a cylindrical model of human body exposed to the extremely low frequency (ELF) electromagnetic field is presented. The analysis is based on the solution of the simplified integral equation for thick wires. The numerical solution of the integral equations is performed by the Galerkin–Bubnov variant of the boundary element method. Several numerical results for the ELF exposures are presented.

Electromagnetic modeling of finite length wires buried in a lossy half-space

Abstract: The horizontal buried wire of a finite length is analyzed by using the scattering theory. The current distribution along the wire due to an external electromagnetic interference (EMI) source is governed by the half-space Pocklington integral equation. The effect of the lower half-space is taken into account via the transmission coefficient (TC) appearing within the integral equation kernel. The principal advantage of the TC approach vs rigorous Sommerfeld integral approach is the formulation simplicity and reduced computational cost. The variational boundary element procedure is used for solving the Pocklington integral equation and the current induced along the buried wire due to the transmitted plane wave or current source excitation is obtained.

A dynamic adaptive sampling technique in frequency-domain transient analysis

Abstract: The transient response of a structure may be obtained directly by solving a problem in the time domain. However, there are certain advantages in obtaining the time-domain waveform from frequency-domain data. Taking samples to characterize the frequency spectrum of a resonant structure with no prior knowledge of its behavior, poses difficulty. There is no foolproof way to determine the sampling resolution that will yield an accurate result while keeping the number of samples to a minimum. We propose a frequency sampling technique using a dynamic adaptive algorithm. The algorithm zeroes in on the resonant peaks without user intervention and computes the samples to the required resolution. The resolution is relaxed where appropriate, to achieve economy of samples. A modified discrete Fourier transform formula is used to process the nonuniformly spaced frequency data into the time-domain waveform. Computation time is vastly reduced. This technique enables the frequency-domain approach to be used for modeling transients in very high-Q structures accurately.

Transient Analysis of Two Coupled Horizontal Wires Over a Real Ground

Abstract: Transient behaviour of two coupled wires immersed in a two-media configuration is analysed. The active wire is excited by a time-dependent voltage source. As the wires are identical, the symmetry of the configuration is expoited, and two coupled wires are considered as two single-wire problems. Each mode is represented by the corresponding space–time integral equation of the Hallen type. The effect of real ground is taken into account by the space–time reflection coefficient appearing within integral-equation kernels. The set of decomposed Hallen integral equations is solved by the direct time-domain finite-element technique, and the corresponding transient response is obtained. The computed numerical results are compared with the time-domain data obtained by solving the frequency-domain electric field integral equation for thin wires and with the aid of the Fourier transform approach. The mathematical model is applicable to an arbitrary ground, and numerical implementation and calculations are presented for lossless cases. Illustrative numerical results for transient current along the active and the parasitic wire are shown for the case of a perfectly conducting half-space and a dielectric half-space.

Plane wave coupling to finite length cables buried in a lossy ground

Abstract: The cable of a finite length below the ground surface is analysed applying the scattering theory. The problem is formulated via the electric field integral equation (EFIE) for thin wires. The EFIE is solved by the Galerkin–Bubnov boundary element procedure and the current induced along the buried cable due to the transmitted plane wave excitation is obtained.

Electromagnetic Transient Modelling Using Dynamic Adaptive Frequency Sampling

Abstract: The main difficulty in modelling transients via the frequency domain in highly resonant structures is to extract the complete information from its frequency response spectrum. The selection of suitable values for the number of samples and the frequency resolution determines the accuracy of the result. However, neither of these parameters are known prior to simulation. A high Q spectrum requires high resolution samples which if taken at uniform intervals for the FFT will result in a large number of samples. The proposed dynamic adaptive sampling technique takes the samples at intervals according to the requirement at different points of the spectrum. It will, without a priori knowledge of the spectrum, concentrate samples around resonant frequencies. The method has successfully overcome the difficulty without incurring the penalty of increasing computer time.

Galerkin-Bubnov Boundary Element Analysis Of The Yagi-Uda Array

Abstract: Currents induced along the elements of a wire antenna arrey are calculated by solving the set of electric field integral equations (EFIEs). These coupled integral equations are handled via the Galerkin-Bubnov Boundary Element Method (GB-BEM). Once obtaining the currents along the wires an electric field radiated ba wire structure and the corresponding input ompedance are evaluated.

Shipboard RF equipment radiation measurements and hazard analysis

Abstract: Shipboard HF transmitter and navigational radar radiation are analyzed as the most common and the most powerful contributors to shipboard RF electromagnetic environment, posing a possible threat to human health. The particular situation involved 100W HF transmitter and 20kW peak output power X-band navigational radar on a 45m long steel ship. Electromagnetic fields were measured on the deck separately for each source. The results are analyzed according to ICNIRP recommendation for human exposure to electromagnetic fields. The fields were found to be about 10dB below appropriate limits, for the particular analyzed situation.