Showing papers by "Dragan Poljak published in 2003"

Human equivalent antenna model for transient electromagnetic radiation exposure

Abstract: Thin-wire antenna model of the human body exposed to the transient excitation is presented in the paper. The analysis is based on the solution of the corresponding integral equation and it is carried out directly in the time domain (TD) . The integral equation is handled via the TD Galerkin-Bubnov scheme of the boundary element method. Numerical results are presented for the time-harmonic and transient exposures.

Integral Equation Techniques in Transient Electromagnetics

Abstract: Introduction: Introduction Time domain and frequency domain methods Survey of electromagnetics analysis methods Finite Element Integral Equation Method (FEIEM) The Method of Moments. The frequency domain - Method of Moments: Introduction The Method of Moments for EM field Frequency-time domain transformation Application examples Frequency sampling Frequency sampling using adaptive integration Application example Frequency data from time domain waveform Chapter summary. Time domain Finite Element Integral Equation Method: Time domain Hall n integral equation Finite Element Integral Equation Method. Transient analysis of wire antennas: Introduction Time domain approach Wire transient numerical examples. Transient analysis of transmission lines: Time domain analysis Frequency domain analysis. Transient analysis of lightning electromagnetics: Time domain model of the lightning channel Lightning induced overvoltage along the line Numerical results Closure. Transients on printed circuit boards (PCBs): Introduction Problems in PCB modelling Summary. Interaction of the human body with electromagnetic fields: Introduction Equivalent antenna model of the human body Frequency domain modelling of the human body The boundary element solution of the Pocklington equation Time domain modelling of the human body Solution of the time domain Hall n integral equation Frequency domain examples Time domain examples.

The assessment of human exposure to low frequency and high frequency electromagnetic fields using the boundary element analysis

Abstract: Analysis of the human body exposed to low frequency and high frequency electromagnetic fields is presented in this work. The formulation of the problem is based on a simplified thick wire model of the human body. The current distribution induced in the body is determined by solving the Pocklington integral equation for a straight thick wire via the Galerkin–Bubnov boundary element method. Once the axial current along the equivalent antenna of the body is obtained, one may calculate the induced current density, electric field, specific absorption rate, and the total absorbed power in the human body. Several realistic exposure examples are given.

Safety aspects of the GSM base station radiation concerning human health

Abstract: Assessment of the health risk in the vicinity of the GSM base station have been done. The numerical modeling of the human body was performed by utilizing the antenna theory and BEM numerical procedure. The simplified model of the body represented by thick cylindrical scatterer placed vertically on the perfect conducting ground was used. Measurements of the radiated fields have been done at a few sites, and the results were incorporated in the numerical calculations as an incident field.

Root-mean-square measure of nonlinear effects to the transient response of thin wires

Abstract: A root-mean-square (rms) measure of effect of nonlinear loading on the transient response of thin wires is proposed. The transient behavior of nonlinearly loaded wires is analyzed directly in the time domain. The problem is formulated via the space-time Hallen integral equation. The equation is solved by the space-time Galerkin Bubnov boundary element procedure. Numerical results for the transient response of a thin wire computed by a time domain code based on this method are compared with results obtained from a frequency domain code. Some illustrative numerical results for the spatial distribution of the rms values of time varying currents are also presented.

Time domain integral equation method for transient scattering from thin wire structures

Abstract: The transient scattering from various thin wire structures in the presence of a real ground is analyzed directly in the time domain (TD). The mathematical model is based on the corresponding space-time Hallen integral equation. The effect of a two-media configuration is taken into account via the space-time reflection coefficient. The corresponding integral equations are handled by the time domain scheme of the Galerkin–Bubnov boundary integral equation method. The effect of nonlinear loading and the time-domain energy measures associated with the current and charge on thin wires are analyzed by spatially integrating the square of the current and charge along the wire as a function of time. Some illustrative TD computational examples are presented in the paper.

Electromagnetic field coupling to multiple finite length transmission lines above an imperfect ground

Abstract: The scattering approach for the calculation of currents induced on the multiple overhead wires illuminated by a plane wave with an arbitrary angle of incidence is presented In this work. The influence of a lossy ground is taken into account via the Fresnel reflection coefficient appearing within the kernel of the thin wire electric field integral equations (EFIE). The set of EFIE is solved by means of the finite element integral equation method (FEIEM). Various numerical results are presented.

The electromagnetic-thermal analysis of human exposure to radio base station antennas

Abstract: Electromagnetic-thermal analysis of the human body exposed to base station antenna radiation is presented in this work. The formulation of the problem is based on a simplified cylindrical representation of the human body. Electromagnetic part of the analysis involves incident and internal field dosimetry, while the thermal model deals with the bio-heat transfer processes in the body. The electric field induced in the body is determined from the axial current induced in the body. This current distribution along the body is obtained by solving the Pocklington integral equation for a thick cylinder. The Pocklington integral equation is solved numerically via the Galerkin-Bubnov boundary element method (GB-BEM). Once the internal electric field and related total absorbed power in the human body is obtained, it is possible to calculate a corresponding temperature rise in the body due to the GSM exposure. This temperature rise is determined by solving the bio-heat transfer equation.

Analysis of a GSM base station antenna near conductive object: far field pattern distortion

Abstract: In the real life, antenna is not placed in the free space. It is backed by a pole, wall or other structure, and often surrounded by other conductive objects in the immediate vicinity. Modern GSM base stations even employ configurations of multiple antennas per sector, where two antennas are placed so close that they can scatter each other's radiation. This work shows how conductive objects in the close proximity of the antenna can significantly distort the radiation pattern of the antenna. GSM operators should take this effect into account, since antenna gain can vary a few dB in the boresight direction, and even more in the other directions of the main lobe. The manufacturer-provided radiation pattern for antenna in free space should then be considered with added uncertainty. Results suggest that pattern distortion effect could be employed deliberately if needed, adding a simple rod or reflector in the vicinity of the antenna, to add a few dB in wanted direction.

Analysis of a GSM base station antenna near conductive object: estimating EM field levels in the near field

Abstract: When estimating the potential radiation hazard of a base station antenna system, one often relies on the antenna far-field radiation pattern, while the estimation often refers to the antenna near-field zone. It is widely accepted that this leads to overestimation of the field amplitudes. This work analyzes the typical sector antenna, widely used in GSM system. Antenna near field distribution is calculated using NEC2, for various configurations of antenna installations. Analysis of the antenna in free space shows that the overestimation only happens in the mainlobe, while in all other directions even underestimation can happen. Furthermore, conductive objects in close proximity of the antenna, like in widely-used multiple-antenna configurations, can significantly distort the radiation pattern in a generally unknown manner, leading to unexpected higher amplitudes in the unknown directions. For truly conservative, worst-case EM field estimation, this should be taken into account. The paper concludes with some guidelines on using the modified radiation pattern for such estimation.

Time Domain calculation of the Transient Current Distribution along a Thin Wire Antenna Array

Abstract: Transient current distribution along an arbitrary thin wire antenna array is considered. The mathematical model is based on a set of coupled space-time integral equations of the Hallen type. The effect of inhomogeneous medium is taken into account by the space-time reflection coefficient appearing within the integral-equation kernels. Space-time current distributions along the wires are obtained by solving the integral equation set using the time-domain GalerkinBubnov Boundary Integral Equation Method (GB-BIEM). Numerical calculation is performed for the three and two wire antenna arrays horizontally located over a dielectric half-space, when the central wire is excited by a time-dependent Gaussian pulse voltage source.

Transient response of the earthing electrode in a homogeneous lossy medium

Abstract: The antenna theory model of a grounding electrode is presented in this paper. The frequency domain electric field integral equation for a thin wire in a homogeneous lossy medium is solved by means of the boundary element procedure and the equivalent current distribution along the wire is obtained. The frequency spectrum of the input impedance of the grounding system is calculated from the computed current distributions. Multiplying this spectrum with the Fourier transform of the input current impulse results in the frequency response of the grounding system. The transient impedance is then obtained using the inverse fast Fourier transform (IFFT).