Man-Fai Wong

Electromagnetic propagation into reinforced-concrete walls

A rigorous method for analyzing building construction materials, using finite-element techniques and an expansion of fields in Floquets modes, is presenteded in this paper. It allows us to precisely study the electromagnetic properties of buildings walls in terms of transmission and reflection characteristics, which can be useful in the design of wireless communication systems. First, we present the influence of the walls parameters, namely, its thickness, the square side length, and the steel diameter of a concrete grid. The influence of the angle of arrival of the incident wave and the effect of considering the diffused field on the electromagnetic properties are then presented.

A new global finite element analysis of microwave circuits including lumped elements

A new fullwave global analysis of complex inhomogeneous microwave structures including passive or active, linear or nonlinear lumped elements is presented. For a given structure, only one electromagnetic simulation of the distributed part, by a three-dimensional (3-D) finite element method using edge elements, is needed corresponding to the insertion of variable lumped elements placed at the same position. Simulation results of various test cases, containing either resistor, diode, or active component, are compared with those provided by a commercial circuit analysis software or with measurements results. Our validated electromagnetic simulator is then used for analyzing a planar balanced mixer operating in the millimetric range.

Exposure induced by WCDMA mobiles phones in operating networks

The objective of this study is to investigate the transmitted (Tx) power of 3G terminals during real use. Such analysis reveals the exposure induced by mobile phone devices and provides a precise idea about the margin between time averaged and maximum (standardized) exposure. For this purpose, data streams exchanged on a live network were recorded and processed to extract a histogram of received power at the handset in indoor, outdoor, rural, and urban environments. The real Tx power is found to be generally a few percents of the maximum power. Moreover, the influences of some main factors like the handset model and the usage mode are investigated. A data mode for example increases the Tx power of about 6 dB compared to a voice call.

Influence of traffic variations on exposure to wireless signals in realistic environments.

In this article, the general public daily exposure to broadcast signals and Global System for Mobile Communications (GSM) or Universal Mobile Telecommunications System (UMTS) mobile telephone signals in indoor areas is investigated. Temporal variations and traffic distributions during a day at different indoor sites in urban and rural zones are presented. The goal is to analyze the real exposure compared to the maximum assessment imposed by radio protection standards and to characterize the ratio between daily and maximum theoretical values. Hence, a realistic maximum is proposed based on the statistical analysis performed using measurements. Broadcast signals remain constant over the day so they are best fitted with a Normal distribution while the mobile telephone signals depend on the traffic demand during the day so they fit a three-Gaussian distribution model. A general mask is also constructed for underlining the maximum equivalent active traffic for different periods in the day. Also, relations between the mean values over 24 h, the realistic maximal values (at 99%) and the maximal theoretical values are presented. The realistic maximum is also presented with a sliding time average of 6 min applied to the measurements in accordance with international standards. An extrapolation factor is given for the different systems to easily assess the maximum values starting from an instantaneous measurement. The extrapolation factor is also given for a broadband measurement to estimate the maximum potential exposure during the day.

Analysis of electric field averaging for in situ radiofrequency exposure assessment

The impact of small-scale fading on the estimation of local average power density for radiofrequency exposure assessment is studied in the case of a Rayleigh fading, a Rician-k fading, and a Nakagami-m fading. In all cases, it is shown that the significant parameter is the coefficient of variation of power density. We give the relation between the error on the estimation of local average power density and the number of independent points that are used in the averaging process. We apply this analysis to a distribution of fading statistical properties provided by measurements.

Efficient models for base station antennas for human exposure assessment

Two simple and accurate models for base-station (BS) panel antennas are proposed for human-exposure assessment. Panel antennas comprise an antenna array with low coupling between its unit cells. The proposed model is based on the superposition of shifted radiating field contributions in amplitude and phase of a unit cell of the panel antenna. In the first model, the electric field is obtained via a full wave analysis of the antenna unit cell. In the second model, a far-field approximation of the unit cell is utilized, and is valid at about two wavelengths away from the antenna. It is shown that the second model can be used as an interactive tool for the verification of compliance to exposure limits of BS panel antennas as required by standards.

Influence of Plane-Wave Incidence Angle on Whole Body and Local Exposure at 2100 MHz

Exposure of human population to electromagnetic waves remains an important issue. Many studies have considered exposure to plane waves with only one incidence angle. This paper investigates the exposure of the anthropomorphic model visible human (VH) induced by plane waves with different incidence angles. The incident-field-propagation direction describes in 10° steps all the azimuth around the model (0°-360°) for three elevation angles (90° and 90 ± 20°). Both vertical and horizontal polarizations are considered. Tilt at ±20° does not involve a significant difference on the exposure. Whole-body-exposure levels vary periodically with the azimuth as well as the illuminated surface of the model. A good correlation between the whole-body exposure and the illuminated surface is noted. Moreover, the illuminated surface of the VH can be quite accurately assessed by substituting the VH with an ellipsoid. Concerning the local exposure, the localization of 10 g peak spatial-averaged specific absorption rate is highly depending on the incidence angle. However, the most common position is located in the limbs or in the genital parts.

On the FEM Modal Approach for a Reverberation Chamber Analysis

We review the difficulties linked to the modal approach when modeling a reverberation chamber by the finite element method (FEM). The numerical challenge is due to the large-scale problem involved by the overdimensioned cavity. Moreover, the field singularity on the stirrer has to be captured by the FEM. First, the following issues are discussed: existence of null-frequency solutions, convergence rate for h and p adaption, and formulation type in E or H field. The modal analysis is then compared to the classical harmonic one. Focus is put on the field singularity at the source point

Specific absorption rate assessment near a base-station antenna (2,140 MHz) : some key points

In this paper, a numerical dosimetry study for a typical base-station antenna used in third generation system is presented. This study is based on the limits defined by the International Commission on Non-Ionizing Radiation Protection. The primary goal is to analyze the relationship between the antenna input powers required to reach the specific absorption rate (SAR) limit and those ones which are required to reach the power density limit. The secondary goal is to underline the key points which impact the local SAR in the case of such a directive antenna. Moreover, for these studies, two numerical approaches are used: the first one is only based on the finite difference time domain method and, in the second one, this algorithm is coupled with a method of moments simulator via a Huygens box. Investigations are made to ensure that a more suitable numerical approach is used.

Uncertainty analysis of the specific absorption rate induced in a phantom using a stochastic spectral collocation method

Uncertainty analysis of human exposure to radio waves is studied with a spectral approach of stochastic collocation methods. This approach allows determining in an efficient way the statistical moments of the output variable, the specific absorption rate, with respect to uncertain input parameters. Polynomial chaos expansions are used for the random output, and the spectral coefficients are determined by projection or regression. These techniques are used with an electromagnetic solver based on a finite difference time domain scheme. The convergence of the statistical moments is analyzed for two case studies. Global sensitivity is also analyzed for the uncertain position of a cellular phone in the close vicinity of a human head model.