Modeling and characterization of the uplink and downlink exposure in wireless networks

This paper deals with a new methodology to assess the exposure induced by both uplink and downlink of a cellular network using 3D electromagnetic simulations. It aims to analyze together the exposure induced by a personal device (uplink exposure) and that induced by a base station (downlink exposure). The study involved the major parameters contributing to variability and uncertainty in exposure assessment, such as the user's posture, the type of wireless device, and the propagation environment. Our approach is relying basically on the modeling of the power radiated by the personal device and the ambient electric field, while taking into account the effects of human body shadowing and the propagation channel fluctuations. The exposure assessment as well as the human-wave interactions has been simulated using the finite difference in time domain method (FDTD). In uplink scenarios, four FDTD simulations were performed with a child model, used in two postures (sitting and standing) and in two usage scenarios (voice and data), which aimed to examine the exposure induced by a mobile phone and a tablet emitting, respectively, at 900 MHz and 1940 MHz. In the downlink scenario, a series of FDTD simulations of an exposure to a single plane wave and multiplane waves have been conducted, and an efficient metamodeling of the exposure using the Polynomial Chaos approach has been developed

A surrogate model to assess the whole body SAR induced by multiple plane waves at 2.4 GHz

International audienceThe assessment of the exposure to electromagnetic waves is nowadays a key question. Dealing with the relationship between exposure and incident field, most of previous investigations have been performed with a single plane wave. Realistic exposure in the far field can be modeled as multiple plane waves with random direction of arrival, random amplitude, and random phase. This paper, based on numerical investigations, studies the whole body specific absorption rate (SAR) linked to the exposure induced by five random plane waves having uniformly distributed angles of arrival in the horizontal plane, log-normal distributed amplitudes, and uniformly distributed phases. A first result shows that this random heterogeneous exposure generates maximal variations of +/- 25% for the whole body specific absorption. An important observation is that the exposure to a single plane wave arriving face to the body, used for the guidelines, does not constitute the worst case. We propose a surrogate model to assess the distribution of the whole body SAR in the case of an exposure to multiple plane waves. For a sample of 30 values of whole body SAR induced by five plane waves at 2.4 GHz, this simple approach, considering the resulting SAR as the sum of the SAR induced by each isolated plane wave, leads to an estimated distribution of whole body SAR following the real distribution with a p value of 76% according to the Kolmogorov statistical test

Electromagnetic Absorption by the Human Body from 1 - 15 GHz

Microwave radiation is emitted by a wide variety of computing, communications and other technologies. In many transport, industrial and medical contexts, humans are placed in close proximity to several of these sources of emission in reflective, enclosed cavities. Pseudo-reverberant conditions are created, in which absorption by human bodies can form a significant, even the dominant loss mechanism. The amount of energy stored, and hence the field intensities in these environments depend on the nature of electromagnetic absorption by the human body, so quantifying human absorption at these frequencies is necessary for accurate modelling of both electromagnetic interference and communications path loss in such situations. The research presented here aims to quantify absorption by the body, for the purpose of simulating its effect on the environments listed above. For this purpose, nine volunteer participants are enlisted in a preliminary study in which their height and mass are taken and their electromagnetic absorption cross section is measured in a reverberation chamber. The preliminary study is unable to gather enough data to provide precise measurements during the time that a participant is willing to sit motionless in the chamber. Issues also exist due to power loss in some parts of the equipment. A number improvements are made to both the experimental equipment and methodology, and the study is repeated with a sample of 60 adult volunteer participants. The results are compared to the preliminary data and found to match, once unwanted absorption in the latter has been subtracted. The results are also validated using data from absorption by a spherical phantom of known absorptive properties. The absorption cross section of the body is plotted and its behaviour is compared to several biometric parameters, of which the body’s surface area is found to have a dominant effect on absorption. This is then normalised out to give an absorption efficiency of the skin, which is again compared to several biometric parameters; the strongest correlation is found to be with an estimate for average thickness of the subcutaneous fat layer. These data are used to model the effect of 400 passengers on the Q-factor of an airliner’s cabin. Absorption by the passengers is shown to be the dominant loss mechanism in the cabin, showing the importance of accounting for human absorption when modelling electromagnetic propagation and interference in situations that include human occupants. The relationship between subcutaneous fat and absorption efficiency is suggested for further research, as it promises development of new tools to study body composition, with possible medical applications