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

Ultra-wide bandwidth backscatter modulation: processing schemes and performance

Future advanced radio-frequency identification (RFID) systems are expected to provide both identification and high-definition localization of objects with improved reliability and security while maintaining low power consumption and cost. Ultrawide bandwidth (UWB) technology is a promising solution for next generation RFID systems to overcome most of the limitations of current narrow bandwidth RFID technology, such as reduced area coverage, insufficient ranging resolution for accurate localization, sensitivity to interference, and scarce multiple access capability. In this article, the UWB technology is applied to passive RFID relying on backscatter modulation. A signaling structure with clutter and interference suppression capability is proposed and analyzed. The potential performance is investigated in terms of range/data rate trade-off, clutter suppression, and multiple access capability using experimental data obtained in both the controlled and realistic environments

Buffer layers inhomogeneity and coupling with epitaxial graphene unravelled by Raman scattering and graphene peeling

The so-called buffer layer (BL) is a carbon rich reconstructed layer formed during the sublimation of SiC (0001). The existence of covalent bonds between some of the carbon atoms in this layer and the underlying silicon atoms makes it different from epitaxial graphene. We report a systematical and statistical investigation of the BL signature and its coupling with epitaxial graphene by Raman spectroscopy. Three different kinds of BLs are studied: bare buffer layer obtained by direct growth (BL 0), interfacial buffer layer situated between graphene and SiC (c-BL 1) and the interfacial buffer layer without graphene above (u-BL 1). To obtain the latter, we develop a mechanical exfoliation of graphene by depositing and subsequently removing an epoxy-based resin or nickel layer. The observed BLs are ordered-like on the whole BL growth temperature range. BL 0 Raman signature may vary from sample to sample but also forms patches on the same terrace. u-BL 1 share similar properties with BL 0 , albeit with more variability. These BLs have a strikingly larger overall intensity than BL with graphene on top. The signal onset on the high frequency side upshifts upon graphene coverage, that cannot be explained by a simple strain effect. Two fine peaks situated at 1235 and 1360 cm-1 are present for epitaxial monolayer while absent for BL and transferred graphene. These findings point to a coupling between graphene and BL

Quantifying the performances of SU-8 microfluidic devices: high liquid water tightness, long-term stability, and vacuum compatibility

Despite several decades of development, microfluidics lacks a sealing material that can be readily fabricated, leak-tight under high liquid water pressure, stable over a long time, and vacuum compatible. In this paper, we report the performances of a micro-scale processable sealing material for nanofluidic/microfluidics chip fabrication, which enables us to achieve all these requirements. We observed that micrometric walls made of SU-8 photoresist, whose thickness can be as low as 35 $\mu$m, exhibit water pressure leak-tightness from 1.5 bar up to 5.5 bar, no water porosity even after 2 months of aging, and are able to sustain under $10^{-5}$ mbar vacuum. This sealing material is therefore reliable and versatile for building microchips, part of which must be isolated from liquid water under pressure or vacuum. Moreover, the fabrication process we propose does not require the use of aggressive chemicals or high-temperature or high-energy plasma treatment. It thus opens a new perspective to seal microchips where delicate surfaces such as nanomaterials are present

Characterization of far-field and near-field exposure of the population for RF-EMF in realistic configurations of ICT usages

International audienceThe study presented in this paper is part of a larger study within the European FP7 project LEXNET framework. The project LEXNET aims at considering new technologies and architectures for minimizing the global exposure of a population to radiofrequency electromagnetic fields. In the framework of the project a new exposure metric named Exposure Index (EI) is proposed. The EI quantifies the global exposure of a population induced by both mobile devices and base station antennas or wireless access points. The EI requires a set of SAR values (whole-body and local-body) for typical postures and usages of mobile devices in a population. In our study, we assessed these SAR values by 3D electromagnetic simulations. We used an adult and a child numerical model in two postures (sitting and standing) and in three usages (voice, data and laptop).The whole-body SAR for each exposure configuration was evaluated at four different frequencies (400, 900, 1940 and 2600MHz).</p