Scientific articles and publications
Abstract
This paper introduces a rigorous and fast procedure for accurate assessment of the peak averaged specific absorption rate (SAR), quantifying the user exposure to the electromagnetic field radiation from new-radio communication devices. Focus is lent to the specific class of user equipment that exploit multiple-input multiple-output (MIMO) technology and using exclusive simultaneous excitations of the active antenna-array system, such as expected on 5G devices. In contrast with the required N(N-1)+1 measurements on traditional SAR systems that only take measurements of the amplitude of the electric field, it is demonstrated in this paper that only N+1 number of measurements are required to evaluate the true SAR of a N- antenna MIMO thanks to using a vector near-field based SAR measurement system.
SHARE
Abstract
Plane-wave expansions (PWEs) based on Fourier transform and their physical interpretation are discussed for the case of homo- geneous and isotropic lossy media. Albeit being mathematically correct, standard Fourier-based definition leads to nonphysical properties, such as the absence of homogeneous plane waves, lack of dissipation along transversal directions and inaccurate identi- fication of single plane waves. Generalizing the PWE definition using Laplace transform, which amounts to switching to complex spectral variables, is shown to solve these issues, reinstating physical consistency. This approach no longer leads to a unique PWE for a field distribution, as it allows an infinite number of equivalent definitions, implying that the interpretation of the individual components of a PWE as physical plane waves does not appear as justified. The multiplicity of the generalized definitions is illus- trated by applying it to the near-field radiation of an elementary electric dipole, for different choices of Laplace cuts, showing the main differences in the generalized PWEs.
SHARE
Abstract
This paper introduces an efficient procedure for the evaluation of the true exposure level, quantified by the peak averaged specific absorption rate (SAR), of multiple-input multiple-output (MIMO) communication devices operating transmission diversity. As compared to the traditional conservative evaluation of the SAR, that results from the unpractical testing of all the antenna-array states of the device, the assessment of the true exposure level enables higher margin for minimizing the SAR while maximizing the radiation performance of the device.
SHARE
Abstract
The complexity of radiofrequency technologies used in smartphones and tablets has considerably increased the need for more efficient Specific Absorption Rate assessment approaches. SAR measurement systems covered by IEC 62209-3 which implement vector near-field techniques appear as the most promising alternatives to legacy robot equipment. While showing the benefits of Maxwellian field reconstruction compared to more simplistic fast SAR extrapolations, this paper presents the new angle of view that amplitude and phase measurements combined with near-field transforms introduce in RF dosimetry.
Share
Abstract
Standard Specific Absorption Rate (SAR) measurement methods are highly time consuming. Compliance test lead times for mobile wireless devices are incompatible with current needs in the industry and become a growing pain with the emergence of 4G communications. This paper introduces a new technology designed for solving this problem and providing instantaneous and accurate peak spatial-average SAR evaluation.
Share
Characterization of Head and Body Phantoms for Radiofrequency Dosimetry up to 6 GHz
Abstract
New phantoms suitable for radiofrequency dosimetry are introduced. These materials have dielectric properties meeting SAR measurement standard requirements over a broad frequency range (600 MHz – 6 GHz), and mimic human body and/or head tissues. Physico-chemical aspects have been investigated to explain extended stability and appropriate texture of the materials.
Share
A Dispersion Modeling Approach for Designing Broadband Tissue-Simulating Fluids
Abstract
Fluids with dielectric properties meeting SAR measurement standard requirements over a broad frequency range are of particular interest for the wireless industry. This paper introduces an analytical model suitable for describing frequency dispersion of normative target permittivity and conductivity from 30 MHz up to 6 GHz. The proposed model allows easier interpretation of physical mechanisms to involve in a chemical system meeting standard requirements. It also provides significant help in designing broadband tissue- simulating materials.
Share
Analysis of Vector E-field Sensor Array for Real-Time SAR Assessment
Abstract
A novel Specific Absorption Rate (SAR) measurement approach using a finite but electrically large array of vector field sensors embedded in a phantom is introduced and analyzed. In particular, the cross-polarization rejection of the array and mutual coupling between probes are investigated.
Share
Abstract
Cet article présente la conception d’un nouveau matériau permettant de simuler les propriétés diélectriques des tissus biologiques (de la tête ou du corps humain), sur une large bande de fréquences s’étendant de 600 MHz à 6 GHz. Les applications recherchées intéressent la dosimétrie radiofréquence et plus précisément le test de conformité des téléphones mobiles en termes de valeur de DAS (Débit d’Absorption Spécifique).
Share
Rational Chemical Design of Broadband Tissue-Simulating Liquids
Abstract
Standard method for Specific Absorption Rate (SAR) measurement of wireless devices is highly time consuming. Changing between a number of biological tissue simulating fluids to cover a large frequency range is one of the tedious aspects in radiofrequency dosimetric assessment. Materials capable of broadband matching with standard target dielectric parameters are hence of great utility. This paper illustrates how the application of basic physical chemistry principles can be used to define a straightforward methodology for deriving new broadband and stable tissue-simulating liquids.
Share
Experimental Study on the Relationship between Specific Absorption Rate and RF Conducted Power for LTE Wireless Devices
Abstract
Specific Absorption Rate (SAR) testing of 4G/LTE mobile devices shows a greater complexity than that of previously available radio equipment. Because of the many parameters of 4G signal, the number of possible measurement conditions has become so large that time and cost of regulatory compliance protocols have easily tripled in the past few years. Based on an experimental investigation of the relationship between conducted power at device amplifier output and peak spatial-average SAR, this paper deduces important characteristics of the LTE mode yielding the highest exposure in a given band. It also exhibits how quasi-proportionality between SAR and conducted power can be used to support significant test reduction. The reported results were used as a basis for the development of LTE SAR standard measurement procedures at the International Electrotechnical Commission (IEC) level.
Share
Abstract
Evaluation of Specific Absorption Rate (SAR) for multiple antenna systems is becoming important, with the upcoming deployment of LTE-Advanced. In this work, the influence of different antenna locations and antenna types was investigated for stand-alone SAR and simultaneous SAR, to provide some guidelines for antenna design in multi-antenna handsets. For simultaneous SAR, different phase shifts between antenna ports were considered and the averaged SAR was used as a metrics for comparison. The SAR performances were evaluated in simulation for the body worn scenario, and different placements of the mobile handset, i.e., with either the screen or back side closer to the body, were studied.
SHARE
Abstract
At the end of the nineties, the FDTD simulation of a basic coaxial-MSL transition typically took about an hour; real- life problems were practically impossible to solve without supercomputing resources. Thanks to the tremendous performance boost in hardware and the advent of more efficient simulation technologies, computational power no longer limits to accurately simulate the most complex electromagnetic (EM) problems. As for near field antenna-body interactions, computations of detailed CAD-based radiating sources in the proximity of anatomical human models can be effectively carried out even with inexpensive commercial PCs. For cost and productivity reasons, replacing complex RF measurements by simulations is surely attractive. Then, what is the barrier to the 100%-numerical stage?
Without pretending to deliver a comprehensive response to this question, this paper explains why defining an accurate model of a complex wireless device remains a major difficulty. Changing from the viewpoint of radiation performances evaluation to exposure assessment, the authors introduce a novel concept based on the combination of near-field vector measurement and simulation techniques which may offer an alternative to the 100%-numerical, with the advantage to get around source modelling difficulties under certain conditions.
SHARE
An international interlaboratory comparison for nu- merical calculations of head phantom SAR involving three mo- bile phones with computer-aided design-based models has been conducted in order to evaluate the repeatability of such calcu- lations and for providing input in the development of standard- ized procedures. SAR in the standardized specific anthropomor- phic mannequin (SAM) head phantom was calculated by ten lab- oratories in a blind study manner. The agreement in calculated SAR between the participating laboratories is very similar to the agreement obtained in interlaboratory comparisons involving SAR measurements. The results support the opinion that standardized procedures for numerical calculations of SAR can be developed. The agreement between calculated SAR results and corresponding measurement results ranges from good to poor for the three phone models. Most probably, a significant reason for the observed de- viations is the simplifications made to the models, which implies that device modeling specifications are of utmost importance in standards.
SHARE
The influence of the user’s hand holding a mobile phone to the ear on the peak spatial-average Specific Absorption Rate (psSAR) averaged over any 1 g and 10 g of tissue in the head is investigated. This study is motivated by recent reports that found substantial increases in psSAR by the presence of the hand in some cases. Current measurement standards prescribe the measurement of SAR in a head phantom without a hand present. The mechanisms of interaction between the hand and mobile phone models are studied. Simulations and measurements at 900 and 1800 MHz have been conducted to complement the understanding of the hand grip parameters leading to higher SAR in the head. Numerical simulations were conducted on four mobile phone models, and parameters such as the palm-phone distance and hand position were varied. Measurements of 46 commercial mobile phones were made, and the maximum psSAR with dif- ferent hand positions and palm-phone distances was recorded. Both simulations and measurements have found increases in the psSAR in the head of at least 2.5 dB due to the presence of the hand. Furthermore, the psSAR is sensitive to the hand grip, i.e., the variations can exceed 3 dB.
