Sensibilité électromagnétique

La sensibilité électromagnétique (ou syndrome HSE, pour hyper-sensibilité électromagnétique) fait référence à des symptômes fonctionnels divers non spécifiques, souvent attribués par les sujets eux-mêmes à une exposition à des champs électromagnétiques (CEM) ou à des ondes électromagnétiques, sans preuves cliniques ni biologiques. Ce syndrome est à distinguer des effets biologiques des champs électromagnétiques sur l'être humain, en particulier les champs statiques d'extrêmement basse fréquence dont on reconnaît le caractère peut-être cancérogène en cas d'exposition de long terme. On parle aussi parfois d'« intolérance environnementale idiopathique attribuée aux champs électromagnétiques » (IEI-CEM, formulation recommandée par l'organisation mondiale de la santé, OMS), d'électro-sensibilité, d'électro-hypersensibilité, ou de « syndrome d'intolérance aux champs électro-magnétiques » (SICEM). Les personnes qui déclarent souffrir d'hypersensibilité électromagnétique affirment réagir à

Mode interference and UV-induced mode conversion in few-mode fibers

Soham Basu

Resonant and non-resonant effects in few-mode fibers have found use in versatile devices. From sensing perspective, extensive research has been done on fringe sensitivity of nonresonant two-mode interference. Resonant mode converter gratings are promising candidates for the fields of mode division multiplexing and active devices based on few-mode fibers. This thesis explores multi-parameter sensing using two effects of two-mode interference (TMI), namely fringe shift and shift of group-velocity equalization (GVE) wavelength. The following sensing parameters were achieved: a) TMI fringe shift can be used for measuring the effect of changes in temperature and strain on intermodal dispersion. For exposure of the fiber with a scanning laser spot of constant velocity, the change in intermodal dispersion due to such particular exposure can also be measured using TMI fringes. b) GVE wavelength shift can be used for straightforward sensing of temperature and strain, without suffering from any dependency on the fiber length like TMI fringes. Using the shift of GVE wavelength during exposure of the full fiber with a scanning laser spot, the change in core index can be estimated due to a simple model. This allows measurement of small index changes due to irradiation, which is not possible with FBGs due to imperceptible strength of FBGs for small index changes and lower sensitivity. Combining the GVE and FBG resonance wavelengths provides a method for differentiating strain and temperature. The GVE wavelength also has an approximately three times higher temperature sensitivity compared to FBG resonance at similar wavelengths. The strain sensitivity of GVE and FBG resonance wavelengths are of similar magnitude but of opposite sign. TMI fringe shift can also be used to measure the extra phase added between two modes by each mark of laser irradiation. Two methods have been developed for completely characterizing the intermodal dispersion, which were verified experimentally for the LP01-LP02 dispersion. Intermodal and intramodal reflection peaks of two excited modes from an FBG written in the few-mode fiber can be used to approximately estimate the offset of the intermodal dispersion of the pristine fiber. Combining this with TMI phase unwrapping provides estimate of complete intermodal dispersion including offset. Measuring the resonance wavelength for a mode converter written using marks already characterized using TMI provides a precise estimate of the offset of the intermodal dispersion of the pristine fiber. From the estimate of extra phase added by each mark and intermodal dispersion of the pristine fiber, the intermodal dispersion experienced by resonantly interacting modes in an MC can be predicted. Fabrication of broadband mode converter gratings at any desired wavelength is an ongoing field of research. Different strategies were evaluated for making broadband MCs: a) Partial core irradiation with a tightly focussed laser spot was simulated with simple approximate models. In was concluded that the losses might be too high due to poor mode overlaps. b) It was determined using simulations that phase-shifted mode converter gratings can provide broader than 35 nm bandwidth at 20 dB conversion strength using reasonable irradiation parameters. The method was verified by achieving 41 nm bandwidth at 16 dB conversion strength.

EPFL2020

Electromagnetic Modelling of Planar Circuits Embedded in Laterally Shielded Multilayered Media

Laleh Golestanirad

Multilayered media with printed circuits embedded between their dielectric layers are one of the most successful technologies for manufacturing planar structures with a very promising performance-to-price ratio. These planar structures include many different geometries ranging from cavity-backed microstrip antennas through Frequency Selective Surfaces (FSS) and photonic band-gap structures, to shielded printed circuits and ultra-wide-band slot-line microwave filters. The electromagnetic characteristics of such structures can be modeled with a wide range of numerical techniques. In recent years we have witnessed a remarkable progress in developing numerical solvers specialized in analyzing specific electromagnetic problems including the Integral Equation technique (IE) solved by the Method of Moments (MoM) which has proven to be very robust and efficient in the framework of partially open or shielded planar structures. As a part of this study an efficient CAD tool was developed based on the IE formulation and implemented in the context of the MoM technique. It includes a rigorous mathematical formulation of the electromagnetic problem which automatically incorporates the effects of the metallic shield (cavity) and the multilayered substrate which supports different layers of metallization (interfaces). A comprehensive study has been carried out to point out the convergence of the proposed algorithm along with a detailed validation, verification and benchmarking plan. The tool is developed in such a way that is capable of working with a hybrid mesh (combination of both rectangular and triangular cells) which gives it a great flexibility in analyzing any arbitrarily-shaped embedded circuitry. To enhance the overall performance of the algorithm, symmetry options have been formulated and implemented. These additional features have shown to dramatically reduce the computational and temporal requirements and thus expand the range of microwave devices which can be efficiently analyzed by the software, such as filters based on waveguide structures and FSSs. Other enhancement techniques have been envisaged based on selective MoM matrix member calculation which successfully reduce the number of unknowns in large microstrip layouts while maintaining an acceptable accuracy. Mathematical formulations are developed to provide the capability of handling lumped ports (representing coaxial-line feeds) and waveguide excitations. The implementation of combined ports in the framework of planar multilayered structures is shown to be practically useful in analyzing systems that have both waveguide connections and planar circuitries in their structure as it enables the application of highly specialized algorithms in the analysis of each part of the system and subsequent communication of the network characterizations at the ports' interfaces. This approach has considerably enhanced the overall performance of the analysis tool by reducing the computation time and memory requirements to a great extent.

EPFL2011

Assessment of the Electromagnetic Field Exposure due to 5G Base Stations using a Monte-Carlo Method: Initial Results

Tingyong Jiang, Anja Skrivervik Favre

The realistic assessment of the Electromagnetic Field exposure due to wireless telecommunication base stations is critical to protect the population from harm due to excessive exposure, and allow wireless service providers to use the available technology in the most rational way. The classic approach based on the worst-case scenario used in 2G to 4G leads to over conservative results in the 5G base stations, due to the use of massive MIMO and dynamic pattern beamforming. A statistical approach is required to obtain a more realistic assessment. In this contribution, we propose first results obtained using a Monte Carlo simulation method to assess electromagnetic field exposure levels for different scenarios.

IEEE2021