Spectre électromagnétique | EPFL Graph Search

vignette|redresse=1.5|Diagramme montrant le spectre électromagnétique dans lequel se distinguent plusieurs domaines spectraux en fonction des longueurs d'onde (avec des exemples de tailles), les fréquences correspondantes, et les températures du corps noir dont l'émission est maximum à ces longueurs d'onde. Le spectre électromagnétique est le classement des rayonnements électromagnétiques par fréquence et longueur d'onde dans le vide ou énergie photonique. Le spectre électromagnétique s'étend sans rupture de zéro à l'infini. Pour des raisons tant historiques que physiques, on le divise en plusieurs grandes classes, dans lesquelles le rayonnement s'étudie par des moyens particuliers. Domaines du spectre électromagnétique Vue générale On décrit un rayonnement électromagnétique par ses caractéristiques les plus accessibles, selon sa forme et son utilisation. On caractérise habituellement les ondes radio par la fréquence, qui s'applique aussi bien aux circuits d

Effect of intelligent antennas on radio system planning and on mitigation

Juliane Iten Chaves Simoes

Smart antennas have been recently applied to improve the capacity and the performance of second generation wireless mobile communication systems. In general, smart antennas reduce the effects of multipath fading and improve the signal-to-noise-plus-interference ratio (SNIR). Additional advantages such as channel capacity increase in urban areas, coverage extension in urban areas and spectrum efficiency in general can be obtained with the aid of smart antennas at the base station. Drawbacks are the cost, and both hardware and software complexity. Smart antennas promise a clear advantage in multi-service traffic scenario in comparison with non-adaptive antenna techniques. It is generally accepted that the adaptive antennas technique will be a key enable for the success of the European third generation mobile communication system known as Universal Mobile Telecommunication System (UMTS). The first part of this thesis presents two types of smart antenna systems: switched beam antennas and adaptive arrays. It introduces statistical models for them and investigates the performance measures of cellular radio systems with and without smart antennas deployed at base stations. Employing Monte-Carlo methodology, a tool has been developed to analyze the interference between two different systems that share the same geographical area and have neighboring frequency channels. The statistical smart antennas model has been used to verify the mitigation of the interference compared with others antennas used at the base station. These simulations have been done for TDMA, FDMA and CDMA systems. Wireless communication operating at different frequencies on the non-ionizing radiation (NIR) region of the electromagnetic spectrum has greatly increased in the last few decades, with important benefits for the population. These include mobile communication, such as cellular telephone systems. However, the radiated electromagnetic field levels increased substantially in areas where people may stay during long periods each day. This may result in long-term exposure to the population. International guidelines and standards were developed aiming at protecting the population, and limiting the maximum radiation produced. The methods used by regulation authorities to evaluate the field levels at places of sensitive use yield very conservative results. They need thus to be refined prior to the introduction of adaptive antennas. In the second part of the thesis, a 3D ray tracing tool is developed to predict the propagation for real scenarios using UMTS systems. This tool takes into account 3D radiation diagrams and multipath propagation. It was used in real scenarios to compare the real field levels with the levels obtained by the approximate methods defined by the regulation standards. Finally, this tool was used to predict the field levels in a scenario containing smart antennas. Scenario not foreseen in the method described in the standards.

EPFL2008

Computational Analysis and Methods for Electromagnetic Exposure Limits, Antenna Optimization and Cell Phone Design

Chen Xi Lin

In recent years, the advancements of wireless technologies have led to rapid developments in the field of telecommunication, power delivery and bio-medical applications. During the evolution of a wireless technology, the electromagnetic compatibility (EMC) between a radiating source (e.g., an antenna) and nearby active or passive elements (e.g., a closely integrated electronic component or a human body) often introduces challenging design requirements. This thesis focuses on the applications of state-of-the-art computational electromagnetic compatibility (CEMC) techniques in multidisciplinary engineering design tasks, with an emphasis on computational bio-electromagnetic compatibility (CBEMC). The analyses reported in this thesis span practical applications from power frequency (Hz) to radio frequency (GHz), providing research outcomes which significantly benefit the understandings of low-frequency human body exposure safety and radio-frequency antenna integration and optimization. The research aspect of the thesis is initiated with a thorough review of the existing low-frequency exposure safety guidelines recommended by international regulatory committees. The subsequent analyses suggest essential scientific basis for the update and revision of the existing exposure limits. Practical exposure scenarios (e.g., magnetic resonant wireless power transfer) are investigated with novel assessment techniques. Subsequently, a computer-aided optimization scheme based on network-distributed genetic algorithms is applied to highly detailed numerical mobile phone model and human body phantoms. The investigated optimization technique is proven to be superior than traditional empirical approaches. Finally, the CEMC techniques are applied in the context of non-dosimetry related engineering design environment by investigating the integration of a miniature loudspeaker (acoustic component) and a mobile device antenna (radio frequency component). Based on simulation and measurement data, the coupling mechanisms are determined to establish the fundamental design guidelines for optimum antenna-speaker co-existence and performance. In summary, this thesis details several novel applications of CEMC in the most stringent and complex industrial design environments. The presented research findings serve as indispensable basis for future research oriented towards the exposure-compliant and electromagnetic- compatible designs for novel wireless technologies.

EPFL2013

Studying the interactions between electro-magnetic elds and biological tissue

Laurine Kolly

Drug delivery systems (DDS) were engineered to overcome the drawbacks of more common methods such as oral pills and intravenous injections. Implantable capsules that release anesthetic drugs locally for pain management after Total Knee Arthroplasty (TKA) are currently in development within the LMIS1. The capsule will be implanted at the site of the wound during the operation and will be controlled wirelessly through resonant inductive coupling, enabling a local release of analgesics. Within this framework, this project aimed to investigate the interaction of electro-magnetic elds with the tissue that separates the transmitting coil of the controller from the implanted capsule. The main aspects that were studied consisted of the penetration of the magnetic eld and the Specic Absorption Rate (SAR). As the receiving coils on the reservoirs of capsule will each resonate at specic frequency between 300 MHz and 1.1 GHz, the aforementioned aspects were assessed at the two ends of the frequency spectrum. This was performed through the means of Finite Element Analysis, using COMSOL simulation software. To do so, models with three dierent types of media were built: air as a baseline, multi-layered tissue as an anatomically representative model, that reproduced remote power transfer to a capsule implanted at the level of the knee, and water as an approximation of the multi-layered tissue model. As a result, it appeared that, at the higher frequencies, the magnetic eld is subject to considerable attenuation, such that the power input necessary to generate sucient eld intensity at the level of the capsule in a multi-layered tissue model must be increased from a baseline of 5 W, to 10 W at 300 MHz and to 50 W at 1.1 GHz. The analysis of the SAR revealed that average peak SAR values reached are higher than the safety limit (in an uncontrolled environment) at a frequency of 1.1 GHz, and that the SAR is proportional to the power input. This implies that there is a trade-o to increasing the power input to adjust the intensity of the magnetic eld that could potentially be resolved by modifying the circuit design. Furthermore, it was concluded that approximating tissue with water may cause for the magnetic eld intensity as well as the SAR to be underestimated, due to the diering dielectric properties and to the density of water being lower than that of skin or tendon. Thus, a more anatomically accurate multi-layered tissue model should be favoured.

2020