Ray tracing | EPFL Graph Search

vignette|upright=1.5|Exemple d' montrant la réfraction dans cinq milieux différents : dans l'air, dans le liquide bleu, dans le liquide rouge, dans le verre et dans le tube de plastique (les images sont déformées par le changement d'indice optique). Le lancer de rayons, ou lancer de rayon, également appelé ray tracing, est une technique de calcul d'optique par ordinateur, utilisée pour le rendu en ou pour des études de systèmes optiques. Elle consiste à simuler le parcours inverse de la lumière : on calcule les éclairages de la caméra vers les objets puis vers les lumières, alors que dans la réalité la lumière va de la scène vers l'œil. Cette technique reproduit les phénomènes physiques (principe du retour inverse de la lumière de Fermat, lois de Snell-Descartes) que sont la réflexion et la réfraction. Une mise en œuvre naïve du ray tracing ne peut rendre compte de phénomènes optiques tels que les caustiques, l'illumination globale ou encore la dispersion lumineuse

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

Interactive Real-Time Simulation and Auralization for Modifiable Rooms

Dirk Schröder

To study the effects of any changes to a room or setting on the room acoustics, a framework was developed that enables immediate acoustic and visual feedback to the user. This is achieved by running interactive room acoustics simulations and auralizations in real-time. Physically based binaural room impulse responses (BRIRs) are calculated using the image source method and ray tracing and are divided into direct sound, early reflections and late reverberation. Any part of the BRIR is updated as quickly as possible depending on the user’s interaction with the scene. This includes changes to sources and receivers (positions/orientations/directivities/HRTF), to surface materials and to the room geometry itself. Using streaming low-latency convolution, an immediate feedback is provided to the user. A parallelization concept features multi-threading and networked PC-clusters, so that the workload can be effectively distributed, offering a scalability to simulate small to huge scenes, depending on the available computation power. For convenient scene design and interaction, a plug-in for Trimble SketchUp was developed that enables real-time room acoustics and room acoustics parameter visualization to this easy-to-use CAD modeling tool.

2014

Contactless deflection sensing of concave and convex shapes assisted by soft mirrors

Michal Karol Dobrzynski, Dario Floreano, Ionut Halasz, Ramon Pericet Camara

Typical deflection sensors like strain gauges or devices based on optical fibers require physical contact with the deflected substrate during the measurement process. Such contact, however, impacts on the softness of the substrate and may falsify the measurements. In order to overcome this drawback, a novel method of contactless deflection sensing was proposed in a recent work. It was verified that the deflection angle between two planes can be extracted using only a photosensor and a light source bearing a bell-shape angular emission profile. Yet, the range of operation was limited to concave shapes. In this paper, we introduce an alternative configuration of this light-based deflection sensing method to extend its functionality to convex surfaces. Here, a spheroidal mirror bearing a customized profile is introduced above the light source. This mirror redirects part of the emitted light towards the photosensor hindered by the bending surface during convex deflections.We make use of a ray tracing simulation method to design the mirror profiles, which are accurately reproduced in the manufactured prototypes by tuning the fabrication variables of the manufacturing process. Using a shape-sensing prototype, it is verified that the use of the mirror extends the range of detectable deflections by 55deg. to convex bendings, yielding a deviation of only 8.3% from simulated results. Our deflection sensing solution is a promising method to be used as a shape sensor in numerous applications, such as soft robotics platforms or prosthetic devices.

2012

Effect of intelligent antennas on radio system planning and on mitigation

Juliane Iten Chaves Simoes

EPFL2008