Grâce au diverse applications prévues dans le divertissement, l’éducation et les domaines professionnels, la création d’un monde virtuel interactif a intéressé beaucoup de chercheurs dans l’académie et l’industrie. L’espace acoustique trois-dimensionnelle peut être synthétisé à partir de deux perspectives : les approches physiques et les approches perceptives. Méthode de transfert de rayonnement acoustique est une méthode efficace pour modéliser les réflexions diffuses et la réverbération tardive. Une extension de la méthode de transfert de rayonnement est proposée dans cette thèse, qui permet de modéliser les réflexions précoces et spéculaires, en conservant son avantage pour la simulation de réverbération tardive. Les approches perceptives utilisent des paramètres acoustiques pour modéliser la perception acoustique principale de l’environnement modélisé. Des réseaux récursifs de lignes à retard sont beaucoup utilisés pour générer de la réverbération tardive. Dans cette thèse, une nouvelle méthode est présentée, qui hérite l’efficacité de la structure des réseaux récursifs de lignes à retard, mais en le même temps, relie les paramètres des réseaux directement à la géométrie de l’environnement modélisé. Puis, l’approche physique et l’approche perceptive ont été combinées. La méthode de transfert de rayonnement acoustique simplifiée, avec extension à modéliser les réflexions spéculaires et diffuses, est incorporée à la structure des réseaux récursifs de lignes à retard. Le nouveau filtre réverbérant, en dépit de la modélisation des réfections diffuses et la réverbération tardive, est également capable de simuler les réflexions précoces et spéculaires avec précision. / There is an increasing interest in creating interactive virtual worlds due to the wide variety of potential applications in entertainment and education. The 3D acoustic scene can be synthesized from two perspectives : the physical approaches and the perceptual approaches. Acoustic radiance transfer method is an efficient ray-based method to model the diffuse reflections and the late reverberation. An extension of the Radiance Transfer Method (RTM) is proposed in this thesis, which allows modeling the early part of specular reflections while keeping the advantage of the original model for the late reverberation simulation. Feedback delay networks are widely used structures to generate the late reverberation. A new method is presented in this thesis, which inherits the efficiency of the Feedback Delay Network (FDN) structure, but aims at linking the parameters of the FDN directly to the geometries of the modeled environment. The relation is achieved by assigning a physical meaning to each delay line and studying the sound energy exchange between them. Then the physical approachand the perceptual approach are combined. The simplified acoustic Radiance Transfer Method, with extension for both specular and diffuse reflections, is incorporated with the Feedback Delay Networks. The new reverberator, despite of modeling the diffuse and late reverberation, is also capable of simulating the early and specular reflections with accuracy.

L'objectif de la thèse a été de mettre en place dans un premier temps des modèles analytiques et statistiques permettant d'évaluer les performances d'un système à retournement temporel de fortes-puissances puis de les vérifier grâce à des mesures.Des campagnes de mesures ont alors permis de vérifier les modèles. Des simulations numériques ont aussi montrées les possibilités offertes par un tel système.En parallèle, des travaux sur l'impact des antennes dans une chambre réverbérantes ont été menés afin d'évaluer les performances d'un système ayant plusieurs sorties.Les résultats de thèses ont permis l'élaboration de nouvelles métriques des performances du système.Le développement d'un prototype a nécessité la conception et la réalisation de chacune des branches du système complet.Les premières campagnes de mesures ont permis la validation complète des modèles. / A main aspect of this work has been to develop analytical and statistical models of the power efficiency of a time-reversal amplification system (TRAS).It is also important to evaluate the efficiency of a reverberation chamber. This allows quantifying the power received by one or more antenna when the reverberation chamber is excited. This factor is important when considering construction of the most efficient chamber for time-reversal amplification.Measurements assessing the loading effect of antennas in reverberation chambers when the field can be considered diffused were also undertaken. The study focuses on the evaluation of the varying quality factor when adding loaded antennas in the chamber.Another focus of this work is to evaluate the ratios between signals during calibration and focusing phase. An important aspect of the studies presented in this work thus concerns evaluation of the maximum value of the impulse response in a complex propagation system.We also present the power gain of time-reversal techniques and its statistical advantages compared to a classic use of a reverberation chamber.The development of a prototype required the design and implementation of each of the branches of the complete systems.The first measurement campaigns allowed the complete validation of the models.

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For the past several decades, mass estimates for supermassive black holes hosted by active galactic nuclei (AGN) have been made with the reverberation mapping (RM) technique. This methodology has produced consistent results and has been used to establish several relations that link the characteristics of the host galaxy to the mass of the central black hole. Despite this success, there are less than 50 AGN with black hole masses derived from RM. This low number is generally attributed to the difficulties in coordinating large blocks of telescope time for making simultaneous photometric and spectroscopic observations. Spectroscopic observations also generally require several months of nightly observations with moderate to large size telescopes as the signal-to-noise ratio is too low for smaller telescopes. We have made photometric observations of NGC 5548 in four filters (a custom-made Hα10 filter, the Strömgren y filter, the Johnson/Cousins V filter and the Johnson/Cousins R filter) in order to evaluate a photometric methodology for determining the lag time between the variations observed in the continuum and the Hα emission from the broad-line region (BLR) gas. This time delay represents the mean light travel time to the BLR and is therefore a measurement of the mean BLR radius. Multiple JAVELIN analyses of the three continuum light curves (y, V, and R), relative to the light curve from the Hα10 filter yields a value for τ = 3.3 ± 0.1 days. Adopting a value of f = 5.5, along with a single-epoch spectroscopic measurement from Park et of Δv = 4354±25 km/s, enables us to estimate a black hole mass of M_BH = 67.2±2.2x10^6 M_sun.

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Active control of sound transmission through an elastic plate placed between two reverberation chambers is studied experimentally. Active acoustic control is performed using piezoelectric sensors and actuators bonded to the plate. The control technique uses an adaptive control algorithm. Results are presented for harmonic excitation provided by a speaker in the source chamber at two resonant frequencies of the plate. Influence of different types of error sensors, varied actuator locations, and varied speaker locations are studied. Compared to microphone sensors in the receiving chamber, piezoelectric sensors are shown to be effective in reducing sound transmission through the plate. Average reduction of sound pressure level (SPL) on the order of 20 dB or 13 dB are achieved when the plate vibrates at mode (3,1) or (3,3). Microphone sensor locations are shown to influence the controlled sound field, those located where the direct sound field is dominant result in larger SPL reductions. SPL reductions are caused by two mechanisms: modal reduction and modal restructuring, and the dominance of either is shown to depend on actuator locations. When the sound field is non-diffuse, speaker locations influence the SPL and the SPL reduction by changing the plate's structural response. Also included in this work, previously developed one-dimensional (I-D) modal sensor theory for beams is used to develop modal sensors for a clamped plate. Two I-D modal sensors are applied to a fully clamped plate and each shown to observe a particular subset of plate vibration modes. Previous work developed the theory for two-dimensional (2-D) modal sensors for simply-supported plates. A necessary and sufficient condition for the spatial functions of 2-D modal sensors are developed for plates with arbitrary boundary conditions. / Master of Science

One of the mixing engineers most important tool when listening, analyzing and taking decisions is the physical space in which the reproduction system and the monitors are placed. The space needs to fulfill certain aspects to be able to qualify as a control room considered good for taking these decisions. In this study an active listening test was conducted to investigate if the RT60 of the natural reverberation in the room affected a mixing engineers’ decisions when adjusting parameters on an artificial reverb. 16 subjects participated, the subjects adjusted reverb level and reverb time of an artificial reverb in two different acoustical environments, with two different values of RT60. The environments were based on a professional control room made for mixing and mastering. The two values for RT60 was achieved through manipulating the room with diffusors and absorbing material. It was found that the subjects were able to adapt to the different acoustical environments, although other differences were found. The order of the which of the environments the subjects started in and which parameter the subject started adjusting, showed a considerable impact on the result. As well as what kind of factors the subjects considered when adjusting the artificial reverb.

RCs (Reverberation Chambers) has historically been used mainly for aerospace and military purposes in EMC (Electromagnetic Compatibility) testing, but the interest also seems to increase in the automotive industry (the development of an international standard for vehicles is in progress). The vehicles of the future will most likely be electrified, wirelessly connected and autonomous, i.e., more control units, more communication systems, and more sensors, will be implemented in the vehicles requiring increased robustness against all possible electromagnetic interferences. EMC testing in an RC is a step in the direction of ensuring this robustness for the future vehicle platforms. Compared to a traditional EMC test method in a fully or semi-AC (Anechoic Chamber), testing in an RC has the advantage that the electromagnetic field will be isotropic, randomly polarized and homogeneous in a statistical sense, i.e., the exposed object will be surrounded by electromagnetic energy from all directions. It can be considered relatively expensive to build a brand new RC with motorized stirrers and associated measurement instrumentation, instead it would be desirable to perform immunity tests in a more cost-effective conductive fabric tent. The great advantage is the flexibility, the tent can be set up almost anywhere, even in already existing semi-ACs, such set-up is referred to as VIRC (Vibrating Intrinsic Reverberation Chamber). This thesis aims to develop a new test method in a VIRC environment. In order to achieve good RC conditions, the electromagnetic field must be statistically Rayleigh distributed. Furthermore, it is of great importance to avoid LoS (Line of Sight) between the antenna and the test object, and to achieve good stirring in the tent. Provided this can be achieved, there are still some challenges by testing in a tent. For example, the classical dwell time of two seconds for immunity testing in EMC is not possible to achieve in a VIRC environment. The validation in this thesis shows that the dwell time or the total exposure time in the tent might be enough to trigger possible malfunctions in today's modern high-speed communication vehicles. Furthermore, it is showed, testing in a VIRC gives good field uniformity and repeatability, and can trigger malfunctions that are not triggered in traditional EMC testing in semi-AC, i.e., ALSE (Absorber-Lined Shielded Enclosure) testing.

No description available.