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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
261

Štěrbinová anténa pro pásmo X / Slot antenna for X band

Buriánek, František January 2013 (has links)
This work familiarizes readers with the issues of slot antennas. It presents design and simulation of slot antenna for X band in CST Microwave Studio program. The simulation procedure is described here, including all the settings required for proper operation of the simulation. Then there is the description of the principle of the Half-Mode Substrate Integrated Waveguide - HMSIW. In the end the designed structure of HMSIW and the slot antenna are assembled and measured. The results of the simulation are compared with the results acquired by measurements. The designed antenna at the frequency 10 GHz achieves the impedance bandwidth 255 MHz, and the gain 8,81 dBi (the simulated values in CST Microwave studio).
262

Návrh anténní jednotky přístupového bodu pro off-body komunikaci v ISM pásmu 61 GHz / Design of the antenna unit of access point for off-body communication in the 61 GHz ISM band

Miřácký, Jan January 2015 (has links)
The Master´s thesis deals with the theoretical design, practical numerical analyses and optimalization of disc-like antenna and disc-like slot antenna. The antennas have relative omnidirectional radiation characteristics in the horizontal plane, respectively in the vertical plane. Antennas exploit the substrate integrated waveguide technology. The antennas themselves are designed for the purpose of making the antenna array that will be work as an antenna unit for access point. The antennas are manufactured and experimentally verified. The program CST Microwave Studio is used for simulation in the thesis.
263

Vliv polohy zesíleného štěrbinového sacího nástavce nad pracovním stolem na účinnost odsávání / Influence of location of reinforced slot exhaust hood above work table on capture efficiency

Winkler, Martin January 2012 (has links)
The present thesis explores the reinforced exhaust slot system above work table. Its objective was to measure the capture efficiency in front of the suction extension in various elevation levels of the workbench, taking into consideration four mobility ratios, while in the first case we performed traditional suction. The thesis also presents the results of capture efficiency measurements recorded in figures and tables of measured values. The conclusion analyzes the uncertainty in performed measurements.
264

Stavěcí mechanismus štěrbiny kuželového drtiče / Slot adjusting mechanism of cone crusher

Huňka, Jan January 2015 (has links)
This master’s thesis deals with the obtuse-angled cone crushers especially about design of the individual parts of the adjustment mechanism. Most space is devoted to functional calculation and subsequent technical construction of the new design of obtuse-angled crusher where the output setting is adjusted using the motion thread and hydraulic locking system for compensating the thread clearance. The parameters are chosen with regard to the already established older types of cone crushers produced by PSP Engineering, a.s. An inseparable part is the calculation verifying the functionality of the motion thread and gearing. Another essential part of this work are stress analysis of the slot adjusting mechanism design using finite element method and considering two states - adjusting of the slot and crushing itself.
265

Rekonfigurovatelná štěrbinová anténní řada / Reconfigurable slot antenna array

Weigel, Filip January 2016 (has links)
This master's thesis deals with the basic principles of slot antennas. Models of antennas were simulated in a selected electromagnetic simulator CST MICROWAVE STUDIO (CST MWS). There are several models of slot antennas which are optimized for communication in the car at a frequency 8 GHz.
266

Design Flow für IP basierte, dynamisch rekonfigurierbare, eingebettete Systeme

Meisel, André 22 June 2010 (has links)
Der achte Band der wissenschaftlichen Schriftenreihe EINGEBETTETE, SELBSTORGANISIERENDE SYSTEME widmet sich der Synthese von partiell dynamisch rekonfigurierbaren, eingebetteten Systemen. Mit der Möglichkeit Hardwareblöcke zur Laufzeit auf programmierbaren Bausteinen neu zu konfigurieren, lässt sich eine höhere Flexibilität im Vergleich zu einer Hardwarerealisierung in eingebettete Systeme integrieren. Gleichzeitig sind diese Systeme durch eine gesteigerte Performance gegenüber Software gekennzeichnet. Die Flexibilität kann ausgenutzt werden, um kleinere Schaltkreise bei gleichem Funktionsumfang einzusetzen. Für die Integration von Rekonfigurierung sind zusätzliche Entwurfschritte im Design Flow notwendig. Herr Meisel stellt hierfür in seiner Arbeit eine Entwurfsmethodik vor und geht im Besonderen auf die Partitionierung, Platzierung und Steuerung in dynamisch rekonfigurierbaren, eingebetteten Systemen ein. Um eine vergleichsweise effizient zu realisierende Partitionierung des Systems zu erhalten, wurde das Overlaying Verfahren aus dem Bereich der Speicherverwaltung für dynamische Rekonfigurierung adaptiert. Für das Platzierungsverfahren wurden Rekonfigurierungen als Markov Kette modelliert, um so zu einer Minimierung der durchschnittlichen Rekonfigurierungsdauer zu gelangen. Die vorgestellte Rekonfigurierungssteuerung fokussiert auf einer ressourcensparenden Hardware Implementierung. Mit einem Entwurfsbeispiel werden die Vorteile und Ergebnisse des Ansatzes anschaulich illustriert. So kann der Leser die Mächtigkeit des entwickelten Ansatzes nachvollziehen und wird motiviert, die entwickelte Methodik auf weitere Anwendungsfälle zu übertragen. / Volume 8 of scientific series EINGEBETTETE, SELBSTORGANISIERENDE SYSTEME (Embedded Self-Organized Systems) addresses the synthesis of partially dynamically reconfigurable embedded systems. With the ability to configure hardware blocks during run-time, more flexibility can be integrated in embedded systems. At the same time, these systems have better performance than functions implemented in software. Through this flexibility it is possible to use smaller circuits without limiting the functionality. For the integration of reconfiguration into embedded systems, additional design steps are required. Mr. Meisel presents a design methodology for the design flow and primarily concerns the problem of partitioning, placement, and reconfiguration control in dynamically reconfigurable embedded systems. The implemented partitioning of the system is based on the adapted memory management concept of Overlaying. For the placement method the configurations are modeled as Markov chain, in order to minimize the average reconfiguration time. The presented reconfiguration control unit focuses on a resource-saving hardware implementation. The benefits and results of the approach are clearly illustrated with a design sample. The reader can understand the power of developed approach and is motivated to transfer the developed methodology to more use cases.
267

Magnet Losses in Inverter-fed High-speed PM Machines / Förluster i magneter av högvarviga PM maskiner med växelriktare

Garcia Gonzalez, Adolfo January 2015 (has links)
This master thesis deals with the estimation of magnet losses in a Permanent Magnet(PM) motor inserted in a nut-runner. This type of machine has interesting featuressuch as being slot-less and running at a very high speed (30000 rpm). An extensiveliterature review was performed in order to investigate the state of the art in estimationof the losses in magnets of a PM machine. Analytical models to calculate the no-loadback-emf and the magnetic ux density in the air-gap due to the currents in the statorare presented rst. Furthermore, several of the analytical models for calculating lossesin magnets described in the literature were tested and adapted to the case of a slotlessmachine with a parallel-magnetized ring. Then, a numerical estimation of thelosses with nite element method (FEM) 2D was carried out. In addition, a detailedinvestigation of the eect of simulation settings (e.g., mesh size, time-step, remanentmagnetic ux density in the magnet, superposition of the losses, etc.) was performed.Finally, calculation of losses with 3D FEM are also included in order to compare thecalculated losses with both analytical and FEM 2D results. The estimation of thelosses includes the variation of these with frequency for a range of frequencies between10 and 100 kHz. / Detta examensarbete handlar om uppskattningen av magnetforluster i en permanentmagnetmotor (PM) inford i en mutterdragare. Denna typ av maskin har intressantafunktioner, som att den ar slot-less och att den kors i en hog hastighet (30000rpm). En omfattande litteraturstudie utfordes for att kunna uppskatta forluster imagneterna pa basta satt. Forst presenteras analytiska modeller for att berakna denelektromotoriska kraften (EMK) och den magnetiska odestatheten i luftgapet somuppkommer pa grund av strommarna i statorn. Dessutom har era av de analytiskamodellerna for berakning av forlusterna som beskrivits i litteraturen testats och anpassatstill en slot-less maskin med en parallelmagnetiserad ring. En numerisk uppskattningav forlusterna har sedan utforts med hjalp av nita elementmetoden (FEM) 2D.Dartill har en detaljerad undersokning genomforts hur olika parameterinstallningarpaverka utfallet. De FEM parametrar som har undersokts har bland annat bestattav berakningsnatets storlek, tidssteg, remanens odestatheten i magneten och om superpositionav forlusterna galler. Till sist har berakningar for forluster med 3D FEMutforts och jamforts med resultaten for bade de analytiska och FEM 2D resultaten.Uppskattning av forluster innefattar variationen av dessa med ett frekvensomrade mellan10 och 100 kHz.
268

Design and optimization of access control protocols in Vehicular Ad Hoc Networks (VANETs) / Conception et optimisation de protocoles de contrôle d’accès pour les réseaux véhiculaires VANETs

Hadded, Mohamed 30 November 2016 (has links)
Les accidents routiers et leurs dommages représentent un problème croissant dans le monde entier. Dans ce contexte, les réseaux véhiculaires (VANETs) peuvent être déployés pour réduire les risques et pour améliorer le confort. Ils permettent aux véhicules d'échanger différents types de données qui vont des applications de sécurité et de gestion du trafic aux applications de confort. De nos jours, les applications de sécurité sont l’objet de beaucoup d'attention des chercheurs ainsi que des fabricants d'automobiles. Dans cette thèse, nous étudierons les applications critiques pour la sécurité routière visant à fournir une assistance dans des situations dangereuses ou difficiles. Notre objectif principal sera de proposer de nouveaux protocoles de contrôle d'accès au support de transmission (MAC) et de routage, qui peuvent s’adapter dynamiquement aux changements fréquents de topologies des VANETs. Après un aperçu des protocoles d’accès sans contention dans les VANETs, nous proposons des solutions basées sur la technique de division du temps: Time Division Multiple Access (TDMA). D’abord, nous nous concentrons sur le développement d’un nouveau protocole distribué (DTMAC), qui ne repose pas sur l’utilisation d’infrastructure. DTMAC utilise les informations de localisation et un mécanisme de réutilisation des slots pour assurer que les véhicules accèdent au canal efficacement et sans collision. Les résultats obtenus ont confirmé l’efficacité de notre protocole, DTMAC se comporte très significativement mieux que VeMAC (protocole MAC basé sur TDMA.) Ensuite nous proposons TRPM, un protocole de routage basé sur une approche cross-layer. Dans TRPM, l’ordonnancement des slots TDMA construit par DTMAC et la position de la destination sont utilisés pour choisir le meilleur relais. Les résultats montrent que TRPM offre de meilleures performances, du nombre moyen de relais et de la fiabilité de livraison des messages comparé à d’autres protocoles. Dans la deuxième partie de cette thèse, nous nous focaliserons sur les mécanismes centralisés d’allocation de slots qui utilisent des coordinateurs. D’abord, nous proposons CTMAC, un protocole basé sur TDMA centralisé utilisant les RSUs (RoadSide Units) pour créer et maintenir les ordonnancements. CTMAC met en œuvre un mécanisme qui permet d’empêcher les “Access Collisions” de se produire plus que deux fois entre les véhicules qui tentent d’acquérir un même slot disponible. Les résultats ont montré que CTMAC permet de mieux minimiser les collisions, ainsi que le surcoût généré pour créer et maintenir les ordonnancements par rapport aux protocoles MAC, basés sur TDMA distribué. Cependant, dans CTMAC, les véhicules roulant vite devront acquérir des nouveaux slots après une courte période de temps à chaque fois qu’ils quittent les zones de leurs RSUs courants. Cette situation rend les protocoles centralisés inefficaces et couteux dans les réseaux à grande vitesse. Afin de pallier à ce problème inhérent à l’utilisation des RSUs, nous adaptons un algorithme d’ordonnancement basé sur le clustering dans lequel certains véhicules sont élus pour gérer l'accès au canal. Ceci permet aux véhicules de rester attachés à leurs clusters plus longtemps. Pour ce faire, nous proposons 1- un protocole de clustering nommé AWCP afin de former des clusters stables avec une longue durée de vie. AWCP est basé sur l’algorithme de clustering pour les réseaux mobiles WCA dans lequel les têtes des clusters sont élues en se basant sur une fonction de poids. 2- Nous formulons le réglage des paramètres de protocole AWCP comme un problème d’optimisation multi-objective et nous proposons un outil d’optimisation qui combine la version multi-objective de l’algorithme génétique appelé NSGA-II avec le simulateur de réseau ns-2 pour trouver les meilleurs paramètres du protocole AWCP. 3- Nous proposons ASAS, une stratégie adaptative pour l’attribution des slots temporels basée sur une approche cross-layer entre TDMA et AWCP / Road crashes and their damages represent a serious issue and are one of the main causes of people death. In this context, Vehicular Ad hoc NETworks (VANETs) are deployed to reduce the risk of road accident as well as to improve passengers’ comfort by allowing vehicles to exchange different kinds of data which ranges widely from road safety and traffic management to infotainment. Nowadays, safety applications are receiving a great deal of attention from researchers as well as from automobile manufacturers. In this thesis, we particularly focus on safety-critical applications, designed to provide drivers assistance in dangerous situations and to avoid accidents in highway environments. Such applications must guarantee to the vehicles access to the medium and have strict requirements regarding end-to-end delay and packet loss ratio. Therefore, our main goal is to propose new medium access control and routing protocols, which can efficiently adapt to frequent changing VANET network topologies. After a comprehensive overview of free-contention MAC protocols, we propose several solutions, based on Time Division Multiple Access Technique (TDMA). We have designed DTMAC, a fully distributed TDMA-based MAC protocol, which does not rely on an expensive infrastructure. DTMAC uses vehicles’ locations and a slot reuse concept to ensure that vehicles in adjacent areas have collision-free schedule. Using simulations, we prove that DTMAC provides a lower rate of access and merging collisions than VeMAC, a well-known TDMA based MAC protocol in VANET. Then, in order to ensure that event-driven safety messages can be sent over a long distance, we propose TRPM, a TDMA aware Routing Protocol for Multi-hop communication. Our routing scheme is based on a cross layer approach between the MAC and the routing layers, in which the intermediate vehicles are selected using TDMA scheduling information. Simulation results show that TRPM provides better performances in terms of average end-to-end delay, average number of hops and average delivery ratio. In the second part, we focus on coordinator-based TDMA scheduling mechanisms. First, we propose the Centralized TDMA based MAC protocol (CTMAC) which uses Road Side Units (RSUs) as a central coordinator to create and maintain the TDMA schedules. CTMAC implements an Access Collision Avoidance mechanism that can prevent the access collision problem occurring more than twice between the same vehicles that are trying to access the channel at the same time. Using simulation we show an improvement in terms of access and merging collisions as well as the overhead required to create and maintain the TDMA schedules compared to distributed scheduling mechanisms. However, in the CTMAC protocol, fast moving vehicles will need to compete for new slots after a short period of time when they leave their current RSU area, which makes a centralized scheduling approach very expensive. In order to further improve the performance of coordinator-based TDMA scheduling mechanisms, we focus on cluster-based TDMA MAC protocols in which some vehicles in the network are elected to coordinate the channel access, allowing the vehicles to remain connected with their channel coordinator for a longer period of time. To this end, first we propose an adaptive weighted clustering protocol, named AWCP, which is road map dependent and uses road IDs and vehicle directions to make the clusters’ structure as stable as possible. Then, we formulate the AWCP parameter tuning as a multi-objective problem and we propose an optimization tool to find the optimal parameters of AWCP to ensure its QoS. Next, we propose ASAS, an adaptive slot assignment strategy for a cluster-based TDMA MAC protocol. This strategy is based on a cross layer approach involving TDMA and AWCP. The objective is to overcome the inter-cluster interference issue in overlapping areas by taking into account vehicles’ locations and directions when the cluster head assign slots
269

Nouvelles architectures de composants photoniques par l'ingénierie du confinement électrique et optique / News architectures for photonic components using electric and optical confinement engineering

Lafleur, Gaël 05 December 2016 (has links)
Le confinement électrique et optique par oxydation des couches minces d'AlGaAs est une étape essentielle dans la réalisation des composants photoniques actifs et passifs dans la filière de matériaux GaAs. La recherche de performances ultimes sur ces composants nécessite une meilleure maîtrise du procédé d'oxydation ainsi qu'une meilleure connaissance des propriétés optiques de l'oxyde d'aluminium (AlOx). Dans cette perspective, j'ai d'abord réalisé une étude expérimentale de la vitesse d'oxydation des couches d'AlGaAs en fonction de la température du substrat, de la composition en gallium des couches étudiées, de la pression atmosphérique et de la géométrie des mesas considérés. Puis, j'ai établi un modèle anisotrope permettant une meilleure résolution spatiale et temporelle de la forme du front d'oxydation de l'AlAs. Enfin, j'ai exploité ce procédé pour réaliser des composants d'optique guidée notamment des micro-résonateurs puis réalisé des guides optiques à fente et caractérisé leurs performances optiques. / Optical and electrical confinement using Al(Ga)As layer oxidation is a key milestone in the fabrication of active and passive GaAs-based photonic components. To optimize those devices, through the control of the optical and electrical confinements, a better modelling of oxidation process and a better understanding of optical properties of aluminum oxide (AlOx) is required. One part of this work is focusing on a throughout experimental study of AlGaAs oxidation kinetics, where I studied different important parameters such as wafer temperature, gallium composition, atmospheric pressure and mesa geometry. Then, I developed a new predictive model taking into account the process anisotropy, thus allowing a better temporal and spatial of AlAs oxidation front evolution. Finally, I could exploit this technological process to realize whispering gallery mode microdisks as well as slot optical waveguides, and I have characterized this latter photonic devices.
270

A Travelling Wave Slot Array based on a Double-Layer Lens for 77 GHz Automotive Radar

Ugle, Ashray January 2023 (has links)
Automotive radars have gained considerable interest in recent years for applications of road safety for vulnerable road users. The use of multipleinput and multiple-output (MIMO) technology in automotive radar has helped in realising a virtual aperture greater than the physical aperture of the antenna which has reduced the size of the overall radar module. But increasing the number of MIMO channels for greater angular resolution can introduce increased computational complexity, processing time and latency. A new type of radar using the multiple input multiple steered output (MIMSO) radar can alleviate these concerns by replacing the angle-FFT with beamforming by means of a lens. A double-layer lens with a beamforming layer and a radiating layer with a radiating aperture on the 2-D footprint of the lens is proposed as an antenna system for this new radar technique. This work focuses on the radiating aperture which has been realised as a travelling wave planar slotted array in gap waveguide technology due to its benefit of low losses and ease of manufacturing. A ridged gap waveguide is chosen for the reduction of the waveguide size and to avoid the appearance of grating lobes in the visible range for large scan angles. The planar slotted array is synthesised in the travelling wave configuration and reflection cancelling notches are used in the ridge to cancel the reflections from the slots. The aperture is chosen to be of a circular shape for a compact design and to maximise aperture efficiency. The planar array is verified with a full-wave simulation with a bandwidth of 76 to 81 GHz and a realised gain of 27.7 dBi at the centre frequency. The array can be scanned up to ±50◦ with a scan loss of 2.4 dBi. / Fordonsradarer har fått stort intresse under de senaste åren för tillämpningar av trafiksäkerhet för utsatta trafikanter. Användningen av MIMO-teknik (multipleinput och multiple-output) i bilradar har hjälpt till att realisera en virtuell bländaröppning som är större än antennens fysiska bländaröppning, vilket har minskat storleken på den totala radarmodulen. Men att öka antalet MIMOkanaler för större vinkelupplösning kan introducera ökad beräkningskomplexitet, bearbetningstid och latens. En ny typ av radar som använder MIMSO-radarn (multiple input multiple steered output) kan lindra dessa problem genom att ersätta vinkel-FFT med strålformning med hjälp av en lins. En dubbelskiktslins med ett strålformande skikt och ett strålande skikt med en strålande bländare på linsens 2D-fotavtryck föreslås som ett antennsystem för denna nya radarteknik. Detta arbete fokuserar på strålningsöppningen som har realiserats som en plan slitsad array i gap-vågledarteknologi på grund av dess fördel med låga förluster och enkel tillverkning. En vågledare med räfflade gap väljs för att minska vågledarstorleken och för att undvika uppkomsten av gitterlober i det synliga området för stora avsökningsvinklar. Den plana uppsättningen syntetiseras i den vandringsvågkonfigurationen och reflektionsupphävande skåror används i åsen för att eliminera reflektionerna från slitsarna. Bländaren är vald för att ha en cirkulär form för en kompakt design och för att maximera bländareffektiviteten. Planar arrayen verifieras med en helvågssimulering med en bandbredd på 76 till 81 GHz och en realiserad vinst på 27, 7 dBi vid mittfrekvensen. Arrayen kan skannas upp till ±50◦ med en skanningsförlust på 2, 4 dBi.

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