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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.
11

3D-Printed Geodesic Reflective Luneburg Lens Antenna for X-Band

Oxelmark, David, Jonasson, Lukas January 2021 (has links)
With the rise of 5G and the increasing number ofdevices, novel antenna designs are needed to meet the demandof the future. In this report, the authors present a design andexperimental verification of a 3D-printed Geodesic ModulatedReflective Luneburg lens antenna working at the X-Band, 8-12GHz. The lens profile is calculated from the refractive index of aflat system using transformation optics. Furthermore, the lens ismodulated to minimize the height and chamfers are implementedto reduce reflections. A sliding waveguide connected to a coaxialcable is used to excite the lens while the transmitted signal isradiated from a sinusoidal flare. A copper-lined PLA substrateconstitutes the 3D-printed lens. The authors achieved a S11 below-10 dB across the spectrum and a realized gain exceeding 10 dBacross the sweeping angles at 12 GHz, showcasing the usabilityas a directed antenna. / Med det nya 5G nätverket och den ökandemängden enheter behövs nya antenner för att möta framtidensefterfrågan. I denna rapport presenterar författarna en designoch experimentell verifiering av en 3D-printad geodesisk moduleradreflekterande Luneburg linsantenn i X-bandet, 8-12 GHz.Linsprofilen beräknas från brytningsindexet för ett platt systemmed transformationsoptik. Dessutom är linsen modulerad föratt minimera höjden och kantavfasningar implementeras föratt minska reflektioner. En glidande vågledare ansluten till enkoaxialkabel används för att excitera linsen medan den sända signalenutstrålas från en vågledare med sinusformad avrundning.Ett kopparfodrat PLA-substrat utgör den 3D-printade linsen.Författarna uppnådde en S11 under -10 dB över spektrumet ochen realiserad förstärkning överstigande 10 dB över svepvinklarnavid 12 GHz, vilket visar linsens användbarhet som riktad antenn. / Kandidatexjobb i elektroteknik 2021, KTH, Stockholm
12

A Discrete Cylindrical Luneburg Lens With Liquid Layers

Normark Frisk, Curt-Herman, Algarp, Erik January 2020 (has links)
In this project, a cylindrical Luneburg lens isdesigned operating at optical frequencies. A Luneburg lens isa gradient index lens that transforms a point source into aplane wave or vice versa. The lens is rotational symmetric whichallows wide-angle beam scan. In this work, the gradient indexis discretized in layers. The refractive index of each layer isrealized with a transparent liquid. Ray tracing is used to designand evaluate the lens performance. We have simulated Luneburglenses with 4 - 10 layers. Increasing the number of layersimproves the performance. However, difficulties are present inthe manufacturing part of the lens considering that liquids withdesired refractive index cannot be mixed. / I detta projekt designas en cylindrisk Luneburg-lins som fungerar vid optiska frekvenser. En Luneburg-lins är en gradientindexlins som omvandlar en punktkälla till en plan våg eller vice versa. Linsen är rotationssymmetrisk vilket möjliggör vidvinkelstrålescanning. I detta arbete diskretiseras gradienta indexet i lager, brytningsindex för varje lager realiseras med en transparent vätska. Raytracing används för att designa och utvärdera linsprestandan. Vi har simulerat Luneburg-linser med 4 - 10 lager. Genom att öka antalet lager förbättras prestandan. Svårigheter förekommer i linsens tillverkningsprocess med tanke på att vätskor med önskat brytningsindex inte kan blandas. / Kandidatexjobb i elektroteknik 2020, KTH, Stockholm
13

Recherches sur la géométrie de l'espace visuel : le cas particulier de l'appréciation de la distance / Research on the geometry of the visual space : the particular case of the appreciation of the distance

Gueirard, Ninuwe 15 December 2017 (has links)
Cette thèse se propose d’étudier la difficulté de l’estimation de la distance dans le cadre de la géométrie de l’espace visuel. En philosophie de la perception, cette thèse est d'abord discutée au plan épistémologique : comment savoir que cette distance n'est pas connue ou connaissable, quoique perçue et discutée. Les travaux de Berkeley nous servent de point de départ et fixent un cadre spéculatif, puisque Berkeley soutient en effet que le jugement porté sur la distance résulte entièrement de l'expérience, quoique cette distance ne puisse être vue phénoménalement. La thèse se propose d'examiner une question essentielle supportée par cette alternative centrale mais au plan ontologique cette fois : comme déterminer de quel type est la distance : est-elle inconsciemment visible ? tangible ? ou visible et tangible à la fois ? Peut-elle être une entité assignable dans un espace hyperbolique, ou sphérique, un espace strictement euclidien, ou hyperbolique et sphérique en même temps qu'euclidien ? Pour appuyer notre propos et notre recherche nous mettrons à l’épreuve différents textes et expériences en passant de Berkeley à I. Rock ou de T. Reid à M. Wagner. Notre but aura été d'explorer les limites argumentatives et de montrer ce qui est impliqué par ces différentes appréciations et assignations de la distance dans tel ou tel espace déterminé. A chaque fois s'affrontent la géométrie de l’espace visuel et l’optique physiologique, mais au sein d'un même débat de fond qui consiste à savoir comment définir philosophiquement l’estimation de la distance ? / This thesis examines the difficulties in estimating the geometrical distance of visual space. Submitted in the field of Philosophy of Perception, this thesis is first discussed from an epistemological standpoint: how does one know that this distance is unknown or unknowable despite being perceived and discussed. The various works of Berkeley serve as a point of depart and establish a speculative framework as Berkeley held that judgment of distance results entirely from experience despite the fact that this distance cannot be seen in a phenomenal way. This thesis examines an essential question supported by this central problem, this time from an ontological position: how is the type of distance to be determined: is it unconsciously visible?tangible? or both visible and tangible at the same time? Can it be categorized in a hyperbolic space, or spherical space, or a strictly Euclidean space, or hyperbolic and spherical at the same time as Euclidean? In support of the thesis and research, various texts and experiences have been examined and contrasted, including those of Berkeley and I. Rock as well as T. Reid and M. Wagner. The goal has been to explore the limits of argumentation and to show what is implicated by these different accounts and assignment of distance in one, versus another, determined space; additionally studying subjects including the experience of the alleys or the so-called the moon illusion, which appeared to be demonstrative examples. In each instance, geometry of visual space and physiological optics confront one another, but at the center of this same fundamental debate is the question of how to define the estimation of distance philosophically?

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