Dissertations / Theses on the topic 'Directivity'
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Basta, Nina Popovic. "Multilayer scalable coupler with high directivity." Thesis, Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53955.
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This thesis addresses the design, analysis, and experimental validation of a high-directivity and high coupling microwave directional coupler. The motivating application is in broadband signal routing between cores of multi-core processors, where the delay of simple wire interconnects introduces unacceptable latency. The performance goals include scalability with frequency, a coupling coefficient of 3 dB, directivity larger than 40 dB, high return loss, low insertion loss below 3 dB at the center frequency, and small footprint.
The approach to this problem taken in the thesis is a combination of edge and broad-side coupling in a multi-layer, multi-conductor microstrip coupled-line system. The two coupling mechanisms between neighboring pairs of coupled lines, along with appropriate end interconnections, allow for reduced size and design that achieves equal propagation velocities for the different modes supported by the five-conductor guiding structure that contribute to coupling.
To validate the approach, a coupler designed for operation at 1 GHz is demonstrated to have a isolation of -22 dB with a coupling coefficient of 3\,dB and a return loss of -20 dB. The coupler is implemented on a FR-408 substrate with a permittivity of 3.66 and 1.17mm and 0.17mm thicknesses, and a total area of 12.65 cm^2. Three metalization layers are used in the design, with edge and broad-side coupled pairs of lines on the top two layers and diagonal end interconnects between the top and bottom lines. The coupler design is then scaled to 3 GHz by shortening the coupled-line length, and established -24 dB isolation, coupling of 3 dB, return loss of -20 dB, and has a total area of 6.9 cm^2.
The analysis of the coupler shows that full-wave electromagnetic modeling agrees well with measurements and is necessary during the design process, while circuit analysis with built-in coupled-line models shows poorer agreement with experimental data. A tolerance analysis shows that the coupler performance is most sensitive to milling precision and separation between coupled-lines. Based on the measured and simulated results, it is shown that this type of coupler can be further scaled to higher frequencies and on-chip implementations for signal distribution in multi-core processors, or any other application where a number of components need to be interconnected with low latency and no reflection.
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Loveridge, M. M. "Marine seismic source signatures : directivity and the ghost." Thesis, University of Oxford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355760.
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Ivars, Morón Diego. "Optimizing the directivity index of a two-way loudspeaker." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for elektronikk og telekommunikasjon, 2010. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-11108.
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Performance of the loudspeaker in a common living room is analyzed in this project. Moreover, directivity parameters like Directivity Index and polar Directivity Diagram are studied taking as example one specific tweeter construction. Some writers suggest that largely frequency-independent Directivity Index is preferable for loudspeakers in an ordinary indoor stereo setup. To achieve this goal, variation of the original radiation diagram of the studied tweeter is performed including reflectors in the system. A measurement protocol is designed and used. Obtained data is processed by developed software that presents the results.
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Foltz, Eleanor R. (Eleanor Ruth). "Two dimensional control of metamaterial parameters for radiation directivity." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/37199.
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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.Includes bibliographical references (leaves 77-80).
This work examines the feasibility of using metamaterials to direct radiation. The limits of required index of refraction and the required material depth are explored using MATLAB simulations. A wedge of connected S-shape metamaterial is chosen and simulated in CST Microwave Studio. The incident radiation is Transverse Magnetic (TM) and negative deflection is achieved. The S-shape wedge is adjusted in small ways, and a specific wedge is chosen for further study. The S-shape metamaterial wedge is then adjusted by adding lumped elements of capacitance throughout the structure. A beam through this adjustable material is deflected -76° to +580 by adding 0pF to 6pF additional capacitance. The deflection is not monotonic, but most pronounced between 0.lpF and 0.8pF. The deflection is discussed, as well as the regions of strongest signal power.
by Eleanor R. Foltz.
M.Eng.
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Sviridova, T. V. "The development to ecological directivity of the operation enterprise." Thesis, Вид-во СумДУ, 2010. http://essuir.sumdu.edu.ua/handle/123456789/13191.
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Wang, Zhiwei, and Shen Zhang. "Design of 5G antenna arrays based on Multi-directivity." Thesis, Linnéuniversitetet, Institutionen för fysik och elektroteknik (IFE), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-95135.
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As communication technology evolves, the focus shifts to 5G. The discussion of 5G cannot be separated from a discussion of related antenna systems. Chapter 1 is a brief introduction to our work, which is an antenna array for a 5G communication system operating in the band 3.4 to 3.8 GHz. This is a common band for 5G in Europe. Background and theory are presented in Chapters 2 and 3. In Chapter 4, the design has been simulated with the software CST Studio Suite. We study an antenna group that consists of four linear arrays that together cover all directions. The gain eventually reaches 12dB in each of the main directions after optimization. Based on simulation, this gain could be implemented as described in Chapter 5. The specification requires that the antenna should have four main directions with high directivity and a reasonable performance elsewhere. The realized gain is 11 dB for the four main directions. Our data shows that the arrays have two different work modes depending on feeding: one as a directive antenna with 11 dB gain, the other as an omnidirectional antenna with 7.5 dB gain. High directivity is very important for 5G communication. A summary with conclusions is given in Chapter 6 where also some improvements are suggested.
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Juyal, Prateek. "Directive microstrip disc radiators based on TM1m modes." IEEE TAP, 2016. http://hdl.handle.net/1993/32074.
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Fundamental TM11 mode of circular microstrip antennas has a limitation of low broadside gain. This thesis explores and investigates the possibility of designing high gain circular microstrip antennas by using higher zeros of the first order mode, or the TM1m modes. Deficiencies in the existing methods of gain enhancement, motivates the need to look for new methods. This is done by first investigating the radiation characteristics of TM1m modes, and then providing techniques for sidelobe suppression in their radiation patterns. Several approaches are proposed and corresponding to each developed technique, an example of high gain antenna is designed, fabricated and experimentally evaluated.
First, through the radiation characteristics of a magnetic loop over an infinite ground plane, we explain the occurrence of high sidelobes in the E-plane radiation patterns of the TM1m modes. By noting the peak directivity and sidelobe variation with loop size, we propose, investigate and demonstrate the use of high permittivity substrates to reduce the sidelobes in the TM12 mode. Second, to remove the dependence of the radiation characteristics on high permittivity substrates, another technique to suppress the high sidelobes of TM12 mode, is presented. It is found that introducing a narrow nonresonant rectangular slot at the patch center, sidelobes of the TM12 mode can be effectively suppressed. Sidelobe level (SLL) suppression is demonstrated by both simulation and measurement, using various configurations.
Third, it is proposed that linearly superimposing the radiation fields of either odd or even zeros of the first order mode, can achieve both high gain and low sidelobes. To show this, stacked antenna configurations of TM11 and TM13 modes are thoroughly investigated and SLL suppression is demonstrated. Finally, to leverage further advantage of the linear superposition of modes, a single layer annular slot loaded antenna configuration is proposed.
The proposed new configurations are based on higher order TM1m modes, which, for excitation, requires electrically large conducting discs. This property offers one more advantage at high frequencies, where antenna size becomes too small for the fundamental mode to fabricate and feed. The proposed electrically large antennas eliminate these problems, and become more practical to fabricate.February 2017
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Larsson, Kristina. "Assessment of directivity of real noise sources- Application to vehicles." Thesis, KTH, Farkost och flyg, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-151025.
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The aim of this project is to evaluate a new method for noise directivity measurements; whether a room correction factor can be used to compensate for the effect of a light reverberation field. Another aim is to find if there is any suitable standard to use. No standard to use fully was found, but SS-EN ISO 3744:2010 has a method to compensate for reverberation upon which the present method is based. Measurements were performed for three objects in a semi anechoic room and two ordinary rooms. Sound pressure was measured for all multiples of 30° in the horizontal plane where the acoustic centre for each object was situated. Thereafter, the room correction factor was calculated and from that compensated values could be found. The room correction factor did not fully make the wanted difference. The results only showed subtle connections, but tendencies show that the method might be valid for 250 and 500 Hz. To get a stronger correlation, the method must be refined. The distance to the microphone is for example one factor that depends on the environment.Målet med projektet är att utvärdera en ny metod för ljuddirektivitetsmätningar; om en rumskorrektionsfaktor kan användas för att kompensera för ett svagt efterklangsfält. Utöver detta görs en litteraturstudie för att finna relevanta standarder. Någon standard att använda helt fanns inte, men SS-EN ISO 3744:2010 har en metod för att kompensera för efterklangsfält som metoden i detta arbete är baserad på. Mätningar utfördes för tre objekt i ett halvekofritt rum och två mer vanligt förekommande omgivningar i en industriell miljö. Där mättes ljudtryck i alla vinklar som är en multipel av 30° i samma horisontella plan där den akustiska mitten i mätobjektet befann sig. Utifrån dessa mätningar kunde rumskorrektionsfaktorn beräknas och från den kunde kompenserade värden hittas. Resultaten visade att rumskorrektionsfaktorn inte fungerade helt önskvärt. De visade bara svaga kopplingar med vissa tendenser till att metoden fungerade bättre för 250 och 500 Hz. Nya mätningar måste därför utföras där metoden förbättrats. Exempelvis är avståndet till mikrofonen, som beror av omgivningen, viktigt.
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Friman, Manne. "Directivity of sound from wind turbines : A study on the horizontal sound radiation pattern from a wind turbine." Thesis, KTH, MWL Marcus Wallenberg Laboratoriet, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-48926.
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In the present paper, a study on the directivity of sound from a wind turbine has been conducted. The aim of the study is to investigate the horizontal sound radiation pattern through a field study compared to a noise prediction. The benefit of the results may be used to optimize the output effect from the wind turbine while the guidelines for noise levels at nearby residential areas still are met. The complete directivity pattern around the wind turbine was investigated by performing emission measurements around the wind turbine from a method described in IEC 61400-11 Wind turbine generator systems – Part 11: Acoustic noise measurement technique. Furthermore, the dominant sound source from the wind turbine, the turbulent boundary layer trailing edge noise, and the frequency range where it is dominating has also been scrutinized. The results show that the dipole character of the trailing edge noise has an impact on the entire horizontal radiation pattern from the wind turbine. From a field study it was found that there was a distinguishable directivity of the sound. On a distance of 125 m from the wind turbine the sound pressure level in the crosswind direction of the wind turbine is close to 3 dBA less than the sound pressure level in the downwind direction of the wind turbine when the wind speed is 8 m/s at a height of 10 m. The difference between other directions compared to the downwind direction is less significant. This could be utilized to optimize the power output, however the difference in sound level is relatively small but the advantage for power output have to be quantified before a conclusion of the benefits can be made.
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Bonvalot, Eliot. "Dynamic response of bridges to near-fault, forward directivity ground motions." Online access for everyone, 2006. http://www.dissertations.wsu.edu/Thesis/Summer2006/e%5Fbonvalot%5F072606.pdf.
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Ziolkowski, Richard W. "The directivity of a compact antenna: an unforgettable figure of merit." EDP SCIENCES S A, 2017. http://hdl.handle.net/10150/626104.
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When an electrically small antenna is conceived, designed, simulated, and tested, the main emphasis is usually placed immediately on its impedance bandwidth and radiation efficiency. All too often it is assumed that its directivity will only be that of a Hertzian dipole and, hence, its directivity becomes a minor consideration. This is particularly true if such a compact antenna radiates in the presence of a large ground plane. Attention is typically focused on the radiator and its size, while the ground plane is forgotten. This has become a too frequent occurrence when antennas, such as patch antennas that have been augmented with metamaterial structures, are explored. In this paper, it is demonstrated that while the ground plane has little impact on the resonance frequency and impedance bandwidth of patch antennas or metamaterial-inspired three-dimensional magnetic EZ antennas, it has a huge impact on their directivity performance. Moreover, it is demonstrated that with both a metamaterial-inspired two-element array and a related Huygens dipole antenna, one can achieve broadside-radiating electrically small systems that have high directivities. Several common and original designs are used to highlight these issues and to emphasize why a fundamental figure of merit such as directivity should never be overlooked.
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Sterba, Ron. "Distortion directivity and circuit modeling of a needle array plasma loudspeaker." Ohio : Ohio University, 1991. http://www.ohiolink.edu/etd/view.cgi?ohiou1183749470.
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Bodon, K. Joshua. "Development, Evaluation, and Validation of a High-Resolution Directivity Measurement System for Played Musical Instruments." BYU ScholarsArchive, 2016. https://scholarsarchive.byu.edu/etd/5653.
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A high-resolution directivity measurement system at Brigham Young University has been renovated and upgraded. Acoustical treatments have been installed on the microphone array, professional-grade audio hardware and cabling have been utilized, and user-friendly MATLAB processing and plotting codes have been developed. The directivities of 16 played musical instruments and several loudspeakers have been measured by the system, processed, and plotted. Using loudspeakers as simulated musicians, a comprehensive analysis was completed to validate the system and understand its error bounds. A comparison and evaluation of repeated-capture to single-capture spherical systems was made to demonstrate the high level of detail provided by the 5 degree resolution system. Analysis is undertaken to determine how nonanechoic effects in anechoic chambers influence results. An overview of directivity measurement systems from the literature is provided as well as a dedicated discussion of the directivity measurement system at Brigham Young University.
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Mobley, Frank Spencer. "Further development of 3-D rotary-wing acoustic directivity using a spherical harmonic representation." University of Dayton / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1335543552.
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Eyring, Nicholas J. "Development and Validation of an Automated Directivity Acquisition System Used in the Acquisition, Processing, and Presentation of the Acoustic Far-Field Directivity of Musical Instruments in an Anechoic Space." BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/4004.
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A high spatial resolution acoustic directivity acquisition system (ADAS) has been developed to acquire anechoic measurements of the far field radiation of musical instruments that are either remote controlled or played by musicians. Building upon work performed by the BYU Acoustic Research Group in the characterization of loudspeaker directivity, one can rotate a musical instrument with sequential azimuthal angle increments under a fixed semicircular array of microphones while recording repeated notes or sequences of notes. This results in highly detailed and instructive directivity data presented in the form of high-resolution balloon plots. The directivity data and corresponding balloon plots may be shown to vary as functions of time or frequency. This thesis outlines the development of a prototype ADAS and its application to different sources including loudspeakers, a concert grand piano, trombone, flute, and violin. The development of a method of compensating for variations in the played amplitude at subsequent measurement positions using a near-field reference microphone and Frequency Response Functions (FRF) is presented along with the results of its experimental validation. This validation involves a loudspeaker, with known directivity, to simulate a live musician. It radiates both idealized signals and anechoic recordings of musical instruments with random variations in amplitude. The concept of coherence balloon maps and surface averaged coherence are introduced as tools to establish directivity confidence. The method of creating composite directivities for musical instruments is also introduced. A composite directivity comes from combining the directivities of all played partials to approximate what the equivalent directivity from a musical instrument would be if full spectral excitation could be used. The composite directivities are derived from an iterative averaging process that uses coherence as an inclusion criterion. Sample directivity results and discussions of experimental considerations of the piano, trombone, flute, and violin are presented. The research conducted is preliminary and will be further developed by future students to expand and refine the methods presented here.
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Anagnostopoulos, Eleftherios. "Modélisation de la génération d'ultrasons par laser : application à l'inspection de composants aéronautiques métalliques et composites." Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0043/document.
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Le Contrôle Non Destructif par ultrasons-laser est une technique attractive pour l'industrie aéronautique de par son caractère entièrement sans contact et permet l'inspection rapide etefficace de composants mécaniques complexes. L'objectif de ces travaux de thèse concerne lamodélisation de la génération d'ultrasons par laser dans les composants aéronautiques, métalliques etcomposites, de géométrie bicouche. Nous cherchons en effet à étudier l’influence sur le mécanisme degénération ultrasonore d’un revêtement tel qu’une couche superficielle de peinture ou de résine. Dansun premier chapitre, nous proposons une modélisation semi-analytique unidimensionnelle de lagénération et propagation d’ultrasons par laser dans une géométrie bicouche au travers de deuxapproches. L’apport en termes de coût numérique d’une des deux méthodes nous conduit à montrerleur équivalence en traitant rigoureusement le problème des conditions aux limites. Dans les troisderniers chapitres, des modèles de directivité des ondes ultrasonores générées par laser sont proposésdans des géométries de complexité croissante, d’un matériau homogène jusqu’au cas d’un bicoucheen passant par le cas intermédiaire de deux demi-espaces aux propriétés optiques variées. L’influencede l’épaisseur d’une couche superficielle de résine à la surface d’un matériau composite est trèsnettement mise en évidence et expliquée à l’aide des différents outils développés. Nous discutonségalement de l’intérêt du calcul de ces directivités dans la prise en compte des sources élastiquesengendrées par laser dans un formalisme de type rayon utilisé par le logiciel dédié au contrôle nondestructif CIVA développé au CEAThe laser-ultrasonic technique is an attractive Non Destructive Testing technology forthe aviation industry. Indeed, its non-contact ultrasonic generation process could allow inspectingcomplex mechanical part at high sampling rates. The purpose of this work consists in the modelling ofthe generation of ultrasonic waves by a laser pulse in metallic or composite materials in bilayer geometry.In this work, we seek to analyze in detail the influence of coatings on the ultrasonic generation processsuch as paint or resin coatings usually used in industrial parts. In a first chapter, we propose two differentapproaches of a semi-analytical modelling of the generation and propagation of ultrasonic waves in aone-dimensional assumption of a bilayer sample. As one of them handles shorter computation times,we decide to rigorously show the equivalence of these different approaches focusing on the boundaryvalue problem. In the three last chapters, different models of the directivity patterns of ultrasonic wavesgenerated by a laser pulse are given in geometries of increasing complexity, from a homogeneousmaterial to a bilayer considering the intermediate case of two half-spaces of various optical properties.As a result, we clearly show the influence of a superficial skin layer on the laser-generated ultrasoundsemitted in composite materials. We also discuss briefly on the interest of the directivity patterns to modelelastic sources generated by laser in a ray formalism used in the CIVA software dedicated to NDTsimulations and developed at CEA
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Pollow, Martin Verfasser], Michael [Akademischer Betreuer] [Vorländer, and Peter [Akademischer Betreuer] Vary. "Directivity patterns for room acoustical measurements and simulations / Martin Pollow ; Michael Vorländer, Peter Vary." Aachen : Universitätsbibliothek der RWTH Aachen, 2015. http://d-nb.info/1127337165/34.
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Pollow, Martin [Verfasser], Michael [Akademischer Betreuer] Vorländer, and Peter [Akademischer Betreuer] Vary. "Directivity patterns for room acoustical measurements and simulations / Martin Pollow ; Michael Vorländer, Peter Vary." Aachen : Universitätsbibliothek der RWTH Aachen, 2015. http://nbn-resolving.de/urn:nbn:de:hbz:82-rwth-2015-047810.
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Varada, Vijay K. "Acoustic Localization Employing Polar Directivity Patterns of Bidirectional Microphones Enabling Minimum Aperture Microphone Arrays." University of Toledo / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1290118825.
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Miranda, Jofre Luis Alejandro. "The acoustics of concentric sources and receivers – human voice and hearing applications." Thesis, The University of Sydney, 2016. http://hdl.handle.net/2123/15506.
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One of the most common ways in which we experience environments acoustically is by listening to the reflections of our own voice in a space. By listening to our own voice we adjust its characteristics to suit the task and audience. This is of particular importance in critical voice tasks such as actors or singers on a stage with no additional electroacoustic or other amplification (e.g. in ear monitors, loudspeakers, etc.). Despite the usualness of this situation, there are very few acoustic measurements aimed to quantify it and even fewer that address the problem of having a source and receiver that are very closely located. The aim of this thesis is to introduce new measurement transducers and methods that quantify correctly this situation. This is achieved by analysing the characteristics of the human as a source, a receiver and their interaction in close proximity when placed in acoustical environments. The characteristics of the human voice and human ear are analysed in this thesis in a similar manner as a loudspeaker or microphone would be analysed. This provides the basis for further analysis by making them analogous to measurement transducers. These results are then used to explore the consequences of having a source and receiver very closely located using acoustic room simulation. Different techniques for processing data using directional transducers in real rooms are introduced. The majority of the data used in this thesis was obtained in rooms used for performance. The final chapters of this thesis include details of the design and construction of a concentric directional transducer, where an array of microphones and loudspeakers occupy the same structure. Finally, sample measurements with this transducer are presented.
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Hildebrandt, Andre [Verfasser]. "Design and fundamentals of optical nanoantennas for high intensity enhancement or high directivity / Andre Hildebrandt." Paderborn : Universitätsbibliothek, 2017. http://d-nb.info/1129252361/34.
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Joshi, Varun Anil. "Near-Fault Forward-Directivity Aspects of Strong Ground Motions in the 2010-11 Canterbury Earthquakes." Thesis, University of Canterbury. Department of Civil and Natural Resources Engineering, 2013. http://hdl.handle.net/10092/8987.
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The purpose of this thesis is to conduct a detailed examination of the forward-directivity characteristics of near-fault ground motions produced in the 2010-11 Canterbury earthquakes, including evaluating the efficacy of several existing empirical models which form the basis of frameworks for considering directivity in seismic hazard assessment.
A wavelet-based pulse classification algorithm developed by Baker (2007) is firstly used to identify and characterise ground motions which demonstrate evidence of forward-directivity effects from significant events in the Canterbury earthquake sequence. The algorithm fails to classify a large number of ground motions which clearly exhibit an early-arriving directivity pulse due to: (i) incorrect pulse extraction resulting from the presence of pulse-like features caused by other physical phenomena; and (ii) inadequacy of the pulse indicator score used to carry out binary pulse-like/non-pulse-like classification. An alternative ‘manual’ approach is proposed to ensure 'correct' pulse extraction and the classification process is also guided by examination of the horizontal velocity trajectory plots and source-to-site geometry. Based on the above analysis, 59 pulse-like ground motions are identified from the Canterbury earthquakes , which in the author's opinion, are caused by forward-directivity effects. The pulses are also characterised in terms of their period and amplitude. A revised version of the B07 algorithm developed by Shahi (2013) is also subsequently utilised but without observing any notable improvement in the pulse classification results.
A series of three chapters are dedicated to assess the predictive capabilities of empirical models to predict the: (i) probability of pulse occurrence; (ii) response spectrum amplification caused by the directivity pulse; (iii) period and amplitude (peak ground velocity, PGV) of the directivity pulse using observations from four significant events in the Canterbury earthquakes. Based on the results of logistic regression analysis, it is found that the pulse probability model of Shahi (2013) provides the most improved predictions in comparison to its predecessors. Pulse probability contour maps are developed to scrutinise observations of pulses/non-pulses with predicted probabilities.
A direct comparison of the observed and predicted directivity amplification of acceleration response spectra reveals the inadequacy of broadband directivity models, which form the basis of the near-fault factor in the New Zealand loadings standard, NZS1170.5:2004. In contrast, a recently developed narrowband model by Shahi & Baker (2011) provides significantly improved predictions by amplifying the response spectra within a small range of periods. The significant positive bias demonstrated by the residuals associated with all models at longer vibration periods (in the Mw7.1 Darfield and Mw6.2 Christchurch earthquakes) is likely due to the influence of basin-induced surface waves and non-linear soil response.
Empirical models for the pulse period notably under-predict observations from the Darfield and Christchurch earthquakes, inferred as being a result of both the effect of nonlinear site response and influence of the Canterbury basin. In contrast, observed pulse periods from the smaller magnitude June (Mw6.0) and December (Mw5.9) 2011 earthquakes are in good agreement with predictions. Models for the pulse amplitude generally provide accurate estimates of the observations at source-to-site distances between 1 km and 10 km. At longer distances, observed PGVs are significantly under-predicted due to their slower apparent attenuation. Mixed-effects regression is employed to develop revised models for both parameters using the latest NGA-West2 pulse-like ground motion database. A pulse period relationship which accounts for the effect of faulting mechanism using rake angle as a continuous predictor variable is developed. The use of a larger database in model development, however does not result in improved predictions of pulse period for the Darfield and Christchurch earthquakes. In contrast, the revised model for PGV provides a more appropriate attenuation of the pulse amplitude with distance, and does not exhibit the bias associated with previous models.
Finally, the effects of near-fault directivity are explicitly included in NZ-specific probabilistic seismic hazard analysis (PSHA) using the narrowband directivity model of Shahi & Baker (2011). Seismic hazard analyses are conducted with and without considering directivity for typical sites in Christchurch and Otira. The inadequacy of the near-fault factor in the NZS1170.5: 2004 is apparent based on a comparison with the directivity amplification obtained from PSHA.
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Woolston, Scott R. "Development of methods to propagate energy density and predict farfield directivity using nearfield acoustic holography /." Diss., CLICK HERE for online access, 2009. http://contentdm.lib.byu.edu/ETD/image/etd3016.pdf.
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Warren, Linda M. "Analysis of global compressional-wave spectra to determine anelastic earth structure and earthquake rupture directivity /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2003. http://wwwlib.umi.com/cr/ucsd/fullcit?p3100367.
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Woolston, Scott Richard. "Development of Methods to Propagate Energy Density and Predict Farfield Directivity Using Nearfield Acoustic Holography." BYU ScholarsArchive, 2009. https://scholarsarchive.byu.edu/etd/1726.
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Acoustical-based imaging systems have found merit in determining the behavior of vibrating structures. This thesis focuses on the continued development of the nearfield acoustic holography (NAH) approach. Conventional NAH consists of first measuring the pressure field on a two-dimensional conformal surface and then propagating this data back to the vibrating structure to obtain information about the source, such as the normal velocity distribution. Recent work has been done which incorporates particle velocity information into the traditional NAH measurements to reduce the number of measurements required. This advancement has made NAH a more affordable tool for acoustical imaging and sound field characterization. It is proposed that the inclusion of velocity information into traditional NAH can further increase its usefulness. By propagating the velocity and pressure values independently and recombining them on the reconstruction surface, the pressure field and energy density fields can be predicted at any point in the sound field. It is also proposed that the same NAH measurement can be used to predict farfield directivity. The inclusion of velocity values into the NAH technique also provides a means for predicting energy density (ED) anywhere within the acoustic field. These two developments would allow a single NAH measurement to provide much more information about an acoustic source and its radiated sound field. Experimental testing shows that NAH is successful at predicting the shape of the resulting ED field and directivity pattern with some error in amplitude. The best performance of the technique is with a planer source resulting in an average amplitude error of 18.5% over the entire field.
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Ramanandraibe, Marosoa Esthelladi. "Miniaturisation des antennes de station de base RFID dans la bande UHF et leur fonctionnement en multibande, par l'utilisation de métamatériaux." Thesis, Rennes 1, 2016. http://www.theses.fr/2016REN1S125.
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Les dimensions d’une antenne sont inversement proportionnelles à leurs fréquences de fonctionnement. De plus, la miniaturisation d’une antenne entraîne la dégradation de ses performances électriques et de rayonnement. Par conséquent, il est important pour le concepteur de trouver un bon compromis entre le taux de miniaturisation et les performances souhaitées. L’objet de cette thèse est de proposer une antenne miniature possédant les meilleures caractéristiques possibles dans la bande UHF de la RFID (860MHz – 960MHz), facile à réaliser et à moindre coût d’industrialisation. Les travaux de cette thèse ont montré qu’un couplage magnétique d’une cellule de métamatériaux avec une demi-boucle permet d’obtenir des structures antennaires intéressantes de par leurs dimensions de l’ordre de λ0/10, leur efficacité et leur fonctionnement en multibande. Différentes techniques sont appliquées pour améliorer les performances des antennes développées à savoir le gain, la directivité et la polarisation circulaire et/ou elliptiqueAntenna dimensions are inversely proportional to their operating frequencies. Besides, the antenna miniaturization degrades its electrical and radiation performances. Therefore it is important for the antenna designer to find a good compromise between the miniaturization rate and the desired performances. The purpose of this thesis is to obtain a miniature antenna which has good characteristics in the UHF band of RFID (860MHz - 960MHz), easy to implement and with low industrialization cost. The works described in this thesis showed that a magnetic coupling of a metamaterial cell with a half loop provides interesting antennas in terms of dimensions of about λ0/10, efficiency and multiband behavior. Different techniques are applied to improve the performances of realized antennas as gain, directivity and circular and/or elliptical polarization
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Sharma, R. "Simulation studies on effects of dual polarisation and directivity of antennas on the performance of MANETs." Thesis, Coventry University, 2014. http://curve.coventry.ac.uk/open/items/4cc65581-8030-45bc-8136-82fdf902052e/1.
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In the purview of efficient communication in MANETs for enhanced data rates and reliable routing of information, this thesis deals with dual polarised directional antenna based communication. This thesis proposes a dual polarised directional communication based cross-layer solution to mitigate the problems of interference, exposed nodes, directional exposed nodes, and deafness, and to achieve efficient routing of information. At the physical layer of network protocol stack, this thesis proposes the use of dual polarised directional antenna for the mitigation of interference. Use of dual polarised directional communication at the physical layer calls for appropriate modifications in the functionality of MAC and network layers. At the MAC layer, the DPDA-MAC protocol proposed in this thesis achieves mitigation of the problems of exposed nodes, directional exposed nodes and deafness, by using dual polarised directional antenna at physical layer. At network layer, the DPDA-MRP protocol presented in this thesis facilitates the discovery of multiple routes between the source and destination nodes to route information in accordance with the desired dual polarised directional communication. To achieve efficient dual polarised directional communication and routing of information, it is essential to maintain well populated Neighbour Table (NT) and Routing Table (RT). This thesis proposes a novel Corruption Detection Pulse (CDP) based technique to handle corruption of broadcast packets such as Link ID and RREQ arising due to hidden node problem. Since the nodes participating in the formation of MANETs have limited battery energy, the protocols proposed in this thesis are featured with a provision for dynamic power control to achieve energy efficient communication. Nodes maintain Received Signal Strength Indicator (RSSI) information in the NT, which along with the information of node location is used in the formulation of decision logic of dynamic power control. Through numerous simulation studies, this thesis demonstrates the benefits of dual polarised directional communication to enhance the performance of MANET. The design principles, benefits and conceptual constraints of proposed DPDA-MAC protocol are analysed with SPDA-MAC and CSMA/CA, while those for DPDA-MRP are analysed with SPDA-MRP and DSR through performance metrics of throughput, Packet Delivery Ratio (PDR) and per hop delay. The thesis also analyses the impact of variations of channel capacity, node density, rate of packet transmission and mobility of nodes on the performance of the proposed and conventional protocols invoked in MANETs.
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Ouarradi, Noureddine. "Etude théorique et expérimentale du champ ultrasonore transitoire généré par un transducteur plan dans un milieu solide homogène et isotrope : Approche de la réponse impulsionnelle de diffraction." Valenciennes, 1999. https://ged.uphf.fr/nuxeo/site/esupversions/00c238b0-7907-4a5d-a70f-ddf9c707e8e9.
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L’objet de cette thèse est le développement d'un code de calcul, basé sur une formulation mathématique explicite, permettant de calculer le champ de déplacement transitoire généré par un transducteur ultrasonore plan, en contact direct avec un milieu solide, homogène et isotrope. La formulation adoptée introduit la fonction de green élastodynamique temporelle. La réponse impulsionnelle de déplacement est donnée sous forme d'une somme de trois intégrales de surface, qui représentent respectivement les contributions des ondes de compression, de cisaillement et de la combinaison de ces deux ondes (terme du champ proche). Le calcul de ces intégrales est réalisé grâce à la méthode de la représentation discrète (dr), basée sur l'approche de la réponse impulsionnelle. Ceci a donné naissance au code dream/s (discrete representation acoustical modelling in solids). Le calcul, ne nécessitant aucune opération mathématique préalable, est purement numérique et ne présente aucune singularité mathématique. Le logiciel dream/s offre plusieurs possibilités à l'opérateur, en mettant à sa disposition différentes bibliothèques pour effectuer une large gamme d'études pratiques. Au regard des solutions explicites existantes dans la littérature, qui sont limitées à un seul type de sources (circulaire ou annulaire), notre approche permet d'étudier un transducteur plan ayant une forme arbitraire, en un temps de calcul très intéressant. Dream/s a été validé par rapport à des solutions analytiques et exactes dans le cas d'un transducteur circulaire ou carre travaillant en mode épaisseur. De nouveaux cas d'études ont été analysés et interprétés tels que les transducteurs rectangulaires et les barrettes linéaires. Une vérification expérimentale des résultats de dream/s est réalisée. Pour ceci, une présentation multi-canaux des signaux enregistrés est adoptée. Cela a permis de développer un outil d'interprétation du champ ultrasonore complexe. La comparaison calcul/mesure a montré une bonne concordance des résultats en ce qui concerne les formes spatio-temporelles.
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Habert, Benjamin. "Contrôle de la fluorescence par des nanoantennes plasmoniques." Phd thesis, Palaiseau, Institut d'optique théorique et appliquée, 2014. http://pastel.archives-ouvertes.fr/pastel-01023199.
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Dans ce travail de these, nous étudions comment des nano-structures métalliques modifient le processus d'émission spontannée d'objets fluorescents et jouent ainsi un rôle d'antenne. Ces structures supportent des modes optiques confinés aux interfaces metal-diélectrique: ce sont des modes plasmoniques.De par leur fort confinement, ces modes modifient la densité locale d'états optiques et permettent notamment d'accélérer le processus d'émission spontannée (facteur de Purcell). Nous étudions le cas d'une structure planaire metal-isolant-métal de type patch couplée à un ensemble de nanocristaux colloïdaux fluorescents. Nos mesures, soutenues par des calculs numériques, montrent une acceleration de l'émission fluorescente d'un facteur 80 ainsi qu'une augmentation de la directivité de l'émission. Nous décrivons ensuite le procedé de fabrication d'une structure patch metal-semiconducteur-métal pour laquelle la source fluorescente est un puits quantique émettant dans le proche infra-rouge. Nous montrons que l'antenne permet d'augmenter l'extraction fluorescente d'un facteur 8. Enfin, nous considérons le cas d'une structure sphérique composée d'un unique nanocristal fluorescent au centre d'une bille de silice entourée par une fine coquille métallique. Cette structure plasmonique accélère l'émission d'une facteur 10 et permet de supprimer le scintillement caractéristique de l'émission des nanocristaux. La coquille métallique permet également d'isoler chimiquement le nanocristal de l'environnement, assurant ainsi une grande photostabilité et une toxicité réduite. L'émetteur ainsi obtenu est donc un candidat prometteur pour des applications de marquage de fluorescence in-vivo.
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Weiler, Bradley. "Finite Element Method Based Analysis and Modeling in Rotordynamics." University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1510917784717535.
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Souai, Sana. "Réseaux d’antennes miniatures super-directifs reconfigurables basses fréquences pour l’IoT." Thesis, Université Côte d'Azur, 2021. http://www.theses.fr/2021COAZ4020.
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L'Internet des objets (IoT) fait référence à tout système où les objets sont connectés à Internet, il intègre une architecture de connectivité réseau, des capteurs et des appareils intelligents. Selon des recherches récentes, environ 30 milliards d'objets collectent désormais des données et effectuent toutes sortes de tâches. Déployées dans des environnements intelligents, tels que les maisons intelligentes, les villes intelligentes et les transports intelligents.Le but de cette thèse est le développement dans un espace réduit, réseau d'antennes miniatures basse fréquence, en vue d’atteindre une super directivité et reconfigurable pour une communication longue portée et dans des zones difficiles d'accès. Le couplage sera pris en compte dans cette tâche et les pondérations optimales nécessaires pour maximiser la directivité seront déterminées. Des prototypes seront également produits pour valider les résultats de la simulation. L'étude et la simulation électromagnétique 3D des antennes seront réalisées principalement avec des logiciels commerciaux (HFSS, CST,…).Dans notre première étude, un réseau parasite d’antennes formé de deux éléments électriquement petits pour les applications Internet de l’objet, déployé à la fréquence 868 MHz , a été présenté qui est capable de commuter son faisceau suivant deux directions différentes. La reconfigurabilité est obtenue à l'aide de diodes PIN pour réduire le rayonnement arrière et diriger le faisceau dans la direction souhaitée. La structure proposée génère une directivité élevée de 6,8 dBi en simulation et 6,7 dBi en mesure à 868 MHz pour chaque direction dans le plan azimutal.Dans la seconde étude, nous avons tenté d'améliorer le gain de l'antenne présentée précédemment. En nous inspirant de la structure de l'antenne Yagi, nous avons pensé à ajouter quatre directeurs de chaque coté pour améliorer la directivité et orienter le lobe principal dans deux directions différentes. La directivité simulée est d’environ 8,5 dBi en simulation et de 8,4 dBi en mesure à 868 MHz dans deux directions différentes dans le plan azimutal.En vue de réduire le rayonnement arrière, le potentiel de l’électronique active a été exploité. Nous proposons l'utilisation d'un circuit Non-Foster pour convertir une impédance positive en impédance négative, comme charge à appliquer sur l'élément parasite. La partie résistive de la charge a été prise en considération pour maximiser le gain total du réseau. L'autre avantage de ce type de circuit est qu'il facilite la reconfigurabilité dans plusieurs directions en faisant simplement varier l'impédance de charge à convertirThe Internet of Things (IoT) refers to any system where objects are connected to the Internet; it incorporates network connectivity architecture, advanced sensors and devices. According to recent research, about 30 billion objects are now collecting data and performing all sorts of tasks.The aim of this thesis is the development in a small space of a low frequency miniature and super-directive antenna array. Coupling will be taken into account in this work and the optimal weightings necessary to maximize directivity will be determined. Prototypes will also be produced to validate the simulation results. The study and 3D electromagnetic simulation of the antennas will be carried out mainly with commercial software (HFSS, CST, …).In our first study, a switchable beam and super-directive Electrically Small Antenna (ESA) dipole deployed at an IoT network gateway at 868 MHz was presented. Reconfigurability is achieved using PIN diodes to reduce the back radiation and to steer the beam to the desired direction. The proposed structure generates a high directivity of 6.8 dBi in simulation and 6.7 dBi in measurement at 868 MHz for each beam in the azimuth plane.In the second study, we thought about improving the antenna gain previously presented. Getting inspired by the Yagi antenna structure, we added four directors to each element to enhance the directivity and to steer the main bean in two different directions. A simulated directivity of 8.5 dBi in simulation and 8.4 dBi in measurement at 868 MHz for both directions.To maintain low-side lobes, we propose the use of a Non-Foster circuit to convert positive impedance into negative impedance, as a load for the parasitic element to take into account the resistive part of the load and thus maximize the gain of the array. The other advantage with this kind of circuit is that it facilitates reconfigurability in several directions by just varying the load impedance to be converted
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Mieskoski, Randy. "Capturing and Modeling a Three-Dimensional Stationary Noise Source Directivity Pattern with a Dynamic Array in the Near Field." Wright State University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=wright1387979181.
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Oliveira, Lucas Rangel de. "Concepção de um índice para localização de trincas em eixos rotativos através da análise do SDI (Shape and Directivity Index) /." Ilha Solteira, 2019. http://hdl.handle.net/11449/180841.
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Orientador: Gilberto Pechoto de MeloResumo: A identificação de trincas ainda é um desafio na área de monitoramento da integridade estrutural em eixos rotativos. Embora muitas técnicas e modelos tenham sido desenvolvidos, encontrar uma técnica eficiente que possa localizar uma única ou múltiplas trincas ao longo do eixo, ainda é um grande desafio. Nesse trabalho, um novo índice para localização de trincas em eixos rotativos é apresentado. A equação do movimento do rotor com trinca utiliza a notação em coordenadas complexas a fim de separar as contribuições dos modos de precessão direta e retrógrada. O índice SDI (shape and directivity index) é calculado para o rotor, cujo modelo matemático considera a variação instantânea da rigidez do elemento finito devido à abertura e o fechamento gradual da trinca, conhecido como efeito breathing. Através da manipulação do SDI no modelo de cores HSV (hue, saturation and value), desenvolve-se uma escala métrica, visualizada em um mapa de cores, que possibilita localizar a anisotropia causada pela trinca ao longo do eixo. Profundidade e posição da trinca, presença de múltiplas trincas, entre outros fatores que afetam a assinatura da trinca em outros métodos de identificação são analisados. Bons resultados demonstram a eficiência e robustez do novo índice para diversos casos de operação do rotor. Essa métrica de dano acrescenta uma contribuição para os métodos de localização de trincas em sistemas rotativos.
Abstract: Crack identification is still a challenge in the area of structural health monitoring dedicated to rotating shafts. Although many techniques and models have been developed, finding an efficient technique capable of locating a single or multiple cracks along the shaft is still a challenge. In this work, a new index for locating cracks in rotating shafts is proposed. The equation of motion of the cracked rotor uses notation in complex coordinates in order to separate the contributions of forward and backward precession modes. The SDI (shape and directivity index) is calculated for the cracked rotor, which mathematical model considers the instantaneous variation of the finite element stiffness due to the gradual opening and closing of the crack, known as the breathing effect. By manipulating the SDI in the HSV (hue, saturation and value) color model, a metric scale is developed to locate the anisotropy caused by cracks along the shaft, visualized on a color map. Depth and position of the crack, presence of multiple cracks, among other factors that affect the signature of the crack in other identification methods are analyzed. Good results demonstrate the efficiency and robustness of the new index for several rotor operation conditions. This damage metric contributes to crack localization methods in rotating systems.
Doutor
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Cambridge, Jason Esan. "The Sound Insulation of Cavity Walls." Thesis, University of Canterbury. Mechanical Engineering, 2012. http://hdl.handle.net/10092/7332.
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Lightweight building materials are now commonly employed in many countries in preference to heavyweight materials. This has lead to extensive research into the sound transmission loss of double leaf wall systems. These studies have shown that the wall cavity and sound absorption material placed within the cavity play a crucial role in the sound transmission through these systems. However, the influence of the wall cavity on the sound transmission loss is not fully understood.
The purpose of this research is to obtain a comprehensive understanding of the role played by the wall cavity and any associated sound absorption material on the sound transmission loss through double leaf wall systems. The research was justified by the fact that some of the existing prediction models do not agree with some observed experimental trends.
Gösele’s theory is expanded and used in the creation of an infinite and finite vibrating strip model in order to acquire the desired understanding. The sound transmission loss, radiated sound pressure and directivity of double leaf systems composed of gypsum boards and glass have been calculated using the developed model. A method for calculating the forced radiation efficiency has also been proposed. Predictions are compared to well established theories and to reported experimental results.
This work also provides a physical explanation for the under-prediction of the sound transmission loss in London’s model; explains why Sharp’s model corresponds to Davy’s with a limiting angle of 61° and gives an explanation for Rindel’s directivity and sound transmission loss measurements through double glazed windows. The investigation also revealed that a wide variety of conclusions were obtained by different researchers concerning the role of the cavity and the properties of any associated sound absorption material on the sound transmission loss through double wall systems. Consequently recommendations about the ways in which sound transmission through cavity systems can be improved should always be qualified with regard to the specific frequency range of interest, type of sound absorption material, wall panel and stud characteristics.
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Oliveira, Alexandre Maniçoba de. "Desenvolvimento e otimização de antenas Vivaldi antipodais para aplicações a altas frequências." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/3/3140/tde-21062016-145910/.
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Esta tese propõe a síntese e o estudo de uma nova técnica de cavidades de borda aplicada a antenas Vivaldi, com o intuito de melhorar suas características de diretividade. Embora as antenas do tipo Vivaldi possuam características diretivas, elas produzem radiações laterais indesejáveis, o que se reflete nos elevados índices de lóbulos laterais devido a correntes superficiais que fluem ao longo das bordas metalizadas nas laterais da antena. Estas correntes são a origem das radiações laterais que vêm sendo mitigadas pela aplicação de cavidades ressonantes, triangulares ou retangulares, que aprisionam tais correntes e, consequentemente, atenuam os lóbulos laterais, sem o incremento do lóbulo principal, uma vez que toda a energia dos lóbulos laterais é apenas confinada nos ressonadores e por isso literalmente perdida. Ao contrário desses esforços, este trabalho propõe cavidades radiantes tanto na forma de abertura exponencial, como na forma do fractais de Koch, que funcionam como radiadores auxiliares (antenas auxiliares), canalizando as correntes de borda e aproveitando-as para aumentar os níveis do lóbulo principal, mitigando os níveis de lóbulo lateral. A síntese desta nova técnica foi implementada em uma antena Vivaldi antipodal com características de baixa diretividade, como qualquer antena Vivaldi, o que foi corrigido e a aplicação da técnica de cavidades radiantes deu origem a duas novas antenas Vivaldis efetivamente diretivas. Os resultados foram obtidos através de simulações do modelo numérico no CST Microwave Studio e confirmados com medidas de laboratório, o que evidenciou a melhora das características de diretividade da antena pela aplicação da nova técnica de cavidades radiantes.This work presents a new Slot Edge technique applied to Vivaldi antennas to improve their characteristics of directivity, resulting in two new Vivaldi antennas: the Palm Tree Vivaldi antenna and the Koch Vivaldi antenna. This new technique proposes to add lateral radiators which reduce the side lobe level, increasing the gain of the main lobe in an unprecedented way. This technique is called radiating slot edges, and acts as parasitic antennas, surface currents draining edges of the antenna, and using them to increase the gain in the main lobe. The development was done systematically, starting with an extensive literature review, design and simulation in CST, as well as prototyping and measurements of several antenna designs. All this effort proved the functionality of this technique.
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Bonfanti, Thierry. "Phénoménologie de la situation médiative." Thesis, Brest, 2012. http://www.theses.fr/2012BRES0007/document.
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M’interrogeant sur l’inflation du mot « médiation », j’ai passé en revue quelques unes des pratiques les plus courantes invoquant un terme dont j’ai pu en constater, dans certains cas, l’usage abusif. À partir de là, j’ai tenté de tracer les contours d’un concept en mal de définition. J’ai ainsi dégagé deux caractéristiques intrinsèques de la médiation, à savoir la triangularité et la non-directivité ainsi que ses deux prérequis que sont le libre consentement des participants et la légitimation du médiateur. Par ailleurs, j’ai constaté que la médiation ne s’appliquait pas qu’aux situations conflictuelles et que son enjeu n’était pas exclusivement affectif. Il peut être également matériel, donnant alors lieu à une médiation de type « négociatif ». En croisant ces deux variables, j’ai proposé une typologie des pratiques de médiation. Dans une seconde partie de ma thèse, je me suis livré à une analyse phénoménologique de la médiation, me servant de l’enregistrement de jeux de rôles. Cette analyse m’a conduit à élargir mon champ de vision, d’une «médiation» comprise comme « action du médiateur » à une réalité plus complexe que j’ai appelée « situation médiative » où le médiateur agit autant sur les participants qu’il est agi par eux. Cette situation, loin de se réduire à une pratique instituée, constitue un véritable phénomène social, fréquent dans la vie courante. La confiance que les participants accordent au médiateur, le rôle qu’ils lui font jouer en tant que « base de sécurité » comme alternative au face à face et sa fonction d’étayage de la communication constituent des conditions essentielles de la situation médiative avant même les techniques de médiationWondering about the increasing use of the word « mediation », I reviewed some of the most common practices referring to this word which was, in some cases, misused. On this basis, I strived to draw the outline of a concept in need of definition. In doing so, I identified two characteristics of mediation, namely the triangularity and the non-directivity, as well as its two prerequisites, i.e. the consent of the participants and the recognition of the mediator. Moreover, I noted that mediation does not apply only to situations of conflict and that its stake is not exclusively emotional. It could be material, leading to a negotiating mediation. Crossing these two variables, I then propose a typology of mediation practices. In a second part of my thesis, I set up a phenomenological analysis of mediation, using video recordings of role playing. This analysis led me to broaden my own perspective, from a mediation as « mediator’s action » to a more complex scenario that I called « mediative situation », where the mediator influences the participants and is in turn influenced by them. This situation, far from being restricted to an established practice, is indeed a social and frequent phenomenon. The confidence the participants have in the mediator, the role they give him/her as a “secure base” and as an alternative to the face to face situation, and his function in supporting communication, lay the basic condition of the mediative situation, a long way ahead of mediations techniques
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Batista, Ana Carla Schiavinato. "A (não)diretividade pedagógica na educação a distância." Universidade Federal de São Carlos, 2013. https://repositorio.ufscar.br/handle/ufscar/2659.
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Previous issue date: 2013-03-04Financiadora de Estudos e Projetos
This search presents a subject that is on top of the currently education scenario, the Distance Education. This new education mode that comes as a promess to breaking barriers of timing and space, still have many things to say about their real consequences regarding education of the individual. Thus arises the importance of this research which aims investigating issues related to pedagogical directivity/non-directivity in UAB-UFSCar with a target of analysis the Philosophy of Education into the Pedagogy graduate. However it should be noted that the goal is not handle the data in order to make categorical statements, i.e, do not say if the pedagogical relations in UAB-UFSCar are directives or non-directives but trying think about such relations and how it occurs at the enviroment of learning to propose new thoughts. The main theoretical framework to be used will be the Critical Theory of Society that supported the analyzes and reflections made in the course of the four chapters of the dissertation.
A presente dissertação trata de um tema que está em pauta no cenário educativo atual, a Educação a Distância (EAD). Esta nova modalidade de ensino, que vem com a promessa de romper barreiras de tempo e espaço, ainda tem muito a nos dizer sobre suas reais consequências no que se refere à formação do indivíduo. Por isso se dá a importância deste trabalho, que objetivou investigar questões referentes a diretividade/não-diretividade pedagógica na UAB-UFSCar, tendo como objeto de análise a disciplina de Filosofia da Educação do curso de Licenciatura em Pedagogia. No entanto, vale salientar que o objetivo não foi tratar os dados com a finalidade de realizar afirmações categóricas, ou seja, não pretendemos dizer se as relações pedagógicas na UAB-UFSCar são ou não diretivas, mas sim buscamos pensar sobre tais relações e sobre como elas ocorrem no ambiente de aprendizagem, com o intuito de propor novas reflexões. O referencial teórico principal utilizado foi a teoria Crítica da Sociedade, que subsidiou as análises e reflexões feitas no decorrer dos quatro capítulos da dissertação.
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Pavasovic, Vladimir, and vpavasovic@wmgacoustics com au. "The radiation of Sound from Surfaces at Grazing Angles of Incidence." RMIT University. Applied Sciences, 2006. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20060911.115939.
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It is difficult to predict the sound radiation from large factory roofs. The existing infinite panel theories of sound insulation are not sufficient when the sound radiates at grazing angles. It has been shown that the reason for the collapse of the theory is the well known result for the radiation efficiency. This research will present a simple analytic strip theory, which agrees reasonably well with numerical calculations for a rectangular panel. Simple analytic strip theory has lead to the conclusion that it is mainly the length of the panel in the direction of radiation, rather than its width that is important in determining its radiation efficiency. The findings of the current research also indicated that apart from the effect due to coincidence, a panel was non-directional compared to an opening.
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Ma, Hua. "Localisation de sources par méthodes à haute résolution et par analyse parcimonieuse." Phd thesis, Université de Franche-Comté, 2011. http://tel.archives-ouvertes.fr/tel-00839142.
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Cette thèse a pour but d'estimer la position et la puissance de sources sonores ponctuelles à l'aide d'une antenne acoustique. Nous nous intéressons d'abord à la directivité des antennes acoustiques pondérées. On montre qu'une telle antenne, appelée antenne conventionnelle, même si elle est à directivité optimale, est inutilisable pour localiser plusieurs sources sonores. Des traitements adaptatifs d'antenne sont donc exigés et les méthodes dites à haute résolution sont introduites. Elles sont basées sur l'estimation de la matrice de covariance des signaux issus des capteurs et présentent l'avantage de s'affranchir des limitations naturelles du traitement d'antenne conventionnel. Cependant, ces méthodes nécessitent l'emploi d'un modèle de propagation et sont donc par nature peu robustes aux erreurs de modèle, ce qui peut être parfois un handicap et dégrader leurs performances. Par la suite, nous présentons une nouvelle méthode de séparation des sources utilisant une représentation parcimonieuse des signaux. Nous montrons que ses performances sont meilleures que celles obtenues par les méthodes à haute résolution et notre algorithme parvient à une bonne résolution spatiale, même sous des conditions défavorables. Cette méthode est appliquée aux sources corrélées et décorrélées, à bande étroite et à large bande, en champ proche et en champ lointain. Pour finir, nous présentons des méthodes pour estimer la puissance des sources sonores. Des simulations numériques et des expérimentations en chambre anéchoïque sont effectuées afin de vérifier et de valider les analyses et les résultats théoriques
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Goncharova, Iuliia. "Investigation of a small-sized omnidirectional antenna." Thesis, Linnéuniversitetet, Institutionen för datavetenskap, fysik och matematik, DFM, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-17835.
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The purpose of this research is to find ways to create an omnidirectional antenna with high directivity in the vertical plane. The investigation is based on computer simulation using the program CST 2011. The objective is a narrow-band antenna that is omnidirectional in the horizontal plane and has maximum achievable directivity for a fixed size. Three of the most promising antenna designs are selected based on the current state of antenna technology. Their maximum directivities are estimated by means of well known relations in antenna theory. It is shown that the most suitable design is an omnidirectional antenna in the form of a cylindrical dipole antenna array with an active central dipole. For this antenna, excitation by means of a radial traveling wave, with a phase velocity smaller than speed of the light, is possible. It is found that for a certain value of a moderating factor it is possible to obtain a directivity that is 2.5 – 3 dB larger than that of a dipole or a linear antenna with uniform excitation. The antenna structures are modeled to determine the number of dipoles, their dimensions and the spacing between them that maximizes the directivity.
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Raetz, Samuel. "Développement de méthodes numériques pour l’imagerie de sources optoacoustiques en milieu solide." Thesis, Bordeaux 1, 2012. http://www.theses.fr/2012BOR14624/document.
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L’objectif de ces travaux est le développement d’une méthode d’imagerie de sources optoacoustiques en milieu solide. Afin d’analyser l’influence de la géométrie de la source sur les ondes acoustiques qu’elle génère et ainsi prévoir qualitativement si l’image de la source peut être obtenue avec une précision suffisante, la directivité d’une source acoustique est d’abord considérée. Pour quantifier plus précisément cette influence, la résolution complète de la propagation des ondes générées par cette source est ensuite menée. L’analyse de l’influence de l’incidence oblique d’un faisceau laser lors de la génération photoacoustique est proposée en illustration. La seconde partie de ce manuscrit est consacrée à la résolution du problème inverse qui permet d’obtenir l’image de la source initiale. Un algorithme de rétropropagation est alors mis en place. Il est basé sur les principes du retournement temporel et de Huygens, et simule la propagation, en milieu solide, des ondes mesurées vers la position initiale de la source acoustiqueThe purpose of this work is to develop a method to image optoacoustic sources in solid media. To analyze the influence of the source geometry on laser-generated acoustic waves and thus qualitatively predict if the image of the source can be obtained with sufficient accuracy, the directivity of an acoustic source is considered first. In order to quantify more precisely this influence, the complete resolution of the propagation of acoustic waves generated by this source is then achieved. The analysis of the effect of oblique incidence of a laser beam in the photoacoustic generation process is proposed as an illustration. The second part of this thesis is devoted to the inverse problem resolution, which provides the image of the initial acoustic source. A backpropagation algorithm is then implemented. It is based on the time-reversal principle and the Huygens’ principle, and simulates, in a solid medium, the propagation of the measured acoustic waves back to the initial position of the acoustic source
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Hickling, Christopher John. "Inhomogeneous, Anisotropic Turbulence Ingestion Noise in Two Open Rotor Configurations." Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/100637.
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Two rotor configurations with different non-uniform inflows were studied: a rotor ingesting the wake of an upstream cylinder and a rotor ingesting a thick axially symmetric boundary layer from an upstream centerbody. In both cases, the undisturbed inflow was measured without the rotor present in order to characterize the inflow, in particular to calculate the unsteady upwash velocity distribution at the location of the rotor. In addition, detailed acoustic measurements were completed using a 251-channel large-area microphone array. In all, over 400 conditions covering different advance ratios, angles of yaw, and inflow conditions were measured. Measurements of the sound show that the source has a complex directivity, different from that of a streamwise aligned dipole, due to the inhomogeneous unsteady upwash distribution. In addition, observers at different far field locations will perceive sources from different locations on the rotor disk. The directivity is a function of both the rotor geometry and turbulent inflow. A simplified model of the sound source was developed using these inputs and accurately predicts trends observed in the far field noise. For the cylinder wake ingestion case, on-blade measurements of the flow field show that the wake is drawn to the center of the rotor disk with increasing thrust. This is particularly noticeable if the wake does not strike the center of the rotor disk. The effects of this flow distortion on the far field directivity are well predicted by the model. The effects of yaw to rotate the produced sound field can be inferred from this model as well. A novel beamforming procedure was used to isolate sources across the face of the rotor for the cylinder wake ingestion case for an upstream observer position. This method may be used to isolate different sound sources on a rotor if multiple sources are present or if different regions of the rotor disk need to be isolated. The directivity of a rotor ingesting an axially symmetric boundary layer is far less complex than the ingestion of a two-dimensional cylinder wake, but measurements still show the perceived source location shift with observer location. Overall, the proposed noise modeling technique is an efficient method to predict the directivity of turbulence ingestion noise for inhomogeneous inflows. This can enable quick absolute noise predictions at all far field locations using only a single point measurement or far field noise prediction to establish absolute levels.Doctor of Philosophy
In many engineering applications, rotors interact with turbulence. Aircraft and ships with rear mounted propellers can have upstream appendages or discontinuities that generate turbulence that travels downstream and is drawn into the propeller. Wind turbines interact with turbulence in the atmosphere and with turbulent wakes from other turbines. Interaction of a rotor with turbulence results in unsteady loading on the rotor blades that can radiate as sound, causing unwanted community noise or vehicle detection. As such, prediction and reduction of noise due to turbulence ingestion is highly desirable and remains an active area of research. Turbulence ingestion noise is well understood from first principles and can be successfully predicted provided an accurate description of the turbulent inflow and unsteady aerodynamic response of the rotor blades. Much work has focused on homogenous, isotropic turbulence ingestion noise, however, in practical applications, the rotor inflow is often non-uniform, anisotropic, and can change dramatically with the thrusting condition of the rotor. Research efforts to develop noise predictions considering these more complex, but practical inflows have focused on the inflow modeling and measurement and have relied on a small subset of sound measurements for validation. The present study seeks to provide new physical insight into inhomogeneous, anisotropic turbulence ingestion noise through wind tunnel experiments. In particular, two rotor configurations with different practical non-uniform inflows are studied: a rotor ingesting the wake of an upstream cylinder and a rotor ingesting a thick axially symmetric boundary layer from an upstream center body. In both cases, the undisturbed inflow was measured without the rotor present in order to characterize the inflow, and detailed acoustic measurements were completed using a 251-channel large-area microphone array. In all, over 400 rotor operating conditions were measured. The acoustic directivity in each case is examined in detail as a function of rotor operating condition. A simplified directivity model is developed and validated with measurements. Ultimately, the directivity model can provide a good engineering approximation of the full directivity with reduced computational time or can be used to extrapolate measured results to positions in the far field where placement of sensors is not possible. The results can also be used to guide the analysis and interpretation of single point or microphone array measurements in the acoustic far field of a rotor.
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Olsson, Mikael, and Anders Söderberg. "Design guideline for audible warning signal and determination of sound pressure characteristics : Second version." Thesis, Örebro universitet, Akademin för naturvetenskap och teknik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:oru:diva-19412.
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Today Atlas Copco Rock Drills AB hasn’t got any method to determine how many warning alarms they need on their machines and how they should be mounted to use their full potential. At the moment a travel alarm is usually placed in the front of the machine and a reverse alarm in the back. Then a measurement of the sound pressure level around the machine is performed to see if it is enough to pass the limit according to different ISO-standards. Otherwise they have to mount some extra alarms and then do the measurements again until the standards are fulfilled. The aim of this thesis work is to develop a method for determine how many alarms Atlas Copco Rock Drills AB need on the machines, and also how they should be mounted to fulfil the different criteria according to ISO-standards in the early phase of construction. From the different divisions within Atlas Copco Rock Drills AB (LHD, SDE and TME) arrived four different alarms, which are used on their machines. Sound pressure level measurements were conducted on these, in the anechoic chamber at audiological research centre at the university hospital in Örebro. In the LMS Test.Lab software a measurement sphere was built around the horns and based on the data obtained at the anechoic chamber sound directivity plots were made. Together with earlier machine measurement data from Atlas Copco Rock Drills AB, an Excel program was made constituting an example of how the horns should be mounted. LHD = Loaders and trucks/underground rock excavation SDE = Surface drilling equipment TME = Tunnelling and mining equipmentIdag har Atlas Copco Rock Drills AB inte någon metod för att bestämma hur många varningsalarm som behövs på sina maskiner samt var de ska placeras så de utnyttjar sin fulla potential. I nuläget monteras ett signalhorn vid främre delen och ett backlarm i bakre delen av maskinen. Sedan utförs en ljudtrycksmätning runt maskinen för att kontrollera om man uppfyller kraven från olika ISO-standader. Annars monteras fler alarm och mätningen utförs på nytt tills standarderna uppfylls. Detta examensarbete har som mål att ta fram en metod som bestämmer hur många alarm Atlas Copco Rock Drills AB behöver på sina maskiner, samt hur de skall placeras för att uppfylla kriterierna från olika ISO-standarder redan i konstruktionsstadiet. Från de olika avdelningarna inom Atlas Copco Rock Drills AB (LHD, SDE och TME) mottogs fyra olika alarm, som används på maskinerna. På dessa utfördes ljudtrycksmätningar i det ekofria rummet vid audiologiskt forskningscentrum på universitetssjukhuset i Örebro. I programmet LMS Test.Lab byggdes en sfär av mätpunkter runt alarmen och baserat på insamlade data från det ekofria rummet konstruerades direktivitetsdiagram. Tillsammans med data som Atlas Copco Rock Drills AB redan hade från tidigare mätningar på maskiner gjordes ett Excel-program, som ger ett exempel på hur alarmen bör monteras. LHD = Loaders and trucks/underground rock excavation SDE = Surface drilling equipment TME = Tunnelling and mining equipment
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Baleshan, Tharunie. "Analysis of distributed beamforming in cooperative communications network with phase shifter based smart antenna nodes." Thesis, Queensland University of Technology, 2015. https://eprints.qut.edu.au/84539/1/Tharunie_Baleshan_Thesis.pdf.
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This research study investigates the application of phase shifter-based smart antenna system in distributed beamforming. It examines the way to optimise the transmit power by jointly maximising the directivity of the array antennas and the weight vector for distributed beamforming. This research study concludes that maximising directivity can lead to better transmit power minimisation compared to maximising field intensity. This study also concludes that signal to noise power ratio maximisation subject to a power constraint and power minimisation subject to a signal to noise power ratio constraint yield the same results.
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Demontis, Hugo. "Identification de sources acoustiques complexes en milieu réverbérant par grands réseaux de microphones." Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS196.
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La directivité d'une source sonore intervient dans de nombreuses applications en acoustique, allant de la compréhension des phénomènes physiques aéro-acoustiques jusqu'à la reproduction sonore spatialisée. Pour estimer expérimentalement cette signature spatiale, il est d’usage de déployer les microphones de sorte à englober partiellement ou totalement les sources. Le rayonnement acoustique est ainsi capté dans toutes les directions de l'espace. Sur ce principe, nous proposons dans ce manuscrit le développement d'un réseau microphonique 3D de grandes dimensions. L'antenne baptisée MODO ("Les Murs Ont Des Oreilles") comprend un total de 1024 MEMS digitaux, répartis sur les murs et les parois d'une salle rectangulaire classique. Pour localiser les sources acoustiques et caractériser leur directivité, nous résolvons le problème inverse associé sous contrainte de parcimonie structurée. La méthode choisie exploite le faible nombre de sources dans la salle, autorisant une représentation parcimonieuse du champ sonore mesuré. Le formalisme des harmoniques sphériques est utilisé pour décomposer efficacement la directivité des sources et les composantes élémentaires de rayonnement qui la compose. Les trajets de propagation acoustique sont modélisés via l'intégration des fonctions de transfert de la salle, qui sont synthétisées grâce au principe des antennes virtuelles. Nous validons la méthode de caractérisation proposée sur des sources directives connues, dont la directivité est étalonnée au préalable à l'aide d'une antenne sphérique d'ordre élevéKnowing the directivity pattern of an acoustic source is useful in many applications in acoustics. To experimentally estimate the spatial signature, it is common to deploy microphones partially or totally surrounding the source. The acoustic radiation is then captured in all possible directions. In this thesis, we discuss the development of a large-scale 3D microphone array. This array, named "MODO" ("Les Murs Ont Des Oreilles", or, "The Walls Have Ears"), is comprised of 1024 digital MEMS microphones, flush mounted on the walls and the ceiling of a typical shoe-box room. In order to localize the sources and identify their directivity pattern, we solve the associated inverse problem under block-sparsity constraints. The chosen method exploits the small number of sources inside the room, allowing a sparse representation of the measured sound field. We use the spherical harmonics formalism to efficiently describe the directivity of the sources and their individual contributions to the radiation pattern. The acoustic path is modelled via integration of room transfer functions, synthesized with the mirror microphone method. We validated the proposed characterization method \textit{in situ} by comparison with known directivity patterns, calibrated using a high order spherical microphone array in controlled conditions
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Lardies, Joseph. "Etude d'antennes acoustiques a directivite constante sur une large bande." Toulouse 3, 1987. http://www.theses.fr/1987TOU30214.
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Cette etude porte sur la conception et la realisation d'antennes acoustiques a largeur de faisceau constante sur une large bande. On examine deux techniques, dont l'une est basee sur un reseau d'antennes maintenant la largeur du lobe principal constant sur plusieurs octaves, tandis que l'autre methode permet de maintenir la largeur du faisceau d'une antenne constante sur plusieurs octaves. Etude de l'estimation de la direction et de la puissance de signaux acoustiques en vue d'applications possibles
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Boissinot, Philippe. "Impedance acoustique de rayonnement dans les antennes planes : impedances mutuelles avec un milieu de propagation de type viscoelastique et application aux directivites d'antenne." Paris 6, 1988. http://www.theses.fr/1988PA066092.
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Baktir, Yasemin. "Investigation Of Superdirective Antenna Arrays." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/12611038/index.pdf.
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In some antenna applications, having high directivity while keeping the antenna dimensions small is desired, which can be obtained by use of superdirective arrays. Superdirective arrays have been popular in academic world since a superdirective array provides higher directivity than the uniformly excited antenna array of same length.
In this thesis, superdirective arrays are investigated by making high precision numerical computations. Superdirective array element excitations, array factors and directivities are inspected for different number of elements. Superdirective array pattern and directivity features are compared to uniformly excited array pattern and directivities. Superdirective array tolerance is investigated by examination of array element excitation sensitivities. Bandwidth of superdirective arrays is also inspected. Multiple Precision Toolbox is used during numerical computations in Matlab.
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Ugurhan, Beliz. "Stochastic Strong Ground Motion Simulations On North Anatolian Fault Zone And Central Italy: Validation, Limitation And Sensitivity Analyses." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612413/index.pdf.
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Assessment of potential ground motions in seismically active regions is essential for purposes of seismic design and analysis. Peak ground motion intensity values and frequency content of seismic excitations are required for reliable seismic design, analysis and retrofitting of structures. In regions of sparse or no strong ground motion records, ground motion simulations provide physics-based synthetic records. These simulations provide not only the earthquake engineering parameters but also give insight into the mechanisms of the earthquakes. This thesis presents strong ground motion simulations in three regions of intense seismic activity. Stochastic finite-fault simulation methodology with a dynamic corner frequency approach is applied to three case studies performed in Düzce, L&rsquo
Aquila and Erzincan regions. In Dü
zce study, regional seismic source, propagation and site parameters are determined through validation of the simulations against the records. In L&rsquo
Aquila case study, in addition to study of the regional parameters, the limitations of the method in terms of simulating the directivity effects are also investigated. In Erzincan case study, where there are very few records, the optimum model parameters are determined using a large set of simulations with an error-minimization scheme. Later, a parametric sensitivity study is performed to observe the variations in simulation results to small perturbations in input parameters. Results of this study confirm that stochastic finite-fault simulation method is an effective technique for generating realistic physics-based synthetic records of large earthquakes in near field regions.
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Nejedlý, Miroslav. "Návrh a realizace mikrovlnné směrové odbočnice." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2010. http://www.nusl.cz/ntk/nusl-218411.
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The diploma thesis deals with microwave directional coupler. The paper presents some of the microwave directional coupler and an analysis of bifurcations. The paper also discussed the various techniques of bifurcations and the bandwidth to which they are making. Proposal is implemented in two selected directional couplers and determining their size. They also performed using the selected simulation program selected two bifurcations. Furthermore, these couplers are made on the perimeter of the analyzer is verified by their actions and are verified by the actual parameters of the coupler.