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1
Rosenlind, Johanna. "The Impulse-Radiating Antenna". Thesis, Karlstad University, Faculty of Technology and Science, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-4527.
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As the interest in intentional electromagnetic interference (IEMI) increases, so does the need of a suitable antenna which endures those demanding conditions. The ultrawideband (UWB) technology provides an elegant way of generating high-voltage UWB pulses which can be used for IEMI. One UWB antenna, invented solely for the purpose of radiating pulses, is the impulse radiating antenna (IRA). In the course of this master thesis work, a suitable geometry of the IRA is suggested, and modelled, for the high-voltage application of 90 kV.
2
Karaismail, Ertan. "Numerical Simulation Of Radiating Flows". Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606452/index.pdf.
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Predictive accuracy of the previously developed coupled code for the solution of the time-dependent Navier-Stokes equations in conjunction with the radiative transfer equation was first assessed by applying it to the prediction of thermally radiating, hydrodynamically developed laminar pipe flow for which the numerical solution had been reported in the literature. The effect of radiation on flow and temperature fields was demonstrated for different values of conduction to radiation ratio. It was found that the steady-state temperature predictions of the code agree well with the benchmark solution.
In an attempt to test the predictive accuracy of the coupled code for turbulent radiating flows, it was applied to fully developed turbulent flow of a hot gas through a relatively cold pipe and the results were compared with the numerical solution available in the literature. The code was found to mimic the reported steady-state temperature profiles well.
Having validated the predictive accuracy of the coupled code for steady, laminar/turbulent, radiating pipe flows, the performance of the code for transient radiating flows was tested by applying it to a test problem involving laminar/turbulent flow of carbon dioxide through a circular pipe for the simulation of simultaneous hydrodynamic and thermal development. The transient solutions for temperature, velocity and radiative energy source term fields were found to demonstrate the physically expected trends.
In order to improve the performance of the code, a parallel algorithm of the code was developed and tested against sequential code for speed up and efficiency. It was found that the same results are obtained with a reasonably high speed-up and efficiency.
3
Kamenkovich, Igor V. "Radiating instability of nonzonal ocean currents". Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/54424.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1997.Includes bibliographical references (leaves 192-195).
by Igor V. Kamenkovich.
Ph.D.
4
Lakkis, Issam Adnan 1970. "Lagrangian computations of radiating fire plumes". Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/89262.
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Agunlejika, Oluwafunmilayo. "Efficient discrete modelling of axisymmetric radiating structures". Thesis, Loughborough University, 2016. https://dspace.lboro.ac.uk/2134/21714.
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This thesis describes research on Efficient Discrete Modelling of Axisymmetric Radiating Structures . Investigating the possibilities of surmounting the inherent limitation in the Cartesian rectangular Transmission Line Modelling (TLM) method due to staircase approximation by efficiently implementing the 3D cylindrical TLM mesh led to the development of a numerical model for simulating axisymmetric radiating structures such as cylindrical and conical monopole antennas. Following a brief introduction to the TLM method, potential applications of the method are presented. Cubic and cylindrical TLM models have been implemented in MATLAB and the code has been validated against microwave cavity benchmark problems. The results are compared to analytical results and the results obtained from the use of commercial cubic model (CST) in order to highlight the benefit of using a cylindrical model over its cubic counterpart. A cylindrical TLM mesh has not previously been used in the modelling of axisymmetric 3D radiating structures. In this thesis, it has been applied to the modelling of both cylindrical monopole and the conical monopole. The technique can also be applied to any radiating structure with axisymmetric cylindrical shape. The application of the method also led to the development of a novel conical antenna with periodic slot loading. Prototype antennas have been fabricated and measured to validate the simulated results for the antennas.
6
Dillon, Bernice Mary. "Finite element analysis of radiating waveguide discontinuities". Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357770.
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Luettgen, Mark R. (Mark Robert). "Trajectory estimation of an optically radiating source". Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/14027.
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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1990.Includes bibliographical references (leaves 115-117).
by Mark R. Luettgen.
M.S.
8
Andera, Craig. "Trajectory estimation of an optically radiating source". Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/36634.
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Charnley, Debra. "Radiating flamelet models of turbulent buoyant diffusion flames". Thesis, University of Southampton, 1986. https://eprints.soton.ac.uk/52291/.
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It is widely accepted that thermal radiative emission is often the controlling mechanism in the growth and spread of unwanted fire. Existing models of fire radiation, however, are limited by our understanding of the interactions between the turbulent flame dynamics and the complex integral nature of radiative transfer. It is the aim of this thesis to study the radiative emission from buoyant diffusion flames, characteristic of fire, and assess the importance of these interactions in order to develop more accurate models of turbulent flame radiation. The laminar flamelet-conserved scalar probability density function approach is used to predict the scalar distributions throughout a laboratory-scale axisymmetric buoyant methane diffusion flame. Conserved scalar statistics are determined by comparison of published flame temperatures with those predicted by the laminar flamelet model. Physically unacceptable discontinuities between the time-averaged fuel-rich conditions near the flame centreline and the fuel-lean outer regions of the flame are unavoidable when employing an experimentally-derived near-adiabatic laminar flamelet description. Consideration of the individual model components and the procedure of matching predicted and experimental temperature statistics leads to the definition of a critical stoichiometric boundary in (bar T, (bar T bar ' bar 2)1/2) space. This boundary can only be reconciled with measured temperatures if the laminar flamelet employed possesses a temperature profile substantially reduced from its adiabatic value. Radiative emission is identified as the most plausible mechanism of heat loss from the flamelet. A simple but representative flamesheet model of laminar diffusion flame radiation is formulated in conserved scalar coordinates from which radiating laminar flamelet relationships are derived. Grey but inhomogeneous radiation from both gaseous species and an empirically-derived soot distribution are considered. These relationships are used successfully as the thermochemical sub-model in the prediction of buoyant flame scalar structure, enabling the rather low mean temperatures typical of these low initial-momentum flows to be reconciled with the concept of intermittent laminar flame burning. As an extension of this approach, a model of turbulent flame radiation is reported in which the flame is envisaged as an array of radiating laminar flamelets. The complete range of instantaneous laminar burning states observed in the flame are thus incorporated into the calculation of flame emission. The flexibility of this intuitive interpretation allows the relative importance of the various phenomena determining turbulent flame radiation to be identified. The radiation emitted along a path through the flame is shown to depend primarily on the number of flamelets present, rather than the geometric pathlength, and the radiative properties of the intervening turbulent eddies. Measurements are reported of both the time-resolved total radiant and mean spectral intensities emitted by the buoyant flame. A non-grey model of the low-intensity continuum radiation, extrapolated to longer wavelengths, indicates that soot emission contributes almost half the observed total mean intensity. Although accurate numerical predictions using the flamelet array model are currently restricted by limited knowledge of turbulent flame dynamics, comparisons with these measured values are encouraging and clearly indicate the areas requiring further research.
10
Toalá, Enríquez Rosemberg. "Stationarity of asymptotically flat non-radiating electrovacuum spacetimes". Thesis, University of Warwick, 2016. http://wrap.warwick.ac.uk/89265/.
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It is proven that a solution to the Einstein-Maxwell equations whose gravitational and electromagnetic radiation fields vanish at infinity is in fact stationary in a neighbourhood of spatial infinity. That is, if in adapted coordinates the Weyl and Faraday tensors decay suitably fast and there is an asymptotically-to-all-orders Killing vector field, then this is indeed a Killing vector field in the region outside the bifurcate horizon of a sphere of sufficiently large radius. In particular, electrovacuum time-periodic spacetimes, which are truly dynamical, do not exist. This can be interpreted as a mild form of the statement: “Gravitational waves carry energy away from an isolated system". This is an extension of earlier work by Alexakis and Schlue, and Bičák, Scholtz and Tod, to include matter/energy models, in this case electromagnetism. It is also shown that the same result holds when the Einstein's equations are coupled to a massless Klein-Gordon field.
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Ali, Hassan O. "Finite-element time-domain analysis of axisymmetrical radiating structures". Thesis, University of Ottawa (Canada), 1992. http://hdl.handle.net/10393/7897.
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A method of computation based on the finite element method was used to solve axisymmetrical electromagnetic wave propagation problems directly in the time-domain. The finite element method, employing first order triangular elements, was used to generate a system of second order linear differential equations. The system of differential equations was solved for the magnetic field using a suitable differential equation solving algorithm written in the course of this work. The method was used to model several situations involving axisymmetrical radiating structures directly in the time domain and the results compared well with the published data. Situations involving pulses, which are of particular interest to EMI/EMC field, were successfully studied. Conclusions were drawn on the suitability of the method in modeling radiated emissions from printed circuit board configurations, under the influence of transient exciting fields.
12
Cox, Daniel Paul Goodhall. "Black holes and radiating bodies in non-flat backgrounds". Thesis, Queen Mary, University of London, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.497899.
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McColl, Iain. "Radiating and coupling elements in waveguide planar array antennas". Thesis, Heriot-Watt University, 1992. http://hdl.handle.net/10399/788.
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Richards, John A. (John Alfred). "Time-to-intercept estimation for an optically radiating source". Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/41391.
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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1996.Includes bibliographical references (leaves 93-94).
by John A. Richards.
M.Eng.
15
Fuscaldo, Walter. "Advanced radiating systems based on leaky waves and nondiffracting waves". Thesis, Rennes 1, 2017. http://www.theses.fr/2017REN1S015/document.
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La focalisation du champ électromagnétique dans les zones de champ proche et lointain est un sujet de forte actualité pour l'imagerie médicale et la radiométrie des microondes jusqu'aux ondes millimétriques. Dans ce cadre, la théorie des ondes de fuite est un formalisme élégant qui permet de décrire d'une même façon les problèmes radiatifs en champ proche et en champ lointain des microondes aux fréquences optiques. Dans cette thèse, on utilise la polyvalence de la théorie des ondes de fuite pour développer des systèmes rayonnants complexes afin de contrôler les caractéristiques radiatives en champ lointain aux fréquences submillimétriques et pour focaliser la radiation électromagnétique en champ proche aux fréquences millimétriques. Ainsi, l'utilisation de matériaux uniques comme le graphène et les cristaux liquides ont été considérés pour la conception des antennes à ondes de fuite, en obtenant des résultats très intéressants en termes de reconfigurabilité, d'efficience et de directivité. Dans ce contexte, une analyse théorique originale a fourni de nouvelles formules pour l'évaluation des caractéristiques radiatives (c.à.d. la largeur de faisceau, le niveau des lobes secondaires, etc.) des antennes à ondes de fuite. En effet, la largeur du faisceau de ces antennes est, jusqu'à présent, estimée au moyen des formules proposées pour la première fois dans les années '60 par Prof. Arthur A. OLINER. Ces formules ne tiennent en compte ni de la longueur de l'antenne (sauf pour des cas très particuliers), ni du rayonnement longitudinal, elles ne permettent donc pas une évaluation rigoureuse.En complément à la reconfigurabilité en champ lointain, les ondes de fuite offrent aussi la possibilité de focaliser la radiation en champ proche. Dans ce cas, on voit que les ondes de fuite peuvent être utilisées d'une façon efficace pour générer des faisceaux non diffractifs de Bessel à travers des systèmes rayonnants à bande étroite aux ondes millimétriques. De plus, le caractère non diffractif des faisceaux de Bessel peut aussi être utilisé pour générer des impulsions très localisées (comme les solitons en optiques) à travers la superposition continue des faisceaux de Bessel sur une large bande de fréquence. Dans ce cadre, une nouvelle formulation a été développée afin de comprendre les limitations physiques et technologiques concernant la génération des impulsions non diffractives et non dispersives, c.à.d. les X-waves. Les résultats ont montré qu'un type de systèmes rayonnants à large bande, notamment les antennes RLSA (en anglais « Radial Line Slot Array »), semblent très favorables pour la génération des X-wavesIn recent years, microwave, millimeter-wave, and THz applications such as medical and security imaging, wireless power transfer, and near-field focusing, just to mention but a few, have gained much attention in the area of ICT due to their potentially high social impact. On one hand, the need of highly-directive THz sensors with tunable radiating features in the far-field region has recently boosted the research activity in the design of flexible, low-cost and low-profile devices. On the other hand, it is of paramount importance to focus energy in the near-field region, and thus the generation of limited-diffraction waves in the microwave and millimeter-wave regime is a topic of recent increasing interest. In this context, leaky-wave theory is an elegant and extremely useful formalism which allows for describing in a common fashion guiding and radiating phenomena in both the near field and the far field, spanning frequencies from microwaves to optics passing through THz. In this PhD thesis we aim to exploit the intrinsic versatility of the leakywave approach to design advanced radiating systems for controlling the far-field radiating features at THz frequencies and for focusing electromagnetic radiation in the near field at millimeter waves. Specifically, the use of relatively new materials such as graphene and liquid crystals has been considered for the design of leaky-wave based radiators, achieving very promising results in terms of reconfigurability, efficiency, and radiating capabilities. In this context, an original theoretical analysis has provided new general formulas for the evaluation of the radiating features (e.g., half-power beamwidth, sidelobe level, etc.) of leaky-wave antennas. Indeed, the current formulations are based on several simplifying hypotheses which do not allow for an accurate evaluation of the beamwidth in different situations. In addition to the intriguing reconfigurable capabilities offered by leaky waves in far-field applications, interesting focusing capabilities can be obtained in the near field. In particular, it is shown that leaky waves can profitably be used to generate limited-diffraction Bessel beams by means of narrow-band radiators in the microwave range. Also, the use of higherorder leaky-wave modes allows for achieving almost the same performance in the millimeter-wave range, where previous designs were subjected to severe fabrication issues. Even more interestingly, the limited-diffractive character of Bessel beams can also be used to generate limited-diffraction pulses as superpositions of monochromatic Bessel beams over a considerable fractional bandwidth. In this context, a novel theoretical framework has been developed to understand the practical limitations to efficiently generate limited-diffraction, limited-dispersion pulses, such as X-waves, in the microwave/millimeter-wave range. As a result of this investigation, a class of wideband radiators has been thoroughly analyzed, showing promising capabilities for the generation of both zeroth-order and higher-order Xwaves. The latter may pave the way for the first localized transmission of orbital angular momentum in the microwave range
16
Ireland, David John, i n/a. "Realization of Dielectric Embedded Monopole Radiating Structures For Wireless Computing". Griffith University. School of Microelectronic Engineering, 2006. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20070117.175717.
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With the rapid of growth of wireless connectivity more demand is placed on the need for innovative technologies capable of satisfying increasing user demand and network capacity. Adaptive antennas systems or most commonly known as Smart Antennas are expected to be implemented in the next generation of wireless systems. Their implementation avails in dynamic adaptation to spatial and temporal conditions affecting the quality of communication, while offering tremendous flexibility to wireless providers. However one of the major challenges facing Smart Antenna technology is the inherent complexity of the antenna structure, associated control algorithm and implemented RF components possibly contributing to the delay of commercial interest. This thesis will present various adaptive antenna configurations that utilize an embedded dielectric in order to achieve significant size reduction and mechanical rigidity while maintaining favorable electromagnetic performance. In order to constrict the lateral ground plane dimension, a cylindrical shaped hollow ground skirt was attached to the antenna structures effectively compromising between effective beam forming in the azimuth plane and physical size. The complexity of these antenna structures requires a more contemporary design approach which involved computer modeling using a commercial available Finite Element software package and optimization using a developed generic Genetic Algorithm based optimization program. A dielectric embedded 7-element monopole array antenna featuring switched parasitic elements is presented and optimized for maximum vertically polarized gain in the horizontal plane, producing an antenna structure with a radial length of less then 0.25λ and total height of 0.4&alamba which was shown to radiate a main lobe beamwidth of 80 degrees with an absolute gain of 4.8dBi at 2.45GHz. Further on a dielectric embedded 7-element monopole array antenna featuring parasitic elements terminated with finite set of terminating reactive loads is presented with a radial length of less then 0.25&alambda and total height of 0.4&alambda. The antenna structure and reactive load combination were optimized for maximum horizontal gain producing a principal main lobe with a measured gain of 5.1dBi and beamwidth of 110 degrees at 2.48GHz. Finally it was shown single and dual radiation lobes maybe produced when active monopoles elements are placed eccentric in a circular shaped dielectric material. A circular array of elements embedded in a dielectric material was realized with measured gains of single and dual beam radiation at 2.45GHz was shown to be 5.18dBi and 3.65Bi respectively with corresponding beamwidths of 78.5 degrees and 53 degrees.
17
Schlub, Robert Walter, i n/a. "Practical Realization of Switched and Adaptive Parasitic Monopole Radiating Structures". Griffith University. School of Microelectronic Engineering, 2004. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20040610.112148.
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Switched and adaptive parasitic monopole array radiating structures are investigated. Antenna design is orientated toward increasing practicability for implementation in terrestrial wireless communication systems. A number of antennas are designed with the aid of optimization and commercial simulation software. Simulation procedure was verified with the experimental manufacture and measurement of the arrays. The antennas presented in this thesis comprise an active monopole surrounded by a ring of parasitic monopoles. Parasitic radiators are constructed with static loading to enable simple experimental realization. Beam positions of an electrically steered equivalent antenna are thus simulated. Antenna symmetry ensures the beam can be reproduced throughout the azimuth. Complex antenna geometries require antenna design through optimization. A genetic algorithm is employed with HFSS and NEC for electromagnetic analysis. The robust optimization method couples with simulation software flexibility to provide an effective design tool for arbitrary structures. The genetic algorithm is employed strictly for design and not complete structural optimization. Dual band, five and six element switched parasitic antennas are presented. Lumped elemental loading along the radiators provide resonance and directed radiation at two GSM frequencies. Load value, radiator dimension and spacing are incorporated as design parameters. Experimentally built, 10dB return loss bandwidths of 17.2% and 9.6% and front to back ratios of 12.6dB and 8.4dB at 900MHz and 1900MHz respectively are measured. To reduce the ground requirements of monopole arrays, a skirted ground structure for switched parasitic antennas is analyzed. A six element switched parasitic monopole array with conductive ground skirt exhibits a front to back ratio of 10.7dB and main lobe gain of 6.4dBi at 1.575GHz. Radiation is not elevated despite lateral ground terminating at the parasitic elements. Skirt height is observed to linearly control radiation elevation, depressing the principal lobe through 40 degrees from 23 degrees above the horizontal. The Electronically Steerable Passive Array Radiator or ESPAR antenna is an adaptive parasitic monopole array. An ESPAR radiating structure incorporating a conductive ground skirt is designed for operation at 2.4GHz. Utility is confirmed with a frequency sensitivity analysis showing consistent electrical characteristics over an 8.1% bandwidth. The antenna design is improved with optimization to reduce average principal lobe elevation from 25 degrees to 9.7 degrees.
18
Baretela, Michael J. "Increasing prompt response from impulse radiating antenna by aperture shaping". Thesis, Monterey California. Naval Postgraduate School, 2002. http://hdl.handle.net/10945/6094.
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Approved for public release, distribution is unlimitedIn order to improve the prompt response from an impulse radiating antenna (IRA)number of studies have suggested controlling the spatial distribution of the aperture fields by changing the feed arm angle. Other work has suggested that proper shaping of the aperture can further enhance the radiated signal for a given feed structure. This paper shows how the radiated prompt response can be maximized for a given feed arm configuration by shaping the aperture to eliminate fields orientated in the wrong direction. The percent increase in the prompt radiated electric field for a 200 . IRA with a ideally shaped aperture compared to a standard circular aperture ranged from 0.42% to 39.94% depending on the input electrode angle. For the most common electrode angles of 45Ê» and 60Ê» the increases are 6.00% and 16.63% respectively.
19
Buxton, Carey G. "Design of a Broadband Array Using the Foursquare Radiating Element". Diss., Virginia Tech, 2001. http://hdl.handle.net/10919/28363.
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Broadband scanning arrays require small element spacing over a broad frequency band to achieve the desired scan capabilities. Previous research has concentrated on the development of small broadband elements to meet the demands of broadband arrays. However, mutual coupling between elements in a tightly spaced array can change the operating frequency and bandwidth from that of the single isolated element. Several research efforts have focused on minimizing the mutual coupling to maintain the frequency response of the single isolated element. This dissertation focuses on using the strong coupling between Foursquare antennas to obtain the broadband frequency response while maintaining a small element spacing.
The isolated Foursquare antenna was modeled using an in-house FDTD code. The modeled current distribution over the frequency band of operation revealed how the antenna achieved a broadband frequency response. Because of this understanding of the single element, the downward shift in the frequency response of the Foursquare antenna in a fully active array could be anticipated. Furthermore, the infinite array models of the Foursquare revealed an increase in bandwidth. Both are desirable characteristics for a broadband scanning array. Therefore, through this research using the Foursquare element, it has been shown that the strong mutual coupling in a tightly spaced array can have advantages if initially taken into consideration when designing the array.Ph. D.
20
Ireland, David John. "Realization of Dielectric Embedded Monopole Radiating Structures For Wireless Computing". Thesis, Griffith University, 2006. http://hdl.handle.net/10072/367819.
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With the rapid of growth of wireless connectivity more demand is placed on the need for innovative technologies capable of satisfying increasing user demand and network capacity. Adaptive antennas systems or most commonly known as Smart Antennas are expected to be implemented in the next generation of wireless systems. Their implementation avails in dynamic adaptation to spatial and temporal conditions affecting the quality of communication, while offering tremendous flexibility to wireless providers. However one of the major challenges facing Smart Antenna technology is the inherent complexity of the antenna structure, associated control algorithm and implemented RF components possibly contributing to the delay of commercial interest. This thesis will present various adaptive antenna configurations that utilize an embedded dielectric in order to achieve significant size reduction and mechanical rigidity while maintaining favorable electromagnetic performance. In order to constrict the lateral ground plane dimension, a cylindrical shaped hollow ground skirt was attached to the antenna structures effectively compromising between effective beam forming in the azimuth plane and physical size. The complexity of these antenna structures requires a more contemporary design approach which involved computer modeling using a commercial available Finite Element software package and optimization using a developed generic Genetic Algorithm based optimization program. A dielectric embedded 7-element monopole array antenna featuring switched parasitic elements is presented and optimized for maximum vertically polarized gain in the horizontal plane, producing an antenna structure with a radial length of less then 0.25λ and total height of 0.4&alamba which was shown to radiate a main lobe beamwidth of 80 degrees with an absolute gain of 4.8dBi at 2.45GHz. Further on a dielectric embedded 7-element monopole array antenna featuring parasitic elements terminated with finite set of terminating reactive loads is presented with a radial length of less then 0.25&alambda and total height of 0.4&alambda. The antenna structure and reactive load combination were optimized for maximum horizontal gain producing a principal main lobe with a measured gain of 5.1dBi and beamwidth of 110 degrees at 2.48GHz. Finally it was shown single and dual radiation lobes maybe produced when active monopoles elements are placed eccentric in a circular shaped dielectric material. A circular array of elements embedded in a dielectric material was realized with measured gains of single and dual beam radiation at 2.45GHz was shown to be 5.18dBi and 3.65Bi respectively with corresponding beamwidths of 78.5 degrees and 53 degrees.Thesis (Masters)
Master of Philosophy (MPhil)
School of Microelectronic Engineering
Full Text
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Schlub, Robert Walter. "Practical Realization of Switched and Adaptive Parasitic Monopole Radiating Structures". Thesis, Griffith University, 2004. http://hdl.handle.net/10072/366803.
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Switched and adaptive parasitic monopole array radiating structures are investigated.
Antenna design is orientated toward increasing practicability for implementation in terrestrial wireless communication systems. A number of antennas are designed with the aid of optimization and commercial simulation software. Simulation procedure was verified with the experimental manufacture and measurement of the arrays. The antennas presented in this thesis comprise an active monopole surrounded by a ring of parasitic monopoles. Parasitic radiators are constructed with static loading to enable simple experimental realization. Beam positions of an electrically steered equivalent antenna are thus simulated. Antenna symmetry ensures the beam can be reproduced throughout the azimuth. Complex antenna geometries require antenna design through optimization. A genetic algorithm is employed with HFSS and NEC for electromagnetic analysis. The robust optimization method couples with simulation software flexibility to provide an effective design tool for arbitrary structures. The genetic algorithm is employed strictly for design and not complete structural optimization. Dual band, five and six element switched parasitic antennas are presented. Lumped elemental loading along the radiators provide resonance and directed radiation at two GSM frequencies. Load value, radiator dimension and spacing are incorporated as design parameters. Experimentally built, 10dB return loss bandwidths of 17.2% and 9.6% and front to back ratios of 12.6dB and 8.4dB at 900MHz and 1900MHz respectively are measured. To reduce the ground requirements of monopole arrays, a skirted ground structure for switched parasitic antennas is analyzed. A six element switched parasitic monopole array with conductive ground skirt exhibits a front to back ratio of 10.7dB and main lobe gain of 6.4dBi at 1.575GHz. Radiation is not elevated despite lateral ground terminating at the parasitic elements. Skirt height is observed to linearly control radiation elevation, depressing the principal lobe through 40 degrees from 23 degrees above the horizontal. The Electronically Steerable Passive Array Radiator or ESPAR antenna is an adaptive parasitic monopole array. An ESPAR radiating structure incorporating a conductive ground skirt is designed for operation at 2.4GHz. Utility is confirmed with a frequency sensitivity analysis showing consistent electrical characteristics over an 8.1% bandwidth. The antenna design is improved with optimization to reduce average principal lobe elevation from 25 degrees to 9.7 degrees.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Microelectronic Engineering
Full Text
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Partal, Hakan Pasa. "Circular loop antennas radiating in the presence of symmetrically placed scatterers". Related electronic resource: Current Research at SU : database of SU dissertations, recent titles available full text, 2005. http://wwwlib.umi.com/cr/syr/main.
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Xu, Xin. "MODULAR FAST DIRECT ANALYSIS USING NON-RADIATING LOCAL-GLOBAL SOLUTION MODES". UKnowledge, 2008. http://uknowledge.uky.edu/gradschool_diss/690.
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This dissertation proposes a modular fast direct (MFD) analysis method for a class of problems involving a large fixed platform region and a smaller, variable design region. A modular solution algorithm is obtained by first decomposing the problem geometry into platform and design regions. The two regions are effectively detached from one another using basic equivalence concepts. Equivalence principles allow the total system model to be constructed in terms of independent interaction modules associated with the platform and design regions. These modules include interactions with the equivalent surface that bounds the design region. This dissertation discusses how to analyze (fill and factor) each of these modules separately and how to subsequently compose the solution to the original system using the separately analyzed modules.
The focus of this effort is on surface integral equation formulations of electromagnetic scattering from conductors and dielectrics. In order to treat large problems, it is necessary to work with sparse representations of the underlying system matrix and other, related matrices. Fortunately, a number of such representations are available. In the following, we will primarily use the adaptive cross approximation (ACA) to fill the multilevel simply sparse method (MLSSM) representation of the system matrix. The MLSSM provides a sparse representation that is similar to the multilevel fast multipole method.
Solutions to the linear systems obtained using the modular analysis strategies described above are obtained using direct methods based on the local-global solution (LOGOS) method. In particular, the LOGOS factorization provides a data sparse factorization of the MLSSM representation of the system matrix. In addition, the LOGOS solver also provides an approximate sparse factorization of the inverse of the system matrix. The availability of the inverse eases the development of the MFD method. Because the behavior of the LOGOS factorization is critical to the development of the proposed MFD method, a significant part of this dissertation is devoted to providing additional analyses, improvements, and characterizations of LOGOS-based direct solution methods. These further developments of the LOGOS factorization algorithms and their application to the development of the MFD method comprise the most significant contributions of this dissertation.
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Brooks, David Hamilton. "On the radiating and dynamic properties of the solar upper atmosphere". Thesis, University of Strathclyde, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.415098.
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Foster, Adam. "On the behaviour and radiating properties of heavy elements in fusion plasmas". Thesis, University of Strathclyde, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.501815.
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Radiation from Impurities in magnetically confined fusion devices is regularly utilised on existing tokamaks for both diagnostic purposes (to reveal plasma conditions) and to estimate the impurity content itself to detect any detrimentally high radiation power losses. For the light elements (Z <8) commonly found in tokamaks the atomic physics infrastructure to allow such observations and model the results is well developed. The proposed design for ITER calls for a partially tungsten divertor. This has led to a resurgence of interest in the behaviour of heavy impurities in plasma. Many codes for generating fundamental atomic data and for modelling plasma behaviour encounter significant difficulties when dealing with heavy elements. This work addresses some of these issues.
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Cook, Gregory Gildroy. "High resolution three dimensional imaging of the current distributions on radiating structures". Thesis, University of Sheffield, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.431745.
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Dumont, Joey. "On the modelization of optical devices: from dielectric cavities to radiating structures". Master's thesis, Université Laval, 2014. http://hdl.handle.net/20.500.11794/25371.
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Premièrement, nous allons explorer la modélisation des cavités diélectriques bidimensionnelles. Plus spécifiquement, nous allons développer différentes méthodes de modélisation valides pour des cavités diélectriques à géométrie et profil d’indice de réfraction arbitraires. Ce degré de liberté supplémentaire pourra être utilisé dans le design de microcavités pour des applications spécifiques. Un formalisme de diffusion permettra de définir les modes caractéristiques de ce type de structure et d’en calculer les résonances. Une analyse numérique des équations résultantes montrera que les méthodes intégrales sont possiblement meilleures que les méthodes différentielles. Deuxièmement, nous discuterons de la modélisation de structures radiatives. Nous utiliserons les méthodes développées dans la section précédente pour modéliser les propriétés lasers des microcavités bidimensionnelles prédites par la théorie SALT. Nous aborderons aussi la modélisation de fibres-antennes RF, plus particulièrement les câbles coaxiaux à perte radiative, dans le but d’intégrer des fonctionnalités radio dans un textile de manière transparente à l’utilisateur.In this essay, we will develop different modelization techniques valid for bidimensional dielectric cavities having arbitrary geometries and refractive index profiles and provide a way to accurately compute the resonances of such structures. The refractive index thus becomes an additional design variable for dielectric cavities. A numerical analysis of of the underlying equations of the theory will reveal that perhaps it is best to forego differential equations in favour of integral ones for the scattering problem. In the second part, we will discuss the modelization of radiating structures. Using the formalism developed in the previous section, we will study the lasing properties of bidimensional cavities using the newly developed self-consistent ab initio laser theory (SALT). We will also touch on the modelization of the class of antenna known as leaky coax
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Uygur, Ahmet Bilge. "A Non-iterative Pressure Based Algorithm For The Computation Of Reacting Radiating Flows". Phd thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/12608274/index.pdf.
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A non-iterative pressure based algorithm which consists of splitting the solution of momentum energy and species equations into a sequence of predictor-corrector stages
was developed for the simulation of transient reacting radiating flows. A semi-discrete approach called the Method of Lines (MOL) which enables implicit time-integration at
all splitting stages was used for the solution of conservation equations. The solution of elliptic pressure equation for the determination of pressure field was performed by a
multi-grid solver (MUDPACK package). Radiation calculations were carried out by coupling previously developed gray and non-gray radiation models with the algorithm. A first order (global) reaction mechanism was employed to account for the chemistry.
The predictions of the algorithm for the following test cases: i) non-isothermal turbulent pipe flow and ii) laminar methane-air diffusion flamewere benchmarked against experimental data and numerical solutions available in the literature and the capability of the code to predict transient solutions was demonstrated on these test cases. Favorable agreements were obtained for both test cases. The effect of radiation and non-gray treatment of the radiative properties were investigated on the second test case. It was found that incorporation of radiation has significant effect on Temeprature and velocity fields but its effect is limited in species predictions. Executions with both radiation models revealed that the non-gray radiation model considered in the present study produces similar results with the gray model at a considerably higher computational cost. The algorithm developed was found to be an efficient and versatile tool for the timedependent simulation of different flow scenarios constitutes the initial steps towards the computation of transient turbulent combustion.
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Kim, Kangwook. "Numerical and experimental investigation of impulse-radiating antennas for use in sensing applications". Diss., Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/14944.
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Kojima, Seishiro. "Novel Beamforming and Antenna Techniques for Microwave Power Transmission in Radiating Near Field". Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/263667.
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Emidio, Fernando. "Analysis of multidimensional radiating structures by the spatial Fourier transform and computational electromagnetics". Thesis, Saint-Etienne, 2013. http://www.theses.fr/2013STET4011.
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Ce manuscrit présente les travaux de recherche qui concernent l'analyse et la synthèse de structures rayonnantes multidimensionnelles en utilisant une approche qui combine méthode des moments et la transformée de Fourier spatiale. La distribution source (courant électrique) et le diagramme de rayonnement sont liées par la transformée de Fourier spatiale - la théorie de la Relation de Fourier (FR). La distribution des courants est déterminée en utilisant une méthode d'analyse en électromagnétisme (EM), à savoir la Méthode des Moments (MoM). Des travaux antérieurs utilisant la théorie FR ont été réalisés par d'autres auteurs sur des réseaux linéaires - uniformément espacés ou non uniformes. Les sources radiantes élémentaires des dipoles électriques filaires. Les travaux actuels se développent en utilisant la théorie FR à deux et trois dimensions sur des structures réelles. En utilisant la méthode MoM nous pouvons prendre en compte le rayon du fil, sur n'importe quel point d'excitation (générateur de tension ou onde incidente) et le couplage mutuel entre les éléments, créant ainsi un modèle électromagnétique réaliste pour la structure d'antenneThis manuscript presents the research work in the analysis and synthesis of multidimensional radiating structures using an approach that combines Method of Moments and Spatial Fourier Transform. The source distribution (electric current) and radiation pattern are related by the spatial Fourier Transform - Fourier Relation theory (FR). Current distribution is determined using Computational Electromagnetics (CEM), namely Method of Moments (MoM). Previous work using FR theory was done by other authors on linear arrays – uniformly or nonuniformly spaced elemental radiators laid on a straight line. Present work expands FR theory to two and three dimensions on real-world structures. By using MoM we can take into account wire radius, excitation on any point (voltage generator or incident wave) and mutual coupling between elements, thus creating a realistic electromagnetic model for the antenna structure
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Moslemi, Parisa. "Design, fabrication, and test of a radiating element for a KU-BAND smart antenna". Mémoire, École de technologie supérieure, 2012. http://espace.etsmtl.ca/1107/7/MOSLEMI_Parisa.pdf.
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Les antennes planaires multiéléments ont fait l'objet de nombreuses recherches ces dernières années en tant que candidates pour diverses applications telles que les communications par satellite. Parmi les nombreux avantages de ce type d'antenne on compte la capacité de diriger le faisceau de façon électrique, sa haute fiabilité, ainsi que son moindre coût à long terme; cela motive de pousser encore plus loin la recherche dans ce domaine.
Les antennes microrubans sont largement utilisées dans les réseaux d’antennes en raison de leur faible coût et de leur légèreté. De plus, elles peuvent facilement être imprimées sur un substrat diélectrique avec des techniques de photolithographie.
L'objectif de ce mémoire est la conception et la fabrication d'une antenne patch large bande, afin qu’elle soit utilisée dans un réseau d’antennes dans le contexte d’application de la communication par satellite. Ce patch est conçu pour fonctionner dans le domaine fréquentiel entre 10.7 GHz et 12.7 GHz. Dans ce projet, nous avons utilisé la technologie de la céramique cocuite à basse température à côté du circuit imprimé, ce qui n'a jamais encore été appliqué auparavant. En outre, nous proposons une nouvelle structure de l'antenne patch qui augmente la bande passante jusqu'à 19%. Les correctifs proposés sont fabriqués avec les matériaux 591 et 9K7 Green Tape et Rogers RT5870. Les dessins ont été effectuées en utilisant le simulateur de champ électromagnétique planaire Momentum, faisant partie de Advanced Design System (ADS) de Agilent technologies.
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Cohen, Brian S. Ph D. Massachusetts Institute of Technology. "Multidisciplinary design of thermally radiating structures using a level set based topology optimization approach". Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/119287.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 267-282).
The need for efficient thermally radiating structures for aerospace applications is apparent in many system designs including satellites, launch vehicles and hypersonic aircraft. While multidisciplinary structural optimization methods have been employed to design these systems, few have incorporated thermal radiation as part of their multi-physics analysis capability. Moreover, with the rapid advancement of manufacturing technologies, the ability to fabricate flight hardware with unprecedented geometric complexity has challenged the limits of human design intuition. As a result, there is a critical need for free-form design methods to harness the full potential of these new manufacturing techniques. This thesis presents a level set based topology optimization approach for designing thermally efficient radiating structures considering multiple objectives, constraints and disciplines. Level set based methods offer a key advantage of defining crisp structural boundaries while seamlessly handling complex geometric transformations. The first contribution of this thesis is deriving a shape sensitivity of the thermal heat power radiated objective function using the adjoint method. This sensitivity is a necessary ingredient for our gradient-based algorithm. The second contribution is developing a topology optimization framework capable of handling multiple objectives and constraints via the augmented Lagrangian method. Both von Mises stress and first mode frequency constraints are implemented since they are commonly found in aerospace design problems where severe structural loads can lead to catastrophic failure. The final contribution is testing several data mining techniques to identify prominent topological features of a large set of designs found using our topology optimization approach. The CUR matrix decomposition is best suited for identifying the principal designs and also aids in categorizing the solution topologies. These contributions are demonstrated on several 2D example problems where the goal is to identify thermally efficient radiating structures able to reject heat using limited material. Both von Mises stress and first mode frequency constraints are enforced to ensure that solutions are sufficiently rigid. The results indicate that many locally optimal solutions exist in the design tradespace with topologically diverse features. Additionally, we show that the thermal compliance objective function commonly used to design conductive structures is not sufficient when a radiating surface exists.
by Brian S. Cohen.
Ph. D.
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Iliopoulos, Ioannis. "Engineering the near field of radiating systems at millimeter waves : from theory to applications". Thesis, Rennes 1, 2017. http://www.theses.fr/2017REN1S165.
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L'objectif général est de développer un nouvel outil numérique dédié à la focalisation en 3D de l'énergie en zone de champ très proche par un système antennaire. Cet outil permettra de définir la distribution spatiale complexe des champs dans l'ouverture rayonnante afin de focaliser l'énergie sur un volume quelconque en zone de champ réactif. L'hybridation de cet outil avec un code de calcul dédié à l'analyse rapide d‘antennes SIW par la méthode des moments permettra de synthétiser une antenne SIW ad-hoc. Les structures antennaires sélectionnées seront planaires comme par exemple les antennes RLSA (Radial Line Slot Array). Les dimensions de l'antenne (positions, dimensions et nombre de fentes) seront définies à l'aide des outils décrits ci-dessus. Les résultats numériques ainsi obtenus seront validés d'abord numériquement par analyse électromagnétique globale à l'aide de simulateurs commerciaux, puis expérimentalement en ondes millimétriques (mesure en zone de champ très proche). Pour atteindre ces objectifs, nous avons défini quatre tâches principales : Développement d'un outil de synthèse de champ dans l'ouverture rayonnante (formulation théorique couplée à une méthode dite des projections alternées) ; développement d'un outil de calcul rapide (sur la base de traitements par FFT) du champ électromagnétique rayonné en zone de champ proche par une ouverture rayonnante, et retro-propagation ; hybridation de ces algorithmes avec un code de calcul (méthode des moments) en cours de développement à l'IETR et dédié à l'analyse très rapide d'antennes en technologie SIW ; conception d'une preuve ou plusieurs preuves de concept, et validations numérique et expérimentale des concepts proposésWith the demand for near-field antennas continuously growing, the antenna engineer is charged with the development of new concepts and design procedures for this regime. From the microwave and up to terahertz frequencies, a vast number of applications, especially in the biomedical domain, are in need for focused or shaped fields in the antenna proximity. This work proposes new theoretical methods for near-field shaping based on different optimization schemes. Continuous radiating planar apertures are optimized to radiate a near field with required characteristics. In particular, a versatile optimization technique based on the alternating projection scheme is proposed. It is demonstrated that, based on this scheme, it is feasible to achieve 3-D control of focal spots generated by planar apertures. Additionally, with the same setup, also the vectorial problem (shaping the norm of the field) is addressed. Convex optimization is additionally introduced for near-field shaping of continuous aperture sources. The capabilities of this scheme are demonstrated in the context of different shaping scenarios. Additionally, the discussion is extended to shaping the field in lossy stratified media, based on a spectral Green's functions approach. Besides, the biomedical applications of wireless power transfer to implants and breast cancer imaging are addressed. For the latter, an extensive study is included here, which delivers an outstanding improvement on the penetration depth at higher frequencies. The thesis is completed by several prototypes used for validation. Four different antennas have been designed, based either on the radial line slot array topology or on metasurfaces. The prototypes have been manufactured and measured, validating the overall approach of the thesis
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Ross, Bradley W. "Attenuation of Low Frequency Structurally Radiated Noise With an Array of Weak Radiating Cells". Thesis, Virginia Tech, 1998. http://hdl.handle.net/10919/36555.
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The concept of a weak sound radiating cell is proposed to reduce the low frequency radiated noise from structures. The cell consists of two coupled surfaces such that, when placed on a vibrating structure, the responses of the two surfaces are nearly out-of-phase and of equal strength over a wide frequency range. This structure response leads the cell to behave as an acoustic dipole and thus as a poor sound radiating source. The control of low frequency structurally radiated noise is then achieved by covering the structure with an array of these weak radiating cells, i.e. surface treatment. Thus, the surface treatment essentially transforms the response of the structure to that of a distributed array of dipoles yielding a low sound radiating structure. Theoretical models are developed to predict the performance of the cell. Experimental verification is performed for a single cell applied to a piston-like structure to demonstrate the concept on a simple radiating structure. The results demonstrated an overall sound power level reduction of 5.2 dB between 400-1600 Hz with maximum reductions over 30 dB at discrete frequencies. Finally, an array of weak radiating cells is experimentally applied to a more complex structure, a rectangular plate. The results of the plate experiments reveal an overall sound power level reduction of 10.2 dB between 100-1600 Hz with maximum reductions of 25 dB at discrete frequencies. These results demonstrate the potential of the weak radiating cell concept to reduce low frequency structurally radiated noise.Master of Science
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Kumar, Saurabh. "Radiating Macroscopic Dark Matter: Searching for Effects in Cosmic Microwave Background and Recombination History". Case Western Reserve University School of Graduate Studies / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=case1606996786558263.
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Kitts, Zachary Todd. "An Analytical Study of the Weak Radiating Cell as a Passive Low Frequency Noise Control Device". Thesis, Virginia Tech, 2000. http://hdl.handle.net/10919/35507.
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At low frequency where the acoustic wavelength is greater than the size of the vibrating structure, the radiated acoustic power is directly related to the volume velocity of the structure. Thus, minimizing the volume velocity is an effective noise reduction approach for low frequency structurally radiated noise. This thesis analytically investigates a passive volume velocity noise control device for acoustic surface treatment of planar structures. The device is referred to as a weak radiating cell. This device consists of two mechanically coupled surfaces such that, when placed on a vibrating structure, the response of the two surfaces are nearly out-of-phase and of equal strength over a wide frequency range. The response of the two surfaces forms a local acoustic dipole, with minimum volume velocity, that results in noise reduction. Thus, the control of low frequency structurally radiated noise is achieved by covering the structure with an array of these weak radiating cells. Several numerical models are developed to investigate the weak radiating cell noise control mechanisms. The first model consists of a simply supported beam treated with an array of weak radiating cell. In this model, the dynamic interaction effects between the beam and the cells are included. Results from this model predict an overall sound power level reduction of 9.8 dB between 0-1600 Hz and 20 dB between 0-251 Hz. In addition, this model is used to investigate techniques to improve the noise reduction capabilities of the device. A model of weak radiating cells applied to a simply supported plate is next developed as an extension of the beam model. The results from this model are compared to previous experimental data. Good agreement is observed between results, which validates the modeling technique. Lastly, a model of an infinite 2D plate treated with weak radiating cells is developed. The model does not consider any dynamic interaction effect between the structure and the cells. Only the acoustic behavior of the weak radiating cell is included in this model. In addition, both the structural and acoustic responses are obtained in closed form through a wavenumber transform approach. Each of these models and their results offer valuable information that results in a better understanding the weak radiating cell and it potential as a low frequency passive noise control device.Master of Science
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Tang, Ming-Chun, Ting Shi i Richard W. Ziolkowski. "Electrically Small, Broadside Radiating Huygens Source Antenna Augmented With Internal Non-Foster Elements to Increase Its Bandwidth". IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2017. http://hdl.handle.net/10150/623616.
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A broadside radiating, linearly polarized, electrically small Huygens source antenna system that has a large impedance bandwidth is reported. The bandwidth performance is facilitated by embedding non-Foster components into the near-field resonant parasitic elements of this metamaterial-inspired antenna. High-quality and stable radiation performance characteristics are achieved over the entire operational bandwidth. When the ideal non-Foster components are introduced, the simulated impedance bandwidth witnesses approximately a 17-fold enhancement over the passive case. Within this -10-dB bandwidth, its maximum realized gain, radiation efficiency, and front-to-back ratio (FTBR) are, respectively, 4.00 dB, 88%, and 26.95 dB. When the anticipated actual negative impedance convertor circuits are incorporated, the impedance bandwidth still sustains more than a 10-fold enhancement. The peak realized gain, radiation efficiency, and FTBR values are, respectively, 3.74 dB, 80%, and 28.01 dB, which are very comparable to the ideal values.
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Böttcher, Maximilian A. [Verfasser]. "Design of an active direct radiating array antenna for regional coverage in the Ka-band / Maximilian A. Böttcher". München : Verlag Dr. Hut, 2019. http://d-nb.info/120216918X/34.
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LaPean, James William. "Analysis of infinite arrays of arbitrarily shaped planar radiating elements using a Floquet mode based Method of Moments approach". Diss., This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-06062008-152047/.
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Sarray, Sadreddine. "Proposed Revisions to Procedures for Testing and Evaluating Radiating Noise Sources from Small Firearms, including the ANSI/ASA S12.42-2010 Procedure". Thesis, Université d'Ottawa / University of Ottawa, 2020. http://hdl.handle.net/10393/40549.
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The escalating cost of claims for Noise Induced Hearing Loss (NIHL) in the Canadian Armed Forces (CAF) supports the need to review and upgrade current hearing conservation practices.
The rise of these escalating costs and the need to protect the military personnel when training in extreme noise conditions has initiated an engineering investigation within the Department of National Defence (DND) and in collaboration with the University of Ottawa, to review the existing standards in the field of hearing protection test and evaluation, to propose technical recommendations and to identify the possible technical problems and gaps impacting the quality of the existing procedures.
This study dealt with the estimation of the protection capability of Hearing Protection Devices (HPDs) in the case of high-level impulse noise from small firearms weapons that are a particularly damaging source of noise in military environments, representing an important cause of NIHL.
Testing and evaluation based on a system engineering approach have been used in this work introducing:
- A new testing approach, based on ANSI/ASA S12.42-2010, for testing HPDs when the impulse noise is generated by a small firearm; - A new evaluation approach for HPD performance, introducing a characterization approach using a sub-band analysis for dealing with impulse noise generated by a small firearm.
The effectiveness of HPDs, taking into account the physiological human limitations induced by Bone Conduction (BC), is computed by using an innovative method attempting to better prevent the risk of NIHL when using small firearms.
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Watkins, Richard. "The impact of the urban environment on the energy used for cooling buildings". Thesis, Brunel University, 2002. http://bura.brunel.ac.uk/handle/2438/5553.
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Cities are often warmer than their surroundings, and this can lead to more energy being used to cool buildings. This study looks at one city, London, and assesses the impact of the urban environment on the amount of energy used for air-conditioning. There are three main strands to the work. First, it was important to determine just how great the variation in air temperature is, and how this varies through time and through the urban space. Eighty measurement stations were established along radiating lines from the centre of London as far as rural areas. These measured the air temperature simultaneously at hourly intervals for over a year. Second, to support the main data acquisition, short-term tests within London looked at specific aspects of the urban environment that affect air temperature: the effects of vegetation in parks, and facade colour in streets. Third, the impact on energy use of the measured temperature variation was then determined by using simulation to model a standard building in different urban contexts. The mean heat island intensity was found to vary with distance from the centre of London, and with the local degree of urbanization at any given distance. The maximum intensity reached 8°C on occasion but was more usually 1-2°C in the daytime and 3-4°C at night. The proximity of areas of vegetation, such as parks, to a site was associated with cooler daytime temperatures. The annual cooling load for a standard building at the centre of London was found to be 25% more than at a rural site. However, at the most urban sites over-shadowing reduced the cooling load to 14% more than at a rural site. Heating load decreased towards the centre, but on balance total annual load (for heating and cooling) rose towards the centre to 8.5% more than rural use, and then reduced at the most overshadowed sites. The balance of the effect of urbanization on heating and cooling load depended on the level of internal gain in the building. This study makes a significant contribution to understanding the balance of the impact of urban environments on the energy used for cooling and heating buildings.
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Gelmini, Angelo. "Advanced Analysis and Synthesis Methods for the Design of Next Generation Reflectarrays". Doctoral thesis, Università degli studi di Trento, 2019. http://hdl.handle.net/11572/243312.
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The design of reflectarray surface currents that satisfy both radiation and user-defined antenna feasibility constraints is addressed through a novel paradigm which takes advantage of the non-uniqueness of inverse source (IS) problems. To this end, the synthesis is formulated in the IS framework and its non-measurable solutions are employed as a design DoF.
Thanks to the adopted framework, a closed-form expression for the design of reflectarray surface currents is derived which does not require any iterative local/global optimization procedure and which inherently satisfies both the radiation and the feasibility design constraints. The features and potentialities of the proposed strategy are assessed through selected numerical experiments dealing with different reflectarray aperture types/sizes and forbidden region definitions.
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Ampadu, Boateng Derrick. "Kinetics of Formation and Oxidation of 8-oxo-7,8-dihydroguanine (8oxoG)". Digital Commons @ East Tennessee State University, 2014. https://dc.etsu.edu/etd/2314.
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8-oxo-7,8-dihydroguanine (8oxoG) is one of the most important base lesions formed during oxidative damage of DNA. The aim of the present research was to investigate the effects of DNA concentration, G content, and the nature of oxidizing species on the kinetics of 8oxoG in model DNA solutions by using HPLC. The experimentally obtained yields of 8oxoG were typically in the range of 2-2.5% of total concentration of guanine. The ratios of the rate constant of hole diffusion in DNA to the rate constant of conversion of the hole into 8oxoG (kd/kr) were calculated from the experimental data using the diffusion model of charge transfer in DNA to be in the range of 200-300, in agreement with previously reported kd/kr ratios in the duplex DNA oligonucleotides (GGA)n or (GGTT)n. Our current diffusion model cannot satisfactorily explain the absence of the G content dependence of the 8oxoG yields, which indicates that a more advanced model is required.
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Christidis, Nikolaos. "Halocarbon radiative forcing in radiation and general circulation models". Thesis, University of Reading, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312563.
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Matthysen, Nardus. "Time domain metrology for MeerKAT systems". Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/95963.
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Thesis (MEng)--Stellenbosch University, 2014.ENGLISH ABSTRACT: This work in this study covers a powerful technique to derive propagation and scattering information in an expedient fashion. Expedient because time-domain (TD) data gathers a broad spectrum in a single transmitted pulse. TD has been criticised because of a lack of dynamic range, which has now been overcome by the direct sampling system, RATTY and RTA. This study focuses on the investigation of a TD metrology system, to assist with the characterisation of MeerKAT systems. The elementary components of the system include a fast-rising impulse generator that was coupled with an impulse radiating antenna (IRA). The system was calibrated and tested before practical measurements and preliminary testing in the Karoo were done. For TDmetrology a larger bandwidth accelerates measurements without the loss of accuracy. The pulse generator’s (PG’s) fundamental components are an avalanche transistor and a step recovery diode (SRD), to sharpen the leading edge of the pulse. Improving the rise-time of a pulse increases its bandwidth in the spectrum. The external circuitry around these components is pivotal and it determines the shape, amplitude and rise-time of the pulse. In the course of the investigation, the general circuitry around the PG was improved to obtain the best possible pulse for measurements inside a reverberation chamber (RC) and for measurements in the Karoo. In light of this, a second and third PG source were obtained. For measurements in the Karoo, a larger amplitude pulse was required to increase the spectral content and this is essential for propagation measurements over distance and the shielding effectiveness (SE) of structures. Stacking avalanche transistors allow larger amplitude pulses and it improves the dynamic range of the spectrum. A PG incorporating stacked avalanche transistors, was designed, built and measured to assist with RC and small-scale field measurements in the Karoo. The third PG was bought for the practical measurements in the Karoo. The PG produces kilovolt pulses with pico-second rise-times that extend the spectral range of the current PGs at our disposal. With these PGs, an antenna is required for the radiation of impulse-like transients. The IRA is a high-gain large-bandwidth antenna. The IRA consists of a parabolic reflector, conical-plate transmission lines that are terminated through resistors onto the dish, and a feeding balun. The IRA design was thoroughly discussed and a first model for metrology was designed, measured and optimised. The IRA was also simulated with computation software code, FEKO. Before deployment of theTDsystem, calibration and characterisation measurements are required. The measuring devices used within this study were sampling oscilloscopes and direct sampling systems. The limitations of each device were explored and are discussed. The final measurements that were conducted contribute to work related to the SKA. This incorporated antenna pattern calibration, propagation over distance and the SE of a berm built from Karoo soil. The system investigated the propagation attenuation over the Karoo soil and vegetation, with great promise. A broad spectrum was measured over a few kilometres and compared to free-space loss. The SE of the berm covered the same spectral bandwidth. In this measurement, scattering effects and knife-edge diffraction were observed.
AFRIKAANSE OPSOMMING: Die werk in hierdie studie dek ’n kragtige tegniek wat gebruik kan word om die voortplanting en die verstrooiingsinligting van elektromagnetiese golwe op ’n voordelige manier af te lei. Dit is voordelig, want tydgebieddata versamel ’n wye spektrum in ’n enkele oordraagbare puls. Tydgebied is in die verlede baie gekritiseer omdat dit ’n dinamiese reikwydte kortkom en dit is nou oorwin deur die direkte steekproefnemingstelsel, RATTY en RTA. Hierdie studie fokus op die ondersoek van ’n tydgebiedmetingssisteem en dit help met die karakterisering van MeerKAT sisteme. Die elementêre komponente van die sisteem bestaan uit ’n vinnig-stygende impulsgenerator wat gekoppel is aan ’n impulsuitstralende-antenna (IRA). Die sisteem is gekalibreer en getoets voordat praktiese metings en toetse in die Karoo uitgevoer kon word. Vir tydgebiedmetings versnel ’n groter bandwydte die metings sonder om die akkuraatheid daarvan te beïnvloed. Die pulsgenerator se fundamentele komponente is ’n stortvloedtransistor en ’n stap-herstel diode (SRD) wat die voorpunt van die puls verskerp. Die eskterne stroombaan rondom hierdie komponente is noodsaaklik en dit bepaal die vorm, amplitude en die stygtyd van die puls. Deur die loop van hierdie ondersoek is die algemene stroombaan rondom die puls verbeter, om die beste moontlike puls vir metings binne in die weerkaatsingskamer en vir metings in die Karoo, te verkry. Na aanleiding van dit is ’n tweede en derde pulsgenerator bron verkry. Vir die metings in die Karoo is ’n puls met ’n groter amplitude vereis om die spektrale inhoud te vermeerder. Dit is noodsaaklik vir elektromagnetiese golf voortplantingsmetings oor afstand asook die beskermings effektiwiteit (SE) van die strukture. Stapel-stortvloed transistors skep pulse met groter amplitudes en dit verbeter die dinamiese reikwydte van die spektrum. ’n Pulsgenerator wat gestapelde stortvloedtransistors insluit is ontwerp, gebou en gemeet om te help met metings in die weerkaatsingskamer en kleinskaal veldmetings in die Karoo. Die derde pulsgenerator is gekoop vir praktiese metings in die Karoo. Die pulsgenerator vervaardig kilovolt pulse met pikosekond stygtye, wat die reikwydte van die spektrum van ons huidige puls uitbrei. Hierdie pulsgenerators vereis ’n antenna vir die uistraling van impulsagtige seine. Die IRA is ’n hoë-wins, groot-bandwydte antenna. Die IRA bestaan uit ’n paraboliese weerkaatser, konieseplaat transmissielyne wat deur weerstande op die skottel getermineer word, asook ’n voedings "balun". Die IRA ontwerp is deeglik bespreek en ’n model is ontwerp, gemeet en verbeter. Die IRA is ook gesimuleer met behulp van ’n rekenaarsagtewareprogram, FEKO. Voordat die tydgebiedsisteem benut kan word, moet dit gekalibreer word en karakteriseringsmetings moet ook daarmee uitgevoer word. Die meetinstrumente wat in hierdie studie gebruik is, is steekproefneming-ossilloskope en direkte steekproefneming-sisteme. Die tekortkominge van elke instrument is ondersoek en bespreek. Die finale meting wat uitgevoer is, dra by tot die werk wat geassosieer word met die SKA. Dit behels antennapatroonkalibrasie, voortplanting van elektromagnetiese golwe oor afstand en die SE van ’n "berm"wat gebou is uit Karoo-grond. Hierdie sisteem is gebruik om die voortplantings-verswakking oor die Karoo-grond en plantegroei te ondersoek en dit lyk baie belowend. ’nWye spektrumis oor ’n paar kilometer gemeet en dit is met wrywinglose ruimte vergelyk. Die SE van die "berm"het dieselfde spektrale bandwydte gedek. In hierdie meting is verstrooiingseffekte en mespunt-diffraksie waargeneem.
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Булашенко, Андрій Васильович, Андрей Васильевич Булашенко i Andrii Vasylovych Bulashenko. "Аналіз антени витікаючої хвилі". Thesis, Сумський державний університет, 2016. http://essuir.sumdu.edu.ua/handle/123456789/47186.
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Більшість публікацій з антен витікаючих хвиль відносяться до періодичних
випромінюючих структур. Хоча існує багато робіт з цих типів антен, але дослідження
та розробки в цій області тривають. Удосконалюються методи моделювання та
технології виготовлення, також розширюється область використання таких антен.
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Noor, Azman Nurul Zahirah Binti. "Design of nanostructured polymeric materials for radiation shielding of ionizing radiations". Thesis, Curtin University, 2013. http://hdl.handle.net/20.500.11937/2338.
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This study seeks to provide a novel approach for producing technologically viable new radiation shielding materials to meet the safety requirements for use in medical X-ray imaging facilities. The approach was based on dispersing micro-sized and nano-sized heavy element fillers into polymeric materials using different filler dispersion methods such as melt-mixing, ion implantation and electrospinning. These materials have high potential application for shielding of X-rays in diagnostic radiology purposes.
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Haidekker, Andras. "Radiation modelling in complex three dimensional enclosures". Thèse, Chicoutimi : Université du Québec à Chicoutimi, 1991. http://theses.uqac.ca.
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Xiang, Xuwu. "The delta-Sobolev approach for modeling solar spectral irradiance and radiance". Diss., Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/25801.
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