Дисертації з теми "Radio waves (Theory)"
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1
Weidt, Sebastian. "Towards microwave based ion trap quantum technology." Thesis, University of Sussex, 2014. http://sro.sussex.ac.uk/id/eprint/48893/.
Повний текст джерелаАнотація:
Scalability is a challenging yet key aspect required for large scale quantum computing and simulation using ions trapped in radio-frequency (rf) Paul traps. In this thesis 171Yb+ ions are used to demonstrate a magnetic field insensitive qubit which has a measured coherence time of 1.5 s, making it an ideal candidate to use for storing quantum information. A magnetic field sensitive qubit is also characterised which can be used for the implementation of multi-qubit gates using a potentially very scalable scheme based on microwaves in conjunction with a static magnetic field gradient instead of using lasers. However, the measured coherence time is limited by magnetic field fluctuations and will prohibit high fidelity gate operations from being performed. To address this issue, the preparation of a dressed-state qubit using a microwave based stimulated rapid adiabatic passage (STIRAP) pulse sequence will be presented. This qubit is protected against the noisy environment making it less sensitive to magnetic field fluctuations. The lifetime of this qubit is measured to demonstrate its suitability for storing quantum information. A powerful method for manipulating the dressed-state qubit will be presented and is used to measure a coherence time of the qubit of 500 ms which is two orders of magnitude longer compared to the magnetic field sensitive qubit. It will also be shown that our method allows for the implementation of arbitrary rotations of the dressed-state qubit on the Bloch sphere using only a single rf field. This substantially simplifies the experimental setup for single and multi-qubit gates. Furthermore, this thesis will present a experimental setup capable of successfully operating microfabricated surface ion traps. This setup is then used to operate and characterise the first two-dimensional (2D) lattice of ion traps on a microchip. A unique feature of the microfabrication technique used for this device is the extremely large voltage that can be applied which allows long ion lifetimes along with large secular frequencies to be measured, demonstrating the robustness of this device. Rudimentary shuttling between neighbouring lattice sites will be shown which could be used as part of a efficient scheme to load a large lattice of ions. One of the many applications of a 2D lattice of ions lies in the field of quantum simulations where many-body systems such as quantum magnetism, high temperature superconductivity, the fractional quantum hall effect and synthetic gauge fields can be simulated. It will be shown how making only minor modifications to the microchip the ion-ion separation can be reduced sufficiently to offer an exciting platform for the successful implementation of 2D quantum simulations. A theoretical investigation on the optimal 2D ion trap lattice geometry will also be presented with the aim to maximise the ratio of ion-ion coupling strength to decoherence from motional heating of the ions and to laser induced off-resonant coupling.
2
Seguin, Sarah Ann. "Detection of low cost radio frequency receivers based on their unintended electromagnetic emissions and an active stimulation." Diss., Rolla, Mo. : Missouri University of Science and Technology, 2009. http://scholarsmine.mst.edu/thesis/pdf/Seguin_09007dcc80708216.pdf.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--Missouri University of Science and Technology, 2009.Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed November 23, 2009) Includes bibliographical references.
3
Pham, Edward Carleton University Dissertation Engineering Electrical. "SER prediction for transmission of PSAM 16-QAM in frequency selective fading channels." Ottawa, 1992.
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4
Karlsson, Roger. "Theory and Applications of Tri-Axial Electromagnetic Field Measurements." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-5916.
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5
Gordon, Matthew D. "A uniform theory of diffraction approach to determine endfire glide slope performance in the presence of ground plane irregularities." Ohio : Ohio University, 1994. http://www.ohiolink.edu/etd/view.cgi?ohiou1176926845.
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Rushton, Elliott C. "Predicting the effects of shadowing and scattering from planar surfaces on localizer course structure using geometrical optics and the uniform theory of diffraction as implemented in the near zone basic scattering code." Ohio : Ohio University, 1994. http://www.ohiolink.edu/etd/view.cgi?ohiou1178731752.
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Cui, Huajian. "Extraction of input parameters for the theory of radiative energy transfer using deconvolution." Thesis, University of South Wales, 2009. https://pure.southwales.ac.uk/en/studentthesis/extraction-of-input-parameters-for-the-theory-of-radiative-energy-transfer-using-deconvolution(4eb05b79-5ef1-4a06-8cba-471d9fb82431).html.
Повний текст джерелаАнотація:
The ever growing application of wireless communication systems requires accurate models for characterising radiowave propagation when affected by the presence of a variety of obstacles. In particular if the obstacles take the shape of vegetation volumes, like single trees or groups of trees and are present in the radio path, they give rise to absorption and scattering of radio signals. This thesis presents a literature review of common models for radiowave propagation through vegetation, the theory of Radiative Energy Transfer (RET) is one of these models and provides an accurate analysis of radiowave propagation through a vegetation media. Extensive measurements have been designed and conducted in a controlled indoor environment to provide valuable measurement data for later development of deconvolution approaches. It can be shown that the measured directional spectra are convolution products of the phase function pattern and the receiver antenna radiation patterns, which impacts determination of the RET input parameters. Consequently, in order to achieve more accurate determination of the RET input parameters, the adverse influence caused by receiver antenna radiation patterns have to be removed from measured directional spectra by implementing a process of deconvolution. This thesis provides successful implementation of two iterative based deconvolution techniques on the measurement directional spectra. To the author's knowledge, this is its first kind of application to eliminate distortion caused by the receiver antenna radiation pattern during measurements. This thesis reports a number of novel approaches. These include the further development and extension of deconvolution techniques such as combining the Bennia-Riad criterion and an error function to determine optimal parameters, as well as using pre-filtering techniques to improve the deconvolution results. Development of clearly defined criteria based on the knowledge of the central-limit theorem and discussion of loss of information avoidance during convolution is another novel contribution. Further novelty lies in the modification of the two methods to suit implementation on the measurement data from radiowaves impacting on vegetation volumes. As a result of these refinements, extracted RET input parameters from the restored patterns after applying the deconvolution processes show evident improvements compared to those extracted from directly measured patterns. Early stage results of this project are published in the IEEE Proceedings on Next Generation Applications, Services and Technologies.
8
Enjamio, Cabado Cristina. "Dynamic microscale rain structures and their application to millimetre wave radio communication systems." Thesis, University of Portsmouth, 2006. https://researchportal.port.ac.uk/portal/en/theses/dynamic-microscale-rain-structures-and-their-application-to-millimetre-wave-radio-communication-systems(b3d41210-0c79-4a3e-8d91-f4d1d6f5f8de).html.
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9
Aloi, Daniel Nicholas. "Development and verification of a mathematical model to investigate the effects of earth-surface-based multipath reflections at a differential global positioning system ground reference site." Ohio : Ohio University, 1999. http://www.ohiolink.edu/etd/view.cgi?ohiou1175264170.
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10
Mehrotra, Prateek. "High Aspect Ratio Lithographic Imaging at Ultra-high Numerical Apertures: Evanescent Interference Lithography with Resonant Reflector Underlayers." Thesis, University of Canterbury. Electrical and Computer Engineering, 2012. http://hdl.handle.net/10092/6935.
Повний текст джерелаАнотація:
A near-field technique known as evanescent interferometric lithography allows for high resolution imaging. However its primary limitation is that the image exponentially decays within the photoresist due to physical limits. This thesis aims to overcome this limitation and presents a method to considerably enhance the depth of focus of images created using evanescent interferometric lithography by using a material underlay beneath the photoresist.
A key enabler of this is the understanding that evanescent fields couple to surface states and operating within proximity of a resonance, the strength of the coupling allows for considerable energy extraction from the incident beam and redistribution of this energy in a photoresist cavity. This led to the analysis of the Fresnel equations, which suggested that such coupling was in fact the result of an enhanced reflectance that takes place at boundaries of carefully chosen materials. While it is known that metals and lossy dielectrics result in surface plasmon polaritons (SPP) and surface exciton polaritons (SEP) as conventional solutions to the Fresnel reflection equations for the TM polarization of light, there is no such naturally occurring surface state that allows evanescent wave enhancement with the TE polarization of light. Further investigation of the Fresnel reflection equations revealed both for TM and TE that in fact another solution exists that is but unconventional to enhance the reflectivity. This solution requires that one of the media have a negative loss. This is a new type of surface resonance that requires that one of the media be a gain medium; not one in the optical pumped sense but one that would naturally supply energy to a wave to make it grow. This new surface resonance is also a key result of this thesis. Clearly, however this is only a hypothetical solution as a real gain medium would violate the conservation of energy.
However, as it is only the reflectance of this gain medium that is useful for evanescent wave enhancement, in fact a multilayered stack consisting of naturally occurring materials is one way to achieve the desired reflectivity. This would of course be only an emulation of the reflectivity aspect of the gain medium. This multilayered stack is then an effective gain medium for the reflectivity purposes when imaging is carried out at a particular NA at a particular wavelength. This proposal is also a key idea of this thesis. At λ = 193 nm, this method was used to propose a feasible design to image high resolution structures, NA = 1.85 at an aspect ratio of ~3.2. To experimentally demonstrate the enhancements, a new type of solid immersion test bed, the solid immersion Lloyd's mirror interference lithography test-bed was constructed. High quality line and space patterns with a half-pitch of 55.5 nm were created using λ = 405 nm, corresponding to a NA of 1.824, that is well in the evanescent regime of light. Image depths of 33-40 nm were seen. Next, the evanescent image was coupled to an effective gain medium made up of a thin layer of hafnium oxide (HfO) upon silicon dioxide (SiO2). This resulted in a considerable depth enhancement, and 105 nm tall structures were imaged.
The work in this thesis details the construction of the solid immersion lithography test-bed, describes the implementation of the modeling tools, details the theory and analysis required to achieve the relevant solutions and understanding of the physical mechanism and finally experimentally demonstrates an enhancement that allows evanescent interferometric lithography beyond conventional limits.
11
Porwal, Anmol. "Drivers of Australian merger waves industry shocks, mis-valuation, and capital liquidity : a thesis submitted to Auckland University of Technology in partial fulfilment of the requirements for the degree of Master of Business (MBus), 2008." Click here to access this resource online, 2008. http://hdl.handle.net/10292/648.
Повний текст джерелаАнотація:
The purpose of this thesis is to test the extended industry shock hypothesis, which accounts for a macro-economic capital liquidity element, in determining the drivers of merger waves. Various theories have been extended by the literature and these are broadly classified under the neo-classical theory of merger waves and the behavioural theory of merger waves. Behavioural theories have explained merger waves by taking into account the psychology of stock markets and the occurrence of merger waves during a stock market boom. The industry shock hypothesis (a neo-classical theory) however, argues that merger waves are due to the clustering of industry shocks that affect an industry’s operating environment. Along with this shock, the mis-valuation caused by a stock market boom increases asset values, thereby lowering transaction costs and hence increasing capital liquidity in the economy. This capital liquidity factor causes merger waves to cluster even if industry shocks do not. The findings in this study show that industry level merger waves exist in Australia and they occur when there is sufficient capital liquidity in the economy. The industry shock variables are found to be insignificant; however they do improve the explanatory power of the explanatory variables used in predicting the start of a merger wave. The mis-valuation variables used in this study: market-to-book ratio, 3-year return and standard deviation of the 3-year return, are insignificant and do not have any explanatory powers in predicting the start of a merger wave. Merger and acquisition announcements made to acquire Australian firms listed on the Australian Stock Exchange (ASX), are collected and analysed for the period from 1996 to 2007. The methodology used in this study is adopted from Harford (2005), which uses legit models to predict the start of merger waves. The explanatory variables are also adopted from Harford’s (2005) study and include proxies for mis-valuation, industry shock and capital liquidity. Overall, the results obtained for the Australian merger and acquisition data are inconclusive as to whether industry shocks because industry merger waves as Harford (2005) documented for the US merger and acquisition data. However, industry level merger waves do exist, as there is clustering in time of firm-level mergers within industries. Moreover, sufficient capital liquidity must be present to accommodate the necessary transactions.
12
Daniele, Norbert. "Étude d'un système de transmission radio courte portée à 60 GHz par étalement de spectre." Grenoble INPG, 1995. http://www.theses.fr/1995INPG0145.
Повний текст джерелаАнотація:
Nous considerons dans ce memoire le probleme des transmissions radio numeriques de courte portee d'exterieurs a 60 ghz. Dans cette gamme de frequence, nous avons montre theoriquement et constate experimentalement, grace a la realisation d'un sondeur de canal radio, que les conditions de propagation etaient tres difficiles. Cependant, des phenomenes de reflexion et plus rarement de diffraction permettent d'etablir des liaisons hors visibilite, mais on se heurte alors aux degradations induites par la propagation multi-trajets. Pour combattre ces degradations, nous avons mis au point un couple emetteur-recepteur a etalement de spectre par sequence directe a 59,45 ghz utilisant en reception un filtre adapte a ondes acoustiques de surface. Ce systeme permet de tirer profit de tous les trajets de propagation, tout en assurant une grande discretion des liaisons puisque la densite spectrale de puissance emise est etalee sur une large bande. Les mesures de liaisons numeriques a 256 kbit/s realisees confirment les difficultes de propagation et tout particulierement dans un environnement rural ou les taux d'erreurs de bit (teb) sont rarement acceptables. En milieu suburbain et urbain la presence de reflecteurs favorise les echos ce qui devrait permettre dans une structure cellulaire de couvrir des zones dont le diametre maximal est compris entre 150 et 200 m. Moyennant une optimisation des parametres de modulation et l'elaboration d'une version numerique du filtre a ondes de surface, le systeme de transmission presente dans ce memoire constituera une excellente solution pour la realisation des futures liaisons de proximite. L'optimisation des parametres doit etre facilitee a court terme par l'emploi des outils de simulation decrits en derniere partie de cette these. L'incertitude sur l'avancement des technologies integrees en ondes millimetriques demeure aujourd'hui un frein
13
Herbert, Steven John. "Wireless communication in vehicles." Thesis, University of Cambridge, 2015. https://www.repository.cam.ac.uk/handle/1810/280675.
Повний текст джерелаАнотація:
There is an increasing interest in the deployment of wireless communication systems in vehicles. The motivation for this work is to provide a fundamental characterisation of the in-vehicle Electromagnetic (EM) wave propagation environment, and to demonstrate how this can be used to aid the deployment of wireless communication systems in vehicles. The fundamental characterisation of the in-vehicle EM wave propagation environment presented in this dissertation yields a number of useful outcomes. The instantaneous impulse response of the in-vehicle channel is characterised, which is presented in the form of a statistical model for arriving rays. Noticing that it is impractical to undertake a full statistical characterisation of the time-varying impulse response, the time variation of the in-vehicle channel is instead characterised as a Doppler spread. This approach provides parameters which are sufficient to perform an information theoretic analysis to lower bound the capacity of the in-vehicle channel. For typical operating conditions, it is found that the channel capacity is approximately equal to that of the same channel with perfect channel state information available at the receiver. Having established the fundamental EM wave propagation characteristics for a single in-vehicle wireless channel, the EM properties of the cavity itself are characterised. This is achieved through a thorough investigation into the analogy between vehicle cavities and reverberation chambers, specifically considering the quality factor (and hence time constant), EM isolation, and electric field uniformity of typical vehicle cavities. This approach yields the important insight that the root mean square delay spread is approximately the same for all wireless links in a typical vehicle cavity. Also, that the angular spread of energy received at any given location (away from the cavity boundaries) is approximately uniform, and that over short distances the coherence distance is well defined, and hence Multiple Input Multiple Output antenna arrays should work well in vehicles. To what extent a typical wireless system can exploit this characterisation depends on how well the parameters can be estimated by a typical wireless communication system. This is also addressed, specifically investigating the estimation of the cavity time constant, and channel time variation. It is found that both of these can be estimated well using a typical wireless sensor network system.
14
Hee, Sonke. "Computational Bayesian techniques applied to cosmology." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/273346.
Повний текст джерелаАнотація:
This thesis presents work around 3 themes: dark energy, gravitational waves and Bayesian inference. Both dark energy and gravitational wave physics are not yet well constrained. They present interesting challenges for Bayesian inference, which attempts to quantify our knowledge of the universe given our astrophysical data. A dark energy equation of state reconstruction analysis finds that the data favours the vacuum dark energy equation of state $w {=} -1$ model. Deviations from vacuum dark energy are shown to favour the super-negative ‘phantom’ dark energy regime of $w {< } -1$, but at low statistical significance. The constraining power of various datasets is quantified, finding that data constraints peak around redshift $z = 0.2$ due to baryonic acoustic oscillation and supernovae data constraints, whilst cosmic microwave background radiation and Lyman-$\alpha$ forest constraints are less significant. Specific models with a conformal time symmetry in the Friedmann equation and with an additional dark energy component are tested and shown to be competitive to the vacuum dark energy model by Bayesian model selection analysis: that they are not ruled out is believed to be largely due to poor data quality for deciding between existing models. Recent detections of gravitational waves by the LIGO collaboration enable the first gravitational wave tests of general relativity. An existing test in the literature is used and sped up significantly by a novel method developed in this thesis. The test computes posterior odds ratios, and the new method is shown to compute these accurately and efficiently. Compared to computing evidences, the method presented provides an approximate 100 times reduction in the number of likelihood calculations required to compute evidences at a given accuracy. Further testing may identify a significant advance in Bayesian model selection using nested sampling, as the method is completely general and straightforward to implement. We note that efficiency gains are not guaranteed and may be problem specific: further research is needed.
15
Shao, Hui Liu Guosheng. "Assimilation of GPS radio occultation observations." Diss., 2005. http://etd.lib.fsu.edu/theses/available/etd-11142005-161814.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--Florida State University, 2005.Advisor: Guosheng Liu, Florida State University, College of Arts and Sciences, Dept. of Meteorology. Title and description from dissertation home page (viewed Jan. 25, 2006). Document formatted into pages; contains xix, 150 pages. Includes bibliographical references.
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Zhen, Yurong. "Plasmonic properties and applications of metallic nanostructures." Thesis, 2013. http://hdl.handle.net/1911/72071.
Повний текст джерелаАнотація:
Plasmonic properties and the related novel applications are studied on various
types of metallic nano-structures in one, two, or three dimensions. For 1D nanostructure,
the motion of free electrons in a metal-film with nanoscale thickness is confined in
its normal dimension and free in the other two. Describing the free-electron motion at
metal-dielectric surfaces, surface plasmon polariton (SPP) is an elementary excitation
of such motions and is well known. When further perforated with periodic array of
holes, periodicity will introduce degeneracy, incur energy-level splitting, and facilitate
the coupling between free-space photon and SPP. We applied this concept to achieve
a plasmonic perfect absorber. The experimentally observed reflection dip splitting
is qualitatively explained by a perturbation theory based on the above concept. If
confined in 2D, the nanostructures become nanowires that intrigue a broad range of
research interests. We performed various studies on the resonance and propagation
of metal nanowires with different materials, cross-sectional shapes and form factors,
in passive or active medium, in support of corresponding experimental works. Finite-
Difference Time-Domain (FDTD) simulations show that simulated results agrees well
with experiments and makes fundamental mode analysis possible. Confined in 3D,
the electron motions in a single metal nanoparticle (NP) leads to localized surface
plasmon resonance (LSPR) that enables another novel and important application:
plasmon-heating. By exciting the LSPR of a gold particle embedded in liquid, the
excited plasmon will decay into heat in the particle and will heat up the surrounding
liquid eventually. With sufficient exciting optical intensity, the heat transfer from NP
to liquid will undergo an explosive process and make a vapor envelop: nanobubble.
We characterized the size, pressure and temperature of the nanobubble by a simple
model relying on Mie calculations and continuous medium assumption. A novel
effective medium method is also developed to replace the role of Mie calculations.
The characterized temperature is in excellent agreement with that by Raman scattering.
If fabricated in an ordered cluster, NPs exhibit double-resonance features and
the double Fano-resonant structure is demonstrated to most enhance the four-wave
mixing efficiency.