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Design and performance of resonant cavities for communication systems. The theory and performance of resonant cavities for application-, in mobile radio and base-stations in the VHF and UHF bands are investigated.Adeniran, S. Adekunle January 1984 (has links)
It is often necessary to operate a number of radio communication
channels from a single control room without time-sharing between the
various channels. Here it is necessary to operate a number of transmitters
and receivers simultaneously from the same base station or
mobile unit without interference. The best method to achieve this
has been found in the use of filters inserted in the transmission line
between the antenna and the transmitter(s) on one hand and the receiver(s)
on the other hand.
The basic unit employed in the design of microwave filters is
usually a cavity resonator of which the most important factors are the
Q, insertion loss and resonant frequency. However, a problem which
frequently arises with cavity resonators is the accurate determination
of these resonant characteristics complicated by the presence of coupling
port, materials and various design and geometrical deviations. Such
cavities have been investigated in several cases and the results have
been generalised, but this investigation has been conducted to examine
thoroughly most of the problems being met in present practice. Design
and development of some common resonant structures are considered.
Emphasis is placed on solutions found to special problems especially
regarding complicated boundary conditions. Furthermore, investigation
includes methods for optimising resonant parameters such as insertion
loss and Q, trading of insertion loss with coupled cavity selectivity,
frequency tuning and compensation for frequency variations due to wide
ranges of operating temperatures. By comparing Q values obtained in
practice with theoretical values, it has been possible to establish an
appropriate Q loss budget to as to facilitate accurate prediction of coupled
cavity unloaded Q. A satisfactory agreement between theory and practice
has been obtained.
By application of the results of theoretical analysis and experiment,
it is shown that microwave filters can be designed to have a desired
insertion loss and off-band attenuation slope. Steps leading to
designs of any number of cascaded cavities in a two-port network and,
subsequently, multi-port networks are discussed in detail.
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Improvements to the modelling of radiowave propagation at millimetre wavelengths. In-depth studies are reported on resonance phenomena in the scattering of spherical ice particles, extinction and backscattering properties of clouds and on the absorption and dispersion spectra of atmospheric gases.Papatsoris, Anastassios Dimitriou January 1993 (has links)
Various physical mechanisms that affect radiowave propagation at millimetre
wavelengths are considered. Current modelling weaknesses are highlighted and new
improved models or more appropriate modelling approaches are suggested.
Interference and resonance phenomena in the scattering of spherical ice and water
particles are reviewed. The long standing problem of the numerous resonances
observed in the scattering diagrams of dielectric spheres is answered.
The spatial structure and the physical characteristics of non-precipitable ice and water
clouds are reviewed. Extinction and back scattering calculations for a wide variety of
cloud models over the entire millimetre frequency spectrum are given. Multiple
scattering and the effects of super-large drops in clouds are also dealt with. The
potential of a spaceborne instrument in deducing information about the vertical
structure of various cloud types is examined. Attenuation and reflectivity profiles
resulting from various cloud types are calculated for a nadir pointing fixed beam
millimetre wave radar operating at 94 GHz.
The physics and application of the equation of radiative transfer to millimetre wave
propagation in the earth's atmosphere are given and also is the solution of this
equation for a typical millimetre wave remote sensing application. The theory of
gaseous absorption at millimetre wavelengths is presented and an improved modelling
approach is proposed for the calculation of the absorption and dispersion spectra of
atmospheric gases. The effects of trace gases on communication systems operating at
high altitudes are for the first time reported.
Finally the use of the 60 GHz oxygen absorption band for top-side air traffic
control/navigation and broadband transmission purposes is studied.
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Film Thickness Monitor for the Controlled Evaporation of Vacuum Deposited FilmsGroth, Leonhard 05 1900 (has links)
<p> A thin film thickness monitor has been designed and constructed based on the "mass loading" effect of a resonant quartz crystal. A 6.0 MHz Y-cut crystal, having a theoretical "mass determination sensitivity" of 8.15x10^7 Hz. - cm^2/gm, serves as the sensor element. This sensitivity can be closely approached in practice if the entire active area of the quartz plate is exposed to the evaporant stream. However, due to source, substrate and crystal geometry the "effective" sensitivity of the monitor is only 0.433 of the above value. </p> <p> Both film thickness and deposition rate can be measured by the monitor in terms of equivalent frequency changes. The actual thickness and rates depend upon the density of the evaporant. In the case of silver (density 10.5 gm/cm^3), the monitor measures average thicknesses from several (oA) to 1.36 microns in one single deposition. Each crystal can be used to monitor a total of 4.5 microns of silver before replacement. Deposition rates for silver can be measured from as low as 0.l (oA)/sec to 1360 (oA)/sec. </p> <p> By combining the thickness monitor with apparatus for controlled evaporation, a system was set up which can control film thickness to within 2% and deposition rate to within 5%. </p> / Thesis / Master of Engineering (MEngr)
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The Aerodynamic Excitation of Trapped Diametral Acoustic Modes in Rectangular Ducted CavitiesBolduc, Michael 11 1900 (has links)
The excitation mechanism of trapped diametral acoustic modes within a rectangular cavity-duct system is investigated both numerically and experimentally. The asymmetry inherent within the rectangular geometry introduces a preferred orientation, ensuring the excited diametral modes remain stationary. Three separate cavities are manufactured and tested. This included two asymmetric rectangular cross-sections and one symmetric square cavity. Experimental results indicate that the aeroacoustic responses of the three cavities are dominated by the strong excitation of trapped diametral modes. Numerical simulations indicate that the resolved radial acoustic particle velocity distributions are non-uniform at the upstream separation edge where the formation of vortical structures is initiated. As the cavity became smaller, and more asymmetric, the trapped nature of the acoustic modes decreased with an accompanied increase in the radiation losses and reduction in pulsation amplitude. Observations of the aeroacoustic measurements show evidence of three unique modal behaviours. The first case is the independent excitation of a single stationary mode where specific circumferential sections of the shear layer were excited and initiating the formation of vortical disturbances. These circumferential sections, and distribution of disturbances, were akin to the excited mode shape. The second case involved simultaneous excitation of two stationary modes. This suggested that the shear layer was exciting two modes simultaneously. Neighbouring circumferential sections, at the initial region of the shear layer, were being excited independently and at different resonant frequencies. Finally, a spinning trapped acoustic mode was observed in the symmetric square cavity. Due to the spinning nature, the excited circumferential portions and formation of vortices were non-uniform and rotated with the spinning acoustic mode. This resulted in the formation of a three-dimensional helical structure. / Thesis / Master of Applied Science (MASc)
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Design of a LLC Resonant Converter Module with Wide Output Voltage Range for EV Fast Charging ApplicationsElezab, Ahmed January 2023 (has links)
The move toward electric vehicles (EVs) has a significant impact to reduce greenhouse
gas (GHG) emissions and make transportation more eco-friendly. Fast-charging stations
play a crucial role in this transition, making EVs more convenient for adoption
specifically when driving in long distance. However, the challenge is to create a fast-charging
system that can work with the different types of EVs and their varying power
needs while still being efficient and effective. In this context, this thesis embarks on
this journey by introducing an innovative solution for efficient universal fast charging,
spanning both low voltage and high voltage battery systems.
A novel, configurable dual secondary resonant converter is proposed, which empowers
the charging module to extend its output range without imposing additional
demands on the resonant tank components. This solution addresses the pressing
need for a wide output voltage range in fast-charging standard in the growing EV
landscape.
To ensure optimal performance across a broad voltage and power range, the thesis
employs an analytical model for LLC resonant converters to optimize the resonant
components. This strategic component selection aims to achieve the desired output
voltage and power range while minimizing conduction losses. The proposed topology
and design methodology are rigorously validated through the development of a 10 kW prototype. Furthermore, the study introduces a two degrees of freedom (2DoF) control scheme for the proposed LLC resonant converter with the configurable dual secondary LLC
converter topology. An analytical model is formulated to guide the selection of control
parameters, ensuring coverage of the desired output voltage and power range
without compromising system efficiency. The steady-state analytical model is utilized
for determining optimized control parameters at each operating point within
the converter's output range.
To enhance the charging module's power density and efficiency, a high-frequency
litz-wire transformer design methodology is introduced. The transformer's core size
is optimized to achieve high power density and efficiency, while the winding configuration is chosen to minimize conduction losses. Finite Element Analysis (FEA) simulations validate transformer losses and operating temperatures.
The culmination of this research is the development of a 30 kW charging module
prototype. This prototype features an LLC resonant converter with a configurable
dual secondary and two degrees of freedom control for output voltage control. The
component ratings, estimated losses, and power board design are carefully considered
to create a compact and efficient charging module. Experimental testing across a
universal output voltage and power range con rms the effectiveness of the proposed
solution.
In summary, this thesis presents a comprehensive approach to design of a module
for EV fast charging application addressing voltage range, efficiency, and component
optimization, resulting in the successful development of a high-performance charging
module prototype. / Thesis / Doctor of Engineering (DEng)
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A Measurement of the Neutrino Neutral Current π<sup>0</sup> Cross Section at MiniBooNERaaf, Jennifer Lynne 13 July 2005 (has links)
No description available.
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Search for Resonant Impurities in Bismuth and Bismuth-Antimony Alloys: Lithium, Magnesium, and SodiumOrovets, Christine M. 22 June 2012 (has links)
No description available.
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High Figure of Merit Lead Selenide Doped with Indium and Aluminum for Use in Thermoelectric Waste Heat Recovery Applications at Intermediate TemperaturesEvola, Eric G. 25 June 2012 (has links)
No description available.
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TUNNELING BASED QUANTUM FUNCTIONAL DEVICES AND CIRCUITS FOR LOW POWER VLSI DESIGNRamesh, Anisha 27 June 2012 (has links)
No description available.
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Development of a Si-Based Resonant-Cavity-Enhanced Infrared PhotodetectorGagnon, Adrian J. 04 1900 (has links)
<p>Resonant-cavity-enhanced (RCE) photodetectors have recently attracted attention due to their wavelength selectivity and high efficiency in comparison to conventional photodetectors. The goal of this ongoing research initiative is to develop a Si-based RCE infrared photodetector using inductively coupled plasma chemical vapor deposition (ICP-CVD) as the primary fabrication method. At the current stage of the project, wavelength-selective optical structures have been successfully fabricated using Si/SiO<sub>2</sub> layer pairs. These structures demonstrate sharp transmission peaks at their intended wavelength, making them potentially useful for efficient photodetection. The next phase of the photodetector development process involves using ion implantation to introduce dopants and create the bias.The project also explores the temperature sensing capability of the resonant-cavity structures. The temperature sensitivity tests indicate that the specific type of structure fabricated in this project may be relevant for fiber-optic temperature sensing applications. Additional testing is required to evaluate the performance characteristics of such structures as Fabry-Perot sensors capable of wavelength-encoded temperature measurement.</p> / Master of Applied Science (MASc)
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