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The noise in the Langmuir Probe and Plasma Wave Instrument (LP-PWI) on board ESA:s future Jupiter satellite JUICE (Jupiter ICy Moons Explorer) was investigated. Thermal Johnson-Nyquist noise and shot noise, caused by fluctuations in the probe-plasma currents, were combined with the quasi-thermal noise (QTN) due to thermal fluctuations in the electric field in the plasma, using a small signal equivalent circuit model. The contributions and effects of each of the considered noise sources were examined and compared for a number of representative space plasma conditions, including the cold dense plasma of Ganymede's ionosphere and the hot tenuous plasma out in the Jovian magnetosphere. The results showed that in the cold dense plasma of Ganymede's ionosphere, the antenna was long compared to the Debye length and the quasi-thermal noise had a clearly pronounced peak and a steep high-frequency cut-off. For an antenna biased to 1 V with respect to the plasma, the shot noise due to the ambient plasma was the dominant source of noise. For a an antenna at the floating potential the photoelectron shot noise coalesced with the shot and Nyquist noises of the ambient plasma to form almost a single curve. In the hot tenuous plasma out in Jupiter's magnetosphere, the antenna was short compared to the Debye length and the QTN spectrum was much flatter, with little or no peak at the plasma frequency and a very weak high-frequency cut-off. For an antenna biased to 1 V, the shot noise due to photoelectron emission dominated at Callisto's orbital position whereas at Ganymede's and Europa's orbital positions the Nyquist and shot noises of the ambient plasma particles were the dominant noise components. For an antenna at the floating potential, the shot and Nyquist noises of the ambient plasma also dominated the output noise, except at Europa's orbital position, where the quasi-thermal noise was the largest noise component for frequencies at and above the plasma frequency. The numerical calculations were performed using MATLAB. The code was made available in a Git repository at https://github.com/eliasodelstad/irfuproj_JUICE_noise.

Low-frequency noise is a health concern for workers in industrial workshops; rooms of highly varying size and dimensions, usually containing obstacles (the ‘fittings’). Low-frequency noise can be generated from sources such as reciprocating or rotating machinery, or ventilation systems. As the exposure time to the noise lengthens, workers are increasingly at risk to harmful effects such as hearing loss, communication difficulty, personal discomfort, and even nausea from induced body vibrations. Passive methods of noise control, such as absorption or barriers, generally perform better at high frequencies, but are inadequate at low frequencies. A proposed solution is active noise control, which relies on destructive interference of sound waves to reduce noise levels. However, this depends on phase, and how it is affected when sound waves encounter diffracting obstacles. In addition, the geometrical configuration of the active-control system must be optimized, which can be done using a prediction model. Sound-prediction models can also estimate the decibel level of sound within a given room configuration created by a source and the attenuation provided by the control system. Therefore, it is of interest to develop a model that predicts sound propagation in fitted rooms with phase. In this thesis, sound-pressure fields were investigated in rooms containing parallelepiped obstacles at low frequencies for which the wavelength is comparable to the obstacle dimensions. The geometric theory of diffraction (GTD) was used to model edge diffraction from an obstacle and, thus, the pressure field in shadow regions. A ray-tracing prediction model was improved to consider both the amplitude and phase of sound fields, and also the effects of edge diffraction. To validate the prediction model, experiments were performed in an anechoic chamber where a source and diffracting objects were located. In collaboration with Dr Valeau at the Université de Poitiers in France, a second model based on the finite element method (FEM) was used to compare prediction results. It was found that the phase depends mostly on the direct unblocked source-to-receiver distance. The FEM and experimental results showed that occluding objects cause phase shifts. The implementation of first-order diffraction into the ray-tracing program was successful in predicting shadow zones, thus producing a better prediction of realistic sound fields in rooms with obstacles.

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Delivering high bandwidth to the individual household or small business is currently a major bottleneck in the high speed network, a problem referred to as the last mile issue. Multimode fibre is widely deployed in the last mile for cost reasons. Recently, the tremendous high-speed data transport potential of multimode fibre has been demonstrated by utilizing offset launch techniques and a laser source. However, modal noise, caused by interference among the various propagating modes of a multimode fibre in the presence of mode selective loss, is a significant roblem when a laser source is employed. This thesis investigates several aspects of modal noise for what we believe to be the first time. By utilizing single mode fibre launching, modal noise is measured at different transverse offset launching positions with both continuous wave and pulse waveform input at several different fibre lengths. Modal noise is also measured for both waveforms in conjunction with a multimode optical fibre taper in an “in line” configuration, and timing jitter is investigated for the case of pulse waveform input. Performance improvements are found in some offset positions with the fibre taper in line. / Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2007-11-15 09:37:44.887

Aircraft noise is one of the most controversial environmental concerns in the aviation industry, partly due to the difficulty in harmonizing countries' regulation regarding this issue. The purpose of this thesis is to analyze the ways in which aircraft noise is regulated at the national and international levels, and to compare the legislative responses to aircraft noise issues in Europe and North America. Each of the four main chapters of the thesis takes into consideration a different aspect of the problem. The first chapter describes the objective and subjective ways of measuring aircraft noise. This process is necessary in order to allow the legislation to meet its purpose, namely, to protect the environment, the sources of the aircraft noise, and the effects of the aircraft noise on people. The second chapter describes the evolution of aircraft noise issues at the national levels in the US and throughout the EU, respectively, as well as at the international level, such as at the ICAO. The third chapter analyses the EU Regulation 925/1999, which created tension between the EU and the US due to its alleged discriminatory nature. This thesis examines the arguments of both sides. Finally, the fourth chapter analyses the noise certification standards developed by ICAO, namely the "balanced approach".