Transformers are essential for modern power distribution system. They are efficient and enable the voltages to be transformed up for transportation of electricity and back down for consumer use. The reliability of the transformer is affected by faults and fatigue of the copper. The bigger faults a transformer is subjected to, the shorter life time it will have due to damage to the winding and other parts of the transformer. This thesis investigates if it is possible to characterise the noise made from the windings during a short circuit fault or lightning strike, to see if it can be replicated and if transformers can be diagnosed with the help from the noise. Faults creates forces on the windings, these forces can be so great that the windings collide with each other and in worst case breaks. The sound sources that are interesting are the thermal expansion due to the current, the radial forces and the axial forces acting on the coil. Simulations were made in Comsol multiphysics to see how the currents and forces behaved in a winding. A simplified microphone circuit was built and tested to see if it could detect the noise made from the collisions in the coil. Two microphone types and amplifier circuits were tested to see which ones was most suited for the experiments. The microphone circuit was used to record the sound made from the coils when being compressed. An experiment with a capacitor bank sending a large current pulse through different coils and the noise made from the coil was recorded with a microphone circuit connected to an oscilloscope. The currents are recorded by a computer using the program Picoscope. The capacitor bank was charged to different voltages to get different current amplitudes. A microphone circuit was built and tested so it could detect the sound from the collision. Sound occured with a current pulse with an amplitude of 2 kA, and permanent deformation occured when the amplitude of the current pulse was 4.5 kA. The frequency content of the impact was within the audible spectrum. Possibly even higher frequencies than 20 kHz was present during the fault. The microphone had a bandwidth between 20-20000 Hz, which limits the frequencies that is picked up by the microphone. / Transformatorer är viktiga för det morderna elsystemet. Transformatorer är effektiva och tillåter spänningen att transformeras upp för transport vilket minimerar förlusterna i lendningarna och sedan ned igen för kunder. Tillförlitligheten av transformatorer blir påverkad av fel, felen kan orsaka utslitning av kopparen i lindningarna. Ju större fel som transformatorn blir utsatt för, ju kortare livstid får transformatorn på grund av skada på lindningarna eller andra delar av transformatorn. Denna avhandling undersöker om det är möjligt att karaterisera ljudet från transformator lindningar under ett kortslutningsfel eller blixtnedslag. Felströmmarna skapar krafter på lindningarna, dessa krafter kan vara så stora att lindningarna kolliderar med varandra och i värsta fall går lindningarna sönder. Några intressanta ljudkällor är termisk expansion av kopparen från strömmarna, den radiella kraften på spolen och den axiella kraften på spolen. Simuleringar gjordes i Comsol Multiphysics för att se hur strömmar och krafterna beter sig i transformator lindningarna. En mikrofonkrets byggdes och testades för att se om den kunde detektera ljudet från kollisionerna i spolen. Två olika mikrofontyper och två olika förstärkartyper testades för att se vilka som passade bäst för experimenten. Mikrofonkretsen användes för att spela in ljudet från spolarna. Experimenten gjordes med med hjälp av en kondensatorbank som genererar en strömpuls genom de olika lindningarna/spolarna och ljudet från spolarnas kompression var inspelade av mikrofonkretsen som var inkopplad till ett oscilloskop. Strömpulsen var sparad på datorn med programmet Picoscope. Kondensatorbanken var uppladdad med olika spänningar för att få strömpulser med olika amplituder. Experimenten gjordes på fyra olika spolar, en två varvs spole, en 19 varvs spole, en 40 varvs tätlindad spole och en deformerad 19 varvs spole, för att se om det var skillnad mellan kollisionerna. Ljud uppstod vid en strömpuls med amplituden 2 kA och permanent deformation uppstod vid 4.5 kA. Frekvensinnehållet från kollisionen befann sig inom det hörbara spektrumet. Det fanns möjligen frekvenser över 20 kHz, men mikrofonen hade en bandbredd mellan 20-20000 Hz vilket begränsar de upptagna frekvenserna.

Acoustic and aerodynamic measurements have been carried out on a rotor operating in a planar turbulent boundary layer near a wall for a variety of thrust conditions and yaw angles with respect to the inflow. At the highest thrust condition a strong flow reversal in the wall-rotor tip gap was observed. Average velocity fields filtered by the angular position of the rotor show that the flow reversal is fed by jets of fluid that tend to form below the blade as it passes by the wall. Instantaneous velocity measurements show the presence of strong vortices in the tip gap. These vortices were characterized and found to be both stronger and more numerous on the downstroke side of the tip gap. Additionally, vortices with the same handedness as the bound circulation in the blade were more numerous and only located on the downstroke side of the tip gap. Those with the opposite handedness were found to be only located on the upstroke side. Unexpectedly strong far-field acoustic response at the blade passage frequency at this highest thrust condition and is believed to be due to an interaction of the blade tip with these vortices. At moderate thrust, when the rotor was yawed toward the downstroke side the far field acoustic response at the blade passage frequency was found to increase. The opposite was true as it was yawed toward the upstroke side. At the highest thrust, however the unyawed rotor had the strongest blade passage frequency response which is believed to be due to stronger vortex-tip interaction in this case. / Master of Science

The objective of this research is to develop and design front-end analog circuits for Capacitive Micromachined Ultrasound Transducers (CMUTs) and optical grating MEMS microphone. This work is motivated by the fact that with micro-scaling, MEMS sense capacitance gets smaller in a CMUT array element for intravascular ultrasound imaging, which has dimensions of 70um x 70um and sub pico-farad capacitance. Smaller sensors lead to a lower active-to-parasitic ratio and thus, degrads sensitivity. Area and power requirements are also very stringent, such as the case of intravascular catheter implementations with CMOS-First CMUT fabrication approach. In this implementation, capacitive feedback charge amplifier is an alternative approach to resistive feedback amplifiers. Capacitive feedback charge amplifier provides high sensitivity, small area, low distortion and saving power. This approach of charge amplifiers is also suitable in capacitive microphones where it provides low power and high sensitivity. Another approach to overcome capacitive detection challenges is to implement optical detection. In the case of biomimetic microphone structure, optical detection overcomes capacitive detection's thermal noise issues. Also with micro-scaling, optical detection overcomes the increased parasitics without any sensitivity degradation, unlike capacitive detection. For hearing aids, along with sensitivity, battery life is another challenge. We propose the use of 1-bit front-end sigma-delta ADC for overall improved hearing aid power efficiency. Front-end interface based on envelope detection and synchronous detection schemes have also been designed. These interface circuits consume currents in microampere range from a 1.5V battery. Circuit techniques are used for maximizing linear range and signal handling with low supplies. The entire front end signal processing with Vertical Cavity Surface Emitting Laser (VCSEL) drivers, photodiodes, filters and detectors is implemented on a single chip in 0.35um CMOS process.

Les microphones capacitifs sont des transducteurs réciproques dont les qualités (sensibilité, bande passante et tenue dans le temps) en font des instruments de mesure performants. Couramment utilisés jusqu’à présent en récepteurs dans l’air à pression atmosphérique et à température ambiante, dans la gamme de fréquences audibles, ils sont correctement caractérisés dans ce cadre depuis près de trente ans. Mais aujourd’hui, leur miniaturisation (par procédé MEMS) et leur usage nouveau en métrologie fine (en récepteurs comme en émetteurs) - qui exigent une connaissance précise de leur comportement dans des domaines de fréquences élevées (jusqu’à 100 kHz), dans des mélanges gazeux aux propriétés différentes de celles de l’air et dans des conditions de pression et de température beaucoup plus élevées ou beaucoup plus basses que les conditions standards - nécessitent une caractérisation beaucoup plus approfondie, aussi bien en terme de modélisation qu’en terme de résultats expérimentaux. C’est ainsi que ici -i/ les effets des couches limites thermiques (seules les couches limites visqueuses sont habituellement retenues) sont introduits dans le modèle, ce qui amène dans le chapitre premier à une étude analytique de la diffusion thermique en parois minces (dont la portée dépasse le cadre strict du transducteur), -ii/ l’influence des orifices de l’électrode arrière sur la déformée de la membrane est traitée au départ par une méthode analytique originale, qui permet de traduire les conditions en frontière non uniformes sur la surface de l’électrode sous forme de sources locales virtuelles, associées à des conditions de frontière rendues uniformes (chapitre second), -iii/ des solutions analytiques nouvelles, dépendant à la fois des coordonnées radiales et azimutales, sont obtenues pour le champ de déplacement de la membrane et pour les champs de pression dans les cavités du microphone par usage de théories modales compatibles avec les couplages multiples qui y prennent place (troisième chapitre), -iv/ un modèle de « circuit à constantes localisées » (reporté pour l’essentiel en annexe) est proposé, à des degrés divers de précision, qui permet en particulier d’accéder de façon simple à la sensibilité et au bruit thermique du microphone (fin du quatrième chapitre), -v/ une étude au vibromètre laser à balayage a été réalisée (début du quatrième chapitre), qui permet non seulement de mettre en évidence pour la première fois les déformées de membrane complexes qui apparaissent en hautes fréquences, mais encore de les quantifier et par-delà de valider les résultats théoriques obtenus et donc les modèles proposés (même s’ils restent perfectibles comme indiqué dans la conclusion). / Condenser microphones are reciprocal transducers whose properties (sensitivity, bandwidth and reliability) make them powerful measurement tools. So far, they have been commonly used as receivers in the audible frequency range, in air at atmospheric pressure and ambient temperature, they have been appropriately characterised in this context for nearly thirty years. But nowadays, their miniaturisation (using MEMS processes) and their new use for metrological purposes (as receivers as well as transmitters) require much deeper theoretical and experimental characterisations because they require an accurate knowledge of their behaviour in high frequency ranges (up to 100 kHz), in gas mixtures, whose properties differ from those of air, and under pressure and temperature conditions much higher or much lower than standard conditions. Thus, here, -i/ the effects of the thermal boundary layers are introduced in the model (only viscous boundary layers are usually accounted for), leading, in the first chapter, to an analysis of the thermal diffusion of thin bodies (whose scope is beyond the strict frame of capacitive transducers), ii/ the influence of the holes in the backing electrode on the dynamic behaviour of the membrane is initially handled with an original analytical method which allows expressing the non-uniform boundary conditions at the surface of the backing electrode as fictitious localised sources associated to uniform boundary conditions (second chapter), -iii/ new analytical solutions, depending both on the radial and azimuthal coordinates, for the pressure field and for the displacement field inside the cavities behind the membrane are expressed using modal theories in agreement with the strong couplings which occur between the different parts of the transducer (chapter three), -iv/ "lumped element circuits", which are more or less approximated (presented in the Appendix), more particularly result in expressing and assessing the sensitivity and the thermal noise (end of chapter three), -v/ experimental results, obtained from measurements of the displacement field of the membrane using a laser scanning vibrometer, both highlight and quantify for the first time the complex behaviour of the membrane in the highest frequency range, and finally lead to the validation of the theoretical results and therefore, the models presented here (even if the latter may still be improved as outlined in the conclusion).

Les microphones capacitifs sont des transducteurs réciproques dont les qualités (sensibilité, bande passante et tenue dans le temps) en font des instruments de mesure performants. Couramment utilisés jusqu'à présent en récepteurs dans l'air à pression atmosphérique et à température ambiante, dans la gamme de fréquences audibles, ils sont correctement caractérisés dans ce cadre depuis près de trente ans. Mais aujourd'hui, leur miniaturisation (par procédé MEMS) et leur usage nouveau en métrologie fine (en récepteurs comme en émetteurs) - qui exigent une connaissance précise de leur comportement dans des domaines de fréquences élevées (jusqu'à 100 kHz), dans des mélanges gazeux aux propriétés différentes de celles de l'air et dans des conditions de pression et de température beaucoup plus élevées ou beaucoup plus basses que les conditions standards - nécessitent une caractérisation beaucoup plus approfondie, aussi bien en terme de modélisation qu'en terme de résultats expérimentaux. C'est ainsi que ici -i/ les effets des couches limites thermiques (seules les couches limites visqueuses sont habituellement retenues) sont introduits dans le modèle, ce qui amène dans le chapitre premier à une étude analytique de la diffusion thermique en parois minces (dont la portée dépasse le cadre strict du transducteur), -ii/ l'influence des orifices de l'électrode arrière sur la déformée de la membrane est traitée au départ par une méthode analytique originale, qui permet de traduire les conditions en frontière non uniformes sur la surface de l'électrode sous forme de sources locales virtuelles, associées à des conditions de frontière rendues uniformes (chapitre second), -iii/ des solutions analytiques nouvelles, dépendant à la fois des coordonnées radiales et azimutales, sont obtenues pour le champ de déplacement de la membrane et pour les champs de pression dans les cavités du microphone par usage de théories modales compatibles avec les couplages multiples qui y prennent place (troisième chapitre), -iv/ un modèle de " circuit à constantes localisées " (reporté pour l'essentiel en annexe) est proposé, à des degrés divers de précision, qui permet en particulier d'accéder de façon simple à la sensibilité et au bruit thermique du microphone (fin du quatrième chapitre), -v/ une étude au vibromètre laser à balayage a été réalisée (début du quatrième chapitre), qui permet non seulement de mettre en évidence pour la première fois les déformées de membrane complexes qui apparaissent en hautes fréquences, mais encore de les quantifier et par-delà de valider les résultats théoriques obtenus et donc les modèles proposés (même s'ils restent perfectibles comme indiqué dans la conclusion).

The theme of the master´s thesis is design a microphone preamplifier which uses vacuum tube as a main amplifying element. Part of the work is theoretical assumptions for the optimal design and implementation of peripheral involvement, comparing the properties of components used and the resulting parameters of modeled device. The thesis also includes a proposal of the source unit for supplying all parts of the preamplifier. The results are accompanied by circuit simulations and laboratory measurements of the main parameters of the designed device.

The theme of the master´s thesis is design a microphone preamplifier which uses vacuum tube as a main amplifying element. Part of the work is theoretical assumptions for the optimal design and implementation of peripheral involvement, comparing the properties of components used and the resulting parameters of modeled device. The thesis also includes a proposal of the source unit for supplying all parts of the preamplifier. The results are accompanied by circuit simulations and laboratory measurements of the main parameters of the designed device.

Mechanomyography (MMG) has been proposed as a control modality for alternative access technologies for individuals with disabilities. However, MMG recordings are highly susceptible to contamination from limb movements. Pressure-based transducers are touted to be the most robust to external movement although there is some debate about their optimal chamber geometry, in terms of low frequency gain and spectral flatness. To investigate the question of preferred geometry, transducers with varying chamber shapes were designed, manufactured and tested. The best performance was achieved with a transducer consisting of a low-frequency MEMS microphone, a 4 micron thick aluminized mylar membrane and a rigid conical chamber 7 mm in diameter and 5 mm in height. Furthermore, microphone-derived MMG spectra were found to be less influenced by motion artifact than corresponding accelerometer-derived spectra. However, artifact harmonics were present in both spectra, suggesting that bandpass filtering may not remove artifact influences permeating into MMG frequency bands.

Mechanomyography (MMG) has been proposed as a control modality for alternative access technologies for individuals with disabilities. However, MMG recordings are highly susceptible to contamination from limb movements. Pressure-based transducers are touted to be the most robust to external movement although there is some debate about their optimal chamber geometry, in terms of low frequency gain and spectral flatness. To investigate the question of preferred geometry, transducers with varying chamber shapes were designed, manufactured and tested. The best performance was achieved with a transducer consisting of a low-frequency MEMS microphone, a 4 micron thick aluminized mylar membrane and a rigid conical chamber 7 mm in diameter and 5 mm in height. Furthermore, microphone-derived MMG spectra were found to be less influenced by motion artifact than corresponding accelerometer-derived spectra. However, artifact harmonics were present in both spectra, suggesting that bandpass filtering may not remove artifact influences permeating into MMG frequency bands.

<p>Intake and Exhaust system noise makes a huge contribution to the interior and exterior noise of automobiles. There are a number of linear acoustic tools developed by institutions and industries to predict the acoustic properties of intake and exhaust systems. The present project discusses and validates, through measurements, the proper modelling of these systems using BOOST-SID and discusses the ideas to properly convert a geometrical model of an exhaust muffler to an acoustic model. The various elements and their properties are also discussed.</p><p>When it comes to Acoustic properties there are several parameters that describe the performance of a muffler, the Transmission Loss (TL) can be useful to check the validity of a mathematical model but when we want to predict the actual acoustic behavior of a component after it is installed in a system and subjected to operating conditions then we have to determine other properties like Attenuation, Insertion loss etc,.</p><p>Zero flow and Mean flow (M=0.12) measurements of these properties were carried out for mufflers ranging from simple expansion chambers to complex geometry using two approaches 1) Two Load technique 2) Two Source location technique. For both these cases, the measured transmission losses were compared to those obtained from BOOST-SID models.</p><p>The measured acoustic properties compared well with the simulated model for almost all the cases.</p>