Les sources infrarouges sont indispensables à la détection locale de gaz dans de nombreux domaines, que ce soit pour l'environnement (détection de polluants et gaz à effets de serre) ou la défense (détection de menaces biologiques et chimiques). Elles sont également nécessaires en tant que mires de calibration pour le développement de caméras multispectrales infrarouges. Pour toutes ces applications, il est nécessaire de disposer de sources performantes, capables d'émettre un rayonnement spécifique dans une direction donnée. L'objectif de cette thèse est de concevoir des sources thermiques infrarouges compactes et à coût modéré, à spectre accordable et à pertes réduites, pouvant être juxtaposées dans un même dispositif. Pour cela, ces travaux s'organisent autour de deux axes. Le premier concerne l'étude de nouveaux matériaux nanostructurés résonants, appelés métamatériaux ou métasurfaces selon les directions de la structuration, permettant de contrôler l'émissivité spectrale et spatiale afin de maîtriser la réponse spectrale en tout point. Cette étude repose à la fois sur des simulations numériques et sur des mesures expérimentales et démontre le potentiel de ces résonateurs pour la conception de sources thermiques accordables. Cependant, ces matériaux étant composés de métal, ils présentent des pertes par absorption dans l'infrarouge qui limitent leurs performances. Le deuxième axe de recherche est alors de gérer les pertes liées à l'utilisation de métaux grâce à une ingénierie des champs dans des métamatériaux, menant à des émissions spectralement très fines. Les résultats obtenus sur ce contrôle des pertes ouvrent de nombreuses perspectives pour tout le domaine des métamatériaux. / Infrared sources are essential for local gas detection for civil applications (detection of pollutant and greenhouse gas) or military applications (detection of chemical and biological threats). They are also used as calibration targets for the development of multispectral infrared cameras. For these applications, the sources must be efficient and able to emit a specific light in a given direction. The aim of this thesis is to develop infrared thermal emitters with the following features: low cost with a compact volume, with a tunable spectral response and low losses, able to be juxtaposed on the same device. This work begins with the study of new resonant nanostructured materials, called metamaterials or metasurfaces according to the direction of the structuration, that spectrally and spatially control the emitted light up to the wavelength scale. This study relies on numerical simulations and experimental measurements and demonstrates the potential of these resonators as tunable thermal sources. However, due to the use of metals in these materials, their performance is limited by metal losses. The second study of this work is then to deal with these losses thanks to a field engineering in metamaterials, leading to very narrow spectral responses. The results on this loss control open up promising breakthroughs in the plasmonic and metamaterials field

Enhanced field emission (EFE) presents the main impediment to higher acceleration gradients in superconducting niobium (Nb) radiofrequency cavities for particle accelerators. The strength, number and sources of EFE sites strongly depend on surface preparation and handling. The main objective of this thesis project is to systematically investigate the sources of EFE from Nb, to evaluate the best available surface preparation techniques with respect to resulting field emission, and to establish an optimized process to minimize or eliminate EFE. To achieve these goals, a scanning field emission microscope (SFEM) was designed and built as an extension to an existing commercial scanning electron microscope (SEM). In the SFEM chamber of ultra high vacuum, a sample is moved laterally in a raster pattern under a high voltage anode tip for EFE detection and localization. The sample is then transferred under vacuum to the SEM chamber equipped with an energy-dispersive x-ray spectrometer for individual emitting site characterization. Compared to other systems built for similar purposes, this apparatus has low cost and maintenance, high operational flexibility, considerably bigger scan area, as well as reliable performance. EFE sources from planar Nb have been studied after various surface preparation, including chemical etching and electropolishing, combined with ultrasonic or high-pressure water rinse. Emitters have been identified, analyzed and the preparation process has been examined and improved based on EFE results. As a result, field-emission-free or near field-emission-free surfaces at ~140 MV/m have been consistently achieved with the above techniques. Characterization on the remaining emitters leads to the conclusion that no evidence of intrinsic emitters, i.e., no fundamental electric field limit induced by EFE, has been observed up to ~140 MV/m. Chemically etched and electropolished Nb are compared and no significant difference is observed up to ~140 MV/m. To address concerns on the effect of natural air drying process on EFE, a comparative study was conducted on Nb and the results showed insignificant difference under the experimental conditions. Nb thin films deposited on Cu present a possible alternative to bulk Nb in superconducting cavities. The EFE performance of a preliminary energetically deposited Nb thin film sample are presented. / Ph. D.

This thesis relates to the feasibility of monitoring dental implants using the transmission of Acoustic Emission (AE) from an intra-oral source to a sensor mounted on the patient’s face. A number of in vitro and in vivo experiments have been carried using different AE sources on teeth and dental implants with the ultimate aim of defining the characteristics of the AE signatures in the time- and frequency-domains that are affected by the implant-bone interface. An initial feasibility study was carried out to assess the transmission of simulated AE signals through human teeth and hard and soft tissues by biting on different types of hard food. The tests demonstrated that the transmission of AE signals through human tissues was feasible. However, the source was not reproducible. Further preliminary experiments were carried out to assess the transmission of AE in various dental materials as well as in bone and bone-implant combinations in various states of hydration. The main systematic body of work centred around establishing whether AE signals could discriminate between implants with different amounts of contact with bone. AE signals were generated by applying a standard impulse source through a specially-designed abutment onto dental implants of various sizes (large and small) inserted in bovine ribs under tight and loose fitting conditions. The findings suggested that this simple transmission test was able to assess the quality of the contact between the implant and the bone in the in vitro situation and that it might be possible to extend this to the clinical environment. The (standard) pencil lead break method was not suitable for use intra-orally, so a more suitable source for in vivo testing needed to be developed. After considering various options a continuous source (based on an air jet) was developed and this was applied to dental implants in the same set of systematic tests as for the pencil lead source. The analysis revealed that the air jet source was a little better at discriminating between the various implant contact conditions. Finally, an in vivo study was conducted to assess the characteristics of the transmitted AE form air jet source applied to the dental implants of a number of volunteers. The findings demonstrated that the AE transmission through the implants, soft and hard tissues using an air jet source was feasible, with the degree of transmission depending on a number of variables, some related to the patients themselves and some related to other, tractable engineering factors. The overall conclusion of the work is that the technique is very likely to be successful for monitoring implant stability, and is feasible to apply with minimum invasion to patients whose implants have been newly installed. An in vivo study in which the test is applied to patients during the stages of stabilisation of their implants is required in order to validate the technique.

Spectroscopic investigations have been carried out on hollow cathode discharges adapted from laser technology for use as a spectroscopic light source and the argon inductively coupled plasma (ICP) as an excitation source for nonmetal emission. High and low voltage aluminum and copper hollow cathode discharges were studied as a source of ionic and resonant atomic metal emission. The high voltage versions achieve strongly positive current-voltage behavior through utilization of the obstructed discharge phenomenon. The current-pressure-intensity-voltage relationships for low and high voltage copper hollow cathode discharges were studied with the inert gases He, Ne, Ar, Kr, and Xe. The intensity for copper resonant atomic emission with the fill gases Ar, Kr, and Xe improved relative to neon in the high voltage lamp when compared to the low voltage lamp. Absorption measurements through the cathode bore show the ground state atom density to increase with the atomic weight of the fill gas at any given level of intensity, at the fill gas pressure yielding highest resonant atomic copper emission. The estimated ion/atom intensity ratio is increased with fill gases which have metastable or ionization energies greater than the excitation energy of the ion transition. A copper hollow cathode lamp incorporating a short positive column discharge in front of the cathode opening was investigated for its lineshape as measured spectroscopically and by its atomic absorption sensitivity. Incorporation of this positive column allowed higher intensities to be obtained at the same line quality as a commercial hollow cathode lamp. An enlarged cathode volume also improves the lineshape at a given intensity. Inductively coupled plasma spectra for the elements C, O, N, Cl, P, S, and Br were obtained in the vacuum ultraviolet utilizing a vacuum polychromator and SWR film. The detection limit for injected O₂ and N₂ detected electronically by the VUV emissions is 1.3 and 0.9 micrograms respectively with this system. A VUV filter photometer was utilized for oxygen and phosphorus analysis. The detection limit for injected oxygen was 1 microgram with this photometer; the detection limit for phosphorus as inorganic phosphate in aqueous solution is 10⁻³ M. The bandpass of the photometer limits its selectivity.

The aim of this project is to evaluate the possibility to integrate, in terms of energy, the future Nya Studenternas IP and Uppsala University Hospital. The focus is on integration of thermal energy solutions. To cover the cooling demand a seasonal snow storage and the use of cooling machines is studied. For the heat demand a joint heat storage is investigated which is heated partly with the excess heat from cooling machines. The environmental impact in terms of CO2 emissions is investigated. A conclusion drawn from the project is that the use of district heating and cooling of Nya Studenternas IP and the Uppsala University Hospital could be reduced in several ways by integrating the energy systems of the two facilities. For instance, with the support of a seasonal snow storage and cooling machines for cooling, and heat obtained from the cooling machines for heating, the emissions of CO2 could be reduced with 36% based on a Nordic electricity mixture. Out of the suggested integrated energy solutions the most efficient when it comes to reducing CO2 emissions is cooling and heating through cooling machines with a capacity of reducing the CO2 emissions of 20.6 %.

Barkhausen emission (B.E.) and Magneto-acoustic emission (M.A.E.) can be detected from specimens in a magnetic field varying at a few millihertz. Comparison of the two signals can indicate the nature of the domain walls responsible for the activity at any particular field. In order to characterize a specimen the strength of the emissions around the hysteresis loop are measured together with the distribution of Barkhausen event sizes. This technique has been used to measure the effects of: (A) Microstructure. Both B.E. and M.A.E. are sensitive to dislocations, and the effects of cold-working and its removal by isochronal annealing has been studied in alpha-iron. A simple model of domain wall pinning is presented which enables the dislocation density to be estimated. M.A.E. and B.E. are also sensitive to the growth of precipitates in Incoloy 904 alloy and, for a certain regime of sizes, can potentially be used to monitor the precipitate diameter. B.E. is sensitive to smaller precipitates (-100 nm) than M.A.E. but, unlike M.A.E., its dependence on precipitate size is not monotonic. An understanding of the signal dependence is obtained from Lorentz microscopy. (B) Radiation damage. The sensitivity of B.E. and M.A.E. to radiation damage is quite small by virtue of the small size of defects present. Nevertheless measurements on neutron irradiated alpha-iron specimens in several microstructural states indicate: (a) an accelerated recovery from the cold-worked condition on isochronal annealing and (b) dissolution of nitrides and carbides which formed in preparatory heat treatments. Measurements on a neutron irradiated iron-copper alloy which was subsequently isochronally annealed indicated effects which were consistent with: (a) removal of dislocation loops formed during irradiation at 550°C and (b) growth of precipitates (probably copper) at 600°C which presumably formed during the irradiation, (i.e. the effect was smaller in unirradiated control specimens). These results suggest that B.E. and M.A.E. might be useful tools for the characterization of radiation effects. (C) Tensile stress. Both B.E. and M.A.E. are sensitive to applied tensile stress and measurements on a number of different materials indicate that the dependence of M.A.E. is monotonic (except in nickel) whereas that of B.E. is generally quite complex. Since the microstructural and stress dependences are often interrelated it would be difficult to use the technique to measure say residual stress in a practical material unless the exact condition of the microstructure could be determined. Consequently B.E. and M.A.E. were measured from mild steel specimens (4360 steel) which had recieved a number of different heat treatments. The effects of applied tensile stress on the amplitude and shape of the B.E. and M.A.E. profiles were investigated with a view to be able to use the M.A.E. to measure stresses without prior knowledge of the microstructure. It was found that certain parameters in the signal profile were much more strongly dependent upon the stress than on the microstructure for many of the material conditions. Therefore M.A.E. is potentially useful for residual stress measurements.

published_or_final_version / Chemistry / Master / Master of Philosophy

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