<p>Non-destructive characterization of multi-layered structures that can be accessed from only a single side is important for applications such as well-bore integrity inspection. Collimated beam ultrasound systems are a technology for imaging inside multi-layered structures such as geothermal wells. These systems work by using a collimated narrow-band ultrasound transmitter that can penetrate through multiple layers of heterogeneous material. A series of measurements can then be made at multiple transmit frequencies. However, commonly used reconstruction algorithms such as Synthetic Aperture Focusing Technique (SAFT) tend to produce poor quality reconstructions for these systems both because they do not model collimated beam systems and  they do not jointly reconstruct the multiple frequencies.</p> <p><br></p> <p>In this thesis, we first propose a multi-frequency ultrasound model-based iterative reconstruction (UMBIR) algorithm designed for multi-frequency collimated beam ultrasound systems. The combined system targets reflective imaging of heterogeneous, multi-layered structures. For each transmitted frequency band, we introduce a physics-based forward model to accurately account for the propagation of the collimated narrow-band ultrasonic beam through the multi-layered media. We then show how the joint multi-frequency UMBIR reconstruction can be computed by modeling the direct arrival signals, detector noise, and incorporating a spatially varying image prior.</p> <p><br></p> <p>We also propose a ringing artifact reduction method for ultrasound image reconstruction that uses a multi-agent consensus equilibrium (RARE-MACE) framework. Our approach integrates a physics-based forward model that accounts for the propagation of a collimated ultrasonic beam in multi-layered media, a spatially varying image prior, and a denoiser designed to suppress the ringing artifacts that are characteristic of reconstructions from high-fractional bandwidth ultrasound sensor data.</p> <p><br></p> <p>Results using both simulated and experimental data indicate that multi-frequency UMBIR reconstruction yields much higher reconstruction quality than either single frequency UMBIR or SAFT. In addition, our results demonstrate the capability of our RARE-MACE method to suppress ringing artifacts and substantially improve the image quality over single frequency UMBIR and SAFT.</p>

The research developed a UV Taylor Couette reactor for disinfecting milk as a model opaque fluid. The principal of the reactor was to generate laminar vortices to support efficient mixing and homogenous UV photon distribution. The UV reactor parameters were optimized to generate laminar vortices that were stabilized by modification of the unit with baffles. A model was developed to predict the UV dose required to inactivate model microbes in milk. Through verification trials it was noted the predicted UV dose underestimated that required to support a 5 log cfu reduction of microbes. It was subsequently identified that the deviation from predicted values could be attributed to fat content that enhances the UV inactivation of microbes in milk with proteins providing protection to microbes. In conclusion, the UV Taylor Couette reactor has strong potential for disinfecting opaque fluids although matrix effects need to be considered when undertaking validation trials.

The goal of this project was to develop a measuring method and software code to determine and compare the focal ratio degradation of optical fibers for two different coupling technologies. One of the couplings used a fusing technology to splice the fiber, and the other coupling used a refractive index matching technology. Also, an optical fiber without any cleaving or splicing was used as a reference. A collimated beam test was developed as a method for measuring the focal ratio degradation for these different fiber couplings, and a software code was developed to process the results of the experiment. Using the collimated beam test and software code, the focal ratio degradation was calculated and compared between the couplings, and the results clearly stated that the reference fiber had the least focal ratio degradation. The fusing technology used for splicing the fiber had in comparison the least focal ratio degradation of the two different coupling technologies. The results were as expected and therefore the developed measuring method and software were estimated to have been carried out successfully. However, improvements to the measuring method and parts of the software could be done, especially regarding the background light which was a substantial source of error. In conclusion, the goal of the project was reached. / Inom astronomisk forskning används ofta optiska fibrer som informationslänk mellan teleskop och mätinstrument, eftersom de bidrar till att mätningar blir mer tillförlitliga då vibrationer och yttre miljöfaktorer får en mindre påverkan på resultaten. Inom detta projekt undersöktes ett par olika kopplingar av optiska fibrer och deras ljusförluster inom benämningen FRD (Focal ratio degradation). En mätmetod utvecklades tillsammans med en mjukvara som användes för nödvändiga beräkningar och analyser som ledde till att FRD kunde bestämmas. Metoden som användes kallas collimated beam test och innebar att parallellt ljus skickades in i ena fiberänden, vilket genererade en ring av ljus från den andra fiberänden. Mätningarna utfördes på tre olika fiber: en fiber var klyvd och sedan sammansmält, en annan fiber var klyvd och sedan ihopkopplad med hjälp av en vätska av matchande refraktionsindex och den tredje fibern var inte klyvd och fungerade som referens. Resultaten givna av mätningarna och mjukvaran var som man hade förväntat sig; FRD var minst för referensfibern och som högst för fibern med en koppling där refraktionsindex-matchande vätska användes. Även om det finns goda möjligheter att utveckla och förbättra mätmetoden, påvisades ett godtagbart resultat och målet med projektet ansågs därför vara uppnått.