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Alignment of a Ferroelectric Nematic Liquid Crystal on Surfaces Treated with Obliquely Evaporated SiO2

(2025) Grönfors, Ebba

A nematic liquid crystal is an orientationally ordered liquid where molecules align along a local director but with no polar order. The material RM734 is one of very few discovered substances that can assume the ferroelectric nematic phase, a liquid crystal phase first practically realized in 2017 where the director has not only an orientation, but also a direction. This thesis qualitatively describes the alignment of RM734 in the nematic and ferroelectric nematic phase on a surface treated with oblique evaporation of SiO2. The alignment is studied by means of a thin cell where one surface has been treated with oblique evaporation of SiO2 and the opposite surface is covered by a polymer which has been rubbed to achieve circular boundary conditions. The alignment is revealed by the formation and behavior of domains, depending on the local mutual alignment directions on the two surfaces. The domains created in the higher symmetry nematic phase has a large impact on the alignment in the ferroelectric nematic phase. It is found that the material aligns at an azimuthal angle 0◦ < ϕ < 90◦ from the evaporation plane in either of two symmetrical directions approximately in the substrate plane, potentially opening up for the design of devices based on bistable alignment. The angle ϕ depends on both temperature and evaporation angle, and turns out to fixate under certain conditions. This adds a new layer of complexity to the alignment, as time becomes an important factor in its behavior. RM734 is also studied in a cell with parallel non-polar boundary conditions. Using this cell, the behavior of the liquid crystal at the transitions between the nematic and ferroelectric nematic phases is mapped, and a spontaneous twist without a preferred handedness is demonstrated in the ferroelectric nematic phase.

Theory and measurement of low-frequency structure-borne sound in concrete buildings

(2024) Cheng, Jiali

Low-frequency structure-borne sound is a critical issue because this type of noise travels long distances with little attenuation. This has become a growing concern with the advancement of audio technology and loudspeakers. It is especially problematic in spaces like home theatres and concert halls, where it can cause discomfort and long-term health effects for residents, even those located at a distance. Therefore, predicting effective sound insulation in the early building design process is essential. This thesis investigates the behaviour of low-frequency vibrations in a concrete floor within an office building, focusing on the relationship between the propagation speed of bending waves, the loss factor, and the attenuation of vibrations over distance. It is built on the work of Østvik1, who described the correlation between structural reverberation and distance-dependent damping of vibrations of a concrete slab within a building. A theoretical model of vibration decay, based on the propagation speed and the loss factor of the structure, was proposed and validated through vibration measurements. These measurements were conducted at multiple excitation points on both the floor and the wall, with results confirming that the propagation speed of bending waves follows the expected square-root dependence on frequency. A lower propagation speed was observed when the floor was excited on the wall, compared to direct excitations on the floor. The level decay predicted by the model generally followed a logarithmic pattern, with geometric spreading being dominant. More significant decay was observed at higher frequencies than at lower ones. Furthermore, the structural reverberation time was found to decrease with increasing frequency, indicating that the vibrations last longer at low frequencies. The total loss factor also decreased with increasing frequency, suggesting that energy loss per oscillation is greater at low frequencies. These findings provide valuable insights into lowfrequency vibration propagation. Further research with additional excitation and measurement positions is needed to validate the proposed relationship and better understand the variations observed in this study.

Flanking sound transmission over CLT-joints

(2024) Andersson, Eric

Cross-laminated timber (CLT) is a sustainable and efficient building material that has gained popularity due to its high stiffness, low density, and reduced environmental impact. However, predicting low-frequency sound and vibration transmission across CLT joints remains a significant challenge. This thesis focuses on improving the modeling of flanking sound transmission over different CLT joint configurations, using finite element modeling (FEM) validated through experimental measurements. The study involves measurements of vibration reduction index (Kij) for undamped and isolated joint setups. The FEM simulations closely matched experimental trends for non isolated setups, though some discrepancies arose due to possible differences in coupling conditions and measurement resolution. In isolated setups, FEM predictions highlighted limitations in accurately simulating the effect of vibration-isolation brackets, particularly in representing their behavior when fastened to the CLT panels. The results emphasize the need for refined FEM approaches to better model the dynamic behavior of joints and connections in CLT structures. Future work should focus on enhancing joint coupling simulations, modeling of vibration-isolation brackets and optimizing experimental setups to achieve free boundary conditions. Thereby advancing the acoustic performance prediction for CLT constructions.

Gradient descent based adaptive IIR filtering with direct and lattice form filter structures; applied to estimation of a headphone compensation filter and binaural head related transfer functions

(2025) Lendon, Alexander

In acoustic Digital Signal Processing (DSP), Finite Impulse Response (FIR) filters are commonly used due to their stability and ease of design. However, Infinite Impulse Response (IIR) filters offer better frequency resolution at lower filter orders, making them ideal for hardware-constrained applications like portable AR/VR headsets. With advances in computational methods, optimising IIR filters has become straightforward, making it important to compare their performance against traditional FIR filters. This thesis investigates adaptive IIR filtering algorithms using Gradient Descent (GD) methods, applied to both direct form and lattice form filter structures. Lattice form filter structures provide the benefit of an in-built stability test which can guarantee that the produced IIR filter remains stable at each step. This is essential for reliable IIR filter design and allows for further modifications to the optimisation routine. For the studies, the Modified GD direct form and the Simplified Partial Gradient Descent (SPGD) lattice form algorithms were used to model a headphone compensation filter and binaural Head-Related Transfer Function (HRTF), comparing the resulting IIR filters to equivalent FIR filters. Parameter studies on step-size coefficient and filter order were conducted to assess accuracy in both frequency and time domain. The study found that both IIR filter forms reduced order length to 20% of the HRTF filter order and 40% of the compensation filter order, both within a 1 dB accuracy threshold in the magnitude response. This results in reduction in numerical operations of 60% for the HRTF filter and 20% for the headphone compensation filter. This work demonstrates the that significant order reduction is possible using lattice form, gradient decent based adaptive filters. The exact reduction depends on the target filter and requires similar simulations and analysis to those used here.

Enhancing project management and inspection efficiency through advanced data integration in construction projects

(2024) Ali, Isaac; Shahul Hameed, Ashiq Ahmed

The construction industry is increasingly adopting advanced digital tools to enhance project management practices, improve data accuracy, and streamline communication. This master’s thesis investigates the integration of StreamBIM, a Building Information Modeling (BIM) software, with Power BI, a powerful data visualization and analytics tool, to enhance project management within the construction industry. The study focuses on a real-world project exploring the benefits and challenges associated with this technological integration. Through a detailed case study approach, including semistructured interviews and thorough document analysis, the research identifies significant improvements in data management, inspection protocols, and overall project efficiency. The integration allows for advanced data filtering, customized visual representations, and the creation of interactive dashboards, which enhance the ability to monitor progress, identify issues, and make informed decisions. Key findings demonstrate that this integration not only improves the accuracy and timeliness of data but also facilitates better communication and collaboration among project stakeholders. The results highlight the transformative impact of integrating StreamBIM with Power BI, showing marked enhancements in the preparation and planning stages of inspections, standardization and automation of reporting processes, and overall quality control. The study concludes with recommendations for further improving digital tools in construction management, emphasizing the need for comprehensive training programs and the adoption of a model-based construction approach to fully leverage the capabilities of BIM and data visualization technologies. This research contributes to the body of knowledge on BIM integration, offering practical insights and solutions for industry professionals aiming to achieve more efficient and effective project management outcomes.