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Ultrasound-based assessment of skin and bone thickness in the temporal bone region
(2026) Steen, Victoria; Gasparetto, Allegra
Hearing loss is a major global health concern, and bone-anchored hearing systems (BAHS) such as the Ponto™ system provide an important solution for patients who cannot benefit from conventional air conduction (AC) hearing aids. Successful implantation, however, depends strongly on the anatomical conditions at the implant site, where both cortical bone thickness and soft tissue thickness play critical roles in implant stability and soft tissue healing. In current clinical practice, bone thickness is typically assessed intraoperatively using a multi-step drilling procedure, while soft tissue thickness is measured manually with a needle and ruler during surgery. Preoperative computed tomography (CT) is therefore reserved mainly for patients with suspected abnormal anatomy, due to the associated ionizing radiation exposure and clinical cost. Ultrasound presents an attractive alternative because it is non-invasive, radiation-free, and widely accessible, and can be performed in the office prior ordering implants and performing the surgery. While previous studies have explored ultrasound-based estimation of either soft tissue thickness or cranial bone thickness individually, limited research has addressed the combined assessment required for preoperative assessment in BAHS implantation. This thesis therefore investigated the feasibility of using ultrasound to simultaneously and site-specifically determine soft tissue and cortical bone thickness in the temporal bone region relevant to implantation of the Ponto™ system. The study was conducted using analytical modelling and numerical simulations of ultrasound wave propagation in a multilayer structure. Different excitation waveforms, operating frequencies, and anatomical configurations were evaluated for their effects on signal amplitude, spatial pulse length (SPL), echo separability, and timeof- flight (ToF) accuracy. The results demonstrated that ultrasound-based thickness determination is technically feasible under the investigated conditions. Across all simulated configurations, consistent interface reflections enabled reliable identification of relevant tissue boundaries. The findings showed that accurate determination of ToF is governed not by signal amplitude or SPL alone, but by the balance between signal strength, temporal compactness, and echo separability. Chirp excitation achieved a favourable combination of high voltage peak and low SPL, while pulse excitation demonstrated comparable overall performance. Stable ToF errors below 2–3 % were achieved in several configurations, with cortical bone consistently exhibiting lower error than soft tissue. The simulations further demonstrated robustness in the presence of blood vessels and secondary reflections, with a selected intermediate-frequency range providing the best compromise between penetration depth and temporal resolution. Overall, the findings indicate that ultrasound has strong potential as a complementary tool for preoperative assessment in Ponto™ system implantation. Although further experimental validation is required, this work establishes a theoretical and numerical foundation for future development of ultrasound-based assessment methods for BAHS.
Development of a Verification Process for Truck Pneumatic Systems
(2026) Falkhage, Cornelia; Graad, Matilda
This thesis investigates the development of a verification process for pneumatic systems in heavy-duty trucks, with a focus on air-leakage detection at the End-of-Line stage. The study was conducted at Volvo Group Trucks Technology & Industrial Division in Tuve, Sweden, and evaluates the feasibility of integrating digital pressure decay measurement equipment to improve quality assurance, reduce operator dependency, and enable data-driven decision-making. A combined methodology was applied, including a literature review, stakeholder interviews, benchmarking across production sites, and experimental testing utilizing PDCA methodology. Key process parameters were assessed through statistical hypothesis testing, including equivalence testing and paired one- and two-tailed t-tests. These were utilized to evaluate the effects of test duration, stabilization time, filling method, and subsystem activation on leakage detection accuracy. The results demonstrate that pressure decay testing can be significantly optimized. Equivalent detection accuracy was achieved with reduced test durations compared to the current 4-minute reference, enabling cycle time reductions of up to 2–3 minutes under controlled conditions. However, the inclusion of a stabilization phase was shown to be critical for reliable measurements due to transient pressure variations caused by thermodynamic effects. The required stabilization time was also found to vary across trucks, supporting the implementation of a dynamic threshold-based approach to balance measurement reliability and efficiency. Furthermore, subsystem activation was shown to influence measured pressure decay, indicating the need to adapt leakage thresholds depending on test conditions. Based on these findings, a standardized verification process with automated OK/NOK decision-making is proposed, integrating digital measurement equipment into the existing production environment. The process improves consistency, enables data collection, and reduces operator dependency. While the concept is technically feasible, further validation is required before full-scale implementation.
Autonomous Fixed-Wing Drone Landing on Maritime Vessels
(2026) Möller, Ludvig; Almqvist, William
To improve the effectiveness of maritime search and rescue (SAR) operations, the Swedish Sea Rescue Society (SSRS) is developing autonomous fixed-wing drones through its Eyes-On-Scene project. While these drones can autonomously launch and loiter over areas of interest, they currently lack automated recovery capabilities. This thesis presents a guidance and navigation framework that enables fixed-wing drones to autonomously land on moving SSRS rescue vessels without requiring modifications to either platform. The system integrates AIS and camera-based tracking through an Extended Kalman Filter to estimate vessel position. A multi-stage landing algorithm is introduced, consisting of follow, descent, and diversion phases, designed to ensure safety under uncertain conditions. The algorithm enables controlled landing velocities and supports flexible approach angles for robust operations. The complete system is tested in a simulated environment under various disturbances, including wind, position, altitude, and speed fluctuations. Simulation results demonstrate high landing accuracy, indicating the feasibility of autonomous landings in realistic SAR scenarios. The results highlight the potential to strengthen SSRS’s autonomous drone capabilities and contribute toward more efficient recovery in future SAR operations.
Automation of a Drone Swarm Surveillance System
(2026) Backman, Sebastian; Hansen, Filip; Hägge Lundberg, Eric; Lilja, Isac; Magnusson, Ludvig; Nyström, Lisa
This thesis addresses the need for a scalable and flexible drone-based surveillance platform for the autonomous vehicle testing industry. The platform should support cooperation between drones from different manufacturers through a unified communication interface and automatically generate missions in response to detected objects. The project was conducted as a collaboration between Chalmers University of Technology, Sweden, and The Pennsylvania State University, USA, for AstaZero, a research and testing facility for automated and connected vehicles. The developed platform integrates a backend system responsible for drone coordination, mission planning, and communication between system components with a web-based operator interface. The interface allows operators to define surveillance areas on an interactive map, monitor live video streams and telemetry data, and manage the generated missions when objects are detected. The system also evaluates available drones based on hardware capabilities and operational status to autonomously select the most suitable one for a selected mission, and determine appropriate flight parameters for effective surveillance coverage. Experimental validation, including on-site testing at AstaZero, demonstrated the platform’s ability to communicate with multiple drones, dispatch missions, stream real-time video, and integrate object detection into the surveillance workflow. Limitations regarding object detection reliability and hardware dependencies were identified during the project. Nevertheless, the project shows the feasibility of a scalable multi-drone surveillance platform for autonomous vehicle testing environments.
Converter interaction stability analysis tools
(2026) Andersson, Rasmus; Rasmusson, Victor
As a result of efforts to reduce greenhouse gas emissions, the use of renewable energy has increased and, with these, power sources being integrated into the power system through power electronic interface devices (PEIDs). The dynamic behavior that PEIDs introduce has resulted in new stability challenges. Multiple cases of undamped oscillations originating from converters interacting with other grid elements has already occurred and understanding the instability mechanism is essential. This thesis investigates methods and tools for converter interaction stability analysis and develops an automated tool for frequency domain stability assessment. Existing open source tools and different methodologies are evaluated with respect to their accuracy, computational efficiency and applicability. Requirements in the area from transmission system operators (TSO) are also reviewed. The tool proposed in this thesis is based on sequence-domain frequency injections with multi-frequency perturbations to improve computational efficiency. Both Single-Input-Single-Output (SISO) and Multiple-input-Multiple-Output (MIMO)-based analysis methods are implemented and compared, including Nyquist-based criterion, disk margin evaluation and passivity-based a valuation. The tool is validated against an existing mathematical framework and benchmarked against already existing tools, as well as tested on a detailed MMC model. The results show that the developed framework provides accurate, fast and detailed results when compared to established tools. The studies performed also show the importance of the perturbation magnitude when it comes to analyzing non ideal systems where insufficient or excessive injection magnitude can lead to noisy measurements or non-linear effects. The comparison between SISO and MIMO methods has provided similar results for a given system. The system under study has been varied to increase cross coupling on the converter admittance, and it has been found that SISO methods can provide inaccurate conclusions regarding system stability. The outcome from the review of the transmission system operator (TSO) requirements related to converter interaction stability is that, in general, there is no suggested method available, except for the Swedish TSO. Typically, the methodology and acceptance criteria regarding converter interaction stability is agreed with TSOs at the start of each project. With regards to stability margins, a more robust approach can be the use of a disk margin, due to its multi-loop capability in a MIMO system and the ability to analyze phase and gain at the same time.