https://www.um.edu.mt/library/oar/handle/123456789/2069 Tue, 23 Jun 2026 20:08:54 GMT 2026-06-23T20:08:54Z https://www.um.edu.mt/library/oar/handle/123456789/146097 Title: Design of a VHF guard three-way lumped component unequal high power splitter Authors: Casha, Owen; Cutajar, Joseph; Catania, Luke; Deguara, Joe; Sciberras, Clayton; Zammit, Leslie Abstract: Implementing microstrip or stripline-based power splitters or couplers for high-power VHF applications is typically prohibitive due to the large wavelength, cost considerations, and power handling. This paper revisits and derives the complete set of design equations for a two-way lumped component Wilkinson’s unequal power splitter by using standard circuit theory, rather than odd and even mode analysis, given the non-symmetric nature of the circuit. Using these equations, a simplified and modular design of a three-way unequal high power splitter for the International Aeronautical Emergency Frequency is presented, while considering a lumped component equivalent circuit of a quarter wavelength transmission line section. A measured return loss of less than dB was obtained on each port at a frequency of 121.5 MHz together with an isolation of around dB from the main output port to the other output ports. Thu, 01 Jan 2026 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/146097 2026-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/146079 Title: Record field in a 10 mm-period bulk high-temperature superconducting undulator Authors: Zhang, Kai; Pirotta, Andrew; Liang, Xiaoyang; Hellmann, Sebastian; Bartkowiak, Marek; Schmidt, Thomas; Dennis, Anthony; Ainslie, Mark; Durrell, John; Calvi, Marco Abstract: A 10 mm-period, high-temperature superconducting (HTS) undulator consisting of 20 staggered-array GdBa2Cu3O7−x (GdBCO) bulk superconductors has been fabricated and tested successfully. Each GdBCO disk was machined into a half-moon shape with micro-meter accuracy and shrink-fitted into a slotted oxygen-free copper disk which provided pre-stress and effective conduction-cooling. The HTS undulator prototype, consisting of GdBCO disks, copper disks, and CoFe poles fitted in a long copper shell, was field-cooled magnetized in fields of up to 10 T at 10 K. An undulator field of 2.1 T in a 4 mm magnetic gap was obtained. This field is the largest reported yet for the same gap and period length and exceeds the target value of 2 T for the meter-long HTS undulator scheduled for the hard x-ray I-TOMCAT beamline in the Swiss Light Source 2.0. We have demonstrated that bulk superconductor based undulators can provide significantly improved performance over alternative technologies. Sun, 01 Jan 2023 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/146079 2023-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/144078 Title: Adoption of the LoRa transmission protocol for a low power indoor air quality monitoring system Abstract: Indoor air quality (IAQ) is a critical, often-overlooked public health concern, driving the need for robust Internet of Things (IoT) monitoring systems to optimise building ventilation and energy efficiency. This research addresses two major gaps: the high power consumption of existing wireless sensor nodes and the lack of cost-effective, scalable big data systems for large-scale IAQ monitoring. The core contribution is an ultra-low-power, low-cost wireless sensor node integrating state-of-the-art (SOA) sensors for carbon dioxide, volatile organic compounds, particulate matter, temperature, humidity, and pressure. Utilising dynamic power management, a sleep mode current draw of 270 nA and an average active current of 38 mA is achieved. This translates to an overall energy consumption of approximately 327 μAh per hour, and a projected battery life of 40 months on a 10,500 mAh battery. The achieved power efficiency is significantly better than both comparable academic and commercial SOA devices, even while offering a broader range of sensing capabilities. Complementary to this, the work introduces a cost-effective, LoRa-based big data system for large-scale IAQ monitoring. This system features a novel data forwarding server that calculates Air Quality Index (AQI) and Thermal Comfort Index (TCI) values, storing the enriched data in a document-oriented database. The research also validated a theoretical simulation model for indoor LoRa propagation. Advanced data visualisation was also developed, including a coordinate-based AQI heatmap, enabling smarter building management system (BMS) control. This research establishes a new benchmark for ultra-low-power, modular IAQ technology, coupled with a proven, scalable big data solution, accelerating the adoption of high-density IoT for healthier, smarter buildings. Description: Ph.D.(Melit.) Wed, 01 Jan 2025 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/144078 2025-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/143683 Title: Design and electronic interfacing of FR4 and polyimide PCB-based electromagnetic resonating micro-mirrors Authors: Dimech, Nikolai; Grech, Ivan; Farrugia, Russell; Casha, Owen; Portelli, Barnaby; Micallef, Joseph Abstract: This paper presents the design and fabrication of an electromagnetically actuated PCB-based resonating scanning micro-mirror for LiDAR applications, with optimization targeted towards low-cost fabrication and a high scanning angle. Traditional silicon MEMS-based micro-mirrors, while offering high precision and compatibility with CMOS processing, are limited by fragility at low scanning frequencies and costly fabrication processes. To overcome these challenges, novel alternative polymer-based substrates, namely FR4 and polyimide (PI), were employed to implement PCB-compatible mirror prototypes. Electromagnetic actuation was chosen because it achieves a high scanning angle at low driving voltages and is therefore compatible with modern electronic drive circuitry. The resonant frequency and von Mises stresses were assessed via COMSOL finite element simulations. Various scanning mirror prototypes, each featuring an optical mirror aperture of 10 mm by 10 mm, were fabricated using two different materials: 0.3 mm-thick FR4 and polyimide substrates. Different electromagnetic coil structures, embedded on the mirror plate, were evaluated with the aim of optimizing the scanning performance. The magnetic field was generated using neodymium permanent magnets. The performance attained by each prototype is compared and discussed. The scanning mirrors were designed to have a low resonant frequency in the range of 250 Hz to 550 Hz. The maximum optical scanning angle achieved for the FR4 and polyimide substrates are 31.3° and 52.1°, respectively. The paper also delves into the design of a microcontroller-based electromagnetic actuation and sensing circuitry of the mirror. Custom electronic circuitry comprising a low-power STM32L432KC microcontroller, H-bridge motor drivers for mirror actuation, and INA241-based coil voltage and current sensing was designed for this purpose. The coil voltage and current sensing circuitry enable the eventual real-time sensor less angular position feedback of the micro-mirror. Thu, 01 Jan 2026 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/143683 2026-01-01T00:00:00Z