https://www.um.edu.mt/library/oar/handle/123456789/2070 2026-06-07T17:18:50Z 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. 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. 2023-01-01T00:00:00Z 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. 2026-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/143682 Title: Characterization of PCB fabrication processes for a systematic and efficient design of microstrip circuits Authors: Casha, Owen Abstract: This paper proposes an algorithm to aid in the characterization of a printed circuit board fabrication process before the design of microstrip circuits. By accurately characterizing the electrical properties of a printed circuit board process, one can achieve a systematic and efficient design of microstrip circuits with reduced iteration cycles. The algorithm employs a mean-squared-error optimization technique while making use of de-embedded scattering parameter data from some sample microstrip transmission lines, to estimate printed circuit board electrical parameters such as the tangent loss and the relative permittivity, for a particular frequency range. 2025-07-01T00:00:00Z