https://www.um.edu.mt/library/oar/handle/123456789/11955 2026-04-15T07:16:15Z 2026-04-15T07:16:15Z https://www.um.edu.mt/library/oar/handle/123456789/144078 2026-02-24T14:19:49Z 2025-01-01T00:00:00Z

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.)

2025-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/132375 2025-02-25T08:59:54Z 2024-01-01T00:00:00Z

Title: Design and fabrication of RF MEMS devices for wide-band VHF applications Abstract: This Ph.D. research work investigates the potential application of PiezoMUMPs technology to the design of a Lateral Bulk Acoustic Piezoelectric MUMPs (LBAW PiezoMUMPs) resonators that can operate in the VHF band. By analysing the effects of resonator size, number of electrode elements, and tether shape on parameters like resonant frequency and Quality factor (Qf). This work is based on analytical, Finite Element simulations, validated by prototype characterisation. Fine tuning through is essential in order to compensate for process related variation, for this reason thermal tuning using both ovenisation as well as on chip electrothermal tuning was investigated. Furthermore, volage tuning was also evaluated. Tuning via ovenisation achieved a tuning range of 300KHz over temperature range of 273 to 573K. Voltage tuning achieved a 30KHz over a range of 1 to 9 V. Electrothermal tuning resulted a 50KHz range for a thermal power of 50mW. This part of the study showed that thermal tuning results in a wider tuning range than voltage tuning. The study also investigates mechanical contact type RF-MEMS switches for VHF band applications, implemented on the same PiezoMUMPs process, in order to achieve a cost-effective wide frequency tuning. In this investigation, several electrostatically actuated switches, having different signal contact profiles were analytically studied and simulated using CoventorWare FEM software. These switches were optimized for different parameters depending on the design geometry and actuator comb fingers. Subsequently, different switch prototype configurations such as 1-way including the deep off option, as well as 2-way structures have been manufactured and characterised. Description: Ph.D.(Melit.)

2024-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/127769 2024-10-21T07:14:40Z 2024-01-01T00:00:00Z

Title: ASIC interface design for resonating micro-mirror MOEMS spectrometer Abstract: In recent years there has been an increased interest in air quality monitoring both at large scale and small scale. One useful tool to identifying different gases in the air is an IR absorption spectrometer. This device measures the attenuation of various spectral lines as an IR beam passes through a sample of the air in order to measure the concentration of individual gases. With the miniaturisation of air quality sensors, the move from benchtop spectrometers to micro-spectrometers is becoming more popular. A commonly-used approach for IR micro-spectrometers uses an IR detector array to determine the spectral response of an IR beam. However, increasing the spectral resolution of such a micro-spectrometer requires a proportional increase in the number of pixels in the detector, significantly increasing the fabrication costs of the detector. An alternative approach uses micro-mirrors in order to sweep a diffracted IR beam over a single IR sensor, where the spectral resolution does not depend on the number of pixels but on the accuracy of the micro-mirror angular position. For such an approach a precisely controlled micro-mirror with a known frequency and oscillation amplitude is needed. In this research an innovative closed loop controller for achieving such precision is presented. The controller has been developed by designing individual blocks which have been simulated and evaluated separately. The complete digital controller is then implemented on an FPGA for initial testing and then converted for implementation as an ASIC where the high voltage circuitry necessary to drive the electrostatically-actuated micro-mirror is also integrated, leading to a more compact implementation. The fabricated prototypes are then tested using an optical testbench. An analysis of the different waveforms that can be used to drive the micro-mirror and the ideal phase between the applied waveform and the micro-mirror angle is first carried out and used as a basis for the design of an all-digital closed loop controller. An improvement over previously published micro-mirror oscillation amplitude and phase measurement technique is then presented. This technique can be implemented in an all-digital controller since it relies on timing measurements from pulses generated by a single photodiode in the path of a reflected laser beam. An analysis is also carried out on different approaches that can be used to change the duty cycle of the drive waveform in order to change the amplitude of oscillation of the micro-mirror. The mentioned innovations are used to design an all-digital micro-mirror closed loop controller. The controller was simulated in MATLAB Simulink before implementation on an FPGA in order to verify its ability to control the micro-mirror. It is also demonstrated that the output signal of the controller can be synthesised using an adapted dithering-based fractional-N divider. The proposed controller is also implemented together with a high voltage output driver on the XFAB XT-018 BCD-on-SOI in order to demonstrate its feasibility of implementation in commercial applications. It is shown that the proposed controller is effective in accurately controlling the micro-mirror oscillation amplitude and thus validating the design. Description: Ph.D.(Melit.)

2024-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/124011 2026-04-13T09:10:56Z 2023-01-01T00:00:00Z

Title: Development of a piezoelectric micromachined ultrasonic transducer optimised to operate in the pore solution of reinforced concrete structures Abstract: Structural Health Monitoring (SHM) of Reinforced Concrete (RC) is important to ensure that necessary interventions on concrete structures are conducted in a timely manner. Structural integrity may be effected by various chemical substances such as chloride ions which ingress the concrete’s pore structure and corrode the rebar. Timely detection of such chemical substances and subsequent intervention can avoid potential structural deterioration with ensuing potentially disastrous consequences. The conduct of an effective Structural Health Monitoring regime on civil engineering structures such as bridge decks, can be challenging due to inherent difficulties required to access specific, inaccessible parts of the structure, such as the underside of a bridge deck. This points to the setup of a SHM system, through a microscale distributed sensor network as being an effective proposition. Such a system can be made up of Micro Electromechanical Systems (MEMS) devices. The sensory elements forming the distributed network would be embedded within the concrete structure during the construction phase. To achieve a durable system which is also easy to install during the structure’s construction phase, communication between the sensory elements would need to be conducted through wireless means. This dissertation explored the possibility of using microscale ultrasonic transducers as a means of implementing the inter device wireless communication channel required to achieve a viable distributed sensor system. This work’s primary contribution to the body of knowledge was therefore the development of the devices required to build the ultrasonic transmission path required to form the wireless communication channel. It needs to be clear that while the author has conducted prior work focusing on the sensory part of the system and also published papers in fields such as, the use of galvanic methods for detecting chloride ion ingress, research on the sensory system itself does not form part of this dissertation. Reviewed literature indicated that for microscale ultrasonic devices to operate within an RC structure, two particular components needed to be considered. Firstly, liquid coupling was needed to effectively couple the transducer to the concrete structure. Secondly the frequency of the PMUTs’ operation needed to be in the region of 100 kHz and below. The focus of this dissertation was therefore the development of Piezoelectric Micromachined Ultrasonic Transducers (PMUTs) optimised to operate inside a liquid coupling fluid at this particular frequency range. This was found to be an area in which very sparse background research had been conducted and therefore it must be said that the nature of most of the research conducted in this dissertation was novel. This makes this dissertation a valuable tool which can act as an important background to other researchers in fields involving PMUTs deployed in liquid coupling fluids. Applications that may potentially utilise such technology are not limited to civil engineering but also encompasses areas such as the biomedical and marine engineering fields. This dissertation outlines the extensive analytical, Finite Element Modelling (FEM) and experimental work conducted to explore the dynamics of PMUT design and operation. This included studies conducted with various variables being modified such as, filling the PMUT cavity with gas or liquid, the utilisation of different excitation frequencies, and also the utilisation of coupling fluids having different densities such as isopropanol or glycerine. Furthermore this dissertation also presents the development of various novel PMUT designs which were found to provide enhancements in ultrasonic reception or transmission performance. Such enhancements were based on designs such as multi electrode patterns and modified diaphragm structures. The devices developed in this dissertation were based on the PiezoMUMPSTM Multi Project Wafer (MPW) design concept. Aluminium nitride was used as the piezoelectric material found at the core of the devices’ operational dynamics. Description: Ph.D.(Melit.)

2023-01-01T00:00:00Z