Actuator Disk Theory for Compressible Flow

Because compressibility effects arise in real applications of propellers and turbines, the Actuator Disk Theory or Froude’s Momentum Theory was established for compressible, subsonic flow using the three laws of conservation and isentropic thermodynamics. The compressible Actuator Disk Theory was established for the unducted (bare) and ducted cases in which the disk was treated as the only assembly within the flow stream in the bare case and enclosed by a duct having a constant cross-sectional area equal to the disk area in the ducted case. The primary motivation of the current thesis was to predict the ideal performance of a small ram-air turbine (microRAT), operating at high subsonic Mach numbers, that would power an autonomous Boundary Layer Data System during test flights. The compressible-flow governing equations were applied to a propeller and a turbine for both the bare and ducted cases. The solutions to the resulting system of coupled, non-linear, algebraic equations were obtained using an iterative approach. The results showed that the power extraction efficiency and the total drag coefficient of the bare turbine are slightly higher for compressible flow than for incompressible flow. As the free-stream Mach increases, the Betz limit of the compressible bare turbine slightly increases from the incompressible value of 0.593 and occurs at a velocity ratio between the far downstream and the free-stream that is lower than the incompressible value of 0.333. From incompressible to a free-stream Mach number of 0.8, the Betz limit increases by 0.021 while its corresponding velocity ratio decreases by 0.036. The Betz limit and its corresponding velocity ratio for the ducted turbine are not affected by the free-stream Mach and are the same for both incompressible and compressible flow. The total drag coefficient of the ducted turbine is also the same regardless of the free-stream Mach number and the compressibility of the flow; but, the individual contributions of the turbine drag and the lip thrust to the total drag differs between compressible and incompressible flow and between varying free-stream Mach numbers. It was concluded that overall compressibility has little influence on the ideal performance of an actuator disk

Saving Mothers and Children in a Post-Conflict Setting: Improving the Quality of Maternal & Child Health Services in Afghanistan

Since the Taliban government was toppled in 2001, Afghanistan has been rebuilding its devastated health system through implementation of the Basic Package of Health Services (BPHS). The BPHS was initiated in 2003 and subsequently complemented by integration with the Essential Package of Hospital Services (EPHS) in 2005. Together, the BPHS and EPHS form the core of Afghanistan’s main health care delivery system. Since the initiation of BPHS, one of the key strategies has been improving the quality of maternal and child health services in Afghanistan. This dissertation focuses on the quality of maternal and child health services and assesses the effects of improving quality of services provided at frontline facilities on selected key outcomes. Study Aim 1 (SA (1)) is to quantify the association between the structural quality of maternal health services and utilization of institutional delivery services. Study Aim 2 (SA (2)) is to estimate the association between health workers’ adherence to clinical guidelines for Integrated Management of Childhood Illnesses (IMCI) and their likelihood of providing accurate diagnosis for pneumonia and diarrhea in children under 5 years of age. The analyses in the dissertation draw on 8 rounds of nation-wide data collected between 2004 and 2013 as part of National Health Service Performance Assessments in Afghanistan. Each year’s sample included a stratified random sample of different types of health facilities and systematic random samples of patients and health workers in the chosen facilities. The longitudinal and multilevel data analysis methods employed in SA (1) and (2) respectively, take advantage of the temporality of datasets and control for clustering in accordance with the sampling methods. The analysis for SA (1) provides strong evidence that structural quality improvement of maternal health services was positively associated with increases in facility births. Facilities supported by Non-Governmental Organizations (NGO) had higher institutional delivery rates than did facilities without any support. Increased rates of institutional deliveries were also associated with higher level facilities, a higher number of staff, and higher total volume of non-delivery services at the facilities. The analysis for SA (2) found a significant positive association between process quality of pediatric care, as measured by health workers’ adherence to IMCI clinical guidelines, and their likelihood of providing accurate diagnosis for pneumonia and diarrhea for children under 5 years of age. The analysis also indicated that context mattered, i.e. there were contextual factors at the province level at play either positively or negatively affecting accurate diagnosis, which lies at the heart of successful clinical management of the two diseases. The findings also highlighted that there is considerable room to strengthen IMCI skills and performance of health workers to reduce under-diagnosis of children with serious illnesses. The dissertation adds evidence, from post-conflict Afghanistan, that improving quality of maternal and child health services can contribute to increased service utilization by mothers, as well as to more accurate diagnoses of the top two diseases that kill children. Since quality improvement, increased utilization rates and more accurate diagnoses are part of key strategies for tackling maternal and child morbidity and mortality, the findings should stimulate continued investment in, and focus on, improving the quality of health services in Afghanistan through the BPHS and EPHS. The findings also serve as a reminder that health systems strengthening efforts should be contextualized at appropriate levels, i.e. individual, facility, provincial or national, through an ongoing exchange of insight and evidence among multiple stakeholders at and between different levels

Switched Capacitor DC-DC Converter for Miniaturised Wearable Systems

Motivated by the demands of the integrated power system in the modern wearable electronics, this paper presents a new method of inductor-less switched-capacitor (SC) based DC-DC converter designed to produce two simultaneous boost and buck outputs by using a 4-phases logic switch mode regulation. While the existing SC converters missing their reconfigurability during needed spontaneous multi-outputs at the load ends, this work overcomes this limitation by being able to reconfigure higher gain mode at dual outputs. From an input voltage of 2.5 V, the proposed converter achieves step-up and step-down voltage conversions of 3.74 V and 1.233 V for Normal mode, and 4.872 V and 2.48 V for High mode, with the ripple variation of 20–60 mV. The proposed converter has been designed in a standard 0.35 μm CMOS technology and with conversion efficiencies up to 97–98% is in agreement with state-of-the-art SC converter designs. It produces the maximum load currents of 0.21 mA and 0.37 mA for Normal and High modes respectively. Due to the flexible gain accessibility and fast response time with only two clock cycles required for steady state outputs, this converter can be applicable for multi-function wearable devices, comprised of various integrated electronic modules

Lifelong Effectiveness of Caries Prevention Programs by System Dynamics Model

Doctor of Philosophy in Oral Health Sciences, 2022Dental caries is still considered a burden of disease not only in Thailand but also around the world. Various preventive and promotion programs are implemented for dental caries in individuals and communities among the population. For long-term assessment of preventive programs, simulation models are gaining attention to be approached. Objective: This study aims to estimate the lifelong outcomes of caries prevention programs among Thai age groups by conducting the System Dynamics Model (SDM). Methodology: Systematic reviews and meta-analyses were conducted to identify the efficacy of interventions: supervised toothbrushing, fluoride varnish, dental sealant, and oral health examination for dental caries according to age groups. Based on the effectiveness of interventions from meta-analyses and their coverage rates, the SDM was simulated to estimate the lifelong dental caries outcome under interventions: supervised toothbrushing, fluoride varnish, combined supervised toothbrushing and fluoride varnish, dental sealant, combined supervised toothbrushing, and sealant, and oral health examination by comparing base case (no intervention was provided). Results: it is found that at the age of 5 years old, the population with caries in deciduous teeth was the lowest in combined supervised toothbrushing and fluoride varnish, 258,876 (38.17 %) followed by supervised toothbrushing, 266,049 (39.23%), fluoride varnish, 276,703 (40.79 %), and base case, 290,829 (42.88 %). All these interventions can reduce the caries population until above 15 years old compared to the base case. The caries population was lowest under combined supervised toothbrushing and sealant, 257,655 (37.99%), followed by a sealant, 264,507 (38.99%) at 15 years old. From above 23 years old, the caries population under all of the above interventions and the oral health examination were not different from the base case. Conclusion: according to SDM simulation, it is considered that combined interventions are more effective than other interventions provided separately. Each intervention could reduce the caries population by above 15 years from they started compared to the base case. If the interventions have better effective rates and coverage rates, the caries population could be reduced by more than the estimated result from the model

Power management systems based on switched-capacitor DC-DC converter for low-power wearable applications

The highly efficient ultra-low-power management unit is essential in powering low-power wearable electronics. Such devices are powered by a single input source, either by a battery or with the help of a renewable energy source. Thus, there is a demand for an energy conversion unit, in this case, a DC-DC converter, which can perform either step-up or step-down conversions to provide the required voltage at the load. Energy scavenging with a boost converter is an intriguing choice since it removes the necessity of bulky batteries and considerably extends the battery life. Wearable devices are typically powered by a monolithic battery. The commonly available battery such as Alkaline or Lithium-ion, degrade over time due to their life spans as it is limited by the number of charge cycles- which depend highly on the environmental and loading condition. Thus, once it reaches the maximum number of life cycles, the battery needs to be replaced. The operation of the wearable devices is limited by usable duration, which depends on the energy density of the battery. Once the stored energy is depleted, the operation of wearable devices is also affected, and hence it needs to be recharged. The energy harvesters- which gather the available energy from the surroundings, however, have no limitation on operating life. The application can become battery-less given that harvestable energy is sufficiently powering the low-power devices. Although the energy harvester may not completely replace the battery source, it ensures the maximum duration of use and assists to become autonomous and self-sustain devices. The photovoltaic (PV) cell is a promising candidate as a hypothetical input supply source among the energy harvesters due to its smaller area and high power density over other harvesters. Solar energy use PV harvester can convert ambient light energy into electrical energy and keep it in the storage device. The harvested output of PV cannot directly connect to wearable loads for two main reasons. Depending on the incoming light, the harvested current result in varying open-circuit voltage. It requires the power management circuit to deal with unregulated input variation. Second, depending on the PV cell's material type and an effective area, the I-V characteristic's performance varies, resulting in a variation of the output power. There are several works of maximum power point tracking (MPPT) methods that allow the solar energy harvester to achieve optimal harvested power. Therefore, the harvested power depends on the size and usually small area cell is sufficient for micro-watt loads low-powered applications. The available harvested voltage, however, is generally very low-voltage range between 0.4-0.6 V. The voltage ratings of electronics in standard wearable applications operate in 1.8-3 V voltages as described in introduction’s application example section. It is higher than the supply source can offer. The overcome the mismatch voltage between source and supply circuit, a DC-DC boost converter is necessary. The switch-mode converters are favoured over the linear converters due to their highly efficient and small area overhead. The inductive converter in the switch-mode converter is common due to its high-efficiency performance. However, the integration of the inductor in the miniaturised integrated on-chip design tends to be bulky. Therefore, the switched-capacitor approach DC-DC converters will be explored in this research. In the switched-capacitor converter universe, there is plenty of work for single-output designs for various topologies. Most converters are reconfigurable to the different DC voltage levels apart from Dickson and cross-coupled charge pump topologies due to their boosting power stage architecture through a number of stages. However, existing multi-output converters are limited to the fixed gain ratio. This work explores the reconfigurable dual-output converter with adjustable gain to compromise the research gap. The thesis's primary focus is to present the inductor-less, switched-capacitor-based DC-DC converter power management system (PMS) supplied by a varying input of PV energy harvester input source. The PMS should deliver highly efficient regulated voltage conversion ratio (VCR) outputs to low-power wearable electronic devices that constitute multi-function building blocks

Energy-Efficient Start-up Power Management for Batteryless Biomedical Implant Devices

This paper presents a solar energy harvesting power management using the high-efficiency switched capacitor DC-DC converter for biomedical implant applications. By employing an on-chip start-up circuit with parallel connected Photovoltaic (PV) cells, a small efficiency improvement can be obtained when compared with the traditional stacked photodiode methodology to boost the harvested voltage while preserving a single-chip solution. The PV cells have been optimised in the PC1D software and the optimal parameters modelled in the Cadence environment. A cross-coupled circuit with level shifter loop is also proposed to improve the overall step up voltage output and hybrid converter increases the start-up speed by 23.5%. The proposed system is implemented in a standard 0.18-μm CMOS technology. Simulation results show that the 4-phase start-up and cross coupled with level-shifter can achieve a maximum efficiency of 60%

Energy-Efficient Start-up Power Management for Batteryless Biomedical Implant Devices

This paper presents a solar energy harvesting power management using the high-efficiency switched capacitor DC-DC converter for biomedical implant applications. By employing an on-chip start-up circuit with parallel connected Photovoltaic (PV) cells, a small efficiency improvement can be obtained when compared with the traditional stacked photodiode methodology to boost the harvested voltage while preserving a single-chip solution. The PV cells have been optimised in the PC1D software and the optimal parameters modelled in the Cadence environment. A cross-coupled circuit with level shifter loop is also proposed to improve the overall step up voltage output and hybrid converter increases the start-up speed by 23.5%. The proposed system is implemented in a standard 0.18-μm CMOS technology. Simulation results show that the 4-phase start-up and cross coupled with level-shifter can achieve a maximum efficiency of 60%

Power management using photovoltaic cells for implantable devices

This paper presents a novel inductor-less switched capacitor (SC) DC-DC converter, which generates simultaneous dual-output voltages for implantable electronic devices. Present dual output converters are limited to fixed ratio gain, which degrade conversion efficiency when the input voltage changes. The proposed power converter offers both step-up and step-down conversion with 4-phase reconfigurable logic. With an input voltage of 1 V provided by photovoltaic (PV) cells, the proposed converter achieves step-up, step-down and synchronised voltage conversions in four gain modes. These are 1.5 V and 0.5 V for Normal mode, 2 V and 1 V for High mode, 2 V for Double Boost mode, as well as 3 V and 2 V for Super Boost mode with the ripple variation of 14-59 mV. The converter circuit has been simulated in standard 0.18 μm CMOS technology and the results agree with state-of-the-art SC converters. However, our proposed monolithically integrated PV powered circuit achieves a conversion efficiency of 85.26% and provides extra flexibility in terms of gain, which is advantageous for future implantable applications that have a range of inputs. This research is therefore an important step in achieving truly autonomous implantable electronic devices

Modelling of Implantable Photovoltaic Cell based on Human Skin Types

Implantable electronic devices are emerging as important healthcare technologies due to their sustainable operation and low risk of infection. To overcome the drawbacks of the built-in battery in implantable devices, energy harvesting from the human body or another external source is required. Energy harvesting using appropriately sized and properly designed photovoltaic cells enable implantable medical devices to be autonomous and self-powered. Among the challenges in using PV cells is the small fraction of incident light that penetrates the skin. Thus, it is necessary to involve such physical properties in the energy harvesting system design. Consequently, we propose a novel photodiode model that considers skin loss in different ethnic groups. Our physical simulations have been implemented using COMSOL and MATLAB. Circuit and system modelling have been performed using Cadence 180nm TSMC technology. Our results show that the transmittance of near infrared light is almost the same in three skin types: Caucasian, Asian and African. Maximum power delivery of 12 μW (African skin) and 14 μW (Caucasian and Asian skin) were achieved at 0.45 V. With the help of a power management unit, an output voltage of 1.8–2 V was achieved using the PV cells

Energy-Efficient Start-Up Dickson Charge Pump for Batteryless Biomedical Implant Devices

This paper presents a power management concept for solar energy harvesting power management using an on-chip switched-capacitor (SC) DC-DC converter for biomedical implantable applications. This design eliminates potential reversion losses caused by the switching scheme. It also mitigates the bottom plate loss by employing the charge recycling technique. Moreover, instead of using a single step clock pulse, the two-step adiabatic charge sharing clock helps reduce the energy drawn from the PV cell by 65%. Furthermore, with the help of clock disabler scheme, the power dissipation has been further reduced by disabling the entire start-up charge pump once the desired reference output voltage was reached. However, due to additional circuitry for the clock disabler, there is a tradeoff between power efficiency and power dissipation. The proposed system was implemented and fabricated in a standard 0.18-µm TSMC RF CMOS technology. The proposed converter has achieved a maximum efficiency of 73%