Mobile sensing applications (MSAs) are an emerging class of applications that process continuous sensor data streams to make time-sensitive inferences. Representative application domains range from environmental monitoring, context-aware services to recognition of physical activities and social interactions. Example applications involve city air quality assessment, indoor localization, pedometer and speaker identification. The common application workflow is to read data streams from the sensors (e.g, accelerometers, microphone, GPS), extract statistical features, and then present the inferred high-level events to the user. MSAs in the healthcare domain especially draw a significant amount of attention in recent years because sensor-based data collection and assessment offer finer-granularity, timeliness, and higher accuracy in greater quantity than traditional, labor-intensive, data gathering mechanisms in use today, e.g., surveys methods. The higher fidelity and accuracy of the collected data expose new research opportunities, improve the reliability and accuracy of medical decisions, and empower users to manage personal health more effectively. Nonetheless, a critical challenge to practical deployment of MSAs in real-world is to effectively manage limited resources of mobile platforms to meet stringent quality of service (QoS) requirements in terms of processing throughput and delay while ensuring long term robustness. To address the challenge, we model MSAs in dataflows as a graph of processing elements that are connected by communication channels. The processing elements may execute in parallel as long as they have sufficient data to process. A key feature of the dataflow model is that it explicitly capture parallelism and data dependencies between processing elements. Based on the graph composition, we first proposed CSense, a stream-processing toolkit for robust and high-rate MSAs. In this work, CSense provide a simple language for developers to describe their sensing flow without the need to deal with system intricacy, such as memory allocation, concurrency control and power management. The results show up to 19X performance difference may be achieved automatically compared with a baseline using the default runtime concurrency and memory management. Following this direction, we saw the opportunities that MSAs can be significantly improved from the perspective of memory performance and energy efficiency in view of the iterative execution. Therefore, we next focus on optimizing the runtime memory management through compile time analysis. The contribution is a stream compiler that captures the whole program memory behavior to generate an efficient memory layout for runtime access. Experiments show that our memory optimizations reduce memory footprint by as much as 96% while matching or improving the performance of the StreamIt compiler with cache optimizations enabled. On the other hand, while there is a significant body of work that has focused on optimizing the throughput or latency of processing sensor streams, little to no attention has been given to energy efficiency. We proposed an accurate offline energy prediction model for MSAs that leverages the pipeline structure and iterative execution nature to search for the most energy saving batching configuration w.r.t. a deadline constraint. The developers are expected to visualize the energy delay trade-off in the parameter space without runtime profiling. The evaluation shows the worst-case prediction errors are about 7% and 15% for energy and latency respectively despite variable application workloads.

Les micro-résonateurs (MRs) sont devenus des éléments clés de la conception de capteurs optiques intégrés, car étant plus miniaturisés que l’existant, ils s’intègrent mieux dans des systèmes ''lab-on-chip'', ce qui permet aussi de réduire le volume des molécules à détecter. Les MRs sont de plus très sensibles à la variation d’indice effectif provoquée par la présence de molécules dans le milieu de détection. Dans cette thèse, nous avons utilisé deux types de matériaux différents: les polymères et le silicium poreux. Les polymères, facilement réalisables avec des méthodes de fabrication peu onéreuses, sont dans un premier temps utilisés pour valider les outils de simulation développés pour l’étude des caractéristiques des MRs pour l’application capteur basée sur la détection par évanescence. Le silicium poreux permet d'exploiter un autre mode de détection, la détection en volume. Les molécules présentes dans le milieu de détection s'infiltrent dans le matériau et réagissent de manière directe avec la lumière. En utilisant les outils de simulation développés et en adaptant le procédé de photolithographie classique utilisé pour la fabrication de MRs en polymères, des premiers MRs constitués de guides ridges à base de silicium poreux sont mis en œuvre et caractérisés. Ces travaux de thèse démontrent expérimentalement la possibilité de détecter des concentrations de glucose avec une meilleure sensibilité que l'état de l'art pouvant atteindre les 600 nm/RIU, pour les domaines utilisant la détection et l'analyse de molécules (santé-agro, défense-sécurité, environnement). / Micro-resonators have become key element for integrated optical sensor because they offer the advantage of significantly minimizing the device size, which allows an easily integration on lab-on-chip and greatly reduces the amount of molecules to be detected. Moreover, micro-resonators are extremely sensitive to the effective index variation induced by the presence of molecules in the detection medium. The thesis focuses on two different materials: polymers and porous silicon. Firstly, polymers, easily implementable with a low cost fabrication, are used to validate the simulation tools developed for the study of micro-resonators characteristics in order to perform sensing application based on the detection by evanescence. Then, porous silicon is investigated in order to operate another type of detection, the detection by volume. The molecules to be detected and present in the medium detection infiltrate into the material and interact directly with the light. Using simulation tools and by adapting the photolithographic process used for polymers micro-resonators fabrication, the first micro-resonators based on porous silicon ridge waveguides are obtained and characterized. The work contained in this thesis demonstrate experimentally the possibility of sensing concentrations of glucose with a sensitivity of 600 nm/RIU, using volume detection, which is higher than the state of the art, for domains using the sensing and analysis of molecules (health, food industries, security and environment).

Yttria stabilized Zirconia (8YSZ) is an extensively used solid electrolyte, which finds applications in electrochemical sensors, solid oxide fuel cells and gate oxide in MOSFETs. Recent studies report that YSZ thin films are better performers than their bulk counterparts, in terms of ionic conductivity even at moderate temperatures. YSZ thin films also attract attention with the scope of device miniaturization. However, most of the studies available in the literature on YSZ thin films focus mainly on their electrical characterization. In this work, YSZ thin films were deposited, characterized and possible use of sensors were evaluated. In the present work, 8 mol% yttria stabilized zirconia thin films were deposited using RF magnetron reactive sputtering under different deposition conditions. Films with thicknesses ranging from few tens to few hundreds of nanometres were deposited. The deposited films were subjected to morphological, structural, compositional and electrical characterizations. Deposition and annealing conditions were optimized to obtain dense, stoichiometric and crystalline YSZ thin films. The ionic conductivity of 200 nm nanocrystal line thin film was found to be two orders of magnitude higher than the bulk. The ionic conductivity increased with the decrease in film thickness. Compositional analyses of a set of YSZ thin films revealed free surface yttrium segregation. The free surface segregation of dopants can locally alter the surface chemistry and influence the oxygen transfer kinetics across the electrode-electrolyte interface. Although number of reports are available on the segregation characteristics in YSZ bulk, no reports are available on yttria segregation in YSZ thin film. Hence, this work reports detailed investigations on the free surface yttria segregation in YSZ thin films using angle resolved X-ray photoelectron spectroscopy (XPS). Influence of annealing temperature, film thickness, annealing time, and purity on the segregation concentration was determined. It was found that the most important factor that determines the segregation was found to be the target purity. The segregation depth profile analysis showed that the segregation layer depth was proportional to segregation concentration. Free surface segregation reduced the ionic conductivity of the YSZ thin films roughly about a factor. However, segregation did not affect the film’s morphology, grain size, crystallinity and activation energy. The difference in ionic conductivity observed in the segregated and clean YSZ films suggests that dopant free surface segregation could also be one of the reasons for the variable ionic conductivity reported in the literature. For using YSZ in miniaturized devices, micro-structuring of YSZ is important. It has been reported that the wet etching techniques available for YSZ were not repeatable and do not etch annealed YSZ samples. Reactive ion etching (RIE) is better suited for YSZ patterning due to its capability to offer high resolution, easy control and tenable anisotropic/isotropic pattern transfer for batch processing. Although reports are available on the dry etching of zirconia and yttria thin films, no studies were reported on the dry etching of YSZ thin films. In this work, inductively coupled reactive ion etching (ICP-RIE) using fluorine and chlorine chemistries were employed to etch YSZ thin films. Optimized etching conditions were identified by varying different process parameters like, type of gas, gas flow rate, RF power, ICP power, chamber pressure and carrier wafer in the ICP-RIE process. Optimized conditions were chosen by examining the etch depth, composition analyses before and after etch using XPS, selectivity towards SiO2 (which is the most common buffer layer) and surface roughness. Etch chemistries involved in a particular plasma (SF6, Cl2 and BCl3) were discussed with the help of surface composition and etch thicknesses. The results showed that etching YSZ with BCl3 plasma at optimized conditions yielded best results through oxygen-scavenging mechanism. A maximum etch rate of 53 nm/min was obtained in BCl3 plasma using PECVD Si3N4 carrier wafer at an ICP power of 1500 W, RF power of 100 W, chamber pressure of 5 mTorr with 30 sccm BCl3 flow. Sensing devices were designed by employing YSZ thin film as solid electrolyte and nickel oxide and gold thin film as sensing and reference electrodes, respectively to evaluate the possible use of YSZ thin film in miniaturized NO2 sensor. The electrodes were deposited in inter-digitated pattern. Two types of electrodes were designed with different number of fingers in symmetric and asymmetric configurations. The NO2 sensing was performed in the concentration range of 25 to 2000 ppm at three different temperatures, 673, 773 and 873 K in mixed potential and impedance metric modes. The mixed potential type measurements were carried out only for asymmetric cell in two different electrode configurations. The impedance metric type measurements were carried out for both symmetric and asymmetric cells in two different electrode configurations. Preliminary NO2 sensing experiments in both the types of measurements revealed that in devices with electrodes having more fingers were better in performance. In mixed potential type sensors, sensitivity was measured as the amount of voltage generated when the sensor was exposed to a test gas. The generated voltage was found to be proportional to the logarithm of NO2 concentration in the entire measurement range (50 to 2000 ppm) with the regression fitting parameter, adj.R2 around 0.97 to 0.99 in all the cases. A maximum potential of 271 mV was measured with 2000 ppm NO2 at 873 K. The response and recovery times of the sensors were sensitive to the operating temperature. In impedance metric mode, the sensitivities were measured as the variation in the low frequency phase angle (∆ φ) when the gas concentration is changed. The frequency range of the measurement was from 0.01 Hz to100 kHz. The response time in the impedance metric sensors was comparable to that of mixed potential sensors. But the recovery time in impedance metric sensors was much was slower than the mixed potential type for all the concentrations. The sensors showed linear response only in a narrow range of 50 to 500 ppm with regression fitting value, R2 around 0.98 in all the cases. Above 500 ppm, the sensitivity value was observed to be saturated. From the gas sensing studies performed on the miniaturized sensors, it was found that the mixed potential type sensing mode is better than the impedance metric type in YSZ thin film based devices. However detailed interference gas studies were needed before drawing any conclusion. In summary, the studies presented in the work have contributed to the understanding of free surface yttria segregation behaviour in YSZ thin films. Micromachining conditions were optimized for both pristine and annealed YSZ thin films. Suitability of YSZ thin film based miniaturized NO2 gas sensor was evaluated.

[pt] Dores no pé e joelho estão relacionadas com patologias ortopédicas e lesões nos membros inferiores. Desde a corrida de rua até o treinamento funcional CrossFit, estas dores e lesões estão correlacionadas com a distribuição iregular da pressão plantar e o posicionamento inadequado do joelho durante a prática física de longo prazo, e podem levar a lesões ortopédicas graves se o padrão de movimento não for corrigido. Portanto, o monitoramento da distribuição da pressão plantar do pé e das características espaciais e temporais das irregularidades no posicionamento dos pés e joelhos são de extrema importância para a prevenção de lesões. Este trabalho propõe uma plataforma, composta de uma rede de sensores vestíveis e um classificador de Reconhecimento de Atividade Humana (HAR), para fornecer feedback em tempo real de exercícios funcionais, visando auxiliar educadores físicos a reduzir a probabilidade de lesões durante o treinamento. Realizamos um experimento com 12 voluntários diversos para construir um classificador HAR com aproximadamente de 87 porcento de precisão geral na classificação, e um segundo experimento para validar nosso modelo de avaliação física. Por fim, realizamos uma entrevista semi estruturada para avaliar questões de usabilidade e experiência do usuário da plataforma proposta.Visando uma pesquisa replicável, fornecemos informações completas sobre o hardware e o código fonte do sistema, e disponibilizamos o conjunto de dados do experimento. / [en] Foot and knee pain fave been associated with numerous orthopedic pathologies and injuries of the lower limbs. From street running to CrossFitTM functional training, these common pains and injuries correlate highly with unevenly distributed plantar pressure and knee positioning during long-term physical practice and can lead to severe orthopedic injuries if the movement pattern is not amended. Therefore, the monitoring of foot plantar pressure distribution and the spatial and temporal characteristics of foot and knee positioning abnomalities is of utmost importance for injury prevention. This work proposes a platform, composed af an lot wearable body sensor network and a Human Activity Recognition (HAR), to provide realtime feedback of functional exercises, aiming to enhace physical educators capability to mitigate the probability of injuries during training. We conducted an experiment with 12 diverse volunteers to build a HAR classifier that achieved about 87 percent overall classification accuracy, and a second experiment to validate our physical evaluation model. Finally, we performed a semi-structured interview to evaluate usability and user experience issues regarding the proposed platform. Aiming at a replicable research, we provide full hardware information, system source code and a public domain dataset.

Ternary luminescent copper and silver indium sulfide quantum dots (QDs) can be an attractive alternative to cadmium and lead chalcogenide QDs. The optical properties of Cu–In–S and Ag–In–S (AIS) QDs vary over a broad range depending on the QD composition and size. The implementation of ternary QDs as emitters in bio-sensing applications can be boosted by the development of mild and reproducible syntheses directly in aqueous solutions as well as the methods of shifting the photoluminescence (PL) bands of such QDs as far as possible into the near IR spectral range. In the present work, the copper-doping of aqueous non-stoichiometric AIS QDs was found to result in a red shift of the PL band maximum from around 630 nm to ∼780 nm and PL quenching. The deposition of a ZnS shell results in PL intensity recovery with the highest quantum yield of 15%, with almost not change in the PL band position, opposite to the undoped AIS QDs. Size-selective precipitation using 2-propanol as a non-solvent allows discrimination of up to 9 fractions of Cu-doped AIS/ZnS QDs with the average sizes in the fractions varying from around 3 to 2 nm and smaller and with reasonably the same composition irrespective of the QD size. The decrease of the average QD size results in a blue PL shift yielding a series of bright luminophors with the emission color varies from deep-red to bluish-green and the PL efficiency increases from 11% for the first fraction to up to 58% for the smallest Cu-doped AIS/ZnS QDs. The rate constant of the radiative recombination of the size-selected Cu-doped AIS/ZnS QDs revealed a steady growth with the QD size decrease as a result of the size-dependent enhancement of the spatial exciton confinement. The copper doping was found to result in an enhancement of the photoelectrochemical activity of CAIS/ZnS QDs introduced as spectral sensitizers of mesoporous titania photoanodes of liquid-junction solar cells.

Sensor interfaces are needed to communicate the measured real-world analog values to the base¬band digital processor. They are dominated by the presence of high accuracy, high resolution analog to digital converters (ADC) in the backend. On most occasions, sensing is limited to small range measurements and low-modulation sensors where the complete dynamic range of ADC is not utilized. Designing a subsystem that integrates the sensor and the interface circuit and that works with a low resolution ADC requiring a small die-area is a challenge. In this work, we present a CMOS based area efficient, integrated sensor interface for applications like capacitance, temperature and dielectric-constant measurement. In addition, potential applica-tions for this work are in Cognitive Radios, Software Defined Radios, Capacitance Sensors, and location monitoring. The key contributions in the thesis are: 1 High Sensitivity Frequency-domain CMOS Capacitance Interface: A frequency domain capacitance interface system is proposed for a femto-farad capacitance measurement. In this technique, a ring oscillator circuit is used to generate a change in time period, due to a change in the sensor capacitance. The time-period difference of two such oscillators is compared and is read-out using a phase frequency detector and a charge pump. The output voltage of the system, is proportional to the change in the input sensor capacitance. It exhibits a maximum sensitivity of 8.1 mV/fF across a 300 fF capacitance range. 2 Sensitivity Enhancement for capacitance sensor: The sensitivity of an oscillator-based differential capacitance sensor has been improved by proposing a novel frequency domain capacitance-to-voltage (FDC) measurement technique. The capacitance sensor interface system is fabricated in a 130-nm CMOS technology with an active area of 0.17mm2 . It exhibits a maximum sensitivity of 244.8 mV/fF and a measurement resolution of 13 aF in a 10-100 fF measurement range, with a 10 pF nominal sensor capacitance and an 8-bit ADC. 3 Frequency to Digital Converter for Time/Distance measurement: A new architecture for a Vernier-based frequency-to-digital converter (VFDC) for location monitoring is pre¬sented, in which, a time interval measurement is performed with a frequency domain approach. Location monitoring is a common problem for many mobile robotic applica¬tions covering various domains, such as industrial automation, manipulation in difficult areas, rescue operations, environment exploration and monitoring, smart environments and buildings, robotic home appliances, space exploration and probing. The proposed architecture employs a new injection-locked ring oscillator (ILR) as the clock source. The proposed ILR oscillator does not need complex calibration procedures, usually required by Phase Locked Loop (PLL) based oscillators in Vernier-based time-to-digital convert¬ers. It consumes 14.4 µW and 1.15 mW from 0.4 V and 1.2 V supplies, respectively. The proposed VFDC thus achieves a large detectable range, fine time resolution, small die size and low power consumption simultaneously. The measured time-difference error is less than 50 ps at 1.2 V, enabling a resolution of 3 mm/kHz frequency shift. 4 A bio-sensor array for dielectric constant measurement: A CMOS on-chip sensor is presented to measure the dielectric constant of organic chemicals. The dielectric constant of these chemicals is measured using the oscillation frequency shift of a current controlled os¬cillator (CCO) upon the change of the sensor capacitance when exposed to the liquid. The CCO is embedded in an open-loop frequency synthesizer to convert the frequency change into voltage, which can be digitized using an off-chip analog-to-digital converter. The dielectric constant is then estimated using a detection procedure including the calibration of the sensor. 5 Integrated Temperature Sensor for thermal management: An integrated analog temper¬ature sensor which operates with simple, low-cost one-point calibration is proposed. A frequency domain technique to measure the on-chip silicon surface temperature, was used to measure the effects of temperature on the stability of a frequency synthesizer. The temperature to voltage conversion is achieved in two steps i.e. temperature to frequency, followed by frequency to voltage conversion. The output voltage can be used to com¬pensate the temperature dependent errors in the high frequency circuits, thereby reduc¬ing the performance degradation due to thermal gradient. Furthermore, a temperature measurement-based on-chip self test technique to measure the 3 dB bandwidth and the central frequency of common radio frequency circuits, was developed. This technique shows promise in performing online monitoring and temperature compensation of RF circuits.

Ternary luminescent copper and silver indium sulfide quantum dots (QDs) can be an attractive alternative to cadmium and lead chalcogenide QDs. The optical properties of Cu–In–S and Ag–In–S (AIS) QDs vary over a broad range depending on the QD composition and size. The implementation of ternary QDs as emitters in bio-sensing applications can be boosted by the development of mild and reproducible syntheses directly in aqueous solutions as well as the methods of shifting the photoluminescence (PL) bands of such QDs as far as possible into the near IR spectral range. In the present work, the copper-doping of aqueous non-stoichiometric AIS QDs was found to result in a red shift of the PL band maximum from around 630 nm to ∼780 nm and PL quenching. The deposition of a ZnS shell results in PL intensity recovery with the highest quantum yield of 15%, with almost not change in the PL band position, opposite to the undoped AIS QDs. Size-selective precipitation using 2-propanol as a non-solvent allows discrimination of up to 9 fractions of Cu-doped AIS/ZnS QDs with the average sizes in the fractions varying from around 3 to 2 nm and smaller and with reasonably the same composition irrespective of the QD size. The decrease of the average QD size results in a blue PL shift yielding a series of bright luminophors with the emission color varies from deep-red to bluish-green and the PL efficiency increases from 11% for the first fraction to up to 58% for the smallest Cu-doped AIS/ZnS QDs. The rate constant of the radiative recombination of the size-selected Cu-doped AIS/ZnS QDs revealed a steady growth with the QD size decrease as a result of the size-dependent enhancement of the spatial exciton confinement. The copper doping was found to result in an enhancement of the photoelectrochemical activity of CAIS/ZnS QDs introduced as spectral sensitizers of mesoporous titania photoanodes of liquid-junction solar cells.

This study explores the utilisation of spatial technologies as a tool to analyse and combat crime. The study deals specifically with remote sensing and its potential for being integrated with geographical information systems (GIS). The integrated spatial approach resulted in the understanding of land use class behaviour over time and its relationship to specific crime incidents per police precinct area. The incorporation of spatial technologies to test criminological theories in practice, such as the ecological theories of criminology, provides the science with strategic value. It proves the value of combining multi-disciplinary scientific fields to create a more advanced platform to understand land use behaviour and its relationship to crime. Crime in South Africa is a serious concern and it impacts negatively on so many lives. The fear of crime, the loss of life, the socio-economic impact of crime, etc. create the impression that the battle against crime has been lost. The limited knowledge base within the law enforcement agencies, limited logistical resources and low retention rate of critical staff all contribute to making the reduction of crime more difficult to achieve. A practical procedure of using remote sensing technology integrated with geographical information systems (GIS), overlaid with geo-coded crime data to provide a spatial technological basis to analyse and combat crime, is illustrated by a practical study of the Tshwane municipality area. The methodology applied in this study required multi-skilled resources incorporating GIS and the understanding of crime to integrate the diverse scientific fields into a consolidated process that can contribute to the combating of crime in general. The existence of informal settlement areas in South Africa stresses the socio-economic problems that need to be addressed as there is a clear correlation of land use data with serious crime incidents in these areas. The fact that no formal cadastre exists for these areas, combined with a great diversity in densification and growth of the periphery, makes analysis very difficult without remote sensing imagery. Revisits over time to assess changes in these areas in order to adapt policing strategies will create an improved information layer for responding to crime. Final computerised maps generated from remote sensing and GIS layers are not the only information that can be used to prevent and combat crime. An important recipe for ultimately successfully managing and controlling crime in South Africa is to strategically combine training of the law enforcement agencies in the use of spatial information with police science. The researcher concludes with the hope that this study will contribute to the improved utilisation of spatial technology to analyse and combat crime in South Africa. The ultimate vision is the expansion of the science of criminology by adding an advanced spatial technology module to its curriculum. / Criminology / D.Litt. et Phil. (Criminology)

This study explores the utilisation of spatial technologies as a tool to analyse and combat crime. The study deals specifically with remote sensing and its potential for being integrated with geographical information systems (GIS). The integrated spatial approach resulted in the understanding of land use class behaviour over time and its relationship to specific crime incidents per police precinct area. The incorporation of spatial technologies to test criminological theories in practice, such as the ecological theories of criminology, provides the science with strategic value. It proves the value of combining multi-disciplinary scientific fields to create a more advanced platform to understand land use behaviour and its relationship to crime. Crime in South Africa is a serious concern and it impacts negatively on so many lives. The fear of crime, the loss of life, the socio-economic impact of crime, etc. create the impression that the battle against crime has been lost. The limited knowledge base within the law enforcement agencies, limited logistical resources and low retention rate of critical staff all contribute to making the reduction of crime more difficult to achieve. A practical procedure of using remote sensing technology integrated with geographical information systems (GIS), overlaid with geo-coded crime data to provide a spatial technological basis to analyse and combat crime, is illustrated by a practical study of the Tshwane municipality area. The methodology applied in this study required multi-skilled resources incorporating GIS and the understanding of crime to integrate the diverse scientific fields into a consolidated process that can contribute to the combating of crime in general. The existence of informal settlement areas in South Africa stresses the socio-economic problems that need to be addressed as there is a clear correlation of land use data with serious crime incidents in these areas. The fact that no formal cadastre exists for these areas, combined with a great diversity in densification and growth of the periphery, makes analysis very difficult without remote sensing imagery. Revisits over time to assess changes in these areas in order to adapt policing strategies will create an improved information layer for responding to crime. Final computerised maps generated from remote sensing and GIS layers are not the only information that can be used to prevent and combat crime. An important recipe for ultimately successfully managing and controlling crime in South Africa is to strategically combine training of the law enforcement agencies in the use of spatial information with police science. The researcher concludes with the hope that this study will contribute to the improved utilisation of spatial technology to analyse and combat crime in South Africa. The ultimate vision is the expansion of the science of criminology by adding an advanced spatial technology module to its curriculum. / Criminology and Security Science / D.Litt. et Phil. (Criminology)