4,269 research outputs found
Review: optical fiber sensors for civil engineering applications
Optical fiber sensor (OFS) technologies have developed rapidly over the last few decades, and various types of OFS have found practical applications in the field of civil engineering. In this paper, which is resulting from the work of the RILEM technical committee âOptical fiber sensors for civil engineering applicationsâ, different kinds of sensing techniques, including change of light intensity, interferometry, fiber Bragg grating, adsorption measurement and distributed sensing, are briefly reviewed to introduce the basic sensing principles. Then, the applications of OFS in highway structures, building structures, geotechnical structures, pipelines as well as cables monitoring are described, with focus on sensor design, installation technique and sensor performance. It is believed that the State-of-the-Art review is helpful to engineers considering the use of OFS in their projects, and can facilitate the wider application of OFS technologies in construction industry
Low-power Wearable Healthcare Sensors
Advances in technology have produced a range of on-body sensors and smartwatches that can be used to monitor a wearerâs health with the objective to keep the user healthy. However, the real potential of such devices not only lies in monitoring but also in interactive communication with expert-system-based cloud services to offer personalized and real-time healthcare advice that will enable the user to manage their health and, over time, to reduce expensive hospital admissions. To meet this goal, the research challenges for the next generation of wearable healthcare devices include the need to offer a wide range of sensing, computing, communication, and humanâcomputer interaction methods, all within a tiny device with limited resources and electrical power. This Special Issue presents a collection of six papers on a wide range of research developments that highlight the specific challenges in creating the next generation of low-power wearable healthcare sensors
Bridges Structural Health Monitoring and Deterioration Detection Synthesis of Knowledge and Technology
INE/AUTC 10.0
Wireless body sensor networks for health-monitoring applications
This is an author-created, un-copyedited version of an article accepted for publication in
Physiological Measurement. The publisher is
not responsible for any errors or omissions in this version of the manuscript or any version
derived from it. The Version of Record is available online at http://dx.doi.org/10.1088/0967-3334/29/11/R01
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Integrated temperature sensors in deep sub-micron CMOS technologies
textIntegrated temperature sensors play an important role in enhancing the performance of on-chip power and thermal management systems in today's highly-integrated system-on-chip (SoC) platforms, such as microprocessors. Accurate on-chip temperature measurement is essential to maximize the performance and reliability of these SoCs. However, due to non-uniform power consumption by different functional blocks, microprocessors have fairly large thermal gradient (and variation) across their chips. In the case of multi-core microprocessors for example, there are task-specific thermal gradients across different cores on the same die. As a result, multiple temperature sensors are needed to measure the temperature profile at all relevant coordinates of the chip. Subsequently, the results of the temperature measurements are used to take corrective measures to enhance the performance, or save the SoC from catastrophic over-heating situations which can cause permanent damage. Furthermore, in a large multi-core microprocessor, it is also imperative to continuously monitor potential hot-spots that are prone to thermal runaway. The locations of such hot spots depend on the operations and instruction the processor carries out at a given time. Due to practical limitations, it is an overkill to place a big size temperature sensor nearest to all possible hot spots. Thus, an ideal on-chip temperature sensor should have minimal area so that it can be placed non-invasively across the chip without drastically changing the chip floor plan. In addition, the power consumption of the sensors should be very low to reduce the power budget overhead of thermal monitoring system, and to minimize measurement inaccuracies due to self-heating. The objective of this research is to design an ultra-small size and ultra-low power temperature sensor such that it can be placed in the intimate proximity of all possible hot spots across the chip. The general idea is to use the leakage current of a reverse-bias p-n junction diode as an operand for temperature sensing. The tasks within this project are to examine the theoretical aspect of such sensors in both Silicon-On-Insulator (SOI), and bulk Complementary Metal-Oxide Semiconductor (CMOS) technologies, implement them in deep sub-micron technologies, and ultimately evaluate their performances, and compare them to existing solutions.Electrical and Computer Engineerin
Condition assessment of bridge structures using statistical analysis of wavelets
La surveillance Ă distance des structures a Ă©mergĂ© comme une prĂ©occupation importante pour les ingĂ©nieurs afin de maintenir la sĂ©curitĂ© et la fiabilitĂ© des infrastructures civiles pendant leur durĂ©e de vie. Les techniques de surveillance structurale (SHM) sont de plus en plus populaires pour fournir un diagnostic de "l'Ă©tat" des structures en raison de leur vieillissement, de la dĂ©gradation des matĂ©riaux ou de dĂ©fauts survenus pendant leur construction. Les limites de l'inspection visuelle et des techniques non destructives, qui sont couramment utilisĂ©es pour dĂ©tecter des dĂ©fauts extrĂȘmes sur les parties accessibles des structures, ont conduit Ă la dĂ©couverte de nouvelles technologies qui Ă©valuent dâun seul tenant l'Ă©tat global d'une structure surveillĂ©e. Les techniques de surveillance globale ont Ă©tĂ© largement utilisĂ©es pour la reconnaissance d'endommagement dans les grandes infrastructures civiles, telles que les ponts, sur la base d'une analyse modale de la rĂ©ponse dynamique structurale. Cependant, en raison des caractĂ©ristiques complexes des structures oeuvrant sous des conditions environnementales variables et des incertitudes statistiques dans les paramĂštres modaux, les techniques de diagnostic actuelles n'ont pas Ă©tĂ© concluantes pour conduire Ă une mĂ©thodologie robuste et directe pour dĂ©tecter les incrĂ©ments de dommage avant qu'ils n'atteignent un stade critique. Câest ainsi que des techniques statistiques de reconnaissance de formes sont incorporĂ©es aux mĂ©thodes de dĂ©tection d'endommagement basĂ©es sur les vibrations pour fournir une meilleure estimation de la probabilitĂ© de dĂ©tection des dommages dans des applications in situ, ce qui est habituellement difficile compte tenu du rapport bruit Ă signal Ă©levĂ©. NĂ©anmoins, cette partie du SHM est encore Ă son stade initial de dĂ©veloppement et, par consĂ©quent, d'autres tentatives sont nĂ©cessaires pour parvenir Ă une mĂ©thodologie fiable de dĂ©tection de l'endommagement. Une stratĂ©gie de dĂ©tection de dommages basĂ©e sur des aspects statistiques a Ă©tĂ© proposĂ©e pour dĂ©tecter et localiser de faibles niveaux incrĂ©mentiels d'endommagement dans une poutre expĂ©rimentale pour laquelle tant le niveau d'endommagement que les conditions de retenue sont rĂ©glables (par exemple ancastrĂ©e-ancastrĂ©e et rotulĂ©e-rotulĂ©e). PremiĂšrement, des expĂ©riences ont Ă©tĂ© effectuĂ©es dans des conditions de laboratoire contrĂŽlĂ©es pour dĂ©tecter de faibles niveaux d'endommagement induits (par exemple une fissure correspondant Ă 4% de la hauteur dâune section rectangulaire Ă©quivalente) simulant des scĂ©narios d'endommagement de stade prĂ©coce pour des cas rĂ©els. DiffĂ©rents niveaux d'endommagement ont Ă©tĂ© simulĂ©s Ă deux endroits distincts le long de la poutre. Pour chaque sĂ©rie d'endommagement incrĂ©mentiel, des mesures rĂ©pĂ©tĂ©es (~ 50 Ă 100) ont Ă©tĂ© effectuĂ©es pour tenir compte de l'incertitude et de la variabilitĂ© du premier mode de vibration de la structure en raison d'erreurs expĂ©rimentales et du bruit. Une technique d'analyse par ondelette basĂ©e sur les modes a Ă©tĂ© appliquĂ©e pour dĂ©tecter les changements anormaux survenant dans les modes propres causĂ©es par le dommage. La rĂ©duction du bruit ainsi que les caractĂ©ristiques des agrĂ©gats ont Ă©tĂ© obtenues en mettant en Ćuvre l'analyse des composantes principales (PCA) pour l'ensemble des coefficients d'ondelettes calculĂ©s Ă des nĆuds (ou positions) rĂ©guliĂšrement espacĂ©s le long du mode propre. En rejetant les composantes qui contribuent le moins Ă la variance globale, les scores PCA correspondant aux premiĂšres composantes principales se sont rĂ©vĂ©lĂ©s trĂšs corrĂ©lĂ©s avec de faibles niveaux d'endommagement incrĂ©mentiel. Des mĂ©thodes classiques d'essai d'hypothĂšses ont Ă©tĂ© effectuĂ©es sur les changements des paramĂštres de localisation des scores pour conclure objectivement et statistiquement, Ă un niveau de signification donnĂ©, sur la prĂ©sence du dommage. Lorsqu'un dommage statistiquement significatif a Ă©tĂ© dĂ©tectĂ©, un nouvel algorithme basĂ© sur les probabilitĂ©s a Ă©tĂ© dĂ©veloppĂ© pour dĂ©terminer l'emplacement le plus probable de l'endommagement le long de la structure. DeuxiĂšmement, se basant sur l'approche probabiliste, une sĂ©rie de tests a Ă©tĂ© effectuĂ©e dans une chambre environnementale Ă tempĂ©rature contrĂŽlĂ©e pour Ă©tudier les contributions relatives des effets de lâendommagement et de la tempĂ©rature sur les propriĂ©tĂ©s dynamiques de la poutre afin dâestimer un facteur de correction pour l'ajustement des scores extraits. Il s'est avĂ©rĂ© que la tempĂ©rature avait un effet rĂ©versible sur la distribution des scores et que cet effet Ă©tait plus grand lorsque le niveau d'endommagement Ă©tait plus Ă©levĂ©. Les rĂ©sultats obtenus pour les scores ajustĂ©s indiquent que la correction des effets rĂ©versibles de la tempĂ©rature peut amĂ©liorer la probabilitĂ© de dĂ©tection et minimiser les fausses alarmes. Les rĂ©sultats expĂ©rimentaux indiquent que la contribution combinĂ©e des algorithmes utilisĂ©s dans cette Ă©tude Ă©tait trĂšs efficace pour dĂ©tecter de faibles niveaux d'endommagement incrĂ©mentiel Ă plusieurs endroits le long de la poutre tout en minimisant les effets indĂ©sirables du bruit et de la tempĂ©rature dans les rĂ©sultats. Les rĂ©sultats de cette recherche dĂ©montrent que l'approche proposĂ©e est prometteuse pour la surveillance des structures. Cependant, une quantitĂ© importante de travail de validation est attendue avant sa mise en Ćuvre sur des structures rĂ©elles. Mots-clĂ©s : DĂ©tection et localisation des dommages, Poutre, Mode propre, Ondelette, Analyse des composantes principales, Rapport de probabilitĂ©, TempĂ©ratureRemote monitoring of structures has emerged as an important concern for engineers to maintain safety and reliability of civil infrastructure during its service life. Structural Health Monitoring (SHM) techniques are increasingly becoming popular to provide ideas for diagnosis of the "state" of potential defects in structures due to aging, deterioration and fault during construction. The limitations of visual inspection and non-destructive techniques, which were commonly used to detect extreme defects on only accessible portions of structures, led to the discovery of new technologies which assess the "global state" of a monitored structure at once. Global monitoring techniques have been used extensively for the recognition of damage in large civil infrastructure, such as bridges, based on modal analysis of structural dynamic response. However, because of complicated features of real-life structures under varying environmental conditions and statistical uncertainties in modal parameters, current diagnosis techniques have not been conclusive in ascertaining a robust and straightforward methodology to detect damage increments before it reaches its critical stage. Statistical pattern recognition techniques are incorporated with vibration-based damage detection methods to provide a better estimate for the probability of the detection of damage in field applications, which is usually challenging given the high noise to signal ratio. Nevertheless, this part of SHM is still in its initial stage of development and, hence, further attempts are required to achieve a reliable damage detection methodology. A statistical-based damage detection strategy was proposed to detect and localize low levels of incremental damage in an experimental beam in which the level of damage and beam restraint conditions are adjustable (e.g. fixed-fixed and pinned-pinned). First, experiments were performed in controlled laboratory conditions to detect small levels of induced-damage (e.g. 4% crack height for an equivalent rectangular section) simulated for early stage damage scenarios in real cases. Various levels of damage were simulated at two distinct locations along the beam. For each sate of incremental damage, repeat measurements (~ 50 to 100) were performed to account for uncertainty and variability in the first vibration mode of the structure due to experimental errors and noise. A modal-based wavelet analysis technique was applied to detect abnormal changes occurring in the mode shapes caused by damage. Noise reduction as well as aggregate characteristics were obtained by implementing the Principal Component Analysis (PCA) into the set of wavelet coefficients computed at regularly spaced nodes along the mode shape. By discarding components that contribute least to the overall variance, the PCA scores corresponding to the first few PCs were found to be highly correlated with low levels of incremental damage. Classical hypothesis testing methods were performed on changes on the location parameters of the scores to conclude damage objectively and statistically at a given significance level. When a statistically significant damage was detected, a novel Likelihood-based algorithm was developed to determine the most likely location of damage along the structure. Secondly, given the likelihood approach, a series of tests were carried out in a climate-controlled room to investigate the relative contributions of damage and temperature effects on the dynamic properties of the beam and to estimate a correction factor for the adjustment of scores extracted. It was found that the temperature had a reversible effect on the distribution of scores and that the effect was larger when the damage level was higher. The resulted obtained for the adjusted scores indicated that the correction for reversible effects of temperature can improve the probability of detection and minimize false alarms. The experimental results indicate that the combined contribution of the algorithms used in this study were very efficient to detect small-scale levels of incremental damage at multiple locations along the beam, while minimizing undesired effects of noise and temperature in the results. The results of this research demonstrate that the proposed approach may be used as a promising tool for SHM of actual structures. However, a significant amount of challenging work is expected for implementing it on real structures. Key-words: Damage Detection and Localization, Beam, Mode Shape, Wavelet, Principal Component Analysis, Likelihood Ratio, Temperatur
Intelligent Sensor Networks
In the last decade, wireless or wired sensor networks have attracted much attention. However, most designs target general sensor network issues including protocol stack (routing, MAC, etc.) and security issues. This book focuses on the close integration of sensing, networking, and smart signal processing via machine learning. Based on their world-class research, the authors present the fundamentals of intelligent sensor networks. They cover sensing and sampling, distributed signal processing, and intelligent signal learning. In addition, they present cutting-edge research results from leading experts
Integrated reference circuits for low-power capacitive sensor interfaces
This thesis consists of nine publications and an overview of the research topic, which also summarizes the work. The research described in this thesis concentrates on the design of low-power sensor interfaces for capacitive 3-axis micro-accelerometers. The primary goal throughout the thesis is to optimize power dissipation. Because the author made the main contribution to the design of the reference and power management circuits required, the overview part is dominated by the following research topics: current, voltage, and temperature references, frequency references, and voltage regulators.
After an introduction to capacitive micro-accelerometers, the work describes the typical integrated readout electronics of a capacitive sensor on the functional level. The readout electronics can be divided into four different functional parts, namely the sensor readout itself, signal post-processing, references, and power management. Before the focus is shifted to the references and further to power management, different ways to realize the sensor readout are briefly discussed.
Both current and voltage references are required in most analog and mixed-signal systems. A bandgap voltage reference, which inherently uses at least one current reference, is practical for the generation of an accurate reference voltage. Very similar circuit techniques can be exploited when implementing a temperature reference, the need for which in the sensor readout may be justified by the temperature compensation, for example.
The work introduces non-linear frequency references, namely ring and relaxation oscillators, which are very suitable for the generation of the relatively low-frequency clock signals typically needed in the sensor interfaces. Such oscillators suffer from poor jitter and phase noise performance, the quantities of which also deserve discussion in this thesis.
Finally, the regulation of the supply voltage using linear regulators is considered. In addition to extending the battery life by providing a low quiescent current, the regulator must be able to supply very low load currents and operate without off-chip capacitors
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Ultra-Low-Power Sensors and Receivers for IoT Applications
The combination of ultra-low power analog front-ends and CMOS-compatible transducers enable new applications, such as environmental monitors, household appliances, health trackers, etc. that are seamlessly integrated into our daily lives. Furthermore, wireless connectivity allows many of these sensors to operate both independently and collectively. These techniques collectively fulfil the recent surge of internet-of-things (IoT) applications that have the potential to fundamentally change daily life for millions of people.In this dissertation, the circuit and system design of wireless receivers and sensors is presented that explores the challenges of implementing long lifespan, high accuracy, and large coverage range IoT sensor networks. The first is a wake-up receiver (WuRX), which continuously monitors the RF environment to wake up a higher-power radio upon detection of a predetermined RF signature. This work both improves sensitivity and reduces power over prior art through a multi-faceted design featuring an impedance transformation network with large passive voltage gain, an active envelope detector with high input impedance to facilitate large passive voltage gain, a low-power precision comparator, and a low-leakage digital baseband correlator.Although pushing the prior WuRX performance boundary by orders of magnitude, the first work shows moderate sensitivity, inferior temperature robustness, and large area with external lumped components. Thus, the second work shows a miniaturized WuRX that is temperature-compensated, yet still consumes only nano-watt power and millimeter area while operating at 9 GHz. To further reduce the area, a global common-mode feedback is utilized across the envelope detector and baseband amplifier that eliminates the need for off-chip ac-coupling components. Multiple temperature-compensation techniques are proposed to maintain constant bandwidth of the signal path and constant clock frequency. Both WuRXs operate at 0.4 V supply, consume near-zero power and achieve ~-70 dBm sensitivity.Lastly, the first reported CMOS 2-in-1 relative humidity and temperature sensor is presented. A unified analog front-end interfaces on-chip transducers and converts the inputs into a frequency vis a high-linearity frequency-locked loop. An incomplete-settling switched-capacitor-based Wheatstone bridge is proposed to sense the inputs in a power-efficient fashion
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