High-temperature piezoelectric wafer active sensors (HT-PWAS) have been developed for structure health monitoring at hazard environments for decades. Different candidates have previously been tested under 270 °C and a new piezoelectric material langasite (LGS) was chosen here for a pilot study up to 700 °C. A preliminary study was performed to develop a high temperature sensor that utilizes langasite material. The Electromechanical impedance (E/M) method was chosen to detect the piezoelectric property. Experiments that verify the basic piezoelectric property of LGS at high temperature environments were carried out. Further validations were conducted by testing structures with attached LGS sensors at elevated temperature. Additionally, a detection system simulating the working process of LGS monitoring system was developed with PZT material at room temperature. This thesis, for the first time, (to the best of author’s knowledge) presents that langasite is ideal for making piezoelectric wafer active sensors for high temperature structure health monitoring applications.

This work is an experimental study of applying an impedance-based health monitoring technique to complex structures. The work is presented in three parts. In the first part we consider effects of the following three factors on damage detection abilities: actuator excitation level, test wire length and ambient conditions (temperature, structural loading and vibration). It was concluded that increasing the applied voltage improves the signal to noise ratio and damage detection abilities. Test wire lengths under 30m do not affect damage detection abilities. The technique is able to distinguish and detect damage even with variations in temperature, structural loading and vibration. In the second part we apply our health monitoring technique to a complex truss structure and a massive steel steam header. We discovered that with multiplexing (acquiring a single signal from distributed actuators) the actuators on the truss structure we could detect damage but with less location information. Damage detection on the steel pipe ended in inconclusive results. The use of this technique on massive structures needs further investigation. Finally, we conducted a detailed experimental study of monitoring the integrity of composite-reinforced masonry structures. We developed a software package which enables even a casual user to determine if significant damage has occurred in these structures. The technique was successfully applied to detect damage (particularly due to delamination) in these composite-concrete structures. Most significantly, the technique was also able to detect damage well in advance of actual failure. This work relies mainly on frequency response plots and damage metric charts to present the data and to arrive at any conclusions. While frequency response plots give a qualitative approach to the analysis, damage metric charts attempt to quantify the data. / Master of Science

With the goal to continue interplanetary exploration and search for past or existent life on Mars, software and hardware for unmanned subsurface drills are being developed. Unlike drilling on Earth, interplanetary exploration drills operate with very low available power and require on-board integrated health monitoring systems, with quick-response recovery procedures, under complete autonomous operations. As many drilling faults are not known a priori, Earth-based direction and control of an unmanned interplanetary drilling operation is not practical. Such missions also require advanced robotic systems that are more susceptible to structural and mechanical failures, which motivates a need for structural health monitoring techniques relevant to interplanetary exploration systems. Structural health monitoring (SHM) is a process of detecting damage or other types of defects in structural and mechanical systems that have the potential to adversely affect the current or future performance of these systems. Strict requirements for interplanetary drilling missions create unique research problems and challenges compared with SHM procedures and techniques developed to date. These challenges include implementing sensors and devices that do not interfere with the drilling operation, producing "real-time" diagnostics of the drilling condition, and developing an automation procedure for complete autonomous operations. Thus, the completed thesis work presents basic research leading to the dynamic analysis of rotating structures with specific application to interplanetary subsurface drill systems, and the formulation of an autonomous, real-time, dynamics-based SHM technique for drilling applications. This includes modeling and validating the structural dynamic system, with and without damage or faults, for a prototype interplanetary subsurface drill, exploring the use of Laser Doppler Velocimeter sensors for use in real-time SHM, developing signal filters to remove inherent harmonic components from the dynamic signal of rotating structures, developing an automation procedure with the associated software, and validating the SHM system through laboratory experiments and field tests. The automated dynamics-based structural health monitoring technique developed in this thesis presents advanced research accomplishments leading to real-time, autonomous SHM, and it has been validated on an operating dynamic system in laboratory and field tests. The formulated SHM and drilling operation also met or exceeded all specified requirements. Other major contributions of this thesis work include the formulation and demonstration of real-time, autonomous SHM in rotating structures using Laser Doppler Velocimeter sensors.

Structural Health Monitoring (SHM) with emerging technologies like e.g. fibre optic sensors, lasers, radars, acoustic emission and Micro Electro Mechanical Systems (MEMS) made an entrance into the civil engineering field in last decades. Expansion of new technologies together with development in data communication benefited for rapid development. The author has been doing research as well as working with SHM and related tasks nearly a decade. Both theoretical knowledge and practical experience are gained in this constantly developing field. This doctoral thesis presents lessons learned in SHM and sensory technologies when monitoring civil engineering structures, mostly bridges. Nevertheless, these techniques can also be used in most applications related to civil engineering like dams, high rise buildings, off-shore platforms, pipelines, harbour structures and historical monuments. Emerging and established technologies are presented, discussed and examples are given based on the experience achieved. A special care is given to Fibre Optic Sensor (FOS) technology and its latest approach. Results from crack detection testing, long-term monitoring, and sensor comparison and installation procedure are highlighted. The important subjects around sensory technology and SHM are discussed based on the author's experience and recommendations are given. Applied research with empirical and experimental methods was carried out. A state-of-the art-review of SHM started the process but extensive literature studies were done continuously along the years in order to keep the knowledge up to date. Several SHM cases, both small and large scale, were carried out including sensor selection, installation planning, physical installation, data acquisition set-up, testing, monitoring, documentation and reporting. One case study also included modification and improvement of designed system and physical repair of sensors as well as two Site Acceptance Tests (SATs) and the novel crack detection system testing. Temporary measuring and testing also took place and numerous Structural Health Monitoring Systems (SHMSs) were designed for new bridges. The observed and measured data/phenomena were documented and analysed.  Engineers, researchers and owners of structures are given an essential implement in managing and maintaining structures. Long-term effects like shrinkage and creep in pre-stressed segmental build bridges were studied. Many studies show that existing model codes are not so good to predict these long-term effects. The results gained from the research study with New Årsta Railway Bridge are biased be the fact that our structure is indeed special. Anyhow, the results can be compared to other similar structures and adequately used for the maintenance planning for the case study. A long-term effect like fatigue in steel structures is a serious issue that may lead to structural collapse. Novel crack detection and localisation system, based on development on crack identification algorithm implemented in DiTeSt system and SMARTape delamination mechanism, was developed, tested and implemented. Additionally, new methods and procedures in installing, testing, modifying and improving the installed system were developed. There are no common procedures how to present the existing FOS techniques. It is difficult for an inexperienced person to judge and compare different systems. Experience gained when working with Fibre Optic Sensors (FOS) is collected and presented. The purpose is, firstly to give advice when judging different systems and secondly, to promote for more standardised way to present technical requirements. Furthermore, there is need to regulate the vocabulary in the field. Finally, the general accumulated experience is gathered. It is essential to understand the complexity of the subject in order to make use of it. General trends and development are compared for different applications. As the area of research is wide, some chosen, specific issues are analysed on a more detailed level. Conclusions are drawn and recommendations are given, both specific and more general. SHMS for a complex structure requires numerous parameters to be measured. Combination of several techniques will enable all required measurements to be taken. In addition, experienced specialists need to work in collaboration with structural engineers in order to provide high-quality systems that complete the technical requirement. Smaller amount of sensors with proper data analysis is better than a complicated system with numerous sensors but with poor analysis. Basic education and continuous update for people working with emerging technologies are also obligatory. A lot of capital can be saved if more straightforward communication and international collaboration are established: not only the advances but also the experienced problems and malfunctions need to be highlighted and discussed in order not to be repeated. Quality assurance issues need to be optimized in order to provide high quality SHMSs. Nevertheless, our structures are aging and we can be sure that the future for sensory technologies and SHM is promising. The final conclusion is that an expert in SHM field needs wide education, understanding, experience, practical sense, curiosity and preferably investigational mind in order to solve the problems that are faced out when working with emerging technologies in the real world applications.  The human factor, to be able to bind good relationship with workmanship cannot be neglected either. There is also need to be constantly updated as the field itself is in continuous development. / QC 20111117 / SHMS of the New Årsta Railway Bridge

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La limite des connaissances techniques ou fondamentale, est une réalité dont l’industrie fait face. Le besoin de mettre à jour cette connaissance acquise est essentiel pour une compétitivité économique, mais aussi pour une meilleure maniabilité des systèmes et machines. Aujourd’hui grâce à ces systèmes et machine, l’expansion de données en quantité, en fréquence de génération est un véritable phénomène. À présent par exemple, les avions Airbus génèrent des centaines de mégas de données par jour, et intègrent des centaines voire des milliers de capteurs dans les nouvelles générations d’avions. Ces données générées par ces capteurs, sont exploitées au sol ou pendant le vol, pour surveiller l’état et la santé de l’avion, et pour détecter des pannes, des incidents ou des changements. En théorie, ces pannes, ces incidents ou ces changements sont connus sous le terme d’anomalie. Une anomalie connue comme un comportement qui ne correspond pas au comportement normal des données. Certains la définissent comme une déviation d’un modèle normal, d’autres la définissent comme un changement. Quelques soit la définition, le besoin de détecter cette anomalie est important pour le bon fonctionnement de l'avion. Actuellement, la détection des anomalies à bord des avions est assuré par plusieurs équipements de surveillance aéronautiques, l’un de ces équipements est le « Aircraft condition monitoring System –ACMS », enregistre les données générées par les capteurs en continu, il surveille aussi l’avion en temps réel grâce à des triggers et des seuils programmés par des Airlines ou autres mais à partir d’une connaissance a priori du système. Cependant, plusieurs contraintes limitent le bon fonctionnement de cet équipement, on peut citer par exemple, la limitation des connaissances humaines un problème classique que nous rencontrons dans plusieurs domaines. Cela veut dire qu’un trigger ne détecte que les anomalies et les incidents dont il est désigné, et si une nouvelle condition surgit suite à une maintenance, changement de pièce, etc. Le trigger est incapable s’adapter à cette nouvelle condition, et il va labéliser toute cette nouvelle condition comme étant une anomalie. D’autres problèmes et contraintes seront cités progressivement dans les chapitres qui suivent. L’objectif principal de notre travail est de détecter les anomalies et les changements dans les données de capteurs, afin d’améliorer le system de surveillance de santé d’avion connu sous le nom Aircraft Health Monitoring(AHM). Ce travail est basé principalement sur une analyse à deux étapes, Une analyse unie varie dans un contexte non supervisé, qui nous permettra de se focaliser sur le comportement de chaque capteur indépendamment, et de détecter les différentes anomalies et changements pour chaque capteur. Puis une analyse multi-variée qui nous permettra de filtrer certaines anomalies détectées (fausses alarmes) dans la première analyse et de détecter des groupes de comportement suspects. La méthode est testée sur des données réelles et synthétiques, où les résultats, l’identification et la validation des anomalies sont discutées dans cette thèse. / The limitation of the knowledge, technical, fundamental is a daily challenge for industries. The need to updates these knowledge are important for a competitive industry and also for an efficient reliability and maintainability of the systems. Actually, thanks to these machines and systems, the expansion of the data on quantity and frequency of generation is a real phenomenon. Within Airbus for example, and thanks to thousands of sensors, the aircrafts generate hundreds of megabytes of data per flight. These data are today exploited on the ground to improve safety and health monitoring system as a failure, incident and change detection. In theory, these changes, incident and failure are known as anomalies. An anomaly is known as deviation form a normal behavior of the data. Others define it as a behavior that do not conform the normal behavior. Whatever the definition, the anomaly detection process is very important for good functioning of the aircraft. Currently, the anomaly detection process is provided by several health monitoring equipments, one of these equipment is the Aircraft Health Monitoring System (ACMS), it records continuously the date of each sensor, and also monitor these sensors to detect anomalies and incident using triggers and predefined condition (exeedance approach). These predefined conditions are programmed by airlines and system designed according to a prior knowledge (physical, mechanical, etc.). However, several constraints limit the ACMS anomaly detection potential. We can mention, for example, the limitation the expert knowledge which is a classic problem in many domains, since the triggers are designed only to the targeted anomalies. Otherwise, the triggers do not cover all the system conditions. In other words, if a new behavior appears (new condition) in the sensor, after a maintenance action, parts changing, etc. the predefined conditions won't detect any thing and may be in many cases generated false alarms. Another constraint is that the triggers (predefined conditions) are static, they are unable to adapt their proprieties to each new condition. Another limitation is discussed gradually in the future chapters. The principle of objective of this thesis is to detect anomalies and changes in the ACMS data. In order to improve the health monitoring function of the ACMS. The work is based principally on two stages, the univariate anomaly detection stage, where we use the unsupervised learning to process the univariate sensors, since we don’t have any a prior knowledge of the system, and no documentation or labeled classes are available. The univariate analysis focuses on each sensor independently. The second stage of the analysis is the multivariate anomaly detection, which is based on density clustering, where the objective is to filter the anomalies detected in the first stage (false alarms) and to detect suspected behaviours (group of anomalies). The anomalies detected in both univariate and multivariate can be potential triggers or can be used to update the existing triggers. Otherwise, we propose also a generic concept of anomaly detection based on univariate and multivariate anomaly detection. And finally a new concept of validation anomalies within airbus.

Master of Science / Department of Electrical and Computer Engineering / Steven Warren / Networks of low-power, in-suit, wired and wireless health sensors offer the potential to track and predict the health of astronauts engaged in extra-vehicular and in-station activities in zero- or reduced- gravity environments. Fundamental research questions exist regarding (a) types and form factors of biomedical sensors best suited for these applications, (b) optimal ways to render wired/wireless on-body networks with the objective to draw little-to-no power, and (c) means to address the wireless transmission challenges offered by a spacesuit constructed from layers of aluminized mylar. This thesis addresses elements of these research questions through the implementation of a collection of ZigBee-based wireless health monitoring devices that can potentially be integrated into a spacesuit, thereby providing continuous information regarding astronaut fatigue and state of health. Wearable biomedical devices investigated for this effort include electrocardiographs, electromyographs, pulse oximeters, inductive plethysmographs, and accelerometers/gyrometers. These ZigBee-enabled sensors will form the nodes of an in-suit ZigBee Pro network that will be used to (1) establish throughput requirements for a functional in-suit network and (2) serve as a performance baseline for future devices that employ ultra-low-power field-programmable gate arrays and micro-transceivers. Sensor devices will upload data to a ZigBee network coordinator that has the form of a pluggable USB connector. Data are currently visualized using MATLAB and LabVIEW.

Résumé : La surveillance de l’intégrité des structures (Structural Health Monitoring - SHM) est une nouvelle technologie, et comme toute nouvelle avancée technologique, elle n’a pas encore réalisé son plein potentiel. Le SHM s’appuie sur des avancées dans plusieurs disciplines, dont l’évaluation non-desctructive, les matériaux intelligents, et les capteurs et actionneurs intégrés. Une des disciplines qui permet son déploiement est la simulation numérique. Le SHM englobe une variété de techniques basées sur la génération d’ondes vibratoires et d’ondes ultrasonores guidées. L’utilisation d’ondes guidées offre en particulier une vaste gamme d’avantages. Le défi majeur associé à la pleine utilisation de la simulation numérique dans la conception d’un système SHM basé sur l’utilisation d’ondes guidées réside dans les ressources de calcul requises pour une simulation précise. La principale raison pour ces exigences est la dispersion induite par la discrétisation numérique, tel qu’indiqué dans la littérature. La méthodes des éléments spectraux (SEM) est une variante de la p-version de la méthode des éléments finis (FEM) qui offre certains outils pour solutionner le problème des erreurs de dispersion, mais la littérature souffre toujours d’une lacune dans l’étude systématique des erreurs de dispersion numérique et de sa dépendance sur les paramètres de simulation. Le présent ouvrage tente de combler cette lacune pour les théories d’ingénierie en vibrations. Il présente d’abord le développement de la formulation des éléments spectraux pour différentes théories d’ingénierie pertinentes pour la propagation des ondes vibratoires dans différents types de structures, comme des tiges et des plaques. Puis, une nouvelle technique pour le calcul des erreurs de dispersion numériques est présentée et appliquée systématiquement dans le but d’évaluer la dispersion numérique induite en termes d’erreurs dans les vitesses de propagation. Cette technique est utilisable pour les différentes formes de propagation des ondes vibratoires dans les éléments structuraux visés dans la présente thèse afin d’évaluer quantitativement les exigences de précision en termes de paramètres de maillage. Les ondes de Lamb constituent un cas particulier de la déformation plane des ondes élastiques, en raison de la présence des doubles frontières à traction libre qui couplent les ondes longitudinales et de cisaillement et qui conduisent à une infinité de modes propagatifs qui sont dispersifs par nature. La simulation des ondes de Lamb n’a pas fait l’objet d’analyse systématique de la dispersion numérique dans la littérature autant pour la SEM que la FEM. Nous rapportons ici pour la première fois les résultats de l’analyse de dispersion numérique pour la propagation des ondes Lamb. Pour toutes les analyses de dispersion numérique présentées ici, l’analyse a été effectuée à˘ala fois dans le domaine fréquentiel et dans le domaine temporel. En se basant sur la nouvelle compréhension des effets de discrétisation numérique de la propagation des ondes guidées, nous étudions l’application de la SEM à la simulation numérique pour des applications de conception en SHM. Pour ce faire, l’excitation piézoélectrique est développée, et une nouvelle technique de condensation statique est développée et mise en œuvre pour les équations de la matrice semi-discrète, qui élimine le besoin de solution itérative, ainsi surnommée fortement couplée ou entièrement couplée. Cet élément piézoélectrique précis est ensuite utilisé pour étudier en détails les subtilités de la conception d’un système SHM en mettant l’accent sur la propagation des ondes de Lamb. Afin d’éviter la contamination des résultats par les réflexions sur les bords une nouvelle forme particulière d’élément absorbant a été développée et mise en œuvre. Les résultats de simulation dans le domaine fréquentiel jettent un éclairage nouveau sur les limites des modèles théoriques actuels pour l’excitation des ondes de Lamb par piézoélectriques. L’excitation par un élément piézoélectrique couplé est ensuite entièrement simulée dans le domaine temporel, et les résultats de simulation sont validés par deux cas de mesures expérimentales ainsi que par la simulation classique avec des éléments finis en utilisant le logiciel commercial ANSYS. // Abstract : Structural health monitoring (SHM) is a novel technology, and like any new technological advancement it has yet not realized its full potential. It builds on advancements in several disciplines including nondestructive evaluation, smart materials, and embedded sensors and actuators. One of the enabling disciplines is the numerical simulation. SHM encompasses a variety of techniques, vibration based, impedance and guided ultrasonic waves. Guided waves offers a wide repertoire of advantages. The major challenge facing the full utilization of the numerical simulation in designing a viable guided waves based SHM System is the formidable computational requirements for accurate simulation. The main reason for these requirements is the dispersion induced by numerical discretization as explained in the literature review. The spectral element (SEM) is a variant of the p-version finite element (FEM) that offers certain remedies to the numerical dispersion errors problem, yet it lacks a systematic study of the numerical dispersion errors and its dependence on the meshing parameters. The present work attempts to fill that gap for engineering theories. It starts by developing the formulation of the spectral element for different relevant engineering theories for guided waves propagation in various structural elements, like rods and plates. Then, extending the utility of a novel technique for computing the numerical dispersion errors, we systematically apply it in order to evaluate the numerically induced dispersion in terms of errors in the propagation speeds. This technique is employed for the various forms of guided waves propagation in structural elements covered in the present thesis in order to quantitatively assess the accuracy requirements in terms of the meshing parameters. The Lamb guided waves constitute a special case of the plane strain elastic waves, that is due to the presence of the double traction free boundaries, couple in the section plane and this coupling leads to an infinitude of propagating modes that are dispersive in nature. Lamb waves simulation have not been a subject of numerical dispersion analysis in the open literature neither for SEM nor FEM for that matter. We report here for the first time the numerical dispersion analysis results for Lamb waves propagation. For all the numerical dispersion analysis presented here, the analysis was done for both the frequency domain and time domain analysis. Based on the established understanding of the numerical discretization effects on the guided waves propagation, we utilize this knowledge to study the application of SEM to SHM simulations. In order to do so the piezoelectric excitation is developed, and a new static condensation technique is developed for the semidiscrete matrix equations, that eliminate the need for iterative solution, thus dubbed strongly coupled or fully coupled implementation. This accurate piezoelectric element are then used to study in details the intricacies of the design of an SHM system with specific emphasis on the Lamb waves propagation. In order to avoid the contamination of the results by the reflections from the edges a new special form of absorbing boundary was developed and implemented. The Simulation results in the frequency domain illuminated the limitations of the current theoretical models for piezoelectric excitation of Lamb waves. The piezoelectric excitation of a fully coupled element is then simulated in the time domain, and the results of simulation was verified against two cases of experimental measurements as well as conventional finite element simulation using the commercial software ANSYS.

A structural health monitoring system is desired to monitor the integrity of cylindrical, multi-layer carbon over-wrapped pressure vessels intended to house hydrogen at high pressures. In order to develop the system based on ultrasonic guided wave technology, the interaction between ultrasonic guided waves and defect types of interest must be understood. Finite element models in two and three dimensions are developed to predict guided wave motion in the reservoirs. Key parameters are optimized including frequency range, excited modes, detected modes, and transducer dimensions. A novel baseline subtraction technique in the frequency wavenumber domain is presented to increase lower level detection limits. Some experiments are carried out to corroborate the findings in the finite element environment.

The work presented in this thesis investigates novel transducer implementations that take advantage of directional sensing and generation of acoustic waves. These transducers are conceived by exploiting a Fourier-based design methodology. The proposed devices find application in the broad field of Structural Health Monitoring (SHM), which is a very active research area devoted to the assessment of the structural integrity of critical components in aerospace, civil and mechanical systems. Among SHM schemes, Guided Waves (GWs) testing has emerged as a prominent option for inspection of plate-like structures using permanently attached piezoelectric transducers. GWs-based methods rely on the generation and sensing of elastic waves to evaluate structural integrity. They offer an effective method to estimate location, severity and type of damage. It is widely acknowledged among the GWs-SHM community that effective monitoring of structural health is facilitated by sensors and actuators designed with ad hoc engineered capabilities. The objective of this research is to design innovative piezoelectric transducers by specifying their electrode patterns in the Fourier domain. Taking advantage of the Fourier framework, transducer design procedures are outlined and tailored to relevant SHM applications, such as (i) directional actuation and sensing of GWs, (ii) simultaneous sensing of multiple strain components with a single device, and (iii) estimation of the location of impact sites on structural components. The proposed devices enable significant reductions in cost, hardware, and power requirements for advanced SHM schemes when compared to current technologies.