Wind turbine blades experience tremendous stresses while in operation. Failure of a blade can damage other components or other wind turbines. This research focuses on developing an electromagnetic energy harvester for powering structural health monitoring (SHM) equipment inside a turbine blade. The harvester consists of a magnet inside a tube with coils outside the tube. The changing orientation of the blade causes the magnet to slide along the tube, inducing a voltage in the coils which in turn powers the SHM system. This thesis begins with a brief history of electromagnetic energy harvesting and energy harvesters in rotating environments. Next a model of the harvester is developed encompassing the motion of the magnet, the current in the electrical circuit, and the coupling between the mechanical and electrical domains. The nonlinear coupling factor is derived from Faraday's law of induction and from modeling the magnet as a magnetic dipole moment. Three experiments are performed to validate the model: a free fall test to verify the coupling factor expression, a rotating test to study the model with a load resistor circuit, and a capacitor charging test to examine the model with an energy storage circuit. The validated model is then examined under varying tube lengths and positions, varying coil sizes and positions, and variations in other parameters. Finally a sample harvester is presented that can power an SHM system inside a large scale wind turbine blade spinning up to 20 RPM and can produce up to 14.1 mW at 19 RPM. / Master of Science

Wind power is a fast-growing source of non-polluting, renewable energy with vast potential. However, current wind technology must be improved before the potential of wind power can be fully realized. One of the key components in improving wind turbines is their blades. Blade failure is very costly because blade failure can damage other blades, the wind turbine itself, and possibly other wind turbines. A successful structural health monitoring (SHM) system incorporated into wind turbines could extend blade life and allow for less conservative designs. Impedance-based SHM is a method which has shown promise on a wide variety of structures. The technique utilizes small piezoceramic (PZT) patches attached to a structure as self-sensing actuators to both excite the structure with high-frequency excitations, and monitor any changes in structural mechanical impedance. By monitoring the electrical impedance of the PZT, assessments can be made about the integrity of the mechanical structure. Recent advances in hardware systems with onboard computing, including actuation and sensing, computational algorithms, and wireless telemetry, have improved the accessibility of the impedance method for in-field measurements. The feasibility of implementing impedance-based SHM on wind turbine blades is investigated in this work. Experimentation was performed to determine the capability of the method to detect damage on blades. First, tests were run to detect both indirect and actual forms of damage on a section of an actual wind turbine blade provided by Sandia National Laboratories. Additional tests were run on the same blade section using a high-frequency response function method of SHM for comparison. Finally, based on the results of the initial testing, the impedance method was utilized in an attempt to detect damage during a fatigue test of an experimental wind turbine blade at the National Renewable Energy Laboratory's National Wind Technology Center. / Master of Science

The data rich nature of instrumented civil structures has brought attention to alternative applications outside of the traditional realm of structural health monitoring. An interest has been raised in using these vibration measurements for other applications such as human occupancy. An example of this is to use the vibrations measured from footsteps to locate occupants within a building. The localization of indoor footsteps can yield several benefits in areas such as security and threat detection, emergency response and evacuation, and building resource management, to name a few. The work described herein seeks to provide supplementary information to better define the problem of indoor footstep localization, and to investigate the use of several localization techniques in a real-world, operational building environment. The complexities of locating footsteps via indoor vibration measurements are discussed from a mechanics perspective using prior literature, and several techniques developed for localization in plate structures are considered for their applicability to indoor localization. A dispersion compensation tool is experimentally investigated for localization in an instrumented building. A machine learning approach is also explored using a nearest neighbor search. Additionally, a novel instrumentation method is designed based on a multi-point coupling approach that provides directional inference from a single point of measurement. This work contributes to solving the indoor footstep localization problem by consolidating the relevant mechanical knowledge and experimentally investigating several potential solutions. / Ph. D.

This dissertation presents the exploration of two fiber optics techniques involving high power pulse laser delivery. The first research topic is "Embedded Active Fiber Optic Sensing Network for Structural Health Monitoring in Harsh Environments", which uses the fiber delivered pulse laser for acoustic generation. The second research topic is "Fiber Optics Guided Laser Micromachining", which uses the fiber delivered pulse laser for material ablation. The objective of the first research topic is to develop a first-of-a-kind technology for remote fiber optic generation and detection of acoustic waves for structural health monitoring in harsh environments. Three different acoustic generation mechanisms were studied in detail, including laser induced plasma breakdown (LIB), Erbium-doped fiber laser absorption, and metal laser absorption. By comparing the performance of the acoustic generation units built based on these three mechanisms, the metal laser absorption method was selected to build a complete fiber optic structure health monitoring (FO-SHM) system. Based on the simulation results of elastic wave propagation and fiber Bragg grating acoustic pulse detection, an FO-SHM sensing system was designed and built. This system was first tested on an aluminum piece in the room temperature range and successfully demonstrated its capability of multi-parameter monitoring and multi-point sensing. With additional studies, the upgraded FO-SHM element was successfully demonstrated at high temperatures up to 600oC on P-91 high temperature steels. During the studies of high power pulse laser delivery, it was discovered that with proper laser-to-fiber coupling, the output laser from a multimode fiber can directly ablate materials around the fiber tip. Therefore, it is possible to use a fiber-guided laser beam instead of free space laser beams for micromachining, and this solves the aspect ratio limitation rooted in a traditional laser beam micromachining method. In this dissertation, this Guided Laser MicroMachining (GLMM) concept was developed and experimentally demonstrated by applying it to high aspect ratio micro-drilling. It was achieved that an aspect ratio of 40 on aluminum and an aspect ratio of 100 on PET, with a hole diameter less than 200 um. / PHD / This dissertation presents two research topics both related to high power laser and fiber optic. The first topic studies the application of using optical fiber and high power laser for ultrasonic non-destructive evaluation. The general idea is to use fiber optic to remotely generate and monitor ultrasonic waves on a workpiece. Due to the fact that there are no electronic components involved in the sensing part of the system, this system can work at high temperature and is unsusceptible to EMI. The second topic studies the usage of optical fiber in high aspect ratio micromachining. The key concept is to use a fiber tip and the output high power laser as a "drilling tip", which eliminate the aspect ratio limitation rooted in the traditional free-space laser micromachining method. With this concept and a demonstrative micromachining system, we achieved record-breaking aspect ratio on both aluminum and plastic.

Civil infrastructure failure is hard to predict, both in terms of occurrence and impact. This is due to combination of many factors, including highly variable environmental and operational conditions, complex construction and materials, and the sheer size of these structures. Often, the mitigation strategy is visual inspection and regular maintenance, which can be time-consuming and may not address root causes of failure. One potential solution to anticipating infrastructure failure and mitigating its consequences is the use of distributed sensors to monitor the physical state of a structure, an area of research known commonly as structural health monitoring, or SHM. This approach can be applied in a variety of contexts: safety during and after natural disasters, evaluation of building construction quality and life-cycle assessment for performance based design frameworks. In one way or another, SHM methods always require a ``baseline,'' a set of physical features which describes the behavior of a healthy structure. Often, the baseline is defined in terms of modal parameters: natural frequencies, damping ratios, and mode shapes. Although changes in modal parameters are indicative of structural damage, they are also indicative of a slew of non-damage factors, such as signal-to-noise ratio, environmental conditions, and the characteristics of forces exciting the structure. In many cases, the degree of observed modal parameter changes due to non-damage factors can be much greater than that due to damage itself. This is especially true of low-frequency modal parameters. For example, the fundamental frequency of a building is more sensitive to global influences like temperature than local structural changes like a cracked column. It has been proposed that extracting modal parameters at higher frequencies may be the key to improving the damage-sensitivity of SHM methods. However, for now, modal analysis of civil structures has been limited to low frequency ambient excitation and sparse sensor networks, due to practical limitations. Two key components for high-frequency modal analysis have yet to be studied: 1) Sufficient excitation at high frequencies and 2) high-resolution (high sensor density) measurements. The unifying goal of this work is to expand modal analysis in these two areas by applying novel instrumentation and experimental methods to two full-scale buildings, Goodwin Hall and Ernest Cockrell Jr. Hall. This enables realistic, practical insights into the limitations and benefits of the high-frequency SHM approach. Throughout, analyses are supported through the novel integration of uncertainty quantification techniques which so far has been under-utilized in the field. This work is divided into three experimental areas, with approaches centering on the identification of modal parameters. The first area is the application of high spacial resolution sensor networks in combination to ambient vibration testing. The second is the implementation of a robust automation and monitoring strategy for complex dynamic structures. The third is the testing of a novel method for performing experimental modal analysis on buildings emph{in situ}. The combination of results from these experiments emphasizes key challenges in establishing reliable high-frequency, high-resolution modal parameter ``baselines'' for structural health monitoring (SHM) of civil infrastructure. The first study presented in this work involved the identification of modal parameters from a five-story building, Goodwin Hall, using operational modal analysis (OMA) on ambient vibration data. The analysis began with a high spacial density network of 98 accelerometers, later expanding this number to 117. A second extensional study then used this data as reference to implement a novel automation method, enabling the identification of long-term patterns in the building's response behavior. Three dominant sources of ambient excitation were identified for Goodwin Hall: wind, human-induced loading, and consistent low-level vibrations from machinery, etc. It was observed that the amplitude of excitation, regardless of source, had significant effects on the estimated natural frequencies and damping ratios. Namely, increased excitation translated to lower natural frequencies and higher damping. In addition, the sources had different characteristics in terms of excitation direction and bandwidth, which contributed to significantly different results depending on the ambient excitation employed. This has significant implications for ambient-based methods that assume that all ambient vibrations are broadband random noise. The third and final study demonstrated the viability of emph{in situ} seismic testing for controlled excitation of full-scale civil structures, also known as experimental modal analysis (EMA). The study was performed by exciting Ernest Cockrell Jr. Hall in Austin, Texas with both vertical and lateral ground waves from seismic shaker truck, T-Rex. The EMA results were compared to a standard operational modal analysis (OMA) procedure which relies on passive ambient vibrations. The study focused on a frequency bandwidth from 0 to 11 Hz, which was deemed high frequency for such a massive structure. In cases were coherence was good, the confidence comparable or better than OMA, with the added advantage that the EMA tests took only a fraction of the time. The ability to control excitation direction in EMA enabled the identification of new structural information that was not observed OMA. It is proposed that the combination of high spacial resolution instrumentation and emph{in situ} excitation have the potential to achieve reliable high-frequency characterization, which are not only more sensitive to local damage but also, in some cases, less sensitive to variations in the excitation conditions. / Ph. D. / Civil structures, like buildings and bridges, become weaker as they age, increasing their risk of collapse due to sever weather, earthquakes, and heavy traffic. Engineers regularly inspect civil structures to ensure they are in good shape, but it is difficult do a full assessment by eye since many defects can be hidden. Structural Health Monitoring, or SHM for short, is an approach that uses permanent vibration sensors to continuously inspect civil structures. Any activity, like blowing wind or moving traffic on bridge, produces small vibrations which can be analyzed to assess the “health” of the structure. This approach can detect some invisible defects, but there is still debate about whether it can detect them when they are small and early on in the life of a structure. If SHM can’t issue early warnings, then there is little incentive to spend large amounts of money on a sensor system. To capture small defects, a sensor system needs a large number of sensors, hence the term high-resolution in the title. In addition, the structure being tested needs to vibrate rapidly (that is at high-frequencies) in order for the high-resolution information to be useful. So far, there have been no tests of this kind on civil structures, especially buildings. Instead, most sensor systems have contained a relatively low number of sensors tested with low-frequency vibrations. This works fills in this gap by testing two different buildings with SHM sensor systems. The first experiment uses a very high number of sensors to analyze the vibrations of Goodwin Hall on the Virginia Tech campus. The vibrations in this building are produced by wind and people walking inside. The second experiment uses a standard number of sensors, but explores a new method of vibrating buildings. This method uses a truck with a large hydraulic piston to shake the ground near the E. Cockrell Jr. building (University of Austin-Texas), essentially creating a tiny earthquake. The experiments show that both testing techniques provide more useful information than standard ones alone. For the first experiment, using more sensors meant the analysis could better distinguish the structural characteristics of the building. For the second, the artificial “earthquake” enabled the measurement of high-frequency vibrations, something which was not possible by relying on wind or people to vibrate the building. Although these new approaches are not used to inspect for damage, they have laid the foundation for improving the early-warning capabilities of SHM systems. This could mean that buildings and other structures can be repaired sooner, remain in operation longer, and cost the owners less money in the end!

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.

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

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.