Aquesta tesi presenta treball original i aplicat en l'àrea del control i la col·locació de sensors/actuadors (S/A) en sistemes de Control Actiu de Soroll (ANC). Primer, s'han aplicat tècniques de control i identificació robustes per a aconseguir ANC. La fase d'identificació està basada en una proposta d'identificació robusta orientada al control, considerant descripcions del sistema tant paramètriques com no-paramètriques, així com quantificant la incertesa. El disseny del controlador compara les estructures de control feedback (FB), feedforward (FF) i híbrida (FB/FF). El controlador feedback és sintetitzat i avaluat en el marc del control robust, i s'ha dissenyat utilitzant control òptim H∞ plantejat com un problema de sensibilitats mixtes. El controlador FF és un identificador adaptatiu, basat en l'algorisme σ robustament normalitzat. S'han desenvolupat dues propostes per a decidir quina de les estructures de control és més eficient, aplicades a un conducte de 4 metres amb soroll de banda ampla. A més a més, s'han mostrat de manera explícita els compromisos entre identificació i control, les limitacions inherents a un llaç de control feedback, així com qüestions relatives a la implementació de sistemes ANC. També s'han tractat altres qüestions com la relació entre acompliment, ordre del controlador, models paramètrics/no-paramètrics i implementació en processadors digitals de senyal (DSP), així com s'han comparat resultats teòrics i experimentals en el conducte. Les llacunes que encara resten entre teoria i pràctica en aquest tipus d'aplicacions també s'han resumit. D'altra banda, en aquest treball també es tracta el problema de com quantificar la col·locació de sensors i actuadors, amb la finalitat de controlar un sistema físic determinat. La mesura per a determinar la millor localització de S/A es basa en un criteri de llaç tancat orientat al control, el qual optimitza tant acompliment com qüestions pràctiques d'implementació. Aquesta mesura hauria de calcular-se abans del disseny, implementació i prova del controlador. La utilització d'aquesta mesura minimitza la prova combinatòria de controladors en totes les possibles combinacions de S/A. Per a aconseguir-ho, s'han definit diferents mesures que pesen l'acompliment potencial en llaç tancat, la robustesa, el número de condició de la planta (guanys relatius entrada/sortida (I/O)) així com altres qüestions d'implementació, com l'ordre del controlador. Aquestes poden calcular-se utilitzant software estàndard, tant per a models d'una-entrada-una-sortida (SISO) com per a models de múltiples-entrades-múltiples-sortides (MIMO) i poden aplicar-se a múltiples problemes d'enginyeria, ja siguin mecànics, acústics, aeroespacials, etc. En aquest treball, aquests resultats també s'han il·lustrat amb l'aplicació ANC presentada i validat amb dades experimentals. Com a resultat d'aplicar aquestes mesures, s'obté la localització de S/A que aconsegueix la millor atenuació del soroll en llaç tancat amb el menor ordre possible del controlador. / Esta tesis presenta trabajo original y aplicado en el área del control y la colocación de sensores/actuadores (S/A) en sistemas de Control Activo de Ruido (ANC). Primero, se han aplicado técnicas de control e identificación robustas para conseguir ANC. La fase de identificación está basada en una propuesta de identificación robusta orientada al control, considerando descripciones del sistema tanto paramétricas como no-paramétricas, así como cuantificando la incertidumbre. El diseño del controlador compara las estructuras de control feedback (FB), feedforward (FF) e híbrida (FB/FF). El controlador feedback es sintetizado y evaluado en el marco del control robusto, y se ha diseñado utilizando control óptimo H∞ planteado como un problema de sensibilidades mixtas. El controlador FF es un identificador adaptativo, basado en el algoritmo σ robustamente normalizado. Se han desarrollado dos propuestas para decidir cual de las estructuras de control es más eficiente, aplicadas a un conducto de 4 metros con ruido de banda ancha. Además, se han mostrado de manera explícita los compromisos entre identificación y control, las limitaciones inherentes a un lazo feedback, así como cuestiones relativas a la implementación de sistemas ANC. También se han tratado otras cuestiones como la relación entre desempeño, orden del controlador, modelos paramétricos/no-paramétricos e implementación en procesadores digitales de señal (DSP), así como se han comparado resultados teóricos y experimentales en el conducto. Las lagunas que aún quedan entre teoría y práctica en este tipo de aplicaciones también se han resumido. Por otra parte, en este trabajo se trata también el problema de como cuantificar la colocación de sensores y actuadores, con la finalidad de controlar un sistema físico determinado. La medida para determinar la mejor localización de S/A se basa en un criterio de lazo cerrado orientado al control, el cual optimiza tanto desempeño como cuestiones prácticas de implementación. Esta medida debería calcularse antes del diseño, implementación y prueba del controlador. La utilización de esta medida minimiza la prueba combinatoria de controladores en todas las posibles combinaciones de S/A. Para conseguirlo, se han definido distintas medidas que pesan el desempeño potencial en lazo cerrado, la robustez, el número de condición de la planta (ganancias relativas entrada/salida (I/O)) y otras cuestiones de implementación, como el orden del controlador. Éstas pueden calcularse utilizando software estándar, tanto para modelos de una-entrada-una-salida (SISO) como para modelos de múltiples-entradas-múltiples-salidas (MIMO) y pueden aplicarse a múltiples problemas ingenieriles, ya sean mecánicos, acústicos, aeroespaciales, etc. En este trabajo, estos resultados también son ilustrados con la aplicación ANC presentada y validados con datos experimentales. Como resultado de aplicar estas medidas, se obtiene la localización de S/A que consigue la mejor atenuación de ruido en lazo cerrado con el menor orden posible del controlador. / This thesis presents novel and applied work in the area of control and sensor/actuator (S/A) allocation in Active Noise Control (ANC) systems. First, robust identification and control techniques to perform ANC have been applied. The identification phase is based on a control-oriented robust identification approach that considers both parametric and nonparametric descriptions of the system, and quantifies the uncertainty. The controller design compares the feedback (FB), feedforward (FF) and hybrid (FB/FF) control structures. The feedback control is synthesized and evaluated in the robust control framework, and it is designed using H∞ optimal control as a mixed-sensitivity problem. The FF controller is an adaptive identifier, based on the robustly normalized σ-algorithm. Two approaches are developed to decide which control structure is more efficient on a 4-m duct example with broadband noise. In addition, the compromises between identification and control, the inherent limitations of feedback and implementation issues in ANC are explicitly pointed out. Relations between performance, controller order, parametric/nonparametric models and digital signal processor (DSP) implementation are discussed. Theoretical and experimental results on the duct are compared. The gaps that still remain between theory and practice in this type of applications, are also outlined. Furthermore, this work considers the problem of quantifying the location of sensors and actuators in order to control a certain physical system. The measure to determine the best S/A location is based on a closed loop control-oriented criteria, which optimizes overall performance and practical implementation issues. In addition, it should be computed before the actual controller is designed, implemented and tested. The use of this measure minimizes the combinatorial controller testing over all possible S/A combinations. To this end, several measures have been defined which weight the potential closed-loop performance, robustness, plant condition number (input/output (I/O) relative gains) and implementation issues, such as the controller order. These may be computed with standard software, either for Single Input Single Output (SISO) models or Multiple Input Multiple Output (MIMO) models, and may be applied to many engineering problems: mechanics, acoustics, aerospace, etc. Here, these results are also illustrated with the prior ANC example and validated against experimental data. The outcome of applying these measures is the selection of the S/A location which achieves the best closed loop noise attenuation with the lowest possible controller order.

A transducer consisting of multiple layers of ionic polymer material is developed for applications in sensing, actuation, and control. The transducer consists of two to four individual layers each approximately 200 microns thick. The transducers are connected in parallel to minimize the electric field requirements for actuation. The tradeoff in deflection and force can be controlled by controlling the mechanical constraint at the interface. Packaging the transducer in an outer coating produces a hard constraint between layers and reduces the deflection with a force that increases linearly with the number of layers. This configuration also increases the bandwidth of the transducer. Removing the outer packaging produces an actuator that maintains the deflection of a single layer but has an increased force output. This is obtained by allowing the layers to slide relative to one another during bending. A Finite Element Analysis (FEA) method capable of modeling the structure of the multilayer transducers is developped. It is used to model the interfacial friction in multilayer transducers. Experiments on transducers with one to three layers are performed and the results are compared to Newbury's equivalent circuit model, which was modified to accommodate the multilayer polymers. The modification was performed on four different boundary conditions, two electrical the series and the parallel connection, and two mechanical the zero interfacial friction and the zero slip on the interface. Results demonstrate that the largest obstacle to obtaining good performance is water transport between the individual layers. Water crossover produces a near short circuit electrical condition and produces feedthrough between actuation layers and sensing layers. Electrical feedthrough due to water crossover eliminates the ability to produce a transducer that has combined sensing and actuation properties. Eliminating water crossover through good insulation enables the development of a small (5 mm x 30 mm) transducer that has sensing and actuation bandwidth on the order of 100 Hz. Due to the mechanical similarities of ionic transducers to biological muscles and their large flapping displacement capabilities we are studying the possibility of their use in flapping Micro Air Vehicle (MAV) application, as engines, controllers and sensors. The FEA modeling technique capable is used to design two ionic polymers actuated flapping wings. / Master of Science

This dissertation explores strategies to create micro-scale tools with integrated electronic and mechanical functionalities. Recently developed approaches to control the shape of flexible micro-structures are employed to fabricate micro-electronic instruments that embed components for sensing and actuation, aiming to expand the toolkit of minimally invasive surgery. This thesis proposes two distinct types of devices that might expand the boundaries of modern surgical interventions and enable new bio-medical applications. First, an electronically integrated micro-catheter is developed. Electronic components for sensing and actuation are embedded into the catheter wall through an alternative fabrication paradigm that takes advantage of a self-rolling polymeric thin-film system. With a diameter of only 0.1 mm, the catheter is capable of delivering fluids in a highly targeted fashion, comprises actuated opposing digits for the efficient manipulation of microscopic objects, and a magnetic sensor for navigation. Employing a specially conceived approach for position tracking, navigation with a high resolution below 0.1 mm is achieved. The fundamental functionalities and mechanical properties of this instrument are evaluated in artificial model environments and ex vivo tissues. The second development explores reshapeable micro-electronic devices. These systems integrate conductive polymer actuators and strain or magnetic sensors to adjust their shape through feedback-driven closed loop control and mechanically interact with their environment. Due to their inherent flexibility and integrated sensory capabilities, these devices are well suited to interface with and manipulate sensitive biological tissues, as demonstrated with an ex vivo nerve bundle, and may facilitate new interventions in neural surgery.:List of Abbreviations 1 Introduction 1.1 Motivation 1.2 Objectives and structure of this dissertation 2 Background 2.1 Tools for minimally invasive surgery 2.1.1 Catheters 2.1.2 Tools for robotic micro-surgery 2.1.3 Flexible electronics for smart surgical tools 2.2 Platforms for shapeable electronics 2.2.1 Shapeable polymer composites 2.2.2 Shapeable electronics 2.2.3 Soft actuators and manipulators 2.3 Sensors for position and shape feedback 2.3.1 Magnetic sensors for position and orientation measurements 2.3.2 Strain gauge sensors 3 Materials and Methods 3.1 Materials for shapeable electronics 3.1.1 Metal-organic sacrificial layer 3.1.2 Polyimide as reinforcing material 3.1.3 Swelling hydrogel for self assembly 3.1.4 Polypyrrole for flexible micro actuators 3.2 Device fabrication techniques 3.2.1 Photolithography 3.2.2 Electron beam deposition 3.2.3 Sputter deposition 3.2.4 Atomic layer deposition 3.2.5 Electro-polymerization of polypyrrole 3.3 Device characterization techniques 3.3.1 Kerr magnetometry 3.3.2 Electro-magnetic characterization of sensors 3.3.3 Electro-chemical analysis of polypyrrole 3.3.4 Preparation of model environments and materials 3.4 Sensor signal evaluation and processing 3.4.1 Signal processing 3.4.2 Cross correlation for phase analysis 3.4.3 PID feedback control 4 Electronically Integrated Self Assembled Micro Catheters 4.1 Design and Fabrication 4.1.1 Fabrication and self assembly 4.1.2 Features and design considerations 4.1.3 Electronic and fluidic connections 4.2 Integrated features and functionalities 4.2.1 Fluidic transport 4.2.2 Bending stability 4.2.3 Actuated micro manipulator 4.3 Magnetic position tracking 4.3.1 Integrated magnetic sensor 4.3.2 Position control with sensor feedback 4.3.3 Introduction of magnetic phase encoded tracking 4.3.4 Experimental realization 4.3.5 Simultaneous magnetic and ultrasound tracking 4.3.6 Discussion, limitations, and perspectives 5 Reshapeable Micro Electronic Devices 5.1 Design and fabrication 5.1.1 Estimation of optimal fabrication parameters 5.1.2 Device Fabrication 5.1.3 Control electronics and software 5.2 Performance of Actuators 5.2.1 Blocking force, speed, and durability 5.2.2 Curvature 5.3 Orientation control with magnetic sensors 5.3.1 Magnetic sensors on actuated device 5.3.2 Reference magnetic field 5.3.3 Feedback control 5.4 Shape control with integrated strain sensors 5.4.1 Strain gauge curvature sensors 5.4.2 Feedback control 5.4.3 Obstacle detection 5.5 Heterogenous integration with active electronics 5.5.1 Fabrication and properties of active matrices 5.5.2 Fabrication and operation of PPy actuators 5.5.3 Site selective actuation 6 Discussion and Outlook 6.1 Integrated self assembled catheters 6.1.1 Outlook 6.2 Reshapeable micro electronic devices 6.2.1 Outlook 7 Conclusion Appendix A1 Processing parameters for polymer stack layers A2 Derivation of magnetic phase profile in 3D Bibliography List of Figures and Tables Acknowledgements Theses List of Publications

In this dissertation, we propose service-oriented sensor-actuator networks (SOSANETs) as a new paradigm for building the next generation of customizable, open, interoperable sensor-actuator networks. In SOSANETs, nodes expose their capabilities to applications in the form of service profiles. A node's service profile consists of a set of services (i.e., sensing and actuation capabilities) that it provides and the quality of service (QoS) parameters associated with those services (delay, accuracy, freshness, etc.). SOSANETs provide the benefits of both application-specific SANETs and generic SANETs. We first define a query model and an architecture for SOSANETs. The proposed query model offers a simple, uniform query interface whereby applications specify sensing and actuation queries independently from any specific deployment of the underlying SOSANET. We then present μRACER (Reliable Adaptive serviCe-driven Efficient Routing), a routing protocol suite for SOSANETs. μRACER consists of three routing protocols, namely, SARP (Service-Aware Routing Protocol), CARP (Context-Aware Routing Protocol), and TARP (Trust-Aware Routing Protocol). SARP uses an efficient service-aware routing approach that aggressively reduces downstream traffic by translating service profiles into efficient paths. CARP supports QoS by dynamically adapting each node's routing behavior and service profile according to the current context of that node, i.e. number of pending queries and number and type of messages to be routed. Finally, TARP achieves high end-to-end reliability through a scalable reputation-based approach in which each node is able to locally estimate the next hop of the most reliable path to the sink. We also propose query optimization techniques that contribute to the efficient execution of queries in SOSANETs. To evaluate the proposed service-oriented architecture, we implemented TinySOA, a prototype SOSANET built on top of TinyOS with uRACER as its routing mechansim. TinySOA is designed as a set of layers with a loose interaction model that enables several cross-layer optimization options. We conducted an evaluation of TinySOA that included a comparison with TinyDB. The obtained empirical results show that TinySOA achieves significant improvements on many aspects including energy consumption, scalability, reliability and response time. / Ph. D.

No description available.

Thin Film Transistors (TFTs) are widely used in large area electronics because they offer the advantage of low cost fabrication and wide substrate choice. TFTs have been conventionally used for switching applications in large area display arrays. But when it comes to designing a sensor actuator system on a flexible substrate comprising entirely of organic and inorganic TFTs, there are two main challenges – i) Fabrication of complementary TFT devices is difficult ii) TFTs have a drift in their threshold voltage (VT) on application of gate bias. Also currently there are no circuit simulators in the market which account for the effect of VT drift with time in TFT circuits. The first part of this thesis focuses on integrating the VT shift model in the commercially available AIM-Spice circuit simulator. This provides a new and powerful tool that would predict the effect of VT shift on nodal voltages and currents in circuits and also on parameters like small signal gain, bandwidth, hysteresis etc. Since the existing amorphous silicon TFT models (level 11 and level 15) of AIM-Spice are copyright protected, the open source BSIM4V4 model for the purpose of demonstration is used. The simulator is discussed in detail and an algorithm for integration is provided which is then supported by the data from the simulation plots and experimental results for popular TFT configurations. The second part of the thesis illustrates the idea of using negative feedback achieved via contact resistance modulation to minimize the effect of VT shift in the drain current of the TFT. Analytical expressions are derived for the exact value of resistance needed to compensate for the VT shift entirely. Circuit to realize this resistance using TFTs is also provided. All these are experimentally verified using fabricated organic P-type Copper Phthalocyanine (CuPc) and inorganic N-type Tin doped Zinc Oxide (ZTO) TFTs. The third part of the thesis focuses on building a robust amplifier using these TFTs which has time invariant DC voltage level and small signal gain at the output. A differential amplifier using ZTO TFTs has been built and is shown to fit all these criteria. Ideas on vertical routing in an actual sensor actuator interface using this amplifier have also been discussed such that the whole system may be “tearable” in any contour. Such a sensor actuator interface can have varied applications including wrap around thermometers and X-ray machines.

Structural Health Monitoring (SHM) systems for future structures and vehicles would involve a process of damage identification and prediction of certain quantities of interest that concerns the function and safety. This process provides SHM systems the ability to not only save cost but also enhance the service life, safety and reliability of the structures and vehicles. Integrated SHM system (ISHM) is an advancement of SHM system that has additional capability of predicting the component life/failure. ISHM system development involves detailed understanding of diagnostic waves, hardware components, signal processing paradigms and intelligent use of algorithms. Diagnostic waves like the guided waves are the elastic waves that propagate in a direction defined by the material boundaries. These waves have the capability of traveling large distance probing the entire thickness in plates/shells. Thus, they are widely used by SHM systems in monitoring the plate structures. Piezoelectric transducers are often employed in the interrogation using guided waves. Most SHM systems employing guided waves are designed for specific structures. Current paradigms of SHM systems are unable to enable the transition from simple or ideal structures to realistic and complicated structures. This is due to the challenges at the fundamental level involving transducer, wave propagation and phenomena of guided wave scattering with damages to evaluate the possible solutions through mathematical modeling and signal analysis capability required by ISHM systems. This thesis aims to develop understanding of these problems at a fundamental level. Complex system level understanding is still needed which is left out as open problem. A primary requirement in designing SHM system is the proper understanding of wave characteristics such as number of modes, wavelength and dispersiveness. Although three-dimensional elasticity solution and simplified theories are available to understand them, their applicability in SHM problem requires a much more detailed look. Effort toward this direction has led to the development of simpler models. However, mathematical models are not available for understanding the wave characteristics in complex structures involving stiffeners and adhesive joints. This problem is addressed in this thesis. There is a fair amount of understanding developed regarding transducer characteristics. This is accomplished by analytical and finite element models of transducers in the past. However, simplified transducer model that are computationally fast to suit SHM system requirements needs to be developed. The development of such model is presented in this thesis. Apart from modeling the transducers and wave scattering due to damage, signal correlation and calibration are needed for practical implementation in SHM. Characterization studies reported in published literature are limited to quasi-static and low frequencies applications. However, SHM of aerospace structures employ guided waves typically in the frequency range of 100-500 kHz. Methods to characterize the transducers at this frequency range needs to be developed, which is addressed in this thesis. Another major requirement of SHM system is the design and development of sensor-actuator network and appropriate algorithm. Techniques developed earlier involving transducer arrays in this regard have limitation due to complexity of geometry and signal interpretation that needs to be addressed. The network with suitable algorithm should ideally monitor large area including the critical areas of failure with minimum number of transducers. ISHM systems further require some capability to estimate the useful life of the damaged structure in order to take suitable decisions. Efficient techniques to achieve these are not developed. Overall, there is a need to improve highly interdisciplinary areas involving mathematical modeling, transducer design, fabrication and characterization, damage detection and monitoring strategies. In this thesis, various novel techniques to combine mathematical model with experimental signals to enhance the damage detection capability are presented. In this thesis, developments in the three main aspects of SHM systems are focused upon. They are (1) development of mathematical models of sensors/actuators, wave propagation and scattering due to damage (2) characterization and calibration of transducers and (3) development of technique to monitor wide variety of damages within the scope of ultrasonic guided wave based SHM. The thesis comprises of ten chapters. First chapter is devoted to the background and motivation for the problem addressed in this thesis. In second chapter, brief overview of available mathematical models and conventional damage monitoring strategy is presented. The significant contributions reported in the subsequent chapters in this thesis are outlined below In chapter 3, a reduced-order model of guided wave propagation in thick structures with reduced-order approximation of higher-order elasto-dynamic field is formulated. The surface normal and shear tractions of the thick structure are satisfied in a closed form. The time-frequency Fourier spectral finite element is developed and is validated using detailed and computationally intensive finite element simulations. Natural frequencies obtained from the developed spectral finite element and the detailed finite element simulations are compared. Transient response due to broad frequency band and narrow frequency band excitations given in the form of surface tractions are validated by comparing with the detailed finite element simulations. Using the developed spectral finite element, wave scattering from a free edge and a notch are simulated and validated by comparing with the detailed finite element simulations. In chapter 4, two-dimensional plane wave and flexural wave scattering models for more complicated features such as stiffener with delamination and stiffener with bolt failures in a stiffened panel are derived using ultrasonic ray tracing based approach combined with wave-field representation. Dispersion relations are reformulated for the base plate where it is bolted with the stiffener. Surface conditions due to contact stiffness and contact damping are modeled by introducing springs and dampers. Scattering coefficients for the bonded and bolted stiffeners are derived. The scattering coefficients are evaluated for various different frequencies. Results are compared for different stiffener parameters. In chapter 5, a simplified analytical model of a piezoelectric actuator with uniform electrodes is modeled. The problem is to determine the launched guided wave characteristics in the structure. The analytical model is derived considering two-dimensional elasticity based approach and Airy’s stress function. The actuator model is used to specify the displacement boundary conditions in the detailed finite element model. The radiated wave patterns in a plate due to actuation from transducers of different shapes are obtained and validated with experiments. Phased array actuators are modeled in the detailed finite element model using the displacements estimated from the actuator model. The radiated wave pattern from the detailed finite element simulations are validated with experiments. Chapter 6 is devoted to the design and characterization of transducers for ultrasonic guided wave applications. The characterization techniques involve the estimation of voltage response for the induced strain by the guided wave at various different frequencies. First, a novel removable bonding technique and a calibration technique are demonstrated and related advantages are discussed. Performance of the piezoelectric thin film under quasi-static, dynamic and transient impact loadings are analyzed first. Next, a guided wave technique is developed to characterize piezoelectric thin film sensors and actuators at ultrasonic frequencies. The transducers with inter digital electrodes are characterized for frequency tuning and directional sensitivity. This characterization study enables in the selection of optimal frequency bands for interrogation. Further, the characterization of transducers with thermal degradation is presented. In chapter 7, a novel guided wave technique to calibrate the thin film sensors for ultrasonic applications is presented. Calibration procedure involves the estimation of the piezoelectric coefficient at ultrasonic range of frequencies. Calibration is done by the measurement of voltage generated across thin films when guided waves are induced on them. With the proposed technique, piezoelectric coefficient can be estimated accurately at any frequency of the propagating wave. Similarly, the measurement of piezoelectric coefficient of thin films with inter digital electrodes is presented. The estimation of piezoelectric coefficient at various different directions using laser Doppler vibrometer is presented. Lastly, the degradation of piezoelectric coefficient is studied for increasing thermal fatigue. In chapter 8, toward SHM methodology development, a guided wave based technique to detect and monitor cracks in a structure is presented. To establish the methodology, a detailed study is carried out on the effect of crack and specimen size on the guided wave propagation characteristics. Using the wave characteristics, an analytical way of modeling Lamb wave propagation in the specimen with plastic zone is proposed. The feasibility to determine plastic zone and fatigue crack propagation with integrated piezoelectric transducers is demonstrated experimentally and the results are verified analytically. A method is further established to detect damage at initial stage and crack-tip plastic zone size along with crack length for a given stress amplitude or vice-versa. An approach to estimate fatigue life from the transducer signals is also proposed. In chapter 9, a compact circular array of sensor-actuator network and an algorithm is presented to monitor large plate structures. A method based on the wavelet transforms of transducer signals is established to localize and estimate the severity of damages. Experiments are conducted to demonstrate the capability of the circular array based method in the localization and quantification of various types of damages like debonding of stiffeners, failure of bolted joints, corrosion and hole-enlargement. A damage index is then computed from wavelet time-frequency map that indicates the severity of damage. Chapter 10 ends with the concluding remarks on the work done with simultaneous discussion on the future scope. The work reported in this thesis is interdisciplinary in nature and it aims to combine the modeling and simulation techniques with realistic data in SHM to impart higher confidence levels in the prediction of damages and its prognosis. The work also aims in incorporating various mathematical models of wave propagation and ray tracing based algorithm to optimize the detection scheme employed in SHM. The future direction based on this study could be aimed at developing intelligent SHM systems with high confidence levels so that statistical machine learning would be possible to deal with complex real-world SHM problems.