This PDF file contains the front matter associated with SPIE Proceedings Volume 6932, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

Decentralized computing is required to harvest the rich information that a dense array of smart sensors can make available for structural health monitoring (SHM). Though smart sensor technology has seen substantial advances during recent years, implementation of smart sensors on full-scale structures has been limited. Direct replacement of wired sensing systems with wireless sensor networks is not straight-forward as off-the-shelf wireless systems are unlikely to provide the data users expect. Sensor component characteristics limit the quality of data collected due to packet loss during communication, time synchronization errors, and slow communication speeds. This paper describes a scalable, decentralized approach to SHM using smart sensors, including the middleware services which address these issues common to smart sensor applications for structural health monitoring. In addition, the results of experimental validation are given. Finally, ongoing research addressing other factors critical to successful implementation of a full-scale smart sensor network for SHM are discussed.

Curved concrete bridge girders have very complex internal forces, stress and strain distribution. As a consequence of their shape, not only the usual bending moments and shear forces are generated, but also important torsion moments are created. These moments "rotate" the axes of principal tensional stresses increasing the risk of cracking. Post-tensioning can prevent the cracks, but the added compression forces introduced in different directions increase the complexity of stress and strain fields. Therefore, the curved post-tensioned concrete girders must be particularly designed and carefully constructed. However, the real structural behavior should be verified, and risks and uncertainties related to structural design and quality of construction minimized. Structural health monitoring is a natural solution for these issues. Structural health monitoring method, based on the use of fiber optic interferometric technology including long-gage sensors and inclinometers, is presented in this paper. A 36 meters long curved post-tensioned bridge box girder is equipped with so-called parallel and so-called crossed sensor topologies, and inclinometers, in order to monitor axial strain, both horizontal and vertical curvature changes, torsion, average shear strain and rotations in both vertical plans. Important parts of structure life such as construction, post-tensioning and first years of service are registered, analyzed and presented.

The integrity and safety of metallic structures can be jeopardized by structural damage (e.g., yielding, cracking, impact, corrosion) that can occur during operation or service. While a variety of sensors have been proposed and validated for structural health monitoring, most sensors only provide data regarding a discrete point on the structure, thereby requiring densely-distributed sensors; however, such an approach may be infeasible for many structures due to geometrical and economic constraints. In this study, a nanoengineered carbon nanotube-polyelectrolyte sensing skin is proposed for monitoring strain, impact, and corrosion of metallic structures. Experimental validation studies have verified that these conformable films exhibit highly sensitive electromechanical and electrochemical responses to applied strain and corrosion processes, respectively. Here, the proposed nanocomposite is coupled with an electrical impedance tomographic (EIT) conductivity imaging technique. Unlike traditional point-based sensing transducers, EIT reconstructs two-dimensional skin conductivity distributions for damage identification of large structural components. Since EIT relies solely on boundary electrical measurements, one does not need to physically probe each structural location for data acquisition. Instead, any structural damage that affects the nanocomposite coating will produce localized changes in film conductivity detectable via EIT and boundary electrical measurements.

Piezoelectric ceramic transducers were made and embedded in concrete structures in this paper in order to monitor cracks under static load. In the experiment, the component was made in concrete with rebars. The transducers were used as sensors according to the direct piezoelectric effect and actuators according to the indirect piezoelectric effect. During the experiment, sine pulse signals are applied on the transducer to generate elastic wave to scan the area between the transducers. As being electronic device, signal of piezoelectric material will be disturbed by electromagnetic wave in environment. Wavelet analysis with its good ability both in time and frequency domain was adopted in filtering the interfering signal. Then damage index was established based on continuous wavelet analysis. From the change of the damage index, the information of crack occurring and developing in the concrete component has been acquired. And the trend of the damage index also has a good correlation with that of the strain gauges used in the experiment. The results have shown that this method has the advantages that do not require sensors placed on the point of damage occurring and can protect sensors from damage. Thus it can be used in the monitoring of civil structure.

Nearly 90% of the bridges in California are post-tensioned box-girders. Prestressing (PS) tendons are the main load-carrying components of these and other post-tensioned structures. Despite their criticality, much research is needed to develop and deploy techniques able to provide real-time information on the level of prestress and on the presence of structural defects (e.g. corrosion and broken wires) in the PS tendons. In collaboration with Caltrans, UCSD is investigating the combination of ultrasonic guided waves and embedded sensors as an approach to provide both prestress level monitoring and defect detection capabilities in concrete-embedded PS tendons. This paper will focus on the prestress level monitoring by first discussing the behavior of ultrasonic guided waves propagating in seven-wire, 0.6-in diameter twisted strands typically used in post-tensioned concrete structures. A semi-analytical finite element analysis is used to predict modal and forced wave solutions as a function of the applied prestress level. This analysis accounts for the changing inter-wire contact as a function of applied loads. A feature shown sensitive to load levels is the inter-wire energy leakage. In order to monitor such feature, the method uses low-profile piezoelectric sensors able to probe the individual, 0.2-in wires comprising the strand. Results of load monitoring in free and embedded strands during laboratory tests will be presented.

A wavelength interrogation system based on an arrayed-waveguide-grating (AWG) is evaluated. The transmission wavelengths are capable of shifting by thermally scanning the AWG. By employing this AWG wavelength tunability scheme, the center wavelength of a long-period-grating (LPG) sensor is precisely interrogated. The theoretical principle and the experimental result are presented in this paper. An interrogated wavelength resolution of 0.5 pm is achieved by introducing this technique. Furthermore, a palm-size LPG sensor interrogator based on a chip integrated with an AWG demultiplexer, a photodiode, a signal processing module and an electronic controlling module is proposed.

Whatever may be the material used to build the engineering structures, they are bound to undergo damage at some point in their lifetime. The damage could develop because of continuous usage, degradation, environmental factors, earthquakes or man-made disasters. Structural health monitoring (SHM) has emerged as an important area that has attracted intensive research attention in the recent time. Smart materials like piezoceramics (e.g. lead zirconate titanate or PZT) and fibre optical sensors (FOSs) based effective SHM tools are rapidly developing. Especially, the FOSs offer great potential as monitoring sensors due to their small size, immunity to electromagnetic interference, robustness and survivability in harsh environment. Conventional FOSs use phase modulation techniques for sensing. In spite of the above advantages, they are dependent heavily on source intensity fluctuations and coupling loses. However the fibre Bragg grating (FBG) sensors developed from FOSs are immune to source intensity fluctuations, thus addressing some potential problems of the conventional FOSs. This paper presents a review on the current development of FBG based monitoring techniques and their applications.

Complex stress monitoring test of big scale offshore platform T-shape tubular joint is designed and accomplished. To assist this study, a finite element model of the T-shape tubular joint is established to predict the complex strain distribution in the hot spot of the joint. Installation principle and scheme of FBG sensors are proposed. The right angle FBG strain rosette is developed to measure the principle strain, along with the strain distribution of the hot point, in comparison with results from strain gauges. The results show that FBG rosette can monitor the principle strain precisely, and single FBG sensor is acceptable for the hot point strain monitoring. A method is proposed to correct the FBG sensor measurement for its relatively long sensing gauge. Further experimental results show that a single FBG sensor with data correction can monitor the hot spot strain of the model. Static test using FBG sensors and strain gauges were designed and conducted, respectively. Results show that FBG sensors can precisely measure the axial force, the hot spot strain, and the local strain of the tubular joint model.

In Japan's rapidly aging society, the number of elderly people living alone increases every year. Theses elderly people require more and more to maintain as independent a life as possible in their own homes. It is necessary to make living spaces that assist in providing safe and comfortable lives. "Biofication of Living Spaces" is proposed with the concept of creating save and pleasant living environments. It implies learning from biological systems, and applying to living spaces features such as high adaptability and excellent tolerance to environmental changes. As a first step towards realizing "Biofied Spaces", a system for acquisition and storing information must be developed. This system is similar to the five human senses. The information acquired includes environmental information such as temperature, human behavior, psychological state and location of furniture. This study addresses human behavior as it is the most important factor in design of a living space. In the present study, pyroelectric infrared sensors were chosen for human behavior recognition. The pyroelectric infrared sensor is advantageous in that it has no limitation on the number of sensors put in a single space because sensors do not interfere with each other. Wavelet analysis was applied to the output time histories of the pyroelectric infrared sensors. The system successfully classified walking patterns with 99.5% accuracy of walking direction (from right or left) and 85.7% accuracy of distance for 440 patterns pre-learned and an accuracy of over 80% accuracy of walking direction for 720 non-learned patterns.

The paper is concerned with a geometrically nonlinear finite element formulation to analyze piezoelectric shell structures. The classical shell assumptions are extended to the electromechanical coupled problem. The consideration of geometrical nonlinearity includes the analysis of stability problems and other nonlinear effects. The formulation is based on the mixed field functional of Hu-Washizu. The independent fields are displacements, electric potential, strains, electric field, stresses and dielectric displacements. The mixed formulation allows an interpolation of the strains and the electric field through the shell thickness, which is an essential advantage when using nonlinear 3D material laws. With respect to the numerical approximation an arbitrary reference surface of the shell is modeled with a four node element. Each node possesses six mechanical and one electrical degree of freedom. Some simulations demonstrate the applicability of the present piezoelectric shell element.

Current control and performance requirements for large-aperture deployable structures call for precise displacement control, with some tolerances approaching micron levels. Given that strain gages are one of the most economically-deployed sensor architectures, we explored two methods for reconstructing displacement from a distributed strain sensing array. One method linearly maps displacement fields to local strains in a supervised learning mode. After loading the system with sufficient cases, a matrix can be established to approach the approximate displacement-strain relationship. The other method is based on linear regression of generalized basis function projections, typically mode shapes. Results of these two approaches are compared for accuracy, robustness, training time, and real-time feasibility. The second method has higher accuracy due to natural modal behaviors, while the first method is feasible if large amount of training cases and measuring points are available.

According to the characters of smart piezoelectric concrete structures, the structure health monitoring strategy was researched in the paper in details including three basic contents. Firstly, it was proposed that the placement of piezoelectric transducers in the form of an array. The problem of the distance between adjacent transducers was also discussed. Secondly, several forms of detecting signals, frequency band and modes of the transmitting signals were pointed out in the paper. At last, a feasible damage identification method was proposed. The method combined the wavelet packet analysis with the root-mean-square deviation to evaluate the damage level. Especially, when analyzing the damage location, a concept of a transducer array resolution was proposed and used in the damage identification. The transducer array divided the structure into many sub-regions where the damage locations were approximately determined. The accuracy of the damage location will be better and finer with the increasing of the transducer array resolution.

This paper describes a mechanical monolithic sensor for geophysical applications developed at the University of Salerno. The instrument is basically a monolithic tunable folded pendulum, shaped with precision machining and electric-discharge-machining, that can be used both as seismometer and, in a force-feedback configuration, as accelerometer. The monolithic mechanical design and the introduction of laser interferometric techniques for the readout implementation make it a very compact instrument, very sensitive in the low-frequency seismic noise band, with a very good immunity to environmental noises. Many changes have been produced since last version (2007), mainly aimed to the improvement of the mechanics and of the optical readout of the instrument. In fact, we have developed and tested a prototype with elliptical hinges and mechanical tuning of the resonance frequency together with a laser optical lever and a new laser interferometer readout system. The theoretical sensitivity curve both for both laser optical lever and laser interferometric readouts, evaluated on the basis of suitable theoretical models, shows a very good agreement with the experimental measurements. Very interesting scientific result, for example, is that the measured natural resonance frequency of the instrument is 70 mHz with a Q = 140 in air without thermal stabilization, demonstrating the feasibility of a monolithic FP sensor with a natural resonance frequency of the order of mHz with a more refined mechanical tuning. Results on the readout system based on polarimetric homodyne Michelson interferometer is discussed.

Laser interferometry is one of the most sensitive methods for small displacement measurement for scientific and industrial applications, whose wide diffusion in very different fields is due not only to the high sensitivity and reliability of laser interferometric techniques, but also to the availability of not expensive optical components and high quality low-cost laser sources. Interferometric techniques have been already successfully applied also to the design and implementation of very sensitive sensors for geophysical applications. In this paper we describe the architecture and the expected theoretical performances of a laser interferometric velocimeter for seismic waves measurement. We analyze and discuss the experimental performances of the interferometric system, comparing the experimental results with the theoretical predictions and with the performances of a state-of the art commercial accelerometer. The results obtained are very encouraging, so that we are upgrading the system in order to measure the local acceleration of the mirrors and beam splitter of the velocimeter using an ad hoc designed monolithic accelerometers for low frequency direct measurement of the seismic noise.

A new sensor for web flutter measurement is proposed in this paper. The sensor is based on the principle of scattering of light and directional properties of optical fibers. A collimated beam of light is incident on the web edge and scattered light from the web edge is collected using a linear array of optical fibers. As the web flutters the point of scattering moves. Due to the directional property of the optical fibers, each fiber collects scattered light that is incident on it at certain angles. The motion of the scattering point as the web flutters is directly related to which fibers are being illuminated within the fiber array. The other end of the fiber array is terminated onto a linear array of photodiodes (pixels). Based on which fibers in the array are receiving scattered light and the amount of light received, the transverse displacement (web flutter) of the web can be determined. This paper describes the construction and working of the new sensor for web flutter measurement. Experiments conducted on a web platform show that the sensor is capable of accurately measuring web flutter. The frequency response of the sensor is limited only by the scanning rate of the pixel array and not by the flutter measurement method. A dedicated signal processing circuit can be used to obtain a desired scanning rate, thus, a desired frequency response.

We have presented our preliminary results on studying the effect of two different coupling materials in Sonic Infrared (IR) Imaging, which is a hybrid ultrasonic/infrared NDE technology and can detect defects in materials and structures by detecting the changes of IR radiation of defective objects through sensors during an ultrasound excitation pulse (can be a fraction of a second), in the Smart Structures and NDE in San Diego in March 2007. Those two coupling materials produced different results in the sense of producing different IR signal levels. We have been further investigating the non-linear phenomena of different coupling materials in Sonic IR Imaging because this non-linear effect appears to play a very important role in Sonic IR Imaging technology. We focus our study on the effect of the level of coupling mechanical energy from the ultrasound transducer to the target, and the level of infrared signals produced around the defects. We present our results from those aspects in this paper.

This study experimentally investigates the capabilities of iron-gallium nanowire arrays as artificial cilia transducers. The experiments are conducted with a custom manipulator device incorporated into the stage of a scanning electron microscope (SEM) for observation. Individual nanowires of varying size and composition are mechanically tested statically and dynamically to determine the elastic properties and failure modes. Entire arrays of close packed wires are mounted onto giant magnetoresistive (GMR) sensors to measure the coupled magnetic induction response resulting from bending the array. This data is compared with empirical and simulated results from previous macroscale research.

Radio Frequency IDentification (RFID) tag is a promising device for the management of products at a very low cost. Huge number of such low-cost sensors can be installed to the structure beforehand, after a disaster we can access to these sensors wirelessly and very easily. In this system, an electrically conductive paint or printed sheet is applied to a part of structure in which crack will occur. Copper wire is connected to the attachment on the structure and a RFID tag. When a crack occurs, the paint or printed sheet is broken, resulting in an increase in resistance. Crack width can be estimated by the ability of an RFID transmitter to communicate with the tag. By bending tests of concrete specimens, the relationships between concrete crack width and conductivity of the materials are examined. It is shown that the level of concrete crack width can be related to the ability of the paint or printed sheet to conduct electricity or not. This printed sheet is also applied for steel crack. By fatigue test of steel specimen with a notch, very small steel crack can be detected by this sensor.

Smart dampers with on-demand controllable damping curves are key components for semi-active vibration control of structures. Smart dampers utilize friction or viscosity to dissipate mechanical energy by heat. The potential thermal problems are their major drawbacks. Novel colloidal dampers are recently developed with low-heat generation and high damping efficient, they are, however, passive and with no on-demand controllable damping capability. In this paper, we propose a smart colloidal damper by employing water-based ferrofluids in damping media. We find that the corresponding damping hysteresis loops can be affected by applied magnetic fields significantly and rapidly. We further retrieve the instant stiffness and damping coefficient of the smart colloidal dampers from the measured hysteresis loops. It is shown that the negative stiffness and the negative damping coefficient may occur during the operation of the smart colloidal dampers.

Magnetorheological (MR) dampers are one of the most advantageous control devices for civil engineering applications to natural hazard mitigation due to many good features such as small power requirement, reliability, and low price to manufacture. To reduce the responses of a structural system by using MR dampers, a control system including a power supply, control algorithm, and sensors is needed. The control system becomes complex, however, when a lot of MR dampers are applied to large-scale civil structures, such as cable-stayed bridges and high-rise buildings. Thus, it is difficult to install and/or maintain the MR damper-based control system. To overcome the above difficulties, a smart passive system was proposed, which is based on an MR damper system. The smart passive system consists of an MR damper and an electromagnetic induction (EMI) system that uses a permanent magnet and a coil. According to the Faraday law of induction, the EMI system that is attached to the MR damper can produce electric energy and the produced energy is applied to the MR damper to vary the damping characteristics of the damper. Thus, the smart passive system does not require any power at all. Besides the output of electric energy is proportional to input loads such as earthquakes, which means the smart passive system has adaptability by itself without any controller or sensors. In this paper, the integrated design method of a large-scale MR damper and Electromagnetic Induction (EMI) system is presented. Since the force of an MR damper is controllable by altering the input current generated from an EMI part, it is necessary to design an MR damper and an EMI part simultaneously. To do this, design parameters of an EMI part consisting of permanent magnet and coil as well as those of an MR damper consisting of a hydraulic-type cylinder and a magnetic circuit that controls the magnetic flux density in a fluid-flow path are considered in the integrated design procedure. As an example, a smart passive control system for reducing stay cable responses is considered in this investigation and it will be fabricated and tested through experiment in the future.

The smart passive system consisting of a magnetorheological (MR) damper and an electromagnetic induction (EMI) part has been recently proposed. An EMI part can generate the input current for an MR damper from vibration of a structure according to Faraday's law of electromagnetic induction. The control performance of the smart passive system has been demonstrated mainly by numerical simulations. It was verified from the numerical results that the system could be effective to reduce the structural responses in the cases of civil engineering structures such as buildings and bridges. On the other hand, the experimental validation of the system is not sufficiently conducted yet. In this paper, the feasibility of the smart passive system to real-scale structures is investigated. To do this, the large-scale smart passive system is designed, manufactured, and tested. The system consists of the large-capacity MR damper, which has a maximum force level of approximately ±10,000N, a maximum stroke level of ±35mm and the maximum current level of 3 A, and the large-scale EMI part, which is designed to generate sufficient induced current for the damper. The applicability of the smart passive system to large real-scale structures is examined through a series of shaking table tests. The magnitudes of the induced current of the EMI part with various sinusoidal excitation inputs are measured. According to the test results, the large-scale EMI part shows the possibility that it could generate the sufficient current or power for changing the damping characteristics of the large-capacity MR damper.

This paper presents the performance evaluation of a semi-active controlled floor isolation system for earthquake reduction. The floor isolation system consists of a rolling pendulum system and a semi-active controlled MR damper. The modified Bouc-Wen model is used to represent the behavior of the MR damper. A serious of performance test of the MR damper is made and been used for system identification. Two contrasting control methods including LQR with continuous-optimal control and Fuzzy Logic control are experimentally investigated as potential algorithms and comparisons are made from the results. Unlike the clipped-optimal control, LQR with continuous-optimal control can output the continuous command voltage to control the MR damper, and get smoother control effect. A three-story steel structure with the floor isolation system on the 2nd floor is tested on the shake table. Scaled historical near- and far-field seismic records are employed to examine controller performance with respect to frequency content and PGA level. Experimental results show that both control algorithms can suppress the acceleration of the isolated floor during small and large PGA levels, and alleviate both displacement and acceleration simultaneously in larger, near-field events. Both control algorithms are adaptive and robust to various intensity of excitation. This investigation demonstrates the feasibility and capabilities of a smart semi-active controlled floor-isolation system.

This paper presents the structural control results of shaking table tests for a steel frame structure in order to evaluate the performance of a number of proposed semi-active control algorithms using multiple magnetorheological (MR) dampers. The test structure is a six-story steel frame equipped with MR-dampers. Four different cases of damper arrangement in the structure are selected for the control study. In experimental tests, an EL Centro earthquake, a Kobe earthquake and a Chi-Chi earthquake (station TCU067) are used as ground excitations. Various control algorithms are used for this semi-active control studies, including the Decentralized Sliding Mode Control (DSMC), LQR control and passive-on and passive-off control. Each algorithm is formulated specifically for the use of MR-dampers. Additionally, each algorithm uses measurements of the absolute acceleration and the device velocity for the determination of the control action to ensure that the algorithm can be implemented on a physical structure. The performance of each algorithm is evaluated based on the results of shaking table tests, and the advantages of each algorithm is compared and discussed. The reduction of the story drift and acceleration throughout the structure is examined.

Critical non-structural equipment, including life-saving equipment in hospitals, circuit breakers, computers, high technology instrumentations, etc., are venerable tostrong earthquakes, and the failure of these equipments may result in a heavy economic loss. In this connection, innovative control systems and strategies are needed for their seismic protections. This paper presents the performance evaluation of passive and semi-active control in the equipment isolation system for earthquake protection. Through shaking table tests of a 3-story steel frame with equipment on the 1^nd floor, a MR-damper together with a sliding friction pendulum isolation system is placed between the equipment and floor to reduce the vibration of the equipment. Various control algorithms are used for this semi-active control studies, including the decentralized sliding mode control (DSMC) and LQR control. The passive-on and passive-off control of MR damper is used as a reference for the discussion on the control effectiveness.

Magnetorheological fluid damper (MR damper) has been expected to control the response of civil and building structures in recent years, because of its large force capacity and variable force characteristics. At first, a series of real-time hybrid tests was conducted. The important objective of this paper is to verify the validity of real-time hybrid tests by comparison with the test results of shaking table tests by using the same MR damper. The maximum damping force of the MR damper is 10 (kN), the stroke is 600(p-p) (mm), and the maximum piston velocity is 1(m/s). To determine the control force of the MR damper, optimal control theory and skyhook control were employed. The capability of the MR damper to control the response displacements and accelerations of base isolation system was verified by both shaking table tests and real-time hybrid tests.

This paper is concerned about the basic properties of deployment for shape memory polymer composite (SMPC) and its application in deployable hinge for space structure. Shape-memory polymers (SMP) are an emerging class of active polymers that have dual-shape capability. One of another advantage, compared with other traditional material hinge, the SMPC carpenter type hinge is that it will not produce a large shock when it spring into the deployed position. There are several kinds of shape memory polymer composite (fiber reinforced, powder reinforced, etc,). Epoxy SMPs, carbon fibre fabric reinforced SMPC was introduced in this work. In order to investigate the basic performances of SMPC hinge, the experimental methods are used as follows: dynamic mechanical analysis (DMA), three point bending test and the radio of shape recovery. In the end, the structure of the carpenter type hinge is introduced. The carpenter type hinge is one mechanism that has the advantage of high-reliability of the deployment; light weighted, and low cost. This SMPC carpenter type hinge performs good deployment performances during numerous thermomechanical cycles. So the potential applications for such materials as active medical devices are highlighted.

Cornerstone Research Group Inc. has developed reflexive composites achieving increased vehicle survivability through integrated structural awareness and responsiveness to damage. Reflexive composites can sense damage through integrated piezoelectric sensing networks and respond to damage by heating discrete locations to activate the healable polymer matrix in areas of damage. The polymer matrix is a modified thermoset shape memory polymer that heals based on phenomena known as reptation. In theory, the reptation healing phenomena should occur in microseconds; however, during experimentation, it has been observed that to maximize healing and restore up to 85 % of mechanical properties a healing cycle of at least three minutes is required. This paper will focus on work conducted to determine the healing mechanisms at work in CRG's reflexive composites, the optimal healing cycles, and an explanation of the difference between the reptation model and actual healing times.

Durability and damage tolerance criteria drives the design of most composite structures. Those criteria could be altered by developing structure that repairs itself from impact damage. This is a technology for increasing damage tolerance for impact damage. Repaired damage would enable continued function and prevent further degradation to catastrophic failure in the case of an aircraft application. Further, repaired damage would enable applications to be utilized without reduction in performance due to impacts. Self repairing structures are designed to incorporate hollow fibers, which will release a repairing agent when the structure is impacted, so that the repairing agent will fill delaminations, voids and cracks in les than one minute, thus healing matrix voids. The intent is to modify the durability and damage tolerance criteria by incorporation of self-healing technologies to reduce overall weight: The structure will actually remain lighter than current conventional design procedures allow. Research objective(s) were: Prove that damage can be repaired to within 80-90% of original flexural strength in less than one minute, in laminates that are processed at 300-350F typical for aircraft composites. These were successfully met. The main focus was on testing of elements in compression after impact and a larger component in shear at Natural Process Design, Inc. Based on these results the advantages purposes are assessed. The results show potential; with self repairing composites, compressive strength is maintained sufficiently so that less material can be used as per durability and damage tolerance, yielding a lighter structure.

This paper is concerned about the drive of shape memory styrene copolymer through an infrared optical fiber carrying infrared laser. The infrared laser was chosen to drive the SMP through the optical fiber embedded into the SMP. The working frequency of infrared laser was installed in 3-4μm, the working band of optical fiber was 1-6μm. An optical fiber was embedded into the SMP for delivery of 3-4μm laser light for activation. The surface of the optical fiber was etched by the aqueous solution of sodium-hydroxide in order to increase transmission efficiency of the optical fiber. We synthesized thermoset SMP based on styrene copolymer, and measured Tg of SMP is the 53.7oC by the DMA. The thermally activated SMP is possible to initiate an originally shape by a touchless and highly selective infrared laser stimulus. The infrared laser-activated SMP could be recovered its original shape by less temperature than Tg, it was proved this driving method of SMP is more effective than conventional external heaters. Therefore infrared laser-activated method was advantageous for using in the low temperature condition. The increase in temperature of SMP which was embedded treated optical fiber indicated that the infrared laser irradiated into the SMP from here and heated the SMP. The optical fiber was treated by the aqueous solution of sodium-hydroxide, transmission efficiency of the optical fiber increased, and the total contact area between SMP and the optical fiber. The infrared laser stimulation of SMP was interest for actuator systems as well as medical applications.

Results from our efforts to improve the performance of low-cost, unpowered, wireless, resistance based Electronic Structural Surveillance tags (ESS) will be presented. The ESS tags use an unpowered embedded sensor read by an external reader using an inductively coupled impedance measurement. Read range of coupled tags is largely dependent on the strength of inductive coupling which is influenced by the relative shape and size of the coils. Reader coil geometries can be optimized to increase read range. Additionally, an enhanced circuit model, for data extraction, is developed and tested with the corrosion sensor. The model provides increased information about the sensor and its surroundings. Better coil design and circuit model based data extraction methods can improve the reliability in reading the sensor. Recommendations for design and analysis resulting from this study can be extended to optimize other electronic structural surveillance tag sensors.

In this study, a smart sensor node is developed for hybrid health monitoring of PSC girder bridges. Hybrid health monitoring of those structures is to alarm damage occurrence, to classify damage-types, and to identify damage locations and severities by measuring accelerations and impedance signals. In order to achieve the objective, the following approaches are implemented. Firstly, a smart sensor node with wireless sensing capacity and embedded monitoring algorithms is developed for measuring acceleration. Secondly, we design a hybrid damage monitoring scheme that combines acceleration-based and impedance-based methods for PSC girder bridges. Finally, the performance of the smart sensor node is evaluated using a laboratory-scale PSC girder bridge model for which acceleration and impedance signals were measured for prestress-loss and stiffness-loss cases.

Large Scale Heavy Derrick Lay Barge is very important for sea work. Under intense wind and wave load, the hook on the Barge will vibrate so large that in some cases it can not work. Through installing the Tuned Mass Damper(TMD) on the hook, the vibration will be reduced to a certain range to meet the demand on sea work, which is also important for increasing the efficiency of sea work. To design the suitable TMD for the hook, the dynamical parameters should be specified beforehand. Generally, the related dynamical parameters such as inclinometer and acceleration are measured by wire sensors. But due to the restriction of the actual condition, the wire sensors are very hard to implement. Recently, the wireless sensors have been presented to overcome the shortcomings of wire ones. It is more suitable and also convenient to utilize wireless sensors to acquire the useful data of large scale heavy derrick lay barge. In this paper, the hook reducing swing movement control module is designed for large scale heavy derrick lay barge. Secondly, wireless inclinometer sensor system is integrated using the technique of MEMS, sensing and wireless communication. Finally, the hook reducing swing movement control module is validated by the developed wireless inclinometer data acquisition system. The wireless inclinometer sensor can be used not only in swing monitoring for large scale heavy derrick lay barge's Hook, but also in vibration monitoring for TV tower, large crane. In general, it has great application foreground.

This paper describes an autonomous embedded system for remote monitoring of bridges. Salient features of the system include ultra-low power consumption, wireless communication of data and alerts, and incorporation of embedded sensors that monitor various indicators of the structural health of a bridge, while capturing the state of its surrounding environment. Examples include water level, temperature, vibration, and acoustic emissions. Ease of installation, physical robustness, remote maintenance and calibration, and autonomous data communication make the device a self-contained solution for remote monitoring of structural health. The system addresses shortcomings present in centralized structural health monitoring systems, particularly their reliance on a laptop or handheld computer. The system has been field-tested to verify the accuracy of the collected data and dependability of communication. The sheer volume of data collected, and the regularity of its collection can enable accurate and precise assessment of the health of a bridge, guiding maintenance efforts and providing early warning of potentially dangerous events. In this paper, we present a detailed breakdown of the system's power requirements and the results of the initial field test.

The objective of this research is to develop and verify the wireless micro-electro-mechanical system (MEMS) monitoring system for the health monitoring of high rise buildings. The MEMS accelerometer has advantages of small size, low-cost and low power consumption, and thereby is suitable for wireless monitoring. Consequently, the use of MEMS and wireless communication can reduce system cost and simplify the installation for the structural health monitoring. To assess the applicability, the wireless MEMS monitoring system is applied to a full-scale building structure with hybrid mass damper (HMD) system. The building is a 5-story steel building and the HMD is mounted on the 4th floor to vibrate the building. The field evaluation results indicate that the wireless MEMS monitoring system is reliable and robust for the health monitoring of buildings.

From a traffic safety point-of-view, there is an urgent need for intelligent tires as a warning system for road conditions, for optimized braking control on poor road surfaces and as a tire fault detection system. Intelligent tires, equipped with sensors for monitoring applied strain, are effective in improving reliability and control systems such as anti-lock braking systems (ABSs). In previous studies, we developed a direct tire deformation or strain measurement system with sufficiently low stiffness and high elongation for practical use, and a wireless communication system between tires and vehicle that operates without a battery. The present study investigates the application of strain data for an optimized braking control and road condition warning system. The relationships between strain sensor outputs and tire mechanical parameters, including braking torque, effective radius and contact patch length, are calculated using finite element analysis. Finally, we suggested the possibility of optimized braking control and road condition warning systems. Optimized braking control can be achieved by keeping the slip ratio constant. The road condition warning would be actuated if the recorded friction coefficient at a certain slip ratio is lower than a 'safe' reference value.

In this study, we investigated a promising method for measuring three-axis force based on an optical tactile sensing system. Such system consists of a waveguide, an array of tactile cell, a light source and an image sensor (a CCD camera). When the tactile cells are subjected to external forces, the condition for total internal reflection of the attached waveguide is spoiled. The original symmetrical planar waveguide then changes to an asymmetrical one, leading to light leakage in the transverse direction, which is used as the sensing mechanism for the applied forces. A numerical study involving three-dimensional finite element analysis was carried out to study the deformation of tactile cells due to contact forces. A linear relationship between the applied three-axis force and the spot sizes of the image of the leaked light was obtained and validated by experiments.

Machinery maintenance accounts for a large proportion of plant operating costs. Compared with the conventional scheduled maintenance strategy which is to stop the machine at pre-determined intervals, modern condition-based maintenance strategy stops the machine only when there is evidence of impending failure. It is now possible to use multi-modal sensor input to monitor machine condition in a collaborative and distributed manner. In this paper, three categories of methods for condition monitoring are reviewed - 1. knowledge based, 2. model based 3. data based methods. Knowledge-based systems are derivations from expert systems that use rules and inference engines to determine failures and their causes. Data-driven methods use machine fault data, typically derived during experiments to train a monitoring system. Pattern recognition algorithms then attempt to classify actual sensor data using the results of the training phase. However it is often impractical to obtain data for every type of fault. Model-based techniques on the other hand use mathematical models to predict machine performance. We propose to combine the model based and data based method for machine condition monitoring. The data is used to train the model and derive its parameters. The various fault modes are then identified and simulated. The output is then input to the classification schemes that can be then used to identify and classify real-time data. We apply the technique to condition monitoring of electrical motors.

A pulse-echo ultrasonic guided wave approach that monitors the development of early age mortar during the initial stages of setting and hardening is presented. The method transmits the fundamental torsional wave mode on one end of a cylindrical steel rod partially embedded in mortar and then monitors the reflected signals. Both the reflection from the end of the rod and the reflection from the point where the waveguide enters the material are monitored. The development of the material's mechanical properties is related to the change in signal strength of the reflections. The reflection at the location where the waveguide pierces the material is essentially a surface measurement. It is known that the material properties of concrete vary with depth; specifically, the material in the surface layer possess different material properties than the core material of the specimen. Finite element analysis was used to analyze these differences and to provide a clearer understanding of the entry-reflection. The analysis shows that at early stages, it takes more time for the surface layer to achieve the same properties as that of the core of the specimen. However, after the mortar has achieved measurable strength (e.g. 12-14 hours), the material properties of the surface layer can reasonably approximate those of the core of the specimen.

High-frequency guided longitudinal waves have been used in a through-transmission arrangement to monitor reinforced mortar specimens undergoing both accelerated uniform and localized corrosion. High-frequency guided longitudinal waves were chosen because they have the fastest propagation velocity and lowest theoretical attenuation for the rebar/mortar system. This makes the modes easily discernible and gives them the ability to travel over long distances. The energy of the high-frequency longitudinal waves is located primarily in the center of the rebar, leading to less leakage into the surrounding mortar. The results indicate that the guided mechanical waves are sensitive to both forms of corrosion attack in the form of attenuation, with less sensitivity at higher frequencies. Also promising is the ability to discern uniform corrosion from localized corrosion in a through-transmission arrangement by examination of the frequency domain.

This study focuses on a structural health monitoring (SHM) using case-based reasoning (CBR). Structural condition is diagnosed using propagation patterns of ultra-sonic waves. Firstly, emitted pseudo-AE waves are measured in pencil lead fracture experiments. Then, the AE signals are classified into 90 types according to location, magnitude and structural condition. Secondly, pattern identification is conducted using feature parameters extracted from the signals for damage pattern recognition. Finally, feasibility of the method to real structures using CBR is studied. Results showed that the damage patterns could be determined with 82% accuracy. If only the damage location is needed, of the accuracy was higher with 95%. The proposed method using ultra-sonic waves and CBR is thus feasible for practical applications.

In earlier work we developed inductive coupling for surface-mounted Lamb wave transducers operating at relatively low frequencies, such as 300 kHz. We now report on similar inductively-coupled transducers at higher (multiple MHz) frequencies. Our investigation was motivated by a particular application, to examine a box girder top flange, using transducers mounted along the flange edge. We employ a pair of transducers in pitch-catch mode, offset to create a diagonal path, and show that a shadow is detected when the path is intercepted by a through-thickness crack. We compare results obtained using conventionally wired transducers and using inductively-coupled transducers, showing that effective performance can be achieved with wireless (inductively-coupled) operation. Superior performance is obtained if plexiglas wedges are used to direct the beam along the diagonal path. Reflection from the crack is evident, as is the shadow effect along the direct diagonal path.

We discuss waves created in relatively thick plates by edge excitation at frequency-thickness (fd) products that correspond, in principle, to multiple Lamb wave modes. For relatively low values of the fd product it is clear that Lamb wave modes will be generated, while at large values of the fd product we observe a bulk (longitudinal wave) in the solid, but influenced by reflections from the plate surfaces. We show that for a range of intermediate fd products a train of regularly spaced nearly-longitudinal waves is generated. The development of a lead pulse and trailing pulses, all traveling at the longitudinal (bulk) wave speed, is well known and has been explained in the literature. In this paper we describe the transition from Lamb wave generation to the formation of nearly-longitudinal waves with their trailing pulses. We report experimental results and theoretical results, with good correspondence between them. We also examine the transfer of energy from leading to trailing pulses, which means that such nearly-longitudinal waves will not propagate indefinitely; however, we show that they retain ample energy for flaw detection at distances of several meters. Most importantly, we study the interaction of these trailing pulses with cracks, again showing experimental results and theoretical predictions that are consistent with one another. The results suggest that these nearly-longitudinal waves are an attractive option for flaw detection because of their shorter wavelength (as compared to Lamb waves at low fd products) and because they preserve their pulse train characteristics after scattering.

Miniature and light weight thick piezoelectric films (>40μm) integrated ultrasonic transducers (IUTs) for bulk longitudinal (L) and shear (S) and plate acoustic waves (PAW) propagation are presented. The unique and distinct advantages of these IUTs are that they can be fabricated, using sol-gel based technique, directly onto sample with complex structures including curved surfaces and require no couplant for operation. Using novel mode conversion methods, the L wave generated by IUTs can be converted to S, symmetric, anti-symmetric and shear-horizontal (SH) PAW. The experimental results agreed well with those obtained by a finite difference based method which solves the 3D visco-elastic wave equations. These IUTs can operate at temperatures at least up to 150°C, at center frequencies ranging from 1 to 20 MHz, and provide damage detection range of tens of centimeters in metallic structures. An inductive coupled technique is used to achieve non-contact measurements with these IUTs.

Linear sensor arrays made from small molecule/carbon black composite chemiresistors placed in a low headspace volume chamber, with vapor delivered at low flow rates, allowed for the extraction of chemical information that significantly increased the ability of the sensor arrays to identify vapor mixture components and to quantify their concentrations. Each sensor sorbed vapors from the gas stream to various degrees. Similar to gas chromatography, species having high vapor pressures were separated from species having low vapor pressures. Instead of producing typical sensor responses representative of thermodynamic equilibrium between each sensor and an unchanging vapor phase, sensor responses varied depending on the position of the sensor in the chamber and the time from the beginning of the analyte exposure. This spatiotemporal (ST) array response provided information that was a function of time as well as of the position of the sensor in the chamber. The responses to pure analytes and to multi-component analyte mixtures comprised of hexane, decane, ethyl acetate, chlorobenzene, ethanol, and/or butanol, were recorded along each of the sensor arrays. Use of a non-negative least squares (NNLS) method for analysis of the ST data enabled the correct identification and quantification of the composition of 2-, 3-, 4- and 5-component mixtures from arrays using only 4 chemically different sorbent films and sensor training on pure vapors only. In contrast, when traditional time- and position-independent sensor response information was used, significant errors in mixture identification were observed. The ability to correctly identify and quantify constituent components of vapor mixtures through the use of such ST information significantly expands the capabilities of such broadly cross-reactive arrays of sensors.

An investigation was performed to develop a flexible sensor network that can be stretched and expanded to cover structures with an order of magnitude larger than its original unexpanded size. The increasing need to cover large areas with a high number of sensors, networks, and electronic devices for structural health monitoring leads to this study. In this paper a flexible polymer with ultra- high stretching capability (linear expansions larger than 1000% the original length) is designed, fabricated and tested for sensor network applications. The stretchability of the polymer is achieved by engineering thousands of micronodes, which house the sensors and electronics, interconnected by extendable and flexible polymer microwires. The extendable microwires are the key element to perform uniform expansions of the network in all directions, to allow precise location of the nodes, to maximize the polymer expansion per unit area and to allow translation only of the nodes. With the proposed microwire design, a linear elongation wider than 1000% was achieved for a 256 nodes network, avoiding failure of the microwires and micronodes during fabrication and extension. It is believed that the proposed flexible, expandable polymer design is a cost-effective approach to integrate networks of thousands of sensors, actuators and electronic devices into large structures.

Compact sensing schemes are desirable for feedback control of ionic polymer-metal composite (IPMC) actuators in their targeted bio, micro, and nano applications. In this paper, a novel integrated sensory actuator with both position and force feedback is designed by combining IPMC with polyvinylidene fluoride (PVDF) films. The design adopts differential configurations for both the sensor-actuator structure and the sensing circuit, and thus eliminates capacitive coupling between IPMC and PVDF, minimizes the internal stress at bonding interfaces, and enables excellent immunity to thermal and electromagnetic noises. Closed-loop position control of the IPMC output is demonstrated together with simultaneous tip force measurement, based upon the integrated PVDF position and force sensors.

We present four new findings pertaining to MEMS sensors for acoustic emission detection. Our sensors are resonant-type capacitive transducers, operating with a frequency between 100 kHz and 500 kHz, fabricated in the PolyMUMPS process. The sensitivity of a resonant transducer is related to the sharpness of its resonance, measured by the quality factor Q, and operating in a coarse vacuum will increase Q. We describe a practical laboratory method for sealing and evacuating our MEMS sensor, and present measurements showing Q in the evacuated packages to be 2.4 to 3.6 times greater than under atmospheric pressure. We also describe our theoretical analysis of noise sources in the electromechanical behavior of a resonant, capacitive-type transducer sensitive to out-of-plane motion, with particular interest in noise resulting from mechanical excitation of the moving plate by air molecule impact. We report on a new transducer design to sense out-of-plane motion featuring a moving plate constructed as an open grill rather than as a plate perforated by etch holes. Characterization measurements show the open grill design to have a higher Q than a comparable perforated plate transducer. Finally, we report on another novel transducer designed to sense in-plane motion. The sensor is a comb finger capacitive transducer, and theoretical predications predict the in-plane sensor to have a much higher Q than the out-of-plane sensors. We show experimental measurements confirming these design characteristics, and we show results from pencil lead break experiments.

The development of an in-fiber whitelight interferometric distance sensor based on the mode coupling effect of a Long Period Fiber Grating (LPFG) for absolute distance measurement has been investigated. Unlike the Fabry-Perot interferometric distance sensor that uses a regular single mode fiber as the sensor probe, the LPFG-based distance sensor employs a single mode fiber whose cladding region is coated with a reflective film and having a LPFG located at a distance from the cleaved fiber end. The LPFG serves as a beam splitter that separates the light into a core mode and a cladding mode and recombines the two light waves to generate interference, from which the absolute distance can be deducted. Because the optical path difference of the LPFG-based interferometric distance sensor is contributed by both the free-space cavity distance and the distance between the LPFG and the fiber end, it does not impose a limit on the minimum measurable distance. In this paper, the experimental setup for mechanically inducing LPFG in the optical fiber is first described. It is demonstrated that the transmission characteristics of the LPFG can be easily controlled by adjusting the grating period and the applied pressure. The implementation and data analysis of an LPFG-based whitelight interferometric distance sensor are then discussed in detail. Experimental results verified that the distance sensor is capable of measuring small distances that can not be measured by a Fabry-Perot interferometric distance sensor.

Existing strain gages are mostly point sensors that measure local strains from a few discrete locations, while TDR sensor can interrogate distributed changes along the entire length of the sensor line. The present study investigates feasible applications of a new technique using TDR as a distributed strain sensor for structural health monitoring. First, a specially designed TDR sensor laid out on a substrate successfully measured distributed strains and detected a failure location when the substrate was under an increasing tensile load. Second, a TDR sensor spirally wound around a cylindrical tank measured a circumferential strain and detected a failure location on the tank surface when the tank was increasingly pressurized. The developed TDR monitoring technique shows great potential for real-time health monitoring of various critical structures such as bridge, aircraft, and aerospace applications.

An analytical investigation of the transverse shear wave mode tuning with a resonator mass (packing mass) on a Lead Zirconium Titanate (PZT) crystal bonded together with a host plate and its equivalent electric circuit parameters are presented. The energy transfer into the structure for this type of wave modes are much higher in this new design. The novelty of the approach here is the tuning of a single wave mode in the thickness direction using a resonator mass. First, a one-dimensional constitutive model assuming the strain induced only in the thickness direction is considered. As the input voltage is applied to the PZT crystal in the thickness direction, the transverse normal stress distribution induced into the plate is assumed to have parabolic distribution, which is presumed as a function of the geometries of the PZT crystal, packing mass, substrate and the wave penetration depth of the generated wave. For the PZT crystal, the harmonic wave guide solution is assumed for the mechanical displacement and electric fields, while for the packing mass, the former is solved using the boundary conditions. The electromechanical characteristics in terms of the stress transfer, mechanical impedance, electrical displacement, velocity and electric field are analyzed. The analytical solutions for the aforementioned entities are presented on the basis of varying the thickness of the PZT crystal and the packing mass. The results show that for a 25% increase in the thickness of the PZT crystal, there is ~38% decrease in the first resonant frequency, while for the same change in the thickness of the packing mass, the decrease in the resonant frequency is observed as ~35%. Most importantly the tuning of the generated wave can be accomplished with the packing mass at lower frequencies easily. To the end, an equivalent electric circuit, for tuning the transverse shear wave mode is analyzed.

It is widely known that materials exposed to the severe low earth orbit (LEO) environment undergo degradations. For the evaluation of fiber Bragg grating (FBG) sensors in the LEO environment, the reflective spectrum change and the Bragg wavelength shift of FBG sensor were measured during aging cycles simulating the LEO environment. The LEO environment was simulated by high vacuum (~10^-5 Torr), ultraviolet (UV) radiation (<200nm wavelength), temperature cycling (-30°C~100°C), and atomic oxygen atmosphere (AO flux of 9.12×10¹⁴ atoms/cm²/s and kinetic energy of ~0.04 eV). FBG sensor arrays were embedded into the graphite/epoxy composite material. Through the aging cycles simulated for the LEO environment, the change in the reflective spectrums and the Bragg wavelengths from FBG sensors were investigated.

Recently, a damage detection technique has been developed based on the polarization characteristics of the piezoceramic (PZT) transducers attached on the both sides of a thin and uniform metal plate. Damage is identified using instantaneously measured Lamb wave signals without using previously obtained baseline data. If the propagating waves along a thin plate encounter a discontinuity point such as a crack, mode conversion occurs and this mode conversion is extracted using the proposed technique. So for, the proposed technique is demonstrated for specimens with a uniform thickness although many structural systems have more complex structural features such as stiffeners, holes and bolts. In this study, the effect of through-the-thickness holes on the proposed technique is investigated. An array of holes creates multiple reflections and refractions of Lamb waves, and these multiple reflections and refractions may cause difficulties in analyzing responses of Lamb waves. Because the through-the-thickness holes do not produce mode conversion, it is expected that these holes do not affect the performance of the proposed technique. This study experimentally investigates whether a crack damage can be still identified even in the presence of the holes using the proposed technique.

The amount and magnitude of absorption and scattering of stress waves in concrete, mainly due to internal friction and aggregate inclusions, may be different when the concrete mix proportion varies. In this study, the surface wave spectral energy transmission method is proposed for the estimation of crack depth in concrete structures, in which the effect of the concrete mix proportion on measurements of self-compensated surface wave transmission functions (TRFs) and surface wave spectral energy transmission ratios (SETRs) is investigated and a relationship between the crack depth and the SETR has been determined from experimental data on various concrete specimens with different mix proportions and different crack depths using a regression analysis. In the results, it is found that the self-compensated surface wave TRFs are very sensitive to both concrete mix proportions and crack depths. However, SETR is not much affected by the concrete mix proportion but very sensitive to the crack depth. Therefore, the spectral energy transmission method can be effectively used for crack depth estimation in concrete structures regardless of their material mix proportions.