This PDF file contains the front matter associated with SPIE Proceedings Volume 6530, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

While conventional resistance strain gages show increasing cross-sensitivities to temperature and magnetic field with decreasing temperature down to liquid helium, it has been found that fiber optic Bragg grating strain sensors show negligible thermo-optic and magneto-optic effects in cryogenic environment and allow, therefore, reliable strain measurements. These specific application advantages of optical fiber Bragg grating sensors at low temperatures, together with the electrical isolation and low electro-magnetic interference, low thermal conductivity to a large number of multiplexed sensors, make them attractive for structural health monitoring of super-conductive magnets, e.g., for super-conductive motors, magnetic levitation transport, nuclear fusion reactors, or for measurement of material parameters at low temperature, and, if using special sensor substrates, also for temperature measurements and hot spot detection on superconductors.

Fiber optic grating sensors can be used to measure a wide variety of environmental effects including multi-dimensional strain, pressure, temperature, and corrosion. Recently progress has been made in extending the operational temperatures of fiber gratings in quartz using femto-second fabrication techniques to limits that are associated with the mechanical integrity of the fiber itself and diffusion of fiber core materials. This allows the prospect of stable operation to temperatures in excess of 800 degrees C. These same fabrication techniques could be applied to sapphire and other high temperature materials enabling operation to temperatures in excess of 1500 degrees C. Another interesting aspect of the very short pulse fabrication techniques is that birefringence of the fiber gratings may be induced by the fabrication process which in turn may enable higher temperature multi-parameter fiber grating sensors than may be realized by using conventional polarization preserving quartz fibers with lower melting temperatures. If these processes to enable fiber gratings with birefringence can be used in higher temperature waveguides such as sapphire a new class of very high temperature multi-parameter fiber grating sensors could be realized.

The design and development of a novel opto-mechanical strain sensor-called FlexPatch-based on the use of an optical fiber Bragg grating (FBG) mounted into a custom-made miniature metallic flexure is reported. The FBG sensing element is attached to a carrier flexure using proprietary bonding process which ensures a linear, drift-free and repeatable strain response even under severe moisture and temperature conditions. The sensor is uncompensated for temperature effects, but has undergone extensive mechanical and environmental testing and is qualified for use in a strain range of +/- 2,500&mgr;&egr; with a gage factor of 1.2pm/&mgr;&egr; over a temperature range from -40° to 120°C, and a fatigue life >100x10⁶ cycles. The FlexPatch is intended for use in diverse sensing and monitoring applications and can be installed onto surfaces by epoxy bonding or spot welding.

Advancements in portability and performance are described for a fiber optic sensor readout system capable of monitoring wavelength-multiplexed sensors. The handheld sensor interrogator was designed to readily interface with conglomerate sensor systems as a smart sensor node and process all spectral data within its own system in real time at 20 Hz for +/- 13 picometers resolution mode. Portability was demonstrated by flying the system on a miniature aerial vehicle (MAV) which collected strain and temperature flight data for broadcast to a ground station. Additional improvements upgraded the sensor measurement speed by two orders of magnitude.

BOTDA(R) sensing technique is considered as one of the most practical solution for large-sized structures as the instrument. However, there is still a big obstacle to apply BOTDA(R) in large-scale area due to the high cost and the reliability problem of sensing head which is associated to the sensor installation and survival. In this paper, we report a novel low-cost and high reliable BOTDA(R) sensing head using FRP(Fiber Reinforced Polymer)-bare optical fiber rebar, named BOTDA(R)-FRP-OF. We investigated the surface bonding and its mechanical strength by SEM and intensity experiments. Considering the strain difference between OF and host matrix which may result in measurement error, the strain transfer from host to OF have been theoretically studied. Furthermore, GFRP-OFs sensing properties of strain and temperature at different gauge length were tested under different spatial and readout resolution using commercial BOTDA. Dual FRP-OFs temperature compensation method has also been proposed and analyzed. And finally, BOTDA(R)-OFs have been applied in Tiyu west road civil structure at Guangzhou and Daqing Highway. This novel FRP-OF rebar shows both high strengthen and good sensing properties, which can be used in long-term SHM for civil infrastructures.

A tremendous development in the field of imaging radiation detectors has taken place in the last decade. Conventional X-ray film has been replaced by digital X-ray imaging systems in a number of ways. Such systems mainly consist of silicon charge coupled devices (CCDs) where incident photons create electron-hole pairs in the thin silicon absorption layer near the surface. In contrast to visible light, which is absorbed within a 2 µm layer of silicon, the penetration of X-ray is much deeper due to higher photon energy. This disadvantage is often circumvented by the use of a scintillator absorption layer. Due to scattering of the low energy fluorescence photons, resolution and contrast of the X-ray images decrease. In order to eliminate these disadvantages, hybrid detectors consisting of direct converting semiconductors and readout electronics parts are fabricated. For this configuration, it is advantageous that both parts can be optimized separately and different materials can be used. Because of the well developed technology, the readout chip is fabricated out of silicon. As absorbing material, silicon is less suitable. In a silicon substrate of 500 µm thickness, only 15% of a 30 keV radiation is absorbed and converted into charges. In order to increase the absorption, materials with a higher atomic mass have to be used. Several compound semiconductors can be used for this purpose. One of them is GaAs, which is available as high quality semi-insulating wafer material. For detector optimization, GaAs wafers from several manufacturers with different properties were investigated. Test structures with Schottky and PIN diodes were fabricated. The I/V curves of the diodes, the spectral response from 5 up to 150 keV, the carrier concentration, and the carrier mobility were measured and compared. A survey of the results and the criteria for material selection resulting from these measurements will be provided in the paper.

NASA exploration missions are increasingly seeking to determine existence of past or present life, detect water and examine the mineralogy of various planets in the solar system. Determination of the surface and bulk properties of selected samples currently requires multiple analytical instruments, each with an independent type of radiation source. Using multitude of instruments requires high power, mass and volume resulting in high cost and complexity. Recently, the authors developed a ferroelectric based radiation source, which they named Ferrosource, that was demonstrated to emit five radiation types enabling a new generation of compact, low power, low mass multifunctional NDE analytical instruments. The emitted radiation types include visible light, ultraviolet, X-ray, as well as electron and ion beams. These radiation types are already in use in a multitude of instruments for detecting water, performing mineralogical/chemical analysis and for identifying biological markers. This ferroelectric-based source consists of a disk having a continuous ground electrode on one side and a grid-shaped cathode on the other side. This source is placed in a vacuum tube and is used to generate plasma by switching high voltage pulses and the plasma is harnessed to generate the radiation. To make the source more practical and applicable for NASA missions it was miniaturized by about 50 times the original chamber volume and efforts were made to increase its efficiency to compensate for the size reduction. A series of experiments were performed to demonstrate the capability of the developed miniature source. The source, the experiments, and the test results will be described and discussed in this paper.

In order to meet the requirements of rising flexibility and an automated material inspection in a small batch production environment, an automatically changeable ultrasound sensor tool for milling machines has been developed. This system enables an automated ultrasonic inspection of varying parts to be carried out directly on a machining center and visualizes hidden geometries and material imperfections three-dimensionally. The sensor tool is based on commercialized ultrasonic squirter-probes, which are able to use the cooling lubricant for sound coupling. During the measurement recordings, the milling machine's axes move the sensor numerical-controlled across the workpiece. By this means, automated material inspection tasks can be performed very cost-effectively without setting up separate testing facilities. 4- or 5-axes kinematics capacitates the system to check even very complex-shaped parts.

This paper presents a new monitoring principle for laser transmission welding of plastics. The principle uses two independent detectors: a CCD or CMOS camera to supply an image of the weld seam and a pyrometer to detect heat radiation from the welding process. In laser transmission welding, the weld seam is usually hidden by the laser transparent joining partner, which may still be colored in the visible spectrum. Therefore, a special lighting laser will be used to acquire an image of the weld for CCD or CMOS cameras. If the upper joining partner is not only partly transparent for the laser wavelength of the welding laser, but also for the laser wavelength of the lighting laser, a direct visualization of the weld is possible. Factors influencing the weld quality or leading to defects within the weld are kerfs on the surfaces of the joining partners, moisture uptake of the plastic material and the surface finish of the materials. Which weld defects result from these factors and how they can be detected by the monitoring system are shown. Not all of the resulting defects can be detected with a single detector. Therefore, the information from the two detectors, camera and pyrometer, is correlated.

The application of thermal wave measurement techniques was demonstrated for Strontium Barium Niobate (SBN) and Lithium Tantalate (LT) crystals, Lead Zirconate Titanate (PZT) ceramics, and PZT thin films. We have investigated the influence of poling conditions and of chromium and cerium doping on the polarization distribution and domain wall pinning in SBN crystals, the impact of ion beam etching on the polarization distribution in high-detectivity LT infrared sensors, the influence of poling procedure on the polarization distribution of PZT piezoceramics, and the polarization distribution in self-polarized PZT thin films.

More than 85 years after its discovery, the Barkhausen effect remains one of the basic principles involved in the characterization of magnetic and metallic materials, e.g. to measure their residual stresses and hardness. Reliable testing results can be obtained quickly and nondestructively for a large range of industrial applications using micro-magnetic parameters. This paper summarizes the physical principles and demonstrates applications important for today's nondestructive testing procedures.

Assessment of ultimate bearing capacity and bearing behavior of large concrete piles in existing foundations or during and after installation remains a difficult task. A common and widespread test method is high-strain dynamic load testing using the one dimensional theory of wave propagation to calculate bearing capacity. Another method of quality insurance based on this theory is low-strain dynamic pile integrity testing. Both testing methods use sensors attached onto or near the pile head. In order to get more precise information about the pile response over whose length, highly resolving fiber optic sensors based on Fabry-Perot technology have been developed for integration into concrete piles at several levels. Motivation is the monitoring of pile deformations during dynamic low-strain, high-strain and static load testing with only one measuring device. First small scale piles have been tested in model tests. All signal responses from integrated sensors have been recorded and compared to signals obtained from common methods of instrumentation. The paper describes the sensing principle, sensor head installation as well as test results.

This paper derives the phase response of a single-mode polymer optical fiber (POF) for large-strain applications. The role of the finite deformation of the optical fiber and nonlinear strain optic effects are derived using a second order strain assumption and shown to be important at strain magnitudes as small as 1%. In addition, the role of the core radius change on the propagation constant is derived, however it is shown to be negligible as compared to the previous effects. It is shown that four mechanical and six opto-mechanical parameters must be calibrated to apply the POF sensor under axial loading. The mechanical nonlinearity of a typical single-mode polymer optical fiber is experimentally measured in axial tension and is shown to be more significant than that of their silica counterpart. The mechanical parameters of the single-mode polymer optical fiber are also measured for a variety of strain rates, from which it is demonstrated that the strain rate has a strong influence on yield stress and strain. The calibrated constants themselves are less affected by strain rate.

Fiber Bragg gratings (FBG) are one of several fiber optic sensor technologies currently being used in structural health monitoring systems. When the effective refractive index of a fiber Bragg grating is changed by external environmental variations (e.g. temperature, pH), the wavelength at which incident light experiences a maximum reflection from the grating will correspondingly shift. To detect small environmental variations that occur during certain chemical processes, one can enhance the sensitivity using either side-polished or tilted fiber Bragg gratings. Enhanced sensitivity in each case is achieved by polishing the fiber on one side or writing the grating at some tilt angle. Side polished FBG sensors having a 1542 nm Bragg wavelength and cladding thickness values from 1-3 &mgr;m provide a maximum refractive index sensitivity of 7×10-4. Tilted FBG sensors having a 1566 nm Bragg wavelength and written with a 4° degree tilt angle provide a maximum refractive index sensitivity of 5×10^-5. Experiments on the tilted gratings were done using 50, 80, 125 &mgr;m diameter fibers immersed in solutions in the index range 1.31-1.44. Since tilted FBGs have enhanced sensitivity and the advantage of maintaining their full mechanical strength, they show greater promise as reliable sensors for structural health monitoring applications.

The ability to detect and quantify beneficial surface and subsurface residual stresses, and operational damage in aerospace materials/structures in a reliable and efficient manner presents significant challenges to existing nondestructive inspection technologies. Induced Positron Analysis (IPA) has demonstrated the ability to nondestructively quantify shot peening/surface treatments and relaxation effects in single crystal superalloys, steels, titanium and aluminum with a single measurement as part of a National Science Foundation SBIR program and in projects with commercial companies. IPA measurement of surface treatment effects provides a demonstrated ability to quantitatively measure initial treatment effectiveness along with the effect of operationally induced changes over the life of the treated component. Use of IPA to nondestructively quantify surface and subsurface residual stresses in turbine engine materials and components has the potential to significantly improve the understanding at the microscale level the effects of surface coatings and treatments on the durability and fatigue life of critical components.

The introduction and development of wireless sensor network technology has resulted in rapid growth within the field of structural health monitoring (SHM), as the dramatic cable costs associated with instrumentation of large civil structures is potentially alleviated. Traditionally, condition assessment of bridge structures is accomplished through the use of either vibration measurements or strain sensing. One approach is through quantifying dynamic characteristics and mode shapes developed through the use of relatively dense arrays of accelerometers. Another widely utilized method of condition assessment is bridge load rating, which is enabled through the use of strain sensors. The Wireless Sensor Solution (WSS) developed specifically for diagnostic bridge monitoring provides a hybrid system that interfaces with both accelerometers and strain sensors to facilitate vibration-based bridge evaluation as well as load rating and static analysis on a universal platform. This paper presents the development and testing of a wireless bridge monitoring system designed within the Laboratory for Intelligent Infrastructure and Transportation Technologies (LIITT) at Clarkson University. The system interfaces with low-cost MEMS accelerometers using custom signal conditioning for amplification and filtering tailored to the spectrum of typical bridge vibrations, specifically from ambient excitation. Additionally, a signal conditioning and high resolution ADC interface is provided for strain gauge sensors. To permit compensation for the influence of temperature, thermistor-based temperature sensing is also enabled. In addition to the hardware description, this paper presents features of the software applications and host interface developed for flexible, user-friendly in-network control of and acquisition from the sensor nodes. The architecture of the software radio protocol is also discussed along with results of field deployments including relatively large-scale networks and throughput rates sufficient for bridge monitoring.

The power harvesting technologies for low-power electronic devices, such as wireless sensor networks and biomedical sensor applications, have received a growing attention in recent years. Of all possible energy sources such as mechanical vibrations, electromagnetic radiations and magnetic fields, the mechanical vibrations have been considered a promising choice for power harvesting in a wide variety of applications. This paper presents the development of two different piezoelectric MEMS generators to harvest energy at different vibration frequencies. For power harvesting at 1.5kHz vibration frequency, we present a generator comprising a silicon micro-cantilever with laminated PZT (lead zirconate titanate) material, and the interdigital electrode on the top of the PZT layer to transform mechanical strain energy into electrical charges by using the d₃₃ mode of PZT. The piezoelectric cantilever generator was tested with using a shaker as the external vibration source. For power harvesting at frequency higher than 20kHz, we present a piezoelectric disk-shaped generator which is packaged by cohesive gel. The power generation efficiency of the fabricated devices was characterized. For the application of the power to the implanted medical sensors, the piezoelectric MEMS generator is claimed to be a power receiver of an additional vibration sources. An experimental model was also developed to study the power transmission efficiency and the charge ability of the MEMS generator device. A feasibility study of the piezoelectric MEMS generator as a power receiver was performed and some testing results are presented.

Surface bonded sensors have significant potential for detecting and characterizing damage in legacy aircraft structures as part of a Structural Health Monitoring system. In this effort, research has been undertaken to understand the impact of adhesive viscoelastic properties on the generation of elastic wave energy by surface-bonded sensors in thin plates. Previous work has shown that bonded sensors can degrade and fail due to exposure to weather, vibration, temperature, and mechanical loading. In that work, experimental and analytical studies were performed to characterize the transfer of static load from a structure into a surface-bonded sensor. The results indicated that the sensor should be decoupled from the nearly static loading induced from the structure to improve its durability. In this effort, we build on that original work to determine what effect the adhesive has on elastic wave generation and reception in the host structure. The results indicate that strong coupling with the structure is required for effective generation and reception of elastic waves, where the elastic material properties of the sensor, bond, and host structure were considered. Although the two goals appear to be contradictory (sensor durability and elastic wave generation), the use of a strongly viscoelastic adhesive is viewed as potential solution for both by allowing weak coupling at low frequencies and strong coupling at high frequencies.

Fatigue crack growth in a lap joint specimen extracted from a retired aircraft fuselage was monitored using bonded continuous acoustic emission sensors. The specimen lasted nearly 350,000 cycles of tension-tension cyclic loading. During this period a large number of acoustic emission signals were collected. Two distinct classes of events were observed during this test. The first group of events consist of low amplitude, long rise time and long duration events which could be attributed to fretting between various surfaces. The second group of events had short rise time and short duration and is thought to be from fatigue cracks. This interpretation is based on the waveform characteristics observed during this test and patterns seen in acoustic emission signals from known fatigue cracks in previous studies. Based on this assumption the crack growth process appear to have initiated after 200,000 cycles of fatigue load and accelerated during the final 20,000 cycles. The final fracture of the specimen occurred in the grip area and indications of this impending failure were evident in the acoustic emission data. In addition, acoustic emission data also suggest fatigue crack growth in an area inaccessible for visual examination.

Durable integrated sensor systems are needed for long-term health monitoring evaluations of aerospace systems. For legacy aircraft the primary means of implementing a sensor system will be through surface mounting or bonding of the sensors to the structure. Previous work has shown that the performance of surface-bonded piezo sensors can degrade due to environmental effects such as vibrations, temperature fluctuations, and substrate flexure motions. This performance degradation included sensor cracking, disbonding, and general loss of efficiency over time. In this research effort, the bonding state of a piezo sensor system was systematically studied to understand and improve the long-term durability and survivability of the sensor system. Analytic and computational models were developed and used to understand elastic wave generation and reception performance for various states of sensor disbond. Experimental studies were also conducted using scanning laser vibrometry, pitch-catch ultrasound, and pulse-echo ultrasound methods to understand elastic wave propagation effects in thin plate materials. Significant performance loss was observed for increasing levels of sensor disbond as well as characteristic frequency signatures which may be useful in understanding sensor performance levels for future structural health monitoring systems.

The primary objective of this study was to demonstrate the effectiveness of various strain measurement techniques at detecting the disbonding of a composite repair patch and then using this information to validate a new capacitance based disbond detection technique. The instrumented repair patch was parametrically designed with the help of Finite Element Analysis (FEA) software to have a stress concentration at its tip. This stress concentration was designed to produce a disbond during fatigue testing, without the need for the introduction of any foreign material to create an artificial disbond condition. The aluminum substrate was grit blasted and the instrumented patch was bonded using FM^®73 adhesive, and was cured following the recommendations of the manufacturer. The geometric characteristics of the patch followed standard repair guidelines for such variables as material selection, taper angles and loading conditions, with the exception of the area designed for premature disbond. All test specimens were inspected using non-destructive testing technique (ultrasound pulse echo) to guarantee that no disbonding had occurred during curing of the specimen. The specimens were placed under fatigue loading to induce a disbond condition between the aluminum substrate and the patch. The specimens were cyclically loaded and strain gauges bonded to strategic locations on the aluminum and composite patch surface to be able to measure changes in surface strains as the disbond progressed. A Digital Image Correlation (DIC) system was also used to measure full field strains over the gauge length of the coupon. The DIC results were compared with the strain gauge data and were used to provide a qualitative measure of the load transfer in the bonded specimen, which clearly demonstrated the change in surface strain that occurred as the composite patch disbonded from the aluminum substrate. Thermoelastic Stress Analysis (TSA) was also used to measure surface strains on the composite patch. Thermoelastic stress analysis proved to be the most sensitive technique for experimentally monitoring the disbond process in real time. Failure analysis of the specimens using optical microscope techniques was performed to determine the type of failure between the patch and the substrate. The results of this work will serve to test the different types of sensors available for the design and manufacturing of a "Smart Patch" for aircraft structure applications.

We have been developing a sensing system for checking the health of aircraft structures made of composite materials. In this system, lead zirconium titanate (PZT) actuators generate elastic waves that travel through the composite material and are received by embedded fiber Bragg grating (FBG) sensors. By analyzing the change in received waveforms, we can detect various kinds of damage. The frequency of the elastic waves is several hundred kHz, which is too high for a conventional optical spectrum analyzer to detect the wavelength change. Moreover, a conventional single-mode optical fiber cannot be used for an embedded FBG sensor because it is so thick that it induces defects in the composite material structure when it is embedded. We are thus developing a wavelength interrogator with an arrayed waveguide grating (AWG) that can detect the high-speed wavelength change and a small-diameter optical fiber (cladding diameter of 40µm) that does not induce defects. We use an AWG to convert the wavelength change into an output power change by using the wavelength dependency of the AWG transmittance. For this conversion, we previously used two adjacent output ports that cover the reflection spectrum of an FBG sensor. However, this requires controlling the temperature of the AWG because the ratio of the optical power change to the wavelength change is very sensitive to the relationship of the center wavelengths between an FBG sensor and the output ports of the AWG. We have now investigated the use of a denser AWG and six adjacent output ports, which covers the reflection spectrum of an FBG sensor, for detecting the elastic waves. Experimental results showed that this method can suppress the sensitivity of the power change ratio to the relationship of the center wavelengths between an FBG sensor and the output ports. Although our improved small-diameter optical fiber does not induce structural defects in the composite material when it is embedded, there is some micro or macro bending of the fiber, which causes propagation loss. To suppress this embedment loss, we adjusted the refractive index difference of the fiber to have larger value. Experimental result showed that this reduced the embedment loss by about 0.3 dB/cm. These enhancements make our sensing system more practical and should promote the use of composite materials in a wider range of applications.

The authors tried to construct a structural health monitoring (SHM) system to identify damage in composite grid structure called Advanced Grid Structure (AGS) by using two types of guided waves, compressional and flexural waves, propagating along ribs of AGS. Fiber Bragg grating (FBG) sensors network embedded in AGS is utilized as their receivers. AGS is defined as trussed structures whose ribs are made of Carbon fiber reinforced plastic (CFRP). AGS has often been applied to aerospace structures because it is structurally effective and redundant. The authors had reported one possible method of SHM of AGS by monitoring of static strain distribution with embedded FBG sensors network in AGS. In this paper, we propose another possible method of SHM of AGS. We utilized two types of guided waves, compressional and flexural waves, for damage diagnosis. First, we verified our proposed system experimentally. The results confirmed that FBG sensors could measure both elastic waves and two types of guided waves were generated with the proposed system. Then, some basic characteristics of compressional and flexural wave propagations were clarified experimentally to find that compressional wave has directionality and flexural wave has isotropy. Based on the characteristics, the authors proposed two types of damage diagnosis methods with compressional and flexural waves, respectively. Moreover, those proposed methods were applied to two specific damage types, rib crack and debonding between ribs and skin. The specific damage diagnosis methods were verified experimentally to find that damages could be detected by those methods.

Thermal protection systems (TPS) are frequently subjected to impacts from micrometeoroids and ground handling during refurbishment. The damage resulting from such impacts can greatly reduce the vehicle's overall ability to resist extreme temperatures. Therefore, it is essential to have a reliable method to detect and quantify the damage resulting from impacts. In this effort, the effectiveness of lightweight thin film piezoelectric sensors was evaluated for impact detection and quantification in CMC wrapped TPS. The sensors, which were adhered to the bottom of the TPS tile, were used to sense impact events occurring on the top of the tile, with the ultimate goal of quantifying the level of impact level and damage state based on the sensed signals. A reasonable correlation between impact load levels and sensed response were observed for load levels between 0.07-1.00 Joules. An increase in signal frequency content was also observed as impact levels were increased, with specific frequency bands occurring in the 2-16 kHz range. A preliminary nondestructive evaluation of the impact damage sites was also accomplished, where a reasonable correlation between the gross damage features (i.e. impact crater dimensions) and signal response was observed.

Discussed in this paper is the implementation of a wireless sensor system for performance monitoring of bridges. The advanced wireless sensor system, developed at Clarkson University's Laboratory for Intelligent Infrastructure and Transportation Technologies (LIITT), allows for structural monitoring of bridges. A short-span integral-abutment bridge located in New York State is instrumented with a wireless sensor system measuring acceleration, and strain to monitor the behavior of the structure under various loading conditions including ambient, environmental and traffic loading. Strain and acceleration measurements are recorded simultaneously and in real time to validate various performance characteristics of the bridge, including load distribution along an interior girder, as well as additional stiffness factors (end fixity and composite action of the beams and bridge deck), using existing bridge load testing and condition evaluation guidelines used by the New York State Department of Transportation (NYSDOT) and American Association of State Highway and Transportation Officials (AASHTO). Additionally, acceleration measurements are used to extract the superstructure's first five natural frequencies and corresponding mode shapes. Results are compared to a developed Finite Element Method (FEM) model based on the bridge as built drawings.

This study proposes the use of an innovative array of accelerometers for inertial tracking that is enabled through the use of a non-Cartesian hyper-coordinate frame. Traditional inertial tracking technologies employ an array of accelerometers and gyroscopes oriented in the orthogonal axes of the Cartesian coordinate system. The gyroscope sensors are responsible for deducing the relative orientation of the instrumented object, while the accelerometer measurements are double integrated to approximate the change in linear position relative to the local coordinate frame. Since the position determination is dependent on the orientation derivation, the accuracy and stability of the gyroscope sensors to a large extent determines the overall system performance. Consequently, high-performance gyroscopes are generally used in inertial tracking systems, thereby driving the system cost significantly higher. The proposed approach exclusively utilizes accelerometers in an innovative six axis orientation that, through linear algebra, resolves linear and angular accelerations. The functional layout is processed in the context of hyperdimensional coordinates which ultimately produce an inherent vector redundancy when resolved in the Cartesian coordinate frame. This revised architecture is anticipated to alleviate many of the issues plaguing traditional inertial tracking that stem from the stability of derived orientation from gyroscope readings. In addition, the exclusion of gyroscopes from the design significantly reduces the unit cost of the system. This paper additionally presents the development of a wireless system that incorporates the above described, unique array of dedicated sensors for inertial tracking to provide accurate determination of position and orientation of the sensor over time. The system permits access for additional channels of sensors for application specific monitoring tasks. This allows sensing on objects in motion and in regions or flow patterns that cannot be easily instrumented with traditional wired systems while maintaining knowledge of instantaneous position relative to the initial location. To date, the majority of wireless sensor network deployments have enabled instrumentation of widespread sites, such as civil structures, to alleviate the expense associated with the lengths of cable necessary to connect the sensors to a central acquisition station. The alternative approach sought utilizes the unrestrained nature of the wireless sensor to extend the use of this technology beyond static monitoring into applications in which the sensor node travels across an area without a priori knowledge of the sensor motion. Documentation of the hardware development of the proposed wireless sensing node as well as assessment of the system performance will be provided.

A large number of sensors are required to perform real-time structural health monitoring (SHM) to detect acoustic emissions (AE) produced by damage growth on large complicated structures. This requires a large number of high sampling rate data acquisition channels to analyze high frequency signals. To overcome the cost and complexity of having such a large data acquisition system, a structural neural system (SNS) was developed. The SNS reduces the required number of data acquisition channels and predicts the location of damage within a sensor grid. The sensor grid uses interconnected sensor nodes to form continuous sensors. The combination of continuous sensors and the biomimetic parallel processing of the SNS tremendously reduce the complexity of SHM. A wave simulation algorithm (WSA) was developed to understand the flexural wave propagation in composite structures and to utilize the code for developing the SNS. Simulation of AE responses in a plate and comparison with experimental results are shown in the paper. The SNS was recently tested by a team of researchers from University of Cincinnati and North Carolina A&T State University during a quasi-static proof test of a 9 meter long wind turbine blade at the National Renewable Energy Laboratory (NREL) test facility in Golden, Colorado. Twelve piezoelectric sensor nodes were used to form four continuous sensors to monitor the condition of the blade during the test. The four continuous sensors are used as inputs to the SNS. There are only two analog output channels of the SNS, and these signals are digitized and analyzed in a computer to detect damage. In the test of the wind turbine blade, multiple damages were identified and later verified by sectioning of the blade. The results of damage identification using the SNS during this proof test will be shown in this paper. Overall, the SNS is very sensitive and can detect damage on complex structures with ribs, joints, and different materials, and the system relatively inexpensive and simple to implement on large structures.

Aimed at the practical requirement of tubular joints weld inspection of offshore platform structures of Shengli oil field, the ultrasonic phased array inspection arithmetic for offshore platform structures is proposed. The integrated design of ultrasonic phased array inspection imaging system for offshore platform structures is completed, the ultrasonic phased array inspection imaging system for offshore platform structure is integrated on the basis of the each module and the exploitation of subsystem, which is made up of computer, ultrasonic circuit system, scanning device and phased array transducer. The ultrasonic phased array inspection experiment of T shape tubular joint model is performed with the ultrasonic phased array inspection imaging system for offshore platform structures, the flaws characteristic could be exactly estimated and the flaws size could be measured. Experiment results indicate that the ultrasonic phased array inspection arithmetic for offshore platform structures is practical, the ultrasonic phased array inspection imaging system could inspect artificial defects in tubular joint model, such as slag inclusion, crack, gas porosity, etc., the whole development trend of flaws is factually imaging by the ultrasonic phased array inspection technology of offshore platform structures.

This experimental research is focused on examining the effects of stress concentration due to the embedded Structural Health Monitoring (SHM) sensors on the structural integrity of glass fiber/epoxy laminates subjected to in-plane tensile loads. Recent advances of health monitoring technologies have resulted in development of micro-dimensional sensors that can be embedded into composite laminates. Notwithstanding their small sizes, such inclusions may affect the response of the composite. Damage induced by the peak values of stress concentration around the embedded devices is, in fact, one of the main concerns. To assess this and related issues, we have fabricated a series of samples with and without embedded (dummy) sensors and micro-processors in S2 glass fiber/epoxy laminates, and systematically tested the samples while continuously monitoring the response by the acoustic emission technique. In this manner we have sought to address the process of damage initiation and evolution within the material. The results show that acoustic events begin earlier on during the loading process, in specimens with embedded sensors and the source of the damage is located near the sensors. These early events are associated with matrix failure at the sensor-resin interfaces through micrographic observations.

The study of the mechanical interaction among the host, interface, and a device embedded within a laminated composite is important. Embedding micro-sensors in composite laminates produces material discontinuity around the inclusions. This in turn produces stress concentrations at or near the inclusions. Both 2D plane strain and 3D FEM models are developed to analyze the stress/strain state surrounding the embedded micro-sensors within a unidirectional composite laminate. The objective of the present numerical effort is to take into account the observed resin-rich areas caused by embedment, and to determine their effects on the local stress field around the embedment and the corresponding potential failure modes.

In this paper, the concept, modeling and preliminary testing of an intelligent FRP retrofit with self-monitoring capabilities for critical civil infrastructures are presented. This intelligent system is based on an easy-to-apply configuration of FRP pre-preg tapes with multiple stacked unidirectional layers of piezoelectric or SMA actuators and integrated optical fiber sensors. This intelligent retrofit will be able to not only monitor conditions including bonding of the FRP to the structure and opening of concrete cracks, but also minimize the crack opening and retard the progression of further FRP debonding. Towards this end, a computationally efficient two-dimensional shear stress-transfer model based on a simplified shear lag analysis is developed, with consideration of the fact that the stress transfer between the FRP, actuator and sensor layers in the intelligent system is complex. The effectiveness of this model is demonstrated through one numerical benchmark problem and one typical FRP configuration, with comparison of each to full threedimensional finite element models. The agreement between the two formulations is shown to be further improved by adjustment of the assumed shape functions. A preliminary experiment is also presented in which pre-fabricated optical fiber ribbons are embedded into the FRP strengthening of a full-scale concrete beam. Results from static loading test of the FRP strengthened beam show the feasibility of this technique for the self-monitoring FRP retrofits.

This paper presents the interface transferring mechanism and error modification of the Optical Fiber Bragg Grating (OFBG) sensors based on the mono-scalar isotropic damage constitutive model. The OFBG sensor is made up of optical fiber and encapsulated materials which include protective coating, adhesive layer et al. The accuracy of OFBG sensor is highly dependent on the physical and mechanical properties of the optical fiber and encapsulated materials. The encapsulated materials were regarded as scatheless continuum in the prevenient researches and the elastic modulus, for example, the Young's modulus (E) or shear modulus (G), was keeping constant from the beginning to the end of transformations. However, there is lots of damage, such as microcracks, inclusions and voids, in the encapsulated materials. And these micro-defects can become cores, expand and joint up with together which induce the gradual bad in the materials. Hence, the modulus (E and G) is no longer assumed as a constant but as a variable with the damage. So the mono-scalar isotropic damage model (damage modulus D) is employed to describe the shear constitutive equation of the encapsulated materials along the optical fiber axes. The general expression of multilayer interface strain transferring mechanism of OFBG sensor is given based on the isotropic damage theory. And the error rate and error modification coefficient of OFBG sensor are obtained under the defining of average strains. The results indicate that the damage of encapsulated materials affects the interface strain transferring property of the OFBG sensor.

As common materials or engineering materials, thermoplastic resin based materials can be used not only directly fabricating products but also FRTP(fiber reinforced thermoplastic polymer) materials for other uses. As one kind of FRTP material, GFRPP(glass fiber reinforced polypropylene) has lots of merits, such as: light weight, high strength, high tenacity, high elongation percentage, good durability, reshaping character and no environmental pollution characters. And they also can be conveniently formed hoop rebar in civil engineering. While a new kind of GFRPP-OFBG smart rod which combined GFRPP and OFBG together can be used as not only structure materials but also sensing materials. Meanwhile, PP packaged OFBG strain sensor can be expected for its low modulus, good sensitivity and good durability. Furthermore, it can be used for large strain measuring. In this paper, we have successfully fabricated a new kind of GFRPP-OFBG(Glass Fiber Reinforced Polypropylene-Optic Fiber Bragg Grating) rod by our own thermoplastic pultrusion production line and a new kind of PP packaged OFBG strain sensor by extruding techniques. And we monitored the inner strain and temperature changes with tow OFBG simultaneously of the fabricating process. The results show that: OFBG can truly reflect the strain and temperature changes in both the GFRPP rod and the PP packaged OFBG, these are very useful to modify our processing parameters. And we also find that because of the shrinkage of PP, this new kind of PP packaged OFBG have -13000με storage, and the strain sensing performance is still very well, so which can be used for large strain measuring. Besides these, GFRPP-OFBG smart rod has good sensing performance in strain sensing just like that of FRSP-OFBG rod, the strain sensitivity coefficient is about1.19pm/με. Besides these, the surface of GFRPP-OFBG rods can be handled just as steel bars and also can be bended and reshaped. These are all very useful and very important for the use of FRP materials in civil engineering structures.

Thirty six Fiber Optic Braggs Grating sensors were used during an ambient temperature hydrostatic pressurization testing of a Space Transportation System (STS) 40-inch Kevlar Composite Over-wrapped Pressure Vessel (COPV). The 40-inch vessel was of the same design and approximate age as the STS Main Propulsion System (MPS) and Orbiter Maneuvering System (OMS) vessels. The sensors were surfaces mounted to on the vessel to measure strain during a stress rupture event. The Bragg signals were linear with the applied pressure. The results indicated that the vessel was under an uneven force distribution at various locations on the vessel.

Elastic waves generated by foreign materials impacting surfaces of aerospace vehicle can be used to detect and quantify the severity of damage. Passive acoustical emission sensors, made of piezoelectric elements, are typically used as impact signal detection devices. In this study, we have concentrated on characterizing the bonding qualities of piezoelectric sensors in terms of various bonding materials and adhesion conditions such as bond strength, bond stiffness, partial bonding, and disbonding. The experiment has been performed with an automated impact testing setup under controlled bonding and disbonding conditions in an attempt to establish a standardized sensor bond quality inspection methodology.

When an electromagnetic acoustic transducer (EMAT) is used to generate ultrasound in an electrically conducting sample, eddy currents are generated in the sample's skin depth as the first stage in transduction. The resultant acoustic wave amplitude is proportional to the amplitude of this eddy current, and so anything that we can do to increase the eddy current will lead to the generation of larger amplitude ultrasonic waves. In eddy current testing, wire coils are often wound onto a ferrite core to increase the generated eddy current, with the effect that inductance of the coil increases greatly. When we are dealing with an EMAT, any increase in the coil inductance is usually unacceptable as it leads to a reduction in the amplitude of a given frequency of eddy current from a limited voltage source. This is particularly relevant where current arises from capacitor discharge, as is typically used in EMAT driver current circuitry. We present a method for electromagnetic acoustic transduction where ferrite is used to increase eddy current amplitude, without significantly increasing coil inductance or changing the frequency content of the eddy current or the generated acoustic wave.

The presented paper describes a condition monitoring for Aircraft structures based on the evaluation of acoustical Lamb waves. Methods for effective sensor near signal processing are required to detect wave modes and to reduce noise as much as possible. Frequently, a further necessity exists to integrate the measuring technique into the monitored structure. To meet these requirements, sensor near units for signal processing have to be developed, which can be connected as nodes within a network. A compact, sensor near signal processing structure has been realized containing components for analog preprocessing of acoustic signals, their digitization, algorithms for data reduction and network communication. The core component is a digital signal processor (DSP), which performs the basic algorithms necessary for filtering, down sampling, mode selection and correlation of spectral components particularly effective. As a first application, impact detection and characterization of delaminations were realized for a fiber composite plate. Starting from the simulation of wave propagation, characteristic signal parameters were determined. In some experiments, it could be proven that impact locations and delaminations can be derived from the detected Lamb waves. This work is continued to develop special structural health monitoring systems (SHM) for selected aircraft components (e. g. stringer elements, panels).

The Department of Defense is pursuing efforts to develop ever larger space-based apertures in an attempt to provide better imagery and intelligence for national defense purposes. Unfortunately, due to their shear enormity, many of these apertures will experience displacements and kinematics that work to degrade the resolution of incoming images. Currently, there are multiple efforts to develop software-based compensation schemes, to "clean up the image;" however, these schemes rely on high precision metrology systems to provide accurate information regarding the shape and dynamics of the structure. This paper details a collaborative effort, between the Air Force Research Laboratory/Space Vehicles Directorate (AFRL/VS), the Aerospace Corporation, CSA Engineering, and Jackson and Tull Engineering, conducted to assess the potential of using a fiber-Bragg's system for the metrology of large, space-based apertures.

Bladed disks and turbine wheels in jet engines may after a certain period of service degrade into a condition called mistuning, whereby these cyclically symmetric structures lose their symmetric dynamic properties, leading to imbalance, loss of performance, and ultimately to failure. This paper describes a diagnostic procedure whereby such mistuning may be detected in its early stages, allowing for the scheduled maintenance and replacement of these critical parts.

This paper presents a piezoelectric sensor diagnostic and validation procedure that performs in-situ monitoring of the operational status of piezoelectric (PZT) sensor/actuator arrays used in structural health monitoring (SHM) applications. The validation of the proper function of a sensor/actuator array during operation, is a critical component to a complete and robust SHM system, especially with the large number of active sensors typically involved. The method of this technique used to obtain the health of the PZT transducers is to track their capacitive value, this value manifests in the imaginary part of measured electrical admittance. Degradation of the mechanical/electrical properties of a PZT sensor/actuator as well as bonding defects between a PZT patch and a host structure can be identified with the proposed procedure. However, it was found that temperature variations and changes in sensor boundary conditions manifest themselves in similar ways in the measured electrical admittances. Therefore, we examined the effects of temperature variation and sensor boundary conditions on the sensor diagnostic process. The objective of this study is to quantify and classify several key characteristics of temperature change and to develop effcient signal processing techniques to account for those variations in the sensor diagnosis process. In addition, we developed hardware capable of making the necessary measurements to perform the sensor diagnostics and to make impedance-based SHM measurements. The paper concludes with experimental results to demonstrate the effectiveness of the proposed technique.

This research builds on the work carried out in the area of developing a smart sensor for Single Throw Mechanical Equipment (STME). Limits sensors are the best candidate for observing throw trajectories although their limitation to detect a continuous change in residuals, restricts their usage to discrete applications. Thus research and academia maintains focus on continuous sensors, while industry keeps the limit switches as their key sensor. The paper attempts to bridge the gulf and formally presents a framework for deploying optimal number of limit switches to capture the process dynamics with increased degree of freedom and use them as model based multi sensor residual generator. The energy distribution of Residual Spectra generated by such Model Based Parity Space relationship results in drifts in the form of Eigen value. The Eigen vector in such a multi-dimensional Residual Space is used to maintain the degree and polarity of drift. This paper presents investigations into the issues related to such Eigen analysis. It was found that normalized residuals from multiple sources and parity space relations are neutralized in the form of unified representation of energy that can be used to form a generic framework for fault detection and isolation. It is being investigated, how the proper modeling of quantitative entities as energy, could lead to unified and neutral residual space while keeping the implementation cost reasonably low. Higher degree of freedom allows robust model based self diagnostics to cater for sensor, actuators and system failures isolation model based self diagnostics. An FPGA based implementation of the algorithm is underway based on MEMS to ensure compact very high degree freedom of sensor within financial constraints for Embedded STMEs embedded fault Diagnostics system.

In this study, a novel approach of integrating data interrogation algorithms of active sensing methods for structural health monitoring (SHM) applications, including Lamb wave propagation, impedance method, and sensor-diagnostics, is presented. Contrary to most active-sensing SHM techniques, which utilize only a single signal processing method for damage identification, a suite of signal processing algorithms are employed and grouped into one package to improve the damage detection capability. A MatLab-based user interface called H.O.P.S. (Health Of Plate Structures) was created, which allows the analyst to configure the data acquisition system and display the results from each damage identification algorithm for side-by-side comparison. This side-by-side comparison of results simplifies the task of identifying the relative effectiveness and sensitivity of each algorithm. By grouping a suite of algorithms into one package, this study contributes to and enhances the visibility and interpretation of the active-sensing methods related to damage identification in a structure.

In this paper, the applicability of a nonlinear wave modulation-based crack monitoring methodology has been experimentally investigated. Experiments using a beam specimen with a low-cycle fatigue crack have been conducted for the purpose of preliminary study, in which two PZT patches attached on the beam have been used as the transducer of high frequency probe wave. When the specimen is subjected to a harmonic loading at low frequencies, it vibrates, and the presence of the crack introduces a nonlinear effect to the vibro-acoustic dynamics resulting an interaction between the low frequency structural vibration and the high frequency probe wave. This nonlinearity is observed as the amplitude and phase modulation of the received probe wave synchronous with the structural vibration. To investigate the relationship between the modulations, the structural vibration and the damage extent, the collected signal at the receiver PZT has been separated into low frequency and high frequency components, the former has been used to obtain the information about the structural vibration, while the latter has been demodulated in amplitude and phase. The demodulated waveforms have been examined as a potential indicator of the crack extent, especially focusing on their higher harmonics. Then, a "modulation surface" constructed from the modulated envelopes and the low frequency components has been proposed, which could provide more detailed view of the nonlinear wave modulation effects induced by the crack development. Several candidates for a damage indicator based on the modulation surface have been presented to demonstrate the usefulness of the modulation surface as a sensitive and promising feature relevant to the damage extent.

Fiber reinforced polymer matrix (FRP) composites have a rich history of diagnosis and characterized using acoustic emissions techniques. The highly dispersive, attenuating, and anisotropic nature of unidirectional composites places an emphasis on high density local sensing as opposed to low density more-global sensing strategies. A high density of sensors naturally implies large quantities of data requiring large bandwidth and substantial processing power. By distributing processing with the sensors themselves results in a decreased demand for bandwidth and lower computational power needed at each node in what is now a parallel processing computer. Desired information, time constraints and mechanical considerations place both hard and soft constraints on our network helping to define its architecture. I will present investigated computing architectures and their benefits and limitations as they relate to the various constraints involved.

This article reports on results obtained when applying neural networks to the problem of vehicle classification from SHM measurement data. It builds upon previous work which addressed the issue of reducing vast amounts of data collected during an SHM process by storing only those events regarded as being "interesting," thus decreasing the stored data to a manageable size. This capability is extended here by providing a means to group and classify these novel events using artificial neural network (ANN) techniques. Two types of neural systems are investigated, the first one consists of two neural layers employing both supervised and unsupervised learning. The second, which is an extension of the first, has a data pre-processing stage. In this later system, input data presented to the system is first pre-scaled before being presented to the first network layer. The scaling value is retained and later passed to the second layer as an extra input. The results obtained for vehicle classification using these two methods showed a success rate of 60% and 90% for the first and second ANN systems respectively.

For the health monitoring of existing structures, modeling of entire structure or obtaining data sets after creating damage for training is almost impossible. This raises significant demand for development of a low-cost diagnostic method that does not require modeling of entire structure or data on damaged structure. Therefore, the present study proposes a low-cost statistical diagnostic method for structural damage detection. The novel statistical diagnostic method is a low cost simple system. The diagnostic method employs system identification using a response surface and the damage is automatically diagnosed by testing the change of the identified system by statistical F test. The statistical diagnostic method consists of a learning mode and a monitoring mode. The learning mode is a preparation mode and is performed to create the standard of the diagnosis. The monitoring mode is a diagnosis mode and is performed to diagnose the structural condition. In the learning mode, reference data are measured from an intact structure. A reference response surface is calculated from the reference data using the response surface method. In the monitoring mode, data are measured from a structure to diagnose and a measured response surface is calculated. The statistical similarity of the reference response surface and the measured response surface is tested using the F-test for the damage diagnosis. When the similarity of the response surfaces is adopted, a conclusion of the diagnosis is intact condition. On the other hand, when the similarity is rejected, the diagnosis concludes the structure was damaged. The system does not require the relation between measured sensor data and damages. The method does not require a FEM model of the entire structure. This method diagnoses slight change of the relation between the measured sensor data. In this study, the health monitoring system of the jet fan was developed to investigate the effectiveness of the proposed method. In this study, field test was conducted using an actual jet fan in a tunnel. In the field test, robustness of the proposed method was investigated. As a result, the structural condition of the jet fan was successfully diagnosed and effectiveness of proposed method was confirmed.

The accurate shape sensing method is expected to be useful for large scaled structural health monitoring of aircraft structures. This research is trying to construct a high-accuracy structural shape identification method using distributed strain data from an optical fiber strain sensing system; pulse-prepump Brillouin optical time domain analysis (PPP-BOTDA) system. In addition, the optical fiber can be embedded in composite material, which has recently been applied for the structural material of aircrafts or some other large-scaled structures. In this paper, we carried out an experiment using composite specimen with an embedded optical fiber to show the characteristics of distributed data from PPP-BOTDA system. Moreover, a simple inverse analysis, which derives deformation from measured distributed strain data, was also carried out. From results of these verifications, the strain data from PPP-BOTDA system showed reasonable distributions suitable to the deformation of specimen. At the same time, it was also shown that, in using the distributed strain data for shape identification algorithm, we have to consider the changes in distribution profile at the discontinuous points of strain distribution along the fiber.

In this paper we describe the architecture and the performances of a hybrid modular acquisition and control system prototype we developed in Napoli for the implementation of geographycally distributed monitoring and control systems. The system, an improvement of a VME-UDP/IP based system developed by our group for interferometric detectors of gravitational waves, is based on a dual-channel 18-bit low noise ADC and 16-bit DAC module at 1 MHz, managed by an ALTERA FPGA, that can be used standalone or mounted as mezzanine (also in parallel with other modules) on a motherboard. Both the modules and the motherboard can send/receive the configuration and the acquired/correction data for control through a standard EPP parallel port to an external PC, where the real-time computation is performed. Experimental tests have demonstrated that this architeture allows the implementation of distributed control systems, using a standard laptop PC for the realtime computation, with delay time &Dgr;t < 30 &mgr;s on a single channel, that is a sustained sampling frequency f_c > 30kHz. Each module is also equipped with a 20-bit slower ADC necessary for the acquisition of an external calibration signal. The system is now under extensive test in two different experiments, i.e. the control of a Michelson Interferometer to be used as Velocimeter for Seismic Waves in Geophysics and the control of the end mirrors a suspended Michelson Interferometer through electrostatic actuators, a prototype for mirror control for Interferometric Detectors of Gravitational Waves.

Fiber gratings are proving to provide versatile discrete sensor elements for structural health monitoring systems. For example, they outperform traditional resistive foil strain gages in terms of temperature resistance as well as multiplexing capability, relative ease of installation, electromagnetic interference immunity and electrical passivity. However, the fabrication method and post-fabrication processing influences both performance and survivability in extreme temperature environments. In this paper, we compare the performance and survivability when making strain measurements at elevated temperatures for a range of fabrication and processing conditions such as UV-laser and electric-arc writing and post-fabrication annealing. The optimum method or process will depend on the application temperatures (e.g., up to 300°C, 600°C or 1000°C), and times at these temperatures. As well, other sensing requirements, including the number of sensors, measurand and sensitivity may influence the grating choice (short or long period).

Structural Health Monitoring (SHM) is becoming an increasingly important tool for the maintenance, safety and integrity of aerospace structural systems. Immune to electromagnetic interference, Fiber Bragg Grating (FBG) optical sensor matrices are light-weight and multiplexable, allowing many sensors on a single fiber to be integrated into smart structures. Highly sensitive to minute strains, they can facilitate maximum SHM functionality, with minimum weight and size. Consequently, these optical systems, in conjunction with advanced damage characterization algorithms, are expected to play an increasing role in extending the life and reducing costs of new generations of structures and airframes. In this paper, we discuss the development of both hardware and algorithms to detect, locate and quantify delamination in composite laminated beam structures. We present an integrated SHM system including (a) the capability of interrogating over 50 FBG sensors simultaneously with sub-picometer resolution at over 50 kHz, (b) an FBG-sensor/piezo-actuator matrix smart skin design and methodology, and (c) damage detection location and quantification algorithms based on mode shape or other relevant advanced algorithmic-based damage diagnosis and prognosis techniques. Comparison with other SHM systems (e.g., based on piezo-electric (PVDF) and Scanning Laser Vibrometer sensors) demonstrates better signal-to-noise and damage detection for our FBG system.

We describe the use of swept-wavelength interferometry for distributed fiber-optic sensing in single- and multimode optical fiber using intrinsic Rayleigh backscatter. The interrogation technique is based on measuring the spectral shift of the intrinsic Rayleigh backscatter signal along an unaltered standard telecommunications grade optical fiber and converting the spectral shift to strain or temperature. This technique shows great utility as a method for highly distributed sensing over great distances with existing, pre-installed optical fiber. Results from sensing lengths greater than 1 km of optical fiber with spatial resolutions better than 10 cm are reported.

We describe the results of a study of the performance characteristics of a monolithic fiber-optic shape sensor array. Distributed strain measurements in a multi-core optical fiber interrogated with the optical frequency domain reflectometry technique are used to deduce the shape of the optical fiber; referencing to a coordinate system yields position information. Two sensing techniques are discussed herein: the first employing fiber Bragg gratings and the second employing the intrinsic Rayleigh backscatter of the optical fiber. We have measured shape and position under a variety of circumstances and report the accuracy and precision of these measurements. A discussion of error sources is included.

Monitoring composite materials during their manufacturing process is very important to achieve a good quality. At the same time, a monitoring system, able to continuously identify the stress state and the possible incoming of micro-cracks during the component operative life, may increase the safety levels. Fibre optics, instrumented with FBG (Fibre Bragg Gratings) and embedded in composite materials can be a key sensor system for structural health monitoring, minimally intrusive. In this work, the calibration of a FBG-based sensorial system has been carried out with static and dynamic strain tests and compared with measurements, made with traditional strain gage and piezoelectric sensors. Tests demonstrate that these devices, embedded in a composite laminate, can monitor static and dynamic strains with the same accuracy level of traditional ones. Fiber optic may be also used as refractometer to monitor the advancement of the resin front and the curing reaction during an RTM manufacturing process. In a near future these two fibre optics-based sensor systems could be both applied in operative structures so to increase their reliability level.