This PDF file contains the front matter associated with SPIE Proceedings Volume 7293, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee and Symposium Committee listings.

Fiber Bragg grating Sensors, FBGs, have been widely used as optical sensors for structural health monitoring of different materials. They can be embedded in composite structures or attached on their surface to monitor the entire life cycle of the material or to measure different physical parameters. FIBOS contains two FBGs and will be used to measure temperature and strain during the aerospace mission OPTOS. OPTOS is a picosatellite, designed and manufactured by the Spanish Institute for Aerospace Technology, INTA that will be launched during the summer 2009. The main goal of the mission is to demonstrate the possibility of using some novel technologies for space applications inside a miniaturized space and with big restrictions in terms of mass and power consumption. The paper describes the different units that constitute the FIBOS payload: one tunable laser, two FBGs mounted onto one steel mechanical structure to monitor independently temperature and strain and the processing unit that include all the electronics to control and connect the payload with the DOT of the satellite. Calibration measurements at different temperatures inside a thermalvacuum chamber as well as FIBOS operation during the mission are also presented.

This paper presents experimental measurements of the response of woven composite laminates to multiple low-velocity impacts. Damage initiation and progression occur at multiple physical and temporal scales in heterogeneous materials, including fiber breakage, matrix cracking, delamination and matrix relaxation. The sensor/interrogators were therefore chosen specifically to provide insight into the order and progression of different failure modes. Measurements of the contact force between the impactor and composite are measured throughout impact. Additionally, the dissipated energy per impact event is also calculated from the impactor velocity. Surface mounted and embedded fiber Bragg grating sensors are used for the measurement of the laminate response. Peak wavelength measurements are performed during impact at 1 kHz, while full-spectral scanning is performed at 5 Hz during relaxation period of the laminate immediately after impact and quasi-statically to measure post-impact residual strain states within the laminate. The results highlight the depth of information embedded within the FBG full-spectral data sensors, as well as the added insight to be gained from combined global-local measurements.

This paper presents a new means for collecting fiber Bragg grating (FBG) data during drop tower measurements used to assess damage to composite structures. The high repetition-rate collection process reveals transient features that cannot be resolved in quasi-static measurements. The experiments made at a repetition rate of about 500 Hz show that the detected FBG spectrum broadens for a short period of time and relaxes quickly to a narrower static state. Furthermore, this relaxation time increases dramatically as the strike count increases. The information gained by such measurements will enhance the ability to characterize and distinguish failure modes and predict remaining lifetime in composite laminate structures.

Fiber Bragg Grating Sensors, FBGSs, are very promising for Structural Health Monitoring, SHM, of aerospace vehicles due to their capacity to measure strain and temperature, their lightweight harnesses, their multiplexing capacities and their immunity to electromagnetic interferences, within others. They can be embedded in composite materials that are increasingly forming an important part of aerospace structures. The use of embedded FBGSs for SHM purposes is advantageous, but their response under all operative environmental conditions of an aerospace structure must be well understood for the necessary flight certification of these sensors. This paper describes the first steps ahead for a possible in future flight certification of FBGSs embedded in carbon fiber reinforced plastics, CFRP. The investigation work was focused on the validation of the dependence of the FBGS's strain sensitivity in tensile and compression load, in dry and humid condition and in a temperature range from -150°C to 120°C. The test conditions try to simulate the in service temperature and humidity range and static load condition of military aircraft. FBGSs with acrylic and with polyimide coating have been tested. The FBGSs are embedded in both, unidirectional and quasi isotropic carbon/epoxy composite material namely M21/T800 and also MTM-45-1/IM7. Conventional extensometers and strain gages have been used as reference strain sensors. The performed tests show an influence of the testing temperatures, the dry or wet specimen condition, the load direction and the coating material on the sensor strain sensitivity that should be taken into account when using these sensors.

The curing monitoring of polymeric composite materials has attracted wide interests recently. Monitoring the curing process is necessary to improve the performance of Gr/Epoxy composites, especially for the characterization of residual strains after manufacture. This paper aimed on exploring the use of embedded fiber Bragg grating (FBG) to monitor the characterizations of the curing process in a Graphite/Epoxy composite. The curing development and residual stress measurement were assessed through changes in the shape of the optical spectra, intensity attenuation and shifts in wavelengths in the optical fiber sensors. The curing caused residual stress was presented and analyzed systematically in this paper.

Currently, it is difficult to measure the internal forces of steel tie rods under construction and in long-term service. A novel high-durable smart steel tie rod with functionality of self-monitoring was developed by utilizing fiber Bragg grating (FBG) and installation techniques combined with glass fiber reinforced polymer (GFRP). The sensing features for the smart steel tie rod were investigated. The strain obtained from FBG strain sensors shows very good linearity and repeatability when the steel tie rod is under 85% of its ultimate load. The force calculated from the strain data obtained during the control loading supports those findings, within a 4% error. This type of smart steel tie rod easily reveals any stage of stress and can be regarded as a potential strain-based load cell for adjacent structures in a harsh environment.

Fiber Bragg grating sensors in side-polished optical fiber are sensitive to an external analyte by evanescent field interaction. Deposition of sensor-specific transducer layers can advance such fiber Bragg grating refractometer to the optochemical monitoring of specific substances: absorbed gases, vapors, and adsorbed biomolecules as well. Refractive index range of highest sensitivity can be adjusted to the analyte medium of interest by proper construction of the multilayer waveguide. A specific application example aims at hydrogen detection using a palladium thin film transducer.

The signals measured from the Brillouin Optical Time Domain Analysis (BOTDR), distributed optical fiber sensing system is generally prone to contamination by environmental factors, which may degrade the measurement accuracy in field applications, a suitable method of correcting this degradation is desired. In this paper, the wavelet signal processing method is presented to filter out the noise in measured signals and validated with the strain data taken from a smart BOTDA-based cable. The results show that this method can effectively denoise the information of the measured strain of the smart cable and improve the precision of the cable force. The maximum error between the control cable force and the average cable force are 8.8% and 5.1%, respectively, prior to and after noise filtering. This comparison shows that the wavelet denoising method is suitable for the measured signal obtained from the Brillouin optical sensing system.

Whilst considerable progress continues to be made on the design and deployment of fibre optic sensors for chemical process monitoring and structural integrity assessment, the majority of these sensor designs can only impart information on one or two relevant measurands. For example, in the case of chemical process monitoring of advanced fibrereinforced composites involving thermosetting resins, it is generally appreciated that cross-linking kinetics can be influenced by a number of factors including the following: the stoichiometry of the reagents, temperature, surface chemistry of the substrate and presence or absence of contaminants. Thermosetting resins also shrink during the crosslinking process. When thermosets are used and processed above room temperature during the production of fibrereinforced composites, upon cooling back to ambient temperature, residual stress can develop due to the mismatch in thermal expansions between the reinforcing fibres and the matrix. This paper reports on recent progress on the design and demonstration of a novel multi-functional fibre optic sensor that can provide data on (i) temperature, (ii) strain, (iii) refractive index, (iv) transmission infrared spectroscopy and (v) evanescent wave spectroscopy. A unique and attractive feature of this sensor is that a conventional commercially available Fourier transform infrared spectrometer is used to interrogate the sensor. The sensor design is based on an extrinsic fibre Fabry-Perot interferometer.

Large satellites are equipped with hundreds of sensors for temperature measurement. The large amount of sensors is expensive in terms of integration effort and mass in the case conventional sensors are used. In this article an integrated fiber optic temperature sensor network for the hot spot detection on satellite sandwich panels is introduced. The developed sensor system is integrated with only negligible mechanical impact. It is electro-magnetic immune and decoupled from mechanical loads. In addition to monitoring hotspots, the number and aerial density allows a reliable reconstruction of temperature and displacement fields.

Energy saving and safety evaluation are two key issues for infrastructure. In this paper, the development of a novel smart transparent concrete using plastic optical fiber (POF) and Fiber Bragg Grating (FBG) is discussed, along with its transparent and smart sensing properties. The experimental results show that an optical fiber can be easily combined with concrete and that the POF could provide a steady light transmitting ratio. Moreover, the FBG can be used as a sensing element for strain and temperature. This paper also discusses the mechanical effects of introducing POF into concrete specimens. Because the smart transparent concrete can be regarded as a "green" energy saving construction material and as a smart intrinsic sensor for long-term Structural Health Monitoring (SHM), it is a promising technology for field applications in civil infrastructure.

This study proposes novel hierarchical sensing concept for detecting damages in composite structures. In the hierarchical system, numerous three-dimensionally structured sensor devices are distributed throughout the whole structural area and connected with the optical fiber network through transducing mechanisms. The distributed "sensory nerve cell" devices detect the damage, and the fiber optic "spinal cord" network gathers damage signals and transmits the information to a measuring instrument. This study began by discussing the basic concept of the hierarchical sensing system thorough comparison with existing fiber optic based systems and nerve systems in the animal kingdom. Then, in order to validate the proposed sensing concept, impact damage detection system for the composite structure was proposed. The sensor devices were developed based on Comparative Vacuum Monitoring (CVM) system and the Brillouin based distributed strain sensing was utilized to gather the damage signals from the distributed devices. Finally a verification test was conducted using prototype devices. Occurrence of barely visible impact damage was successfully detected and it was clearly indicated that the hierarchical system has better repairability, higher robustness, and wider monitorable area compared to existing systems utilizing embedded optical fiber sensors.

This article presents the simulation of the dynamics of the self-writing waveguide phenomenon in photopolymerizable resin systems using the finite element method. The rate equation of the photopolymerization process, mechanical shrinkage in the resin and lightwave propagation through the waveguide are included in the finite element model. An emphasis is placed on the simulation of processes occurring at multiple time scales and the introduction of mechanical shrinkage through an equivalent body force. Simulation results predict the features of self-writing previously observed including nonuniformities in the final polymerized waveguide.

For comprehensive fatigue tests and surveillance of large scale structures, a vibration monitoring system working in the Hz and sub Hz frequency range was realized and tested. The system is based on a wireless sensor network and focuses especially on the realization of a low power measurement, signal processing and communication. Regarding the development, we met the challenge of synchronizing the wireless connected sensor nodes with sufficient accuracy. The sensor nodes ware realized by compact, sensor near signal processing structures containing components for analog preprocessing of acoustic signals, their digitization, algorithms for data reduction and network communication. The core component is a digital micro controller which performs the basic algorithms necessary for the data acquisition synchronization and the filtering. As a first application, the system was installed in a rotor blade of a wind power turbine in order to monitor the Eigen modes over a longer period of time. Currently the sensor nodes are battery powered.

This paper presents an artificial immune pattern recognition (AIPR) approach for the damage detection and classification in structures. An AIPR-based Structure Damage Classifier (AIPR-SDC) has been developed by mimicking immune recognition and learning mechanisms. The structure damage patterns are represented by feature vectors that are extracted from the structure's dynamic response measurements. The training process is designed based on the clonal selection principle in the immune system. The selective and adaptive features of the clonal selection algorithm allow the classifier to generate recognition feature vectors that are able to match the training data. In addition, the immune learning algorithm can learn and remember various data patterns by generating a set of memory cells that contains representative feature vectors for each class (pattern). The performance of the presented structure damage classifier has been validated using a benchmark structure proposed by the IASC-ASCE (International Association for Structural Control - American Society of Civil Engineers) Structural Health Monitoring Task Group. The validation results show a better classification success rate comparing to some of other classification algorithms.

Traditional point or quasi-distributed sensors can not cover the full scale monitoring of cables in service. A new kind of smart cable with functionality of full scale monitoring has been developed by combining the optical fiber-fiber reinforced polymer rebar (named as FRP-OF rebar) with the cable wires by using Brillouin sensing technology. Full scale cable's static experimental results show that the FRP-OF can discover the stress distribution along the cable under 60% of the ultimate cable loading. And also the repeatability is very good. The cable load gotten from the average monitored strain agrees well with that from the controlled force within error of 5%. This kind of smart cable shows perfect advantages such as durability, anti-corrosion, electro-magnetic resistance, low cost and fully-distribution sensing and so on, which can meet the long-term on-line health monitoring for practical cable.

Discussed in this paper is the deployment of a universal and low-cost dense wireless sensor system for structural monitoring, load rating and condition assessment of bridges. The wireless sensor system developed is designed specifically for diagnostic bridge monitoring, providing independent conditioning for both accelerometers and strain transducers in addition to high-rate wireless data transmission. The system was field deployed on a three span simply supported bridge superstructure, where strain and acceleration measurements were obtained simultaneously and in realtime at critical locations under several loading conditions, providing reliable quantitative information as to the actual performance level of the bridge. Monitoring was also conducted as the bridge was subjected to various controlled damage scenarios on the final day of testing. Select cases of detected damage using strain and modal based analysis are presented.

In the present study, a smart coating for light metal alloys was developed and investigated. Chemically activated nanodiamonds (CANDiT) were electrophoretically deposited onto anodized aluminum alloy AA2024 substrates in order to increase corrosion resistance, enhance bonding properties and establish a means of corrosion monitoring based on the fluorescence behavior of the particles. In order to create stable aqueous CANDiT dispersions suitable for electrophoretic deposition, mechanical milling had to be implemented under specific chemical conditions. The influence of the CANDiT volume fraction and pH of the dispersion on the electrochemical properties of the coated samples was investigated. Linear voltammetry measurements reveal that the chemical characteristics of the CANDiT dispersion have a distinct influence on the quality of the coating. The fluorescence spectra as well as fluorescence excitation spectra of the samples show that corrosion can be easily detected by optical means. Furthermore, an optimization on the basis of "smart" - algorithms for the data processing of a surface analysis by the laser-speckle-method is presented.

The authors have demonstrated previously that reinforcing glass fibres can be used as light-guides to facilitate chemical process monitoring and structural integrity assessment of fibre reinforced composites. In the current paper, the authors explore concepts for the development of self-sensing, self-healing and crack-arrestor composites. The first part of the papers presents a brief overview of previously reported technologies for self-sensing, self-healing and crack-arrestor; the advantages and disadvantages of the various technologies are discussed. The second part of this paper present the design concept and performance requirements for the self-sensing, self-healing and crack-arrestor composites. The final part of the paper presents preliminary results on the manufacture and evaluation of this class of composite.

The basic technologies of the impact damage detection system (IDDS) of composite structures were developed and demonstrated using a composite structure with embedded small-diameter optical fiber sensors by Authors in FY2002. In our current R&D, the IDDS consisting of composite structure with embedded optical fiber sensors and interrogation units is developed for practical airframe application. The system evaluation by using composite substructures and coupon specimens are planned to proceed towards product. As one of the foremost tasks for the application, it is important to evaluate the system whether having the probability of damage detection sufficiently or not. In this study, to evaluate the probability of detection of the system, the impact tests for barely visible impact damage (BVID) are conducted by using coupon specimens with being embedded small-diameter optical fibers. From the test result, reliability of the IDDS is evaluated.

Thermal protection systems (TPS) of aerospace vehicles are subjected to impacts during in-flight use and vehicle refurbishment. The damage resulting from such impacts can produce localized regions that are unable to resist extreme temperatures. Therefore it is essential to have a reliable method to detect, locate, and quantify the damage occurring from such impacts. The objective of this research is to demonstrate a capability that could lead to detecting, locating and quantifying impact events for ceramic matrix composite (CMC) wrapped tile TPS via sensors embedded in the TPS material. Previous research had shown a correlation between impact energies, material damage state, and polyvinylidene fluoride (PVDF) sensor response for impact energies between 0.07 - 1.00 Joules, where impact events were located directly over the sensor positions¹. In this effort, the effectiveness of a sensor array is evaluated for detecting and locating low energy impacts on a CMC wrapped TPS. The sensor array, which is adhered to the internal surface of the TPS tile, is used to detect low energy impact events that occur at different locations. The analysis includes an evaluation of signal amplitude levels, time-of-flight measurements, and signal frequency content. Multiple impacts are performed at each location to study the repeatability of each measurement.

For near surface characterization a new high frequency eddy current device was been developed. By using a measurement frequency up to 100 MHz information of near surface areas can be acquired. Depending on the investigated material high resolution depth profiles can be derived. The obtained data with the new device were compared to those obtained with a high precision impedance analyser. It could be demonstrated that the new device measures the eddy current conductivity signal in the high frequencies much better than the impedance analyser. By sweeping the frequency from 100 kHz up to 100 MHz the technique delivers a depth profile of the electrical conductivity of the material. This kind of high frequency eddy current technique can be used for quality assurance, surface contamination control or near surface material characterization e.g. microstructure and cold work influences. It can be a powerful tool to obtain information for process control or a good / bad decision in mass production processes like for example rolling, coating, and surface treatments. The big advantage of the high frequency eddy current method is that it is fast und precise. This paper presents results with a new developed prototype Eddy-Current-Device for measurement frequencies up to 100 MHz which is first time suitable in rough industrial environment and makes expensive lab network analysers unnecessary for this kind of investigations.

In this paper, the development of carbon fiber-based piezoresistive linear sensing technique and its application in civil engineering structures is studied and summarized. The sensing mechanism is based on the electrical conductivity and piezoresistivity of different types of carbon fibers. Firstly, the influences of values of signal currents and temperature on the sensing properties are studied to decide the suitable sensing current. Then, the linear temperature and strain sensing feasibility of different types of carbon fibers is addressed and discussed. Finally, the application of this kind of sensors is studied in monitoring the health of reinforced concrete (RC) and prestressed concrete (PC) structures. A good linearity of fractional change in electrical resistance (ER) (ΔR/R0)-strain and &DeltaR/R0-temperature is demonstrated. The &DeltaR/R0-strain and &DeltaR/R0-temperature curves of CFRP/HCFRP sensors can be well fitted with a line with a correlation coefficient larger than 0.978. All these reveal that carbon fibers reinforced polymer (CFRP) can be used as both piezoresistive linear strain and temperature sensors.

An impedance-based structural health monitoring (SHM) system employs a piezoelectric patch to excite the structure under test and capture its response. Impedance-based SHM offers several advantages over other methods such as good performance for local damage detection and simple hardware. A major problem for impedance-based SHM is temperature dependency. Specifically, baseline impedance profiles of structures vary as the ambient temperature changes. In this paper, we propose a new method to compensate the effect of temperature on baseline profiles. Our method is to select a small subset of baseline profiles for some critical temperatures and estimates the baseline profile for a given ambient temperature through interpolation. We incorporated our method into our SHM system and investigated the effectiveness of our method. Our experimental results show that (i) our method reduces the number of baseline profiles to be stored, and (ii) estimates the baseline profile of a give temperature accurately.

Electromechanical impedance (EMI) technique is receiving increasing attention in the area of structural health monitoring (SHM). In this technique, piezoelectric transducer (PZT) is either surface bonded to or embedded inside the host structure to be monitored. The PZT actuates harmonically in the presence of electric field to produce a structural response over a wide range of frequency, which is known as 'admittance signature'. These signatures serve as indicator to predict the health of the structure, any change in the signature is indication of presence of damage or other degradation in the structure. Sometimes the raw data associated with the applied frequency range is in excess of necessary data. In the present paper, an EMI based experimental study was conducted on steel, aluminum and concrete specimens to monitor load, crack and curing respectively for various frequency ranges. Admittance signatures of specimens were acquired for a wide frequency range of excitation. Later, statistical index was adopted to measure and compare the sensitivities for various narrower ranges within the wide frequency range. Additionally a novel signature gradient was used to characterize signatures at each frequency. Thus in this study an evaluation of sensitivity of EMI technique for various frequency bands to monitor load, crack and curing process was carried out in order to find out necessary frequency band suitable form wide frequency range. It is demonstrated that this approach can be applied to real structures and an initial assessment can be made to eliminate unnecessary data acquisition.

A precise two-dimensional MOS magnetic sensor is suggested and its performance is investigated. The dependence of sensor sensitivity on the device geometric parameters and on the biasing conditions is accurately determined by a twodimensional physical simulator which self-consistently solves the magnetic field equations and the carrier transport equations. From the simulation results, a modified equivalent circuit model for MOS magnetic sensor is proposed and included in SPICE model to fully analyze the operation of suggested magnetic field sensor.

Conventionally, modal monitoring of Wind Turbine Rotor Blades is primarily based on the evaluation of eigenfrequencies. Beyond this, combining a sensor network with the Operational Modal Analysis (OMA) method, mode shape and parallely a local component are utilized here. In addition it is expected that the damping, which is also determined by the OMA method, will give a lead on damage development at the rotor already at an early stage. Modal monitoring by means of measurement is combined with FEM simulation and with the comparison of results obtained from measurement and simulation. Moreover, this will establish a connection between the engineer and the design data of a rotor blade, which also are based on FEM analyzes. A further significant increase regarding error resolution is possible by combining the global modal methods with locally sensitive monitoring methods, based on guided elastic waves. These assume plate-like structures through which elastic waves propagate in the low-frequency ultrasonic range (10 - 100 kHz) in certain modes. These different wave modes interact distinctively with inner structural damages such as web fractures and delaminations. It is differentiated between piezoelectrically excited waves (acousto ultrasonics), and waves produced by energy released at fractures, delamination etc. (acoustic emission). Applying a moderate number of sensors, the combination of both methods can allow an effective monitoring of the global structure.

Mechanical properties of materials may be obtained from the inversion of ultrasonic Lamb wave dispersion curves. In order to do this broadband excitation and detection of ultrasound is required. As sample size and, in particular, thickness, are reduced to those of microstructures, ultrasound frequencies in the range of the gigahertz region will be required. We look at two possible cw laser excitation techniques which, having far lower peak powers than the more frequently used Q-switched lasers, therefore give a negligible risk of damaging the sample through ablation. In the first method the modulation frequency of a sinusoidally modulated laser is swept over the required range. In the second, the laser is modulated with a series of square pulses whose timing is given by a PRBS (pseudo random binary sequence) in the form of a modified m-sequence.

We propose an ultrasonic gas leak localization system based on a distributed network of sensors. The system deploys highly sensitive miniature Micro-Electro-Mechanical Systems (MEMS) microphones and uses a suite of energy-decay (ED) and time-delay of arrival (TDOA) algorithms for localizing a source of a gas leak. Statistical tools such as the maximum likelihood (ML) and the least squares (LS) estimators are used for approximating the source location when closed-form solutions fail in the presence of ambient background nuisance and inherent electronic noise. The proposed localization algorithms were implemented and tested using a Java-based simulation platform connected to four or more distributed MEMS microphones observing a broadband nitrogen leak from an orifice. The performance of centralized and decentralized algorithms under ED and TDOA schemes is analyzed and compared in terms of communication overhead and accuracy in presence of additive white Gaussian noise (AWGN).

Over the past decades, discrete or distributed Fiber Optic Sensing (FOS) applications have seen an increased acceptance in many areas. High level optical and mechanical reliability of optical fiber is necessary to guarantee reliable performance of FOS. In this paper, we review recent research and development activities on new specialty fibers. The main approaches to enhancing fiber attributes include new refractive index profile design and fiber coating modification.

This research proposes a novel approach for the shape reconstruction of composite structures using one of Brillouinscattering based distributed optical fiber strain sensors, PPP-BOTDA system. We have constructed a displacement reconstruction algorithm using the finite element model of the target structure. The remarkable point is that, not only using raw distributed strain data, but using an index of the non-uniformity of strain distribution profiles, which is the normalized Laplacian value (NLV), the algorithm can detect modeling changes, such as changes in boundary conditions of the structures. In the verification, the algorithm was applied to the deflection identification of a composite laminate specimen with an embedded optical fiber network. From the NLV distribution, the change of the fixed end condition of the specimen was evaluated, and using the updated FE model, the deflection was able to be reconstructed with high accuracy. From the result, we show the validity of the proposing shape reconstruction algorithm, which has robustness against FE model changes.

In general, macro-strain is an effective index for health monitoring of civil infrastructures, which can reveal the unforeseen damage accumulation. However, it is difficult to acquire precise strain distribution with existing fully-distributed optical fiber sensing techniques. Based on the distributed optical fiber strain sensing technique of pulse-prepump Brillouin Optical Time Domain Analysis (PPP-BOTDA), a new optical fiber sensor with improved strain sensitivity (OFSISS) is proposed to enhance the precision of macro-strain measurements. The most advantage of the OFSISS sensor is that it can markedly reduce the measurement error of strain data with a proper designed magnified coefficient. The OFSISS has also good designability and durability according to detailed sensing requirements. Results of uniaxial tensile experiment show not only the high accuracy and precision of the OFSISS but also an important fact that the measured magnified coefficients of the manufactured OFSISSs with a recoating process agree well with the designed values. The bending experiment of using a steel beam illustrates that the linearity and reliability of macro-strain measurement from the OFSISS are good enough for the application in actual macro-strain monitoring and structural deformation monitoring.

The determination and monitoring of landslide boundaries is essential for analysis of creeping landslides. A novel landslide boundary localization technique has been recently proposed and tested on two large creeping landslides in an urban area. The technique uses asphalt road-embedded distributed fiber optic sensors. This paper deals with the issue of interpretation of the monitoring records. It has been shown that an improved protection of the cable increases the measurement strain range, but leads to non-linear strain-frequency response. Two methods of strain data interpretation have been analyzed: the truncated average method (TAM) and the convolution product (CP). Advantage of the TAM is in its simplicity; disadvantage is that the amount of the valid sampling points is significantly reduced, especially when the fixed strain section lengths are close to the spatial resolution. The alternative CP method uses all sampling points in the vicinity of the fixation point, but is rather complex, especially considering that a proper interpretation of the measured data can be only achieved using a weighting function with parameters dependent on the strain step at the fixation point. Further signal processing and data interpretation models should be encouraged to improve system accuracy.

In this paper, a new type of self-sensing basalt fiber reinforced polymer (BFRP) bars is developed with using the Brillouin scattering-based distributed optic fiber sensing technique. During the fabrication, optic fiber without buffer and sheath as a core is firstly reinforced through braiding around mechanically dry continuous basalt fiber sheath in order to survive the pulling-shoving process of manufacturing the BFRP bars. The optic fiber with dry basalt fiber sheath as a core embedded further in the BFRP bars will be impregnated well with epoxy resin during the pulling-shoving process. The bond between the optic fiber and the basalt fiber sheath as well as between the basalt fiber sheath and the FRP bar can be controlled and ensured. Therefore, the measuring error due to the slippage between the optic fiber core and the coating can be improved. Moreover, epoxy resin of the segments, where the connection of optic fibers will be performed, is uncured by isolating heat from these parts of the bar during the manufacture. Consequently, the optic fiber in these segments of the bar can be easily taken out, and the connection between optic fibers can be smoothly carried out. Finally, a series of experiments are performed to study the sensing and mechanical properties of the propose BFRP bars. The experimental results show that the self-sensing BFRP bar is characterized by not only excellent accuracy, repeatability and linearity for strain measuring but also good mechanical property.

We develop an electric field sensor array based on optical fiber interrogation with electro-optic crystals to measure high energy electromagnetic pulses. The D-shaped optical fiber used in this work provides the platform for resonant coupling with multiple electro-optic crystals to allow an array of sensing points on a single strand of optical fiber. Because of its uniquely small size, this sensor array is suitable for performing electric-field analysis at multiple points within an electronic device due to its flexibility and dielectric composition. Using Lithium Niobate and Potassium Titanyl Phosphate crystals, the sensor array in this work is sensitive to fields as low as 100 V/m.

At the previous SPIE conference in San Diego (2008), the authors presented and compared a range of low-cost optical fibre sensors for monitoring the cross-linking process of a thermosetting resin. The same sensor was used subsequently to monitor and quantify the diffusion of water in the cross-linked polymer. The current paper presents recent data on the deployment of an array of low-cost fibre-optic sensors to monitor the water diffusion front. The data obtained from the sensors are compared with conventional gravimetric measurements and theoretical predictions for the diffusion profile for water ingress in a cross-linked epoxy/amine resin system.

A fiber optic acoustic emission sensor based on fused-tapered coupler and its applications in structural health monitoring are proposed in this paper. The sensor was embedded into the Carbon Fiber Reinforced Polymer (CFRP) laminates and tested using pencil lead break tests compared with the commercial acoustic emission sensor (R15 PZT). It successfully detected the AE signals. FOAES was applied in the Structural Health Monitoring (SHM) of CFRP materials. Failures of carbon fiber/epoxy composite laminates during three-point- bending test were monitored embedded FOAES. Results identified that the sensor embedded into composite structures successfully monitored failures of composite laminates online.

Poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonic acid), PEDOT-PSS, was synthesized via the oxidative polymerization. ZSM-5 zeolites were used as the selective microporous adsorbent to improve selectivity and sensitivity of the conductive polymer towards carbon dioxide (CO). PEDOT-PSS was dry mixed with the zeolites and compressed to form PEDOT-PSS/zeolite thin pellets. Zeolites of type ZSM-5 of various Si/Al mole ratios were chosen to investigate the effect of Si/Al mole ratios on the electrical conductivity response and sensitivity of the composites when exposed to CO. The electrical conductivity sensitivity of PEDOT-PSS_1:1/zeolite composites towards CO negatively increases with decreasing Si/Al mole ratio. The highest electrical conductivity sensitivity response is obtained from the composite with Si/al ratio equal to 23, PEDOT-PSS_1:1/ZSM-5(Si/Al = 23).