This PDF file contains the front matter associated with SPIE Proceedings Volume 6933, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Optical fiber sensors are promising as tools for damage and structural health monitoring (SHM) of aerospace composite structures. Hence many researchers have conceived various kinds of optical fiber sensors. The authors and Hitachi Cable, Ltd. have developed small-diameter optical fiber and its fiber Bragg grating (FBG) sensor for embedment inside a lamina of composite laminates without strength reduction. First, the authors' studies on the small-diameter FBG sensors for damage monitoring and SHM of composite structures are described. Then, some recent results in the current ACS-SIDE (Structural Integrity Diagnosis and Evaluation of Advanced Composite Structures) project are presented on optical fiber based SHM for some feasible applications in aerospace composite structures.

Cryogenic temperature sensing was demonstrated using pressurized fiber Bragg gratings (PFBGs) with polymer coating of various thicknesses. The PFBG was obtained by applying a small diametric load to a regular fiber Bragg grating (FBG). The Bragg wavelengths of FBGs and PFBG were measured at temperatures from 295 K to 4.2 K. The temperature sensitivities of the FBGs were increased by the polymer coating. A physical model was developed to relate the Bragg wavelength shifts to the thermal expansion coefficients, Young's moduli, and thicknesses of the coating polymers. When a diametric load of no more than 15 N was applied to a FBG, a pressure-induced transition occurred at 200 K during the cooling cycle. The pressure induced transition yielded PFBG temperature sensitivities three times greater than conventional FBGs for temperatures ranging from 80 to 200 K, and ten times greater than conventional fibers for temperatures below 80 K. PFBGs were found to produce an increased Bragg wavelength shift of 2.2 nm compared to conventional FBGs over the temperature range of 4.2 to 300 K. This effect was independent of coating thickness and attributed to the change of the fiber thermo-optic coefficient.

Within several countries, the military is undergoing significant economic pressure to extend the use of its air fleet beyond its established design life. The availability of low weight, small size, reliable and cost-effective technologies to detect and monitor incipient damage and to alert prior to catastrophic failures is critical to sustain operational effectiveness. To enable the implementation of distributed and highly multiplexed optical fiber sensors networks to aerospace platforms, the data acquisition (interrogation) system has to meet small size and low weight requirements. This paper reports on our current development of micro-sized Echelle Diffractive Gratings (EDG) based interrogation system for strain monitoring of serially multiplexed fibre Bragg grating sensors. The operation principle of the interrogator and its suitability for strain measurements is demonstrated. Static load measurements obtained using this system are compared to those acquired using a optical multi-wavelength meter and are found to have strong correlation.

1987 DuPont manufactured 4560 denier Kevlar/Epoxy Strands were instrumented with nine and three sensors each. Stress tests were performed at 30,45,60,70 and 80% of ultimate strength with dwell times of 10,000 seconds. FBG showed uneven stress levels which is contrary to conventional observation.

The Surface Relief Fiber Bragg Grating (SR-FBG) is a viable alternative to the thermocouple for high temperature measurements in industry. To fabricate the SR-FBG we etch a grating into the flat surface of an elliptical-core D-fiber. At high temperature (1000 °C) the optical fiber becomes brittle. To overcome brittleness we thread the fiber through a preheated 0.020 inch diameter stainless steel tube. We insert the small tube into a larger one with a diameter of 0.125 inches. The smaller tube rests on ceramic inserts to prevent contact with the large tube. The end of the D-fiber is fitted with a standard fiber optic connecter. With this packaging scheme we conduct a series of test at high temperature. The sensor is robust with no power loss or Bragg wavelength shift, even after heating for 24 consecutive hours.

Fiber optic sensors are of interest because of their robustness against environmental disturbances, low drift, and ease of integration. The relatively high population of measurement points also favors the estimation of displacement and temperature from discrete data. This together with techniques for integration into structural materials is discussed in the context of satellite structures.

We have been developing a system for monitoring the health of aircraft structures made of composite materials. In this system, the Lamb waves that are generated by lead zirconium titanate PZT actuators travel through the composite material structures and are received by the embedded FBG sensors. To detect any Bragg wavelength change due to the reception of the Lamb wave, an arrayed waveguide grating (AWG) is used, which converts the Bragg wavelength change into an output power change. Since the conversion ratio is largely dependent on the initial Bragg wavelength, a temperture control was necessary for obtaining an optimum condition. However, we have developed a system that uses a denser AWG to eliminate the need for a temperature control. We suceeded in detecting 25 kHz to 1 MHz Lamb waves using our new system. We have also tried calculating the Bragg wavelength change of the obtained waveform, and confirmed that the Bragg wavelength change due to the reception of Lamb waves was less than 1 pico meter.

Fiber optic grating sensors have been used to measure multi-dimensional strain, pressure, temperature, corrosion and moisture. This paper presents a method of using fiber grating sensors to measure the position and velocity of a very fast event associated with a blast wave. A chirped fiber grating of 50 mm length is placed in a highly energetic material. The action of the shock wave is to destroy the fiber grating as it propagates along it. By using a spectral filter such as a chirped fiber grating in combination with high speed detectors the position and velocity of the shock wave may be determined. A layout of a system used to experimentally verify this technique is described and results presented for two different highly energetic materials.

In previous work we have described the detection and location of damage in isotropic materials using fibre Bragg gratings rosettes to directionally detect Lamb waves. To extend this technique to composite materials it is necessary to understand the propagation characteristics of ultrasound in these materials as a function of their orientation with respect to the ply, and also the directional response of fibre Bragg gratings to them. Finite element modeling of Lamb wave propagation in a 0°, 90° carbon fibre plate is described, as are experiments to detect these waves for various orientations of the source and alignments of the FBG transducers. Results of the experiments are interpreted with respect to predictions from the FE modeling and are shown to give good qualitative agreement.

A fiber Brag grating sensor interrogator has been developed which is capable of gathering vectors of information from individual fiber Bragg gratings by capturing the full optical spectrum 3 kHz. Using a field programmable gate array with high speed digital-to-analog converters and analog-to-digital components, plus a kilohertz rate MEMS optical filter, the optical spectrum can be scanned at rates in excess of 10 million nanometers per second, allowing sensor sampling rates of many kilohertz while maintaining the necessary resolution to understand sensor changes. The autonomous system design performs all necessary detection and processing of multiple sensors and allows spectral measurements to be exported as fast as Ethernet, USB, or RS232 devices can receive it through a memory mapped interface. The high speed - full spectrum - fiber Bragg grating sensor interrogator enables advanced interrogation of dynamic strain and temperature gradients along the length of a sensor, as well as the use of each sensor for multiple stimuli, such as in temperature compensation. Two examples are described, showing interrogation of rapid laser heating in an optical fiber, as well as complex strain effects in a beam that had an engineered defect.

As electric utility wind turbines increase in size, and correspondingly, increase in initial capital investment cost, there is an increasing need to monitor the health of the structure. Acquiring an early indication of structural or mechanical problems allows operators to better plan for maintenance, possibly operate the machine in a de-rated condition rather than taking the unit off-line, or in the case of an emergency, shut the machine down to avoid further damage. This paper describes several promising structural health monitoring (SHM) techniques that were recently exercised during a fatigue test of a 9 meter glass-epoxy and carbon-epoxy wind turbine blade. The SHM systems were implemented by teams from NASA Kennedy Space Center, Purdue University and Virginia Tech. A commercial off-the-shelf acoustic emission (AE) NDT system gathered blade AE data throughout the test. At a fatigue load cycle rate around 1.2 Hertz, and after more than 4,000,000 fatigue cycles, the blade was diagnostically and visibly failing at the out-board blade spar-cap termination point at 4.5 meters. For safety reasons, the test was stopped just before the blade completely failed. This paper provides an overview of the SHM and NDT system setups and some current test results.

Wind power is a renewable source of energy that is quickly gaining acceptance by many. Advanced sensor technologies have currently focused solely on improving wind turbine rotor aerodynamics and increasing of the efficiency of the blade design and concentration. Alternatively, potential improvements in wind plant efficiency may be realized through reduction of reactionary losses of kinetic energy to the structural and substructural systems supporting the turbine mechanics. Investigation of the complete dynamic structural response of the wind plant is proposed using a large-scale, high-rate wireless sensor network. The wireless network enables sensors to be placed across the sizable structure, including the rotating blades, without consideration of cabling issues and the economic burden associated with large spools of measurement cables. A large array of multi-axis accelerometers is utilized to evaluate the modal properties of the system as well as individual members and would enable long-term structural condition monitoring of the wind turbine as well. Additionally, environmental parameters, including wind speed, temperature, and humidity, are wirelessly collected for correlation. Such a wireless system could be integrated with electrical monitoring sensors and actuators and incorporated into a remote multi-turbine centralized plant monitoring and control system.

For a long time electric power was taken as a natural unlimited resource. With globalization the demand for energy has risen. This has brought rising prices for fossil fuels, as well as a diversification of power generation. Besides conventional fossil, nuclear plants are coming up again. Renewable energy sources are gaining importance resulting in recent boom of wind energy plants. In the past reliability and availability and an extremely long lifetime were of paramount importance. Today this has been added by cost, due to the global competition and the high fuel costs. New designs of power components have increased efficiency using lesser material. Higher efficiency causes inevitably higher stress on the materials, of which the machines are built. As a reduction of lifetime is not acceptable and maintenance costs are expected to be at a minimum, condition monitoring systems are going to being used now. This offers potentials for fiber optic sensor applications.

We report in this paper on the design and development of a novel on-line structural health monitoring and fire detection system based on an array of optical fiber Bragg grating (FBG) sensors and interrogation system installed on a new, precommercial compact aircraft. A combined total of 17 FBG sensors - strain, temperature and high-temperature - were installed at critical locations in an around the wings, fuselage and engine compartment of a prototype, Comp Air CA 12 all-composite, ten-passenger personal airplane powered by a 1,650 hp turbine engine. The sensors are interrogated online and in real time by a swept laser FBG interrogator (Micron Optics sm125-700) mounted on board the plane. Sensors readings are then combined with the plane's avionics system and displayed on the pilot's aviation control panel. This system represents the first of its kind in commercial, small frame, airplanes and a first for optical fiber sensors.

A fiber optic Bragg grating sensor system has been installed in the blades of a wind turbine and was successfully tested for several years. We report the requirements, system design and construction parameters of a sensor system for continuous on-line monitoring of bending loads of the rotor blades, and provide characteristic examples of monitoring results.

The development of low-cost wireless sensor networks has resulted in resurgence in the development of ambient vibration monitoring methods to assess the in-service condition of highway bridges. However, a reliable approach towards assessing the health of an in-service bridge and identifying and localizing damage without a priori knowledge of the vibration response history has yet to be formulated. A two-part study is in progress to evaluate and develop existing and proposed damage detection schemes. The first phase utilizes a laboratory bridge model to investigate the vibration response characteristics induced through introduction of changes to structural members, connections, and support conditions. A second phase of the study will validate the damage detection methods developed from the laboratory testing with progressive damage testing of an in-service highway bridge scheduled for replacement. The laboratory bridge features a four meter span, one meter wide, steel frame with a steel and cement board deck composed of sheet layers to regulate mass loading and simulate deck wear. Bolted connections and elastomeric bearings provide a means for prescribing variable local stiffness and damping effects to the laboratory model. A wireless sensor network consisting of fifty-six accelerometers accommodated by twenty-eight local nodes facilitates simultaneous, real-time and high-rate acquisition of the vibrations throughout the bridge structure. Measurement redundancy is provided by an array of wired linear displacement sensors as well as a scanning laser vibrometer. This paper presents the laboratory model and damage scenarios, a brief description of the developed wireless sensor network platform, an overview of available test and measurement instrumentation within the laboratory, and baseline measurements of dynamic response of the laboratory bridge model.

A major challenge impeding the deployment of wireless sensor networks for structural health monitoring (SHM) is developing means to supply power to the sensor nodes in a cost-effective manner. In this work an initial test of a roving-host wireless sensor network was performed on a bridge near Truth or Consequences, NM in August of 2007. The roving-host wireless sensor network features a radio controlled helicopter responsible for wirelessly delivering energy to sensor nodes on an "as-needed" basis. In addition, the helicopter also serves as a central data repository and processing center for the information collected by the sensor network. The sensor nodes used on the bridge were developed for measuring the peak displacement of the bridge, as well as measuring the preload of some of the bolted joints in the bridge. These sensors and sensor nodes were specifically designed to be able to operate from energy supplied wirelessly from the helicopter. The ultimate goal of this research is to ease the requirement for battery power supplies in wireless sensor networks.

With the increased demand placed on aging infrastructure, there is great interest in new condition assessment tools for bridges. The routine deterioration that bridges undergo causes a loss in the intended performance that, if undetected or unattended, can eventually lead to structural failure. Currently the primary method of bridge condition assessment involves a qualitative bridge inspection routine based on visual observations. Discussed in this paper are methods of in-situ quantitative bridge condition assessment using a dense wireless sensor array. At the core of the wireless system is an integrated network which collects data from a variety of sensors in real-time and provides analysis, assessment and decision-making tools. The advanced wireless sensor system, developed at Clarkson University for diagnostic bridge monitoring, provides independent conditioning for both accelerometers and strain transducers with high-rate wireless data transmission in a large-scale sensor network. Results from a field deployment of a dense wireless sensor network on a bridge located in New York State are presented. The field deployment and testing aid to quantify the current bridge response as well as demonstrate the ability of the system to perform bridge monitoring and condition assessment.

Fiber optic Bragg gratings were used to measure strain fields during Stress Rupture (SSM) test of Kevlar Composite Over-Wrapped Pressure Vessels (COPVs). The sensors were embedded under the over-wrapped attached to the liner released from the Kevlar and attached to the Kevlar released from the liner. Additional sensors (foil gages and fiber bragg gratings) were surface mounted on the COPV liner.

We are now developing an impact damage detection (IDD) system for composite airframe structures. The basic technologies of IDD system were developed and demonstrated using a composite structure with embedded small-diameter optical fiber sensors by Authors in FY2002. IDD system consists of a composite structure with installed optical fiber sensors and a monitoring measurement system. To get the prospect of aircraft application of IDD system is a target of this development. To investigate the durability of embedded optical fibers and composites, cyclic loading test is conducted using composite coupon specimens with embedded small-diameter optical fibers. The evaluation of the system by using composite substructures is also conducted to proceed towards product. This paper presents the development target, our technology, test method, test result and future task.

It is generally appreciated that the ingress of moisture in composites can have adverse effects on matrix-dominated properties such as the glass transition temperature and compressive mechanical properties. Moisture ingress in composites can also lead to swelling and blistering. A number of excellent studies have been reported on the detection, modelling and effects of moisture ingress on the properties of thermosetting resins (matrix) and composites. However, it is generally taken for granted that the quality of the resin and the processing conditions used to cross-link the resin are identical. Given the recent advances in the design and deployment of optical-fibre sensors in composites, it is now possible to use the same sensor to facilitate in-situ cure monitoring and structural health monitoring (after processing). This paper will present recent developments in the design of low-cost fibre-optic sensor systems for in-situ chemical process monitoring and the detection of moisture ingress after curing. The cure kinetics derived from three fibre optic sensor designs is presented as well as those obtained from evanescent-wave spectroscopy using E-glass fibres. After conducting the in-situ cure monitoring experiments, one of the fibre-optic sensor designs was selected and the samples (with the embedded sensors) were dried to constant mass at 50°C then transferred to water baths maintained at 70, 50, and 30 °C. The diffusion kinetics for the samples was determined using samples without and with embedded optical-fibre sensors. The effect of moisture ingress in the resin was also assessed using dynamic mechanical thermal analysis (DMTA), transmission infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). Preliminary results are also presented to demonstrate that the reinforcing fibres in E-glass composites can be used to track the cross-linking kinetics of a commercial epoxy/amine resin is presented.

We developed the on-board BOCDA system for airplane and verified the flight environmental stability and durability through environmental test. The on-board BOCDA system adopted the polarization diversity technique and temporal gating technique to improve robustness of the BOCDA system. We successfully measured distribution of fiber Brillouin gain spectrum over 500m measurement range with 50mm spatial resolution, 60Hz sampling rate and ±13μ strain accuracy. Furthermore, we considered flight test to verify the validity of the BOCDA system. From these results, it was confirmed that BOCDA system has potential to be applied to an aircraft structure health monitoring system.

We report on the development of a complete system for spatially resolved detection of critical soil displacement in river embankments. The system uses Brillouin frequency domain analysis (BOFDA) for distributed measurement of strain in silica optical fibers. Our development consists of the measurement unit, an adequate coating for the optical fibers and a technique to integrate the coated optical fibers into geotextiles as they are commonly used in dike construction. We present several laboratory and field tests that prove the capability of the system to detect areas of soil displacement as small as 2 meters. These are the first tests of truly distributed strain measurements on optical fibers embedded into geosynthetics.

Brillouin based fiber optic sensing turns to be a promising technology for Structural Health Monitoring (SHM). However, the bare optical fiber is too fragile to act as a practical sensor, so high durability and large range (large strain) Brillouin distributed sensors are in great needs in field applications. For this reason, high durable and large range optical fiber Brillouin Optical Time Domain Analysis sensors packaged by Fiber Reinforcement Polymer (FRP), named BOTDA(R)-FRP-OF, have been studied and developed. Besides, in order to study the large strain, crack and slip between the rebar and concrete in reinforced concrete (RC) beams using BOTDR(A) technique, two RC Beams installed with BOTDA(R)-FRP-OF sensors have been set up. And the damage characteristics of the RC beams were investigated by comparing the strain measured by the BOTDA(R)-FRP-OF sensors and the strain from traditional electric strain gauges. The test results show that the BOTDA(R)-FRP-OF sensor can effectively detect the damage (including crack and slip) characteristic of RC beam, and it is suitable for the long-term structural health monitoring on concrete structures such as bridge, big dam and so on.

Fiber optic sensors based on polymer optical fibers (POF) take advantage of the high elasticity and high break-down strain of POF. Because of their outstanding elastic properties, POF are well suited for integration into technical textiles like geotextiles and medical textiles. Smart textiles with incorporated POF sensors, able to sense various mechanical and physical quantities, can be realized. The integration of POF as a sensor into geotextiles for monitoring of displacement of soil is very attractive since POF can be used for distributed strain measurement of strain values of more than 40 %. An online monitoring of critical mechanical deformations of geotechnical structures like dikes, dams, slopes, embankments as well as of masonry structures can be ensured. Medical textiles that incorporate POF sensors can control vital physiological parameters like respiratory movement and can be used for wearable health monitoring of patients requiring a continuous medical assistance and treatment. The biocompatibility of POF is an important criterion for selecting POF as a medical sensor. The paper shows selected examples of using POF sensors for the mentioned monitoring purposes.

We demonstrate the measurement of the phase shift in a polymethylmethacrylate (PMMA) single-mode optical fiber interferometer, operating at a wavelength of 632.8 nm, up to 15.8% nominal strain in the fiber. The phase-displacement sensitivity is measured to be 1.39 x 10⁷ rad m^-1 for this strain range. This strain range is well beyond the yield strain of the polymer fiber and that previously measured for polymer Bragg gratings and silica optical fibers. The measured phase-displacement response is then compared to a previous analytical formulation for the large deformation response of the polymer optical fiber. The formulation includes both the finite deformation of the optical fiber and potential nonlinear strain optic effects at large deformations. Using previously measured values for the linear and nonlinear mechanical response of the fiber, these nonlinear strain optic effects are estimated from the current experimental data. This estimation shows that the nonlinearities in the strain optic effect are of the same order of magnitude as those in the mechanical response of the PMMA.

Several alternative fabrication methods for optical fiber sensors have recently been demonstrated including micro-machining, surface relief etching and self-writing of photopolymerizable resins. In this paper, a multi-physics finite element model of sensor self-generation through optical confinement in a photopolymerizable gel is presented that accounts for the dynamics of photopolymerization, and the opto-mechanical interactions of densification, residual strains, and strain-optic effects. In the future, this model will be applied to predict the geometry and index distribution of a micro-optical fiber sensor. The index of refraction and the material density of the photopolymerizable gel as a function of optical intensity and time will be experimentally determined to characterize the dynamics of the particular photopolymerizable resin and used as inputs for the finite element model.

Polymer optical fiber (POF) elongation sensors have been proposed e.g. by Doering as a low-cost alternative to FBG (single mode Fiber Bragg Gratings) sensors targeting the lower sensitivity range. A recently recovered detection system known from laser distance meters turned out to be very sensitive while staying simple and thus offering low cost potential. The approach is based on measuring the phase shift of a (e.g. sinusoidally) modulated light signal guided in a POF under different tensions resulting in different transit times and thus different phase shifts.

Several different strategies are being considered for ultrasonic structural health monitoring systems using a variety of approaches. Guided wave techniques for interrogating large plate-like structures have probably generated the most interest; these methods have the potential of monitoring large areas with a low sensor density while remaining sensitive to defects. The acousto-ultrasonic nondestructive evaluation method has motivated the use of long-time, reverberating waves which "fill" a structure and hence monitor large areas. Local methods based upon several different wave modes have been considered for monitoring known "hot spots" such as fastener holes and critical bonds. Presented here are examples of these three strategies where the purpose is to both show progress which has been made and illustrate key issues, mainly in the context of aerospace applications. The progress and problems thus far show both the promise of ultrasonic structural health monitoring and the significant challenges in moving from the laboratory to deployed systems.

Nondestructive imaging has been a widely used approach for detection of local structural damage in the engineering community. By combining image analysis methods, quantities describing the type, severity and extent of damage can be extracted within the spatial domain of images. However, the current practice of structural health monitoring requires a temporal characterization of structural damage, or some correlation of structural damage with response data. To accomplish this, one needs to consider the time scale in using any of the nondestructive imaging techniques, which in turn demands the use of spatial-temporal image analysis. In this paper, we address the temporal occurrence of cracks on the surface of concrete structural members, and attempt to monitor cracks, including their inception and propagation, using temporal image data. We assume under some conditions for objects in a pair of temporal images that only planar rigid-body motion takes place in the image domain, while cracks are treated as a type of local anomaly. The unknown motion parameters are estimated by means of a manifold-based optimization procedure, and the obtained manifold distance (MD) measure is used as a motion-invariant feature to describe the temporal occurrence of concrete cracks. Numerical analyses are conducted with the use of video clips from two laboratory experiments. It is concluded in this paper that the MD-based spatial-temporal image analysis can be an effective means for monitoring local damage of structural components that occurs and is accompanied by structural motion induced by loading.

Fiber optical (FO) sensors, especially fiber Bragg grating (FBG) sensors, have been considered as prominent high-durable local monitoring sensors and largely applied in structural health monitoring (SHM). However, it is still a big problem how to develop the feasible optical fiber sensors to fully meet the practical SHM for infrastructures. In this paper, some recent advances of fiber optical sensors developed and applied in bridge monitoring in mainland China, especially in Harbin Institute of Technology, are introduced. The main content include direct FBG-based sensors, indirect FBG-based sensors, FBG based smart structures, and their implementations in over 10 practical case studies of bridge monitoring, which include Yonghe River Bridge in Tianjin, Binzhou and Dongying Yellow River Bridges and Province, Songhua River Bridge, Hulan River bridge and NiutouShan bridge in Heilongjiang Province, Nanjing third Yangtze river Bridge, Maocaojie Bridge in Hunan Province, Erbian bridge in Sichuan and Guangyangdao Bridge in Chongqing, etc. Besides, F-P sensors have been used in Da-Fu-Si bridges and Wufu Bridges, etc. Finally, some directions of researches and applications have been recommended. Researches and practical applications show that FBG sensors are becoming one of the key sensors in long-term SHM instead of some conventional electrical sensors.

Optical fiber Bragg grating (FBG) has been accepted widely throughout the civil infrastructures, especially for bridges. In this paper, a new case study, FBG-based intelligent monitoring system of the Tianjin Yonghe Bridge is introduced. For this case, techniques of FBG sensors installation have been tested and 40 FBG strain sensors, 10 FBG temperature sensors and 96 FRP-OFBG based smart cable sensors have been successfully installed on Yonghe Bridge. The concrete strain change and cables load gradients have been monitored during the bridge static test using those FBG sensors. And besides, after the bridge was completed, the strain course under traffic load and temperature changes were monitored with these sensors. The monitoring results show that traffic fluxes and possible fatigue damages can be conveniently analyzed, which can be applied for structural health diagnosis. The monitoring system has stood the ordeal for more than 2 years, which shows that the FBG can meet the demands of long-term monitoring of the bridge.

The long-term monitoring and performance evaluation techniques for the steel strand based pre-stressed structures are still not mature yet, especially for the prestressing loss monitoring and prediction. The main problem of this issue is lack of reliable monitoring techniques. To resolve this problem, in this paper, a new kind of quasi-distributed smart steel strand based on FRP-OFBG(Fiber Reinforced Polymer-Optical Fiber Bragg Grating) has been developed and its pre-stress monitoring principle has been also given. The test of the post-tension pre-stressed concrete beam with bonded tendons and its tensioning experiments have been conducted. And the prestressing loss of the steel strands has been monitored using the FBG in it. Researches results indicate that this kind of smart steel strand can monitor both instant loss and permanent loss of the prestressing successfully, and it can preferably describe the pre-stress loss state of the pre-stressed structure. Compared with the traditional monitoring instrument, this kind of smart steel strand owns distinct advantages and broad application foregrounds.

This work investigates the torque sensing capabilities for Galfenol. A static test and rotating static test are performed on a single crystal and a rolled polycrystal Galfenol patch. The rotating static test demonstrates Galfenol's noncontact use. Both the static and rotating static tests show a linear response for the Galfenol patches.

A novel technique for the determination of a creeping landslide boundary is demonstrated. It is based on application of distributed optical fiber strain measurements using Brillouin Optical Time Domain Analysis (BOTDA) technology. A road crossing the St. Moritz landslide boundary was instrumented with a fiber optic cable, which turned the road, effectively, into a large scale strain gauge. The obtained monitoring data was in good agreement with visual observation and also followed the trends of the geodetical data. The presented validation of this technology allows for a conclusion that distributed fiber optic strain sensing is a promising new tool in landslide surveillance. At present, until methods and standards in this field are established and reliable, combination with traditional methods is necessary. Ongoing measurements during 2008 may strengthen the conclusions of this paper.

Fiber Bragg grating (FBG) sensors hold a great deal of potential for structural monitoring because of their high sensitivity and exceptional stability for long-term monitoring. FBG sensors have been applied to sense a number of physical measurands including strain, temperature, pressure etc. These applications are based on the same principle, i.e. the measurement of Bragg wavelength shift caused by the measurands. The characters and principle of FBG sensors have been introduced in detail. The relative experiment is done. The results show that FBG sensors have high sensitivity and long-term stability. It is feasible to use the sensors to the structural health monitoring (SHM). Cement hydration produces heat, which may provoke important temperature rises in massive structures. Such a high temperature may be a factor for cracking during the cooling phase. Thus, it is important to be able to calculate and control the heat to be produced by a given concrete at the mixture-proportioning stage. Theory of heat of hydration is also introduced in this paper. FBG sensors have been applied successfully in health monitoring for Guomao subway station structure. Compared with results measured by vibrating wire sensors and computed by finite element method, the monitoring results show temperature and strains can be accurately measured by FBG sensors. It is convenient to study on heat of hydration of massive concrete and guide structural design.

This paper introduces a novel multifunctional fiber sensor with two FBGs (measuring temperature and strain simultaneously) and a fiber optic coupler (monitoring the damage of composite) for structural health monitoring. Two FBGs with different wavelengths are abreast connected to an optical splitter: One is capsulated in glass capillary tube to measure temperature and not affected by strain, the other one is to measure temperature and strain. The other port of the former FBG is connected to the fiber optic coupler, using the transmission intensity in grating for structural health monitoring (SHM) of composite materials. It is pivotal to discriminate the variable of it caused by temperature and strain, as the wavelength of FBG varies with temperature and strain simultaneously. The technique is designed for distinguishing strain and temperature to solve the cross sensitivity problem in this paper. A series experiments demonstrate that the novel multifunctional optical fiber sensor possesses high sensitivity and high precision. With composite materials being used widely in aerospace engineering, national defence, civil engineering, oil field and etc, monitoring the damage of them is more important regarded. The temperature and strain affect the damage of composite materials mostly. Combined with the AE events, according to the temperature and strain of composite materials, the sensor can confirm whether they are demolished and how intensity they are damaged.

We present a simple, low-cost, temperature- and strain-insensitive long-period gratings (LPGs) written in photonic crystal fibers (PCFs) that can be used as sensitive chemical solution sensors or bend sensors for a variety of industrial applications, including civil engineering, aircraft, chemistry, food industry, and biosensing. Three different configurations of PCFs have been used for this study, including a polarization maintaining PCF, a large mode area PCF and an endlessly single mode PCF. These LPGs have been characterized for their sensitivity to temperature, strain, bending, and surrounding refractive index. Transmission spectra of the LPGs were found to exhibit negligible temperature and strain sensitivities, whereas possessing usable sensitivity to refractive index and bending. This type of PCF sensor could in principle be designed for optimum sensitivity to desired measurand(s), while minimizing or removing undesirable cross-sensitivities. The unique sensing features of PCFs are particularly suited for a wide variety of applications in smart structures, embedded materials, telecommunications and sensor systems.

The 3-D foot-shape measurement system under different loads based on laser-line-scanning principle was designed and the model of the measurement system was developed. 3-D foot-shape measurements without blind areas under different loads and the automatic extraction of foot-parameter are achieved with the system. A global calibration method for CCD cameras using a one-axis motion unit in the measurement system and the specialized calibration kits is presented. Errors caused by the nonlinearity of CCD cameras and other devices and caused by the installation of the one axis motion platform, the laser plane and the toughened glass plane can be eliminated by using the nonlinear coordinate mapping function and the Powell optimized method in calibration. Foot measurements under different loads for 170 participants were conducted and the statistic foot parameter measurement results for male and female participants under non-weight condition and changes of foot parameters under half-body-weight condition, full-body-weight condition and over-body-weight condition compared with non-weight condition are presented. 3-D foot-shape measurement under different loads makes it possible to realize custom-made shoe-making and shows great prosperity in shoe design, foot orthopaedic treatment, shoe size standardization, and establishment of a feet database for consumers and athletes.

To power the tiny sensor devices by MEMS generator which scavenging energy from ambient vibrations is becoming practical due to the power consumption of low power electronics is going down to tens to hundreds μW for integrated wireless sensor devices. In this paper, we are going to present the development on two different types of piezoelectric MEMS generators that have the ability to scavenge mechanical energy of ambient vibrations and transform it into electrical energy. These two piezoelectric MEMS generators are both cantilever type made of silicon process and transform energy with thin PZT layer. However, the first one is with the interdigital electrodes on the top and the other one is with laminated electrodes sandwiched the PZT layer. The theoretical prediction and the process development for the two types of generators will all be presented; the evaluation and comparison of the two generators will also be detailed.