A new biosensor technology (SIRE--sensors based on injectable recognition elements) is described. Its application in laboratory equipment, medical survey equipment and process monitoring is reviewed. Furthermore, the promising practical and commercial relevance of SIRE- Biosensors is discussed.

Ultrasonic sensors are widely used in various applications due to advantages of low cost, simplicity in construction, mechanical robustness, and little environmental restriction in usage. But the main purposes of the noncontact sensors are rather narrowly confined within object detection and distance measurement. For the application of object recognition, ultrasonic sensors exhibit several shortcomings of poor directionality which results in low spatial resolution of objects, and specularity which gives frequent erroneous range readings. To resolve these problems in object recognition, an array of the sensor has been used. To improve the spatial resolution, more number of sensors are used in essence throughout the various devices of the sensor arrays. Under the disguise of a fixed number of the sensors, the array can be shifted mechanically in several steps. In this paper we propose a practical sensor resolution enhancement method using an electronic circuit accompanying the sensor array. The circuit changes the transmitter output voltage in several steps. Using the known sensor characteristics, a set of different return echo signals provide enhanced spatial resolution. The improvement is obtained with neither the cost of the increased number of the sensors nor extra mechanical devices.

Molecularly-ordered thin-films comprised of nano-sized inorganic particles and ionic polymer molecules have been fabricated on single crystal silicon, quartz, and glass substrates by a novel molecular self-assembly process. X-ray photoelectron spectroscopy indicates that the formed cationic inorganic particles only adsorb on negatively charged and not on positively charged surfaces. Contact angle measurements demonstrate that the water contact angle oscillates regularly according to which ions form the outermost layer of the films. Thin-films ordered at the molecular level have been formed up to several hundred layers in thickness and characterized by UV/Vis spectroscopy. Incorporation of different inorganic nanoparticles and polymer molecules allows control over electromagnetic, mechanical, thermal and other properties.

The application of the principle of orthogonality of the vibration mode shapes of a structure to the design of shaped modal sensors, which detect the vibrational response of the structure for the mode for which they are designed, is presented. The principle was applied in the design of shaped polyvinylidene fluoride (PVDF) modal sensors for detecting the first and second modes of the bending vibration of a simply-supported beam. These sensors, which are designed as the mode 1 and the mode 2 sensors, respectively, were bonded to the same surface of a simply-supported steel beam. The beam was subjected to random vibration by an electromagnetic exciter connected to the opposite surface of the beam. The vibrational responses of the beam measured by the distributed mode 1 and mode 2 PVDF shaped sensors are compared with the vibrational responses measured using an accelerometer. It is shown that the distributed sensors produce maximum voltage output for modes 1 and 2, respectively, for which they were designed. Furthermore, is shown that by dividing the mode 1 and mode 2 sensors into two separate halves and adding or subtracting the output signals of these halves, the mode 1 sensor can be used to detect the second mode of vibration of the beam while the mode 2 sensor can be used to detect the first mode of vibration of the beam.

Electrical time domain reflectometry (ETDR) stress/strain sensing technique has been successfully demonstrated in geotechnical applications to detect rock deformation and longwall movement. The ETDR sensing method appears to be practical for health monitoring applications of civil engineering structures since durable sensor media can be used. To use the ETDR sensing technique for structural stress/strain measurements, the coupling mechanism between applied loads and TDR signal response of the sensors need to be understood and modeled accurately. In this paper a theoretical model capable of describing the relation between applied loads and TDR signal response of a coaxial cable was developed. The accuracy of the model was verified by comparing theoretical results with those of finite element analyses. Parametric study to investigate the effects of the physical and structural parameters of the cable was also performed using the theoretical model.

Sterilization of biomedical devices may induce bulk and surface modification, responsible for the decrease or loss of their biofunctionality. Pure ethylene oxide (EO) at low temperature and new alternative techniques such as cold gas plasma sterilization have been developed for heat-sensitive polymers. There is a lack of the knowledge concerning their safety in terms of materials damage and consequences on the biofunctionality of sterilized devices. The objective of our work consists in studying bulk and surface changes in biomedical devices induced by these two sterilization techniques. Samples from PVC, Polyurethane, Polyacrylate and Polyethylene-based medical devices are subjected to 1, 5, and 10 sterilization cycles by Steri-Vac-3M (pure EO), Sterrad-100^$TM, J&J (gas plasma + H₂O₂), and studied by X-rays photoelectron spectroscopy. Preliminary results show an increasing in Oxygen/Carbon ratio by a factor of 1.3 to 4.4 between the first and tenth cycle indicating the surface oxidation by gas plasma sterilization processes. Some changes in C-C chemical bounding are associated with EO sterilization.

In this work sensor films made out of ion-exchange membrane- metal composite polymers developed by treating commercially available ion-exchange membrane polyions with a noble metal such as platinum were investigated. These smart composites exhibit characteristics of both actuators and sensors. Strips of these composites cut in a standard size will undergo large bending displacement when placed in a low electric field. Conversely by bending the composite strip, a voltage can be measured across the thin membrane. The output voltage can then be calibrated for a standard size sensor and correlated to the applied loads or stresses. In this research the sensing capability of these materials were investigated by bending the tip end of a sample and measuring the output voltage. The results were then plotted to get characteristic response of the composite for a given imposed tip displacement. In addition a hysteresis curve for a complete cycle of bending was obtained. The preliminary results showed the existence of linear relationship between output voltage and displacement for all except the last quarter of bending cycle. Unlike strain gages where the output voltage needs to be conditioned and amplified by a factor of 1000 or more, these composite polymer sensors can produce up to millivolt output and sense large deformations in the presence of small amplifier gains of two order of magnitude less than conventional sensors. In addition they can be made in the range of micro to several inches in dimension for various applications. Also they don't face the shortcomings and other limitations associated with bonding of typical strain gages to the work piece. The most important advantage of these composites is the fact that they can be used both as large motion sensors and actuators. This means that by using a simple feedback control scheme and double layers of the composite film, it will be possible to use these composites as self-contained robotic manipulators that don't need sophisticated sensors modules for full integration of intelligence.

An analog measurement circuit topology is presented that significantly outperforms the Wheatstone bridge in many measurement and control applications. The initial output level can be simply adjusted to zero volts. Using active subtraction, the topology can provide greater measurement accuracy than the Wheatstone bridge, especially for measurements in difficult environments. When compared to a Wheatstone bridge arrangement of variable impedance elements, some of the advantages of this measurement circuit topology are: double and electrical output for the same sensor element power dissipation, the quantity of sensor elements may be reduced by one half, nearly 6 db improvement in single-to-noise ratio, ratiometric operation, even random lead wire variations are typically irrelevant, linear electrical output even for large changes in a single impedance element, fewer wires from the observing electronics to impedance elements, transducers can have any number of electrical elements (each with different initial impedances), outputs are presented from each individual sensor impedance element as well as an aggregate output from any subset of elements, sensor calibrations can be any function of each individual sensor element change, and temperature at the various monitored impedances can be indicated without additional lead wires.

We present experimental results to demonstrate the simultaneous strain and temperature measurement capability of long-period gratings. It is shown that the distinct spectral shifts of the multiple resonance bands in a single grating can be employed to separate the concurrent perturbations of axial strain and temperature. Static and quasi-static tests are performed to illustrate the effectiveness of a grating written in a standard optical fiber. It is demonstrated that cross-sensitivities and non- linearities in the temperature- and strain-induced shifts result in a tradeoff between the simplicity and the dynamic range of the sensing system. The advantages and limitations of the long-period grating simultaneous sensing configurations are also discussed.

The ability to detect, localize and characterize disturbances in real time is of considerable importance for structures, particularly in light of the increasing use of high performance composite materials with unconventional and often catastrophic failure modes. In this paper, we present the results of a follow on investigation to previous work that demonstrated that use of two spatially weighted distributed fiber optic sensors to detect, localize and characterize impacts along an extended linear region. The results presented here represent an extension of that technique from one to two dimensions. Two long co-located sensors with differing and varying sensitivities to perturbations along their lengths were configured in different 2D patterns with their sensitivity distributions optimized via a genetic algorithm. The ability of these sensor patterns to detect and localize point disturbances on a plate were determined experimentally and compared. Finally, particular applications in which this technique might be beneficially utilized are identified and discussed.

Ultrahigh sensitivity strain sensors are required for precision applications where length changes on the order of nanometers must be detected. Using a single mode fiber as a cavity etalon, a new, ultrahigh sensitivity optical fiber sensor has been developed. The sensor is fabricated by gold- coating the cleaved ends of approximately 1 m long single mode fiber to form a moderate finesse (F approximately equals 50) fiber cavity etalon. The sensor has demonstrated static strain sensitivity of approximately 1 n(epsilon) and low frequency noise performance of approximately 4 p(epsilon) /(root)Hz at 10 Hz. The results of quasi-static stepped strain (< 50 n(epsilon) ) and free vibration dynamic strain measurements of these sensors bonded to low expansion struts will be reported.

Conventional E-glass fibers were surface treated to enable them to act as light guides for short distances. The reinforcing fiber light guides were embedded in glass fiber reinforced epoxy prepregs and processed into composites. The resultant composite was termed the self-sensing composite as any damage to these fibers or its interface would result in the attenuation of the transmitted light. Epoxy, silicone, fluoropolymer and sol-gel derived cladding materials were evaluated as potential cladding materials. RFLGs with a silicone coating was found to give the best light transmission. The self-sensing fibers were capable of detecting a 0.5 J direct impact. The feasibility of using the RFLGs for impact damage location was also demonstrated successfully as bleeding-light could be seen in the vicinity of the impact.

This paper focuses on the mathematical and computational aspects of the modeling and control of thermal manufacturing processes, with a dynamic and distributed-parameter nature. A generic numerical simulation model is first developed for thermal processing, with an embedded melt flow model to the conduction field description. This is linearized by small perturbations near the nominal process conditions, and yields a computationally efficient state space model with a sparse, diagonally banded structure in the system matrices. A multivariable controller with similar structure is then designed, and its independent gains are selected by optimization of the closed-loop thermal eigenvalues. This procedure can be implemented in real time by identification of the model and by adaptation of the controller parameters. This methodology is validated by computer simulation, emulating scan welding and thermal rapid prototyping applications.

This paper reports on a comparative study undertaken for different types of optical fiber sensor developed to monitor the cure of an epoxy resin system. The optical fiber sensors used to monitor the cure process were based on transmission spectroscopy, evanescent wave spectroscopy and refractive index monitoring. The transmission sensor was prepared by aligning two optical fibers within a specially prepared sleeve with a gap between the optical fiber end-faces. During cure, resin from the specimen flowed into the gap between the optical fibers allowing transmission spectra of the resin to be obtained. The evanescent wave sensor was prepared by stripping the cladding from a high refractive index core optical fiber. The prepared sensor was embedded in the sample and attenuated total reflectance spectra recorded from the resin/core boundary. Refractive index monitoring was undertaken using a high refractive index core optical fiber which had a small portion of its cladding removed. The prepared sensor was embedded in the resin specimen and light from a single wavelength source was launched into the fiber. Changes in the guiding characteristics of the sensor due to refractive index changes at the resin/core boundary were used to monitor the progress of the cure reaction. The transmission and evanescent wave spectroscopy sensors were used to follow changes in characteristic near-infrared absorption bands of the resin over the range 1450 - 1700 nm during the cure reaction. Consequently these techniques required tunable wavelength sources covering specific wavelength ranges. However, the refractive index based sensor used a single wavelength source. Therefore the equipment costs for this type of sensor were considerably less. Additionally, the refractive index sensor did not require a single wavelength source at any particular wavelength and could be applied to any spectral region in which the optical fiber would transmit light. The advantages and disadvantages of these three methods are discussed.

A method to determine process-induced residual stress in composite materials using strain measurements from embedded fiber optic sensors is presented. This method allows non- destructive, real-time determination of residual macrostress in composite materials and may be useful for both process monitoring and control. Extrinsic Fabry-Perot interferometer strain sensors were embedded in Hercules AS4/3501-6 graphite/epoxy composite specimens prior to cure. The specimens were cured in a press, and the internal strains and temperatures developed during processing were monitored and recorded. Residual macrostresses were computed using these measurements and a viscoelastic model of the material. The results compare favorably with previous analytical predictions and experimental measurements from a destructive technique.

This paper proposes a flexible 3D coordinate system based on a theodolite pair. The math model of the system is based on the least square method. A transition coordinates system is established to meet the requirement to move the theodolite pair in many on-site situations. This paper gives an example that the flexible 3D coordinate system is employed to complete the global calibration of a vision-based inspection system for the body-in white of car.

In this paper, a distributed control network in autocar-body visual inspection station is presented in which PC is used as the host processor and single-chip microcomputers are employed as slave controllers. The physical interface of the control network and the relevant hardware are introduced in this paper. Meanwhile, a minute research on data communication is performed, relevant protocols on data framing, instruction codes and channel access methods have been laid down and part of related software is presented.

This paper presents the results of Finite Element modeling and experimental investigation of mold filling in an RTM process. Flow measurement experiments were designed to verify the results of the numerical models. Flow experiments in molds having cavities of rectangular and irregular shapes were performed to investigate resin flow behavior. Silicone fluids of 50 and 100 centistoke viscosities as well as EPON 826 epoxy resin were used in the mold filling experiments. Fiberglass and carbon fiber mats were used as reinforcements. Numerical models were developed to simulate resin flow into the mold cavities. The resin flow through fiber mats was modeled as a flow through porous media. The effects of injection pressure, fluid viscosity, type of reinforcement, and mold geometry on mold filling times were investigated.

Long-period gratings have recently been demonstrated as highly versatile strain, temperature and refractive index sensors that can be implemented with simple demodulation schemes. The cross-sensitivity of long-period gratings to ambient temperature variations can be a limiting factor in applications that require their use as strain or refractive index sensors. The thermal-induced spectral shift in the grating transmission spectrum can be attributed to the material and waveguide changes in the grating characteristics. By designing special optical fiber refractive index profiles, these two effects can be counter- balanced to produce gratings that have an order of magnitude smaller temperature wavelength shift than conventional long- period gratings. We present experimental results for strain and refractive index sensors using these temperature insensitive long-period gratings. Such transducers are shown to possess strain- and refractive index-induced wavelength shifts that are comparable to those of standard gratings. The cross-sensitivity to temperature is determined at different magnitudes of strain and ambient index to determine the effectiveness of these gratings in practical applications.

Optical fiber Bragg grating (FBG) sensors have significant potential for use as embedded devices to monitor the structural integrity of engineering materials. The main drawback of the FBG strain sensor is its cross-sensitivity to temperature. This paper reports a simple scheme for multiplexing a FBG and an extrinsic Fabry-Perot interferometric (EFPI) sensor to enable the decoupling of strain from temperature. The EFPI sensor was constructed using a precision bore quartz capillary tube which housed two cleaved optical fibers. The gap between the fiber end- faces served as the Fabry-Perot cavity. Since the coefficients of thermal expansion between the optical fiber and the capillary tube were similar, the EFPI sensor has a very low sensitivity towards temperature. Therefore, when both sensors are placed close together, the EFPI sensor can act as the strain sensor, and temperature can be determined from the FBG wavelength shift after taking out the strain effect. The signal processing for the EFPI sensor was based on a channelled spectrum method using a CCD spectrometer. The same CCD spectrometer was also used to determine the wavelength shift of the FBG. The cross-talk between the EFPI and FBG sensors was evaluated. The feasibility of conducting simultaneous strain and temperature measurements was demonstrated.

In this paper, the second-order sensitivities of the optical fiber sensor for simultaneous measurement of strain and temperature are analyzed theoretically and demonstrated experimentally for a dual-wavelength optical fiber sensor. Error analysis shows that such effects will be important when: (1) large strain (or temperature change) and small temperature change (or strain) are applied simultaneously; (2) large strain and large temperature change are applied simultaneously. But they can be omitted for small changes of the two parameters.

In this paper, we present a method to measure two components of transverse strain in an optical fiber using a single Bragg grating written into high-birefringent, polarization- maintaining (PM) fiber. The reflected spectrum from this grating contains two peaks corresponding to the two orthogonal polarization modes of the fiber. If the axial strain and temperature in the fiber is known, then two components of transverse strain can be computed from the changes in wavelength of the two peaks. A Bragg grating written near 1300 nm in PM fiber was loaded in diametrical compression, and the changes in wavelength of the Bragg peaks were monitored using an optical spectrum analyzer. Transverse strains were computed from the changes in wavelength using available strain-optic coefficients for low-birefringent optical fiber. These strains are compared to finite element analysis predictions, and it is shown that the observed sensor response is greater than the response predicted by the low-birefringent analysis. A calibration factor is developed for the sensor to allow the determination of transverse strains from the measured wavelength shifts.

Development of a novel 3 axis strain and temperature fiber optic grating sensor is described. This sensor relies on dual overlaid fiber gratings written onto birefringent optical fiber resulting in four effective fiber gratings. By using dual overlaid phase masks fabrication costs for this sensor can be expected to be similar to that of a single fiber grating. This paper reports on early development efforts associated with the 3 axis strain and temperature sensor.

A simple method to simultaneously measure temperature and axial strain for a surface mounted Bragg grating sensor is presented. This method uses a single, uniform pitch Bragg grating that is only partially glued on the structure. Thermomechanical strain fields will produce two different Bragg wavelengths from the one fiber Bragg grating sensor. The Bragg wavelength reflected from the sensor section not glued to the structure is used to measure temperature variations; and the Bragg wavelength reflected from the sensor section glued to the specimen is affected by both of strain and temperature variation. However, under conditions of no cross-talk sensitivity between temperature and strain, the spectral separation between two Bragg wavelengths is directly interpreted as a wavelength shift caused by the thermomechanical strain in structures. After the temperature variation is obtained, the mechanical strain can be calculated if the thermal-expansion coefficient of structures is known. Therefore, this method supplies a simple measurement in temperature and axial strain simultaneously.

Life extension programs for military metallic aircraft are becoming increasingly important as defense budgets shrink and world economies realign themselves to an uncertain future. For existing military weapon systems, metallic corrosion damage costs as estimated $DOL8 billion per year. One approach to reducing this cost is to develop a reliable method to detect and monitor corrosion in hidden metallic structure with the use of corrosion sensors which would give an early indication of corrosion without significant disassembly, thereby reducing maintenance costs. This presentation describes the development, analysis, and testing of a fiber optic corrosion sensor developed jointly with the Virginia Polytechnic Fiber and Electro-Optics Research Center and sponsored by Wright Laboratory Materials Directorate. In the sensor which was researched, the normal cladding is removed in the sensor region, and replaced with aluminum alloy and allowed to corrode on coupons representative of C/KC-135 body structure in an ASTM B117 salt spray chamber and a Boeing developed Crevice Corrosion Cell. In this approach, the optical signal output of the sensor was originally designed to increase as corrosion takes place, however interaction with the corrosion byproducts yielded different results than anticipated. These test results to determine a correlation between the sensor output and the structural degradation due to corrosion are discussed.

We present recent progress in the development of optical fiber sensors for early detection of corrosion on aging metallic aircraft. Optical fiber sensing techniques being investigated include fiber optic Bragg grating strain sensor to monitor the mass reduction of metal `witness' capillary tubes and extrinsic Fabry-Perot interferometric strain gages to monitor pillowing in lap joints.

This paper will present the findings from crack detection monitoring on the 777 full-scale aircraft during fatigue testing. Crack detection is a critical component of any comprehensive aircraft structural health-monitoring system. Health monitoring offers the promise of substantially reduced inspection and maintenance costs for military aircraft. To date, most testing has been performed in the laboratory on relatively small coupons and subcomponents. A persistent concern with broadband acoustic emission methods has been their ability to measure crack signals in the presence of noise. There is little broadband acoustic emission test data to provide any indication of the possible difficulties in monitoring a full-scale structure. This paper will present test data, results and discussion from broadband acoustic emission monitoring of the 777 Full-Scale Fatigue Test.

Hidden and inaccessible corrosion in aircraft structures is the number-one logistics problem for the U.S. Air Force, with an estimated maintenance cost in excess of $DOL1.0 billion per year in 1990-equivalent dollars. The Smart Aircraft Fastener Evaluation (SAFE) system is being developed to provide early warning detection of corrosion- related symptoms in hidden locations of aircraft structures. The SAFE incorporates an in situ measurement approach that measures and autonomously records several environmental conditions (i.e., pH, temperature, chloride, free potential, time-of-wetness) within a Hi-Lok aircraft fastener that could cause corrosion to occur. The SAFE system integrates a miniature electrochemical microsensor array and a time-of- wetness sensor with an ultra-low-power 8-bit microcontroller and 5-Mbyte solid-state FLASH archival memory to measure the evidence of active corrosion. A summary of the technical approach, system design definition, software architecture, and future field test plans will be presented.

The condition of concrete structures can be assessed through the monitoring of crack openings. Researchers at MIT and Brown University have recently developed a novel concept for the sensing of cracks in concrete structures. The sensing capability is based on the light loss as microbending occurs in a fiber bridging the crack. To use the sensor, only the crack plane orientation in the structure (rather than the exact crack locations) needs to be known. With the use of OTDR, distributed sensing is possible. In this paper, the novel crack sensing concept is first introduced. To guide the design of sensors for various performance requirements, a theoretical model is developed to relate signal loss and crack opening. Prediction from the mold is compared with experimental results. Using laboratory-sized specimens, the detection of both surface and interior cracks are demonstrated.

The detection of impact damage in fiber reinforced composites is of significant concern because such damage can reduce the load-bearing ability of the composite. A number of factors can influence the nature and extent of impact damage development in composites including: (1) the type of reinforcing fiber and resin system; (2) the magnitude of the residual (fabrication) stresses; (3) the lay-up sequence; and (4) other factors such as the nature of the impactor, impact velocity, impact energy, temperature, moisture content in the composites etc.. From a structural health monitoring point of view, it is necessary to investigate the distribution of damage through the thickness of the composite. This paper reports on a simple, partially multiplexed optical fiber strain sensor system for in-situ strain and residual strain measurements in a carbon fiber reinforced epoxy composite. An extrinsic Fabry-Perot interferometric (EFPI) sensor design was used along with single mode fibers. The multiplexing scheme was based on wavelength division via the use of two super luminescent diodes at different wavelengths. A low-cost fiber optic CCD spectrometer was used as the detector. The multiplexing scheme was demonstrated using two EFPI sensors. In principle, a number of EFPI sensors can be multiplexed using the proposed scheme provided that each sensor is illuminated at a specified and different wavelength. The feasibility of detecting the residual strain in the composite was demonstrated successfully at two specified positions within a 16-ply carbon fiber reinforced composite. Preliminary results indicated that the sensor system was also capable of detecting the effects of a 3.2 J impact. Excellent correlation was obtained between the EFPI sensor output and that obtained using surface mounted strain gauges.

This research is an investigation into the use of adhesive liquid core optical fibers for the detection of cracks, their location and volume in opaque and semi-opaque brittle materials. The study combines work based on the concept of internal adhesive delivery from hollow fibers for repair with nondestructive fiber optic analysis of crack locations and volume within the same system. The liquid filled hollow fibers can carry light in the liquid. The cracked fiber which has released liquid projects diffraction patterns from the meniscuses at the ends of the liquid. The size relationship of these patterns allow us to determine the location of the cracks and the amount of liquid lost into the matrix and perhaps relate it to the volume and location of the cracks in the matrix.

This paper presents preliminary work on a vibration monitoring system for assessing the condition of engineering structures or materials. It consists of an intensity-based fiber-optic vibration sensor, a fast Fourier transform pre- processing stage and a back-propagation neural network. The response of the vibration sensor to sinusoidal acceleration is compared with that of a piezoelectric accelerometer. The sensor was fixed to carbon-fiber composite panels and its response to acoustic transients was investigated. Signals from breaking a pencil lead or dropping a ball bearing on the panel were compared. The system was then trained to distinguish between the sensor response to dropping a ball bearing on panels with either real or simulated impact damage. The trained network then identified previously unseen examples of these signals with complete accuracy.

Optical fiber pressure sensors have been developed for use on a structurally-adaptive `smart wing'; further details of the design, fabrication and testing of the smart wing concept are presented in companion papers. This paper describes the design, construction, and performance of the pressure sensor and a combined optical and electronic signal processing system implemented to permit the measurement of a large number of sensors distributed over the control surfaces of a wing. Optical fiber pressure sensors were implemented due to anticipated large electromagnetic interference signals within the operational environment. The sensors utilized the principle of the extrinsic Fabry-Perot interferometer (EFPI) already developed for the measurement of strain and temperature. Here, the cavity is created inside a micromachined hollow-core tube with a silicon diaphragm at one end. The operation of the sensor is similar to that of the EFPI strain gage also discussed in several papers at this conference. The limitations placed upon the performance of the digital signal processing system were determined by the required pressure range of the sensors and the cycle time of the control system used to adaptively modify the shape of the wing. Sensor calibration and the results of testing performed are detailed.

The informatics of instrumented infrastructure will require multi-level computational abstractions that not only collect and declutter the data but also support higher-level automated reasoning capabilities relevant to decision support needs of both owners responsible for the safe operation of the facilities and users of those facilities. This paper describes the appeal and implemented demonstration of Internet-based paradigms for higher-level automated reasoning about condition of instrumented infrastructure using the Java computing language. This enables interactive program execution from a web page. These notions are presented and demonstrated in the context of illustrative application scenarios involving fatigue monitoring, overweight vehicle detection, and bridge deck surface travel condition monitoring. By means of this demonstration, it is suggested that there is an important role for Java-based expert systems in handling key aspects of the data fusion requirements associated with intelligent, internet-mediated post-processing of data obtained from instrumented civil infrastructure.

The informatics of instrumented infrasiructure will require multi-level computational abstractions that not only collect and declutter the data but also support higher-level automated reasoning capabilities relevant to decision support needs of both owners responsible for the safe operation of the facilities and users of those facilities. This paper describes the appeal and implemented demonstration of Internet-based paradigms for higher-level automated reasoning about condition of instrumented infrastructure using the Java computing language. This enables interactive program execution from a web page. These notions are presented and demonstrated in the context of illustrative application scenarios involving fatigue monitoring, overweight vehicle detection, and bridge deck surface travel condition monitoring. By means of this demonstration, it is suggested that there is an important role for Java-based expert systems in handling key aspects of the data fusion requirements associated with intelligent, internet-mediated post-processing of data obtained from instrumented civil infrastructure.

A fiber Bragg grating sensor array is interrogated using a broad bandwidth passively mode locked fiber laser source. A novel demodulation scheme is demonstrated using highly dispersive fiber to convert the grating wavelength shift to a temporal shift in the arrival time of the reflected pulses. The mode locked fiber laser was then modified and operated in the square pulse regime, where 4 W, 10 ns pulses with bandwidths greater than 60 nm were used successfully to illuminate 2% fiber Bragg gratings.

The twisted optical fiber sensors have been embedded in composite material plate to evaluate the injury position by the methods of using both orthogonal network and neural network. The experimental results show that a 3-layer neural network can be used in wide-ranging treatments as well as fast-on-the-time treatments in injury position evaluation.

A novel single-ended fiber optic sensor capable of making absolute displacement measurements over arbitrarily long distance (a few centimeters to meters) is demonstrated. The sensor's gauge length is defined by an in-fiber broad bandwidth Bragg grating and a mirror coated at the end of the same fiber. This sensor has been demodulated optoelectronically by means of a laser wavelength scanning technique. The absolute measurement of perturbation is achieved by measuring the perturbation induced optical path difference (OPD) changes with respect to the OPD of a reference interferometer that can be isolated from environmental perturbations and remain constant. This sensor is well suited for structural applications, especially the measurement of hoop stress changes in concrete columns that are wrapped within layers of advanced composite material for rehabilitation or strengthening.

Fiber Bragg gratings have been widely used for smart structures sensing applications. Until recently all sensor systems using gratings have only measured the average value of a physical field. The field has been averaged either over the length of a grating or over a length of fiber between gratings. To obtain a spatial image of the physical field, these sensors have been multiplexed to form a sensor array. Recently, fully distributed images of physical fields have been measured along the entire length of a grating. Distributed sensors show great promise for the detection and location of small physical features within structures, such as cracks and hot spots. As the fabrication length of gratings continues to increase, there appears great potential for distributed grating sensors. Distributed grating sensors may be classified as either narrowband or broadband, according to the spectral width of the interrogation source. Both types of sensor are discussed and briefly compared. The various forms of averaging grating sensors are also discussed and their performance is compared with that of distributed grating sensors using two specific smart structures applications. The latest results of our broadband distributed sensor are presented. This distributed sensor may be viewed as an adaptive averaging sensor since the number of interrogation regions, their size, location and the spatial resolution may all be viewed in response to the sensing information. Finally, a sensing network combining the advantages of both multiplexed and distributed sensors is demonstrated and discussed.

Significant weight and space savings have been realized in avionic equipment and structures by using composite materials. Optical fiber provides improved communication between equipment and components on board the aircraft. The marriage of these two technologies by embedding optical fiber in the composites achieves improved signal transmission and reduced weight. The goal of this work is to provide reliable, low-profile, optical interconnects with composite-embedded optical fiber for communication with opto-electronic circuit cards and modules. The design and results of a prototype embedded multimode optical beamsplitter utilizing in-fiber 45 degree(s) dielectric coatings are presented.

Long-period gratings have recently gained popularity as versatile optical fiber sensing elements that are simple and economical to fabricate and demodulate. Long-period gratings are periodic photoinduced structures in fiber cores that couple light from guided to cladding modes. We discuss the applications of these devices to strain measurements in high-performance materials and structures. Experimental results from a preliminary loading test carried out on a reinforcing-bar commonly used in civil structures are presented. The temperature cross-sensitivity of long-period grating-based strain sensors is analyzed and two methods to overcome this limitation are presented. We also demonstrate that strain-insensitive long-period gratings can be fabricated in standard optical fibers. The application of such gratings to temperature measurements in the presence of actively varying axial strain is discussed. Preliminary results indicate that long-period gratings hold tremendous potential for health monitoring of advanced materials and structures.

A laboratory scale pultrusion process has been developed to fabricate smart fiber reinforced plastic (FRP) materials. Microstructural analyses of the smart pultruded FRP was carried out using both an optical microscope and a Scanning Electron Microscope. The tensile properties and shear strength, i.e. modulus and strength, of pultruded carbon/vinylester and glass/vinylester rods were determined through mechanical testing. Testing was carried out on baseline pultruded samples, as well as those containing one and two embedded optical fibers. The pultruded carbon reinforced rods with and without optical fiber showed higher shear and tensile strength, as well as greater tensile modulus than did the glass fiber analogue. An embedded optical fiber did not have a significant effect upon the tensile properties of either glass or carbon pultruded FRP rod, but it slightly affected the shear strength of the glass fiber rods. Increased numbers of embedded optical fibers in the FRP rods had a more pronounced influence upon the shear strength. The interfaces between the resin matrix and the buffer coating on the optical fibers were examined and interpreted in terms of the coating's ability to resist high temperatures and its compatibility with resin matrix. Polyimide buffers proved to be superior to acrylate buffers.

This paper investigates the main effects of drilling parameters (cutting speed, feed rate, tool geometry, and tool material) on cutting force and hole quality during drilling of magnamite graphite fiber reinforced polyether ether ketone (AS4/PEEK) composites. The AS4/PEEK is a one hundred and ninety nine-ply [0 degree(s)/45 degree(s)/90 degree(s)/-45 degree(s)]_s laminate composite. Taguchi orthogonal array L₉ technique is used to plan a 3⁴ robust experiment. The workpiece is supported on a fixture and mounted on a 3-component piezoelectric transducer Kistler type 9257A model. The response signals (cutting force and acoustic emission) are acquired simultaneously during the drilling experiments. The signals are instantaneously sampled and stored in a pentium computer for later processing. The digitized signals are processed in time domain. Surface profilometer is used to measure the surface roughness of the drilled holes. The optimum drilling condition is determined by meticulous examination of the drilling parameter's main effects. The responses are analyzed based on Taguchi's signal-to-noise ratio as opposed to the measurement data and analysis of variance. The results show that sensor signals, delamination and surface roughness measurements are well correlated with the drilling parameters. Optimum drill tool materials, drill point angle and cutting conditions have been determined.

We describe strain data recorded using fiber optic Bragg grating sensors mounted on the hull of a GRP composite ship. Twelve gratings were attached to the structure, in three arrays of four elements. The electro-optic system used was able to monitor a single set of four elements at a time. The preliminary results indicate the usefulness of distributed fiber Bragg grating sensor systems for monitoring transient loading events on such structures.

An optical fiber sensor for simultaneous measurement of axial strain and temperature is reported. This sensor configuration consists of an in-line fiber etalon cascaded with a in-fiber Bragg grating and demultiplexed using a variation of coherence division multiplexing. The strain/temperature sensor is demonstrated by bonding it to the surface of an aluminum cantilever beam and embedding it into a graphite/epoxy composite cantilever beams. They are found to agree with traditional strain and temperature sensors to within 5 (mu) (epsilon) and 0.5 degree(s)C, respectively for a sensor gage length of approximately 1.0 cm.