We report interferometric interrogation of fiber Bragg gratings in separate cores of a multicore fiber for high resolution quasi-static and dynamic bend measurements. Two axis curvature measurements are made by measuring the differential strain between three FBG sensors formed in a singlemode four-core fiber using a common interrogating interferometer. Therefore a measurement of the differential phase from each FBG yields the differential strain and compensates for the common-mode random drift of the interrogating interferometer. A DC curvature accuracy of 3.4×10^-3m^-1, and an AC curvature resolution of 1.2×10^-4m^-1 / Hz^1/2 are reported.

In this paper, we report the development of a new bonding agent and method for the surface mounting of optical fiber Bragg grating (FBG) strain and temperature sensors for use in high temperature environments - where there is a presence of water, moisture, dust, susceptibility to corrosion and/or elevated temperatures up to 800°C. To ensure a stable reflectivity response of FBGs and their survival at elevated temperatures, we are using surface relief fiber Bragg gratings (SR-FBG). These gratings, instead of being written in the core of a photosensitive or hydrogen-loaded fiber, are formed by introducing a periodic surface relief - through photolithographic and etching processes - in the cladding above the core. Samples of SR-FBGs were successfully encapsulated and mounted onto metal shims. The packaged sensors displayed a linear response with temperature and a sensitivity factor of 11pm/°C.

We have been developing a sensing system for monitoring the structural health of aircraft structures made of composite materials. The sensing system is composed of fiber Bragg grating (FBG) sensors, a wavelength interrogator and piezoelectric actuators. The FBG sensors receive 100 kHz to 1 MHz elastic waves generated by the PZT actuators. For the FBG sensors, we previously developed a polyimide-coated optical fiber with a cladding diameter of 40 μm and core-cladding relative refractive index difference Δ of 0.65 %, that can be embedded in composite materials without inducing any mechanical defects. Since the cladding of that fiber is so thin, however, under embedded conditions, the transmission loss of the fiber is larger than that of a normal single-mode optical fiber. We therefore developed a new small-diameter optical fiber with an Δ of 1.8 %, in order to suppress the loss increase caused by micro-bending or transversely applied strain under the embedded condition. On the other hand, the small-diameter optical fiber needs to be connected to a normal optical fiber whose claddingding diameter is 125 μm, because it is fragile and difficult to handle. For practical use, we developed a small-diameter optical fiber module that has a special connector on both ends of the small-diameter optical fiber. The special connector can connect the small-diameter optical fiber to a normal optical fiber that has a standard MU connector. We also developed a high-speed optical wavelength interrogator that can detect the high-frequency vibration of the FBG sensors. It uses an arrayed waveguide grating (AWG) as an optical filter that converts the wavelength shift of the light reflected from the FBG into the output optical power changes. This wavelength interogator is suiatable for high-speed wavelength detection because it has no mechanical moving parts. The development of these components will help put this system to practical use and thus extend the use of composite materials to a wider range of applications.

We report the results of a study of the performance characteristics of a distributed fiber-optic shape and position sensor. Strain measurements from distributed fiber Bragg gratings in a multi-core optical fiber multiplexed via the frequency domain reflectometry technique are used to deduce the shape of the optical fiber. We have measured a range of two- and three-dimensional shapes using a multi-core fiber with a sensor spacing of 1.0 cm and a gage length of 0.5 cm and have reported the accuracy and precision of these measurements. A discussion of error sources is also included.

Fiber Bragg grating (FBG) sensors have been shown to be a good means of nondestructive monitoring of the stress and/or strain of the materials in which they are embedded. Many FBG transverse stress/strain measurement systems can resolve only a single stress and/or strain value for the entire length of the FBG and often require the use of polarization-maintaining fiber. We demonstrate a new method for measuring the two components of transverse stress with high spatial resolution in a distributed FBG sensor. A directional compressive load is applied by placing weights on top of the FBG, creating a transverse stress in the core of the FBG. Small metallic strips are placed under the FBG to create a localized stress in the FBG. The relative index of refraction as a function of position in the FBG is determined with a low-coherence Michelson interferometer and a layer-peeling algorithm. With this method we are able to measure changes in the refractive index with resolution better than 5x10^-6, limited by the signal-to-noise ratio of the measurement system, with a spatial resolution of 16 μm. To determine transverse stress, we repeat the measurement for four different polarization states. A four-state analysis is then used to determine the birefringence as a function of position in the grating. This measurement assumes that the applied transverse load is much larger than any other birefringence in the grating, so that the principal axes do not change with position in the grating. This measurement offers the advantage that it can be implemented with a simple layer-peeling algorithm, and it does not require the use of expensive polarization maintaining fiber. Measurements of the externally induced birefringence agree well with values predicted by the stress-optic properties and the geometry of the fiber.

A multiplexed 4-channel version of two-wave mixing (TWM) wavelength demodulator using InP:Fe photorefractive crystal (PRC) in the C-band (1530-1570nm) is demonstrated. The system can be used as a wavelength demodulator for use with Fiber Bragg Grating (FBG) sensors to monitor both dynamic strains and quasi-static strains. In this configuration, the FBG is illuminated with a broadband source, and any strain in the FBG is encoded as a wavelength shift of the light reflected by the FBG. The reflected light from the FBG is spilt into two unbalanced paths and both beams (pump and signal) mix in the PRC. Any wavelength shift of the reflected light results in an equivalent phase shift between the pump and signal beams as they travel unbalanced path lengths. Since TWM is an adaptive process, the two interfering beams are naturally in quadrature and remain in quadrature even in the presence of large quasi-static strains. In this paper, the demonstrated 4-channel TWM wavelength demodulator is able to demodulate dynamic strains from four FBG sensors simultaneously in the presence of quasi-static drifts. And with the aid of a spectrum analyzer, the quasi-static shifts caused by static strains or temperature changes are obtained by monitoring the spectral shift of the transmitted light through the FBG sensors.

We recently reported on a new fiber Bragg grating etched into the flat surface of a D-fiber and its potential use as a high temperature sensor. Since then we have investigated more in depth many of the characteristics that are unique due to the surface relief nature of the grating. In this paper we show that a surface relief fiber Bragg grating exhibits some significant advantages when compared to standard fiber Bragg gratings including: high temperature operation, polarization selectivity, and the ability for multi axis strain sensing. We also show the uniqueness of these gratings for bend sensing with two degrees of freedom.

Fiber optic Bragg grating (FBG) sensors show promising capabilities in the measurement of strain and temperatures in structures at many locations. In this work, the potential of FBG sensors for high-precision deformation control in opto-mechanical applications is investigated. This requires a strain resolution of < 1 um/m. A test rig with a simply supported steel beam was developed which should represent the geometry of a lightweight optical mirror with a ribbed support structure. The deformation of this beam is controlled by a piezo actuator. The reference deformation measurement is done using six capacitive displacement sensors with a resolution < 0.5 nm. It is being investigated to what level of accuracy FBG sensors can be used to reconstruct the displacement information. Different methods to increase the accuracy are discussed: decreasing the sensor noise by oversampling and increasing the number of sensors. Tests were performed using different diffraction-based interrogation techniques for the wavelength detection: a CCD-based FBG sensor system and a PSD (Position Sensitive Detector)-based high-speed FBG sensor system which - to our knowledge - has not been used for an application of this kind yet. A comparison of both systems discussing the weaknesses and strengths is given for the recording of mechanical strain < 1 um/m. The results showed that a resolution of < 0.3 um/m for the strain measurement using FBG sensors can be achieved. This study shows an interesting application potential for FBG sensors in structural deformation control for various fields such as optics or high-precision machine tools.

Fiber optic grating sensors can be used to measure multi-dimensional strain, pressure, temperature, corrosion and moisture. The application of this technology to structural health monitoring of aerospace platforms includes adhesive bond line measurements, crack detection, damage assessment of composite and moisture/corrosion sensing. One very important application is the emerging field of "strain imaging" that can be used in certain situations to detect, localize and characterize damage in composites. This paper will provide an overview of some of the techniques that have been applied using fiber grating sensors to monitor structural health and comparisons will be made to more traditional methods such as ultrasonic and eddy current scans.

The authors developed a prototype Brillouin measurement system and carried out some application tests to verify the capability for aircraft structural health monitoring (SHM). The prototype Brillouin measurement system is adopted the Brillouin optical correlation domain analysis (BOCDA) method. This system is able to measure the distribute strain of full-length optical fiber sensor with 50mm of spatial resolution and 2.7Hz sampling of high-speed arbitrary point strain. Moreover, we conducted three application tests to evaluate the effectiveness of SHM using BOCDA system, such as the panel buckling test, the dynamic strain measurement test, and the demonstration flight test using the prototype BOCDA system. We verify the effectiveness of the BOCDA system for the aircraft SHM, and clarify the necessary development subject for the actual application.

This paper uses one category of Structural Health Monitoring (SHM) which uses strain variation across a structure as the key to damage detection. The structure used in this study was made from Glass Fibre Reinforced Plastic (GFRP). This paper discusses a technique developed called "Global Neural network Architecture Incorporating Sequential Processing of Internal sub Networks (GNAISPIN)" to predict the presence of multiple damage zones, determine their positions and also predict the extent of damage. Finite Element (FE) models of T-joints, used in ship structures, were created using MSC Patran^(R) . These FE models were created with delaminations embedded at various locations across the bond-line of the structure. The resulting strain variation across the surface of the structure was observed. The validity of the Finite Element model was then verified experimentally. GNAISPIN was then used in tandem with the Damage Relativity Analysis Technique to predict and estimate the presence of multiple delaminations.

Concerns about the safety of concrete dams have increased during recent years, partly because the population at risk in locations downstream of major dams continues to expand and also because these old dams are experiencing long-term damage and the seismic design concepts used to build them were inadequate. Reliable techniques for continuous monitoring of certain key parameters affecting the dams' integrity are currently nonexistent and this is because of the lack of sensing technology capable to function in a hostile environment such as low temperatures and high moisture level. This paper presents new low cost, passive and wireless micro-machined SAW-based sensors to monitor the safety and security of dams. These SAW sensors are composed of MEMS transducers, Nano-polymer actuators and an antenna, and are deposited on a thin film substrate. The sensors are passive, do not require power on-board and can be interrogated wireless using a radar. When embedded into concrete dams, the devices will be able to detect and locate internal cracks and measure certain key parameters affecting the durability of dams such as temperature, moisture, pH, chloride and carbon dioxide.

FRP ( Fiber Reinforced Polymer ) has become the popular material to alternate steel in civil engineering under harsh corrosion environment. But due to its low shear strength ability, the anchor for FRP is most important for its practical application. However, the strain state of the surface between FRP and anchor is not fully understood due to that there is no proper sensor to monitor the inner strain in the anchor by traditional method. In this paper, a new smart FBG-based FRP anchor is brought forward, and the inner strain distribution of FRP anchor has been monitored using FRP-OFBG sensors, a smart FBG-embedded FRP rebar, which is pre-embedded in the FRP rod and cast in the anchor. Based on the strain distribution information the bonding shear stress on the surface of FRP rod along the anchor can also be obtained. This method can supply important information for FRP anchor design and can also monitor the anchorage system, which is useful for the application of FRP in civil engineering. The experimental results also show that the smart FBG-based FRP anchor can give direct information of the load and damage of the FRP anchor.

Recognizing the growing importance of new technologies in the life-cycle management of civil infrastructure, the University of Trento is promoting a research effort aimed at developing a novel construction system that will allow real-time condition monitoring of bridge structures. The general concept is to build new bridges using smart structural elements, i.e. precast RC elements embedding a sensing system and capable of self-diagnosis. Sensors are conceived as an integral part of the prefabricated element, influencing its design criteria, performance and detailing. A first step of the research was accomplished in 2004 with the construction and testing of reduced-scale prototypes of smart elements. The second phase aims at demonstrating the industrial feasibility of the series production of prefabricated elements embedding FOS technology as well as their in-field reliability. In detail, the program includes the production of two 28m-long prestressed RC box-beam elements. One of these will be used in a single span road bridge, while the other will be extensively tested in the laboratory, in order to record and identify the response signature associated with recurrent deterioration scenarios. The general paradigm of the design is to conceive the sensing system in two separate parts, embeddable and external. The embeddable part is to be permanently installed in the element, and therefore must have high durability and robustness, while the external sensing system can be replaced during routine maintenance work or as necessary in the case of malfunction, or for technology upgrade.

A novel self-organizing sub-network (SOS) protocol that improves the lifetime, scalability, and reduces the overall energy consumption is proposed for wireless sensor networks (WSN). In SOS protocol, the nodes are usually in idle or sleep mode but when an event is detected; the nodes near the event become active and form sub-networks. Subsequently, cluster heads (CHs) are selected within each sub-network, and the nodes are grouped into clusters. Nodes in the cluster send data to their respective CH, which in turn aggregates the data. This method of forming sub-networks reduces the amount of energy used, because only a part of the network closer to the unexpected event is active, when compared to the other existing methods. The results of SOS protocol obtained using GloMoSim demonstrate that the protocol minimizes the energy consumed, lowers the end-to-end delay, increases the lifetime of the network, and ensures scalability when compared to LEACH protocol. The applicability of SOS protocols for structural heath monitoring is investigated.

In the Polish brown coal mine Belchatow deformation and stress behaviour are investigated to learn in early stage any reaction of this surface coal mine pit. These values are critical in regard of landslide risks as also important for the most economic excavation geometry. As already reported in GTMM 2002 conference in Karlsruhe, a standard stress monitoring station has been installed and first results have been reported. An important task is to get confident values not in high-precision but in long-term stability. In cooperation with my Polish colleagues and the BAM (German Federal Institute for Material Testing), Berlin, a new EFPI Stress Monitoring Station has been installed in this coal mine and first experiences and results have been reported.

In this article, recently developed high-speed, real-time fiber optic sensor demodulation techniques based on low coherence interferometry and phase-shifting interferometry are presented. The demodulation schemes are used in a pressure sensor system that consists of a Fabry-Perot sensing interferometer and an integrated optical circuit (IOC) phase modulator that is used as a reference interferometer. Various conventional phase-stepping algorithms and novel algorithms with error compensations are investigated in order to reduce the errors in the demodulated phase signals. The errors introduced in the phase demodulation arise from many sources, including random intensity measurement errors, phase-shifting errors, and signal-related errors associated with time delays. Numerical analyses are conducted to compare the performances of the demodulation schemes based on different phase-shifting algorithms. These analyses will provide guidelines for choosing appropriate algorithms in sensor demodulation schemes and improving the sensor accuracy and bandwidth.

In this paper we present a complete non-contact, all-optical inspection tool, for the extraction of the principal mechanical characteristics of plate-like structural materials (effective stiffness, Poisson ratio and plate's thickness). Broadband ultrasonic guided waves - Lamb waves - are optically generated and detected for incremental source detector distances. A two dimensional Fourier transform is applied to these measured time signals in order to extract dispersion information, which is highly affected by elastic properties as well as by sample geometry. The elastic properties and thickness of the structure under test are obtained from this experimentally extracted dispersion information, by an inversion technique which is presented and analysed in the paper. These values are verified with a complementary experiment. Monitoring changes in the estimated material properties could be used to indicate changes in the structural condition.

Lamb wave is a good method to detect some imperfections in a thin plate. In order to use this method, a sensor as well as an actuator is needed. Usually, a piezoceramic transducer is a good sensor and also a good actuator. Nowadays, fiber optic sensors are good alternative transducers for detecting Lamb wave as well as other ultrasonic waves. However, in the case of the fiber optic sensor, its sensitivity has directivity; that is, the sensitivity is variable according to the alignment direction of the sensor because the sensor dominantly measures the displacement induced by the change of gage length along the parallel direction to the sensor. Thus, considering the change of the sensitivity with respect to the alignment direction of the sensor to an ultrasonic source is essential in order to detect the ultrasonic wave using a fiber optic sensor and to determine the absolute amount of the measured value correctly. In this paper, the directivity of the fiber optic sensor was investigated through both a theoretical analysis and an experimental one. The theoretical analysis showed that the sensitivity was related to the alignment angle of the sensor and to the ratio (L/λ)of the gage length (L) of the sensor and the wavelength (λ) of the Lamb wave. In the experimental analysis, an extrinsic Fabry-Perot interferometric sensor was used for detecting the Lamb waves which were excited by a lot of piezoceramic transducers. One fiber optic sensor was attached on the center of the aluminum plate; otherwise these piezoceramic transducers were attached around the fiber optic sensor according to the alignment direction of the fiber optic sensor. Finally, the theoretical results were verified in the experimental analysis.

A new fiber sensor integrated monitor to be used in an embedded instrumentation system is proposed and its operating features are examined. The system integrates a fiber sensor together with a tunable MEMS filter, superluminescent light emitting diode and microcontroller creating a high-speed, low cost, low power smart sensor. The device has applications to a variety of fiber sensing technologies and, as an example, is integrated with a fiber Bragg grating for temperature sensing.

Most applications of fiber optic SPR sensors are designed to measure refractive index (RI) of biological sample by single channel, also the sensitivity and stability of the sensor system is easily affected by the unexpected effects from instrumentation and external environment conditions. In this study, we presented two dual-channel fiber optic SPR sensors based on flat-tip or tetra-taper tip structure with two SPR spectrum located on separate wavelengths that can be used for self-compensating RI measurements of more than one biological samples. The prototyped sensors were fabricated and laboratory characterized. The preliminary experimental results demonstrate the characteristic responses of both SPR wavelengths from two channels are independently correspond to the RI changes of the detected samples or the temperature characters of external environment. Both of these two designs could be extend practicable highly sensitive multi-channel sensor systems that will have extensive applications for biological monitoring.

Temperature responsive hydrogels show a strong ability to change their swelling degree in dependence on organic solvent or salt concentration in aqueous solutions. This behavior can be used for appropriate sensors if a suitable transducer transforms the volume change into an electrical output signal. In the present work, piezoresistive sensors were used where the hydrogel led to a deflection of a silicon membrane within the sensor chip. This principle allows for a strict separation of the fluid from the piezoresistors as well as from other electronic components at the front side of the sensor chip. Poly(N-isopropylacrylamide) (PNIPAAm) as well as photo cross-linkable poly(N-isopropylacrylamide-co-dimethyl-acrylamide-co-2-(dimethyl maleimido)-N-ethyl-acrylamide) (PNIPAAm-DMAAm-DMIAAm) terpolymer have been applied and investigated for organic solvent concentration sensors and salt concentration sensors. The sensor's output voltage was measured during the swelling of the hydrogel under influence of water solutions with different organic and inorganic solute concentrations at different temperatures. A complex "reentrant" swelling behavior of the hydrogel in mixed co-solvents as well as "salting in" and "salting out" effects of different salts were studied. It was found that the change in the gel volume phase transition temperature depends on the solution viscosity and the concentration of the additive affecting the stiffness of the polymer chain in the surrounding solution. The influence of an initial gel conditioning procedure on the signal value and the sensitivity of the proposed chemical sensors was investigated and the measurement conditions necessary for high signal reproducibility and long-term stability were determined.

Solid polymer electrolyte membrane (SPM) acts not only as an actuator but as a small, voltage generating, and fast response sensor. Sensing characteristics of SPM as applied to a flow sensor for a ventilator was studied. SPM was prepared by chemically plating with gold on the surface of Nafion membrane. A new technique using Nafion R-1100 resin was applied to fabricate SPM with an arbitrary thickness between 200-1000 μm. Flow sensing unit and signal amplifier was constructed to measure the induced voltage by bending SPM with air-flow from the ventilator. Induced voltage by SPM ranged 1-100 μV over a ventilator air-flow range of 20-100 L/min. SPM sensor showed linear increase of induced voltage by the increase of flow. This relationship was tested over a range of SPM thickness, length and width. The result was compared with an electro-mechanical coupling model of SPM transducer: data showed consistent result on the relation between the induced voltage and membrane length and thickness while a discrepancy was observed in the relation of membrane width and induced voltage. The result, however, was consistent with the assumption of capacitive component model.

Two different optical fiber-based sensor approaches are compared for the detection of hydrogen gas. The two sensors both use Fabry-Perot techniques that have been investigated for some time for other applications. One involves the use of an Extrinsic Fabry-Perot Interferometric (EFPI) sensor scheme, and the other uses a nanoFabry-Perot (nanoFP) cavity that is formed on the distal end of a fiber endface. It is found in general that the sensitivity of the EFPI sensor is higher than that of the nanoFP, but that its speed of response is slower.

Smart Magnetic Materials (SMM) play growing role in materials science and applications. Due to variety of subjects connected with SMM we have confined ourselves to magnetorheological fluids (MRF), magnetorheological composites (MRC), Giant Magnetostrictive Materials (GMM) and Magnetovision Camera using MR sensors. The MRC used for tests was created by soaking porous material with Magnetorheological Fluid. The experimental set-up used for applying, acquisition, processing mechanical and magnetic signals is shown. Total influence of magnetic field H and amplitude of deformation on damping in tested MRC is presented. Examples of application are discussed. In the second part tests of GMM were performed for rare earth elements alloy (Terfenol-D). High effectiveness in transforming magnetic energy into mechanical one (actuator) as well as mechanical into magnetic (sensor) requires experimental determination and identification. Original stand used in research allowed to fix mechanical and magnetic loads, measurement of signals and signal processing. Exemplary results of model identification comprising own experimental data are presented. The next part of study was aimed at designing a system for measuring the strength of magnetic field surrounding a ferromagnetic specimen subjected to cyclic (or static) loading. A new type of camera for monitoring the magnetic picture of specimen and others objects was constructed. The measurement principle is based on the reverse magnetostriction effect (also called the Villari effect). No external magnetizing field is assumed. The measuring set-up is made up a precision computer controlled X-Y positioner and a basis unit whose main element is a single magnetoresistor or an array of magnetoresistors.

A new class of simple, reliable, lightweight, low packaging volume and cost, self-deployable structures has been developed for use in space and commercial applications. This technology called "cold hibernated elastic memory" (CHEM) utilizes shape memory polymers (SMP) in open cellular (foam) structure or sandwich structures made of shape memory polymer foam cores and polymeric composite skins. Some of many potential CHEM space applications require a high precision deployment and surface accuracy during operation. However, a CHEM structure could be slightly distorted by the thermo-mechanical processing as well as by thermal space environment. Therefore, the sensor system is desirable to monitor and correct the potential surface imperfection. During these studies, the surface control of CHEM smart structures was demonstrated using a Macro-Fiber Composite (MFC) actuator developed by the NASA LaRC and US Army ARL. The test results indicate that the MFC actuator performed well before and after processing cycles. It reduced some residue compressive strain that in turn corrected very small shape distortion after each processing cycle. The integrated precision strain gages were detecting only a small flat shape imperfection indicating a good recoverability of original shape of the CHEM test structure.

Lost Foam Casting (LFC) enables the production of complex castings while offering the advantages of consolidation of components, reduced machining, and recirculation of the casting mold material. In the process, a replica of the desired product is produced of blown polystyrene, coated in refractory slurry, and cast in a dense, unbonded sand mold. In order for the unbonded sand mold to fill into pattern holes and to provide sufficient confining force to prevent the advancing molten front from penetrating beyond the mold boundaries, the sand mold is produced by an overhead raining and flask vibration schedule that encourages fluidization and subsequent densification. The amplitude, frequency, and duration of the flask vibration as well as the rate of sand filling are critical parameters in achieving quality castings. Currently, many foundries use an often-lengthy trial-and-error process for determining an acceptable raining and vibration schedule for each specific mold and rely heavily on simple measurements and operator experience to control the mold making process on the foundry line. This study focuses on developing a wireless sensor network of accelerometers to monitor vibrational characteristics of the casting flask during the mold making stage of LFC. Transformations in the vibrational characteristics of the flask can provide a "signature" for indicating the condition of the unbonded sand mold. Additionally, the wireless nature of the sensor nodes enables the technology to travel across the foundry floor during the casting cycle eliminating the necessity of routine placement and setup.

Vibration and resonance of plates are well known problems in designing and analysis of mechanical structures. While these problems are considered during the design process, significant amount of research has been directed to handle the unforeseen loading situations which may lead to catastrophic events. Different types of techniques (passive and active) were developed to prevent these events. Among these techniques, the implementation of the smart materials such as Shape Memory Alloys (SMAs) and piezoelectric ceramics gained importance for controlling the vibrations through damping or altering the resonant frequencies of the parent structures. Composite materials have become major players in building modern and advanced structures especially plates as a consequence; the development of smart composite structures emerged as an area of high interest. In this paper, the feasibility of SMA wires in controlling the vibration of composite plates through altering the strain energy and hence the natural frequency is investigated. The effect of placing the SMA wires in different directions (longitudinal and angularly transverse) over the composite plates will be studied. Computational and experimental work will be conducted to develop the control strategy to control combined vibration situations. Strain energy analysis of the composite panel using laminate theory considerations was used to relate the strain energy alteration in the panel as a result of the SMA actuation to its effect on the laminate stiffness.

Molecular-level self-assembly processes allow the formation of novel materials with properties that are not achievable using conventional fabrication methods. For example, nanostructured metals and polymers may be combined to form inorganic/organic materials that exhibit properties typically associated with each of these species separately, namely high electrical conductivity and low Young's modulus. The combination of such properties is of interest for a number of engineering applications. For example, methods to form stretchable metal conductors, either on elastomeric substrates or as free-standing materials, have been investigated for some time, in part as a way to overcome the high modulus of sensor and actuator electrode materials, and more generally to address the need for mechanically flexible interconnections in polymer electronic devices, flex circuits, electronic textiles and similar electrical circuit applications. Of particular recent interest for example is summarized in [1] where a process to form electrical connectivity using 100 nm-wide gold stripes evaporated onto polydimethylsiloxane (PDMS) is reported, and where non-zero electrical conductivity was observed for strains up to 22%.

This paper presents intrinsic polymer fiber (POF) sensors for high-strain applications such as health monitoring of civil infrastructure systems subjected to earthquake loading or structures with large shape changes such as morphing aircraft. POFs provide a potential maximum strain range of 6-12%, are more flexible that silica optical fibers, and are more durable in harsh chemical or environmental conditions. Recent advances in the fabrication of singlemode POFs have made it possible to extend POFs to interferometric sensor capabilities. Furthermore, the interferometric nature of intrinsic sensors permits high accuracy for such measurements. However, several challenges, addressed in this paper, make the application of the POF interferometer more difficult than its silica counterpart. These include the finite deformation of the POF cross-section at high strain values, nonlinear strain optic effects in the polymer, and the attenuation with strain of the POF. In order to predict the response of the sensor a second-order (in strain) photoelastic effect is derived and combined with the second-order solution of the deformation of the optical fiber when loaded. It is determined that for the small deformation region four constants are required (two mechanical and two photoelastic properties) and for the large deformation region six additional constants are required (two mechanical and four photoelastic properties). This paper also presents initial measurements of the mechanical response of the sensor and comparison to previously reported POFs.

Optical Fiber Bragg Grating (OFBG) is now widely accepted as smart sensor due to its advantages of electric-magnetic resistance, small size, distributed sensing, durability, and so on. However, to our great regret, the bare FBG can only stand 3000~5000με, which can not satisfy the need of practical strain monitoring of infrastructures, especially for the damage detection, such as crack and large strain. In this paper, new technique of sensitivity-decreasing of FBG strain sensor has been brought forward and a new kind of FBG-based crack sensor is also developed. The novel FBG-based crack sensor (also named large FBG strain sensor) can detect 100,000με at maximum, just like 20mm crack at the calibration length of 20 centimeter, and the accuracy can reach 0.01 mm. The new kind of crack sensor is proper for high accuracy crack detection for long-term structural health monitoring of infrastructures.

For the pump-probe stimulated Brillouin scattering with probe pulse of a few nanoseconds duration and with a finite DC level, the acoustic wave relaxation time varies with the pump power and DC level. For the pump power of 1- 6mW, the acoustic wave relaxation changes between 9 to 90 ns for polarization maintained fiber (PMF) at temperature of -45°C for 2 ns pulse width. When pulse to DC ratio of the probe varies from 10 to 20dB, the acoustic relaxation time changes between 24 to 45ns for single mode fiber (SMF) at 25°C. This induced a power increment spectral feature in detected AC pump signal in the Brillouin loss spectrum of two temperature or strain sections, where both spectral components appeared at the positions much longer than natural phonon relaxation time (~10ns) equivalent length. This can cause problem for the distributed sensor in determining the strain/temperature boundary, and central Brillouin peak fitting due to the multiple peak convolution, and it affects temperature and strain accuracy. We propose the 2^nd order partial derivative of Stokes signal with respect to frequency and position giving a maximum or minimum at the boundary between two different strained sections. This allows finding the true stress or temperature corresponded section.

Recently, strain and temperature measurement results using the first ever spontaneous Brillouin and Raman scattering based fiber optic sensor have been reported (Alahbabi et al., 2004)¹. This contribution reports the performance results of a combined Brillouin and Raman sensor used to measure strain and temperature simultaneously. We report on a sensor based on the combination of a BOTDA loss-based Brillouin sensor and a spontaneous Raman scattering based sensor, which has not been previously reported to date. We have implemented the combined sensor system for operation over useful sensing lengths and show significantly improved temperature and strain accuracy along with superior spatial resolution. This combined sensor system is shown to be capable of separating temperature and strain effects which previously limited Brillouin systems in some applications.

Composite coiled tubing is an emerging technology in the oil and gas sector that presents important advantages compared to the steel coiled tubing and conventional drilling. The composite tube has reduced weight, allowing extended reach and improved fatigue life. An additional advantage resides in the fact that the coiled tube wall can contain and protect additional functional elements, such as electrical conductors and fiber optics for sensing and data communication. Sensing systems based on Brillouin and Raman scattering can be used to verify the pipe operational parameters, prevent failure, optimize oil production from the well, provide strain distribution along the tubing and detect hot-spots in high-power cables. The integration of such sensing elements into composite tubing presents additional advantages and challenges. On one hand the embedded sensors are protected by the composite material and can be installed during production, avoiding external installation that could interfere with the tubing operations. In the other hand, the integration of optical fiber sensors into the composite structure requires the development of appropriate packaging and installation techniques that allow easy handling during production and avoid and damage to the sensor and the composite structure itself. This contribution presents the sensing cable designs for temperature and strain sensing in a composite coiled tubing as well as testing results form initial field demonstrations.

Distributed sensors based on time-domain Brillouin scattering have typically had spatial resolutions in the metre range, with some advanced systems improving upon this by an order of magnitude. Resolution in the centimetre range generally has been made possible by using correlation based systems or frequency-domain approaches. Both of these techniques suffer from practical limits on overall sensing length and/or acquisition speed. We present a new technique which uses dark pulses to implement a time-domain sensor system that provides centimetre resolution, short acquisition times and minimal restrictions on sensing length. The method is verified through simulation and results are shown to demonstrate the technique's efficacy in two practical applications.

Standardization activities for fiber optic sensors are increasingly discussed in the scientific as well as users community. Although numerous standards for the characterization of fiber optic components have been available for years, guidelines or extensive standards for use of fiber optic sensors are still 'in statu nascendi'. Not only fiber sensor users are interested in getting guidelines and technical recommendations, manufacturers are also interested in getting technical standards for validation and specification. Development of standards for fiber optic sensors will be intrinsically very complex and thus different from standards for optical fibers and their components. They have to cover different physical mechanisms due to different sensor principles for a multitude of measurands, application fields, and types. The paper gives, first, a survey of recent international activities in this field. It will propose, second, a possible structure for fiber optic sensor characterization standards as well as a structure for guidelines needed for the most frequent practical applications. Special standardization issues to be included in discussion also concern: * choice and design aspects for sensors for mechanical quantities (particularly strain and deformation) * consideration of possible environmental and measurement-relevant circumstances on-site * proof test conditions * requirements on application techniques to bring the sensor system into service appropriately. The discussion in European and worldwide committees on fiber optic sensors that already exist or recently have started should cover all mentioned standardization aspects. Some problems with the establishing of manpower that is fully available for this extensive work are discussed.

The paper gives an overview of reliability, availability, and maintainability of fiber optical sensors, three key factors on which standards and validation should be based and which are required for successful industrialization. The examples given are based on two long term applications with fiber optical Bragg gratings - the surveillance of two bridges (civil engineering). However, similar reflections are required for any type of application and any optical fiber sensors. Recommendations are given to improve the confidence and acceptance of possible users in fiber optical sensing systems. It is shown that with proper installation lifetimes of 50 years are possible.

This paper describes the use of FOX-TEK's long gage-length FT fiber optic sensors (FOS) for monitoring the integrity of pipelines and refinery components. Site assessment protocols and installation methods are described, in addition to the different FOS configurations required to monitor component integrity. It is shown how sensor information can also be used for process control, involving the monitoring of line temperature, pressure, and pipe wall thinning. Models are described that allow the operator to interpret field data to detect corrosion rates, pipe bending, movement and buckling.

Distributed fiber optic sensing presents unique features that have no match in conventional sensing techniques. The ability to measure temperatures and strain at thousands of points along a single fiber is particularly interesting for the monitoring of large structures such as pipelines, flow lines, oil wells, dams and dikes. Sensing systems based on Brillouin and Raman scattering have been used for example to detect pipeline leakages, verify pipeline operational parameters, prevent failure of pipelines installed in landslide areas, optimize oil production from wells and detect hot-spots in high-power cables. The measurement instruments have been vastly improved in terms of spatial, temperature and strain resolution, distance range, measurement time, data processing and system cost. Analyzers for Brillouin and Raman scattering are now commercially available and offer reliable operation in field conditions. New application opportunities have however demonstrated that the design and production of sensing cables is a critical element for the success of any distributed sensing instrumentation project. Although standard telecommunication cables can be effectively used for sensing ordinary temperatures, monitoring high and low temperatures or distributed strain present unique challenges that require specific cable designs. This contribution presents three cable designs for high-temperature sensing, strain sensing and combined strain and temperature monitoring as well as the respective testing procedures during production and in the field.

Many architectures of fiber Bragg grating (FBG) interrogation systems used for mechanical motion (strain, acceleration, etc.) detection utilize interferometry for some part of the demodulation process. Using a hybrid Mach-Zehnder/tunable filter/3-by-3 coupler system architecture as a testbed, this paper examines error sources in the demodulation process giving rise to both/either accuracy and/or resolution degradation in the demodulated output. In particular, realizations of degradation metrics such as noise rise and harmonic distortion are reported due to inaccuracy in demodulation parameters, such as coupler parameters or photodetector voltages. Error models are developed where appropriate for comparison between prediction and measurement.

Non-destructive evaluation (NDE) techniques for condition monitoring in remote solid structures have evolved vastly in the last few years. Algorithms for estimation of sensor integrity and for noise correction form a crucial aspect of NDE. This paper presents a sensor validation approach that verifies sensor integrity, identifies and corrects noise effects and selects the best possible array of sensors for multi-sensor fusion. The proposed methodology uses a novel change detection algorithm for noise correction and a clustering algorithm to isolate useful signal information from the sensor data. It was used for sensor selection in a NDE field study, where multiple sensors were used to examine a solid structure. The methodology achieved 97% accuracy in the experiments, indicating its efficacy.

Fiber optical strain sensors possess several advantages such as light weight, small dimension, high temperature endurance, dielectric nature, and immunity to electromagnetic interference, that meet the basic requirements to be a smart structure sensing element. As a sensor, it is expected that the strains between the optical fiber and host structure are the same. However, due to the existence of the adhesive layer and protecting coating, part of the energy would convert into the shear deformation. Thus, the strain of the optical fiber is different from the host structure. In this paper, experimental tests are performed to reveal the differential strains between the fiber-optic sensor and test specimen. Mach-Zehnder interferometric type fiber-optic sensor is adopted to measure the strain. The direct peak counting method is used to calculate the induced strain in the fiber-optic sensor. An electric strain gauge is attached to the test specimen to measure the strain in the specimen. Experimental results show that the strain measured at the optical fiber is lower than the true strain in the test specimen. The percentage of the strain in the test specimen actually transferred to the optic fiber is dependent on the bonded length of the fiber. Parametric study shows that the longer of bonded length the more strain is transferred to the optic fiber.

Stay cables are the main load-bearing components of stayed-cable bridges. The cables stress status is an important factor to the stayed-cable bridge structure safety evaluation. So it's very important not only to the bridge construction, but also to the long-term safety evaluation for the bridge structure in-service. The accurate measurement for cable load depends on an effective sensor, especially to meet the long time durability and measurement demand. FBG, for its great advantage of corrosion resistance, absolute measurement, high accuracy, electro-magnetic resistance, quasi-distribution sensing, absolute measurement and so on, is the most promising sensor, which can cater for the cable force monitoring. In this paper, a load sensor has been developed, which is made up of a bushing elastic supporting body, 4 FBGs uniformly-spaced attached outside of the bushing supporting body, and a temperature compensation FBG for other four FBGs, moreover a cover for protection of FBGs. Firstly, the sensor measuring principle is analyzed, and relationship equation of FBG wavelength shifts and extrinsic load has also been gotten. And then the sensor calibration experiments of a steel cable stretching test with the FBG load sensor and a reference electric pressure sensor is finished, and the results shows excellent linearity of extrinsic load and FBG wavelength shifts, and good repeatability, which indicates that such kind of FBG-based load sensor is suitable for load measurement, especially for long-term, real time monitoring of stay-cables.

With more and more broad applications of the cement-based structures such as neat cement paste, cement mortar and concrete in civil engineering, people hope to find out what their performances should like. The in-service performances of cement-based structures are highly affected by their hardening process during the early-age. But it is still a big problem for traditional sensors to be used to monitor the early curing of cement-based structures due to such disadvantages as difficulties to install sensors inside the concrete, limited measuring points, poor durability and interference of electromagnetic wave and so on. In this paper, according to the sensing properties of the Fiber Bragg Grating sensors and self-characters of the cement-based structures, we have successfully finished measuring and monitoring the early-age inner-strain and temperature changes of the neat cement paste, concrete with and without restrictions, mass concrete structures and negative concrete, respectively. Three types of FBG-based sensors have been developed to monitor the cement-based structures. Besides, the installation techniques and the embedding requirements of FBG sensors in cement-based structures are also discussed. Moreover, such kind of technique has been used in practical structure, 3rd Nanjing Yangtze Bridge, and the results show that FBG sensors are well proper for measuring and monitoring the temperature and strain changes including self-shrinkage, dry shrinkage, plastic shrinkage, temperature expansion, frost heaving and so on inside different cement-based structures. This technique provides us a new useful measuring method on early curing monitoring of cement-based structures and greater understanding of details of their hardening process.

Thermo-plastic tape (TPT) provides delineation on highways around the world. The thickness of TPT on pavement is a very important parameter to control the quality of TPT, calculate durability of TPT, and provide information for the maintenance and replacement of TPT. Traditionally, the thickness measurement is conducted by using pre-embedded plates and measuring the thickness of TPT after spraying of the TPT marking materials. This method is labor intensive and cannot obtain a continuous-thickness profile. Developing an automatic thickness measurement system for TPT marking materials is critical to pavement management and public safety. The measurement system developed in this paper uses laser triangulation technique to detect the thickness of TPT. A dedicated digital laser signal processing circuit is developed to restore thickness information. The thickness measurement system provides continuous real-time thickness measurement of TPT. Lab and field tests under various conditions with TPT marking materials on real pavement surfaces were conducted. The test results showed that the measurement system is capable of reaching the resolution of 5 mils on pavement. The developed system for thickness measurement of TPT has a 267 KHz working frequency, which is the highest among similar devices. The high speed allows the system to provide higher accuracy and more flexibility in various applications.

Ground penetrating radar (GPR) is a non-destructive and continuous electromagnetic (EM) detection technique for civil and environmental parameter measurement applications such as pavement condition and soil property characterization. This technique is based on the measurement of the travel time and reflection amplitude of a short EM pulse, which are functions of medium properties. Most GPR measurements of sub-layer thickness are conducted based on the priori knowledge of dielectric constants of the pavement materials. And actually, the dielectric constant is an unknown but important parameter in the applications. For some applications, the dielectric constants are estimated based on manuals or tables that can only provide rough results not the real changes of pavement materials. In some other cases, the dielectric constants are estimated by using the surface reflectivity information. However, such method is not applicable for rough surface and ground-coupled GPR applications. Compared to the air-launching GPR mode, the ground-coupled mode is more complicated because of the coupling effect between the antennas and ground. In this paper, numerical simulations about the wave propagation paths of the ground-coupled GPR are conducted. The simulation results reveal some interesting ray paths of GPRs in the ground-coupled mode. And based on the simulation results, new methods are introduced for calculating the pavement dielectric constant and thickness directly from the ground-coupled GPR data. Finally, applications and field test results for pavement evaluation are presented.

Packaged FBG (optical fiber Bragg Grating) strain sensor with good properties of high durability, low cost and reliable installation is in the great need of practical long-term Structural Health Monitoring (SHM) system for civil insfrastructures, especially for those under harsh environment, such as corrosion, high fatigue, etc. Aiming at the practical applications of FBG in such areas, 2 kinds of low cost strain sensors, prototype-packaged FBG sensor and embracing slice packaged FBG sensor, for steel rebar and small cable are developed. And their sensing properties of the sensors under dead load have been tested. The experimental results show good feasibility and advantages of such kinds of sensors for steel rebar or cable strain measurement for practical civil infrastructures under harsh conditions.

In this paper, we present a feature selection and classification approach that was used to assess highly noisy sensor data from a NDE field study. Multiple, heterogeneous NDT sensors were employed to examine the solid structure. The goal was to differentiate between two types of phenomena occurring in a solid structure where one phenomenon was benign, the other was malignant. Manual distinction between these two types is almost impossible. To address these issues, we used sensor validation techniques to select the best available sensor that had the least noise effects and the best defect signature in the region of interest. Hundreds of features were formulated and extracted from data of the selected sensors. Next, we employed separability measures and correlation measures to select the most promising set of features. Because the NDE sensors poorly described the different defect types under consideration, the resulting features also exhibited poor separability. The focus of this paper is on how one can improve the classification under these constraints while minimizing the risk of overfitting (the number of field data was small). Results are shown from a number of different classifiers and classifier ensembles that were tuned to a set true positive rate using the Neyman-Pearson criterion.

Pavement marking materials provide delineation on highways around the world. The condition of the marking materials is very important for the driver's safety as well as the comfort and the driving expenses. Currently thermoplastic pavement marking materials (TPMM) are widely used in states. Measuring the thickness of TPMM on pavement is an essential index to monitor the contractors, calculate durability of marking materials, and provide better information for the pavement marking evaluation. In recent years to measure the thickness of TPMM, a procedure involving pre-embedded plates sprayed with the marking materials has been widely accepted. This method is labor intensive, and cannot obtain a continuous-thickness profile. Therefore there are demands to develop a high-speed automatic measuring system for determining the thickness and uniformity of marking materials. In this paper, a laser range sensor based on auto-synchronized laser scanning is proposed for the thermoplastic pavement marking material thickness measurement. Compare to classical triangulation method, this approach doesn't scarify the system resolution for large field of view and it is more suitable for highway speed measurement. To achieve high speed measurement, PSD (Position Sensitive Detector) is used in the prototype system instead of CCD (Charge Couple Device) in traditional auto-synchronized system. The standoff distance and transverse scan range of the prototype system both are 1 foot. The lab test results show that the prototype system can measure the thermoplastic type thickness with error in 5mil at laser scanning rate up to 50Hz.

Accurate measurements of soil water content are important to land activities, especially those involving agriculture, forestry, hydrology, and engineering. In this paper, a theoretical and experimental study of the microwave moisture measurement sensors is conducted. A phase-based moisture sensor system using a transmission line sensor is designed. The amplitude of the transmission measurement is a strong function of the conductivity (loss of the media) and the imaginary part of the dielectric constant, and the phase is mainly a strong function of the real part of the dielectric constant. One can obtain the soil moisture information from measuring the phase shift of the transmitted waves. Microstrip resonator sensors are also studied and fabricated. The effective permittivity will change if a dielectric material is present near the substrate of the resonator, which causes the shift of the resonant frequency. The measured data show that both sensors are sensitive and accurate.

A new Sensor Validity Monitoring, Verification, and Accommodation (SVMVA) technique based on an artificial neural network is developed for a self-repairing Flight Control System (FCS). For the proposed system, the Learning Vector Quantization (LVQ) method is employed as the on-line, real time learning, monitoring, and estimation tool. In order to conduct a feasibility study, we applied the developed algorithm to a flight vehicle simulator. The simulation results show that the proposed SVMVA with LVQ can instantly detect the failure of physical sensors and accommodate them for more than 30 minutes. By employing this type of analytical sensor redundancy, a flight vehicle can save power, weight, and space, which are required for installing redundant physical sensors.

A demodulation system employing neural networks is used to process the non-linear signal from an extrinsic Fabry-Perot interferometric (EFPI) sensor. A sinusoidal strain is theoretically shown to produce well-defined Bessel harmonics in the EFPI signal. The neural network demodulator (NND) uses a Fourier Series Neural Network to separate the Bessel harmonic components of the EFPI signal and a Back-Propagation Neural Network is used to predict the strain levels through the analysis of the Bessel harmonics. The NND is first simulated in a computer program and then actually employed in an experimental setting to determine the frequency response of a 25 cm composite cantilever beam. A function generator was used to drive a PZT actuator attached to the composite beam and resulting periodic strain was measured by the EFPI; the frequency of the composite beam was varied between 10 Hz and 900 Hz. The NND demodulated the EFPI signal and determined the frequency response of the composite beam. The results show that the NND accurately reproduced the natural frequencies and mode shapes of the cantilever beam.

The purpose of this work is to make use of hybrid automata for vibration control reconfiguration under system failures. Fault detection and isolation (FDI) filters are used to monitor an active vibration control system. When system failures occur (specifically parametric faults) the FDI filters detect and identify the specific failure. In this work we are specifically interested in parametric faults such as changes in system physical parameters; however this approach works equally well with additive faults such as sensor or actuator failures. The FDI filter output is used to drive a hybrid automaton, which selects the appropriate controller and FDI filter from a library. The hybrid automata also implements switching between controllers and filters in order to maintain optimal performance under faulty operating conditions. The biggest challenge in developing this system is managing the switching and in maintaining stability during the discontinuous switches. Therefore, in addition to vibration control, the stability associated with switching compensators and FDI filters is studied. Furthermore, the performance of two types of FDI filters is compared: filters based on parameter estimation methods and so called "Beard-Jones" filters. Finally, these simulations help in understanding the use of hybrid automata for fault-tolerant control.

Passive vibration shunt control using piezoelectric material (PZT) and an electrical network can remove considerable amount of vibration energy from flexible structures. In this paper, an analytical study of parallel passive resistor-inductor (R-L) piezoelectric vibration shunt control on a beam structure by using the Hamilton's principle, Galerkin's method is presented. However, the efficiency of such vibration control method relies on the optimization of vibration energy transfer between a structure and piezoelectric material. In this paper, the strain energy transfer within the composite material, which is made of two layers of different materials, is analyzed. It indicates that neutral axis of the composite material has some influence on the optimization of the strain energy transfer between the structure and PZT. The passive vibration shunt control is sensitive to frequency shift of structures. However, in reality, the natural frequencies of flexible structures often vary somewhat due to environment change, such as boundary conditions, temperature variation, etc. The effectiveness of the vibration shunt control will be significantly reduced when the frequency of the shunt circuit does not match the natural frequency of the structure. In this paper, a method of estimating the resonant frequencies of structures using adaptive IIR notch filter is presented. With online frequency detection, the inductor value is possible to be adjusted in real time by some kind of controllable capacitors and resistors to track the frequency change of structures.

In vitro biochemical synthesis is considered a major challenge in replicating cellular functions in engineered systems. Presented is the first nanosized hybrid factory where biochemical reactions take place resulting in the production of biomolecules. A cellular ATP synthesis process is reconstructed in vitro within a bubble architecture using engineered artificial organelles. This is the first introduction of biochemical synthesis from a multiprotein polymersome system and the demonstration of complex proteins' stable functionality in an artificial structure. This hybrid system is expected to have wide application in a number of fields ranging from the in vitro investigation of cellular metabolism to the synthesis of a new class of functional materials.