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The propeller will generate a lot of harmful vibration and noise underwater. In order to effectively solve the problem of vibration and noise, it is of great significance to accurately obtain the modal parameters of propeller for the design and optimization of the propeller structure. Since it is difficult to measure the load of propeller when it is running underwater, only operational modal analysis (OMA) method can be used to identify the operational modal parameters of propeller. This paper is aimed at solving this problem by taking the metal propeller as the research object, an open-water test platform was built, and the Fiber Bragg Grating (FBG) sensors were used to obtain the underwater strain information of the propeller. Finally, the operational modal parameters of propeller are identified by the Stochastic subspace identification (SSI) method. In addition, the modal simulation analysis of propeller was carried out by using finite element simulation software, and the experimental results were compared with the simulation results. The results show that the stochastic subspace identification method can accurately identify the operational modal parameters of propeller. • In this paper, a contact measurement method based on Fiber Bragg Grating(FBG) Sensing is used to monitor the underwater operation status of the propeller. • Using the Stochastic Subspace Identification method, after removing the harmonic modes by half-power spectral matrix, the operational modal parameters were identified more accurately. • A propeller underwater monitoring system and open-water test platform were designed based on Fiber Bragg Grating sensing network. • The comparison errors are within 15% proves that it is feasible to identify the operational modal parameters of the underwater propeller by Stochastic Subspace Identification method based on the FBG sensing network. [ABSTRACT FROM AUTHOR]

• A heat-resistant fiber Bragg grating (FBG) sensor was used for in-situ acoustic emission (AE) testing at 1000 °C. • Real damage-induced AE signals in a heat-resistant composite material was received with high sensitivity and high stability at different temperatures. • Machine learning-based clustering analysis and waveform analysis of the acquired AE signals were conducted for damage type identification in the composite. • The AE testing was used to study the failure process of the heat-resistant composite after being oxidized. This research established an acoustic emission (AE) testing method applicable at high temperatures using a fiber Bragg grating (FBG) sensor. The method was employed to inspect the process of flexural failure of a heat-resistant carbon–carbon (CC) composite material during a three-point bending test conducted at a temperature as high as 1000 °C. This paper reported the AE testing results. Also, the AE signals with different waveform features were classified by a clustering analysis based on machine learning. Those different AE signal clusters were further associated with different damages, such as matrix crack, inter-ply delamination, and breakage of the fiber bundles. The relation between the damage mechanism and the material failure was then investigated based on the classified AE testing results. The investigation clarified that the progressive behavior of those damages depended on the extent of the material oxidation at elevated temperatures. The analysis agreed with the microscopic cross-section observation. Hence, this article demonstrated that the FBG-based AE testing method was capable of reliable in-situ damage diagnosis under high-temperature environments. [ABSTRACT FROM AUTHOR]

Accurate monitoring and prediction of the operating status of Li-ion batteries (LiBs) are essential for enhancing the longevity and safety of LiB-powered applications. In contrast to conventional battery management strategies that rely solely on voltage, current, and temperature at module level, we present a smart Li-ion cell with an integrated fiber Bragg grating (FBG) optical fiber sensor that enables simultaneous measurement of temperature, force, and displacement at the cell level with a simple beam structure. The Li-ion smart battery sensor scheme realizes the synchronous monitoring of battery mechanical, electrical and thermal multi-physics parameters. We demonstrate that monitoring force is beneficial for enhancing cell life and safety. Specifically, the evolution of peak force upon cycling correlates linearly with the capacity fade, making the force signal a useful state-of-health indicator. Further, the change in cell force is tens of seconds earlier than the change in cell temperature under nail penetration and thermal abuse tests, exhibiting enormous potential for early detection of battery safety incidents, using the Li-ion smart battery scheme, we realize the quantitative description of the evolution of battery structure. By the Li-ion smart battery, it has the ability to improve the quality, reliability and service life of the battery. [Display omitted] • This paper presents a new type of Li-ion smart battery prototype. • This paper proposes a new Multi-Parameter FBG (MP-FBG) sensor. • The MP-FBG sensor has the advantages of multi-function and strong stability. • The Li-ion smart battery helps improve battery quality, reliability and life features. [ABSTRACT FROM AUTHOR]

The damage of buried oil and gas pipeline has the characteristics of randomness and concealment. Pipeline damage monitoring and safety assessment is a research hotspot at present. Combined with the advantages of local high precision of fiber Bragg grating (FBG) and large-scale measurement of ROTDR, a FBG-ROTDR joint system is proposed and FBG-ROTDR based optical fiber sensor is developed to carry out Pipeline safety monitoring. In order to verify the joint system, one leakage model of PVC pipe is established, and multi-point fiber Bragg grating strings and optical fibers are arranged on the PVC pipe for corresponding strain and temperature measurement. Then the technology is used for urban drainage pipeline safety monitoring. The research results show that the FBG-ROTDR joint system can realize local high accuracy strain measurement and continuous temperature measurement of leakage area, and has the function of temperature compensation for local strain measurement. [ABSTRACT FROM AUTHOR]

The small strain stiffness of soils has a significant role in geotechnical design and analysis. In laboratory, the small strain behavior is examined by different techniques including the bender element method for measuring the maximum shear modulus and local displacement transducer (LDT) for measuring Young's modulus at small strains. However, most commonly used LDTs are based on electrical components and have limitations, such as electromagnetic interference and possibility of short circuit in the presence of water. To overcome these limitations, in the present study, a conventional triaxial apparatus has been modified to measure and study the stress-strain behavior of soils at small strains. The major modifications include addition of piezoceramic sensors (bender elements) for measuring the maximum shear modulus and fiber Bragg grating (FBG) sensor-based local displacement transducers (FBG-LDTs) for measuring the stress-strain behavior at small strains. The modified triaxial apparatus has been used to conduct several tests on a completely decomposed granite soil from a site in Hong Kong. The stress-strain behaviors measured by the newly developed FBG-LDTs and an external displacement transducer are compared and discussed. In particular, the shear modulus values obtained using the bender elements, FBG-LTDs, and the external displacement transducer are also compared, discussed, and evaluated. The comparison and assessment show that the FBG-LTDs are more suitable for measuring the small strain behavior of soils. [ABSTRACT FROM AUTHOR]

The thermal stress and tensile creep of early-age concrete that occur during the exothermic chemical reactions between water and cement may result in harmful cracks. Heat of hydration and creep of early-age concrete are described in this paper. An equation for evaluating hydration degree is presented, and a finite-element program for a thermal analysis of hydration heat is developed. Based on the theory of creep and heat of hydration of early-age concrete, the temperature and strains in a subway station structure were simulated using the finite element method. The predicted results are in good agreement with the site-measured data. A parametric analysis of ambient temperature and concrete slab thickness was also conducted. The analysis results indicate that it is not advantageous to reduce the temperature difference, whether the ambient temperature is too high or too low. Creep does not always reduce the undesirable tensile stresses; it may increase structural tensile stresses during the early-age stage of concrete. [ABSTRACT FROM AUTHOR]

The tunnel collapse problem of coal mine is very common and its damage is very serious. It also seriously endangers people's lives and property safety. At present, a variety of instruments are used for tunnel roof structure health monitoring in most of the coal mines at home and abroad. In this paper, a displacement sensor using optical fiber grating technology was designed, which could be used to prevent the problem of coal mine tunnel collapse by monitoring the coal mine tunnel roof displacement. Firstly, finite element analysis was demonstrated to simulate the stress and displacement of coal mine tunnel roof to determine where to install the sensor. Then the characteristics of the fiber Bragg grating sensor were analyzed in detail and the sensor structure was designed according to the actual requirements in the coal mine. At last, the feasibility of the whole system was experimentally verified. The cross-sensitivity of the temperature and displacement issue with FBG sensors could be eliminated by using matched pairs of FBG. The measuring range of 50 mm and the measurement resolution up to 0.06 mm could be obtained with the proposed sensor. [ABSTRACT FROM AUTHOR]

Fiber Bragg grating (FBG) sensors are the most recent type of fiber optic sensors, which are gaining importance in the field of structural health monitoring of civil infrastructure. These are proven to be more versatile due to their distinct advantages such as high sensitivity, immunity to electromagnetic interference, ease of multiplexing, and remote sensing. These are suitable for the long-term monitoring of the structures. The FBG sensors are found to be very effective in strain and temperature sensing. However, the FBG sensors are not self-temperature compensated and the total strain obtained using FBG sensor is the sum of the strain induced due to mechanical load and the apparent strain induced due to temperature. In this article a method to calibrate the apparent strain is discussed. A study is carried out on various structural materials such as mild steel, aluminium, concrete, and carbon fiber-reinforced plastic (CFRP) using bonded and unbounded FBG sensors. This article presents the result in the form of a temperature calibration curve, which can be used to find the actual mechanical strain. [ABSTRACT FROM AUTHOR]

To study the effect of structure combinations on rutting resistance, firstly, dynamic modulus tests and single-layered wheel tracking tests were earned out to get basic parameters and anti-rutting resistance of seven asphalt mixtures designed. Secondly, double-layered structural wheel tracking tests subjected to heavy loads were conducted for three pavement structure combinations made up of asphalt mixtures utilized, and then compared the results with the single-layered ones. Finally, three-directional strain of pavement was got on site utilizing fiber Bragg grating (FBG) intelligent test technology, and the rutting resistance of actual asphalt pavement was evaluated through these results. Results show that rutting resistance of pavement structures cannot be reflected by single-layered wheel tracking test accurately, while the double-layered does. Additionally, modulus combinations with different layers must be taken into account in order to maximize the rutting resistance of asphalt mixtures. [ABSTRACT FROM AUTHOR]

ABSTRACT In this article, we propose a miniaturized flexible interrogator for polarimetric and fiber Bragg grating (FBG) sensors based hybrid sensing scheme embedded in composite materials. The flexible interrogation module comprises of an arrayed waveguide (AWG) for FBG demodulation and an electro optic mach-zehnder interferometric (EO-MZI) intensity modulator for polarimetric sensor demodulation. A customized design of AWG and EO-MZI are presented, and the designed performance resulted in a wide channel spacing of 5 nm and low cross talk of −34 dB between adjacent channels for the AWG, and a low Vπ voltage of ±1.5 V for the MZI-EO. The method for fabrication of the flexible interrogator device is also presented, based on post processing of platinum coated polyimide substrate. The film type interrogation module is compact, with a size of 3.4 × 0.1 × 0.01 cm3. The surface attachable flexible hybrid sensor interrogator is proposed to integrate with photo detector arrays and wireless communication technology to enhance the competency of hybrid sensing scheme in smart sensing composite parts in motion for applications in aircraft, wind rotor blades and so forth. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1167-1174, 2014 [ABSTRACT FROM AUTHOR]

The composite tank has become the trend and focus for the power system of the new generation aerospace vehicles. However, the evaluation methods and monitoring technologies for composite tanks under cryogenic experiments are still challenging problems. In this paper, fiber Bragg grating (FBG) is used to measure the strain and temperature of the stiffened composite tank under room and cryogenic temperature pressurization experiments. Temperature compensation based on the thermal stratification phenomenon is proposed to increase the reliability and accuracy of strain monitoring in cryogenic environment. A non-linear fitting based calibration method of temperature sensitivity coefficient addresses the non-linear relationship between the FBG wavelength and temperature change from liquid nitrogen temperature to room temperature. The results show that the average absolute error of the nonlinear calibration method in the cryogenic test is less than 50 με. It is also illustrated that the structural features of the sensor location can be qualitatively determined according to the strain changes of different sensors. The comparison of strain increments in the cyclic pressurization illustrated that the different performance degradation phenomena of different regions could be observed. These results provide strong support for the high stability and reliability of FBG-based composite tank strain monitoring. [ABSTRACT FROM AUTHOR]

Abstract: The concept underlying metal-coated optical fiber sensors (MCOFSs) is to evaluate the maximum strains previously experienced by host structures from the residual strains induced by an elasto-plastic metal coating. The performances of MCOFSs are altered by the selection of an adhesive as well as the geometric parameters of the adhesive layer. To investigate their effects on sensor performance, a finite element (FE) model was proposed and verified by experiments involving three different adhesives using metal-coated fiber Bragg grating (FBG) sensors. The strain transfer coefficients, the residual strains, and the sensitivity coefficients for the strain level were calculated to examine the influence of the parameters through a finite element analysis (FEA). We found that the nonlinear and plastic properties of the adhesive should be considered to achieve accurate estimation when evaluating the maximum host strains from the residual strains. Moreover, small underlying adhesive thickness and short bonding length are favorable for a MCOFS with 10mm gauge length. Finally, we presented a relationship (among the residual strain, bonding length of MCOFSs, and the maximum host strains) that helps to quantitatively evaluate the maximum host strains from the residual strains. [Copyright &y& Elsevier]

The development is described of fiber Bragg grating (FBG) probes with single or four cores using spheres fixed onto optical fibers comprising Bragg gratings in their cores. Simulations and preliminary experiments were conducted to evaluate the performance of these FBG probes for dimensional metrology with micro parts of high aspect ratio. Simulation and experimental results indicate that a one-dimensional FBG probe with single core can be used to achieve an axial resolution of 100 nm at an aspect ratio of 15:1. A three-dimensional FBG probe with four cores can be used to achieve a theoretical axial resolution as high as that of a FBG probe with single core, with a capability of decoupling two-dimensional radial displacements with a resolution of 13 nm. [ABSTRACT FROM PUBLISHER]

Measurement of temperature and pressure exerted on the leeward surface of a blunt cone specimen has been demonstrated in the present work in a hypersonic wind tunnel using fiber Bragg grating (FBG) sensors. The experiments were conducted on a 30° apex-angle blunt cone with 51 mm base diameter at wind flow speeds of Mach 6.5 and 8.35 in a 300 mm hypersonic wind tunnel of Indian Institute of Science, Bangalore. A special pressure insensitive temperature sensor probe along with the conventional bare FBG sensors was used for explicit temperature and aerodynamic pressure measurement respectively on the leeward surface of the specimen. computational fluid dynamics (CFD) simulation of the flow field around the blunt cone specimen has also been carried out to obtain the temperature and pressure at conditions analogous to experiments. The results obtained from FBG sensors and the CFD simulations are found to be in good agreement with each other. [ABSTRACT FROM AUTHOR]

This study presents the first investigation into the capability of fiber Bragg grating (FBG) sensors to measure interface pressure between the stump and the prosthetic sockets of a trans-tibial amputee. FBG element(s) were recoated with and embedded in a thin layer of epoxy material to form a sensing pad, which was in turn embedded in a silicone polymer material to form a pressure sensor. The sensor was tested in real time by inserting a heavy-duty balloon into the socket and inflating it by using an air compressor. This test was conducted to examine the sensitivity and repeatability of the sensor when subjected to pressure from the stump of the trans-tibial amputee and to mimic the actual environment of the amputee's Patellar Tendon (PT) bar. The sensor exhibited a sensitivity of 127 pm/N and a maximum FSO hysteresis of around ~0.09 in real-time operation. Very good reliability was achieved when the sensor was utilized for in situ measurements. This study may lead to smart FBG-based amputee stump/socket structures for pressure monitoring in amputee socket systems, which will result in better-designed prosthetic sockets that ensure improved patient satisfaction. [ABSTRACT FROM AUTHOR]

We report a blood pressure evaluation methodology by recording the radial arterial pulse waveform in real time using a fiber Bragg grating pulse device (FBGPD). Here, the pressure responses of the arterial pulse in the form of beat-to-beat pulse amplitude and arterial diametrical variations are monitored. Particularly, the unique signatures of pulse pressure variations have been recorded in the arterial pulse waveform, which indicate the systolic and diastolic blood pressure while the patient is subjected to the sphygmomanometric blood pressure examination. The proposed method of blood pressure evaluation using FBGPD has been validated with the auscultatory method of detecting the acoustic pulses (Korotkoff sounds) by an electronic stethoscope. [ABSTRACT FROM AUTHOR]

Abstract: Optimal placement of sensor network determine the performance and cost of sensor network, and sensor range is a key factor of optimal placement. Unlike the traditional sensor, FBG sensor have different detecting probe length in difference angles, due to the sensitivity of FBG in axial direction is much better than the other directions. Sensor layout angle is not discussed in previous studies about FBG sensor network. The layout angle of sensor considered in placement can greatly impact the performance of FBG sensor network. The paper propose a detective model for FBG sensor which fit it is feature based on probability model, and verified the correctness of it by experiment, then particle swarm optimization is used for optimize the placement of FBG sensor network. Finally, the paper compare this optimization result with method which not consider the layout angle of sensor, and that indicates the performance of sensor network is greatly improved by add the layout angle to placement. [Copyright &y& Elsevier]

A monitoring method and sensing system were established using fiber grating sensing technology for the quantitative study of the strata settlement deformation process in similar material models. The rock movement and stress of overlaying strata that exists in a coal mine were simulated in the laboratory using 0.5 m plane stress models equipped with 2-6 fiber Bragg grating sensors in stainless steel and acetate ethylene plastics. For comparison, 2-3 dial indicators were also installed on the overlaying strata adjacent to the fiber optic sensors. Three similar material plane models (500 mmx425 mmx73 mm) were designed and tested to have a geometric similarity ratio of 1 : 800. The relationship between the settlement deformation of overlaying strata and the model test results from the FBG sensor was analyzed. The experimental results indicate that a linearly correlated relationship between the strata settlement deformation of the model and the wavelength drift of sensors caused by deformation, with a stainless steel sensor ratio of 66.17-290.46 pm/mm, and an acetate ethylene plastics sensor ratio of 778.19 pm/mm. The use of the FBG sensor for horizontal displacement and vertical displacement in these similar material test models show that the FBG sensor can measure the changes in displacement, which provides a reference for detecting the internal stress and strain of similar models. The method tested is considered reliable and effective for the real-time monitoring of movement and stresses of overlaying strata. [ABSTRACT FROM AUTHOR]

A new approach of monitoring low-velocity impact events on composite structures was pre-sented and experimentally evaluated. In this approach, impact strain histories of a composite plate were measured with optical fiber sensors. The recorded signals were used to estimate locations and forces of low-velocity impact events. For experimental validation, four-sensor heads were surface mounted at the four corners of a composite panel. The optical sensors caught dynamic strain due to impacts on the panel, and the optical cables transmitted wave-length changes of the sensors. The multiplexed wavelength changes were measured using a high-speed fiber Bragg grating interrogator for the determination of impact location. The locations of impact events were estimated using a neural network program and measured signals. The estimated locations and converted strain signals were taken as the inputs to the process of reconstructing impact forces. Even though the current study is an initial investiga-tion on a simple impact problem, the result shows the possibility that the proposed technique can be applied to low-velocity impact monitoring of general composite structures. [ABSTRACT FROM AUTHOR]

We demonstrate the feasibility of long-period gratings (LPGs) written in microstructured polymer optical fibers (mPOFs) for detecting and measuring the strain rate and magnitude of engineering structures. We validate and compare the results of our experimental tests to a commercial fiber Bragg grating sensor. The encouraging results open the way to the use of LPG mPOF sensors in structural health monitoring applications. [ABSTRACT FROM PUBLISHER]

The present work proposes a new sensing methodology, which uses Fiber Bragg Gratings (FBGs) to measure in vivo the surface strain and strain rate on calf muscles while performing certain exercises. Two simple exercises, namely ankle dorsi-flexion and ankle plantar-flexion, have been considered and the strain induced on the medial head of the gastrocnemius muscle while performing these exercises has been monitored. The real time strain generated has been recorded and the results are compared with those obtained using a commercial Color Doppler Ultrasound (CDU) system. It is found that the proposed sensing methodology is promising for surface strain measurements in biomechanical applications. [ABSTRACT FROM PUBLISHER]

A new method to estimate bending moments of a blade specimen having a constant cross section throughout was developed using fiber Bragg grating sensors. Based on theories of solid mechanics, strains of the simplified model of the specimen were evaluated for various pitching angles and the forces exerted. It was found by both theory and experiment that at least two FBG sensors are necessary to find out the magnitude and direction of the load acting on the specimen from measured longitudinal strain information. A method was also found to estimate the flatwise and edgewise bending moments from the measured strains. An experimental setup that enables pitching the specimen from 0 ° to 180 ° was used to experimentally verify the theoretical findings. The theory and the experimental results showed a fair agreement. [ABSTRACT FROM AUTHOR]

We propose and demonstrate a fiber Bragg grating (FBG) sensor network employing the code division multiple access (CDMA) technique to identify information from individual sensors. To detect information without considering time delays between sensors, a sliding correlation method is applied, in which two different signals with the same pseudo-random binary sequence (PRBS) pattern, but slightly different frequencies, are applied to the source and detector sides. Moreover, for time domain detection, a wavelength-to-time conversion technique using a wavelength dispersive medium is introduced. The experimental results show that the proposed sensor network has a wide strain dynamic range of 2,400 με and a low crosstalk of 950:1. [ABSTRACT FROM AUTHOR]

Low frequency vibration measurements in composite materials using embedded optical fiber sensors are presented in this paper. The two types of fiber sensors embedded are a polarization maintaining photonic crystal fiber (PM-PCF) polarimetric fiber sensor and a fiber Bragg grating (FBG) sensor. A glass fibre reinforced polymer composite material sample is fabricated with both fiber optic sensors embedded in it. A comparison between the performance of both the PM-PCF polarimetric fiber sensor and the FBG sensor embedded in the composite material is also presented. [ABSTRACT FROM PUBLISHER]

Fiber bragg grating (FBG) sensors are currently in use in various fields. However, it is difficult to use these sensors to obtain strain measurements at locations where it is not physically possible to connect the fibers to each other. In the present study, we performed strain measurements using many FBG sensors connected to a single optical fiber and a pair of collimators. The single optical fiber connected to the FBG sensors was installed on a cantilevered beam with another optical fiber line connected to a stationary optical interrogator. The two optical fiber lines were connected by a pair of collimators making use of the fact that light travels in a straight line through space. Our experiment demonstrated that the wavelength of the light changed linearly as it passed between the two collimators, and that this change increased with the applied strain. Accurate strain measurements could be obtained by applying a proposed collimator collection factor. [ABSTRACT FROM AUTHOR]

In the case of composite structures, low-velocity impact events can cause various types of damage that are mostly hidden inside the laminates or occur on the side opposite to the impact. Thus, damage cannot be easily detected by visual inspection or conventional NDT techniques. Moreover, if the damage occurs between the scheduled inspection periods, the possibilities of extensive damage or catast rophic failure can be increased. For these reasons, built-in NDT systems, such as the real-time impact monitoring system, are required in most composite structures for high reliability and ease of maintenance. In this paper, such an impact monitoring system, including impact location detection and damage assessment techniques, wasstudied for composite flat and stiffened panels. In order to acquire the impact-induced acoustic signals, four multiplexed fiber Bragg gratings (FBGs) and commercial high-speed FBG interrogator were used. In signal processing for the detection of impact locations and damage occurrences, neural networks and wavelet transforms were adopted. Finally, these algorithms were embodied using MATLAB and LabVIEW software to obtain a user-friendly interface. [ABSTRACT FROM PUBLISHER]

We compare the performance of four different damage measures based on the full spectral response of fiber Bragg grating (FBG) sensors: spectral bandwidth, number of peaks, cross-correlation coefficient and fractal dimension. These damage measures provide a rapid indication of the extent of damage near the FBG sensor. Each damage measure is applied to data simulating the response of a FBG to a pure strain gradient and experimental data from FBG sensors embedded in a laminate subjected to multiple impacts. The cross-correlation coefficient and number of peaks did not perform well for the experimental data. The spectral bandwidth presented a low sensitivity to noise and a high sensitivity to rapidly increasing strain fields, whereas the fractal dimension was more sensitive to more gradually changing strain fields. Ultimately, the best strategy would be to fuse the results of the spectral bandwidth and fractal dimension damage measures to incorporate the strengths of each approach. At the same time, this study highlighted the challenges in using such spectral data from FBG sensors embedded in structural materials, primarily due to the variability in response between sensors exposed to the same damage states. [ABSTRACT FROM AUTHOR]