Fiber Optic Sensor System Research Articles

Distributed fiber optic temperature sensor based on dynamic calibration of Raman Stokes backscattering light intensity

In a distributed fiber optic temperature sensing system, the intensity of Raman Stokes backscattering light serving as reference light increases with the increase of temperature, leading to measurement errors in the system. A novel method of dynamically calibrating Raman Stokes backscattering light intensity is proposed to improve temperature accuracy for distributed fiber optic temperature sensors. According to the real-time Stokes intensity distribution in the reference fiber, Stokes intensity curve of the whole fiber at a reference temperature is simulated, and the temperature response of Stokes light is corrected. The ratio of Raman anti-Stokes light intensity to the calculated Stokes light intensity is used to demodulate temperature along the fiber. The experimental results indicate that the temperature accuracy of the distributed optical fiber temperature sensor system after making the Stokes optical dynamic calibration is increased up to 4.3 ℃ compared with that from the conventional method. And the accuracy of temperature measurement is improved by 8.9 ℃ when combined with Rayleigh noise suppression method. This study provides a new solution for a distributed fiber optic temperature sensor system to monitor high temperature environment temperature.

Design a Building Information Modeling (BIM) project concept in combination with foundation monitoring on the example of the Abu Dhabi Plaza construction project

With the advent of new technology in the monitoring of buildings and highrise structures it has become possible to monitor damage and defects in existing structures and infrastructures. The need for timely detection of critical points of building structure defects through the use of sensors, as well as the lack of description tools for understanding, visualizing and documenting sensor output data increasingly encourages designers, builders and facility managers to use the capabilities of such a powerful system as the Building Information Modeling System (BIM). The primary goal of any construction project is safety for people, which can only be ensured by proper monitoring of building health, where the presentation and management of the received information about changes in the system and structure can be ensured by using BIM. The purpose of this paper is to describe the application of a distributed fiber optic strain gauge sensor system, and the possibility of integrating the data obtained from the sensors into the BIM system.

Selective Distributed Optical Fiber Sensing System Based on Silicone Cladding Optical Fiber and Rayleigh Backscattering Reflectometry for the Detection of Hydrocarbon Leakages

Selective Distributed Optical Fiber Sensing System Based on Silicone Cladding Optical Fiber and Rayleigh Backscattering Reflectometry for the Detection of Hydrocarbon Leakages

Design and comprehensive characterization of novel fiber-optic sensor systems using fast-response luminescence-based O2 probes

The detection of O2 using optical techniques has now become very important and significant progress has been made in this area over the past few years. The measurement of O2 concentration is a key parameter for diverse applications such as in life sciences, environmental monitoring, industry and biological research, and luminescence-based sensors are a valuable tool for measurements of this type. Often commercial sensors are unable to respond within a short time frame and drift over time - this demonstrates the importance of developing and validating a new technological approach. Given that need, a new sensor has been developed, with a specially-formed tip design coated with a very thin Platinum(II) 5,10,15,20-Tetrakis(2,3,4,5,6-pentafluorophenyl)-porphyrin (PtTFPP)-containing a polystyrene layer. The performance and reproducibility of the sensor design has been studied by comparing three identically fabricated sensor probes, showing that the new probe design has extreme fast response times – of a maximum value, Δt90max ≈ 390 ms for increasing and Δt90max ≈ 250 ms for decreasing O2 concentrations. The sensors created had an accuracy of better than ± 0.03 % O2 over the detection range investigated (between 0 % and 20 % O2) and showed a very stable performance over many hours of use. Examining this in detail through extended continuous use, over 12 h in a 0 % O2 solution, the probe stability was confirmed, showing a very low drift of luminescence decay time of ≈ 0.025 %/h (0.01 µs/h). Furthermore, the temperature ‘cross-talk’ has been studied in the important region between 25 °C and 40 °C (so that temperature corrections can be applied) and its mechanical stability, as well as allowing for compensation for any effects seen, has been confirmed. Given the success of the design developed, this work offers both an effective probe design and illustrates many important criteria for the selection of highly effective O2-sensitive coating materials and thus their use as a measurement tool for different quality control (QC) applications in industry.

Effect of Temperature Fluctuations on the Bearing Capacity of Cold In-Depth Recycled Pavements

This study investigates the influence of the temperature fluctuations on the bearing capacity of cold in-depth recycled (CIR) pavements stabilized with foamed asphalt (FA). Aiming to achieve this goal, non-destructive testing was conducted during mild and high temperatures on a highway CIR pavement, utilizing mainly the FWD device. The back-calculated moduli values were utilized to estimate the strain values within the body of the pavement, while the strains induced using the FWD device were measured with a fiber optic sensors (FOS) system. Moreover, data from the fatigue behavior of the layer materials was also considered. The results of the related analysis indicate that for every 1 °C temperature increase within the body of the AC overlay, an approximately 5.7% increase of the critical tensile strain is expected. Moreover, for every 1 °C temperature increase within the body of the FA layer, an approximately 1.8% increase of the tensile strain at the bottom of the FA layer is expected. The new constructed layers, i.e., asphalt concrete (AC) and FA, sustain much more damage at high temperatures. This was more evident in the upper layer, i.e., the AC overlay.

Denoising using 3 × 3 coupler demodulation

A simple and effective phase demodulation method is 3 × 3 coupler demodulation, owing to its simpler structure than phase-generated carrier demodulation. However, it is difficult to obtain ideal demodulation results because of the diversity of noise sources in an optical fiber sensor system, particularly due to polarization fading. We present a noise processing method based on morphological filtering. First, the characteristics of various noises and their effects on the demodulation of a 3 × 3 coupler are analyzed. Subsequently, the polarization fading phenomenon in a single-mode fiber is analyzed, and the effect of polarization fading on the elliptic fitting demodulation of 3 × 3 couplers is described. The method uses morphological filtering based on an elliptic template to overcome the distortion in the demodulation signal due to polarization fading and other factors. Simulation and experimental results show that the proposed method can improve the stability and precision of phase demodulation technology based on the 3 × 3 coupler.

Upgraded Fiber-Optic Sensor System for Dynamic Strain Measurement in Spallation Neutron Source

We describe an upgraded fiber-optic sensor system and its performance in measuring the dynamic strains in a mercury target of the Spallation Neutron Source (SNS). Strains result from dynamic pressure waves in the stainless-steel mercury target induced by short (~700 ns), intense (up to 23.3 kJ), high-energy (~1 GeV) proton pulses. In the upgraded sensor system, the output of each sensor head is interrogated with a compact, all-fiber based Faraday Michelson interferometer, which generates interference signals with a steady phase shift. Strain waveforms are recovered from the phase-shifted interference signals using a high-speed digital signal processing procedure developed in our previous work. We demonstrate successful measurements of dynamic strain pulses, e.g., <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$400 \mu \varepsilon $ </tex-math></inline-formula> over <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$190 \mu \text{s}$ </tex-math></inline-formula> , on a recently installed SNS target using the upgraded sensor system. The measured strain waveforms are analyzed for more than 20 sensor locations and/or orientations, and provide information regarding the temporal structure of strain profiles and dependence of the strain magnitude on the proton powers of 200 – 1400 kW. The new interrogator also measures the radiation-induced-attenuation (RIA) in the optical fiber, enabling experimental investigations of RIA profiles induced by a 700-ns radiation pulse. The radiation effects on the strain measurement performance are discussed over a radiation dose range of up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${4}\times {10}^{{8}}$ </tex-math></inline-formula> Gy and an RIA compensation method is proposed. The measurements allow insight into the response of this unique piece of equipment and can be used for validation of simulations.

Machine learning identifies liquids employing a simple fiber-optic tip sensor.

We proposed an extremely simple fiber-optic tip sensor system to identify liquids by combining their corresponding droplet evaporation events with analyses using machine learning techniques. Pendant liquid droplets were suspended from the cleaved endface of a single-mode fiber during the experiment. The optical fiber-droplet interface and the droplet-air interface served as two partial reflectors of an extrinsic Fabry-Perot interferometer (EFPI) with a liquid droplet cavity. As the liquid pendant droplet evaporated, its length diminished. A light source can be used to observe the effective change in the net reflectivity of the optical fiber sensor system by observing the resulting optical interference phenomenon of the reflected waves. Using a single-wavelength probing light source, the entire evaporation event of the liquid droplet was precisely captured. The measured time transient response from the fiber-optic tip sensor to an evaporation event of a liquid droplet of interest was then transformed into image data using a continuous wavelet transform. The obtained image data was used to fine-tune pre-trained convolution neural networks (CNNs) for the given task. The results demonstrated that machine learning-based classification methods achieved greater than 98% accuracy in classifying different liquids based on their corresponding droplet evaporation processes, measured by the fiber-optic tip sensor.

Application of the Proposed Fiber Optic Time Differential BOCDA Sensor System for Impact Damage Detection of a Composite Cylinder

An optical-fiber-embedded composite cylinder was fabricated using the filament winding process with an interval of 12 mm in the longitudinal direction of the cylinder. The optical fiber was wound 160 turns around the cylinder, and the straight length was about 125 m. After a total of twelve impact events of 5, 10, 15, and 20 J, the residual strain in the cylinder was measured using the proposed time differential BOCDA sensor system. This method makes the traditionally used optical delay unnecessary while increasing the degrees of freedom of using the modulation rate, which determines the spatial resolution of this measurement system. The modulation rates of optical light in the system were applied up to 16 Gbps, which is an eight-fold increase compared to our previous experiments. Damage maps were obtained by mapping the measured residual strain onto the structure of the cylinder, and compared using three spatial resolutions of 20, 10, and 6.25 mm. In the measured damage map, expansion deformation due to impact was measured at all impact points, and the impact location on the map and the actual location on the cylinder were exactly the same. The map measured from the composite showed a clear point-symmetrical shape with an increase in sharpness as the measurement resolution increased. At the highest resolution, material expansion and compression were observed to alternate with respect to the center of impact, like the surface deformation of a liquid caused by a thrown object. Furthermore, considered together with our previous experiments, we confirmed that this phenomenon propagated from the surface of the composite material to the interior, where the optical fiber was embedded. The total amount of residual strain formed around each impact point was linearly proportional to the applied external impact energy.

A Preliminary Assessment of an FBG-Based Hard Landing Monitoring System

In aeronautics, hard landing is a critical condition as the aircraft approaches the runway with a vertical velocity that exceeds 2 m/s. Beyond that level, the energy that should be then absorbed by the whole structure could cause severe damage to the landing gear and the whole structural system. This document reports on the set-up, execution and results of a preparatory test campaign performed on a small landing gear (LG) demonstrator instrumented with a fibre-optic sensor system. In detail, a leaf spring landing gear was released from a drop tower to detect information about the strain state and the related acceleration history of some specific components during the impact. The objective of the present research is the development of a method for assessing whether hard landing is experienced, and to what extent. Deformation measurements through an integrated Fibre-Bragg Grating (FBG) network allowed retrieving impact velocity by a devoted, original algorithm. The proposed preliminary methodology is the base for assessing a more complex procedure to correlate structural response to the energy entering the structure during the touchdown event.

Assessment of static and dynamic deformations of the orbital station shell by a system of integrating fiber-optic sensors

The problem of safe functioning of space vehicles is under investigation. Spacecraft safety is essentially affected by the impact of fragments of space debris and meteorites. Impact of small particle can lead to a perforation of the structure of a spacecraft or the Space station. The impact can cause formation of a perforation and gradual loss of atmosphere. Under these conditions, it is crucial detecting the point of perforation and take the measures of precaution for the loss of the internal atmosphere. Practically all known methods for testing the integrity of ground-based structures, aircrafts and other complex technogenic objects are inapplicable for solving similar problems of monitoring the spacecraft condition during a spaceflight. To solve this problem, the integrating fiber-optic sensors (IFOS)-based system for monitoring vibration deformation parameters of spacecraft housings’ surfaces is proposed, which can be developed and implemented in the shortest possible time. Mathematical modeling and laboratory studies have confirmed the possibility of using the Integrating fiber-optic sensors system for assessing the dynamic and static parameters of extended structures.

Static and dynamic response of a carbon composite full-scale hydrofoil manufactured using automated fibre placement

Experimental demonstration and performance evaluation on a shape-adaptive carbon composite full-scale hydrofoil manufactured using automated fibre placement (AFP) are presented in this paper. The experimental responses of the hydrofoil are validated with the finite element analysis (FEA) tools. The static performance of the hydrofoil was investigated using quasi-static cantilever load, whereas the dynamic response was studied using experimental modal analysis (EMA) to assess the structural quality of the manufactured hydrofoil. The variation between predicted and experimental modal and bending stiffness was found to be within 20%. Structural strains were also monitored using a network of distributed fibre optic sensors on the surface as well as embedded in conjunction with a network of strain gauges. The outcomes from this work demonstrates a framework of numerical analysis and experimental validation techniques using multiple sensors, which will pave the way towards further demonstrating the structural adequacy and performance of such hydrofoil, made of automated techniques and embedded with optical fibre sensor systems.

Ex-Vivo Measurement of the pH in Aqueous Humor Samples by a Tapered Fiber-Optic Sensor.

A practical demonstration of pH measurement in real biological samples with an in-house developed fiber-optic pH sensor system is presented. The sensor uses 8-hydroxypyrene-1,3,6-trisulfonate (HPTS) fluorescent dye as the opto-chemical transducer. The dye is immobilized in a hybrid sol-gel matrix at the tip of a tapered optical fiber. We used 405 nm and 450 nm laser diodes for the dye excitation and a photomultiplier tube as a detector. The sensor was used for the measurement of pH in human aqueous humor samples during cataract surgery. Two groups of patients were tested, one underwent conventional phacoemulsification removal of the lens while the other was subjected to femtosecond laser assisted cataract surgery (FLACS). The precision of the measurement was ±0.04 pH units. The average pH of the aqueous humor of patients subjected to FLACS and those subjected to phacoemulsification were 7.24 ± 0.17 and 7.31 ± 0.20 respectively.

High-Temperature Monitoring in Central Receiver Concentrating Solar Power Plants with Femtosecond-Laser Inscribed FBG.

This work deals with the application of femtosecond-laser-inscribed fiber Bragg gratings (FsFBGs) for monitoring the internal high-temperature surface distribution (HTSD) in solar receivers of concentrating solar power (CSP) plants. The fiber-optic sensor system is composed of 12 FsFBGs measuring points distributed on an area of 0.4 m2, which leads to obtain the temperature map at the receiver by means of two-dimensional interpolation. An analysis of the FsFBG performance in harsh environment was also conducted. It describes the influence of calibration functions in high-temperature measurements, determines a required 10 nm spectral interval for measuring temperatures in the range from 0 to 700 °C, and reveals wavelength peak tolerances in the FsFBG fabrication process. Results demonstrate the viability and reliability of this measuring technique, with temperature measurements up to 566 °C.

Iterative normalized cross-correlation method for absolute optical path difference demodulation of dual interferometers.

It is still a challenge to realize the absolute optical path difference (OPD) demodulation of multi-interference systems with a narrow spectral interval and small OPD interval. In this paper, an iterative normalized cross-correlation algorithm is firstly proposed for demodulating the multiple absolute OPDs of a dual-interference system and applied to optical fiber sensing system. By constructing a template function in combined form, the optimal solutions of its components and OPDs are solved iteratively based on the reconstruction matrix method and cross-correlation algorithm, respectively. The simulation and experiment show that the demodulation accuracies near the OPDs of 560 µm and 660 µm are both up to 5 nm in different spectral intervals from 45 to 80 nm. The simulation results show that all demodulation precisions at the spectral interval of 55 nm do not exceed 4 nm when the OPD changes in the range of 650-670 µm. Besides, the experimental verification shows the temperature accuracy (0.125 °C) with 95% confidence of T-distribution is very close to the control accuracy (0.1 °C). The proposed algorithm can improve the multiplexing capability of optical fiber sensor system and reduce its cost.

Wearable and Fully-Portable Smart Garment for Mechanical Perturbation Detection With Nanoparticles Optical Fibers

This paper presents the development of a wearable smart textile for mechanical perturbation assessment during gait based on distributed optical fiber sensor system using the transmission-reflection analysis (TRA). In this case, magnesium and erbium co-doped optical fiber is employed as a high scattering medium, which results in high spatial resolution for the technique (in the order of a few millimeters). The optical fiber was embedded in a garment and controlled displacements at predefined locations on the garment were applied, where the simultaneous assessment of displacement amplitude and location was obtained using a slope-assisted technique. In the proposed technique, the slope inverses of the transmission-reflection curves are correlated with the displacement applied on the fiber, where a determination coefficient (R2) of 0.996 was obtained. Then, the sloped-normalized reflection (or backscattered) response is used on the disturbance location estimation with relative errors as low as 3.7%. The on-body application tests show an inherent insensitivity of the proposed smart garment to body movement due to natural gait movements, indicating the feasibility of the proposed approach on detecting only the transverse induced mechanical perturbations. In the wearable tests, the sensor system shows high correlation (R2 higher than 0.98) in the tests with different volunteers (subjected to similar displacements at predefined locations) and millimeter-accuracy on the disturbance location estimation.

基于FPGA的分布式拉曼光纤传感系统

基于FPGA的分布式拉曼光纤传感系统

Fiber-Optic Sensing System for Investigating Flow Drag in Airflow Field

Fiber-Optic Sensing System for Investigating Flow Drag in Airflow Field

Methodology for developing the configuration of an ice load monitoring system for an iceresistant self-propelled drifting platform

The ice-resistant self-propelled platform (IRSPP) named North Pole that is currently under construction at the JSC Admiralty Shipyards is designed to carry out year-round scientific research in the Arctic Ocean. The IRSPP will be equipped with a unique ice loads monitoring system (ILMS). The technical requirements for the ILMS were developed in the Department of Ship Performance in Ice of the AARI. The ILMS should ensure a safe operation of the IRSPP in ice conditions (operational function) and serve as a measuring tool for researching of the mechanics of deformation and destruction of ice (scientific function). Analysis of ice conditions at different stages of IRSPP operation showed that the main scenario of ice interaction with the IRSPP hull will be the action of ice under compression on the middle part of the hull during drift. The monitoring of the stress-strain state of the hull is carried out by a complex system of fiber-optic strain sensors placed on different elements of the hull structures. The largest number of sensors are located on the side plating in the middle part of the IRSPP hull. The locations of the sensors were determined by finite element analysis of the stress-strain state of the IRSPP hull under the action of ice load. To monitor the stress-strain state of the surrounding ice field, up to 16 pressure sensors frozen into the ice are provided. Also, the system receives and stores data on the angles of roll, trim, yaw of IRSPP, its longitudinal, lateral and vertical accelerations, and the surrounding hydrometeorological conditions: wind speed and direction, air temperature, atmospheric pressure, and the geographical position of the platform. ILMS will significantly improve the safety of IRSPP operation during prolonged drift in ice conditions. Besides, the ILMS provides the platform hull with the functions of a measuring tool for studying the mechanics of deformation and destruction of sea ice in interaction with the engineering structures. The main purpose of this work is to create a comprehensive system for studying the processes of ice impact on structures in order to obtain new data about the parameters and nature of ice loads.

Application of the DIC Technique to Remote Control of the Hydraulic Load System

Displacements or deformations of materials or structures are measured with linear variable differential transducers (LVDT), fibre optic sensors, laser sensors, and confocal sensor systems, while strains are measured with electro-resistant tensometers or wire strain gauges. Measurements significantly limited to a point or a small area are the obvious disadvantage of these measurements. Such disadvantages are eliminated by performing measurements with optical techniques, such as digital image correlation (DIC) or electronic speckle pattern interferometry (ESPI). Many devices applied to optical measurements only record test results and do not cooperate with the system that exerts and controls load. This paper describes the procedure for preparing a test stand involving the Digital Image Correlation system ARAMIS 6M for remote-controlled loading. The existing hydraulic power pack (ZWICK-ROELL) was adapted by installing the modern NI cRIO-9022 controller operating under its own software developed within the LABVIEW system. The application of the DIC techniques to directly control load on the real structure is the unquestionable innovation of the described solution. This led to the elimination of errors caused by the test stand susceptibility and more precise relations between load and displacements/strains which have not been possible using the previous solutions. This project is a synergistic and successful combination of civil engineering, computer science, automatic control engineering and electrical engineering that provides a new solution class. The prepared stand was tested using two two-span, statically non-determinable reinforced concrete beams loaded under different conditions (force or displacement). The method of load application was demonstrated to affect the redistribution of bending moments. The conducted tests confirmed the suitability of the applied technique for the remote controlling and recording of test results. Regardless of the load control method (with force or displacement), convergent results were obtained for the redistribution of bending moments. Force-controlled rotation of the beam section over the support was over 50% greater than rotation of the second beam controlled with an increase in the displacement.