Fiber Optic Strain Sensors Research Articles

Distributed Fiber Optic Strain Sensing for Geomechanical Monitoring: Insights from Field Measurements of Ground Surface Deformation

In recent years, distributed fiber optic strain sensing (DFOSS) technology has demonstrated a solution for continuous deformation monitoring from subsurface to surface along the wellbore. In this study, we installed a single-mode optical fiber cable in a shallow trench to establish an effective technique for ground surface deformation mapping. We conducted three experimental field tests (iron plate load, water tank filling up load, and airbag inflation) in order to confirm the strain sensitivity of DFOSS for static loads, dynamic overload, excavation, subsidence, and uplift. This paper also presents two installation methods to couple the fiber cable with the ground under various environmental conditions; here, the fiber cable was installed in a shallow trench with one part buried in the soil and another part covered with cement. Our results suggest that covering the cable with cement is a practical approach for installing a fiber cable for ground surface deformation monitoring. By combining this approach with wellbore DFOSS, accurate surface–subsurface deformation measurements can be obtained for three-dimensional geomechanical monitoring of CO2 storage and oil and gas fields in the future.

Self‐Powered Stretchable Mechanoluminescent Optical Fiber Strain Sensor

Strain sensors that can work sustainably and continuously without any external power supply are highly desirable for future wearable and implantable devices. Herein, a self‐powered stretchable strain sensor based on the integration of mechanoluminescent phosphors with an elastomer optical fiber is proposed and developed. This mechanoluminescent optical fiber is capable of emitting light just driven by external strain, without the need of an external light source or electric power. The strain‐induced emitted light can be collected and guided along the mechanoluminescent optical fiber. The sensor exhibits linear strain response up to 50% and high‐accuracy strain measurement (±1%). Moreover, this optical fiber strain sensor displays consistent signals over 10 000 stretch–release motion cycles, which demonstrates the good durability of the sensor. Due to the excellent light confinement of the elastomer optical fiber, this strain sensor is demonstrated in both bright‐ and dark‐field measurements, wearable gloves, and an implantable sensing device, thereby demonstrating potential as a promising technology for future self‐powered optical sensor systems.

Noise Cancellation of Helicopter Blade Deformations Measurement by Fiber Bragg Gratings.

The work presents data treatment methods aimed at eliminating the noise in the strain sensor data induced by vibrations of the helicopter blade in flight conditions. The methods can be applied in order to enhance the metrological performance of the helicopter weight estimation system based on the deformation measurement of the main rotor blades. The experimental setup included a composite plate fixed to the vibrating stand on the one end, with six fiber-optic strain sensors attached to its surface. In this work, the procedure of the optimal linear smoothing (POLS) and 3D-invariant methods were used to obtain monotone calibration curves for each detector, thereby making it possible to distinguish the increase of load applied to the free end of the plate with an increment of 10 g. The second method associated with 3D invariants took into account 13 quantitative parameters defined as the combination of different moments and their intercorrelations up to the fourth-order inclusive. These 13 parameters allowed the calculation of the 3D surface that can serve as a specific fingerprint, differentiating one set of initial data from another one. The combination of the two data treatment methods used in this work can be applied successfully in a wide variety of applications.

Effects of bonding on the performance of optical fiber strain sensors

Effects of bonding on the performance of optical fiber strain sensors

One-year operational modal analysis of a steel bridge from high-resolution macrostrain monitoring: Influence of temperature vs. retrofitting

Vibration monitoring from strain data is a promising alternative to the more conventional acceleration-based monitoring because a dense measurement grid can be achieved at a relatively low cost and because strain mode shapes are more sensitive to local stiffness changes than displacement mode shapes. However, the feasibility of monitoring strain mode shapes of full-scale civil structures, where the operational dynamic strain levels are of very low amplitude and temperature changes can influence the modal characteristics, has remained an open question. The present work provides a proof of concept in which the deck of a steel tied arch railway bridge is instrumented with eighty Fiber-optic Bragg Grating strain sensors, multiplexed in four fibers, that are interrogated with a technique that achieves high accuracy and precision. For more than a year, the natural frequencies and strain mode shapes of ten modes have been automatically identified from operational strain time histories, with typical root-mean-square values of 0.01 microstrain, on an hourly basis. Furthermore, using these modal data, the influence of temperature fluctuations and that of a retrofitting of the hangers connecting the bridge deck and the arches, which took place during the monitoring period, are extensively investigated. Both have an influence on the overall stiffness of the bridge and therefore they result in clear changes in the natural frequencies. They do not have an influence on the local stiffness and therefore they do not influence the strain mode shapes, except when the retrofitting induces an interaction between previously well-separated modes.

Laboratory Investigation of the Structural Performance of a Corrugated Steel Culvert under Increasing Cover Depth

The performance of large diameter corrugated steel culverts/pipes under varying cover depth up to deep burial has previously not been investigated in a laboratory setting due to limitations associated with the application of overburden pressures. Using the new deep burial simulator at Queen’s University, it is now possible to test flexible pipes up to 3 m in diameter up to a simulated burial depth of approximately 17 m. In this study, a 2-m diameter corrugated steel pipe (CSP) culvert was instrumented with displacement transducers, strain gauges, and distributed fiber optic strain sensors and was tested under increasing overburden pressure up to a total of 358 kPa (equivalent to a depth of 17.9 m of soil with a unit weight of 20 kN/m3). The diameter change values along the length of the culvert were within 10% of each other, suggesting that the simulator produces approximately uniform loading. The Canadian bridge design code produced thrust estimates within 10% of the measured response but did not predict the development of localized plastic hinges seen in the experiment.

Active Reservoir Pressure Management with Guidance and Surveillance by Distributed Fiber-optic Strain Sensing

CO2 injection and storage in aquifers can cause pore pressure build up and deformation of the aquifer-caprock system due to extra-fluid accumulation. Active reservoir pressure management, a concept that using brine production before or during CO2 injection to reduce reservoir pressure build up, has been suggested to avoid potential risks posed by geomechanical deformation during large-scale CO2 injection [1], [2]. Sedimentary formations usually develop heterogeneities in fluid properties and mechanical properties. When conducting CO2 injection or brine production, acquiring the in-situ information of pore pressure and fluid distribution and rock deformation would be much helpful for the project operating. In this presentation, we propose to give guidance and surveillance of the CO2 injection and brine production operations in real time using a distributed fiber optic strain sensing (DFOSS) system. We show the field and lab studies and numerical simulation results to demonstrate the feasibility and the advantages when using DFOSS for pressure management in a storage reservoir. Existing difficulties when using DFOSS are also presented.

Автоматизированная волоконно-оптическая система мониторинга устойчивости прибортового массива карьера и отвалов

This article ls with the issues related to the development of a system for monitoring the deformation and displacement of the rock mass leading to the collapse of the quarry sides. Monitoring system uses point-to-point fiber-optic sensors. Fiber-optic sensors and control cables of the communication line are made based on the single mode optical fibers, which allows to measure with high accuracy the deformations and displacements of the rock mass at a distance of 30-50 km. To create fiber-optic pressure sensors, an optical fiber of the ITU-T G. 652.D standard is used. Laboratory sample is developed concerning the point fiber-optic sensor made based on the two-arm Mach-Zender interferometer using a single mode optical fiber for monitoring strain (displacements) with a change in the sensitivity and a reduced influence of temperature interference leading to zero drift. The article presents a mathematical apparatus for calculating the intensity of radiation of a light wave passing through an optical fiber with and without mechanical stress. A laboratory sample of single mode optical fibers based on the Mach-Zender interferometer showed a fairly high linearity and accuracy in the measurement and can be used to control the strain of the mass after appropriate refinement of its design. Mathematical expressions are also given for determining the intensity of the light wave when the distance between the fixing points of a single mode optical fiber changes depending on the change in the external temperature. A diagram for measuring strain using a point fiber-optic strain sensor is developed. Hardware and software package is developed, which can be used to perform a number of settings of measuring channels. The work is aimed at solving the production problems of the Kenzhem quarry of AK Altynalmas JSC.

An extension of the strain transfer principle for fiber reinforced materials

Fiber optical strain sensors are used to measure the strain at a particular sensor position inside the fiber. In order to deduce the strain in the surrounding matrix material, one can employ the strain transfer principle. Its application is based on the assumption that the presence of the fiber does not impede the deformation of the matrix material in fiber direction. In fact, the strain transfer principle implies that the strain in fiber direction inside the fiber carries over verbatim to the strain inside the matrix material. For a comparatively soft matrix material, however, this underlying assumption may not be valid. To overcome this drawback, we propose to superimpose the matrix material with a one-dimensional model of the fiber, which takes into account its elastic properties. The finite element solution of this model yields a more accurate prediction of the strain inside the fiber in fiber direction at low computational costs.

Recent developments in polymer optical fiber strain sensors: A short review

Polymer optical fiber (POF) strain sensors have attracted increasing attention owing to the unique features of polymer over silica such as lower Young's modulus, larger elastic strain limit, higher fracture toughness, biocompatibility, and lower production cost. Several POF strain sensors have been developed in recent years for applications in various technological fields, including structural health monitoring in civil construction and aerospace industries, biomedicine, and robotics. The principles of operation, prospects, and challenges of the POF strain sensors are discussed in this article under five broad categories: POF fiber Bragg grating sensors, intensity-based POF sensors, multimodal interference-based sensors, Brillouin-frequency-based sensors, and Fabry–Perot cavity sensor. This review aims to highlight areas where further research is required for improving the performance and operating range of POF strain sensors.

Application of two types of embedded fiber-optic sensors for process-induced strain measurement in cement mixture

Two types of fiber-optic sensors applied to process-induced strain measurements of cement mixture are compared in this study. Point fiber-optic strain sensors based on the Bragg grating and distributed fiber-optic strain sensors were embedded into cement sample at the manufacturing stage. Embedded optical fibers did not have any additional protective coating except standard one (polyimide or acrylate). Both systems remain their integrity and operability after casting and hardening of the studied material and show the good agreement in strain measurements at the period taken into consideration.

NTE material employment in temperature resistive high sensitive fiber optic strain sensor development

In this paper, an optical strain sensor with automatic temperature compensation is presented. The strain sensitivity is 198.547 pm/με, which is nearly 2.8 times that of the latest generation multilayer optical fiber strain sensor based on mode field diameter (70.77 pm/με). This increase in sensitivity is due to the particular structure within which the optical fiber sensor is installed. This structure amplifies the applied strain and transfers it to the optical fiber. In order to compensate for the temperature effects, employing a negative temperature expansion (NTE) element is essential. In addition, applying an initial strain is required to adjust the system performance. As a result, the entire sensor system is automatically compensated for the temperature with less than 1 percent error.

High sensitivity pressure measurement using optical fibre sensors mounted on a composite diaphragm.

A pressure sensor specified for aerodynamic applications and based on optical fibre strain sensors mounted on a circular glass fibre reinforced polymer membrane is presented. The use of two fibre optic strain sensing technologies is explored, the novel intrinsic fibre segment interferometry (FSI) approach and fibre Bragg gratings (FBGs), with the use of FSI shown to offer a pressure resolution that is 15 times larger than that achieved using an FBG. A number of design and fabrication issues are considered, including the position of the fibres relative to the neutral axis of the membrane and the influence of the membrane support structure on the thermal and pressure sensitivities of the sensor, with particular regards to pressure and temperature discrimination.

Monitoring of rebar corrosion in concrete structures using a lens-based plastic optical fiber (LPOF) sensor

Corrosion of reinforcement in concrete is one of the major causes for deterioration of concrete structures. This work presents an approach in the monitoring of concrete structures for damage induced by corrosion of steel in concrete using a lens-based plastic optical fiber (LPOF) strain sensor. The optical fiber sensor offers the advantage of being light weight, small in size, low-cost, immune to electromagnetic interference and it does not pose any spark hazard. The intensity-based optical fiber sensor used in this work consists of an emitter fiber, a ball lens, a receiving fiber and a light detector system. The light from the emitter fiber converges to focal point using the ball lens, before it enters the receiver fiber. A change in distance between the ball lens and the receiver fiber would lead to a change in the light intensity transmitted. The intensity change is correlated to the relative distance using a suitable calibration curve. Following the calibration of the sensor, it was used to monitor response of concrete members subjected to flexural loading. Subsequently, the sensor was tested for its ability to monitor corrosion of steel in concrete using an accelerated corrosion test set-up. The sensor shows promising results for detection of corrosion. The test results were used for identification of the corrosion propagation phase, which can be used for predicting the remaining service life of the structures. The optical fiber sensor strain readings were then correlated to the corrosion penetration depth to estimate the extent of damage during the corrosion of rebar. The test results show that it is possible to monitor concrete structures for damage due to flexural loading and corrosion of rebar using an intensity-based LPOF strain sensor.

Resonant fiber-optic strain and temperature sensor achieving thermal-noise-limit resolution.

In the area of fiber-optic sensors (FOSs), the past decade witnessed great efforts to challenge the thermal-noise-level sensing resolution for passive FOS. Several attempts were reported claiming the arrival of thermal-noise-level resolution, while the realization of thermal-noise-level resolution for passive FOSs is still controversial and challenging. In this paper, an ultrahigh-resolution FOS system is presented with a sensing resolution better than existing high-resolution passive FOSs. A fiber Fabry-Perot interferometer as the sensing element is interrogated with an ultra-stable probe laser by using the Pound-Drever-Hall technique. Both strain and temperature measurements are carried out to validate the performance of the sensor. The measured noise floor agrees with the theoretical thermal noise level very well.

Analysis of strain changes caused by placing the substrate-bonded optical fiber sensor on the structure surface

The paper proposes a mathematical model for estimating changes in the strain fields caused by the installation of a substrate with an optical fiber sensor on the surface of the controlled structure. It also analyzes the information on changes in the strain tensor components in the zone of sensor location at different dimensions of the structure. It has been shown that these changes depend on the ratio of mechanical characteristics of the substrate and the material of the structure with the fiber optic strain sensor placed on its surface. A comparative analysis of strain changes is made under different loading conditions of the structure with the substrate-bonded optical fiber sensor placed on its surface.

基于游标效应的高灵敏光纤温度和应变传感器

基于游标效应的高灵敏光纤温度和应变传感器

Distributed Fiber-Optic Dynamic Strain Sensor Based on Spectra Correlation of Rayleigh Backscattering

Distributed Fiber-Optic Dynamic Strain Sensor Based on Spectra Correlation of Rayleigh Backscattering

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.

Optical fiber refractive index sensor based on SMF-TCF-NCF-SMF interference structure

A novel optical fiber refractive index (RI) and strain sensor based on the combination of single-mode fiber (SMF), thin-core fiber (TCF), and no-core fiber (NCF) was proposed. Due to the inter-mode interference caused by the mode mismatch, the sensor is sensitive to the RI of the environment but insensitive to temperature. The experimental results show that in the RI range of 1.3333–1.3794, the sensitivity of dip A (1543 nm) and dip B (1565 nm) are 101.9446 nm/RIU and 109.9009 nm/RIU, respectively. In the temperature range of 15–85 ℃, the maximum wavelength shifts are only -3.5 pm/℃ and -4.9 pm/℃ respecitvely for dip A and dip B, indicating that the sensor can eliminate the cross-sensitivity of temperature to the RI. The sensor was used to detect alcohol, sucrose, NaCl and glycerin solution with the same RI and there is no obvious dip shift of the interference spectra. This sensor has the advantages of high RI sensitivities, strong anti-temperature interference ability, compact structure and has the potential application in the health and security monitoring.