Integrated Fiber Optic Sensors Research Articles

An Integrated Fiber Optic Sensor Capable of Simultaneously Measuring of Salinity, Pressure, and Temperature

An Integrated Fiber Optic Sensor Capable of Simultaneously Measuring of Salinity, Pressure, and Temperature

Simultaneous measurement of ammonia concentration and gas pressure based on fiber multi-mode and Fabry-Pérot interference.

A design of an integrated fiber optic sensor for simultaneously measuring ammonia (NH3) concentration and gas pressure is proposed, which is based on a single mode fiber (SMF)-capillary-no core fiber (NCF) single-mode fiber (SCNS) structure. The measurement process is achieved by simultaneously monitoring the wavelength drift appearing in the transmission and reflection spectrum based on multi-mode and Fabry-Pérot interference. In achieving the desired sensor response, the NCF is coated with the zinc oxide (ZnO) film serving as the sensitive material for NH3, and a gas micro-channel is created on the sidewall of the capillary for gas pressure measurement. The experimental results indicate that the sensor with structural parameters optimization presents sensitivities of -35.52 pm/ppm for NH3 concentration and 4158.57 pm/MPa for gas pressure. The proposed sensor based on SCNS structure is capable of achieving excellent stability and consistency in the presence of mutual interference induced by simultaneous measurement of dual-parameter, demonstrating significant potential in gas measurement applications.

Distributed fiber optic strain sensing for structural health monitoring of 70 MPa hydrogen vessels

We report on the development and testing of 70 MPa hydrogen pressure vessels with integrated fiber optic sensing fibers for the automotive use. The paper deals with the condition monitoring of such composite pressure vessels using the optical backscatter reflectometry (OBR) which was applied for a distributed fiber optic strain sensing along fully integrated polyimide-coated single-mode glass optical fiber (SM-GOF). The sensing fibers were embedded into the vessel structure by wrapping them over the inside polymer liner during the manufacturing process of the outside carbon fiber reinforced polymer (CFRP). Detecting local strain events by the integrated fiber optic sensors might be an opportunity for monitoring the material degradation. Regarding the investigation of the ageing behavior, both ambient hydraulic cycling tests and slow burst tests were conducted on 70 MPa pressure vessels with embedded fiber optic sensors. The achieved results contribute to the knowledge about material fatigue to guarantee the safe usage during the entire lifetime of the composite hydrogen storage vessels. The presented work stands in context of the European Horizon 2020 research project SH2APED focused on the development of an innovative hydrogen storage system composed of an assembly of nine 70 MPa tubular pressure vessels used as an automotive battery pack.

Integrating fiber optic sensors into metallic components for sensing in harsh environments

The integration of fiber optic sensors into high-temperature materials is critical for real-time monitoring and autonomous operation of engineering systems. This study demonstrated a spark plasma sintering (SPS)-assisted embedding process for integrating sapphire fiber optic sensors into stainless steel components during part fabrication. Optical fibers were encapsulated in stainless steel 316L powders which were sintered at different fabrication conditions using SPS to investigate the effects of sintering parameters on the embedment. Measurements of optical transmittance, combined with microstructural analysis (X-ray computed tomography and scanning electron microscopy) and mechanical testing (tensile and microhardness), were conducted to examine the fiber functionality, fiber–matrix bonding quality, and properties of the sintered materials. The results show that under suitable fabrication conditions, intact optical fibers can be encapsulated in highly-densified (>98 % relative density) stainless steel components. These conditions also led to a good bond at the fiber–matrix interface with micron-sized material interdiffusion across the interface. The sintering parameters were observed to affect fiber optical attenuation, where high temperature, pressure, and hold time during SPS enhanced fiber–matrix bonding and adversely affected optical transmission. Tensile testing confirmed the superior tensile strength and ductility of the matrix fabricated by SPS. Furthermore, the materials exhibited limited strength reduction (∼70 MPa) upon the integration of fibers. This study demonstrates the effectiveness of SPS for fiber-material integration for high-temperature applications.

Real-Time Monitoring of Gas-Phase and Dissolved CO2 Using a Mixed-Matrix Composite Integrated Fiber Optic Sensor for Carbon Storage Application.

Novel chemical sensors that improve detection and quantification of CO2 are critical to ensuring safe and cost-effective monitoring of carbon storage sites. Fiber optic (FO)-based chemical sensor systems are promising field-deployable systems for real-time monitoring of CO2 in geological formations for long-range distributed sensing. In this work, a mixed-matrix composite integrated FO sensor system was developed with a purely optical readout that reliably operates as a detector for gas-phase and dissolved CO2. A mixed-matrix composite sensor coating consisting of plasmonic nanocrystals and hydrophobic zeolite embedded in a polymer matrix was integrated on the FO sensor. The mixed-matrix composite FO sensor showed excellent reversibility/stability in a high humidity environment and sensitivity to gas-phase CO2 over a large concentration range. This remarkable sensing performance was enabled by using plasmonic nanocrystals to significantly enhance the sensitivity and a hydrophobic zeolite to effectively mitigate interference from water vapor. The sensor exhibited the ability to sense CO2 in the presence of other geologically relevant gases, which is of importance for applications in geological formations. A prototype FO sensor configuration, which possesses a robust sensing capability for monitoring dissolved CO2 in natural water, was demonstrated. Reproducibility was confirmed over many cycles, both in a laboratory setting and in the field. More importantly, we demonstrated on-line monitoring capabilities with a wireless telemetry system, which transferred the data from the field to a website. The combination of outstanding CO2 sensing properties and facile coating processability makes this mixed-matrix composite FO sensor a good candidate for practical carbon storage applications.

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.

Study of Distribution of Deformations in Ice Composite Materials Using Integrated Fiber-Optic Sensors

The Arctic region features harsh climatic conditions. The region has underdeveloped industry and infrastructure and it is located far from industrial facilities. This specificity sets forth high requirements for functionality and reliability of materials to be used in the region as well as for various technical devices and structures made from them. In addition, durable structures require assessing the performance status during operations. Optical sensors based on fiber Bragg gratings are promising from the standpoint of monitoring the bulk of construction material. We explored distribution of deformations along the longitudinal axis of a sample in a matrix and in reinforcing filler for ice-based composite materials upon exposing samples to three-point bending. It was demonstrated that unidirectional ice reinforcement using two layers of basalt roving increases the ultimate bending strength by a factor of two. The approach proposed proved to be promising to monitor deformations in reinforced and unreinforced ice materials using integrated fiber-optic sensors by applying external mechanical effects and testing the samples under three-point bending.

Studying Deformation of Ice Composite Materials Using Integrated Fiber-Optic Sensors

Ice-based construction materials used in cold climate regions, including the Arctic, as well as ice itself, exhibit low strength characteristics, which requires constant monitoring of structures created with the use of such materials. In this work, the deformation of samples of unreinforced and basalt-roving reinforced ice is studied and the features of loading and destruction of reinforced ice and unreinforced ice are compared. The unidirectional reinforcement of the ice results in a twofold increase in the strength limit and almost threefold increase in the relative axial deformation before the bending-induced fracture the sample. The possibility of using fiber-optic sensors based on the Bragg grating as monitors of ice deformation is shown. By the example of testing samples for three-point bending, we demonstrate the prospects of the proposed approach to study the deformation of materials based on reinforced and unreinforced ice under external mechanical influence using integrated fiber-optic sensors.

Environmental Testing of a FBG Sensor System for Structural Health Monitoring of Building and Transport Structures

Recently, there has been an increased interest in structural health monitoring (SHM) of building and transport structures. Standard strain gauges placed on a beam surface are mostly used to monitor the mechanical stresses of timber or concrete structures. However, these sensors are susceptible to mechanical damage, electromagnetic interference or negative influences of the measured data during the measurement, such as temperature variations or potential loss of data due to explosive environment. The fibre optic sensor system offers a more suitable and reliable solution – the sensors can be integrated directly into the load bearing structure during its production and thus protected by the construction material against ambient environmental conditions. The first part of this paper presents series of environmental tests of a measuring system based on Fibre Bragg Grating principle performed from 2016 to 2018 in a climate chamber. The chamber can generate defined humidity and/or temperature cycles, which can simulate the behavior of the structure under real environmental conditions. The tested fibre optic sensor system is suitable for load bearing timber (glued laminated timber beams) and concrete structures. In the second part of this paper, mechanical loading tests of glued laminated timber beam with integrated fiber optic sensors performed in 2016, 2017 and 2018 are presented. The article describes the design of test cycles, gives the results of testing, and is concluded with the discussion of given results together with the outline of the future research directions.

Monitoring, Modeling, and Assessment of a Self-Sensing Railway Bridge during Construction

This study shows how integrating fiber optic sensor (FOS) networks into bridges during the construction stage can be used to quantify preservice performance. Details of the installation of a large FOS network on a new steel-concrete composite railway bridge in the United Kingdom are presented. An overview of the FOS technology, installation techniques, and monitoring program is also presented, and the monitoring results from several construction stages are discussed. A finite-element (FE) model was developed and a phased analysis was carried out to simulate strain development in the bridge during consecutive construction stages. The response of the self-sensing bridge to the time-dependent properties of the concrete deck was evaluated by comparing FOS measurements to predicted results according to several model code formulations implemented in the FE model. The preservice strain distribution due to dead loading is typically assumed to act uniformly along the bridge length; however, the monitoring results revealed that the distribution was highly variable as a result of the complex interactions between gravity loading, bridge geometry, time-dependent concrete properties, and temperature effects. Moment utilization of the main girders and composite beams, during preservice conditions, was assessed and found to be between 19.3 and 24.9% of the respective design cross-section capacities. Quantifying preservice performance via integrated sensing also provided a critical baseline for the bridge, which enables future data-driven condition assessments.

Integrated fiber optic sensors for hot spot detection and temperature field reconstruction insatellites

Large satellites are often equipped with more than 1000 temperature sensors during thetest campaign. Hundreds of them are still used for monitoring during launch and operationin space. This means an additional mass and especially high effort in assembly, integrationand verification on a system level. So the use of fiber Bragg grating temperature sensorsis investigated as they offer several advantages. They are lightweight, small insize and electromagnetically immune, which fits well in space applications. Theirmultiplexing capability offers the possibility to build extensive sensor networksincluding dozens of sensors of different types, such as strain sensors, accelerometersand temperature sensors. The latter allow the detection of hot spots and thereconstruction of temperature fields via proper algorithms, which is shown in this paper.A temperature sensor transducer was developed, which can be integrated intosatellite sandwich panels with negligible mechanical influence. Mechanical andthermal vacuum tests were performed to verify the space compatibility of thedeveloped sensor system. Proper reconstruction algorithms were developed toestimate the temperature field and detect thermal hot spots on the panel surface. Arepresentative hardware demonstrator has been built and tested, which shows thecapability of using an integrated fiber Bragg grating temperature sensor network fortemperature field reconstruction and hot spot detection in satellite structures.

Integrated Fiber Optic Sensors For Nondestructive Characterization Of Concrete Structures

ABSTRACTIt is possible to monitor the initiation and progress of various mechanical or environmentally induced perturbations in concrete elements by way of fully integrated optical fiber sensors. Geometric adaptability and ease by which optical fibers can be embedded within concrete elements has led to the development of a number of innovative applications for concrete elements. This article is intended for a brief introduction into the theories, principles, and applications of fiber optic sensors as they pertain to applications in concrete.. However, due to the fact that the transduction mechanism in optical fibers is invariant of the materials employed, the principles introduced here also correspond to other structural materials. The only application related differences among various materials pertain to sensitivity and choice of optical fiber sensor types.

Application of the integrating fiber optic sensor for vibration monitoring

Fiber optic sensors (FOS) for vibration monitoring of smart structures have certain advantages over conventional strain gage based sensors due to electromagnetic environment insensitivity and high response bandwidth. During the present study, a spatially integrating fiber optic sensor was used for vibration monitoring. It is based on the concept that the optimal placement of the sensing element can be sought by using a priori knowledge of the mode shapes of the structure. The applicability of this approach to polarimetric optical fibers is described. The acquired integrating FOS signal was used to sense and control the vibration of an electrorheological adaptive structure subjected to a random external excitation.

Fiber optic sensing for composite smart structures

Structurally integrated fiber optic sensors (SIFORS) will form a necessary part of future Smart Structures and strain sensing will provide valuable information on the loading and response of such structures. Strain measurements may be used to check structural integrity and in the case of Smart Adaptive Structure they will provide the deformation information required by the actuation control system. Continuous monitoring of applied loads could be used to determine the fatigue life of the structure at any point in its operation. In the case of composite materials improved quality control during fabrication may be possible from such a built-in sensing system and this could lead to a more consistent and reliable product. Overall the introduction of an embedded fiber optic strain sensing system to composite structures may enhance confidence in their use and lead to a wider range of application, especially in the aerospace field. In this paper the types of fiber optic sensor are reviewed and it is shown that the intracore Bragg grating and the intrinsic Fabry-Perot interferometer appear to best qualify for continued consideration for a broad range of Smart Structures. The key elements of strain sensing with both types of structurally integrated fiber optic sensor are reviewed and issues such as thermally induced apparent strain are discussed. It is shown that although both sensors now have good methods of demodulation, the Bragg grating sensor has the greatest potential to satisfy the requirements demanded of the ideal sensor for Smart Structures due to the recently developed ratiometric wavelength demodulation system. This system promises the fabrication of a robust, compact, absolute measurement, low cost multisensor system that could be integrated on to an optoelectronic chip that can form part of the interface to any structure and in essence solve the critical interconnect problem. Indeed, an extremely user-friendly, noncontact form of communication could be possible with the developments of this optoelectronic Smart Structure interface—termed an “optical synapse”.

Fiber optic sensors for smart structures

An overview is presented of our research towards the development of structurally integrated fiber optic sensors for Smart Structures. This includes the development of the first full-scale fiber optic damage assessment test system in the form of a composite aircraft leading edge and the fabrication, characterization and evaluation of the first fiber optic strain rosette. This optical strain rosette was shown to be capable of mapping the strain tensor from within composite materials.

Dynamic Strain Sensing of a Composite Lattice with an Integrated Optical Fiber

A fiber-optic sensor was used to investigate the modal response of a highly-flexible graphite/bismaleimide lattice structure. The natural frequencies and modal amplitudes were determined based on strain readings taken from the structurally- integrated fiber-optic sensor. The advanced composite lattice structure to which the sensor was attached is a half-scale model of the aluminum grid currently being used for active control studies at the Air Force Astronautics Laboratory. The dynamically-scaled compos ite lattice structure, which employs 2.604-cm (1.025-inches) wide strips to form a five-by- five grid, is 76.52-cm (30.125-inches) square overall with a nominal thickness of 0.094 cm (0.037 inches). The longitudinal and transverse members employ the same seven-ply [O3/90] s stacking sequence with reference to their local coordinate system, except at the intersections, where the layers are alternated. The scaled lattice structure was fabricated from G40-600/5245C graphite/bismaleimide prepreg tape. The first seven modes from an ANSYS finite element model based on eight-node quadrilateral shell elements were used to optimize the path of the integral fiber-optic sensor. To form this sensor, an optical fiber was bonded to the surface along an "L"-shaped path and spliced into the sensor arm of a modified Mach-Zehnder interferometer, which provides a voltage proportional to sensor elongation to supply real-time integrated strain data. The structure was cantilevered verti cally from a specially-designed vise, and the natural frequencies and modal amplitudes of the lattice structure were measured using the integral fiber-optic strain sensor. The ex perimental results were confirmed with noncontact proximity sensors. The results demon strate that integral fiber-optic strain sensors can provide reliable indications of the dynamic response of a flexible lattice structure.