Search

A fibre loop mirror sensor is proposed and demonstrated for strain and temperature measurements in experiment. In these schemes, fibre loop mirrors are constructed with single‐mode‐multimode‐polarization‐maintaining‐multimode‐single‐mode optical fibre (SMPMS) structures. The strain and temperature characteristics of the sensor, depending on the lengths of multimode fibre (MMF) and polarization‐maintaining fibre (PMF), are studied in the experiment. The results indicate that PMF and MMF lengths have less impact on strain sensitivity but a remarkable impact on temperature sensitivity, which is consistent with the theoretical analysis. The best strain and temperature sensitivities of an SMPMS structure sensor can reach up to 39.0 pm/με and 2.366 nm/°C, respectively. The sensors have the merits of easy fabrication, cost‐efficiency and high temperature sensitivity and are quite suitable for fields requiring high‐precision measurement.

We have developed and experimentally implemented an adaptive laser vector-phase hydroacoustic measuring system, which allows one to determine the total acoustic intensity vector. A receiving element of the measuring system comprises six spatially separated fibre-optic coil-type sensors. Signals from the sensors are phase demodulated by using a six-channel adaptive holographic interferometer based on dynamic holograms multiplexed in a photorefractive CdTe crystal. Performance of the developed measuring system has been experimentally tested by determining the bearing and localisation of a source of a weak hydroacoustic field.

It has been shown experimentally and confirmed by numerical simulation that strong local stretching of sensing fibre distorts the signal detected by a phase-sensitive optical time-domain reflectometer (OTDR) from the fibre section behind the local disturbance region. Comparison of experimental data with theoretical estimates and numerical simulation results leads us to conclude that the physical mechanism underlying the distortion of the OTDR trace is related to the external disturbance-induced variable shift of the optical carrier frequency of probe pulses.

We present the first report on reflectometric optical fiber sensing based on mechanically induced cascaded long-period grating (LPG) structure. This method utilizes in-house designed mechanical casings and a bare fiber. When a fiber is sandwiched between the casings and pressed by tightening screws, an LPG is induced due to a photo-elastic effect. By exploiting Fresnel refection at a fiber end, a cascaded LPG structure can be implemented using a single LPG, enabling reflectometric configuration. When this sensor is subjected to external physical processes, the attenuation bands change clearly, and their shift can be used for non-destructive evaluations. We show experimentally that this sensor can measure loads of up to 10 N without producing any permanent change in the fiber properties, indicating its pressure sensing capability. We also show that this sensor can potentially measure strain and temperature. In our experiments, the strain and temperature sensitivities are 9.4 nm/% and 0.045 nm/°C, respectively.

An all-fibre splicing Fabry–Perot interferometer (FPI) sensor is successfully demonstrated for measurements of pressure, refractive index (RI) and temperature. The sensor structure is fabricated vi...

A new type of a vector hydrophone, a laser adaptive hydroacoustic intensimeter, is investigated. Two identical, spatially separated coil-type sensors are used as a primary receiver of the acoustic signal. The signals received at the sensor output are phase demodulated in a two-channel adaptive holographic interferometer based on two dynamic holograms multiplexed in a CdTe photorefractive crystal. Using a laser intensimeter, the acoustic field formed in a limited volume is studied. The performance characteristics of the intensimeter are determined experimentally; its threshold sensitivity, according to the acoustic field intensity, constitutes 0.1 × 10−13 W m−2.

>A record long external-disturbance detection distance of 140 km without employing optical amplifiers in the fibre line is demonstrated by a phase-sensitive optical time-domain reflectometer (Φ-OTDR) using a fibre section with inscribed chirped fibre Bragg gratings (CFBGs). This solution provides simultaneous operation of Φ-OTDR with a standard single-mode fibre at a distance of up to 100 km and with a CFBG fibre section located from the fibre line input point by at least 140 km.

The paper describes the concept of the smart FRP composite bridge panel with integrated distributed fibre optic sensors (DFOS), intended to monitor its behavior under live load. The system consists of continuous sensors, thanks to which it is possible to measure every part of the panel and the obtained response of the structure is comprehensive. The sensors are placed inside the laminates, thanks to which they are inseparably and securely connected with the structure. This solution required production tests to develop a durable and mass-produced solution. The final effect is an intelligent panel that can diagnose its condition based on algorithms and indicate the occurrence of anomalies.

Health monitoring of gas insulated apparatus is critical to improve the reliability and to reduce the life cycle cost. Among the various methods for monitoring, optical sensing developed fast in recent years due to their highly sensitive and anti-electromagnetic interference behaviour. This study reviews the optical monitoring methods for partial discharge, gas concentration and temperature of gas insulted apparatus. In addition, the challenges of sensor development are carefully discussed here. The future prospects of optical monitoring of gas insulated apparatus are also analysed to inspire new ideas.

Civil infrastructures, being essential for modern and advanced societies, are the foundation of the dynamic economy and improvement of the quality of people’s lives. The design and construction of such infrastructures involve a significant cost to a country, but the proper use of the scientific methods to monitor and maintain these structures can improve their cost-effectiveness. Civil engineers strive to design and construct structures meeting the highest standards of engineering in order to enhance the durability and functionality of such infrastructures. However, civil engineers have been rather slow in adopting civionics engineering to improve the useful life of infrastructures. It is noted that the new term ‘civionics’ was coined recently to denote structural health monitoring of civil structures with the help of electronic sensors. This article will discuss several lessons learned during the implementation of health monitoring systems for civil structures.

Prestressed concrete sleepers with built-in fibre optic–based sensing systems have recently been developed to capture performance data within railway networks and to provide critical decision-support information to route managers and operators. To better understand how self-sensing sleepers can be fully utilized within the rail network, a study of their comprehensive performance under controlled conditions must be undertaken. This article presents the results of the full-scale laboratory testing of a self-sensing sleeper supported on ballast. A primary focus of this study was to investigate whether a self-sensing sleeper could also be used to estimate rail seat load, detect cracking, and identify differential ballast settlement. The ultimate capacity and resilience of the embedded fiber Bragg grating sensing system was tested by applying load up until concrete cracking followed by several cyclic load cycles. Through inference of the load versus strain response, the ability of the self-sensing sleeper to detect damage (concrete cracking and loss of ballast support) was evaluated. The experimental results revealed the effectiveness and robustness of the embedded sensing system to continue to provide reliable dynamic strain measurements well beyond the ultimate loading capacity of the prestressed sleeper. Cracking of the top surface of the sleeper was effectively detected by the fiber Bragg grating strain sensors at the mid-span section. After cracking, subsequent load cycles were carried out. During this period, the bottom fiber Bragg grating measurements captured the effects of differential ballast settlement under the rail seats. A three-dimensional nonlinear finite element model was developed to simulate the experimental test setup and to investigate the relation between fiber Bragg grating sensor measurements and rail track response. The combined experimental and numerical results suggest that a self-sensing sleeper may be deployed on an operational railway to provide reliable and long-term measurements of rail axle load and ballast pressure.

Magnetic resonance imaging (MRI) patients often experience anxiety-related respiratory disorders, including hyperventilation, but their respiratory indicators are not routinely monitored during scanning. Free from metal parts and immune to electromagnetic radiation, fibre-optic sensors have the potential to better control the patient’s condition by providing continuous non-invasive monitoring of the respiratory rate (RR). The study was purposed to assess the relationship between anxiety in MRI patients and their RR acquired by a fibre-optic sensor system. Forty-four subjects were involved in the study. The mean RR values recorded for 2 minutes immediately after the beginning and immediately before the end of the scanning were assessed relative to the State-Trait Anxiety Inventory (STAI) X-1 scores obtained immediately before and immediately after the scanning, respectively. A growth mixture model analysis was performed to statistically differentiate two groups of subjects according to the trends in repeated measures of RR. A significant lowering of the anxiety state was observed in the group characterised by a decrease in RR, whereas essentially no change in anxiety level was observed in the group with a stable RR. The t-test showed significant differences in changes in anxiety between these groups (t(39) = −2.349, p = 0.012, Cohen’s d = 2.13).

Distributed fibre optic sensors (DFOS) provide new possibilities in structural technical condition assessment in comparison with traditional spot measurements. It is possible to analyze strains and temperature changes continuously over structural member length with spatial resolution starting from as fine as 5 mm. Thanks to the appropriate sensor construction and its installation before concreting it is possible to analyze material behaviour starting from its early stage, when thermal-shrinkage strains appear. This phenomenon depends on many factors, such as the type of concrete mix, dimensions of structural member, the way of concrete care, external conditions (temperature, humidity), formwork and constraints related to reinforcing bars or external friction and resulting with crack appearance. Stage of early-age concrete (hydration process) is thus very important for its final durability and performance. The article presents the very new measuring tools which allow for comprehensive analysis of concrete temperatures and strain state including all local nonlinearities (cracks). The attention was paid to hydration process, but sensors installed inside the structural members can be also effectively used during other phases such us: activation of prestressing tendons, construction stages or operation. Selected examples of laboratory tests as well as the unique in situ installations realized in Poland during last few years are presented and discussed hereafter. Except of traditional concrete, also other materials were examined, such as concrete made on lightweight sintered aggregate and fibre-reinforced concrete mixed with the ground.

Due to environmental loads, fatigue effects, corrosion and material aging and other factors, the surface of high-speed railway bridge cables will inevitably be damaged, which affects the safety of the bridge. Therefore, a method for detecting surface defects of high-speed railway bridge cables based on optical fiber sensing technology is proposed. Secondly, based on the theory of high-speed fiber-optic sensor, the defect of the bridge is detected and detected by the method of neural network. The results show that: under the application of the proposed method, the defect judgment is accurate, and the type identification is also accurate, which provides a reference for bridge safety and health monitoring.

In this report, we investigate the single-fiber (SF) Mach-Zehnder interferometer (MZI) based refractive index (RI) sensor, fabricated in house for the RI range from 1.3344 RIU to 1.4532 RIU. The RI sensitivity of fabricated sensor was enhanced, from 20.2 nm/RIU to 25.9 nm/RIU, by incorporating it in fiber loop mirror (FLM) configuration. The enhanced sensitivity may be attributed to the non-reciprocal phase shift present in bend or twist of the fiber loop forming the FLM configuration. A simple method for quantifying the non-reciprocal phase shift in FLM configuration has been proposed.

In this editorial on the special issue “Fibre Optic Sensors for Structural and Geotechnical Monitoring” a review of the contribution papers selected for publication is given. Each paper is briefly summarized, presenting its objective and methods, then a comment is given about the relevance of the work with respect to the advance and the spreading of the fibre optic technology for monitoring applications.

This paper describes an impact detection system using strain signals based on fibre optic sensors(FBG) for the real-time monitoring of the catenary system. The proposed detection system consists of...

A fibre-optic sensor is proposed to conduct acoustic and magnetic measurements simultaneously. The sensor consists of two cascaded fibre Bragg gratings (FBGs), one of which is inserted into a magnetic extension bulk (TbDyFe (Terfenol-D)). This is to conduct the magnetic measurements while the other conducts the acoustic measurements. In this research, some pre-processing has been used to improve the sensitivities of the sensor. Side-band filtering technology-based intensity interrogation is used for the acoustic detection, and wavelength interrogation is used for the magnetic measurement. The results of the present study indicate that the sensor is able to measure acoustic and magnetic simultaneously within a considerable range.

This paper presents a comprehensive critical review of technologies used in the development of fibre optic shape sensors (FOSSs). Their operation is based on multi-dimensional bend measurements using a series of fibre optic sensors. Optical fibre sensors have experienced tremendous growth from simple bend sensors in 1980s to full three-dimensional FOSSs using multicore fibres in recent years. Following a short review of conventional contact-based shape sensor technologies, the evolution trend and sensing principles of FOSSs are presented. This paper identifies the major optical fibre technologies used for shape sensing and provides an account of the challenges and emerging applications of FOSSs in various industries such as medical robotics, industrial robotics, aerospace and mining industry.

Weigh-in-Motion (WIM) systems are designed for weighing vehicles driving across a measurement site. Because during measurements the vehicle has to come in physical contact with the components of the system, WIM systems always use built-in sensors installed in road pavement. Each WIM system consists of force sensors placed in one, two or even several lines, perpendicular to the direction of traffic. The idea behind WIM systems is to measure the dynamic loads that the wheels of a moving vehicle exert on the road surface and, on this basis, to estimate static wheel loads as well as gross vehicle weight.

This article presents a novel study on curvature sensing and crack monitoring in lightweight foamed concrete structural beam using the packaged fibre-based in-line Mach–Zehnder interferometer curvature sensor. The Mach–Zehnder interferometer sensors which consist of two abrupt biconic tapers were fabricated and packaged into polypropylene slabs to protect the sensors under harsh condition of the real sensing environment, as the sensors were embedded into lightweight foamed concrete structural beams for field tests. Pretest characterizations of Mach–Zehnder interferometer sensors based on the packaging thicknesses at different operating wavelengths (1310, 1490 and 1550 nm) were done before the field tests. Three packages with different thicknesses were prepared to justify the effect of the packaging thicknesses on the curvature sensitivity of sensors. Results showed that the Mach–Zehnder interferometer sensor with a thicker bottom slab has the highest sensitivity of up to 3.53 µW m−1 which is capable of detecting a minimum curvature of 0.25 km−1 and a maximum curvature radius of up to 4 km. In the field tests, three Mach–Zehnder interferometer sensors were embedded into the lightweight foamed concrete structural beams with different polypropylene percentages (0.4%, 0.25% and 0%, respectively) to characterize the sensor performance according to the concrete environments with different tensile capacities. Mach–Zehnder interferometer sensor managed to hold up to a maximum loading force of 26 kN in the concrete environment before stopping functioning. Optical powers in response to the loading forces imposed to the beams were mapped to the strains measured by the lead wire alloy foil strain gauges (brand: TML, model: FLK-6-11) with a good correlation value of up to 0.968. Furthermore, the double-sided sensing property of Mach–Zehnder interferometer sensors preponderates over the conventional strain gauges in detecting the internal cracking within the concretes before any earlier sighting of the macrocracks.

A number of health and safety hazards present in underground coal mines, which include methane gas explosion, coal combustion, rock roof collapse, and flooding etc. Methane gas and coal combustion have been two major hazards, which resulted in most of the heavy casualties and economic losses. Conventional catalytic methane gas sensors suffer from poor accuracy and cumbersome maintenance, which is the bottleneck of methane hazard prevention. Coal mine combustion monitoring has been relying on gas tubing bundles system, which suffers from long time delay and poor reliability. Semiconductor laser diode methane gas sensors have been developed which has low power consumption, 0–100% full detection range and high accuracy, and no need of recalibration. Fibre optic Raman distributed sensors have been deployed in coal mine goaf and successfully detected combustion hazard in early phase. The FOS-based mine hazard detection system offers unique advantages of intrinsic safety, multi-location and multi-parameter monitoring. The application of FOS on monitoring of methane, coal combustion, micro-seismic and equipment condition are described, future trend of research in this area is also discussed.

This article is focused on the analysis of the use of distributed fibre-optic technology for security monitoring of road tunnel and motorway tunnel structural load. The authors focused on the measurements of deformation utilizing Brillouin Time Domain Reflectometry (BOTDR). The principle is based on the measurement of stimulated Brillouin scattering. The article describes and analyses real measurements within a period of 5 months, which were carried out during the tunnelling and the whole process of building a new tunnel in Žilina, Slovakia. The performed experimental measurements were carried out using a standard optic telecommunication cable with water-absorbing aramid yarns and a jacket with a diameter of 4.2 mm. The contribution of this article lies in the introductory analysis of the implementation and use of the fibre-optic technology for security monitoring of road tunnel and motorway tunnel structural load.

Cranfield University's National Flying Laboratory Centre (NFLC) has developed a Bulldog light aircraft into a flight test facility. The facility is being used to research advanced in-flight instrumentation including fibre optic pressure and strain sensors. During the development of the test bed, Computational Fluid Dynamics (CFD) has been used to assist the flight test design process, including the sensor requirements. This paper describes the development of the Bulldog flight test facility, including an overview of the design and certification process, the in-flight data taken using the installed fibre optic sensor systems and lessons learned from the development programme, including potential further applications of the sensors.

Compression bandaging is a mainstay practice in the treatment of conditions such as chronic wounds and lymphoedema. However, the ability of practitioners to measure bandage application to a desired pressure profile is difficult because of sensor limitations. We have used a novel fibre-optic-based, high-resolution sub-bandage pressure monitor to measure adherence to a target pressure gradient during compression bandaging. Participants of various experience (n = 46) were asked to bandage a lower-leg manikin to a gradient of 40 (ankle) to 20 mmHg (proximal calf) in both a blinded trial and subsequently with sensor feedback. Mean pressures across all sensors for both the blind and sensor-guided trials approximated a target mean of 30 mmHg. However, the mean gradient achieved in the blinded trial showed an inverse pressure gradient to the target with a high-pressure region at the mid-calf (44 ± 19 mmHg). Correlation to the target gradient improved from R2 = 0·62 during the blind trial to 0·93 using sensor feedback, with a gradient that closely approximated the target. This demonstrates the use of high-resolution sub-bandage pressure sensing in improving the ability of practitioners to achieve a target pressure gradient in compression bandaging for clinical use and training.

To explore fibre refractive index (RI) sensing based on radiation modes, the influences of ambient RI on radiation modes are investigated by a leaky mode approximation in a two-layer fibre. Based on the analytical analysis and simulation results, it is identified that the change of ambient RI has no effect on the real part of the complex propagation constant of a leaky mode, but a remarkable effect on the imaginary part. More importantly, the influence of the medium's absorption loss on the imaginary part is almost negligible. If the medium's absorption loss is lower than 3.521 × 103 dB/cm, the induced average deviation rate of the imaginary part is

Mercury ion (Hg^2+) is one of the common pollutants which exists in the natural environment far and wide. The detection of Hg^2+ usually requires large laboratory equipment, which limits their field applications. Here, a miniaturised optical fibre sensor based on quantum dots (QDs) for detection of Hg^2+ is developed. The sensor is based on the principle of fluorescence quenching caused by Hg^2+ and evanescent wave sensing. It is an all-fibre sensor which composed of an optical fibre probe module, an optical module and a signal acquisition module. Through miniaturisation design of optical system and the structure of the sensor, the sensor is reduced to the volume of 120 × 120 × 100 mm. The experimental results show that in the miniaturised sensor both has high sensitivity and fast response speed. Meanwhile, the ion anti-interference experiment shows that the sensor has good selectivity for Hg^2+ detection. In general, the proposed sensor has significant potential in the field of biochemistry, environmental monitoring, and food safety.

Since fibre optic sensors (FOS) use dielectric materials they can be used in harsh environment conditions; such as high voltage, high electromagnetic radiation, or high temperature. In this chapter, we review the basic concepts and processes related to FOS and some examples of doping materials used to improve the fibre sensitivity.

Harsh environments, distributed systems, space and long-term deployments are typical examples where the characteristics of the fibre Bragg grating FBG systems can make provide the clear advantage and a highly effective solution as compared to conventional electrical sensors.

We describe and characterize a multi-micron silicon photonics platform that was designed to combine performance, power efficiency, manufacturability, and versatility for integrated photonic applications ranging from data communications to sensors. We outline the attributes needed for broad applicability, high-volume manufacturing, and large-scale deployment of silicon photonics, and describe how the platform is favorable with respect to these attributes. We present demonstrations of key technologies needed for the communications and sensing applications, including low-loss fiber attach, compact low-loss filters, efficient hybrid wavelength division multiplexed lasers, and high-speed electro-absorption modulators and integrated photodetectors.

There is an ongoing need to measure strains in reinforced concrete structures more reliably and under a range of circumstances e.g. long term durability (such as effects of cracking and reinforcement corrosion), response to normal working loads and response under abnormal load conditions. Fibre optic sensors have considerable potential for this purpose and have the additional advantages, including of immunity to electromagnetic interference and light weight (Grattan et al., 2000). This is important in railway scenarios and particularly so when the lines are electrified. Their small size allows for easy installation. However, their use as commercial ‘packaged’ devices (traditionally seen as necessary to achieve adequate robustness) is limited by their high cost relative to other sensor devices such as encapsulated electric resistance strain gauges. This paper describes preliminary work to produce a cost-effective and easy-to-use technique for encapsulating fibre optic sensors in resin using 3D printing techniques to produce a robust, inexpensive ‘packaged’ sensor system suitable for use with concrete structures. The work done to date has shown this to be a convenient and economical way of producing multiple sensors which were suitable for both surface mounting and embedment in reinforced concrete structures. The proof-of-concept testing to which the trial packages were subjected is described in the paper and the results indicate that 3D printed packages have considerable potential for further development and use in a variety of civil engineering applications, competing well with more conventional sensor systems.

Grouted connections are intensively used in offshore rigs, platforms as well as jacket and monopile offshore wind turbine structures. Being located in remote offshore conditions, these connections can experience considerable adverse loading during their lifetimes. Degradation was reported inside similar connections, which were installed in the last three decades. Grouting in the offshore sites may often be proven difficult, which eventually leads to reduced load-bearing capacity of connections in the long run. Thus, repair and rehabilitation of such connections should be planned ahead to minimize operational delays and costs. In this study, scaled grouted connections were manufactured using a novel mould, whose integrity were monitored using digital image correlation (DIC). The connections were loaded under static load to visualize the main failure pattern using distributed fibre optic sensors and acoustic emission (AE) analysis. Grouted connections were then repaired using a cementitious injectable grout. The effectiveness of the grout injection was monitored using dye penetration technique. Finally, specimens are reloaded to identify the potential of such repair for grouted connections.

A fiber optic sensor for monitoring mercuric (Hg2+) ions in the aqueous sample have been developed based on modified cladding. To fabricate a D-shaped sensing zone onto the multimode optical fiber lengthwise polishing was utilized using a mechanical end and edge polishing system. The produced sensing region has dimensions of 10 mm × 125 μm × 62 μm (l × w × h). A 2 μm thin layer of Al2O3 nanoparticles sensitized with 4-(2-pyridylazo)-resorcinol was deposited onto the sensing element of multimode fiber optic sensor to make it sensitive and selective for Hg2+ ions. The analytical results demonstrate that the sensing device has a linear response for Hg2+ ions concentration over a range from 4 to 16 ppm along with a 4 ppm limit of detection in an aqueous sample at room temperature. The selectivity of the sensor is examined for the recognition of Hg2+ ions in presence of other cations such as zinc and/or lead ions up to 16 ppm in an aqueous solution. The main merits of this fabricated sensor are easy and safe installation, rapid response, enhanced linear response range, and better selectivity towards Hg2+ ions.

This work proposes a simple, easy-to-fabricate and cost-efficient sensor based on mid-infrared (MIR) spectroscopy for in-situ real-time bioprocess monitoring. A process involving the production of sophorolipid biosurfactants by way of fermentation was studied with the aim of monitoring varying substrate and product concentrations over time and also distinguishing between the main two structurally different types of biosurfactant produced: lactonic and acidic sophorolipids. First, measurements were carried out using ATR-FTIR spectroscopy. This was followed by comparative measurements using a fabricated U-bent fibre-optic sensor designed for in-situ monitoring. It was demonstrated for the first time that varying concentrations of sophorolipids in a fermentation broth could successfully be monitored over time using an in-situ MIR fibre-optic sensor. Moreover, acidic and lactonic sophorolipids could simultaneously be identified at varying concentrations. The utilisation of such a sensor in bioprocesses can provide a wealth of real-time data, allowing for improved control of feeding rates and better process characterisation, providing significant opportunities for bioprocess control, resulting in increased production and decreased overall costs.

For optical fibre sensors applications, nanomaterials have been widely used to enhance sensor performance. Here, the fibre optic uses the transmission of light by total internal reflection along with the fibre and depending on the diameter of the fibre and the wavelength of the light used. Among others, graphene oxides nanostructures (GO) would offer exceptional advantages on the sensing mechanism due to 2D properties of the monocellular layer originally from graphite. The main objectives of this research are to successfully synthesis of GO using a chemical reduction method known as modifies Hummer’s method and later, deposited the GO onto the modified fibre optic layer to create a sensing platform. Prior than that, the standard plastic of fibre optic (POF) was modified by removing the cladding layer (1 cm) using a mechanical etching technique, thus the sensing platform can be created. The morphology and optical properties of the system were characterised using scanning electron microscopy (SEM) and ultraviolet-visible (UV-Vis) spectroscopy. Result of the preparation and characterisation of GO-optical fibre coatings was presented, considering its potential use for sensing applications. The stable GO was prepared by 3 hours of stirring time during the synthesis and longer dipping time was preferred to fully coat the core of the exposed POF. Aiming to explore this scheme for sensing applications, GO-coated tilted fibre will be later measuring via refractive index variations. An improvement on the sensitivity should be obtained and thus become a promising sensing platform for the development of a new line of sensors.

The control of temperature during operation of zero power research reactors participates to the overall control of experimentation conditions and reveals itself of a major importance when measuring neutronic parameters such as multiplication factors. Within the framework of the refurbishment of the MASURCA facility, the development of a new temperature measurement system based on the optical fiber Bragg grating (FBG) technology is under consideration. In a first step, a series of FBGs is irradiated in the EOLE critical facility with the aim to select the most appropriate. Online temperature measurements are performed during a set of irradiations that should allow reaching a fast neutron fluence of nearly $5\cdot 10^{14}$ n.cm $^{-2}$ and a total gamma dose lower than 4 kGy. The results obtained, especially the Bragg wavelength shifts during the irradiation campaign, are discussed in this paper and compared to data from standard PT100 temperature sensors to highlight possible radiation effects on sensor performances. Work to be conducted during the second step of the project, aiming to a feasibility demonstration using a MASURCA assembly, is also presented.

A novel set-up for remote sensing the turbidity of a solution using plastic optical fibres together with a mirror is proposed. The authors have estimated turbidity of a liquid in terms of the nephelometric turbidity unit – NTU, a standard unit that relates the solution appearance with its turbidity for two proposed set-ups. Its performance was also investigated using clay sample measurements over a concentration range of 0–10 g/L. The proposed set-ups are useful for detection of suspended particles in a solution even in small quantities due to its high sensitivity, simplicity and robustness.

This paper reports proof-of-principle of an optical fiber Bragg grating (FBG) operating as an electric field sensor. The system is based on a semiconductor diode laser, emitting around 1577.5 nm that interrogates the fiber sensor around its maximum reflectivity point. The application of a strong electric field causes a small variation of the optical path length of the waveguide due to electrostriction and thus perturbs the grating peak reflectivity wavelength. Calibration and dynamic range tests are performed using a parallel-plate capacitor to create a variable electric field (1-100 kV/cm). A great potential is pointed out in view of possible field applications for voltage graduation in power generators.

pH is an important parameter to indicate the alkalinity level of concrete. The most severe concrete damages are caused or accompanied by dropping of the alkalinity level and consequently, decrease of the pH value of concrete. Therefore, it is crucial to measure the pH of concrete by an accurate and reliable method. This paper critically reviews the methods that have been developed for measuring the pH of fresh and hardened concrete. These methods are categorized in two broad divisions including destructive and non-destructive methods. The expression, ex-situ and in-situ methods are explained in detail as destructive methods, while the use of embedded potentiometric electrodes (mainly metal/metal oxide electrodes) and fibre optic sensors are evaluated as non-destructive methods. Also, advantages and drawbacks of each method are investigated and they are compared based on different technical and practical aspects. Despite the broad range of used methods for measuring the pH of concrete, there is no standardized test procedure. Because of the important role of pH with regard to durability of concrete structures, it is highly recommended that the required measures are taken to develop a specific standard test method for measuring the pH of concrete with a high level of accuracy, repeatability and reproducibility.

A temperature monitoring system based on fibre Bragg grating (FBG) fibre optic sensors has been developed for the gas electron multiplier (GEM) chambers of the Compact Muon Solenoid (CMS) detector. The monitoring system was tested in prototype chambers undergoing a general test of the various technological solutions adopted for their construction. The test lasted about two years and was conducted with the chambers being installed in the CMS detector and operated during regular experimental running. In this paper, we present test results that address the choice of materials and procedures for the production and installation of the FBG temperature monitoring system in the final GEM chambers.

Fibre optic sensor cable technology is relatively a new research area that combines a set of scientific and technical disciplines in order to meet distributed sensor system needs and quality standards. In this paper, we discuss a fibre optic sensor design with three tightly encapsulated fibres for multipurpose and multivalent sensing. It has the potential to integrate more detection and measurement techniques into a small space, and this, in turn, largely contributes to installation and cost optimizations and directly impacts investment plans and industrial success. The developed cable is tested in a specially developed high pressure and high temperature chamber. Furthermore, it is demonstrated that the proposed sensor cable offers the possibility of detection and distributed measurement of temperature, pressure, bending and vibrations.

Uncertainty about the survivability and technological evolution presents its risks when designing the sensors to use on infrastructure health monitoring systems. Fibre optic methods have been available for some time, and are reaching the technological maturity required to provide reliable long-term structural health monitoring solutions. By embedding fibre optic sensors in the structures at construction time, the engineers are able to detect deviations from the structure’s original design and expected dynamics. However, due to the long-term infrastructure’s life span and the relatively new fibre optic techniques, there are very few historical examples to analyse and use as proof for the adequacy of such techniques to the infrastructure’s life-cycle. This study explores the risks and opportunities associated with these technologies through a real case of one of the first Fibre Bragg Grating (FBG) sensorized highway bridge installed in Spain in the year 2000, the «Las Navas» bridge at the A-8 «Autovía del Cantábrico» highway in the north of Spain. The survivability of the fibre optic sensors, after eighteen years of embedded exposure, is compared to the traditional strain gauges solutions and the maintenance challenges they face. And, most importantly, the exciting new opportunities that the new measurement units can offer, are analysed, evaluating the re-purpose capacity of the health monitoring systems fibre optic sensors as sustainable real time operational monitoring systems. The originally designed structural sensors are proved to be useful also to detect, count and classify operational traffic using the infrastructure, by applying machine learning techniques that add another benefit of the use of these type of measurement sensors into the infrastructure’s world. The fibre sensor company SMARTEC and also the R&D H2020-EU.3.4. project RAGTIME (Grant agreement ID: 690660), thanks to which it all started with the first site visit.

In this paper, test measurements of a fibered optically stimulated luminescent dosimeter (OSLD) system performed during a dedicated experimental phase in EOLE zero-power reactor are presented. The measurement setup consists of an OSLD crystal connected onto the extremity of an optical fiber and a laser stimulation system, manufactured by the CEA/LIST, Saclay, France. The OSL sensor is remotely stimulated via an optical fiber using a diode-pumped solid-state laser. The OSL light is collected and guided back along the same fiber to a photomultiplier tube through appropriate optical filters. OSL signals are corrected for background noise and integrated to provide the absorbed doses thanks to calibration coefficients. The light stimulation also fully bleaches the crystal (reusable for the next measurement). Results obtained using this system are compared to usual gamma-heating measurement protocol using OSLD pellets. Both measurement processes were calibrated to ensure the comparison of absolute doses in gray at the same positions in the core. The presence of induced radioluminescence in the OSLD during the irradiation was also observed and could be used to monitor the gamma flux. The feasibility of remote measurements is achieved, whereas further developments could be conducted to improve this technique since the readout procedure still requires to withdraw the OSLD off the gamma flux (hence from the core) on account of the dose rate (around a few Gy $\cdot \text{h}^{\mathrm {\mathbf {-1}}}$ ), and the readout time remains quite long for online applications. Several improvements are foreseen and will be tested in the forthcoming years.