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Distributed acoustic sensing (DAS) leverages an ocean-bottom telecommunication fiber-optic cable into a densely sampled array of strain sensors. We demonstrate DAS applications to passive acoustic monitoring (PAM) through an experiment on a submarine fiber-optic cable in Longyearbyen, Svalbard, Norway. We show that DAS can measure many types of signals in the frequency range from 0.01 to 20 Hz generated by dynamics in the atmosphere, ocean, and solid earth. These include ocean-bottom loading pressure fluctuation of ocean surface waves generated by storms, winds and airflow turbulence, shear-wave resonances in low-velocity near-surface sediments, acoustic resonances in the water column, and propagating seismic waves. We show that DAS can record high-quality, low-frequency seismo-acoustic waves down to 0.01 Hz, which could be used for subsurface exploration. Using the shear-wave resonances recorded by DAS, we can determine the subsurface structure of near-surface sediments with low velocity. In addition, we can trace ocean swells back to their origins of distant storms as far as 13,000 km away from the cable. Because DAS is capable of seismo-acoustic monitoring with high spatial resolution of ~ 1 m over the cable of ~ 100 km long and with a broadband sensitivity down to 0.01 Hz on the low end, it can deliver great scientific value to ocean observation and geophysics community. Distributed acoustic sensing of ocean-bottom seismo-acoustics and distant storms: A case study from Svalbard, Norway

This study proposes a novel approach to surface strain measurement for cylindrical rock specimens subjected to uniaxial compression using distributed fibre optic sensing technology. The capability and accuracy of this approach in measuring the full-field strain distribution of a rock specimen have been verified by a series of uniaxial compressive strength (UCS) tests on cylindrical specimens of aluminium alloy, sandstone, and granite. By analysing the experimental results, this new approach also has the potential of being utilized to detect the potential failure locations and sequence through strain localization zone variations and estimation of the development of crack opening displacement and rock fracturing characteristics during the loading and unloading process. Detailed installation procedures are provided for this study for assistance in the use of this new approach. The boundary issue of fibre measurements is identified, and solved by extending the bonding length of the measuring fibre.

There are many sensitive areas like country borders, banks, forests, army cantonments, jails which requires continuous monitoring and surveillance. Intruders and illegal elements try to break the security and enter into these areas. In the same way there is another sensitive zone called containment zone required protection to prevent spread of viruses like corona. Every country has established their own protocols to maintain containment zone. Security officials monitored the sensitive areas but still it was not safe enough. In this case there is need of an invisible security mechanism which can be applicable in maintaining movements in containment zones. It will be very important to detect any movement in the sensitive area. Therefore, this paper provides a solution to protect sensitive zones. The solution consists of optical fibre sensor along with reporting and alarming system. The design and implementation is explained in the paper along with results. The proposed solution can be implemented to secure zone for multiple applications. © 2021 Karadeniz Technical University. All rights reserved.

Over the past decades, the development of fibre optic cables, which pass light waves carrying data guided by total internal reflection, has led to advances in high-speed and long-distance communication, large data transmission, optical imaging, and sensing applications. Thus far, fibre optic sensors (FOSs) have primarily been employed in engineering, biomedicine, and basic sciences, with few reports of their usage in geophysics as point and distributed sensors. This work aimed at reviewing the studies on the use of FOSs in geophysical applications with their fundamental principles and technological improvements. FOSs based on Rayleigh, Brillouin, and Raman scatterings and fibre Bragg grating sensors are reviewed based on their sensing performance comprising sensing range, spatial resolution, and measurement parameters. The recent progress in applying distributed FOSs to detect acoustic, temperature, pressure, and strain changes, as either single or multiple parameters simultaneously on surface and borehole survey environments with their cable deployment techniques, has been systematically reviewed. Despite the development of fibre optic sensor technology and corresponding experimental reports of applications in geophysics, there have not been attempts to summarise and synthesise fibre optic methods for prospecting as a comprehensive and modern branch of geophysics. Therefore, this paper outlines the fibre optic prospecting methods, with an emphasis on their advantages, as a guide for the geophysical community. The potential of the new outlined fibre optic prospecting methods to revolutionise conventional geophysical approaches is discussed. Finally, the future challenges and limitations of the new prospecting methods for geophysical applications are elucidated.

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.

Intrinsic U-shaped fiber optic sensors (FOSs) are well established in the field. With greater penetration depth and evanescent power, these sensors exhibit profound sensitivity and have supported a wide range of applications. Several sensing mechanisms have been integrated with U-shaped FOSs for physical, chemical, bio, and refractive index (RI) sensing applications. Sensor performance optimization is based on the principles of the associated sensing mechanisms. This paper is the second part of a review on U-shaped FOSs and discusses the sensing mechanisms, applications, possible improvements, and future scope of the U-shaped FOSs. Besides, this paper aims to provide researchers with a general idea of the actual implementation of U-shaped FOSs based on the theoretical model discussed in Part I of this review.

The development of underground spaces generates large amounts of construction wastes, which are generally disposed for the landfill outside of the city in China. This study briefly reviewed a landslide tragedy of a CSW landfill in China; Lessons learned from the failure of risk assessment and preventions were discussed, which showed that two challenging strategies are significant for the risk identification and mitigation. One is the effective early warning system based on field large-deformation measurement; the other is the efficient risk assessment with internal deformation data. To this end, a new sensing method is developed for the large-deformation measurement inside CSW landfills. The proposed fibre-optic based transducer can measure large deformation of up to 1200 mm with a high accuracy. Finally, the risk assessment of CSW landfill was proposed with the combined use of field monitoring data and risk evaluation model. The theoretical equations for stability analysis and potential application framework for the application of this technique in the risk assessment of CSW landfill landslide are presented. This approach possesses the advantages of capturing excessive and irregular deformation of solid waste landfills and of efficient response for the risk mitigation with the help of early warning system.

Fibre‐optic point sensors can be certainly regarded as a significant advancement for structural health monitoring (SHM) over the use of conventional electrical sensors. This chapter provides a brief introduction to the fundamentals of distributed fibre‐optic sensors (DFOS). It focuses on the two main DFOS types that deemed suitable for the SHM: distributed temperature sensors (DTS) based on the Raman scattering effect and distributed temperature and strain sensors (DTSS) based on the Brillouin scattering effect. There are other types of DFOS that are based on Rayleigh scattering effect either working in the time or frequency domains. DTS based on Raman scattering were the first DFOS to be widely deployed in industrial applications. The chapter describes three major application areas for DFOS‐based SHM: civil and geotechnical engineering, hydraulic structures, and electric power transmission and distribution.

The paper aims to evaluate the effectiveness of both distributed fibre optics sensors (DFOs), and fibre Bragg grating sensors (FBGs) to acquire an accurate measurement of the flexural strain of foa...

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...

Fibre optic vibration sensor (FOVS) converts vibration signal to light signal. Due to its prominent features, distributed fibre optic vibration sensor is preferred to conventional methods. Interest in FOVS has greatly increased over the years in structural health monitoring and vehicular traffic, hence the need to embark on this study. Distributed FOS is employed to measure the frequency of vibration caused by uncontrolled vehicular movement at Oluku By-Pass Bridge. Φ-OTDR is used to obtain millisecond snapshots of the stochastic signal arising thereof. A video shot was also recorded to match the exact timing of each excitation. Traces obtained show several frequency peaks at various corresponding backscatter level for high and low vehicular traffic. Sampled data analyzed with Fiberizer Cloud software indicates high attenuation contribute to low total loss and low attenuation lead to high total loss. Spectral analyses of the data at low and high traffic for the stochastic signal. The corresponding frequency peaks were calculated and the results used to classify vehicles at low and high speed. The FWHM obtained with double Gaussian model for differential trace shows that high traffic gives sharp peaks with standard deviation less than 0.6 and above 0.6 for low traffic. The analyses identified peaks above 4.0x10-3 for traces with trucks and cars at high speed, while peaks less than 4.0x10-3 were obtained for traces with cars.

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.

Our oceans are critical to the health of our planet and its inhabitants. Increasing pressures on our marine environment are triggering an urgent need for continuous and comprehensive monitoring of the oceans and stressors, including anthropogenic activity. Current ocean observational systems are expensive and have limited temporal and spatial coverage. However, there exists a dense network of fibre-optic (FO) telecommunication cables, covering both deep ocean and coastal areas around the globe. FO cables have an untapped potential for advanced acoustic sensing that, with recent technological break-throughs, can now fill many gaps in quantitative ocean monitoring. Here we show for the first time that an advanced distributed acoustic sensing (DAS) interrogator can be used to capture a broad range of acoustic phenomena with unprecedented signal-to-noise ratios and distances. We have detected, tracked, and identified whales, storms, ships, and earthquakes. We live-streamed 250 TB of DAS data from Svalbard to mid-Norway via Uninett’s research network over 44 days; a first step towards real-time processing and distribution. Our findings demonstrate the potential for a global Earth-Ocean-Atmosphere-Space DAS monitoring network with multiple applications, e.g. marine mammal forecasting combined with ship tracking, to avoid ship strikes. By including automated processing and fusion with other remote-sensing data (automated identification systems, satellites, etc.), a low-cost ubiquitous real-time monitoring network with vastly improved coverage and resolution is within reach. We anticipate that this is a game-changer in establishing a global observatory for Ocean-Earth sciences that will mitigate current spatial sampling gaps. Our pilot test confirms the viability of this ‘cloud-observatory’ concept. Sensing whales, storms, ships and earthquakes using an Arctic fibre optic cable

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.

Optical fibre sensing technology is a powerful method for long-term reliable sensing in harsh environments, which means it is particularly suitable for the detection of electrical equipment characteristic state parameters, including characteristic gases, abnormal vibration, ultrasonic produced by partial discharge, and abnormal temperature rise. This paper reviews several individual optical fibre sensors for different state parameters detection, discusses the advantages, limitations and possible improvement methods, and finally presents the most promising optical fibre sensor for each state parameter.

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.

In this study, the authors deal with the problem of simultaneous measurement of temperature, pressure, and strain using novel technologies of optical fibre (OF) sensors. Indeed, they address the problem of early surveillance systems to detect disasters in real-time. Through these sensors, they try to predict prospective and possible disasters (landslides, fire, earthquake etc.). Temperature, pressure, and strain should be simultaneously monitored to prevent betimes any damages. They propose a novel design of disaster system, which is able to measure the variation of temperature, pressure, and strain using optical sensors based on Brillouin scattering, two types of these sensors are discussed Brillouin optical time division reflectometers and Brillouin optical time division analysis (BOTDA). Thus, they indicate the performance of BOTDA sensors on disaster detection systems. However, these sensors cannot measure pressure variation, so they introduce the application of hybrid BOTDA/fibre Bragg grating (FBG) system in order to predict disasters caused by pressure.

Fibre Bragg Grating (FBG) sensor is a new sensor with numerous advantages. How to apply in the safety monitoring of landslide engineering is still in experiment and research stage. Here, FBG is used to monitor the landslide process of the gravel soil pile. Before monitoring experiment, the article first tests FBG packaging and burying effect by two tests in lab, one is sand pile landslide test which proves vertical buried is feasible and the other is loading test on the steel bar sensor which proves the wavelength change of FBG on steel bar sensor has a good linear relationship with the loading change. Then, buried the steel bar sensor in the gravel soil slope after simple encapsulation. Stress and strain monitoring results of grating sensors are obtained in landslide which is formed through the simulation of excavation construction. The experimental data show that through correct embedding FBG sensors can effectively monitor the stress–strain change of the slope. FBG provides a new way for the landslide early warning.

Compared with the traditional electrical resistance strain gauge, the fibre Bragg grating (FBG) is a new material that can be used to produce the strain sensor, which has many advantages such as convenient installation, low temperature drifting, less signal interference and higher transmitted quality. In this study, FBG sensor system configuration, design principle, numerical simulation and loading tests for the FBG strain gauge are expatiated extensively. At the last, one-axial and three-axial strain gauges are produced and some conclusions have been put forward. So the FBG strain gauge can meet the precision of the structure monitoring and replace the traditional sensors.

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.

High-voltage transformers are essential for power systems, particularly in the transmission and distribution sectors. The reliability of this equipment typically depends on their insulation condition. Thus, considerable attention must be accorded to the development of diagnostic and monitoring systems for predicting the condition of transformer oil. At present, several electrical, physical and chemical diagnostic techniques have been applied to transformer condition monitoring. This study presents a review of the application of optical sensors to transformer condition monitoring. Optical-sensor-based monitoring of various parameters of transformer oil as part of transformer condition monitoring is discussed. The classification and sensing principles of optical sensors are also reviewed.

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.

Accurate and efficient monitoring of electrical machine (EM) operating parameters, including temperature, mechanical vibration, torque and rotating speed and others that can indicate the EM health conditions is becoming ever more important in the world of electrical drives. The traditional methodology of one sensor per parameter can be theoretically replaced by a “one sensor measures all” technology, which can be achieved through the use of fibre-optic sensors (FOS). In this paper, several FOSs, which use different optical sensing principles for multiple physical parameter measurements of EMs, are reviewed. This paper also provides an insight into the major developments, and discusses the engineering challenges of FOS used for EM monitoring over the last few decades, and compares the advanced features of FOS with those of conventional sensors in use. Finally, a novel FOS-EM observer system scheme employing the Fibre Bragg Grating technique for multi-parameter monitoring of EM health is proposed, after discussion of the preceding industrial and academic FOS cases for EM applications.

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.

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.

This article presents laboratory tests, with the purpose being to verify the suitability of standard optical fibres in a tight jacket for advanced strain analysis within concrete members. An optical reflectometer was used to enable the optical signal to be processed on the basis of the Rayleigh scattering phenomenon, so that strains and/or temperature changes were determined along the length of the measuring fibre. The measurements were carried out continuously in a geometrical sense (distributed measurements), with a spatial resolution starting from as fine as 5 mm. The arrangement of optical fibres inside the heterogeneous concrete medium and on its surface allowed for the identification and detailed analysis of local phenomena such as cracks. Remote and early location of structural damage with an estimation of its scale provides new opportunities for the monitoring of the structural health of reinforced concrete structures, facilitating the interpretation of its behaviour as well as failure risk management based on comprehensive and reliable measurement data. If traditional spot techniques are used, this approach is not possible. The aim of the initial studies was to analyse the strain distributions over compressed and tensioned measurement sections located on the surface of a cylindrical specimen of concrete. In the tests which followed, the reinforced concrete rod was eccentrically tensioned with fibre optics installed inside. Qualitative and quantitative verification of crack widths was made, with a narrow range up to 0.05 mm and a wider one to 0.30 mm. The results of the studies show very good accuracy of optical fibre sensor technology as a reference technique during the analysis of microcracks and narrow cracks, and moderate accuracy in the case of wider cracks. Despite using optical fibres in a tight jacket which mediates in strain transfer, the results obtained can be very suitable for the assessment of the structural condition of the member under consideration. It is also worth noting that the tests conducted indicate the effectiveness of distributed optical fibre technology for the analysis of concrete homogeneity and its structural behaviour within compressed areas, as it is possible to calculate strains over measuring bases that start from lengths as short as 5 mm.

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.

Currently, there are evident contradictions in the literature about how milk protein concentration and added calcium affect the hydrolysis and aggregation phases during milk coagulation. In this study, a near infrared light backscatter sensor and rheology were used to evaluate the effects of protein (3, 4, and 5%), calcium (0.90 and 1.80 m m ), inulin (2, 5 and 8%) concentrations and their interactions on the hydrolysis, aggregation and firming phases during enzymatic coagulation of low fat milk. The increase in both inulin and calcium concentration reduced the duration of the hydrolysis, aggregation and firming phases. The increase in protein concentration reduced the hydrolysis reaction rate, but produced a significant decrease in the aggregation and cutting times. The results demonstrated that the optical sensor is sensitive enough for the inline detection of the effect of variation in milk composition or ingredients addition on each of the coagulation phases.

Fibre optic sensors are well suited to measuring fluid flow in many contexts, and recently there has been burgeoning interest in their application to direct, invasive measurement of blood flow within human vasculature. Depending on the sensing method used and assumptions made, these intravascular measurements of blood flow can provide information about local blood velocity, volumetric flow, and flow-derived parameters. Fibre optic sensors can be readily integrated into medical devices, which are positioned into arteries and veins to obtain measurements that are inaccessible or cumbersome using non-invasive imaging modalities. Measurements of flow within coronary arteries is a particularly promising application of fibre optic sensing; recent studies have demonstrated the clinical utility of certain flow-based parameters, such as the coronary flow reserve (CFR) and the index of microcirculatory resistance (IMR). In this review, research and development of fibre optic flow sensors relevant to intravascular flow measurements are reviewed, with a particular focus on biomedical clinical translation.

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

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.