Query: fibre optic sensors

title: Experimental investigation of strain sensitivity for surface bonded fibre optic sensors
abstract: The strain sensitivity coefficient for a surface mounted fibre optic sensor is strongly affected by the type of adhesive material used for its installation. In the present study, appropriate strain correction factors have been investigated to modify the strain sensitivity coefficient for surface mounted fibre Bragg gratings to achieve accurate strain data. The experimental study adopts a fibre optic sensor (FOS) mounted on a carbon fibre reinforced polyphenylene sulphide specimen using two adhesive types, i.e. a cyanoacrylate and an epoxy resin. For comparison purposes strain data was also captured using strain gauge, contact extensometer and digital image correlation instrumentation. The experiments reveal that the predicted correction factors vary considerably with the adhesive material used for the mounting of the FOS. Further analysis demonstrates that a 37 deviation in the value of the correction factor results in a 27 variation in the strain output. In addition, the microscopic image analysis confirmed that the thickness of the adhesive layer between FOS and the substrate affects the strain sensitivity of FOS and plays a crucial role in transmitting the deformation of the host material to the sensing element.

title: Strain and crack analysis within concrete members using distributed fibre optic sensors
abstract: 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.

title: Development of low cost packaged fibre optic sensors for use in reinforced concrete structures
abstract: 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.

title: Magnetic Resonance Imaging Compatible Non Invasive Fibre Optic Sensors Based on the Bragg Gratings and Interferometers in the Application of Monitoring Heart and Respiration Rate of the Human Body: A Comparative Study
abstract: The publication presents a comparative study of two fibre optic sensors in the application of heart rate (HR) and respiratory rate (RR) monitoring of the human body. After consultation with clinical practitioners, two types of non invasive measuring and analysis systems based on fibre Bragg grating (FBG) and fibre optic interferometer (FOI) have been designed and assembled. These systems use probes (both patent pending) that have been encapsulated in the bio compatible polydimethylsiloxane (PMDS) The main advantage of PDMS is that it is electrically non conductive and, as well as optical fibres, has low permeability. The initial verification measurement of the system designed was performed on four subjects in a harsh magnetic resonance (MR) environment under the supervision of a senior radiology assistant. A follow up comparative study was conducted, upon a consent of twenty volunteers, in a laboratory environment with a minimum motion load and discussed with a head doctor of the Radiodiagnostic Institute. The goal of the laboratory study was to perform measurements that would simulate as closely as possible the environment of harsh MR or the environment of long term health care facilities, hospitals and clinics. Conventional HR and RR measurement systems based on ECG measurements and changes in the thoracic circumference were used as references. The data acquired was compared by the objective Bland Altman (B A) method and discussed with practitioners. The results obtained confirmed the functionality of the designed probes, both in the case of RR and HR measurements (for both types of B A, more than 95% of the values lie within the 1.96 SD range) while demonstrating higher accuracy of the interferometric probe (in case of the RR determination, 95.66% for the FOI probe and 95.53% for the FBG probe, in case of the HR determination, 96.22% for the FOI probe and 95.23% for the FBG probe)

title: Fibre Optic Sensors for Structural Health Monitoring of Aircraft Composite Structures: Recent Advances and Applications
abstract: In service structural health monitoring of composite aircraft structures plays a key role in the assessment of their performance and integrity. In recent years, Fibre Optic Sensors (FOS) have proved to be a potentially excellent technique for real time in situ monitoring of these structures due to their numerous advantages, such as immunity to electromagnetic interference, small size, light weight, durability, and high bandwidth, which allows a great number of sensors to operate in the same system, and the possibility to be integrated within the material. However, more effort is still needed to bring the technology to a fully mature readiness level. In this paper, recent research and applications in structural health monitoring of composite aircraft structures using FOS have been critically reviewed, considering both the multi point and distributed sensing techniques.

title: Fibre optic sensors for coal mine hazard detection
abstract: 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.

title: A Review of Distributed Fibre Optic Sensors for Geo Hydrological Applications
abstract: Distributed optical fibre sensing, employing either Rayleigh, Raman, or Brillouin scattering, is the only physical contact sensor technology capable of accurately estimating physical fields with spatial continuity along the fibre. This unique feature and the other features of standard optical fibre sensors (e.g. minimal invasiveness and lightweight, remote powering/interrogating capabilities) have for many years promoted the technology to be a promising candidate for geo hydrological monitoring. Relentless research efforts are being undertaken to bring the technology to complete maturity through laboratory, physical models, and in situ tests. The application of distributed optical fibre sensors to geo hydrological monitoring is here reviewed and discussed, along with basic principles and main acquisition techniques. Among the many existing geo hydrological processes, the emphasis is placed on those related to soil levees, slopes/landslide, and ground subsidence that constitute a significant percentage of current geohazards.

title: Review of high sensitivity fibre optic pressure sensors for low pressure sensing
abstract: Fibre Bragg grating (FBG) pressure sensors show a great potential in replacing conventional electrical pressure sensors due to their numerous advantages. However, increasing their pressure sensitivity performance for low hydrostatic pressure measurement is still a challenge. This paper reviewed recent pressure sensitivity enhancement methods that could be divided into two groups, namely intrinsic and extrinsic. For the intrinsic enhancement method, this paper reviewed polymer FBGs, special fibre sensors, interferometric sensors, and special grating sensors. For the extrinsic enhancement method, polymer based pressure transducers, diaphragm based pressure transducers, and other structure based pressure transducers were reviewed in detail.

title: Evaluation of flexural behaviour of cemented pavement material beams using distributed fibre optic sensors
abstract: This paper aims to evaluate the reliability and accuracy of the estimation of flexural strains in cemented pavement material (CPM) beams using a distributed fibre optic sensing technique. Static and dynamic four point bending tests were performed on CPM beams equipped with distributed fibre optic sensors (DFOSs) and a linear variable differential transducer (LVDT) The strain data recorded by the DFOSs indicated that the midspan deflection measured by LVDT provides a reliable estimation of the flexural strain in CPM beams under both static and dynamic loading conditions. Moreover, the evolution of the strain profiles measured by DFOSs during the flexural tests clearly demonstrated the capability of DFOSs to detect crack initiation and propagation in CPM beams.

title: Using Distributed Fibre Optic Sensors for Detecting Fires and Hot Rollers on Conveyor Belts
abstract: The use of modern fibre optic sensors based on DTS (distributed temperature sensing) technology has established itself as a proven method for fire detection and temperature measurement. A passive fibre optic cable provides accurate temperature measurements along the length of the conveyor belt, which enables an effective and cost effective monitoring of even very long conveyor routes. Fires and overheating, which can occur during operation and lead to serious damage and long downtimes, are quickly detected and localized to within one meter accuracy. The necessary countermeasures can be quickly activated. Heat detection for hot rollers requires a proper installation of the sensor cable and configuration of the alarm zones and analyses. This paper is based on conveyor belt tests and case studies, and describes the potential of fibre optic based DTS technology with regard to fire and hot roller detection along conveyor belts.