Optical Fiber Sensor For Monitoring Research Articles

Distributed Optical Fiber Sensors for Monitoring of Civil Engineering Structures.

Distributed Fiber Optics Sensing (DFOS) is a mature technology, with known, tested, verified, and even certified performance of various interrogators and measurement methods, which include Distributed Temperature Sensing (DTS), Distributed Temperature-Strain Sensing (DTSS), and Distributed Acoustic Sensing (DAS). This paper reviews recent progress in two critical areas of DFOS implementation in large scale civil engineering structures. First is the substantial improvement in sensing accuracy achieved by replacing Brillouin scattering-based measurements with its Rayleigh counterpart. The second is progress in acquisition speed and robustness, as now engineers can observe parameters of interest in real-time, and make informed, operational decisions regarding quality and safety. This received a high valuation from field engineers when used during the construction stage of the project. Furthermore, this change in the use of DFOS in civil engineering greatly increases the practical possibility of installing FO cables permanently. The same FO cables can be later used for long-term monitoring, during maintenance periods throughout the structure’s lifetime. To illustrate these two advances, we present a comparison between Brillouin and Rayleigh scattering measurements, and their accuracy, and highlight the importance of temperature and strain separation. We also present several important applications in large scale civil engineering infrastructure projects.

Interferometric optical fiber sensor for monitoring of dynamic railway traffic

The optical fiber sensor based on a Fabry-Pérot interferometer was developed and experimentally verified. As a sensing element a conventional optical fiber was used. The prepared optical sensor was placed at the rail and tested in normal operation for 24 h. Practical tests have shown that from the measured signals of the prepared sensor it is possible to determine the time dependence of the elongation of the sensing optical fiber. From this it is possible to determine the speed of the train set, the number of axles, the load of individual wheels and identified a possible flat wheels of train set. The results document that the sensor can be used as a sensitive detector for monitoring of dynamic railway traffic. The main advantages, in addition to sensitivity and a wide range of monitored parameters, include easy implementation and no expensive equipment.

Optical fiber sensors for monitoring in critical care.

Monitoring of key physiological and pharmacological parameters is an important part of a closed loop control system in critical care. Optical fiber sensors provide a versatile platform technology that can be easily incorporated into existing in-dwelling catheters or face masks. With appropriate functional coatings they can be used to monitor a range of relevant parameters and two different examples are presented: (i) respiration monitoring; (ii) drug level monitoring. Respiration monitoring involves monitoring of temperature and humidity in inhaled and exhaled breath. The optical fiber sensor consists of a fiber Bragg grating to measure temperature and a tip coating whose refractive index changes with humidity. The sensor is demonstrated to be able to track breath to breath changes when incorporated into a mask. Drug level monitoring is demonstrated in vitro using a long period grating coated with molecularly imprinted polymer nanoparticles that are sensitive to fentanyl. The sensor has a limit of detection of 50ng/ml.

Plastic Optical Fibre Sensors for Structural Health Monitoring: A Review of Recent Progress

While a number of literature reviews have been published in recent times on the applications of optical fibre sensors in smart structures research, these have mainly focused on the use of conventional glass‐based fibres. The availability of inexpensive, rugged, and large‐core plastic‐based optical fibres has resulted in growing interest amongst researchers in their use as low‐cost sensors in a variety of areas including chemical sensing, biomedicine, and the measurement of a range of physical parameters. The sensing principles used in plastic optical fibres are often similar to those developed in glass‐based fibres, but the advantages associated with plastic fibres render them attractive as an alternative to conventional glass fibres, and their ability to detect and measure physical parameters such as strain, stress, load, temperature, displacement, and pressure makes them suitable for structural health monitoring (SHM) applications. Increasingly their applications as sensors in the field of structural engineering are being studied and reported in literature. This article will provide a concise review of the applications of plastic optical fibre sensors for monitoring the integrity of engineering structures in the context of SHM.

Optical fibre sensors for monitoring of welding residual stresses

Transient and residual strains in the heat affected zone (HAZ) of a TIG arc welded aluminium–magnesium alloy test plate have been measured on line using fibre Bragg grating sensors. The optical fibre sensor operates as a reflection filter: when a light beam travelling along the fibre optic reaches the Bragg grating, only a certain wavelength will be reflected. The reflected wavelength will change if any strain is applied to the fibre sensor. An optical fibre sensor was bonded on the bottom surface of the welding plate; during the weld thermal cycle, the strains experienced by the sensor were correlated to those by the plate. Thermal strains were measured on line during the welding procedure. Subtracting from the total strain the contribution of the fibre thermal expansion, it was possible to determine the pattern and rate of both dynamic and residual strains developed in the HAZ of the welded specimens. The final goal is to act actively during welding in order to minimise the residual stresses and distortions.