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- 2016 (6) (entfernen)
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- Englisch (6)
Schlagworte
- Brillouin scattering (3)
- Backscatter reflectometry (2)
- Brillouin frequency shift (2)
- Distributed measurement (2)
- Distributed sensor (2)
- Gamma radiation (2)
- Optical fiber sensor (2)
- Radiation dosimetry (2)
- distributed sensor (2)
- Adhesive bond (1)
We have studied the influence of gamma rays on physical properties of different commercially available silica optical fibers stepwise irradiated up to a total dose of 100 kGy. The detection of radiation-induced changes in silica glass offers the possibility of using selected optical fibers as distributed radiation sensors. The measurements performed by us were based on optical backscatter reflectometry and Brillouin distributed sensing. The measurement methods enable an analysis of radiation-induced modification of the group refractive index and density of the optical fibers. The most distinct physical effect observed by us concerns the increase of the optical attenuation with rising total radiation doses. Quantitative measurement results indicate a crucial impact of fiber dopants on radiation-induced physical and sensory characteristics of silica optical fibers affected by differences in fiber fabrication techniques. Based on the obtained results, the suitability of distributed Brillouin sensing for dosimetry applications seems to be improved by modifying the refractive index profile of the fiber core.
We have studied the influence of gamma rays on physical properties of different commercially available silica optical fibers stepwise irradiated up to a total dose of 100 kGy. The detection of radiation-induced changes in silica glass offers the possibility of using selected optical fibers as distributed radiation sensors. The measurements performed by us were based on optical backscatter reflectometry and Brillouin distributed sensing. The measurement methods enable an analysis of radiation-induced modification of the group refractive index and density of the optical fibers. The most distinct physical effect observed by us concerns the increase of the optical attenuation with rising total radiation doses. Quantitative measurement results indicate a crucial impact of fiber dopants on radiation-induced physical and sensory characteristics of silica optical fibers affected by differences in fiber fabrication techniques. Based on the obtained results, the suitability of distributed Brillouin sensing for dosimetry applications seems to be improved by modifying the refractive index profile of the fiber core.
A new technique for optical fiber defect detection using Brillouin distributed fiber optic sensor (DFOS) has been proposed and experimentally demonstrated in this paper. This technique is based on stimulated Brillouin scattering (SBS), which offers three wave interaction in single mode optical fiber (SMF -10 μm/125 μm acrylic coated fiber). The nonlinear effect of SBS is manipulated to locate the defect in optical fiber using distributed sensing technology. Various kind of defects may be present in optical fibers. This paper details a case study on observation of a defect, which manifests its presence in certain temperature values. The detail of defect detection through distributed fiber sensor using the SBS has been brought out. SBS is sensitive to temperature and strain. In order to study the effect of defect in distributed fiber sensor as function of temperature and strain, the distributed pre-strained and unstrained optical fiber is subjected to temperature variation and corresponding measurements are obtained with Brillouin optical time domain analyser (BOTDA). This technique enables the utilization of Brillouin parameters, such as decreased amplitude, frequency and increased linewidth in the defect region of the fiber length. The fiber defect location can be determined with spatial resolution accuracy of less than 50 cm of using BOTDA technique.
Bond monitoring in temperature dependent applications using Brillouin optical time domain analyser
(2016)
Adhesive bond has to be evaluated for its integrity over a range of temperature. Adhesive is being used to bond the sensors with structures. There is no validated technique to test its performance. In this paper, we propose a Brillouin Optical Time Domain Analyzer (BOTDA) based methodology to detect temperature-induced adhesive bond failure below room temperature using distributed fiber optic sensor. The differential coefficient of thermal expansion of the structure and fiber sensor can lead to bond failure at low temperature. Optical fiber impregnated in the structure will experience differential temperature/strain due to debond of the adhesive. This leads to the frequency and amplitude decomposition of the Brillouin spectra. This is a good indication for real-time monitoring of the integrity of a bond.
Maintenance and renewal costs of a typical railway, track and substructure represents 50–60% of the total costs of such infrastructure over its entire service life. Innovations in track and substructure are therefore fundamental to achieve a significant
impact on the overall cost reduction for the railways. Therefore new solutions for track improvements that are effective and that can minimize the interruption of traffic are needed. Moreover, failures of railway embankments happened recently in different regions of the world. Such events, such as the one happened in UK in February 2013 (http://www.bbc.co.uk/news/uk-england-south-yorkshire-21441070), are showing the importance of monitoring track and infrastructure coupled with the use of numerical models for the localization of the critical areas and the design of appropriate countermeasures. Indeed embankment failures, landslides and uneven settlements and similar events are becoming much more common than in the past due to climate changes, and this requires the infrastructure managers to look from a different perspective infrastructure maintenance issues. What was previously consider as “extreme” is now “common” and thus actions need to be taken to be ready when such events will happen. The aim is to mitigate their effects on the infrastructure and to minimize disruptions to train services and reduce maintenance costs to restore the normal service conditions. If this mental change happens, then the need for solutions and techniques for global asset monitoring and ground stabilization will probably increase. Among the others, geotextiles and geogrids for soil reinforcement used in combination with condition monitoring techniques have the potential for minimizing catastrophic events, whilst at the same time providing a good balance among costs and benefits (i.e. sustainability).
The paper describe a case study where the use of multifunctional geotextiles, able to provide both strengthening and monitoring functions, has been tested along a railroad near the city of Chemnitz (Germany). The results are here reported to show the potential use and the innovative aspect of this solution.
Concept for investigating mechanical and thermal impacts on distributed subsurface gas monitoring
(2016)
A multifunctional sensor in line shape was developed and introduced in previous work for measuring of gas concentrations, temperature change, and strain. A current field study focuses on a spatially distributed monitoring of subsurface CO 2 gas storage sites in near real time.
Mechanical impacts, e.g., caused by construction work, denudation, and seismic activity, can affect the integrity of underground gas storage sites. Thermal or moisture impacts, e.g., caused by weather conditions, can influence the gas Distribution behavior. In this paper, we briefly describe the setup of a CO 2 injection soil test field. This setup contains actuating elements for the investigation of mechanical and thermal impacts on distributed subsurface gas monitoring. A concept is given for evaluating these impacts and first experimental results are presented.