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- 2015 (9) (entfernen)
Dokumenttyp
Schlagworte
- Fibre-optic sensor (2)
- Monitoring (2)
- Reliability (2)
- Structural health monitoring (2)
- Acoustic emission (1)
- Application (1)
- Brillouin frequency domain analysis (1)
- Brillouin scattering (1)
- Climatic stability (1)
- Coherent Rayleigh OTDR (1)
Systematic investigation of annealing behavior of drawn PMMA fibers was performed. Dynamics of annealing process were measured under different environmental conditions by fiber longitudinal shrinkage monitoring. Process was found to follow stretched exponential decay function indicating heterogeneous nature of underlying molecular dynamics. Consequences of fiber annealing for climatic stability of polymer optical fiber-based sensors are discussed, emphasizing importance of fiber controlled post-fabrication annealing. Dependence of induced fiber shrinkage on annealing time, temperature and fiber drawing conditions is investigated and interpreted. In addition, strong influence of humidity on annealing process was observed, which was not recognized in previous studies. This further highlights role of fiber post-fabrication thermal treatment with respect to intended operating conditions.
We report on the successful application of distributed acoustic sensing (DAS) to the detection of partial discharge (PD). A detection limit of about 1 nC discharge magnitude was achieved for PD in a real-scale model of a high voltage termination. Dedicated ultrasonic fibre-optic transducers were interrogated using coherent optical time-domain Rayleigh backscatter reflectometry (C-OTDR). Random quadrature demodulation was employed for retrieving relevant acoustic information from the raw C-OTDR backscatter traces. To our knowledge, our results are a first-time demonstration that quasi-distributed fibre-optic acoustic sensing is a candidate technology for the acoustic partial discharge monitoring of power cable joints and terminations.
We report on the development of a distributed fiber optical sensor system for structural health monitoring of largc-scale geotechnical and civil infrastructures. The system is based on Brillouin frequency domain analysis (BOFDA) for distributed measurement of strain and temperature along Standard silica optical fibers used as sensors. By additional incorporation of the fiber optic sensors in geosynthetics, two-dimensional sensors can be realized. Such smart geosynthetics can be used for reinforeerneut of geotechnical and masonry structures and the embedded fiber optic sensors can provide information about the condition of the structures and detect the presence of any damages and destructions in real time.
Gamma radiation induced effects in perfluorinated polymer optical fibers for sensing applications
(2015)
Radiation induced attenuation in perfluorinated polymer optical fiber was investigated as a potential mean for online. in situ gamma radiation monitoring. Spectral dependence of radiation induced attenuation was measured in the visible and near infrared range. Attenuation spectrum exhibits sharp increase both towards the ultraviolet and infrared side of the spectrum with 3 distinct peaks around 1400 nm. The fiber sensitivity to gamma radiation was further evaluated at two commonly used IR wavelengths (1310nm and l550nm} by pre- and post-irradiation optical time-domain reflectometry measurements. The examined fiber is sensitive up to lOO kGy of total absorbed dose with only minor saturation towards the large dose values. The influence of gamma radiation on the fiber mechanical properties was studied as well. Up to the maximal dose of 100 kGy, no significant deterioration of fiber strength and elasticity was observed.
Movements in geological areas are often caused by shear zones deep in the underground or by hardly observable slipping zones. Detection of movements reaching critical values is of crucial importance to avoid losses and harms. Optical sensor fibers with gauge lengths of several meters or even distributed fiber-optic sensors with gauge lengths of hundreds of meters allow detecting deformation of such zones with quite good resolution. The paper presents a new technology of detecting deformations and movements in soil or rock massifs. The core part of the sensing system is a tiny pultruded rod with an outer diameter of 3 mm to 6 mm. It contains two fiber-optic sensor systems. One sensor system is used for permanent online measurement and provides integral strain information along the whole length of the rod; in case of critical deformations, it provides a warning signal. The second sensing system uses fiber-optic Bragg grating (FBG) strain sensors located close to the expected shear zone. This measurement system will be activated after the warning signal has been initiated by the integral strain measurement system. The FBG strain sensor system records then resulting deformations in detail. The sensing rod containing both sensor systems can be installed in a borehole to detect beginning soil movements automatically. The electronic equipment is powered by a solar panel; the amount of deformation in soil or rock formations can be estimated from the strain change measured in the sensor fibers. The effectiveness of this warning system will be shown using the example of a critically sliding slope in an open brown coal pit in Germany.
We present the fabrication and characterization of a polycarbonate (PC) microstructured polymer optical fiber (mPOF) and the writing of a fiber Bragg grating (FBG) in it to obtain a polymer optical FBG sen-sor. The manufacturing process of the PC mPOF consists of multiple consecutive stages, such as casting of pol-ymer granulates into a solid rod, machining and drilling of a 3-ring hexagonal lattice of holes into it, and finally drawing into fiber. We demonstrate that the obtained PC mPOF is photosensitive and FBGs can be conveniently inscribed into it, thereby enabling FBG-based temperature and strain sensing. The PC optical fibers are for some applications an attractive alternative to conventional materials used in POF fabrication, such as polymethyl methacrylate (PMMA). In general, PC can be used at temperature up to 120 °C and breaks at considerably higher strains than PMMA.
Smart geosynthetics for structural health monitoring using fully distributed fiber optic sensors
(2015)
We report on the development of a complete system for structural health monitaring of large-scale geotechnical structures. The system uses Brillouin frequency domain analysis (BOFDA) for distributed measurement of strain and temperature along glass optical fibers (GOFs) by determining the so-called Brillouin frequency shift (BFS). ln a number of research activities we managed to optimize the BOFDA measurement setup regarding the spatial resolution and the accuracy of the measured quantities. Moreover, we realized a simultaneaus measurement of strain and temperature by using nonzero dispersion-shifted fibers (NZDSFs) with several multiple Brillouin scattering resonances. ln cooperation with our German and ltalian industry partners we finally succeeded in fabricating low-attenuation smart geosynthetics as a sensor component of a fully distributed Brillouin-based fiber optic monitaring system.
Standardization in fibre-optic sensing for structural safety - activities in the ISHMII and IEC
(2015)
Fiber-optic sensors are increasingly established in the sensor market. Their advantages have unquestionably been verified by numerous demonstrations to enhance the operational performance of aged structures or to monitor the structural behavior of safety-relevant structures or their components. However, there are some barriers in use due to a lack of extensive standardization of fiber-optic sensors. This leads very often to restraints in the users community. The paper shows the status in international standardization of fiber-optic sensors as well as current activities in leading institutions such as IEC and ISHMII and others with the purpose of providing relevant standards for a broader use of selected fiber-optic sensor technologies.