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Sensing characteristics of polymer optical fibers (POF) are studied using the optical
time-domain reflectometry technique. For the first time to our knowledge, investigations are
carried out with respect to integration of POF in technical textiles for distributed measurement
of mechanical deformation. The research on this new sensor type focuses on its application in
monitoring of geotechnical structures such as railway embankments, dikes, slopes and dams.
We report on a distributed sensor system using POF integrated in technical textiles as sensing
elements for measurement of displacement of soil. This sensor system is very robust it
withstands the integration under rough condition at a construction site and can detect strain
of more than 40 % over distances of more than 100 meters.
This paper presents new methods to calculate and interpret Rayleigh scattering profiles in polymer optical fibers (POF) recorded by optical time domain reflectometry (OTDR). In contrast to Silica glass optical fibers (GOF), POF experience inhomogeneous stress when being strained, resulting in small scattering centers which allow for a new distributed sensor based on POF. New methods to overcome issues like blurring due to modal dispersion, uncertainties due to inhomogenious losses in the fiber and signal degradation due to viscoelastic creep in the polymer, are presented, for the first time to our knowledge.
In this document a new distributed sensor based on Rayleigh scattering in polymer optical fibers (POF) is proposed and first measurement results of the proposed sensor are shown. Different from Silica glas optical fibers POF absorb high quantities of water resulting in a change of their molecular structure and thereby reducing the present small scattering centers in areas of high humidity. The interdependence between scattering intensity and relative humidity is being investigated in case of steady cycles as well as stepwise changes of humidity and in the presence of moisture. A quantitative measure of humidity and scattering is presented.
One of the unique advantages of polymer optical fibres (POF) is that they can be used to measure very high strain values up to 100 % and beyond exceeding the strain limits of silica fibre-based sensor principles. In this paper the distributed strain measurement capabilities of POF based on backscatter change evaluation are summarized and distributed backscatter measurement technologies are intro-duced. Application examples in the structural health monitoring (SHM) field are presented: a promising approach is the integration into technical textiles for high-strain measurement in earthwork structures and crack detection in buildings. The potential of POF for future applications in SHM such as distributed relative humidity sensing is discussed.
We propose the application of Distributed Acoustic Sensing (DAS) based on Rayleigh Coherent Optical Time-Domain Reflectometry (C-OTDR) to unconventional sensing tasks in industrial condition monitoring. As examples we present results on the way to fibre-optic remote sensing of dielectric damage processes in high voltage cable joints as well as to condition monitoring of passive rollers in large industrial belt conveyor systems.
We propose the use of alternating pulse wavelengths in a direct-detection coherent optical time domain reflectometry (C-OTDR) setup not only to measure strain and temperature changes but also to determine the correct algebraic sign of the change. The sign information is essential for the intended use in distributed mode shape analysis of civil engineering structures. Correlating relative backscatter signal shifts in the temporal/signal domain allows for measuring with correct magnitude and sign. This novel approach is simulated, experimentally implemented and demonstrated for temperature change measurement at a spatial resolution of 1 m.
We demonstrate (and are the first to do so) 63 km Brillouin Optical Frequency-Domain Analysis (BOFDA) for temperature and strain monitoring using a 100 km fiber loop. The use of BOFDA for long-range applications can be considered a novel approach, as previous investigations focused on the utilization of Brillouin Optical Time-Domain Reflectometry and Analysis (BOTDR and BOTDA, respectively). At 51.7 km, a 100 m hotspot (37 °C) was detected without using distributed Raman amplification or image processing.
Smart geosynthetics with embedded optical fibers as distributed sensors provide solutions both for applications in geotechnical engineering and for cost-effective monitoring of critical infrastructures. The incorporation of glass or polymer optical fibers (GOFs or POFs) in geotextiles and geogrids allows early detection of mechanical deformations, temperature and humidity. This paper presents selected examples of smart geosynthetics based on Brillouin and Rayleigh scattering effects in incorporated fiber optic sensors for monitoring of large geotechnical structures like dikes, dams, railways, embankments or slopes. The focus of the presented work is on real field tests of measurement capability with respect to the chosen measurement principle and used fiber type.
Responding to a growing need for intelligent monitoring of critical geotechnical and civil infrastructures, new multifunctional geotextiles and geogrids with integrated optical fibers were developed and investigated within several research projects. Such smart two-dimensional geosynthetics intercorporating optical fibers as distributed sensors provide solutions both for soil reinforcement, erosion control, drainage or environmental protection and for cost-effective monitoring of critical mechanical deformations and temperature distribution in geotechnical and masonry structures at the same time. The integrated fiber optic sensors provide online information about the condition of the monitored structure and about the occurrence and localization of any damage or degradation for the purpose of preventing a total collapse.