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The presented research is carried out on the background of the development of a new strain sensor, integrated in technical textiles using the optical time domain reflectometry (OTDR) technique. We investigated the effect of increased scattering in POF due to applied strain as a distributed sensor including research on long-term stability and reliability of this sensor.
Recently, we have proposed, to our knowledge for
the first time, to use perfluorinated graded-index polymer
optical fiber (POF) for distributed measurement of strain.
Thanks to their low attenuation and low modal dispersion
compared to standard-POF, this fiber type allows to extend the
measurement length to more than 500 meters at increased
spatial resolution. In this paper, two mechanisms for strain
sensing are introduced. As in standard PMMA POF, strain in the
fiber can be detected by evaluating the local backscatter
increase occurring at strained fiber sections. Further, we
propose, to our knowledge for the first time, a true distributed
length change measurement in POF using cross-correlation
analysis of the fibers characteristic backscatter signature.
Using this technique, it is possible to measure relative
displacement between different fiber sections avoiding signal
fading failures that are inherent in other measurement
principles. Cross-sensitivities to the sensor signal, as fiber
bends and temperature, are investigated and quantified.
Sensing characteristics of standard polymer
optical fibers (POF) are further studied using the optical time
domain reflectometry (OTDR) technique. The level of the
backscattering inside POF, which highly increases at locations
where strain is applied to the fiber, is further investigated with
respect to spectral behavior, strain rate and span of time from
the stretching event. An algorithem to overcome the problem of
the decrease of spatial resolution as a result of pulse
broadening due to modal disperion, is proposed. The research
is carried out on the background of the development of a new
strain sensor that is integrated in technical textiles.
Protection of critical infrastructure using fiber optic sensors embedded in technical textiles
(2010)
Terrorists and criminals more and more attack and destroy important infrastructures like routes, railways, bridges, tunnels, dikes and dams, important buildings. Therefore, reliable on-line and long-term monitoring systems are required to protect such critical infrastructures. Fiber optic sensors are well-suited for that. They can be installed over many kilometers and are able to measure continuously distributed strain, pressure, temperature and further mechanical and physical quantities. The very tiny optical fibers can be integrated into structures and materials and can provide information about any significant changes or damages of the structures. These so-called smart materials and smart structures are able to monitor itself or its environment. Particularly smart technical textiles with embedded fiber optic sensors have become very attractive because of their high importance for the structural health monitoring of geotechnical and masonry infrastructures. Such textiles are usually used for reinforcement of the structures; the embedded fiber optic sensors provide information about the condition of the structures and detect the presence of any damages and destructions in real time. Thus, critical infrastructures can be preventively protected. The paper will introduce this innovative field and will present the results achieved within several German and European projects.
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.
The potential of the use of POF as distributed sensors in several application fields has been successfully demonstrated. The distributed POF sensors have moved from the laboratory to the field. The paper presents the recent progress in the development of distributed POF sensors and addresses the main challenges to this innovative technology.
Technical textiles with embedded fibre optic sensors habe been developed for the purposes of the structural health monitoring in geotechnical and civil engineering as well as for healthcare monitoring in the medical sector. The paper shows selected examples of using such sensor-based smart textiles for different applications.
Distributed fiber optic sensors embedded in technical textiles for structural health monitoring
(2010)
Technical textiles with embedded distributed fiber optic sensors have been developed for the purposes of structural health monitoring in geotechnical and civil engineering. The distributed fiber optic sensors are based on Brillouin scattering in silica optical fibers and OTDR in polymer optical fibers. Such "smart" technical textiles can be used for reinforcement 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. Thus, structural health monitoring of critical geotechnical and civil infrastructures can be realized. The paper highlights the results achieved in this innovative field in the framework of several German and European projects.
In this paper the influence of combined temperature and strain changes as well as changes of moisture content on polymer optical fibers made of polymethyl methacrylat (PMMA) is investigated. The increase of the scattering coefficient with increasing temperature for various strain levels is observed and quantified. The measurement results of influence of humidity on scattering intensity of PMMA-POF encourage to porpose these as a distributed humidity sensor.