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Eingeladener Vortrag
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We characterize the Brillouin gain spectra (BGS) in perfluorinated graded-index polymer optical fibers (PFGI-POFs) at 1.32 µm and 1.55 µm. Three kinds of PFGI-POFs with the same core diameter, but which are fabricated by different manufacturers, are tested. For all the PFGI-POFs, the Stokes power measured at 1.32 µm is higher than that at 1.55 µm due to the lower propagation loss, but significant differences in Stokes power are observed among the three. Based on the measurement obtained by the optical time-domain reflectometry, we show that the actual propagation loss of the PFGI-POFs plays a crucial role in observing BGS.
Structural health monitoring by distributed fiber optic sensors embedded into technical textiles
(2012)
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 are used for reinforcement of geotechnical and masonry structures. The embedded fiber optic sensors provide online information about the condition of the structure and about the occurrence and location of any damage or degradation.--------------------------------------------------------------------------------------------------------------------------------------------------------
Technische Textilien mit integrierten faseroptischen Sensoren eröffnen neue Möglichkeiten der Zustandsüberwachung (structural health monitoring) in Geotechnik und Ingenieurbau. Die verteilt messenden Sensoren basieren auf der Brillouin-Streuung in Glasfasern und auf der OTDR in polymeroptischen Fasern. Derartige 'intelligente' technische Textilien werden in erster Line zur Verstärkung von geotechnischen Bauwerken und von Gebäuden genutzt. Die integrierten Sensoren liefern eine zeitnahe Information über den bestimmungsgemäßen Zustand des Bauwerks sowie über die Entstehung und den Ort von lokalen Bauwerksschäden.
We present the status of our work on a tube shaped 3D deformation sensor based on continuously distributed fiber optic sensing. A sensor tube of very large diameter is used to ensure high sensitivity while the transportability and applicability are still comfortable due to our application strategy. The setup is designed to use different measurement techniques in the applied optical fibers including Brillouin based measurements and interferometric optical frequency domain measurements using an OBR 4400 from Luna Technologies.
Fiber optic sensors based on polymer optical fibers (POF) have the advantage of being very elastic and robust at the same time. Unlike silica fibers, standard PMMA POF fibers can be strained to more than 40% while fully maintaining their light guiding properties. We investigated POF as a distributed strain sensor by analysing the backscatter increase at the strained section using the optical time domain reflectometry (OTDR) technique. This sensing ability together with its high robustness and break-down strain makes POF well-suited for integration into technical textiles for structural health monitoring purposes. Within the European research project POLYTECT (Polyfunctional textiles against natural hazards) technical textiles with integrated POF sensors, among others sensors are being developed for online structural health monitoring of geotechnical structures. Mechanical deformation in slopes, dams, dikes, embankments and retrofitted masonry structures is to be detected before critical damage occurs. In this paper we present the POF strain sensor properties, reactions to disturbing influences as temperature and bends as well as the results of the different model tests we conducted within POLYTECT. We further show the potential of perfluorinated graded-index POF for distributed strain sensing with increased spatial resolution and measurement lengths.
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.
We investigate the suitability of silica graded index multimode fibers (MMF) for distributed Brillouin sensing in structural health monitoring, where the measurement range is limited by small bendings that appear during the integration process of the sensing fibers into the structures. For the investigation of stimulated Brillouin scattering (SBS) in MMF, we use an MMF connected on both ends to the SMF measurement setup by fusion splices to ensure that only the fundamental mode is transmitted. The SBS spectra in MMF are recorded using a 1319 nm single frequency (line width 5 kHz) laser. Results found for standard singlemode fibers and the fundamental mode in multimode silica optical fibers are compared. We present the gain spectra showing the dependence of frequency shift, attenuation and modal noise to both temperature and strain. The dependence of the attenuation due to bending is shown. Finally, the perspective of the excitation of SBS in polymer optical fibers is discussed against the background of our research on SBS in MMF.
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.
Fiber optic sensors based on polymer optical fibers (POF) take advantage of the high elasticity and high break-down strain of POF. Because of their outstanding elastic properties, POF are well suited for integration into technical textiles like geotextiles and medical textiles. Smart textiles with incorporated POF sensors, able to sense various mechanical and physical quantities, can be realized. The integration of POF as a sensor into geotextiles for monitoring of displacement of soil is very attractive since POF can be used for distributed strain measurement of strain values of more than 40 %. An online monitoring of critical mechanical deformations of geotechnical structures like dikes, dams, slopes, embankments as well as of masonry structures can be ensured. Medical textiles that incorporate POF sensors can control vital physiological parameters like respiratory movement and can be used for wearable health monitoring of patients requiring a continuous medical assistance and treatment. The biocompatibility of POF is an important criterion for selecting POF as a medical sensor. The paper shows selected examples of using POF sensors for the mentioned monitoring purposes.
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.
Distributed polymer optical fiber sensors in geotextiles for monitoring of earthwork structures
(2009)
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.
Zustandsüberwachung von Erdbauwerken mittels in Geotextilien integrierter optischer Polymerfasers
(2009)
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.
POF sensors integrated in technical textiles for monitoring of earthwork structures and masonry
(2009)
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.
Polymer optical fiber (POF) sensors have the unique ability to measure high strain distributed along the fiber up to 40% using the optical time-domain reflectometry (OTDR) technique. Both, standard PMMA fibers and perfluorinated (PF) graded-index (GI) POF are introduced and evaluated in potential use and applicability. Further, distributed length change measurement based on cross-correlation analysis of the characteristic fiber signature of PF POF is introduced. We conclude the advances in distributed POF strain sensors technology with respect to application in structural health monitoring. Special focus is on the sensor integration into technical textiles for health monitoring of geotechnical structures and masonry structures. Measurement results of sensor-equipped textiles in different model tests are presented, displacement of soil and cracks in retrofitted masonry structures are detected and evaluated.