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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.
BAM Federal Institute for Materials Research and Testing, in cooperation with the company MeGaSen UG carries out a research project to enhance and validate an innovative approach for distributed subsurface monitoring of gas storage areas. The concept combines different measurement technologies to one multifunctional sensor: membrane-based gas measurement technology for in-situ monitoring of gases in soil and fiber optical sensing of temperature and strain (as a measure for structural change). Key aspect of the research project is the first-time validation of the system in an application relevant dimension. For this purpose a 20 x 20 m2 test field is build. A comprehensive validation of the system is carried out by systematic variation of different parameters like position-dependent gasinjection, temperature and mechanical impact.
We studied Brillouin gain spectrum characteristics in dispersion-shifted fibers having compound GeO2-doping compositions in the fiber core to realize simultaneous measurement of distributed strain and temperature. Due to various dopant concentration alongside the radius of tested nonzero dispersion-shifted fibers several multiple Brillouin scattering resonances were observed in the stimulated Brillouin spectra arose through backscattering on higher acoustic modes which propagated along the fiber axis. As a result of the varying acoustic velocities, the Brillouin resonance peaks featured different temperature coefficients which can be used to accomplish the simultaneous measurement of fiber strain and temperature. We presented our first measurement results for NZDS Fujikura and LEAF Corning fiber and discussed the superior sensory suitability of the former fiber types.
Dyke breaks - caused by e.g. Overflows or Slop breaks during long lasting high water gauge - Play a great role in a failure potential of extreme flood Events.
Using conventional dyke condition Monitoring dyke messengers can undertake only a visual surface inspection. Thus defective Areas can oftentimes be discovered too late.
A critical area in which failures due to soil displacement and moisture Penetration become more significant is located at a landside dyke foot. Geotextiles are integrated here as a Drainage in case of modern three-zone type of dyke.
We report on the development of distributed fiber sensors and their integration into
geosynthetics as they are commonly used in the construction of dikes and dams for flood protection.
The sensing system uses Stimulated Brillouin Scattering (SBS) in silica optical fibers.
Using the Brillouin frequency analysis, the system is capable of detecting changes in both strain
and temperature along the optical fibers. The strain experienced by the optical fibers corresponds
to the deformation of the geosynthetics in case of a critical soil displacement. To satisfy
requirements of dike structures, the system will be optimized to detect soil displacement with a
spatial resolution of 5 m or less over a length in the range of 10 km. These rather modest requirements
leave space for optimization on resolution of the measurement values, measurement
time and cost efficiency.
To our knowledge, this is the first distributed fiber sensor using SBS that is especially designed
for the monitoring of soil displacement in dikes which is made possible by a novel method
for the integration of optical fibers into different types of geosynthetics.
We report on the development of a complete system for spatially resolved detection of critical soil displacement in river embankments. The system uses Brillouin frequency domain analysis (BOFDA) for distributed measurement of strain in silica optical fibers. Our development consists of the measurement unit, an adequate coating for the optical fibers and a technique to integrate the coated optical fibers into geotextiles as they are commonly used in dike construction. We present several laboratory and field tests that prove the capability of the system to detect areas of soil displacement as small as 2 meters. These are the first tests of truly distributed strain measurements on optical fibers embedded into geosynthetics.
We propose a new scheme of Brillouin optical frequency-domain analysis (BOFDA) for distributed fiber-optic strain and temperature sensing, named linear-configured BOFDA (L-BOFDA). In conventional loop-configured BOFDA, light injection into both ends of a fiber under test (FUT) is needed for counter-propagation of pump and probe waves. In contrast, in L-BOFDA, pump and probe waves are injected into the same end of an FUT, and the probe wave Fresnelreflected (or mirror-reflected) at the other end of the FUT is exploited; thus, one-end access is feasible. We show proof-of-concept results of distributed strain measurement in a silica single-mode fiber with L-BOFDA, and discuss the signal-to-noise ratio degradation and the benefit in developing distributed Brillouin sensors based on polymer optical fibers.
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.
This paper reports on the application of distributed Brillouin fiber optic sensing to the monitoring of geotechnical structures. The presented approach to Brillouin sensing offers an alternative to the common pulse-based measurements by using the frequency domain analysis.
The focus of the research and field-testing work is to collect reliable structural health monitoring data from large-scale structures while preserving the System’s versatility in terms of being suitable for different application environments (soil structures, foundations, concrete construction works, pipelines etc.) and its robustness in being well functioning in harsh environments. Upon reviewing the presented application test, it is concluded that Brillouin frequency domain based monitoring, when applied to geotechnical structures, is capable of providing accurate strain readings representing deformations of the soil body, and reliable temperature readings for generating temperature profiles of the entire structure.
An overview of the frequency domain analysis of Brillouin sensing and its digital implementation is given, along with the experiences and insights drawn from an open field test of sensor-equipped geogrid mats.
We present our achievements in the development of distributed fiber optic sensing systems based on Brillouin optical frequency-domain analysis for structural health monitoring. The focus of the applications is on the gapless monitoring of geotechnical structures, large area infrastructures and electrical grids. The work includes the latest use of machine learning algorithms to reduce measurement time by coexistent increasing the measurement accuracy.
Monitoring of construction projects plays increasingly important role in the implementation of growing needs and requirements, especially in geologically difficult areas. This particularly concerns tunnelling and special civil engineering projects. The use of fiber optic sensors for structural health monitoring provides significant economic advantages regarding lower life-cycle costs of the civil infrastructure. We present our achievements in the development of distributed polymer optical fiber sensors based on Rayleigh and Brillouin scattering for early damage detection.
In this paper, a cost-efficient distributed fiber optic measurement system based on Rayleigh scattering is presented. The distributed digital incoherent optical frequency domain reflectometry (I-OFDR) method is developed for detection of significantly large strain in the range from 3 % up to 10 % as required by end users. For this purpose, a vector network analyzer used in the I-OFDR is replaced by a compact and cost-effective digital data acquisition system. This digital emitting/receiving unit enables the recording of the complex transfer function carrying information about the local deformations along the entire sensing fiber.
Es wird ein faseroptisches Messsystem vorgestellt, welches auf Basis der Rayleigh-Rückstreumessung eine ortsauflösende Detektion von signifikant großen Dehnungen bei Bauvorhaben im von Anwendern geforderten Größenordnungsbereich von 3 % bis 10 % ermöglicht. Mit dem Verfahren der digitalen inkohärenten optischen Frequenzbereichsreflektometrie (I-OFDR) werden materialspezifische Vorteile robuster perfluorierter polymeroptischer Fasern (PF-POF) erschlossen. Für den angestrebten industriellen Einsatz für die Zustandsüberwachung im Bereich des Tunnel- und Spezialtiefbaus soll die spezifische Rückstreuzunahme in der PF-POF hochauflösend gemessen werden. Diese Veröffentlichung zeigt in ersten Projektergebnissen die Eignung des digitalen I-OFDR für eine Dehnungsdetektion von bis zu 10%.
Distributed humidity fiber-optic sensor based on BOFDA using a simple machine learning approach
(2022)
We report, to our knowledge for the first time, on distributed relative humidity sensing in silica polyimide-coated optical fibers using Brillouin optical frequency domain analysis (BOFDA). Linear regression, which is a simple and well-interpretable algorithm in machine learning and statistics, is utilized. The algorithm is trained using as features the Brillouin frequency shifts and linewidths of the fiber’s multipeak Brillouin spectrum. To assess and improve the effectiveness of the regression algorithm, we make use of machine learning concepts to estimate the model’s uncertainties and select the features that contribute most to the model’s performance. In addition to relative humidity, the model is also able to simultaneously provide distributed temperature information addressing the well-known cross-sensitivity effects.
In this work, we present our results achieved in several research activities for development of distributed fiber optic radiation sensors using glass and polymer optical fibers. The findings show that both the measurement of the radiation-induced attenuation (RIA) along the entire sensing fiber and the accompanying change in the refractive index of the fiber core can be used for distributed radiation monitoring.
The topic of the presentation are distributed fiber optic measurement techniques that can be used for long-term monitoring of strain, temperature and radiation distribution in the radiation environment. The fiber optic sensors applied to the surface of waste packages provide detection and localization of cracks.
In this work, we present our results achieved in several research activities for development of fiber optic dosimeters. The findings show that both the measurement of the radiation-induced attenuation (RIA) along the entire sensing fiber and the accom panying change in the refractive index of the fiber core can be used for distributed radiation monitoring in the kGy and MGy range, respectively. Depending on the fiber type and material the RIA shows varying response to dose rates, environmental temperatures and the wavelength of the laser source used.
Der Anstieg der Vielfalt nuklearer Anwendungen weit über die Bereiche der kerntechnischen Stromerzeugung erhöht die Relevanz der Entwicklung und Anwendung neuer Technologien zur Strahlungsüberwachung. Auch die offenen Sicherheitsfragen bei der Entsorgung radioaktiver Abfälle einschließlich Zwischen- und Endlagerungsproblematik verstärkt die Nachfrage nach effizienten Monitoringsystemen zum Schutz von Mensch und Umwelt vor ionisierender Strahlung. Aufgrund ihrer messtechnisch vorteilhaften Materialeigenschaften stellen die faseroptischen Strahlungssensoren eine vielversprechende Alternative zu traditionellen Dosimetern dar. Bedingt durch ihre kleinen Abmessungen, elektromagnetische Unempfindlichkeit und ihr geringes Gewicht können faseroptische Sensoren in einer harschen Umgebung an schwer zugänglichen Stellen eingesetzt werden. Darüber hinaus bietet diese Art der Sensoren die Möglichkeit der ortsverteilten Messung entlang der gesamten Sensorfaser. Somit kann durch eine einzelne optische Faser eine Vielzahl an punktuell messenden Sensoren ersetzt werden. Dieser Beitrag beschreibt die in der BAM vorangetriebenen Entwicklungen unterschiedlicher Sensorprinzipien, -lösungen und -verfahren zur Detektion ionisierender Strahlung.
In der vorliegenden Studie wurde der Einfluss der statischen Verkehrsbelastung auf die geringen Durchbiegungseffekte in der Betonkonstruktion einer bestehenden Brücke mittels ortsauflösender faseroptischer Sensoren untersucht. Dabei tragen die Ergebnisse der an der Amsterdamer Brücke 705 durchgeführten Belastungstests wesentlich zum Verständnis des Strukturverhaltens bei. Das Konzept der statischen Belastung basierte auf dem Einsatz von zwei 36-Tonnen-Lastwagen, die an mehreren vorbestimmten Stellen auf der Brücke anhielten. Die auf diese Weise aufgebrachte Last führte zu ortsabhängigen kleinen Durchbiegungseffekten, die als lokale Längsdehnung der an der Unterseite der Brücke integrierten Sensorfaser aufgezeichnet wurden. Die reflektometrischen Messungen beruhten auf dem Prinzip genannt TW-COTDR (Tunable Wavelength Coherent Optical Time Domain Reflectometry). Die Messgenauigkeit lag im Bereich von 0,5 µm/m.
In der vorliegenden Studie wurde der Einfluss der statischen Verkehrsbelastung auf die geringen Durchbiegungseffekte in der Betonkonstruktion einer bestehenden Brücke mittels ortsauflösender faseroptischer Sensoren untersucht. Dabei tragen die Ergebnisse der an der Amsterdamer Brücke 705 durchgeführten Belastungstests wesentlich zum Verständnis des Strukturverhaltens bei. Das Konzept der statischen Belastung basierte auf dem Einsatz von zwei 36-Tonnen-Lastwagen, die an mehreren vorbestimmten Stellen auf der Brücke anhielten. Die auf diese Weise aufgebrachte Last führte zu ortsabhängigen kleinen Durchbiegungseffekten, die als lokale Längsdehnung der an der Unterseite der Brücke integrierten Sensorfaser aufgezeichnet wurden. Die reflektometrischen Messungen beruhten auf dem Prinzip genannt TW-COTDR (Tunable Wavelength Coherent Optical Time Domain Reflectometry). Die Messgenauigkeit lag im Bereich von 0,5 µm/m.
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.
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.
Optical Distributed Sensing Systems and possible Applications in the Geotechnical Measuring Field
(2011)
In comparison with traditional measuring Systems (pressure cells, piezometers and inclinometers which produce only point measurements) fibre optic sensors are well suited for spatiallydistributed monitoring purposes. The very tiny optical fibres of a diameter of less then 1 mm can operate as sensors in strong electromagnetic fields, under “harsh” explosive and Chemical environments and under ionizing radiation.