8.6 Faseroptische Sensorik
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Organisationseinheit der BAM
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- 8.6 Faseroptische Sensorik (237)
- 8.1 Sensorik, mess- und prüftechnische Verfahren (28)
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- 1.4 Prozessanalytik (13)
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- 5.4 Multimateriale Fertigungsprozesse (3)
- 8.5 Röntgenbildgebung (3)
- 5.3 Polymere Verbundwerkstoffe (2)
- 7.1 Baustoffe (2)
- 5.0 Abteilungsleitung und andere (1)
- 7.5 Technische Eigenschaften von Polymerwerkstoffen (1)
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 the present study, the impact of static traffic loading on the slight deflection effects in the concrete structure of an existing bridge has been investigated using distributed fiber optic sensors. In the face of increasing traffic density and severe traffic loading, the results of the load tests on the Amsterdam bridge 705 make an important contribution to the understanding of its structural behavior. The concept of the static loading was based on the use of two 36-ton trucks stopped on the bridge at multiple pre-determined locations. The load applied in this way led to location-dependent small deflection effects recorded as longitudinal strain of the sensing fiber embedded at the underside of the bridge. The measurements were performed with a commercially-available solution based on Tunable Wavelength Coherent Optical Time Domain Reflectometry with the measurement accuracy in the range of 0.5 µm/m.
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.
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.
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.
The substantial progresses in fiber-optic communications in combination with the increasing economic and political interest in structural health monitoring have led to a commercial establishment of distributed Brillouin sensing. The sensor systems, mainly based on the time-domain techniques, have been successfully implemented in the areas such as pipeline leak detection, geohazard effects, and ground movement detection.
This chapter introduces a further advancement in the area of Brillouin sensing in the frequency domain. The so-called Brillouin optical frequency-domain analysis (BOFDA) offers crucial perspectives in terms of dynamic range and cost efficiency.
The main principle of the frequency-domain approach takes advantage of the reversibility between the time and frequency domain given by a Fourier transform in the analysis of linear systems. The hereby presented overview gives a summary of the benefits and challenges of frequency-domain measurements closely tied to the narrowband recording of the complex transfer function. This function relates the counterpropagating pump and probe laser light along the sensor fiber providing the pulse response of the measurement system by applying the inverse Fourier transform (IFT). The strain or temperature distribution can be then determined from the retrieved Brillouin frequency shift (BFS) profile along the fiber.
The ever more ambitious strategic goals of meeting the requirements in ensuring technical safety and security of civil structures have resulted in flourishing development of innovative structural health monitoring (SHM) technologies for early damage diagnosis and prognosis. At the same time, implementing SHM systems provides tangible economic benefits derived from lower life-cycle costs associated with reduction in the maintenance, repair and insurance expenses. Due to the large size and harsh environmental conditions common to most civil structures, the broad range of favorable physical-mechanical properties of POFs allow for customized monitoring solutions for a wide variety of applications.
In addition to common SHM-related advantages of optical fibers including their electromagnetic immunity, small size, lightweight as well as spark-free and non-conductive characteristics, POFs offer better bending and fracture resistance then their glass-counterparts. Particularly, the improved robustness of POFs, their ease of handling, low Young’s Modulus and high elastic limit of 10% compared to 1% in silica glass [1] are relevant to practical applications. Depending on the composition, dopants, drawing process and geometry [2], strain measurement up to 45% [3] or even above 100% [4,5] has been demonstrated with standard POFs. Therefore, the dominant market expected for POF sensors includes monitoring of high-strain-rate deformations in earthwork structures, crack detection in concrete and masonry structures [6] or overstressing in high-rise steel structures exposed to moisture, corrosion, leakage, fatigue, vibration, fire, overflow, earthquake and intentional damage. For fracture monitoring within concrete structures, the sensory usage of POFs becomes especially favorable since the extremely alkaline environment of concrete mixtures is well known to be corrosive to standard silica glass optical fibers (GOFs) [1,7].
Most of advanced distributed sensing techniques are commonly based on Rayleigh backscatter reflectometry using commercially available multimode (MM) POFs. Such typical MM POFs range from a step-index (SI) poly(methyl methacrylate) (PMMA) POF having a core diameter of 1 mm to a low-loss graded-index (GI) perfluorinated (PF) POF based on poly(perfluorobutenyl-vinylether) also known as CYTOP [8] with a 50 µm core diameter. The relatively low optical attenuation value of 30 dB/km at 1.3 µm [9,10] makes PFGI POFs also interesting for distributed Brillouin sensing [11-14]. Compared to GOFs, PFGI POFs offer better potential for temperature measurement and have comparably low theoretical attenuation limit [15]. Therefore, POF-based distributed Brillouin sensing is expected to play an important role in the future of SHM, especially at high-strain ranges. The significance of the Brillouin measurment technique can be also enhanced by further development of the single-mode (SM) POFs which are still subject of research and are used for coherent detection techniques [6]. Furthermore, SM PMMA POFs have been characterized in a Mach-Zehnder interferometer setup for strain values up to 15.8% [16,17].
The current development of SM perfluorinated and microstructured POFs (mPOFs) represents an immense promise for quasi-distributed dynamic measurement at high strain levels based on fiber Bragg grating (FBG) technology. While SM mPOFs with optical losses of about 1 dB/m can be fabricated [6], the SM PF POFs presented by Zhou et al. feature low attenuation of even less than 0.2 dB/m in the wavelength range of 1.41 µm to 1.55 µm [18]. At the same time, the SM PF POFs have the potential for improved thermal stability compared to their PMMA counterparts [19].
This whole chapter provides a comprehensive overview on current POF-based sensing principles and SHM technologies, highlighting their diverse applications in civil engineering structures. In the application-related context, close attention is paid to the development of smart sensor-based geotextiles and geogrids. Such geosynthetics-integrated distributed POF sensors have proven to be a promising solution for two- or even tree-dimensional monitoring of critical high mechanical deformations in both geotechnical and masonry structures. Moreover, geosynthetics in the form of nonwoven geotextiles as well as polymer-based geogrids used as carrier materials for POF sensors enable optimized load transfer from the monitored structure to the measuring fiber without losing their original functionality. In other words, smart geosynthetics provide a cost-efficient dual solution for, on the one hand, well-established increase of structure stability and decrease of erosion effects, on the other hand, early-warning and detection capabilities in the prevention and elimination of potential hazards and lasting damages.
In the present study, the impact of static traffic loading on the slight deflection effects in the concrete structure of an existing bridge has been investigated using distributed fiber optic sensors. In the face of increasing traffic density and severe traffic loading, the results of the load tests on the Amsterdam bridge 705 make an important contribution to the understanding of its structural behavior. The concept of the static loading was based on the use of two 36-ton trucks stopped on the bridge at multiple pre-determined locations. The load applied in this way led to location-dependent small deflection effects recorded as longitudinal strain of the sensing fiber embedded at the underside of the bridge. The measurements were performed with a commercially-available solution based on Tunable Wavelength Coherent Optical Time Domain Reflectometry with the measurement accuracy in the range of 0.5 µm/m.
Auf der Grundlage der in DIN EN 61757-2-2:2017 beschriebenen Standardisierungsmethoden wurden in dieser Arbeit wichtige Leistungsparameter von vier kommerziellen Messsystemen zur ortsaufgelösten faseroptischen Erfassung der temperatur- und dehnungsabhängigen Brillouin-Frequenzverschiebung untersucht. Gemäß der oben genannten Norm konzentrierte sich hier die Ermittlungsprüfung auf messtechnische Aspekte reiner Temperaturmessungen. Dabei diente die Ermittlung von einem festgelegten Satz dreier Betriebsverhaltenskenngrößen in Form von quantitativen Angaben des Messfehlers, der Wiederholgenauigkeit sowie der räumlichen Unsicherheit einem Vergleich der getesteten Messsysteme.
Alle faseroptischen Messungen wurden mit einer Faserschleife ausgeführt, d. h. als Sensorkonfiguration der Messfaser wurde eine Schleifenanordnung gewählt. Die Messverfahren der getesteten Messysteme basierten somit auf der Brillouin-optischen Zeit- bzw. Frequenzbereichsanalyse. Die Betriebsverhaltenskenngrößen wurden ferner bei unterschiedlichen Werten zweier messtechnischer Parameter, des Frequenzschrittes und der Mittelungsrate, für Standardeinstellungen der Laserleistungswerte der in die Sensorfaser einzukoppelnden Laserlichtsignale ermittelt. Auf diesem Weg lassen sich relevante Aussagen zur Optimierung der Messgenauigkeiten in Bezug auf Messdauer treffen.
Auf der Grundlage der in DIN EN 61757-2-2:2017 beschriebenen Standardisierungsmethoden wurden in dieser Arbeit wichtige Leistungsparameter von vier kommerziellen Messsystemen zur ortsaufgelösten faseroptischen Erfassung der temperatur- und dehnungsabhängigen Brillouin-Frequenzverschiebung untersucht. Gemäß der oben genannten Norm konzentrierte sich hier die Ermittlungsprüfung auf messtechnische Aspekte reiner Temperaturmessungen. Dabei diente die Ermittlung von einem festgelegten Satz dreier Betriebsverhaltenskenngrößen in Form von quantitativen Angaben des Messfehlers, der Wiederholgenauigkeit sowie der räumlichen Unsicherheit einem Vergleich der getesteten Messsysteme.
Alle faseroptischen Messungen wurden mit einer Faserschleife ausgeführt, d. h. als Sensorkonfiguration der Messfaser wurde eine Schleifenanordnung gewählt. Die Messverfahren der getesteten Messysteme basierten somit auf der Brillouin-optischen Zeit- bzw. Frequenzbereichsanalyse. Die Betriebsverhaltenskenngrößen wurden ferner bei unterschiedlichen Werten zweier messtechnischer Parameter, des Frequenzschrittes und der Mittelungsrate, für Standardeinstellungen der Laserleistungswerte der in die Sensorfaser einzukoppelnden Laserlichtsignale ermittelt. Auf diesem Weg lassen sich relevante Aussagen zur Optimierung der Messgenauigkeiten in Bezug auf Messdauer treffen.
Faseroptische Strahlungssensoren ermöglichen ein räumlich verteiltes Online-Monitoring entlang der gesamten Sensorfaser. Verschiedene Messverfahren nutzen überwiegend zwei durch die ionisierende Strahlung in optischen Fasern induzierte Effekte, d. h. die Erhöhung der optischen Dämpfung und die damit verbundene Veränderung des Brechungsindex des Fasermaterials. Die Sensitivität der Strahlungssensoren lässt sich je nach Anwendung durch die Wahl der Dotierstoffe im Glasfaserkern sowie der Art des Polymermaterials des POF-Sensors beeinflussen. Ferner ist die Sensitivität auch durch den Betrieb bei geeigneten Wellenlängen einstellbar. Bei dem sensorischen Einsatz von faseroptischen Sensoren muss auch die vorhandene Ausheilung des Sensors sowie die Abhängigkeit der erfassten Messsignale von der Temperatur und der Dosisleistung berücksichtigt werden.
Faseroptische Strahlungssensoren ermöglichen ein räumlich verteiltes Online-Monitoring entlang der gesamten Sensorfaser. Verschiedene Messverfahren nutzen überwiegend zwei durch die ionisierende Strahlung in optischen Fasern induzierte Effekte, d. h. die Erhöhung der optischen Dämpfung und die damit verbundene Veränderung des Brechungsindex des Fasermaterials. Die Sensitivität der Strahlungssensoren lässt sich je nach Anwendung durch die Wahl der Dotierstoffe im Glasfaserkern sowie der Art des Polymermaterials des POF-Sensors beeinflussen. Ferner ist die Sensitivität auch durch den Betrieb bei geeigneten Wellenlängen einstellbar. Bei dem sensorischen Einsatz von faseroptischen Sensoren muss auch die vorhandene Ausheilung des Sensors sowie die Abhängigkeit der erfassten Messsignale von der Temperatur und der Dosisleistung berücksichtigt werden.
We present our research on the development of a Brillouin optical frequency-domain analysis (BOFDA) using a perfluorinated graded-index polymer optical fiber (PFGI-POF) as a sensing fiber. The described works include investigations both on the selection of the setup components with respect to mode coupling effects and on the impact of the humidity cross-sensitivity. The suitability of the developed POF-based BOFDA is proved by a distributed measurement on an 86 m long PFGI-POF recorded with the spatial resolution of 6 m.
Wir präsentieren unsere Forschungsergebnisse zur Entwicklung eines faseroptischen Sensorsystems mit polymeroptischen Fasern integriert in Geokunststoffe für die Überwachung von geotechnischen Anlagen. Das Sensorsystem dient der räumlichen Auflösung lokaler Dehnungsereignisse im für Anwender signifikanten Größenordnungsbereich von 3 % bis 10 %. Das gesamte Sensorkonzept besteht aus einem praxistauglichen Messsystem basierend auf der digitalen inkohärenten optischen Frequenzbereichsreflektometrie (I-OFDR) und einer Sensormatte in Form eines Geotextils mit integrierten faseroptischen perfluorierten polymeroptischen Fasern (PF-POFs).
We present a prototype of a distributed POF sensing system for strain detection in road construction and civil engineering ready to be used in practical applications. The system is based on a cost-efficient digital incoherent optical frequency domain reflectometry (I-OFDR). In this approach, the strain-induced changes in the Rayleigh backscattering profile along a perfluorinated polymer optical fiber (PF-POF) are determined by measuring the complex transfer function of the sensing fiber using a compact digital data acquisition unit. The digital unit replaces an oversized vector network analyzer (VNA) enabling suitability of the measurement system for out-door use and providing a significant reduction of the total system costs at the same time. The entire sensor con-cept includes the use of geosynthetics with integrated PF-POFs as two-dimensional sensor structures for geotech-nical applications. The robustness and the functionality of the distributed POF I-OFDR sensors were proven in the field. The field test involved embedding of two geomats, each with two polymer optical sensor loops, into the embankment of the federal road B 91 in a section near Leipzig. The measurements conducted after the sensor-based geomats had been installed confirmed both the potential of such smart geosynthetics and the functionali-ty of the digital I-OFDR prototype.
Distributed fiber optic strain sensing for structural health monitoring of 70 MPa hydrogen vessels
(2024)
We report on the development and testing of 70 MPa hydrogen pressure
vessels with integrated fiber optic sensing fibers for automotive use. The paper deals with the condition monitoring of such composite pressure vessels (CPVs) using the optical backscatter reflectometry (OBR) applied for a distributed fiber optic strain sensing along fully integrated polyimide-coated single-mode glass optical fiber (SM-GOF). The sensing fibers were embedded into the vessel structure by wrapping them over the polymer liner during the manufacturing process of the carbon fiber reinforced polymer (CFRP). Detecting local strain events by the integrated fiber optic sensors can be an opportunity for monitoring the material degradation of CPVs under static and cyclic loading.
We present a distributed polymer optical fiber sensor system for deformation monitoring of geotechnical infrastructure. The sensor system is based on the digital incoherent optical frequency domain reflectometry (I-OFDR) for the detection of local strain events along a perfluorinated polymer optical fiber (PF-POF) used as a sensing fiber. For the best possible load transfer, the PF-POFs were integrated onto geosynthetics which pose a sensor carrier for the sensing fiber. By using elastic PF-POF instead of a standard glass fiber as a sensing fiber the strain range of geosynthetics-integrated fiber optic sensors could be extended up to 10 % in accordance with the end-user requirements.
Fiber reinforced polymers (FRPs) are a well established material in lightweight applications, e.g. in automotive, aerospace or wind energy. The FRP components are subjected to multiaxial mechanical as well as hygrothermal loads. Common operation temperatures are in the range of 213 K and 373 K (-60 °C and 100 °C) at a relative humidity of 10% to 90%. In spacecraft applications, the environmental conditions are even more extreme. However, the correlation between multiaxial mechanical loading and harsh environment conditions have to-date not been investigated in detail. The project aims to investigate the fatigue behavior of FRPs dependent on multiaxial mechanical loading, temperature, and humidity. Extensive experimental testing is performed on flat plate and cylindrical tube specimens, accompanied by numerical and analytical calculations.
Die Nutzung von Sensortechnologien, insbesondere im Bereich der Gasdetektion mit einem Schwerpunkt auf Wasserstoff, spielt eine entscheidende Rolle in verschiedenen Anwendungsbereichen der Wasserstofftechnologie. Sicherheitsüberwachung, Leckdetektion und Prozesskontrolle gehören zu den prominenten Anwendungsgebieten dieser Sensortechnologien. Ein zentrales Ziel ist die Erkennung von freigesetztem Wasserstoff sowie die genaue Bestimmung des Wasserstoff-Luftverhältnisses mithilfe von Gassensoren. Dies ist von entscheidender Bedeutung, um potenzielle Gefahren frühzeitig zu erkennen und angemessene Maßnahmen zu ergreifen.
Ein weiterer Schwerpunkt dieses Beitrags liegt auf der Analytik und der Verwendung zertifizierter Referenzmaterialien in Verbindung mit Metrologie für die Wasserstoffspeicherung. Dies gewährleistet eine präzise und zuverlässige Charakterisierung von Wasserstoff und unterstützt die Entwicklung sicherer Speichertechnologien. Im Rahmen des Euramet-Vorhabens Metrology for Advanced Hydrogen Storage Solutions (MefHySto) wird eine Kurzvorstellung präsentiert.
Der Vortrag stellt zwei zerstörungsfreie Prüfverfahren zum strukturellen Zustandsüberwachung (Structural Health Monitoring, SHM) für Wasserstofftechnologien vor. Insbesondere die Fehlstellenerkennung mittels geführter Ultraschallwellen spielt eine bedeutende Rolle bei der Lebensdauerüberwachung von Wasserstoffspeichern. Ein weiterer Aspekt ist die Anwendung faseroptischer Sensorik zur Schadensfrüherkennung von Wasserstoffspeichern. Diese zerstörungsfreien Prüfverfahren ermöglichen eine präzise und frühzeitige Identifizierung von Schäden, was die Sicherheit und Effizienz von Wasserstoffspeichersystemen entscheidend verbessert.
Intelligent sensor systems, certified reference materials and instrumental analytical-chemical methods contribute to safety and functionality in hydrogen technologies.
This article gives a brief overview of SensRef activities in the Competence Centre H2Safety@BAM on the issues: Analytical methods for the determination of hydrogen purity, certified reference materials as measurement standards with regard to gas quality (primary calibrators) of BAM, test methods for gas sensor systems to detect hydrogen in air as well as the application of fibre-optic sensor systems to monitor the expansion and ageing behaviour of composite containers in hydrogen technologies.
Der Vortrag zum Mess- und Prüfverfahren mit verschiedenen Sensortechnologien und Ultraschallwellen beinhaltet die Themen:
Metrologie zur Wasserstoffspeicherung - Euramet-Vorhaben "MefHySto",
Erkennung von freigesetztem Wasserstoff sowie die Bestimmung des Wasserstoff-Luftverhälntisses mit Gassensoren, zerstörungsfreie Fehlstellenerkennung mit integriertem Zustandsüberwachungssystem basierend auf geführten Ultraschallwellen zur Lebensdauerüberwachung von Composite-Behältern (Wasserstoffspeicher) sowie faseroptische Sensorik zur Schadenfrüherkennung von Wasserstoffspeichern aufgrund erkennbarer Dehnungsänderungen an Druckbehältern.
Mess- und prüftechnische Verfahren sind zur Prozesskontrolle und Sicherheitsüberwachung in Wasserstofftechnologien von hoher Bedeutung. Typische Anwendungsgebiete von Sensoren sind Sicherheitsüberwachung, Leckdetektion und Prozesskontrolle. In diesem Beitrag werden Themen zur Erkennung von freigesetztem Wasserstoff sowie die Bestimmung des Wasserstoff-Luftverhältnisses mit Gassensoren, Fehlstellenerkennung mit geführten Ultraschallwellen zur Lebensdauerüberwachung (Structural Health Monitoring) von Wasserstoffspeichern sowie der Einsatz faseroptischer Sensoren zur Überwachung des Dehnungs- und Alterungsverhaltens sowie zur Schadensfrüherkennung von Wasserstoffspeichern vorgestellt.
Der Beitrag behandelt verschiedene Themen aus dem H2Safety@BAM-Kompetenzfeld Sensorik, Analytik und zertifizierte Referenzmaterialien (SensRef) mit Schwerpunkt auf Mess- und Prüfverfahren, die verschiedene Analyseverfahren, Sensortechnologien und Ultraschallwellen nutzen. Ein Teil davon ist das Euramet-Vorhaben "MefHySto" zur Metrologie der Wasserstoffspeicherung. Des Weiteren werden Verfahren zur Erkennung von freigesetztem Wasserstoff und zur Bestimmung des Wasserstoff-Luftverhältnisses mithilfe von Gassensoren behandelt. Ein weiterer Aspekt ist die zerstörungsfreie Fehlstellenerkennung mit einem integrierten Zustandsüberwachungssystem, das auf geführten Ultraschallwellen basiert und zur Überwachung der Lebensdauer von Composite-Behältern (Wasserstoffspeicher) dient. Zudem wird die Anwendung faseroptischer Sensorik zur Schadenfrüherkennung an Wasserstoffspeichern diskutiert. Dabei werden erkennbare Dehnungsänderungen an Druckbehältern als Indikatoren genutzt.
Der Beitrag beinhaltet Themen vom H2Safety@BAM-Kompetenzfeld Sensorik, Analytik und zertifizierte Referenzmaterialien (SensRef) mit Fokus auf Mess- und Prüfverfahren mit verschiedenen Sensortechnologien und Ultraschallwellen:
Metrologie zur Wasserstoffspeicherung - Euramet-Vorhaben "MefHySto",
Erkennung von freigesetztem Wasserstoff sowie die Bestimmung des Wasserstoff-Luftverhälntisses mit Gassensoren, zerstörungsfreie Fehlstellenerkennung mit integriertem Zustandsüberwachungssystem basierend auf geführten Ultraschallwellen zur Lebensdauerüberwachung von Composite-Behältern (Wasserstoffspeicher) sowie faseroptische Sensorik zur Schadenfrüherkennung von Wasserstoffspeichern aufgrund erkennbarer Dehnungsänderungen an Druckbehältern.
Es wurde ein Messaufbau realisiert, der die Betriebsedingungen von hydraulisch- pneumatischen Gasdruckkabelsystemen nachbildet und in dieser Veröffentlichung vorgestellt. Mit seiner Hilfe können im Labor diagnostische Messungen und beschleunigte Alterung der Isolierung bei variablen Temperaturen, Druckstufen, Spannungen und Frequenzen durchgeführt werden. Zur Temperatureinstellung wurde im Messaufbau eine Kurzschlussschleife verwendet, die stabile Heizströme über 700 A bei 50 Hz ermöglicht. Der Prüfspannungsbereich während der Verlustfaktor- und Teilentladungsmessungen lag zwischen 1 kV bis 25 kV mit einem Frequenzbereich zwischen 0,1 Hz bis 60 Hz. Um die örtliche und zeitlich lastabhängige Temperatur entlang des Messbelags bestimmen zu können, wurde eine optische Faser (Loose tube) um den Prüfling gewickelt, so dass eine ortsaufgelöste Temperaturermittlung über den Prüflingsmantel erreicht wurde. Aus den erhaltenen Temperaturmessdaten wurde ein einphasiges, planares thermisches Modell erzeugt, das das thermische Verhalten des Prüflings in Abhängigkeit von Laststrom, Raumtemperatur und Materialdaten nachbildet. Dieses wurde mit den aufgenommenen Messdaten verglichen. Aus den Erkenntnissen des einphasigen thermischen Modells soll ein dreiphasiges Modell entstehen, mit dessen Hilfe die Diagnosetemperatur und das Abkühlverhalten von erdverlegten Gasdruckkabeln abgeschätzt werden können. Dadurch kann zukünftig der Temperatureinflusses bei der Interpretation von Vor-Ort-Messungen hinzugezogen werden.
Solution doping of off-the-shelf plastic optical fibers (POFs) represents rather simple and cheap way for preparing custom cladding-doped POFs (CD-POFs) with short to medium lengths. CD-POFs are especially attractive for environmental sensing applications, but might be of interest for illumination task as well. In this work, the proposed doping technique is tested with three different commercial low-cost polymethyl methacrylate (PMMA) POFs; Eska CK-40 and Eska GK-40 from Mitsubishi Rayon and Raytela PGU-FB1000 from Toray. The aim of the work is to aid the selection of the most suitable fiber yielding highest optical quality of prepared CD-POFs. Firstly, the optimal doping times are determined for the individual fiber types using short fiber samples. Secondly, longer 10 m CD-POFs are prepared from all tested fibersusing the optimized doping procedure. Finally, attenuation of pristine POFs and prepared CD-POFs is measured using optical time domain reflectometry in order to characterize the impacts of the doping on fiber optical properties. In addition, the importance of post-doping drying procedure for CD-POF optical performance is investigated as well. The results suggest that, although doping of all tested fibers is generally feasible, Eska CK-40 is the most suitable candidate with regard to the Doping efficiency and fiber post-doping performance.
Solution doping of commercial polymethyl methacrylate (PMMA) polymer optical fibers (POFs) is presented as a novel approach for preparation of custom cladding-doped POFs (CD-POFs). The presented method is based on a solution-mediated diffusion of dopant molecules into the fiber cladding upon soaking of POFs in a methanol-dopant solution. The method was tested on three different commercial POFs using Rhodamine B as a fluorescent dopant. The dynamics of the diffusion process was studied in order to optimize the doping procedure in terms of selection of the most suitable POF, doping time and conditions. Using the optimized procedure, longer segment of fluorescent CD-POF was prepared and its performance was characterized. Fiber’s potential for sensing and illumination applications was demonstrated and discussed. The proposed method represents a simple and cheap way for fabrication of custom, short to medium length CD-POFs with various dopants.
Humidity is one of principal environmental parameters that plays an important role in various application areas. Using measurement of strain induced in an optical fiber by a water swellable coating represents a promising approach for realization of distributed humidity sensing (DHS). In this work, humidity and temperature response of four different commercial PI-coated fibers and four tight-buffered (TB) fibers is investigated with the aim of evaluating their potential for development of DHS in context of water ingress sensor for high-voltage power cable splices. PI-coated fibers exhibited close-to-linear humidity and temperature response. While the temperature response is relatively coating-independent, magnitude of humidity response was broadly correlated to the relative fiber-to-coating thickness ratio. In contrast, both humidity and temperature response of TB fibers is strongly influenced by buffer type, with Leoni TB900L fiber with Hytrel buffer exhibiting largest humidity and temperature sensitivity. While the response of tight-buffered fibers is generally nonlinear, roughly three-times higher humidity response can be achieved with TB900L compared to the most sensitive PI-coated fiber. Using the TB fiber can be, therefore, advantageous for simpler water detection applications, such as one targeted in this study, when larger sensitivity is more important than the linear response of the sensor.
Along temperature, humidity is one of the principal environmental factors that plays an important role in various application areas. Presented work investigates possibility of distributed fiberoptic humidity monitoring based on humidity-induced strain measurement in polyimide (PI)-coated optical fibers. Characterization of relative humidity (RH) and temperature response of four different commercial PI- and one acrylate-coated fiber was performed using optical backscattering reflectometry (OBR). The study addresses issues of temperature-humidity cross sensitivity, fiber response stability, repeatability, and the influence of annealing. Acrylate-coated fiber exhibited rather unfavorable nonlinear RH response with strong temperature dependence, which makes it unsuitable for humidity sensing applications. On the other hand, humidity response of PI-coated fibers showed good linearity with fiber sensitivity slightly decreasing at rising temperatures. In the tested range, temperature sensitivity of the fibers remained humidity independent. Thermal annealing was shown to considerably improve and stabilize fiber RH response. Based on performed analysis, a 20 m sensor using the optimal PI-coated fibers was proposed and constructed. The sensor uses dual sensing fiber configuration for mutual decoupling and simultaneous measurement of temperature and RH variations. Using OBR, distributed dual temperature-RH monitoring with cm spatial resolution was demonstrated for the first time.
In the presented work, the potential of fiber-optic distributed acoustic sensing (DAS) for detection of small gas pipeline leaks (<1%) is investigated. Helical wrapping of the sensing fiber directly around the pipeline is used to increase the system sensitivity for detection of weak leak-induced vibrations. DAS measurements are supplemented with reference accelerometer data to facilitate analysis and interpretation of recorded vibration signals. The results reveal that a DAS system using direct fiber application approach is capable of detecting pipeline natural vibrations excited by the broadband noise generated by the leaking medium. In the performed experiment, pipeline vibration modes with acceleration magnitudes down to single ug were detected. Simple leak detection approach based on spectral integration of time-averaged DAS signals in frequency domain was proposed. Potential benefits and limitations of the presented monitoring Approach were discussed with respect to its practical applicability. We demonstrated that the approached is potentially capable of detection and localization of gas pipeline leaks with leak rates down to 0.1% of the pipeline flow volume and might be of interest for monitoring of short- and medium-length gas pipelines.
The monitoring of oil and gas pipelines by means of distributed fibre optic sensors is becoming common. The most recent development in the field of fibre optic sensing is the distributed acoustic sensing (DAS), which allows to detect and to localize third party threats to pipelines. For this purpose, fibre optic telecommunication cables located close to the pipelines are usually used. However, DAS carries a far greater potential for continuous condition monitoring of pipelines.
The interdisciplinary research project AGIFAMOR (Ageing Infrastructures – Fibre Optic Monitoring of Pipes) at BAM investigates a new technical approach to extend the application field of DAS towards the detection and localization of acoustic signals that indicate critical alterations and certain damage scenarios originated from within the pipeline or the pipe wall. Therefore, the optical fibre sensors are applied onto the pipe itself and the application procedure towards an optimal acoustic signal transduction is optimized.
A number of laboratory scale experiments were performed focusing on the signal transmission of acoustic signals as well as the detection of damages in the pipe wall by means of DAS. Furthermore, real-scale tests on a pipeline DN100 of 38m length have been carried out at the BAM test site for technical safety (BAM-TTS) to study the detection and localization of leaks and of changing flow profiles due to corrosion or sedimentation processes.
The monitoring of oil and gas pipelines by means of distributed fibre optic sensors is becoming common. The most recent development in the field of fibre optic sensing is the distributed acoustic sensing (DAS), which allows to detect and to localize third party threats to pipelines. For this purpose, fibre optic telecommunication cables located close to the pipelines are usually used. However, DAS carries a far greater potential for continuous condition monitoring of pipelines.
The interdisciplinary research project AGIFAMOR (Ageing Infrastructures – Fibre Optic Monitoring of Pipes) at BAM investigates a new technical approach to extend the application field of DAS towards the detection and localization of acoustic signals that indicate critical alterations and certain damage scenarios originated from within the pipeline or the pipe wall. Therefore, the optical fibre sensors are applied onto the pipe itself and the application procedure towards an optimal acoustic signal transduction is optimized.
A number of laboratory scale experiments were performed focusing on the signal transmission of acoustic signals as well as the detection of damage in the pipe wall by means of DAS. Furthermore, real-scale tests on a pipeline DN100 of 38 m length have been carried out at the BAM test site for technical safety (BAM-TTS) to study the detection and localization of leaks and of changing flow profiles due to corrosion or sedimentation processes.
Humidity is one of principal environmental parameters that plays an important role in various application areas. Distributed humidity/water sensing is sought after in wide range of applications including concrete condition monitoring in civil engineering, SHM of large structures such as dykes or dams, soil moisture measurement in agriculture or leak detection in pipeline or sewage industry. Using humidity-induced strain of specialty hygroscopic coating materials, such as polyimide (PI) seems as the most promising approach so far. In this work, relative humidity and temperature response of different commercial PI-coated and tight-buffer fibers is investigated for the development of distributed humidity sensor.
Das Teilprojekt zielt auf die Entwicklung integrierbarer verteilter faseroptischer Sensoren (u. a. verteilte Brillouin-Sensorik, verteilte akustische Sensorik) für die Langzeitüberwachung von Betriebsparametern in Hoch- und Mittelspannungskabelanlagen. Mit Hilfe der Sensoren sollen unzulässige Dehnungen, Übertemperaturen und das Eindringen von Feuchte, z. B. in Unterseekabeln, detektiert werden. Das Teilprojekt beinhaltet ebenfalls die Entwicklung integrierfähiger Sensoren für verteiltes (vibro-)akustisches Monitoring an Unterseekabeln, vor allem zur Lokalisierung und zur Abwendung von Störfällen und Schäden durch äußere mechanische Einflüsse (z. B. Ankerwurf).
Humidity is one of principal environmental parameters that plays an important role in various application areas. Distributed humidity/water sensing is sought after in wide range of applications including concrete condition monitoring in civil engineering, SHM of large structures such as dykes or dams, soil moisture measurement in agriculture or leak detection in pipeline or sewage industry. Using humidity-induced strain of specialty hygroscopic coating materials, such as polyimide (PI) seems as the most promising approach so far. In this work, relative humidity and temperature response of different commercial PI-coated and tight-buffer fibers is investigated for the development of distributed humidity sensor.
Fibreoptic sensors (FOS) represent sensing technology with small footprint, low invasiveness, electromagnetic passivity and immunity, plus potential for remote and real-time monitoring. Modern FOS techniques allow truly temporally- and spatially-continuous monitoring over extended distances; a feature not attainable with any other sensing technology. Moreover, depending on their particular material composition and design, optical fibres can be made resistant to high temperatures, chemicals and ionizing radiation. Due to this unique combination of advantageous properties, ever since their emergence, FOS have been attracting considerable attention for monitoring tasks in harsh, hazardous and difficult-to-access locations. The potential of FOS has been recognized also in the field of radioactive waste management and fibreoptic sensors belong to the most promising technologies for nuclear waste repositories (NWR) monitoring.
Vast majority of distributed fibreoptic sensor applications rely on use of silica-based optical fibres as sensing elements. At the same time, distributed measurement of local temperature and strain along the fibre are the most common monitoring tasks addressed by fibreoptic sensors. Nevertheless, FOS offer much larger flexibility both in terms of utilized sensing fibre as well as targeted measurand. In this contribution, we will review some of more alternative implementations of FOS that are being explored at “Fibre Optic Sensors” division of Federal Institute for Material Research and Testing (BAM), in Berlin. The main focus will be twofold. On one side, we will address FOS applications with polymer optical fibres (POF), that may enable monitoring of large strains (>100%) and high-sensitivity radiation detection. On the other side, we will present our activities in the area of distributed acoustic sensing (DAS); one of the most recent developments in the fibreoptic sensing field enabling highly-dynamic vibration sensing with nanostrain sensitivity. We will introduce the principles of the addressed FOS technologies, present application examples from our case studies, discuss advantages and limitations of the techniques and highlight their potential for NWR monitoring.
Solution doping of off-the-shelf plastic optical fibers (POFs) represents rather simple and cheap way for preparing custom cladding-doped POFs (CD-POFs) with short to medium lengths. CD-POFs are especially attractive for environmental sensing applications, but might be of interest for illumination task as well. In this work, the proposed doping technique is tested with three different commercial low-cost polymethyl methacrylate (PMMA) POFs; Eska CK-40 and Eska GK-40 from Mitsubishi Rayon and Raytela PGU-FB1000 from Toray. The aim of the work is to aid the selection of the most suitable fiber yielding highest optical quality of prepared CD-POFs. Firstly, the optimal doping times are determined for the individual fiber types using short fiber samples. Secondly, longer 10 m CD-POFs are prepared from all tested fibers using the optimized doping procedure. Finally, attenuation of pristine POFs and prepared CD-POFs is measured using optical time domain reflectometry in order to characterize the impacts of the doping on fiber optical properties. In addition, the importance of post-doping drying procedure for CD-POF optical performance is investigated as well. The results suggest that, although doping of all tested fibers is generally feasible, Eska CK-40 is the most suitable candidate with regard to the doping efficiency and fiber post-doping performance.
A phase-sensitive optical time domain reflectometer based on coherent heterodyne detection of geometric phase in the beat signal of light, is reported for the first time to our knowledge. The use of the geometric phase to extract strain makes it immune to polarisation diversity fading. This is because a polarisation mismatch between the interfering beams is not a hindrance to its measurement. The geometric phase is calculated using the amplitude of the beat signal and individual beam intensities without any need for phase unwrapping. It is measured per beat period and can be equated with the traditionally measured dynamic phase with appropriate scaling. The results show that the system based on the geometric phase successfully measures strain, free from polarisation mismatch fading and phase unwrapping errors, providing a completely novel solution to these problems.
Geometric phase measured per beat period in a ϕ-OTDR based on coherent heterodyne detection is used to measure strain. Proposed method is robust to polarisation mismatch fading as a polarisation mismatch between interfering beams is not a hindrance to the measurement of the geometric phase. The Geometric phase is a function of the intensities of the interfering beams as well as the envelope of the beat signal. Its calculation does not require phase unwrapping and accordingly does not suffer the phase unwrapping errors. It is required to be equated with the traditionally measured phase by applying a scaling factor. The spatial resolution of the measured strain is reduced as it is calculated per beat period. Results are verified using a piezo-electric transducer inline a fiber-under-test.
A novel DAS setup based on geometric phases in coherent heterodyne detection is applied for the first time to the characterisation of the Earth’s subsurface. In addition, an optimisation of the proposed setup in terms of its spatial resolution is also presented for the first time. The surface waves are generated by strong blasts of 25 kg of explosives at a dedicated test site. A 10 km dark fiber link in the vicinity of the test site connected to the test setup records the resulting strain signals. The spike-free and low-noise strain data thus obtained minimize post-processing requirements, making the setup a candidate for real-time seismic monitoring. An analysis of the dispersion characteristics of the generated surface waves is performed using a recently reported optimised seismic interferometric technique. Based on the dispersion characteristics, the shear wave velocities of the surface waves as a function of the depth profile of the Earth’s crust are determined using an optimised evolutionary algorithm.