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With polymer optical fibers (POF) attached to geotextiles, optical time domain reflectometry (OTDR) can be used to measure strain of the geotextile spatially resolved in soil. We test the technique in a geotechnical application test and thus demonstrate the functionality of the sensor for field use.
There are various applications in high voltage, explosive or high electromagnetic interfered environments that require sensors with an electrical isolation from other components of a system. The basics of possible solution, based on optically powered sensor links, were shown previously. Because of different requirements for the applications, a variety of system approaches has been developed (available power for sensor purposes; length between the control node and the sensor; speed of transmitted data etc.). Key requirements and the current approaches will be discussed below.
Adhesively bonded pipe-to-socket joints are used in numerous industrial applications. One example is in the transport of media, e.g., in the gas industry or in structural joints for such sectors as construction, wind energy, and the vehicle industry. To monitor such load-transmitting bonded joints, this study investigates a method based on the integration of polymer optical fibers into the adhesive layer. Previous methods for monitoring the condition of pipes, such as acoustic or ultrasonic methods or the use of glass fiber optic-based sensors (FBG or OTDR), are very complex in methodology and require cost-intensive (opto-) electronic devices to generate and evaluate the sensor signals; they are therefore unsuitable for large-scale use. The method investigated in this paper is based on the measurement of integral optical transmission with a simple photodiode under increasing mechanical stress. When tried at coupon level (single-lap joint), the light coupling was varied to obtain a significant load-dependent sensor signal. Based on an angle-selective coupling of 30° to the fiber axis, a drop of 4% of the optically transmitted light power by a load of 8 N/mm2 can be detected for the adhesively bonded pipe-to-socket joint with the structural adhesive Scotch Weld DP810 (2C acrylate).
Adhesively bonded pipe-to-socket joints are used in numerous industrial applications. One example is in the transport of media, e.g., in the gas industry or in structural joints for such sectors as construction, wind energy, and the vehicle industry. To monitor such load-transmitting bonded joints, this study investigates a method based on the integration of polymer optical fibers into the adhesive layer. Previous methods for monitoring the condition of pipes, such as acoustic or ultrasonic methods or the use of glass fiber optic-based sensors (FBG or OTDR), are very complex in methodology and require cost-intensive (opto-) electronic devices to generate and evaluate the sensor signals; they are therefore unsuitable for large-scale use. The method investigated in this paper is based on the measurement of integral optical transmission with a simple photodiode under increasing mechanical stress. When tried at coupon level (single-lap joint), the light coupling was varied to obtain a significant load-dependent sensor signal. Based on an angle-selective coupling of 30° to the fiber axis, a drop of 4% of the optically transmitted light power by a load of 8 N/mm2 can be detected for the adhesively bonded pipe-to-socket joint with the structural adhesive Scotch Weld DP810 (2C acrylate).
Das im hier vorgestellten Forschungsrojekt KlebPOF untersuchte Sensorkonzept der Zustandsüberwachung von Klebungen basiert auf der Integration eines Kunststoff-Lichtwellenleiters (polymere optische Faser, POF)
in die Klebung. Die ähnlichen mechanischen Eigenschaften von POF und
Klebstoff, beides Kunststoffe, haben zur Folge, dass Beanspruchungen
des Klebstoffs auf die POF übertragen werden. Die Auswirkungen einer
Belastung auf die optischen Eigenschaften des Lichtwellenleiters werden
in Bezug auf die transmittierte Lichtleistung sowie auf den Einfluss der
Winkelverteilung der aus der Faser austretenden Lichtstrahlen im Fernfeld
untersucht und für den Einsatz zur Zustandsüberwachung von Klebverbindungen interpretiert. Die Ergebnisse an Couponproben zeigen, dass
sich die Methode insbesondere für semi-strukturelle Klebstoffe, wie zum
Beispiel 2K-Polyurethane oder 2K-Methylmethacrylate und eine Beanspruchung der Klebung auf Scherung gut eignet. In den Untersuchungen an dem Funktionsmuster, einer Rohr-Muffe-Klebung, waren sehr deutliche
Änderungen im Sensorsignal frühzeitig vor Versagen detektierbar. Diese
Änderung konnte mit kostengünstigen opto-elektronischen Komponenten
detektiert werden. Damit eignet sich die Methode für eine integrale
Zustandsüberwachung der gesamten Klebung ohne Ortsauflösung, um
einen kostengünstigen Sensor für den Feldeinsatz zu ermöglichen.
Abstract. Many applications in high voltage or explosive environments require sensors which are electrically isolated from other components of a system. These sensors need remote powering as well as wireless or isolated data transmission links. A possible solution can be based on optically powered optical sensor links. These typically employ four different photonic components: for the data communication a fast LED as a transmitter and a photo diode as a receiver, furthermore for sensor powering a high-power light source and a photonic power converter. Additionally, two optical fibers are required for optical remote powering and the optical data link. In this paper we demonstrate an optically powered optical sensor link using only low-cost high-brightness LEDs and a single polymer optical fiber (POF) for all of these tasks. Coupling efficiencies, power transmission and modulation bandwidths are analyzed for LEDs with different colors. Potentials for many mW of electrical remote powering and Mbit s−1 sensor data links are demonstrated over 10 m of POF. This approach can be used for almost any electronic sensor with moderate power requirements.
In recent decades, adhesive bonding technology has become increasingly important in all industrial sectors, for example in the aerospace industry, the automotive industry or the construction industry. This is accompanied by an increased need for monitoring of adhesive bonds, especially for load-bearing, structural joints. In order to detect a possible failure at an early stage, this work is investigating a cost-effective sensor principle based on embedding of a polymer optical fiber (POF) into the adhesive layer. The strain and stress behavior of the adhesive bond are transferred to the POF and change its light-guiding properties. In the presented work, different light coupling conditions into the fiber (full excitation and angle-selective excitation) and different measurable quantities of the transmitted light decoupled from the fiber (photocurrent and far-field) are studied, to find an optimum sensor performance. The combination of a structural polyurethane adhesive with commercially available POF is investigated. The results show a high potential of the method for simple photocurrent measurement (transmission loss of 8% by half of maximum load) and an even more sensitive sensor effect for mode-dependent light power measurement.
PMMA polymer optical fibers embedded in semi-structural polyurethane adhesive bonds serve as economical load sensor for structural health monitoring by evaluating load-dependent optical transmission as well as modal distribution measured by a far-field camera. Scaling of sensor quantities by the sensitive fiber length is shown.
