In this article, we report on a carbon-coated optical fiber that is suitable to be used simultaneously as a transmission medium and as a sensor. It consists of a standard single mode fiber (SMF) sleeved in two layers of coating, which provide protection and isolation from external elements. The inner layer is made of carbon, whereas the outer is made of polymer. When the fiber is subjected to mechanical stress, the electrical resistance of the carbon layer changes accordingly. The voltage variations caused by the former can be measured with high accuracy and without interfering with the light propagating through the SMF. In this work, the feasibility of this operating principle is demonstrated in a low coherence Michelson interferometer in which electrical and optical signals were measured simultaneously and compared to each other. Results indicate that electrical measurements are as precise as the optical ones and with linear behavior, reaching a sensitivity of 1.582 mV/με and able to detect vibrations down to 100 mHz. © 2024 The Authors

Ultrathin 25μm optical fibers with FBG sensors are manufactured and used as vibration sensors in glass-fiber reinforced composites. The use of ultrathin fibers is discussed, and their manufacture is described. © 2022 The Authors.

The purpose of CF2T project is to develop a competitive foundation, immerse it as part of a precommercial project and validate the concept in a real sea environment. The innovative foundation will be designed to decrease construction costs, with modular interfaces to allow an installation in several packages (foundation parts, ballasts, turbine) in order to limit the installation vessel’s crane capacity requirement, which will also reduce installation costs. The different alternatives to reduce the structure construction costs and modularity will be evaluated including the design of a hybrid foundation combining concrete and steel. The new foundation should also have an adaptive interface with the seabed in order to avoid any seabed preparation. In addition, the project will develop a monitoring system to have a better understanding of loads applied to the structure for future foundations developments. This monitoring will allow to carry out a survey of the structural health for preventive maintenance which will contribute to improve reliability of the foundation. This report is the first deliverable in WP6 (Foundation Monitoring), namely D6.1 Sensor characteristics and implementation report. RISE led the work in collaboration with SAITEC and ALKIT. This report proposes sensor characteristics and implementation for the foundation of tidal turbine designed within the project. A literature review is firstly included on Structural Health Monitoring (SHM), relevant SHM techniques and SHM’s applicability to both concrete and offshore structures. Fibre optics, specifically Fibre Bragg Grating (FBG), were identified to be the most suitable solution for SHM of the concrete foundation. Critical measurement areas and performance indicators for the concrete foundation were identified and a detailed measurement scheme was proposed. Implementation on the laboratory scale was studied for both material and component levels, i.e., steel reinforcement and concrete surface. It was observed that the fibre optics were able to measure the distribution of strains coherently and accurately on steel reinforcement subjected to tensile loading, all while proving to be durable against high levels of corrosion. Detection of strain in the concrete surface which could indicate tilting and/or onset of cracking was also possible with the proposed fibre optic system.

The purpose of CF2T project is to develop a competitive foundation, immerse it as part of a precommercial project and validate the concept in a real sea environment. The innovative foundation will be designed to decrease construction costs, with modular interfaces to allow an installation in several packages (foundation parts, ballasts, turbine) in order to limit the installation vessel’s crane capacity requirement, which will also reduce installation costs. The different alternatives to reduce the structure construction costs and modularity will be evaluated including the design of a hybrid foundation combining concrete and steel. The new foundation should also have an adaptive interface with the seabed in order to avoid any seabed preparation. In addition, the project will develop a monitoring system to have a better understanding of loads applied to the structure for future foundations developments. This monitoring will allow to carry out a survey of the structural health for preventive maintenance which will contribute to improve reliability of the foundation. This report is the second deliverable in WP6 (Foundation Monitoring), namely D6.2 Sensor implemented and calibrated in proof-of-concept. RISE led the work with collaborative efforts from ALKIT. The proof-of-concept was proposed by RISE to enable the implementation of the proposed and developed monitoring system based on fibre optics in a representative reinforced concrete test object. This report covers the implementation in the proof-of-concept, the execution of experiment with mechanical loading on the test object, as well as the calibration of the given sensors and verification using secondary measuring techniques. The results show a complete characterization of the structure strain response along several loading cycles and the compatibility between the fibre optics-based sensors and the strain gauges validating the optical solution for structural monitoring. The system showed its capability for crack detection and also showed a good consistency of the measurements under repeated cycles. Lastly, a description of requirements and details for taking this proof-of-concept to the next phase of offshore monitoring of the concrete foundation is provided.

This work presents an on-field validation of an in-house built real-Time phase-OTDR for monitoring the status of roller bearings. The acoustic sensor prototype was designed and assembled at RISE and evaluated on a 1 m diameter bearing at SKF AB facilities in Göteborg, Sweden. A 0.24 numerical aperture single-mode optical fiber was installed in the bearing lubrication groove, which is 50 mm large and 5 mm deep. Tests were performed to verify the response of the phaseOTDR to acoustic emissions in the bearing such as hammer hits and running the rollers at different loads. The fiber optic sensor results agree with the measurements performed by a standard industrial high sensitivity electronic accelerometer used for comparison. Moreover, as opposed to the reference electronic sensor, the phase-OTDR proved to be insensitive to electrical disturbances present on the environment.

Distributed optical fiber sensors based on phase-sensitive optical time domain reflectometry (Φ-OTDR) are feasible options to detect perturbations in kilometric security perimeters or mechanical structures. This technique takes advantage of electromagnetic interference immunity, small dimensions, lightweight, flexibility, and capability. Moreover, this technique can be combined with dedicated hardware architectures, in order to improve its performance and reliability. This work proposes the use of parallel hardware architectures to implement real-time detecting and locating perturbations in a Φ-OTDR distributed optical fiber vibration sensor. Hardware architectures of the iterative moving average filter and the Sobel filter were mapped on field programmable gate arrays, exploring the intrinsic parallelism in order to achieve real-time requirements. A performance comparison between the proposed solutions was addressed in terms of hardware cost, latency and power consumption.

We propose and experimentally demonstrate a spatially tunable phase-OTDR based distributed microphone for listening to the sound of multiple machines. The distributed acoustic sensing capability, allied with the real-time spatial tuning, enables listening to a drill and to a cooling water system pump placed in two different sections along a single optical fiber, one at a time. The recorded acoustic waveform profile of both machines agreed with their operating cycles. Moreover, the sounds generated by both engines are successfully distinguished with the proposed method even when both machines are operating simultaneously..