For the first time, a gold coated single mode optical fiber has been used to detect a liquid sodium leakage on a pipe of secondary circuit pipe mock-up of nuclear fast reactor (Gen IV) by means of Optical Frequency Domain Reflectometry-based on Rayleigh backscattering. During 150 min of the experiment we were able to detect and monitor the evolution of a liquid sodium leakage on the surface of the pipe.
The regeneration of Tilted Fiber Bragg Gratings photowritten in a singlemode SMF-28e fiber is investigated. Three tilted FBGs, with respectively 0°, 4° and 8° external tilt angles are annealed according to a conventional high temperature regeneration protocol. We monitor the evolution of distinct spectral features during the thermal annealing process. We also propose a method in order to follow the regeneration process of tilted FBG, without focusing on individual spectral resonances. Regeneration of tilted FBGs presents numerous interests for the realization of high temperature sensors and devices, but also to improve their resistance to preliminary manufacturing processes requiring high temperature steps.
KEYWORDS: Buildings, Optical fibers, Optical fiber cables, Energy efficiency, Temperature metrology, Raman spectroscopy, Data storage, Sensors, Solar energy, Optical switching
To reduce greenhouse gas emissions and to promote energy savings in the building sector, a project named Batimetre has been set-up, to measure parameters affecting building energy consumption. For the first time, optical fibers have been deployed on internal and external faces of two experimental houses, designed for low energy consumption. With a DTS Raman system, these cables provide a distributed measurement of walls temperature every meter and every two minutes. Such instrumentation is able to deliver a very large number of data at a reduced operating cost. It allows to isolate thermal phenomena in dynamic thermal simulation tools, and to compare several intermediate predicted and measured parameters.
This paper addresses the metrological stability of spectral measurements performed with a smart FBG sensing instrument. With a sophisticated tracking system based on a real-time drift compensation, we obtained, during 16 days, an unrivalled measurement stability, as low as: 0.0074 fm/h with a standard deviation: 0.032 pm. This level of performance opens the way, not only to high quality metrology, but also to long-term structure monitoring.
Safety must always prevail in Nuclear Power Plants (NPPs), as shown at Fukushima-Daiichi. So, innovations are clearly needed to strengthen instrumentations, which went inoperative during this nuclear accident as a consequence of power supply losses. Possible improvements concern materials and structures, which may be remotely monitored thanks to Optical Fiber Sensors (OFS). We detail topics involving OFS helpful for monitoring, in nominal conditions as well as during a severe accident. They include distributed sensing (Rayleigh, Raman, Brillouin) for both temperature sensing and structure monitoring as well as H2 concentration and ionizing radiation monitoring. For future plants, Fiber Bragg Grating (FBG) sensors are considered up to high temperature for sodium-cooled fast reactor monitoring. These applications can benefit from fiber advantages: sensor multiplexing, multi-km range, no risk-to-people, no common failure mode with other technologies, remote sensing, and the ability to operate in case of power supply lost in the NPP.
Following the pioneering work of the Lawrence Livermore National Laboratory, Chirped Fiber Bragg Gratings are investigated as in situ, real-time, wavelength-position discriminators for measuring detonation speeds inside explosives.
Regenerated Fiber Bragg Gratings have been annealed at high temperatures up to 890°C during 9000 hours in continuous. This test has been conducted in order to experimentally assess the long-term stability of regenerated FBGs dedicated to measurements in high temperature environments. The evolution of both reflectivities and Bragg wavelengths of four wavelength-multiplexed regenerated FBGs simultaneously annealed at respectively 760°C, 810°C, 850°C and 890°C is reported.
Corrosion of reinforced bar (rebar) in concrete structures represents a major issue in civil engineering works, being its detection and evolution a challenge for the applied research. In this work, we present a new methodology to corrosion detection in reinforced concrete structures, by combining Fiber Bragg Grating (FBG) sensors with the electrochemical and physical properties of rebar in a simplified assembly. Tests in electrolytic solutions and concrete were performed for pitting and general corrosion. The proposed Structural Health Monitoring (SHM) methodology constitutes a direct corrosion measurement potentially useful to implement or improve Condition-Based Maintenance (CBM) program for civil engineering concrete structures.
Security is a rising market, and solutions based on distributed sensing provide answers adapted to requests of citizens and
industrials. We developed the SMARTFENCE concept, to provide an innovative solution for enhanced perimeter
security of critical infrastructures. It includes a new kind of optical cable deployed on fences, a Brillouin instrumentation,
and a dedicated signal processing. Several 20 m-long fences were equipped with such sensing cable and tested by
commandos, then intrusion signals were used to develop the signal processing. Field trials resulted in a very sensitive
solution, thanks to an innovative deployment procedure of optical cables on fences. The project ends with a long term
demonstration: an electrical substation, 670 m perimeter, has been equipped with the fiber sensing cable, on two fence
levels. This validation provides an important experience feedback and the monitoring system validation.
High temperature gradient of a conventional tubular furnace is characterized using a single fiber sensing line with
wavelength-multiplexed short-length regenerated Fiber Bragg Gratings. The multiplexed gratings are simultaneously
regenerated using a high temperature annealing process. Temperature calibration from ambient temperature up to 850°C
is conducted leading to a standard deviation of 0.33°C after polynomial fitting of the wavelength shift with temperature.
Underground heat exchangers are instrumented by eight multimode optical fiber cables connected to a distributed
temperature sensing (DTS) Raman system which provides real time temperature monitoring, versus operational
conditions of the installation. A user-friendly Labview® software has been developed, allowing the configuration of the
full installation, the signal processing of raw DTS data and storage, as well as the visualization of any temperature
profile, on request. Preliminary temperature profiles are very promising. This platform will allow R&D about geothermal
exchanges, will provide a full scale bench to characterize new equipments, and will encourage professionals to develop
this renewable energy sector.
Safety while tunneling is one of the main challenges for underground constructions, avoiding
confinement losses, which remain an important risk for public works, leading to additional delays and high
insurance costs. In such applications, usual surface instrumentations cannot be set up because of high building
density in many overcrowded cities. Tunnelling deals with the challenge of requiring ground surface
undisturbed. One original concept proposed in the framework of the European Tunconstruct project, consists
in very early settlement detection close to the tunnel vault and before any detectable effect on the surface. The
adopted solution is to set-up a sensing element inserted into a directional drilling excavated above the
foreseen tunnel. The methodology is based on the well known Brillouin Optical Time Domain Reflectometry
(B-OTDR) in singlemode optical fibres and a special cable design dedicated to bending measurement. Two
cables, based on different industrial manufacturing processes, have been developed taking into account the
strain sensitivity required, the flexibility and the robustness for borehole installation, a low power attenuation
and storage on a drum. Industrial prototypes have been manufactured and validated with tests in open air
where settlement profiles geometry can be accurately controlled. Demonstration on job site took place on The
Greater Cairo Metro Line 3 (CML3) at the beginning of 2009.
Current collection is a key issue in modern electrical railway, and its performances are mainly determined by the
pantograph/catenary interactions. Whilst being the less investigated topic, the pantograph/catenary mechanical interface
is the most crucial one. Many incidents and traffic interruptions are due to degraded, or even damaged, electrical contacts
between current collectors and contact wires. During the 6th European Framework Program (FP6) CATIEMON project
(CATenary InterfacE MONitoring), both FBG-based sensors and systems dedicated to the pantograph/catenary
interaction monitoring - directly from the high voltage contact wire - have been developed and tested. This paper
describes their design and installation but also results coming from field-tests. It highlights their advantages for the
railway stakeholders and end-users in term of train operation enhancement.
We present a study aimed at developing fibre-optic-based biosensors for the specific detection of biological species.
These sensors rely on the combined use of a Tilted short period Fibre Bragg Grating that detects changes in the refractive
index of the surrounding solution and of an electrostatic self-assembly technique: self-assembled polyelectrolyte layers
and immobilization of the sensor protein on the fibre surface were used for sensor fabrication. We observed changes in
the sensor's spectrum induced by specific binding and we imaged fibre surface with atomic force microscopy (AFM).
The results show the feasibility of the sensor for various biological or chemical applications.
The thermal drift of the characteristic wavelength of a Fiber Bragg Grating photowritten in the core of an 18-hole-microstructured
fiber is significantly reduced by inserting a liquid of suitable refractive index into its holes. The
maximum sensitivity is reduced, and the spectral range of variations is divided by a factor of 8, over a temperature range
larger than 20°C. Such passive FBG temperature compensation technique is of great interest for applications involving
accurate sensing free of thermal effects.
A multi-channel fibre optic OSL dosimeter system is developed by the CEA LIST for quality control in cancer radiation
therapy, in the framework of the European Integrated Project MAESTRO.
A wavelength tunable erbium-doped fiber ring laser dedicated to high-speed interrogation of Fiber Bragg Grating (FBG) sensors has been realised and characterized. A standard FBG is used as the output mirror whereas an intra cavity spectral filter formed by a π-phase-shifted FBG is implemented to narrow the output laser spectrum down to 0.5 pm. The emitting wavelength is tuned at 500 Hz over 3.6 nm by simultaneously straining both the standard and π-phase-shifted FBG with a piezoelectric actuator. An all-fiber Michelson interferometer is used to accurately determine the spectral scanning range. Bragg wavelength increments equal to 1.3 pm are resolved combining both wavelength referencing with an absorption gas cell and amplitude normalisation versus the laser output power. This instrumentation is designed to be embedded in a train cabin for making on-board strain and temperature measurements on pantographs with FBG sensors.
The propagation properties of microstructured optical fibers useful for sensing applications are reviewed. The interaction between light and sample can reach 95 % in singlemode hollow core fibers and examples of structures exhibiting such large overlap ratios are described. The generation of 300 nm and 700 nm flat continua of visible and IR light in a single highly nonlinear holey fiber, well suited for the detection of biological species by spectroscopy, is reported. The low temperature sensitivity of long period gratings and of the birefringence in holey fibers is attractive for sensors operating in varying environmental conditions.
In-situ thermal measurements of argillaceous rocks is required by the ANDRA to evaluate the feasibility and dimensioning of a long-life radioactive waste storage in deep geological underground repository sites. The last large scale experiment called HE-D has started in the middle of 2004 in the Mont Terri Underground Rock Laboratory based in Switzerland to evaluate new kinds of thermal instrumentations and improve the understanding of the thermal conductivity coefficient of the Opalinus clay. A thermal cane equipped with 6 optical Fiber Bragg Grating sensors (FBGs) has been developed by the CEA-List and installed in a 15 m-long borehole surrounding a central heating borehole. The sensitivity and thermal transduction of FBG sensor packaging have been characterized in laboratory before installation. Mechanically, the robustness of FBG packaging has been validated during the introduction in the borehole and the two measurement campaigns respectively four and nine months thereafter. In this paper, we report the results of the FBG temperature measurements in comparison with traditional resistive probes (Pt100) at different stages of the experiment. The temperature accuracy and resolution obtained in the laboratory are better than 0.2°C and 0.1°C respectively. In the borehole, the differences between both kinds of sensors were no more than 0.2°C.
In this paper we present results relative to Fiber Bragg Grating (FBG) photowritten in two kinds of Ge-doped microstructured optical fiber cores devoted to sensing applications. A cross-comparison between theoretical and experimental modal field patterns is carried out. We present the first values of spectral sensitivity of Bragg grating in relation to the refractive index of the substance inserted into the holes.
This paper describes the laboratory tests and field trial on the Saint-Jean bridge (Bordeaux, France) of both FBG extensometers (long and short-gage) and associated instrumentation, in the context of its industrial transfer.
Most civil engineering structures have been built in the 50's and 60's and reach similar level of degradation accelerated by loading conditions and corrosion. In Europe, National Authorities and the European Commission promote Health Monitoring concepts, instrumentation of existing structures and help in the design of new durable structures of higher performance. In this context, the CEA-List has achieved a non-exclusive industrial transfer of its Bragg grating sensing technology for civil engineering applications to Hydrolog (French SME), supported by the European Community and the french ministry of Industry. In order to check the reliability and user-friendliness of this instrumentation, eleven spectrally-multiplexed Bragg grating-based extensometers, four FBG temperature sensors and an acquisition unit have been installed into the Saint-Jean bridge in Bordeaux, France with the help of the Infrastructure Regional Direction (DRE-Aquitaine) and the Bordeaux Authority (Communaute Urbaine de Bordeaux). A standardized loading of the bridge has been performed on October 29, 1001, with the purpose of correlating its mechanical reaction to loading conditions. Moreover, the equipment has been operating for one year to take into account the winter-summer cycle.
An FBG-based inclinometer is presented. The opto-mechanical principle is based on a differential method, allowing the temperature, pressure influences and mechanical hysteresis to be compensated for. Metrological qualifications performed in laboratory as well as data gained from a civil engineering field trial are presented.
A new kind of instrumentation based on Optical Fiber Bragg grating sensors is proposed for the main relevant monitoring needs in the electric power industry. The challenging metrological properties of these components are presented and their good resistance to (gamma) -ray irradiations experimentally proved.
Recent developments of stability control in mines, essentially based on Ge-doped Fibre Bragg Gratings
(FBG) are reported including results about the different aspects of the system : accurate characterisations of FBG,
sensor network topology and multiplexing method, user interface design and sensor packaging.
Pierre Sansonetti, Michel Lequime, D. Engrand, Jean-Jacques Guerin, Roger Davidson, Scott Roberts, B. Fornari, Mario Martinelli, Priscilla Escobar Rojo, Valeria Gusmeroli, Pierre Ferdinand, J. Plantey, Margaret Crowther, Brian Culshaw, W. Craig Michie
A collaborative European Programme N degree(s) RI 1B 0173-C(CD) under the auspices of BRITE (Basic Research in Industrial Technologies for Europe), jointly sponsored by the Commission of the European Communities and European Industry, was launched in 1988 to explore and develop an optical sensor network embedded in composite for measuring the strain and temperature distributions. Its objectives and first results were presented at the `Fiber Optic Smart Structures and Skins II' conference (Sept. 1989, Boston). This paper will describe the work and the main results which have been obtained since then. Three main areas have been covered which have concerned the implementation of a coherence based parallel quasi- distributed sensing system, the simultaneous measurement of temperature and strain and the mechanical properties of composite material with embedded sensor. All results have shown the high interest of such an optical sensing network for structure monitoring.
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