Passive Temperature-Compensating Technique for Microstructured Fiber Bragg Gratings

The thermal drift of the characteristic wavelength of fiber Bragg gratings (FBGs) photowritten in the core of microstructured fibers (MOFs) is significantly reduced by inserting a liquid of suitable refractive index into their holes. For instance, the spectral range of variations is divided by a factor of 4 over a temperature range larger than 20\degree C in a six-hole MOF, and the maximum sensitivity is reduced. Such passive FBG temperature compensation technique is of great interest for applications involving accurate sensing free of thermal effects

OFDR Distributed Temperature and Strain Measurements with Optical Fibre Sensing Cables: Application to Drain Pipeline Monitoring in a Nuclear Power Plant

International audienceThis study deals with the testing of innovative Optical Fibre Sensing (OFS) cables deployed on ducts, with the aim to perform distributed temperature and strain measurements. Such cables contain several optical fibres devoted to be interrogated by Optical Frequency Domain Reflectometry (OFDR). The methodology has first been developed and qualified in laboratory. Then, real tests have been performed on a Nuclear Power Plant (NPP) drain system to demonstrate the industrial feasibility of such technology. To do so, two small diameter sensing cables, compatible with distributed temperature and strain measurements, have been qualified and afterwards installed along a sodium drain line at Superphenix NPP (liquid sodium coolant fast breeder reactor in current dismantling). Measurements have been performed during the preheating operation. Recorded data were post-processed according to a semi-empirical model taking into account temperature dependence and thermo-mechanical sensing cable behaviour. Optical fibre distributed temperature measurements were then successfully compared to thermocouple reference measurements, whereas optical sensing cable data were processed to provide distributed strain, then distributed curvature radius, which will enable, after numerical integration, to compute distributed displacement data. The goal is to assess the use of OFS for monitoring both temperature and mechanical strain distribution along a pipe under heat stress

Tilted Fiber Bragg Grating photowritten in microstructured optical fiber for improved refractive index measurement

International audienceWe report what we believe to be the first Tilted short-period Fiber Bragg Grating photowritten in a microstructured optical fiber for refractive index measurement. We investigate the spectral sensitivity of Tilted Fiber Bragg Grating to refractive index liquid inserted into the holes of a multimode microstructured fiber. We measure the wavelength shift of the first four modes experimentally observed when calibrated oils are inserted into the fiber holes, and thus we determine the refractive index resolution for each of these modes. Moreover, a cross comparison between experimental and simulation results of a modal analysis is performed. Two simulation tools are used, respectively based on the localized functions method and on a finite element method. All results are in very good agreement

Three-hole microstructured optical fiber for efficient Fiber Bragg Grating refractometer

International audienceWe present a photosensitive three-hole microstructured optical fiber specifically designed to improve the refractive index sensitivity of a standard Fiber Bragg Grating (FBG) sensor photowritten in the suspended Ge-doped silica core. We describe the specific photowriting procedure used to realize gratings in such a fiber. We then determine their spectral sensitivity to the refractive index changes of material filling the holes surrounding the core. The sensitivity is compared to that of standard FBGs photowritten in a six-hole fiber with a larger core diameter. We demonstrate an improvement of the sensitivity by two orders of magnitude and reach a resolution of 3 x 10-5 and 6 x 10-6 around mean refractive index values of 1.33 and 1.40, respectively

Fibre Bragg grating photowriting in microstructured optical fibres for refractive index measurement

International audienceWe report results relating to fibre Bragg grating photowriting in two kinds of Ge-doped core microstructured optical fibre devoted to sensing applications. A cross-comparison between theoretical and experimental modal field patterns is carried out. We present the first values of the spectral sensitivity of a Bragg grating in relation to the refractive index of calibrated oils inserted into the holes

Using X-ray microtomography to study the initiation of chloride-induced reinforcement corrosion in cracked concrete

International audienceCorrosion is the main cause of premature degradation of reinforced concrete structures. In particular, the mechanisms of chloride-induced corrosion in cracked structures are not fully elucidated. The aim of this study is to investigate by X-ray tomographic imaging the initiation and propagation of chloride-induced corrosion in cracked concrete. On reinforced prismatic cracked specimens exposed to seawater spray-drying cycles, the approach consists in characterizing in a non-destructive way the crack geometry, corroded steel volume and corrosion products migrating in the cementitious matrix and crack, as a function of time. Sub-volume scans and difference images allow a study of the first stage of chloride-induced corrosion in cracked concrete with respect to the number of spraying cycles, geometry and crack opening. The volume of steel consumed measured by 3D imaging is validated against destructive measurements, and it is shown that insights about the phenomenology of pitting (depth, displacement of corrosion products, densification, crack clogging…) can be obtaine

Applications of Fiber Bragg Grating sensors in the composite industry

International audienceOptical-fiber sensors based on fiber Bragg gratings (FBGs) provide accurate, nonintrusive, and reliable remote measurements of temperature, strain, and pressure, and they are immune to electromagnetic interference. FBGs are extensively used intelecommunications, and their manufacture is now cost-effective. As sensors, FBGs find many industrial applications in composite structures used in the civil engineering, aeronautics, train transportation, space, and naval sectors. Tiny FBG sensorsembedded in a composite material can provide in situ information about polymer curing (strain, temperature, refractive index) in an elegant and nonintrusive way. Great improvements in composite manufacturing processes such as resin transfer molding(RTM) and resin film infusion (RFI) have been obtained through the use of these sensors. They can also be used in monitoring the “health” of a composite structure and in impact detection to evaluate, for example, the airworthiness of aircraft. Finally, FBGs may be used in instrumentation as composite extensometers or strain rosettes, primarily in civil engineering applications

N-(tert-butoxycarbonyl)-N-[4-(dimethylazaniumylidene)-1,4-dihydropyridin-1-ylsulfonyl]azanide: A new sulfamoylating Agent. Structure and Reactivity towards Amines

International audienc

Health Monitoring of the Saint-Jean bridge of Bordeaux, France using Fiber Bragg Grating Extensometers

International audienceMost 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 (Communauté Urbaine de Bordeaux). A standardized loading of the bridge has been performed on October 29, 2001, 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