online health monitoring and safety
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Online health monitoring and safety evaluation of the relocation of a research reactor using
fiber Bragg grating sensors
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2006 Smart Mater. Struct. 15 1421
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INSTITUTE OF PHYSICS PUBLISHING SMART MATERIALS AND STRUCTURES
Smart Mater. Struct. 15 (2006) 1421–1428 doi:10.1088/0964-1726/15/5/031
Online health monitoring and safetyevaluation of the relocation of a researchreactor using fiber Bragg grating sensorsYung Bin Lin1, Tzu Kang Lin1, Chun-Chung Chen2,Jen Chang Chiu2 and Kuo Chun Chang2
1 National Center for Research on Earthquake Engineering, 200, Section 3, Xinhai Road,Taipei, 106, Taiwan2 Department of Civil Engineering, National Taiwan University, Taipei, 106, Taiwan
E-mail: [email protected], [email protected], [email protected],[email protected] and [email protected]
Received 7 September 2005, in final form 26 July 2006Published 8 September 2006Online at stacks.iop.org/SMS/15/1421
AbstractThis paper demonstrates the reliability and accessibility functions of fiberBragg grating (FBG) sensors in a radiation structural health monitoring andsafety evaluation application. FBG sensors, dial gages and conventionalresistance strain gages (RSGs) were attached to the temporary H-beamframe, and distributed below the path of the rail tracks for online safetymeasurements during the process of moving the structure of the researchreactor. The results showed the high level of performance of the FBG sensorsfor an online structural health monitoring system. The measurement datafrom the FBG monitoring system were comparable to the theoreticalcalculation results and the FEM simulations as the movement progressed.The result of this investigation also clearly demonstrates that FBG sensorscan overcome the harsh environments of electric and magnetic interference,while conventional RSG sensors are subject to serious fluctuations providinguseless feedback.
(Some figures in this article are in colour only in the electronic version)
1. Introduction
The structural integrity of the civil infrastructure is essentialfor the safety, productivity and quality of life of a society.This integrity is often a concern due to the aging of theinfrastructure, the occurrence of earthquakes, exposure towind and ocean waves, soil movement, excessive loading,temperature excursions and lately even terrorism. However,observing structural integrity in real time during loading isdifficult, especially when a structure has been used and hasbeen exposed to a radiation environment for more than 30years. Nowadays, non-destructive testing (NDT) methodsare used extensively to evaluate the structural integrity inmany engineering structures such as in aerospace, aircraft,automobiles, pipelines, and civil engineering [1–4]. NDTtechnology is definitely very important for the safe useof these structures when in service. Several types ofNDT&E techniques have been developed in the past, including
ultrasonic scanning, acoustic emission (AE), stimulatedinfrared thermography, vibration testing, impact echo testing,sonic, radar, conductivity [1–4] etc. However, these classictechniques of non-destructive evaluation (NDE) are notwell suited for online structural monitoring, because of thedifficulties of implementing them in situ. Conventionally,they are conducted when damage is reported through acousticemission detection, or after damage is reported by meansof ultrasonic or impact echo inspection, liquid penetrantinspection, vibration testing or other techniques. The maindrawback of these techniques is that they rely on a relativelysmall number of sensors, and the obtained data are prone tocontamination by ambient noise, which limits the use of thesetechniques for field measurements, especially in large civilstructures.
The challenge of structural integrity and safety monitoringof the movement for this Taiwan research reactor (TRR)
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is to apply new techniques which can perform onlinestructural health assessment. The hostile environment of anuclear plant demands a more careful than usual approach.However, the reliability and accessibility demands of thishostile environment severely constrain the sensor’s functionalspecifications. Damage sensing for the purpose of hazardmitigation is valuable for structures. Real-time monitoringprovides information on the time, loading condition or otherconditions at which damage occurs, thereby facilitating theevaluation of the cause of the damage. Moreover, real-time monitoring provides information as soon as the damageoccurs, thus enabling timely repairs or other hazard precautionmeasures [5–17].
Online health monitoring sensors must meet threerequirements. They must be small in size, not damage thestructure, have the possibility of being located in remoteand inaccessible areas of the structure, and they must beable to transmit information to a central processor. Thisinformation must be directly related to the physical processbeing monitored and the properties and performances that areto be maintained. It is obvious that they must compete insensitivity with conventional NDE techniques and be able tomonitor a sufficient area of the structure. It is evident thatthe system that is needed must be able to monitor a structure’s‘state of health’ and report this condition in real time in order tominimize any possible detrimental effects from any structuralproblems. Problems such as the radiation aging of the floor,which can not be exactly calculated by finite element method(FEM) modeling, or an earthquake, are also matters of concern,since they make the structural integrity and safety monitoringmuch more difficult during the moving of the research reactor.
One of the most effective sensory devices currentlyavailable for structural integrity applications appears to bethe fiber optic sensor [5–17]. Optical fibers were developedfor long-distance data transmission in the telecommunicationsindustry. However, in their earliest application, the opticalfiber was conceived as a medium for transmission of light inmedical endoscopy. The use of optical fibers for applications inthe telecommunications industry started in the mid-1960s, andthe technology has since undergone tremendous growth andadvancement. The development of optical fiber sensors startedin 1977, although some isolated demonstrations had takenplace prior to this [5–17]. Compared with the above commonNDT methods, fiber optic sensors have many advantages.One of the main advantages is that these sensors are verylight weight and small enough that they can be embeddedin materials in a manner that does not degrade the structuralintegrity [5–17]. Fiber optic sensors, and especially thefiber Bragg grating sensors (FBG) in smart structures, are anenabling technology that allows engineers to add a nervoussystem to their designs, allowing for the detection of damageand the monitoring of the health status of their structures. TheFBG sensor has been recognized as a new NDE techniquesuitable for all structural applications [5–17]. The advantageof using FBG sensors for strain sensing applications is thatit is able to measure strain locally with high resolution andaccuracy.
FBG sensors have also been considered for use in differentnuclear applications: civil, space as well as military [18–22].They have a number of well known advantages with respect to
the traditional forms of data linking, such as electromagneticimmunity, low weight and high bandwidth. The FBG sensoris a wavelength-selective fiber-optic component. Its operationrelies on a periodic modulation of the refractive index insidethe core of an optical fiber [5]. When illuminated with abroadband optical spectrum, FBG sensors reflect only a narrowband of wavelengths, centered around a characteristic valuewhich is called the ‘Bragg wavelength’. FBG sensors are keycomponents in modern fiber-optic telecommunication, e.g.,they act as filters in wavelength division multiplexed systems.They are also used as sensors for measuring temperature ormechanical stress. Here the measurement principle relieson the sensitivity of the Bragg wavelength to these physicalquantities. Based on recent studies it is evident that the nuclearindustry can benefit from the unique properties of these FBGsensors [18–22].
As mentioned earlier, the main problem of this movementproject is the aging steel reinforced concrete (RC) floor thathas been exposed to radiation for over 30 years. In orderto avoid the possibility of an unforeseen incident in theoperation of a conventional hoisting and jacking transportationduring the movement process, a precise surveillance systemis needed. Any unexpected incident such as structuraldamage, overturning, inclined slope, and exceeding theallowable deformation of the structure can all be preventedby distributing a sufficient number of sensors. The real-time monitoring system reports a dangerous state of thestructure in the case of the monitored strains exceeding a giventhreshold strain or deflection level. FBG sensors, immune toelectromagnetic fields, and subsisting on the radiation exposurearrayed in series along a single optical fiber with preciseresolution and high sampling rate, were chosen from lotsof candidate approaches. The safety analysis was carefullycalculated and double-checked by FEM; however, the damageforecast during the process of the research reactor movementneeds to be examined to ensure structural safety. Thecomparison of FBG sensors with conventional resistance straingages is used for online monitoring as a warning announcementsystem during the process of moving of the research reactor inthis paper.
2. Principle of FBG sensors
FBG technology was discovered by Hill et al in 1978 [5]. Itwas found that a reflective grating could be photorefractivelyformed in the core of germanium doped silicate fiber. Currenttechnology allows the FBG sensors to be easily fabricated andplaced in materials through a side exposure technique. Twotypical configurations consist of either exposing a small portionof the optical fiber to two interfering beams of ultraviolet (UV)light or having one UV beam focused through a phase mask.This creates a periodic modulation of the refractive index inthe core of an optical fiber. Due to the periodic nature ofthe index perturbation, only certain discrete optical frequencieswill resonate in the structure. Therefore, if broadband light istraveling in the core of the optical fiber, the incident energyat such a resonant frequency will be reflected back down theoptical fiber.
It is known that the Bragg phase-matching conditiondetermines the Bragg wavelength, λB of a fiber grating. The
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Figure 1. Sketch showing the location of the sensors at the TRRplant.
wavelength shift �λB of an FBG sensor, subject to physicaldisturbance, can be expressed as [5]
�λB
λB= (1 − pe) ε + (α + ξ) �T (1)
in which Pe, ε, α, ξ , and �T are the effective photoelasticconstant, axial strain, thermal expansion coefficient, thermaloptic coefficient and temperature shift, respectively. Thesecoefficients generally depend on the type of optical fibersused and the wavelengths at which they are written andmeasured. However, in sensor applications, the wavelengthshifts induced by variations of the doped materials in opticalfiber can be treated as constants, as compared to those inducedby structural strain, because measurements of the fractionalBragg wavelength variations, induced by the doped materials,are small. As can be seen in equation (1), any changein the periodicity of the refractive index modulation or theoverall index of refraction will change the Bragg wavelength.Consequently, any temperature or strain-induced effect on theFBG can be determined by a corresponding shift in the centerBragg wavelength.
In other words, the shift of the Bragg wavelength, �λ,can be measured directly by the axial strain of an opticalfiber. According to previous experimental studies by severalresearchers, it has been demonstrated that the shift of the Braggwavelength has a linear relationship to the applied strain in theaxial direction [5–17]. Fiber Bragg grating (FBG) sensors arehighly attractive because of the inherent wavelength responseand multiplexing capability in a distributive sensing network.In contrast to conventional strain resistance gages, thesesensors have immunity from electromagnetic interference.Practically, they are flexible, stable and durable in harshenvironments. In addition, FBG sensors are absolute andlinear in response, as well as being interrupt immune andcharacterized by a low insertion loss. Thus, they can bemultiplexed in a series of arrays along a single optical fiber.Furthermore, FBG sensors have been developed for a quasi-distributed or multi-point strain monitoring system in bothsurface mounted and embedded sensing applications.
However, since only one sensing parameter, wavelengthshift, is required in the sensor application, temperature andstrain can not be measured simultaneously with one single
Table 1. H-beam designed value and maximum allowed value(tons). (References: TRRII-01C-DWG-CA-700-01,TRRII-01C-DWG-CA-710-01.)
East track West track
Max. Max.Location (m) Design allowance Design allowance
Column 1 (−9.5) 26.94 148.8 25.17 124.6Column 2 (−6.2) 21.22 130.2 16.56 96.3Column 3 (−3.8) 32.56 144.7 25.75 116.0Column 4 (−1.4) 57.55 164.4 41.92 128.9Column 5 (0.5) 54.88 164.3 29.84 128.0Column 6 (4.0) 27.03 152.7 10.44 90.7Column 7 (7.0) 10.92 160.6 12.51 96.2Column 8 (10.3) 22.06 126.8 14.45 108.6Column 9 (13) 30.45 137.2 14.16 115.1Column 10 (15.5) 30.93 140.0 12.32 117.3Column 11 (17.5) 35.14 132.6 22.31 121.2Column 12 (19.2) 36.52 136.2 27.8 133.0Column 13 (21.5) 32.08 134.2 25.24 126.8
grating. To separate the strain signal from the temperaturesignal, different compensation methods of temperature effectshave been reported in the literature [5–17]. In addition,discriminating techniques have been proposed in recent years,such as using the first-order or second-order diffraction formsto measure temperature and strain simultaneously, or usinga chirped fiber grating written in a tapered fiber to fabricatea temperature-independent fiber Bragg grating strain sensor.Practically, with a matrix inversion technique, most of theapplications utilize two superimposed FBGs written at twodifferent wavelengths to decouple strain and temperature.
3. Monitoring system setup
The research reactor is planned to move 41 m from itsoriginal location to a new building where it will be dismantled(figure 1). For the sake of safety and workability, the moving ofthis reactor was designed to be raised from its pedestal and thenplaced on tracks which are located on the ground floor for themoving process. Meanwhile, a series of steel H-beam columns(H300 × 300 × 10 × 15) will act as reinforcement membersfor the ground floor. They are carefully designed and installedon the basement floor as a temporary support for the groundfloor during the moving of the reactor. The H-beam capacityhas been double checked to meet the code of seismic incidentin Taiwan. The only uncertain event is the strength of theaging and radiation exposed floor; in particular the thicknessof the ground floor is varied and asymmetric. Because theresearch reactor is so huge and heavy, to ensure the successof the transportation, every single process was also simulatedby FEM theoretical analysis, and the entire transport procedurewas rehearsed step by step to eliminate any possible problemfrom occurring.
The design strength and the maximum allowable axialforce of the H-beam columns were calculated by the allowablestress design (ASD) method. The material safety factor ofthe H-beam was 1.66. In addition, the design strength andthe maximum allowable value of the floor deflection werealso calculated for theoretical examination. The analyticalresults are listed in table 1. The baseline value for the early
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FBG & RSGFBG & RSG
Figure 2. Location of the FBG and RSG sensors on the H-beamcolumn.
warning announcement during the movement process was setat the average of the maximum allowable stress value fromthe material design code and the analytical value by FEM.As the measurement data approach or transcend this earlywarning value, the moving must be suspended immediately,and both the status of the research reactor structure and thefloor conditions including the temporary H-beam supportingframe systems must be carefully reexamined.
The process of the moving project was segmentedinto four phases: separate the reactor from its supportingfoundation, remove the south steel wall of the older plant, raisethe reactor and set it down on the rails, and then carry out thefinal moving. The main focus for the health monitoring was onthe steps of the final procedure to guarantee its success.
As mentioned earlier, the thickness of the ground floorvaried and ranged from 1.89 to 0.6 m. Twenty-six FBGsensors and 12 conventional resistance strain gages (RSGs)located at 2.2 m (figure 2) from the basement ground attachedon the temporary H-beam frame and separated into east andwest groups were distributed below the path of the rail tracksas shown in figure 1. Owing to its asymmetry, the verticaldeformation of the floor during the whole operation was alsoa matter of concern. The variation of the physical stiffnesscould cause cracks or structural damage and could result in thetipping or the collapse of the reactor structure. To include thispossibility, five dial gages were used to monitor the deflectionof the rail tracks. These dial gages, installed on the mostcritical points along the moving path, were fastened to theH-beam that was attached to the underside of the groundfloor. The reactor was pulled along the track by actuatorsat a rate of four meters per hour. This low speed offeredenough time to deal with any emergency that might take placeduring the conveyance. For online monitoring, including theFBG and conventional sensing system, the sampling rateswere collected once every second. It should be noted thatall the FBG sensors were annealed and recoated with ametallic film in advance so as to guarantee the consistency oftheir characteristics. The resolution of the FBG wavelengthshift was 1 pm, which corresponds to about 0.86 μm [6].Moreover, all the measurement data were diagrammed on siteand simultaneously compared with the analytic value.
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Figure 3. Early warning value of the TRR during the movingprocess.
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Figure 4. Deflection of the dial gage at column 4 during the TRRmoving process.
4. Results and discussions
The moving stresses from the dead load of the reactor duringthe movement process response to the rail tracks are transferredto the aging ground floor and the H-beams. The deformationstrain of the H-beam, measured by the sensors, was thencompared with the analytic data to check the online statusof the entire structure. The early warning values for theunsymmetrical and aging ground floor were theoreticallycalculated at the east and west rail tracks, respectively, asshown in figure 3. Note that the theoretical simulation onlycalculated the deflection for 15 m after the TRR structuremoves away from the pedestal during the process. After thefirst 15 m, part of the TRR structure placed on the tracks willbe supported by the structure of the new plant. The loadingfrom the TRR on the temporary support frame under the railtracks gradually decreases after having moved 15 m, since theconcrete floor of the new plant is solid. As shown in figure 3,the early warning value at the east side was designed to belarger than that of the west side. This meant that the eastside had a higher loading capacity than the west side. Therewere five dial gages measuring the relative deflections of theground floor during the transportation. The correspondingdesigned deflection values of the dial gages at columns 4 and11 (figure 1) are shown in figures 4 and 5. As shown in figures 4and 5, the FEM-analytic model was analyzed using SAP2000.The deflections measured by the dial gages were less than theanalytic and theoretical designed values during the moving. Itwas concluded that the asymmetric loading condition of thetwo rail tracks in the eastern part significantly reflected moreloading onto the supporting columns.
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Designed deflection value
Dial-gaugeSAP2000
Figure 5. Deflection of the dial gage at column 11 during the TRRmoving process.
The data measured by FBG and conventional sensorsare shown in figures 6–9. As mentioned earlier, due to theunsymmetrical thickness of the concrete floor, the temporarysupporting H-beam frame at the east side took up more loadingduring the moving. This meant that the floor thickness at theeast side was thinner than that of the west side. As shownin figures 6 and 7, the loading distribution of the supportingcolumns in relation to the corresponding TRR locations was
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Figure 6. Online monitoring results of FBG sensors at the east side during the TRR moving process.
quite compatible with the data from the analytical result.The comparison of the data between the experiment and thesimulation are also shown in figures 6 and 7. It is evident thatthe trend of the FBG sensor readings reasonably follows thoseof the simulation result.
Comparisons of the signals between the theoreticalanalysis and the experiment for specific locations are shown infigures 6 and 7. It is evident that the trends of both curves arequite compatible and satisfactory in both figures. The resultsindicate a high performance of the FBG sensors for onlinehealth monitoring system. The measurement data also revealsthe reliability of this FBG monitoring system that correspondswell with the theoretical calculation results and FEMsimulations of the transportation. The difference between thesensors and the numerical simulation may be caused by basicparameter assumption errors or various practical conditions.These errors can be easily modified in the simulation modelto provide a result closer to the real situation. The resultalso clearly demonstrates that FBG sensors can withstand theharsh environment of electric and magnetic interference, whileRSG sensors under the same conditions fluctuate seriously andprovide useless feedback (figures 8 and 9).
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Figure 7. Online monitoring results of the FBG sensors at the west side during the TRR moving process.
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Figure 8. Online monitoring results of the RSG sensors at the east side during the TRR moving process.
5. Conclusions
This paper demonstrated the high level of reliability andaccessibility of FBG sensors for monitoring the structural
health and safety evaluation of a radiation exposed structure inthe hostile environment of a nuclear plant. The entire processof this transportation project, under serious signal interference,which is very troublesome for traditional sensing systems, was
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Figure 9. Online monitoring results of the RSG sensors at the west side during the TRR moving process.
successfully monitored by an FBG-based surveillance system.Distributed FBG sensors offered a global perspective to assurethe safety of the transportation process.
The results clearly showed the high level of performanceof FBG sensors for an online structural health monitoringsystem. The measurement data showed that the reliability ofthis FBG monitoring system corresponds to the theoreticalcalculation results and the FEM simulations during thetransportation process. This result also clearly demonstratesthat FBG sensors can withstand the harsh environment ofelectric and magnetic interference, while RSG sensors underthe same conditions fluctuate seriously and provide uselessfeedback.
References
[1] Clark M R, McCann D M and Forde M C 2003 Application ofinfrared thermography to the non-destructive testing ofconcrete and masonry bridges NDT & E Int. 36 265–75
[2] Pang J W C and Bond I P 2005 A hollow fibre reinforcedpolymer composite encompassing self-healing and enhanceddamage visibility Compos. Sci. Technol. 65 1791–9
[3] Kharkovsky S, Hepburn F, Walker J and Zoughi R 2005Nondestructive testing of the space shuttle external tankfoam insulation using near field and focused millimeter wavetechniques Mater. Eval. 63 516–22
[4] Shibata T, Hashizume H, Kitajima S and Ogura K 2005Experimental study on NDT method using electromagneticwaves J. Mater. Process. Technol. 161 S348–52
[5] Hill K O and Meltz G 1997 Fiber Bragg grating technologyfundamentals and overview J. Lightwave Technol.15 1263–76
[6] Rizvi N H and Gower M C 1995 Production of submicrometerperiod Bragg gratings in optical fibers using wavefrontdivision with a biprism and an excimer laser source Appl.Phys. Lett. 67 739–41
[7] Kuang K S C, Cantwell W J, Zhang L, Bennion I,Maalej M and Quek S T 2005 Damage monitoring inaluminum-foam sandwich structures based on thermoplasticfibre-metal laminates using fibre Bragg gratings Compos.Sci. Technol. 65 1800–7
[8] Lin Y B, Chang K C, Chern J C and Wang L A 2005 Packagingmethods of fiber-Bragg grating sensors in civil structureapplications IEEE Sensors J. 5 419–23
[9] Lin Y B, Chen J C, Chang K C, Chern J C and Lai J S 2005Real-time monitoring of local scour by using fiber Bragggrating sensors Smart Mater. Struct. 14 664–70
[10] Tsuda H, Toyama N and Takatsubo J 2004 Damage detectionof CFRP using fiber Bragg gratings J. Mater. Sci.39 2211–4
[11] Lin Y B, Chang K C, Chern J C and Wang L A 2004The health monitoring of a prestressed concrete beam byusing fiber Bragg grating sensors Smart Mater. Struct.13 712–8
[12] Fan Y and Kahrizi M 2005 Characterization of a FBG straingage array embedded in composite structure SensorsActuators A 121 297–305
[13] Lin Y B, Chern J C, Chang K C, Chan Y W andWang L A 2004 The utilization of fiber Bragg gratingsensors to monitor high performance concrete at elevatedtemperature Smart Mater. Struct. 13 784–90
[14] Tsutsui H, Kawamata A, Sanda T and Takeda N 2004 Detectionof impact damage of stiffened composite panels usingembedded small-diameter optical fibers Smart Mater. Struct.13 1284–90
[15] Takeda S I, Yamamoto T, Okabe Y and Takeda N 2004Debonding monitoring of a composite repair patch usingsmall-diameter FBG sensors Proc. SPIE—The InternationalSociety for Optical Engineering 5390 495–504 (SmartStructures and Materials 2004—Smart Structures andIntegrated Systems)
[16] Tanaka N, Okabe Y and Takeda N 2003 Temperature-compensated strain measurement using fiber Bragg gratingsensors embedded in composite laminates Smart Mater.Struct. 12 940–6
[17] Mizutani T, Okabe Y and Takeda N 2003 Quantitativeevaluation of transverse cracks in carbon fiber reinforcedplastic quasi-isotropic laminates with embeddedsmall-diameter fiber Bragg grating sensors Smart Mater.Struct. 12 898–903
[18] Fernandez F A, Gusarov A, Brichard B, Decreton M,Berghmans F, Megret P and Delchambre A 2004Long-term radiation effects on fibre Bragg gratingtemperature sensors in a low flux nuclear reactor Meas. Sci.Technol. 15 1506–11
[19] Fujita K, Kimura A, Nakazawa M and Takahashi H 2001 Braggpeak shifts of fiber Bragg gratings in radiation environment
1427
Y B Lin et al
Proc. SPIE—The International Society for OpticalEngineering 4204 184–91
[20] Fernandez A F, Berghmans F, Brichard B, Decreton M,Gusarov A I, Deparis O, Megret P, Blondel M andDelchambre A 2001 Multiplexed fibre Bragg gratingsensors for in-core thermometry in nuclear reactors Proc.SPIE—The International Society for Optical Engineering4204 40–9
[21] Koyamada Y 2000 Analysis of core-mode to radiation-modecoupling in fiber Bragg gratings with finite cladding radiusJ. Lightwave Technol. 18 1220–5
[22] Gusarov A I, Berghmans F, Deparis O, Fernandez A F,Defosse Y, Megret P, Decreton M and Blondel M 1999High total dose radiation effects on temperature sensing fiberBragg gratings IEEE Photon. Technol. Lett.11 1159–61
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