螺旋光纤传感技术探究.pdf

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光纤微弯传感器是一种光强度调制的传感器,具有成本低、灵敏度高、适用于多种参量测量的特点。
P, however, are restricted by the durability of bent coil spring fibres and/or by the elasticity limit of the spring matc mode stripper rial. Considering this, some different types of spiral fibre mbs listed bclow were constructed fibre Sensor 1: 0.6mm-diameter piano wire spring; a 2.6mm, P=12mm(hence R=4.0mm detector Sensor 11: 0.6mm-diameter piano wire spring, u=3.0 mm, P= 13mm(hence R= 4.4mm) Fig 6 Schematic diagram far spira? fibre microbend sensoRS Sensor II: FIMt of 1 mm-diameter 6mm-thick stainless steel: a =2.6mn. P 5mm thence R 15 cating I and i. th was bonded on the rcady-made spiral piano wire with to a few ter Sensor Iii was constructcd by using a commercially 角12 available mctal-jacket fibre 'FIMT, in which a single mode fibre is built in the steel pipe with a gelatin B 10 ushion. The FIMT was shaped into a spiral by hand without thermal processin 已12 巴 36 strain e.%s Fig. 7 Measured dependence of pl: ofodetector ouput on applied strain s forditfereni pitch nimbers n in spiral fibre microbend sensor / fortice t=26mm;P=12.0mm;R÷4.0mm 0.2 0.3 1/R. mm Meusured transmittance fiction (I/R)against radius of curva gle-modefitbyre in-plune circular coil for vIious (urn numbers n 1■2◆3▲4×5C67◇8 15 P:9. 6mm 12 10 2 E rain %6 157 Fig 8 Measured dependence of photodetector output Gn applied strain e 0.2 for di fferent pitch numbers n in spiral fibre microbend sensor II for twice EXperiments 30mn;P=13.3mm;R=4 3. 3 Sensor characteristic Fig. 6 shows the schematic diagram for the strain, deformation sensor. The light source and the deteclor were the same as described in Section 3. 1. In sensors I and Il, expansion char acteristics were stildicd becalISC coil radius a. mi Fig 5 Calculated dependence of modulation index m on coil radius a for reproducible uniform axial elongation could be givcn ferent pitches P in ll pring by pulling it with various weights. TH fibre transmittances were measured as a function of JEE Prec. Optoelectron., Vol. i44. No. 3, June 1997 applied strain c for different pitch numbers n, and the In both sensors i and II with various gauge lengths mcasured results are shown in Figs. 7 and 8 for sensors Lo =nP, the modulation index m, the corresponding I and Il, respectively. A very good linearity against transmittance change at and the transmittance t are pplicd strain is obta incd for hoth the sensors. A vcry measured as a function of applied strain e. The meas good reproducibility between two-times experiments 1s ured results are shown in Figs. 9 and 10, together with also observed. The strain sensitivity increased with an the calculations of eqns. 10 12. In both sensors, fairly increase in the pitch number n. The dynamic range emay good agrecment betwcen the mcasured and calculated about 42, lasticity limit of the obtained regarding m AT and t metal spring used. The corresponding maximum t: on of the cxpcrimental rcsults from the thcory is deformation is dmr Era np, which 13 expected because the fibre was not uniformly bonded 7. 2mm for sensor i wi 15. Thus. ill strain or spiral wire on account of the hand working In deformation measurement, a large dynamic range with both sensors I and Il. m could take over 1 and Al lincar scale was demonstrated. The resolution is became almost 10. The maximum at occurred at affected by the mcchanical instability of the spring t auge lengths L of a 100mm and 140mm for sensors I motion and the output light power instability. The and Il, respectively, in good ayreeinent with the theo resultant instability of the sensor system was less than retical results glass d Fig. 11 Diagram for squeezing and stretching a /bre-buit-in metal gauge leng: h Lg, mm Fig. 9 D)pendence s of moduiation index m, transmi ianc e change AT and transmuitanco T on gaige ength Le in spira! fibre microbend sensor I =2.6mn 2. 0mm: R=4. 0mm calculated;△m,冂sT,OT, measured 10 98 squeeze e: ongation Fig 12. Measured dependence ai photodetector onipuuc on applied sti ain prul fibre microbend sensoR III f a fibre-built spring would be convenient Sensor iII was constructed by using the commercially available metal- jacket f:bre 目a日 DBodnoood日口 FIMT with n =5. Both elongation and squeezing G日。6o006。 were applied to he spring in the manncr shown in L Fig. Il, in which a glass cylinder was inserted in the 200 inside of the spring coil for carrying out its stable axia gauge length Lg. mm deformation. The easured strain characteristics are Fig 10 Deperulerncey of medu lution in: ie r m, /run smiitance chinge A shown in fig. 12. The sensor could detect both cnd transmitance T on gauge length Lg imt spiral fibre microbend senscrIl a-30nm: P=130mm:R= 4.4mm strains over a large dynamic range of 10o strain. Some calculated;△m.口ΔT,○T, leasure hysteresis was observed, being attributable Lo the dEL ProL.-Optoelectrur, Fo:. 144. No. 3. Jiarte 1 997 imperfectly reproducible deformation of the hand-made shown in Fig. 14; the piano wire used hias i low spring. Other spiral MBSs are also constructed using thermal expansion coefficient of 1 x 10/degree C mctal tubes in which thc singlc-modc fibrc was inserted and fixed by a chemical bond. Their strain 4 Simulation study characteristics were measured and showed appreciable or little hysteresis, depending on the samples con As good agreement between experiment and calculalion structed. indicatin that the mbs very Faithfully has been demonstrated. a conputer simulation study responds to the real deformation of the fibre would be useful for the optinunnl design of the spiral sensor To evaluate the effect of spiral coil radius a To study the polarisation effect, the transmittance of simulation calculations or different a-values from 2.6 an in-plane fibre coil(R=3mm)was measured when to 5.0mm were conducted us its bend plane was rotated around the fibre axis, but no lo the function f(1!R)of Fig. 4. Figs. 15-18 show the appreciable change was observed, as typically shown in calculated results for m and AT as a function of gauge Fig. 13. length Lg, respectively. It is seen From Figs. 15 and 1o that. for a constant p. the modulation index 77 becomes very large for sufficiently small a, increasing with incrcasing L as wcll. For example, with P=6.4 mm and L =500mm. the values of m are 12500. 250 and 6.0 for a= 2.6, 3.0 and 4.0mm, respectively. B contrast, the transmittance changes AT, resulting from the producl of m and T(total transmittance), are much less sensitive to d-values, as seen from Figs. 17 and 18 For example, with P-157mm and Lg= 500mm, the ATs are 4.3.2.3 and 0.65 for d-26.3.0 and 4.0mm respectively. FurThermore, for a given P, there is an optimun gauge length Lg opt for maximising Al, and both▲f ncrease with increasin mple, with △ T. s takc.8 2 4 and 4.6 at Ly ont =20, 100, 250) and 700mm, respectivcly 20000 =6 .6 10000 120 number of turns n Fig. 13 Mec.red poicrisct on deperdence uf transi iance of ii-f fibre coil of radius R=3pm a afunction of tui77? iatimmber ri for three 140 ferent angles cf orientation of' fibre hend plane 15:7 0°■45°◆90° 1000 1000 gauge length La, mm auge length La, mm b g 15 Calculatcd depside e length Le as a parameter of pitch P for coi! radii 2.0 and 3. Omm in spira! fibre rriicrobene senso g:=2.6m;b=30nm 9.5 120 120 当 P-6.4mm 10 157 15.7 1000 0 1000 gauge length L mm yuuge Leng: h La, mm Fig. 16 Calculated dependence of modularion index on gauge leng!) Ly u. a parurmeler of nitch P for coil radii 4.0 and 5. 0mm in spiral fir 4.0mr;ba=5.0m1 0 temperature, deg C Fig 14 Measured tcmperature dependence of metal spring fibre Besides the use of a one-point sensor, the present spiral fibre sensor has potential for multipoint sensing 2m;P=12.0mm;B=40mm:n=0 owing to the simple implementability of splicing lo a fibre highway, Referrer FigS.15-18, e The temperature dependence of sensor I with n=10 one example case of a=4.0, Then, with the use of was tested in a temperature range between 30 and / =12mm and Lr=60mm, one obtains m=0.5 and T 75C but no appreciable change was observed, as =0.90, so that, with a loss penalty of lodB, we can provide 21 multiple sensors having 2.5 times higher 5 Concluding remarks sensitivity than that of Fig. 12. Extension to km-range continuous distributed sensing would be an interesting The developed spiral-form single-mode fibre microbend future research subject using the spiral fibre microbend sensor uses a sensing principle based on uniform the bend radius of tl fibre so that th sensing cha definitely ficd. both theory and experiment, simply from knowledge of the 15?7 157 circular-bend loss of the single-mode fibre. The efects of the spiral coil radius, pitch and gauge length on the haracteristics al tically analysed and experimentally verified. Good reproducibility. good 14.0 14.0 linearity and large dynamic range in strain/deformation 96P:64mT measurement are demonstrated Simulation P-6.4mm calculations for sensor optimisation are also conducted 0 0 1000 6 References gauge length La, mm gauge length La, mm 1 ASAWA. CK.. YAO S.K. STREANS RC. MOTANL Fig. 17 Calculated ciepende ence of transmittance change AT Un 8z ge and DOWNS,JW:High sensitivity slrain senso: ful measuri as a paraneter of pitch P for coi! radil 2.6 and 3.0mm in spiral tructual distortion, Electron, Leit., 1982, 18, pp. 362-364 fibre microbend sensors 2 VARSHNEYA D. GHERING. W L, and BERThOlD,Jw aa=2.mro: b a =3. 0mm High-temperature fibre-optic microbend sensor. Proceedings or 3rd Optical fiber sensor s conlerence, Sa Diego 3 FIELDSIn. and cole LH: Fiber microbend acoustic ss r2,Am!.Opt,198C,19,pp.3236-326 0.6 4 YOSIIINO.T. NARA.M. and Kurosawa.k:Remote nd multi-point fiber senso s using optical time domain reflec 140 140 ometry,. Proceedigs of 13th congress of the International Com for Optics, Si oro,1984、pp.324- 0.4 157 TOMITA. S. TACHINO. H. and KASAhARA.N : Water sensor with optical fibre,, Lightwave Technol., 1990, 8, pp 12.0 .2 6 BERTHOLD, J w. Historical review of fiber-optic sensors, J Lightwave Technol., 1995,13, pp.1193--119y P=6.4mm 7 MARVIN, D. C. and IvES, N.A. Wide-range fib e-optic strain snor’,AP.Op2,1984,23,pp.42124217 1000 1000 8 OSCROFT G.'otrinsi sensors Proc SPENt Soc gauge length La, mm Eng,1987,734,pp.207-213 gauge length Lg, mm 9 LAGAKOS N. COLE, JH. and BUCARO. J.A.. Microbend fibre-optic sensor, App/. Opf, 1987. 26, pp. 2171-2180 Fig 18 Calculated dependence of transmittance change AT on gaug O YOSHINO.T. INOUE K. KOBAYASHL Y d tAK lergth Ig as a parameter of pitch P for coil radi 4.0 and 5.Omon in spiral HASHI, Y, Spring coil fiber microbend sensor wit well fibre microbend sensors de!ined characteristics. Proceedings of 11th Optical fiber sensors a 4w4, 0mm: tG=50mn conference, Sapno 0, 1996, pp. 264-25 IEL Proc. Optocicctron, VoL 44, 40. 3, Junc 1 i

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