第3卷第2期 智能系统学报 Vol.3 Na 2 2008年4月 CAAI Transactions on Intelligent Systems Apr.2008 Fiber optic strain t win-sensor-array for smart structural health monitoring ZHAO Shi-gang',YUAN Li-bo2 (1.National University Science Park,Harbin Engineering University,Harbin 150001,China;2.College of Science,Harbin En- gineering University,Harbin 150001,China) Abstract:A multiplexed white light interferometric fiber optic twimsensor-array was designed to monitor the structural health of large buildings.In this sensing system,based on a Michelson interferometer,an optical path matching technique is used to demodulate each twimsensor.Each twimsensor-array consists of a 2 XN sensing element linked by a 3 dB coupler.When one of the twim sensor is used to measure strain, variations caused by temperature can be compensated for by referencing the other twimsensor.The multi- plexing capacity of the sensing scheme has been analyzed and experimental results with a 2 X3 twinsensor- array are given. Key words :fiber optic sensor;white light interferometer;multiplexing technique;twimsensor-array;tem- perature compensation;Michelson interferometer CLC nember TP311 Document code:A Article ID 1673-4785(2008)02-0177-04 There has been considerable interest recently white light twim sensor-array scheme that meas- in the development of fiber optic sensors based on ures the absolute optical path lengths of each fiber white light interferometry.The use of such a segment end reflective surfaces. technique for distributed strain or temperature 1 Michelson based fiber optic inter- sensing in advanced composite or other structural materials has been discussed in several recent arti- ferometric twin sensor-array clest>51.Fiber optic Michelson sensor arrays are of The sensing principle is shown in Fig.1.The particular interest for such applications because a broadband LED source is directly coupled into the number of reflective-type sensors networked either fiber optic Michelson interferometer by passing in a serial or a parallel topology may be interroga- thorough a 3 dB coupler and lunched into the twim ted by use of a common path-length variable refer-sensor-array.The twimsensor-array consists of ence,thus keeping the system cost down.Several 2 XN fiber segments (N twimsensors)connected schemes have been reported for multiplexing this in series with partial reflectors im between the adja- type of sensors.These include coherence turn- cent fiber segments,configuring a Michelson inter- ing!1,time-division!,spatial division!s,dupli- ferometer based multiplexed fiber optic sensor ar- cate fiber optic switch!3 and 1 XN star coupler!4 ray.The reflected signals of each sensor pair re- multiplexing technique. tune and travel in the same path towards the PIN In this paper,we propose and demonstrate a detector end.One arm of the fiber optic Michelson interferometer as optical path adjusting part has 收稿日期：2007-0918. been used to demodulate the twimsensor-arrays. 基金项目：National Natural Science Foundation of China(60577005); Specialized Research Fund for the Doctoral Program of So that each individual sensor pair is corresponding Higher Education Institute of MOE,China,to Harbin Engineering University. to a unique interference peak because the optical 通讯作者：YUAN Libo.Email:Ibyuan@vp,sna.com. path length is different from each other.For a sen- 1994-2008 China Academic Journal Electronic Publishing House.All rights reserved.htp://www.cnki.net第 3 卷第 2 期 智 能 系 统 学 报 Vol. 3 №. 2 2008 年 4 月 CAA I Transactions on Intelligent Systems Apr. 2008 Fiber optic strain twin2sensor2array for smart structural health monitoring ZHAO Shi2gang 1 , YUAN Li2bo 2 (1. National University Science Park , Harbin Engineering University , Harbin 150001 ,China ;2. College of Science , Harbin En2 gineering University , Harbin 150001 ,China) Abstract :A multiplexed white light interferometric fiber optic twin2sensor2array was designed to monitor t he structural healt h of large buildings. In t his sensing system , based on a Michelson interferometer , an optical path matching technique is used to demodulate each twin2sensor. Each twin2sensor2array consists of a 2 ×N sensing element linked by a 3 dB coupler. When one of t he twin2sensor is used to measure strain , variations caused by temperat ure can be compensated for by referencing the other twin2sensor. The multi2 plexing capacity of t he sensing scheme has been analyzed and experimental results wit h a 2 ×3 twin2sensor2 array are given. Keywords :fiber optic sensor ; white light interferometer ; multiplexing technique ; twin2sensor2array ; tem2 perat ure compensation ; Michelson interferometer CLC nember :TP311 Document code :A Article ID :167324785 (2008) 0220177204 收稿日期 :2007209218. 基金项目 :National Natural Science Foundation of China (60577005) ; Specialized Research Fund for t he Doctoral Program of Higher Education Institute of MOE , China , to Harbin Engineering University. 通讯作者 : YUAN Li2bo. E2mail :lbyuan @vip . sina. com. There has been considerable interest recently in t he development of fiber optic sensors based on white light interferometry [122 ] . The use of such a technique for distributed strain or temperat ure sensing in advanced composite or ot her struct ural materials has been discussed in several recent arti2 cles [325 ] . Fiber optic Michelson sensor arrays are of particular interest for such applications because a number of reflective2type sensors networked eit her in a serial or a parallel topology may be interroga2 ted by use of a common path2lengt h variable refer2 ence , t hus keeping t he system cost down. Several schemes have been reported for multiplexing this type of sensors. These include coherence turn2 ing [6 ] , time2division [7 ] , spatial division [8 ] , dupli2 cate fiber optic switch [3 ] and 1 ×N star coupler [ 4 ] multiplexing technique. In t his paper , we propose and demonstrate a white light twin2sensor2array scheme t hat meas2 ures t he absolute optical pat h lengt hs of each fiber segment end reflective surfaces. 1 Michelson based fiber optic inter2 ferometric twin2sensor2array The sensing principle is shown in Fig. 1. The broadband L ED source is directly coupled into t he fiber optic Michelson interferometer by passing t horough a 3 dB coupler and lunched into t he twin2 sensor2array. The twin2sensor2array consists of 2 ×N fiber segments ( N twin2sensors) connected in series with partial reflectors in2between the adja2 cent fiber segments , configuring a Michelson inter2 ferometer based multiplexed fiber optic sensor ar2 ray. The reflected signals of each sensor pair re2 t une and travel in t he same pat h towards the PIN detector end. One arm of t he fiber optic Michelson interferometer as optical pat h adjusting part has been used to demodulate the twin2sensor2arrays. So that each individual sensor pair is corresponding to a unique interference peak because the optical pat h lengt h is different from each other. For a sen2 © 1994-2008 China Academic Journal Electronic Publishing House. All rights reserved. http://www.cnki.net