Study On The Degeneration Of FBG Strain Sensing System

FBG sensors have the advantages of simple structure, easily duplicated, low sensitivity towards magnetic, high insulation and good defending bursting capability. So they have extensive application in bridges, large dams and tall buildings. However, FBG sensors are degenerated in external environment little by little, so strain sensing system of FBG may bring about various faults in long-term fieldwork, and leading to abnormal data. So it cannot supply objective and inerrant original information with safety evaluation, thus it will seriously affect final evaluate results about structural health monitoring. Therefore, it is important that study degeneration of strain sensing system of FBG and resolve original data failure as a result of degenerate FBG.FBG sensing principle was introduced at the beginning of this paper. Basic composition and principle of the FBG strain sensing system were analyzed in detail. According to engineering experience we obtained that FBG sensor was most likely degeneration.Based on coupled mode theory, the technological parameter of FBG sensors to the effect of spectrum was analyzed. According to simulation experiment and in contrast the role of color centre model and stress release model, the principal factor of degeneration FBG sensor was refractive index modulation.The effect of the degeneration on the FBG multiplex demodulation was mainly analyzed. After that the link-connection degeneration to the spectrum was analyzed. And the effect of degeneration on system about source, F-P filter, coupler to FBG spectrum and strain measurement were expatiated on.Building FBG degradation testing system, carrying out cycle of alternating high and low temperature degradation test and stress cycle degradation test, the degenerate FBG spectrum and strain measuring data failure were obtained. By the clustering methodology, the degenerate FBG sensor of strain data was processed. According to cubic spline interpolation, the strain measuring data was reconstructed, and system fault owing to the degenerate FBG sensor was solved.