Distributed Bragg grating sensing technique for test article damage detection and monitoring

Abstract

We report the use of a fiber-optic distributed sensing system to monitor structural fatigue on an aircraft undergoing a full scale fatigue test. This technique involves using optical frequency domain reflectometry to demodulate the reflected signals from multiplexed Bragg gratings that have been photoetched in the core of an optical fiber. The optical fibers, containing a high density of Bragg gratings, were applied along the surface of a Lockheed Martin P-3C Orion fatigue test article to assess the suitability of this technique for long-term structural damage detection and monitoring.Preliminary results indicate good agreement with quasi-collocated foil strain gauges and demonstrate great potential for supplementing or replacing conventional non-destructive evaluation techniques.

Complete Analysis of Multireflection and Spectral-Shadowing Crosstalks in a Quasi-Distributed Fiber Sensor Interrogated by OFDR

“…Due to the time-delay property of Fourier analysis, the amount of shift in the time domain is equivalent to a shift in the phase slope in the frequency domain, i.e., and the reflection spectrum of each FBG can be obtained by band-pass filtering the signal in the frequency domain around each beat frequency with a sufficient bandwidth. Then, inverse fast Fourier transform (IFFT) on this selected portion, can be used to recover the complex reflection spectrum of each grating independently from the others [12].…”

“…Use of FBG arrays interrogated by OFDR for strain sensors were studied and experimentally demonstrated [8]- [10], [12]. In these demonstrations, however, the distortions inherent to the concatenated FBG array were included, neither in the calculations nor for the analysis of the experimental results.…”

“…In such a sensor, multireflection and spectral-shadowing crosstalk effects are of paramount importance. It was demonstrated in the literature that FBGs can be seen within a OFDR trace [10], [12] but the error on the demodulated spectrum due to these parasite effects has never been studied.…”

A quasi-distributed temperature sensor interrogated by optical frequency-domain reflectometer

“…r i (t − τ DUT ) ↔ R i (f ) exp(−2π jf τ DUT ) and the reflection spectrum of each FBG can be obtained by bandpass filtering the signal in the frequency domain around each beat frequency with a sufficient bandwidth. Then, inverse fast Fourier transform (IFFT) on this selected portion can be used to recover the complex reflection spectrum of each grating independently from the others [13].…”

Smart film for crack monitoring of concrete bridges

“…The optical fiber distributed sensor [16][17][18][19][20] uses optical time domain reflectometry technology or optical frequency domain reflectometry technology. It is different from the optical fiber used in point monitoring.…”