S.C. Mukhopadhyay (Ed.): New Developments in Sensing Technology for SHM
Disaster prevention in civil infrastructures requires the use of techniques that allow temperature and strain measurements in real time over lengths of a few meters to tens of kilometres. The distributed Brillouin sensor technique has the advantage to combine all these characteristics.
The sensing mechanism of the DBS involves the interaction of two counterpropagating lightwaves, the Stokes and the pump, in an optical fibre. Spatial information is obtained through time domain analysis. An analytical model describing the sensing mechanism based on stimulated Brillouin scattering (SBS) interaction is introduced and validated experimentally. This model development leads to the implementation of a signal processing method grounded in the physics of Brillouin scattering. An analytical approximation, valid for the optimum sensing region, reconstructs the Brillouin spectrum distribution from input sensing parameters and measured data. These data are obtained with a spectrum analysis methodology, based on three original tools: the Rayleigh equivalent criterion, the length-stress diagram, and the spectrum form factors. This methodology has been successfully used on experimental spectra.
The DBS and the signal processing approach were then used to monitor the structural changes of steel pipes, composite columns and concrete elements. The DBS measured the strain distribution of those structures while they were stressed. The DBS provided detailed information on the structure’s health at local and global level, associated with deformations, cracks and buckling. This work demonstrates that the DBS is capable of extracting critical information useful to engineers: engineer’s experience and judgement in conjunction with appropriate data processing methods make possible to anticipate structural failures.
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