Improved Fibre Bragg Grating Interrogation for Dynamic Strain Measurement

Fibre Bragg gratings represent the most common type of fibre sensor for static and dynamic deformation measurements in structural health monitoring; however typical commercial interrogators are quite expensive, require high signal-to-noise ratios and are limited to low frequency operation ranges. To overcome these limitations, a low-cost fibre Bragg grating interrogation arrangement for dynamic strain measurement up to the kilohertz range and aimed at the detection of low-amplitude vibrations, has been developed and tested. The optical system exploits an intensity modulation principle of operation and signal processing techniques are used to complement the reduced-complexity setup in order to improve its performance: a recursive least square adaptive filter yields noise power mitigation and an efficient spectral estimator permits operating spectral analysis even in high noise conditions. With these methods, a strain resolution of 5.6 nε has been achieved in ±60 με range. Experimental assessment tests carried out in typical structural monitoring contexts have demonstrated that the developed sensor is well suited to measure mechanical perturbations of different structures.