Temperature independent FBG based displacement sensor for crack detection in civil structures

•Crack detection using FBG-based displacement sensor for structural health monitoring (SHM).•The technique is immune to electromagnetic interference and independent of environmental temperature change.•The interrogation technique to map wavelength to time delay is the first time used in crack detection. Structural health monitoring (SHM) of civil, industrial, and monumental infrastructures is increasing day by day to provide necessary vitals and avoid the hazardous incident. Crack detection is one of the primary health monitoring techniques for civil structures. A simple and temperature-independent optical displacement sensor using Fiber Bragg Gratings (FBG) for crack monitoring is proposed. The proposed sensing system utilizes a wavelength-to-time delay mapping-based interrogation technique to observe the strain generated on FBG. Initially, the sensor module is analyzed on FEM based simulation platform and later experimental analysis is carried out for the different displacement values which signify the width of the crack. A crack in the structure is detected in terms of time delay with respect to reference pulse. The proposed sensing system provides resolution and sensitivity of 0.18 mm and 8.95 ps/mm respectively. The proposed technique can provide stable temperature-independent sensing data that would minimize the probability of false crack detection in the structure and provide a much more reliable sensing solution.