Long-Period Grating Fiber Optic Sensors Coated With Gold Film and Pulse-Electroplated Iron–Carbon Layer for Reinforcing Steel Corrosion Monitoring

Long-period grating (LPG) fiber sensors sputter coated with an internal gold film and pulse electroplated with an external iron–carbon coating are characterized for reinforcing steel corrosion monitoring. The surface feature of the gold film was analyzed by using atomic force microscopy and microscopy. The transmitted light spectrum of iron–carbon coated and the microstructure of the iron–carbon coating was examined by using scanning electron LPG fiber sensors was measured using an optical instrument, and the corrosion degree of the iron–carbon coating is simultaneously measured with electrochemical methods. Experimental results demonstrate that corrosion of iron–carbon coating leads to a shift of the resonant wavelength, which is linearly correlated with the corrosion penetration depth of the iron–carbon coating. The fiber optic corrosion sensors investigated in this study exhibit better performance than those with inner silver nanowire-/graphene-based or silver-based films and outer direct current-electroplated iron–carbon coatings.