Fiber Optic Sensors Based on Photoacoustic Effect for Rebar Corrosion Measurement

An all-optical ultrasound sensing system based on photoacoustic principle is developed to monitor and investigate the initiation of early stage steel rebar corrosion in real time. The ultrasound generator was developed by small size gold nanocomposites coated optical fibers to generate 8-MHz bandwidth signals. The ultrasound receiver was applied by a fiber Bragg grating sensor. This system was employed for the first time as a disruptive approach in order to replace the application of conventional electrical-based sensors due to their unique advantages including miniature size, lightweight, immunity to electromagnetic interference, resistance to corrosion, and distributed sensing capability. Accelerated corrosion tests were conducted on steel rebars to validate the developed sensing system. The obtained results indicated that the mass loss of corroded steel rebars was characterized by the centroid frequency shift of measured ultrasound signals. The correlation between the centroid frequency shift and the mass loss depicted an exponential relationship.