Fiber optic macro-bend based sensor for detection of metal loss

Metal loss in metallic structures, often as a result of corrosion, is a severe problem across multiple industries. Catastrophic consequence of structural failure due to such loss of structural metal requires an accurate determination and assessment of corrosion. Widely used electrochemical methods can only suggest the likelihood of the metal loss due to corrosion while failing to provide a quantitative measure of the accumulated amount of corrosion. Due to its unique advantages such as small size, light weight, resistance to electromagnetic interference and corrosion, fiber optic sensing technique has been emerging as a promising alternative for most sensing applications. In this paper, a novel type of ferromagnetic distance-based metal loss sensor is proposed based on the principle of fiber optic macro-bend loss. The proposed sensor is composed of the bended optical fiber, the magnet and a spring. The magnet is connected to the spring and the fiber bend is attached to the spring in such a way that the movement of the magnet will induce a change in bending radius of the optical fiber. Metal loss in the monitored sample increases the distance between the magnet and the metal surface and thereby reducing the magnetic force. A change in magnetic force will lead to the variation in light intensity loss of the fiber optic macro-bend, thus metal loss, such as in the form of corrosion pits, can be detected by the proposed metal loss sensor. The practicality of the proposed distance sensor for metal loss measurement is validated through scanning the fabricated corrosion samples.