Guided wave-based pipe damage inspection by ultrasonic fiber optic sensor

Ultrasonic fiber optic sensors (UFOS) based on Mach-Zehnder (M-Z) interferometer is proposed to detect guided waves propagating in the pipe, which is common structural component in aerospace, mechanical or civil structures. The sensitivity of UFOS depends on the long sensing distance, while winding around the circumferential direction of the pipe provides arbitrary sensing length as well as small covering area along the axial direction of the pipe. By the combined analysis of the characteristics of guided waves propagating axial direction of the pipe and the working principle of M-Z interferometer, the sensitivity of UFOS are investigated theoretically at first. Subsequently, a series of experiments are conducted on an aluminum pipe to demonstrate the guided wave sensing and damage inspection performances, including impact loading identification and guided waves reflected from the crack. Results indicate the UFOS has potential for providing quantitative estimation of damage in the pipe structures.