Non-destructive Inspection for FRPM Pipeline Using Self-imaging Effect of Microwave on Cylindrical Dielectric Waveguide

The authors propose a new non-destructive inspection method to inspect an unwanted foreign object remaining underneath the wall of the underground fiberglass-reinforced plastic mortar (FRPM) pipelines. Our method utilizes periodic patterns of microwaves on a hollow cylindrical dielectric waveguide. When the microwave propagating along the wall of the pipe is spatially synthesized utilizing the periodicity in the circumferential direction of a pipe, the authors found that a periodic pattern of the microwaves such as the Talbot effect with producing self-images at the Talbot distance is observed over the pipe-wall. Further, when an unwanted foreign object is attached to the outer surface of the pipe, the authors revealed that the periodic pattern is disturbed by the reflection, scattering, and attenuation of the microwaves due to the presence of the object. This paper experimentally demonstrated the successful detection of a foreign object by utilizing the periodic pattern. This technique enables the non-destructive inspection of underground pipelines using only narrow-band licence-free microwave signals.