Non‐destructive inspection for FRPM pipeline using periodic pattern of microwave guided‐modes on cylindrical dielectric waveguide

Abstract The authors propose a new non‐destructive inspection method for underground fiberglass‐reinforced plastic mortar pipelines utilizing the periodic patterns of microwave guided‐modes on a hollow cylindrical dielectric waveguide. By the spatial synthesis of the microwaves 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, was observed over the pipe‐wall. Further, adjusting the phase relationship between adjoining antenna elements changed the positions of the peak and null in the periodic pattern on the pipe‐wall. Additionally, when an unwanted foreign object was attached to the pipe, the periodic pattern of the microwaves can be disturbed according to the size and position of the object, and it is possible to inspect the pipeline using narrow‐band microwave signals. This paper experimentally demonstrated the successful detection of a foreign object on the pipe‐wall by scanning Talbot‐like patterns with a sensor along the pipe‐wall. This technique enables the non‐destructive inspection of pipelines using only narrow‐band, licence‐free microwave signals