Time-domain Analysis of Microwave Guided-Modes Propagating along FRPM Pipe Wall for Infrastructure Inspection

We have proposed a new nondestructive inspection technique for underground FRPM pipelines by using microwave guided-modes propagating along the pipe wall. Further, we have been investigating a method for estimating the position of a foreign object using measurement results and simulation results. In this paper, as a first step in constructing the estimation method of it, time-domain analyses of measured and simulated microwave signals are discussed. In addition, we investigate a detail of the transmission characteristic of the microwaves propagating along the FRPM pipe wall. The time-domain responses of the simulated microwave signals by using a theoretical equation based on a FRPM slab guide model were in good agreement with that of the measured results. Thereby, we found that the microwaves propagating along the FRPM pipe wall can be represented with the theoretical equation based on the propagating model along the FRPM slab with periodic boundary condition corresponding to the expanded pipe wall. The time-domain analysis of the microwave guided-modes enables us to have easy-to-use inspection methods for various buried pipelines.