Detection of defects in polyethylene pipes using open microwave coaxial line resonator sensor

Abstract

A new method using a microwave coaxial line resonator sensor for the non-destructive evaluation of defects in polyethylene pipes is presented. The sensor consists of a coaxial line section and an extended section of circular waveguide. One end is short-circuited and the other end is open to free space. The sensor aperture is designed to conform to the curvature of the pipe outer surface, so that the common problem of the standoff distance effect by open-ended waveguide scanning is well circumvented. The presence of defects causes local permittivity and volume changes, leading to variations of the resonance frequency and quality factor due to material perturbation. The detection principle is confirmed by electromagnetic simulation. From the experiments, it is shown that the proposed sensor can perform both detection and classification of flat-bottom holes. The minimum diameter of the hole that can be detected is 1 mm, which is lower than that of a hole required in the standard practice. This method can also effectively detect axial defects and determine the lengths. In addition, an open-ended waveguide is used to detect axial holes, and the results were compared with those of coaxial line resonator. The sensor system presented here has the advantages of low cost, convenience for on-site detection and quantitative analysis.