Cross-Polarization Near-Field Microwave Imaging of Back-Surface Volumetric Flaws in Polyethylene Components

ABSTRACT The hostile environments inevitably leave the polyethylene (PE) components vulnerable to such volumetric flaws as localized material loss, which poses a severe threat to structural integrity and safety. The co-polarization reflectometry is one of the modes of microwave testing for detection and imaging of volumetric flaws, particularly those occurring at the back surface of the PE component. However, its testing result would be influenced by the variation in stand-off distance between the antenna aperture and the structure surface. In view of this, the cross-polarization reflectometry (CRPR) for screening the back-surface material loss in a PE slab is intensively investigated. The response characteristics of the cross-polarization reflected signal to the defect and the resultant testing signal are analyzed through simulations and experiments. Following the raw image produced with the CRPR, an image processing method for recovering the defect image insensitive to the stand-off variation is proposed. The image segmentation is subsequently applied to the recovered images for evaluation of the defect opening area. Through comparison with the true defect image and opening area, it is affirmed that the proposed cross-polarization microwave screening method alongside the defect-image recovery algorithm is capable of enhancing the quality of imaging of the back-surface volumetric flaws in PE slabs, in terms of the testing sensitivity and image contrast.