Defect Inspection of Coated CFRP Structural Based on Microwave Split Ring Resonator

This article introduces a microwave sensor designed for defect detection, utilizing a novel split ring resonator, with the primary objective of identifying concealed cracks beneath the coating of carbon fiber reinforced polymer (CFRP) structures. The sensor operates by detecting variations in frequency caused by disturbances in the electric field due to surface cracks in the CFRP material. These frequency shifts are used to characterize the width, depth, and length of the cracks. Initially, a unit sensor is employed, which is based on a 50 transmission line coupled feed, to detect cracks in metal structures. This sensor can provide information about the width, length, and depth of a single crack at a time. Subsequently, an array sensor configuration is utilized, incorporating multiple split ring resonators to enable the detection of multiple cracks simultaneously. The sensor's functionality can be switched between a band-stop and a band-pass filter mode, depending on whether cracks are present or absent in the structure being examined. Operating within the frequency range of 2 to 3 GHz, this sensor system exhibits the remarkable capability to identify cracks with dimensions as small as 0.5 mm, encompassing width, length, or height, without regard to their orientation. This sensor system also extends its utility to the detection of large-area metal surface cracks, expanding its applicability to various scenarios, including the inspection of bridges, oil and gas pipelines, and more.