Detection of micro-cracks on metal surfaces using near-field microwave dual-behavior resonator filters

Abstract

This paper demonstrates how micro-cracks at the surface of metals can be detected and imaged by near-field microwave techniques from the crack-induced variations of the resonance frequency and of the resonant circuit quality factor. It deals with two resonant sensors: a quarter wavelength microstrip line resonator terminated by an electric dipole and an original dual-behavior resonator (DBR) band-pass filter probe. The detection principle is developed, at first, from the use of the electric dipole probe. The low sensitivity of the electric dipole resonator led us to investigate whether first-order band-pass filters based on dual behavior resonators were able to detect a 200 µm wide and 3 mm deep rectangular EDM notch at the surface of a steel plate used to validate our method. Simulation data and measurements results carried out on a stainless steel mock-up with several 200 µm wide EDM rectangular notches showed that the DBR sensor is more sensitive than the electric dipole probe, and highlighted the link between the spatial resolution and the width of the high-frequency stub of the DBR filter. Moreover, we demonstrate the notch detection for any orientation of the defect in relation to the DBR sensor and the ability to differentiate between notches of different depths. Simulation data and measurement results are presented and discussed.

Review of Electromagnetic-Based Crack Sensors for Metallic Materials (Recent Research and Future Perspectives)

“…As described in the literature [29], there are two sensors: a quarter-wavelength microstrip-line resonator, followed by an electric dipole and an innovative DBR band-pass filter probe. The phenomenon of detection is produced primarily using probing of the electric dipole.…”

“…Figures 8 and 9 present a schematic and a photograph of the first-order DBR device used for the detection of micro-cracks on surfaces. Photograph of the first-order DBR probe above the stainless steel plate (from [29]; copyright © 2008; adopted with permission).…”

“…The existence of the Figure 9. Photograph of the first-order DBR probe above the stainless steel plate (from [29]; copyright © 2008; adopted with permission).…”

“…Additionally, the corresponding x value for the electric dipole is 180 µm; its spatial resolution is somewhat enhanced relative to the spatial resolution of the DBR filter with the 50-µm-wide high-frequency stub. Nevertheless, the sensitivity is significantly improved by the DBR filter [29].…”

“…The authors have shown [29], experimentally and theoretically, that a resonant near-field probe can sense a surface crack in a metallic surface. The idea was initially authenticated using research into the microstrip electric dipole resonator developed by Tabib-Azar et al Experiments conducted for the 3-mm-deep and 200-µm-wide rectangular cracks were utilized to confirm their method; results emphasized the high spatial resolution of the electric dipole probe, but they also showed its crumbliness and low sensitivity.…”