Calibration methods of a 2GHz evanescent microwave magnetic probe for noncontact and nondestructive metal characterization for corrosion, defects, conductivity, and thickness nonuniformities

Abstract

A near-field magnetic-dipole probe suitable for noncontact and nondestructive imaging of metals is described and the effects of resonator coupling strength, operation frequency, and the probe wire tip geometry on the conductivity resolution of the probe are experimentally determined. Using a simplified circuit model of the resonator, we were able to interpret the system’s output and predict the magnitude of reflected wave and relate it to the properties of the samples under investigation. Thus, the probe was calibrated to perform quantitative conductivity measurements with the ability to detect metal nonuniformities with 1% accuracy and 5×10−3σ and 2×10−2σ conductivity resolutions at 2GHz operation frequency for both the critical and over-coupling probes, respectively. We also discussed the calibration results of probes with different coupling strengths over a 0.91Ω∕square resistive sample. The calibration results of a critical-coupled resonator probe were also compared with a microstrip transmission line probe. It was observed that the resonator probe has 100 times higher conductivity resolution than that of the transmission line probe. Furthermore, we characterized and compared the calibration results of probes with tip wires of different diameters. Images obtained by an evanescent microwave probe are presented.

Modeling and characterization of a cantilever-based near-field scanning microwave impedance microscope

“…In our SMiNa, the tip is first attached to the end of a piece of λ/4 cable to form a transmission line resonator, as seen in Fig. 3 Finally, the output contrast signal from the matching section, which is proportional to ΔS11 (reflection) or ΔS12 (transmission) [24], can be simulated given a small impedance change at the tip. Assuming 1aF capacitive perturbation in either Z t or Z et , we show the calculated ΔS11 and ΔS12 in the inset of Fig.…”

Detection of Surface Cracks in Metals Using Microwave and Millimeter-Wave Nondestructive Testing Techniques—A Review

“…The basic planar probe concept first described in [68] was subsequently utilized to realize sensitivity-enhanced probes. Inspired by the microstrip resonator probe reported in [69] and [70], the dual-behavior resonator probe was demonstrated to detect notches of width 0.2 mm at 13 GHz [71]. Similar probes with other resonator types such as complementary split-ring resonators (CSRRs) operating around 5 GHz [72] and its enhanced version which operates around 8 GHz [74] were also reported to detect notches with a width of 0.1 and 0.2 mm, respectively.…”

“…Open-resonators employ inefficient EM radiating elements designed to concentrate the field in the proximity of the main radiating structure to increase the sensitivity and resolution [67], [68], [69], [70], [71], [72], [73], [74], [75], [76], [77], [78], [79], [80], [81], [82]. These methods were successfully demonstrated to detect 8-and 2-µm-wide fatigue cracks in steel in 1973 [67] and 1975 [68].…”

Near-field imaging of high-frequency magnetic fields with calorimetric cantilever probes

“…1 This interest is motivated by applications that include measurements of material properties as well as the characterization of high-frequency circuits. Scanning evanescent microwave microscopes based on sharp probe tips protruding from the center conductor of coaxial microwave 2, 3 or microstrip 4 resonators have been used almost exclusively for measuring material properties. Other traditional 5 and apertureless 6 scanning near-field microwave microscopes have also been used for material characterization.…”