On the Crack Characteristic Signal From an Open-Ended Coaxial Probe

Detection of surface-breaking cracks in metals is an important issue in many industries (e.g., transportation, aerospace, nuclear). Commonly, eddy current and ultrasonic techniques are used for this purpose. In recent years, a significant amount of work has also been conducted using microwave methods. Consequently, to better understand the interaction between a microwave probe (i.e., open-ended rectangular waveguide or coax) and a crack, a number of electromagnetic models have been developed. For an open-ended coaxial probe, when a crack coincides with the center conductor region of the probe, all previously developed models significantly underestimate the results obtained from measurements. This paper examines the primary reason for this discrepancy, which turns out to be due to a geometrical perturbation in the probe center conductor geometry and its subsequent interaction with a crack.