A Correlation-Based Approach to Corrosion Detection with Lamb Wave Mode Cutoff

Time of flight and amplitude attenuation are commonly used features for corrosion detection in Lamb wave testing, but the sensitivity is limited by their individual application scenarios. The mode cutoff of Lamb waves is available and sensitive to determine and describe corrosion patches. In this paper, an approach is proposed by detecting envelope variations of a particular higher order mode after propagating through the inspected area. The excitation frequency is selected slightly above its cutoff frequency, leading to a preferable sensitivity for corrosion detection. After dispersion compensation and windowing, envelope difference coefficient is established as a correlation-based indicator to describe these variations. Such a technique could be used to scan multiple paths and provide a comprehensive corrosion map. Experiments are performed on a corroded aluminum plate. The interference from scattered components has also been discussed in detail. Based on our proposed indicator, the probability reconstruction algorithm provides an acceptable diagnosis map. In addition, the effectiveness of our indicator under different corrosion widths and depths is verified by a series of finite element simulations.