Boundary Reflection Compensation in Guided Wave Baseline-free Imaging

Guided ultrasonic waves are frequently used for both structural health monitoring and nondestructive testing of metallic plate-like structures. Signals resulting from waves generated by one or more fixed piezoelectric transducers can be recorded around the periphery of an area of interest using a non-contact approach such as a scanning laser vibrometer. It is desired to determine the location of a possible flaw from this recorded data without using any baseline information. Prior work has employed delay-and-sum imaging after applying a source removal algorithm, but this process did not consider the effects of boundary reflections. While these effects may be sufficiently small to neglect in a large plate, in smaller structures boundary effects are significant and can completely obscure small flaws. Proposed here is an iterative method to perform baseline-free imaging of damage in a rectangular plate with edge reflections. Results are shown for simulated data to evaluate the efficacy of the proposed method.