A robust baseline removal method for guided wave damage localization

Guided waves can propagate long distances and are sensitive to subtle structural damage. Guided-wave based damage localization often requires extracting the scatter signal(s) produced by damage, which is typically obtained by subtracting an intact baseline record from a record to be tested. However, in practical applications, environmental and operational conditions (EOC) dramatically affect guided wave signals. In this case, the baseline subtraction process can no longer perfectly remove the baseline, thereby defeating localization algorithms. In previous work, we showed that singular value decomposition (SVD) can be used to detect the presence of damage under large EOC variations, because it can differentiate the trends of damage from other EOC variations. This capability of differentiation implies that SVD can also robustly extract a scatter signal, originating from damage in the structure, that is not affected by temperature variation. This process allows us to extract a scatterer signal without the challenges associated with traditional temperature compensation and baseline subtraction routines. . In this work, we use to approach to localize structural damage in large, spatially and temporally varying EOCs. We collect pitch-catch records from randomly placed PZT transducers on an aluminum plate while undergoing temperature variations. Damage is introduced to the plate during the monitoring period. We then use our SVD method to extract the scatter signal from the records, and use the scatter signal to localize damage using the delay-and-sum method. To compare results, we also apply several temperature compensation methods to the records and then perform baseline subtraction. We show that our SVD-based approach successfully localize damage while current temperature-compensated baseline subtraction methods fail.