Active Sensing Using LDV and T-Shaped Arrays in Metallic Plates for Damage Localization

Abstract

In this work, T-shaped arrays of sensors generated by a single laser Doppler vibrometer (LDV) are used for damage localization in a metallic plate. Previous studies have used a single T-shaped array of piezoelectric patches to estimate the direction of arrival of waves in plate-like structures. Here, by comparing the measurements of two and four T-shaped arrays with baseline information, this technique could be extended for damage localization, resulting in an active sensing application. Instead of piezoelectric transducers, a LDV is used to create the T-shaped arrays, which enables the testing of arrays with different numbers of measuring points and different positions. The difference between test and baseline measurements is used, as it contains information on waves from a known acoustic source that scatter and reflect at a damage site. Beamforming is then applied to these residual signals, and the resulting beamforming maps are transformed into a map of positions in the inspected area. The measurements of each array results in one position map, and combining all maps results in an estimated location of the damage. This is demonstrated in a square metallic plate with a single source of vibration located at its center, while the arrays are located at the boundaries of the inspection area. The tests show that even for low density arrays, increasing the number of arrays enables damage detection with reasonably good results, even when employing simple delay-andsum beamforming instead of more advanced and complicated processors. This work also serves as a proof of concept that a set of T-shaped arrays can be reliably used for active sensing of damage in plane plates.