Guided Wave Beamforming Imaging Using Polar Coordinate Laser Scanning

In this study, a guided ultrasonic wave-based beamforming imaging technique is proposed for efficient damage detection of plate-like structures. A piezoelectric actuator was attached to excite the monitored structure, and the ultrasonic response was measured using a mirror tilting device and laser Doppler vibrometer. The detection and visualization of the damage over a large area was performed via local area laser scanning using the time-variant feature of guided ultrasonic waves in two steps. First, the signal in the direction of damage was extracted via polar coordinate based wavenumber filtering, and a beamforming-based imaging technique was applied to the damaged signal from each angle to identify the location of the damage. The polar coordinate-based scan improves signal processing efficiency compared to existing Cartesian coordinate-based scans. Additionally, applying polar coordinate-based filters for signal extraction is more straightforward compared to other existing methods. To verify the proposed technique, experiments were conducted on aluminum plates with various defects, and the performance was evaluated by estimating the exact damage location.