An Integrated Ultrasonic Imaging Technique using Laser Scanning System

This paper presents an integrated methodology to improve the performance of laserscanning based damage detection for large structures with various obstacles. Two different ultrasonic imaging schemes are integrated in this technique, which involves the use of beamforming imaging with local scanning, along with standing wave based full field laser scanning. Two types of excitation methods (guided waves and standing waves) are used for damage detection. The wave field measurements are obtained from a Laser Doppler Vibrometer and a mirror tilting device using a single fixed frequency (>80 kHz) excitation from a mounted piezoelectric transducer. First, a newly developed beamforming imaging technique with frequency-wavenumber filtering using local guided wave measurement is performed to identify the presence and location of damage in large structures without full field measurements. Once the damage is identified, the steady-state response based full field laser scanning is used to quantitatively assess the damage. Time variant and invariant feature based damage visualization is used to estimate the damage size and depth. To demonstrate the performance of the proposed technique, several experiments are performed on thin walled structures with several different types of damage. The results show that the technique is very effective in localizing damage and estimating depth with potential for the improved speed and performance.