High-Speed, Non-Contact, Baseline-Free Imaging of Hidden Defects Using Scanning Laser Measurements of Steady-State Ultrasonic Vibration

Abstract

We present an approach to visualize damage through rapid, full-field measurements of a plate-like structure’s steady-state response to a single-tone ultrasonic excitation. In our setup, a piezoelectric transducer provides the excitation while a 2D scanning laser Doppler vibrometer (LDV) makes the full-field response measurement. In taking measurements of a structure’s relatively high amplitude single-tone steady-state response, we enable significantly faster scans by avoiding many of the signal-to-noise ratio issues typically associated with LDV ultrasonic measurements. Damage is visualized by making automated estimates, on a pixel-bypixel basis, of the wavenumber of the excited response through wavenumber-domain processing. We provide sample imaging results for hidden corrosion spots in a metallic plate and delamination in two composite specimens.