Adapting the Time-Domain Synthetic Aperture Focusing Technique (T-SAFT) to Laser Ultrasonics for Imaging the...

Area of Science:

• Materials Science
• Non-Destructive Testing
• Optics and Photonics

Background:

• Traditional ultrasonic testing methods (T-SAFT, phased array) are contact-based and have bandwidth limitations.
• Laser ultrasonics offers a noncontact approach for generating and detecting ultrasonic waves.

Purpose of the Study:

• To develop a noncontact ultrasonic testing technique by integrating T-SAFT and phased array principles using laser ultrasonics.
• To compare defect visualization capabilities between thermoelastic and ablation laser regimes.

Main Methods:

• Generated ultrasonic waves using pulsed laser beams in thermoelastic and ablation regimes.
• Acquired signals with a laser Doppler vibrometer.
• Synthesized a 1D linear phased array by moving the specimen.
• Processed data using the T-SAFT algorithm for image reconstruction.

Main Results:

• The ablation regime yielded higher amplitude signals, resulting in better defect visibility compared to the thermoelastic regime.
• Defect reflections were clearly visualized using the T-SAFT algorithm with the synthesized phased array.
• A 5 mm separation distance between laser beams did not significantly affect defect localization.

Conclusions:

• The proposed noncontact laser-based T-SAFT and phased array method is effective for defect detection.
• The ablation regime is more suitable for generating high-amplitude signals for enhanced defect imaging.
• This technique advances non-destructive evaluation by offering a noncontact, high-resolution imaging solution.