Feasibility verification of multiple defects imaging using phase information of Lamb waves generated by high-intensity airborne ultrasound

We propose an airborne ultrasound non-destructive testing method to visualize multiple defects in thin metal plates. Conventional amplitude-based imaging struggles to detect multiple defects due to signal attenuation caused by scattering at preceding defects. To address this, we investigated phase imaging and compared it with a method applying amplitude attenuation compensation to conventional imaging. Verification was conducted through finite element method (FEM) analysis and experiments using a duralumin plate with three series-aligned wall-thinning defects. While conventional amplitude imaging identified only the defect closest to the excitation point, both investigated approaches successfully visualized all three defects, confirming the effectiveness of phase imaging. Furthermore, assuming practical field applications, phase imaging was evaluated at various incident angles (0°, 45°, and 90°) relative to the defect alignment. Results demonstrated successful imaging across all angles, proving its robustness.