Assessment of Laser-Generated Ultrasonic Total Focusing Method for Battery Cell Foil Weld Inspection

The feasibility of using laser-generated ultrasonic Total Focusing Method (TFM) was assessed for guided ultrasonic waves in finite plates. The application under consideration is for inspection of ultrasonically welded battery tab-to-electrode foil stack joints. The testing constraints for this weld necessitate couplant-free, remote, guided-wave conditions making laser ultrasonic TFM an ideal inspection technique. It was determined that laser-generated guided wave TFM can be used to remotely assess defects in a finite plate when the defects are strong reflectors in the plane of wave propagation. The finite dimensions of the tab require a strong understanding of the edge reflection effects on the TFM image. The guided wave modes used in this study were strongly affected by scattering due to the complex weld geometry, which most resembles that of a periodic triangular grated wave guide. Future work will investigate methods to compensate for the strong scattering/guided wave effects, the use of other guided wave geometries, out of plane TFM reconstruction for other weld defect types, as well as apodization effects.