Non‐Contact Inspection of Composites Using Air‐Coupled Ultrasound

Conventional ultrasonic tests are conducted using water as a transmitting medium. Water coupled ultrasound cannot be applied to certain water‐sensitive or porous materials and is more difficult to use in the field. In contrast, air‐coupled ultrasound is non‐contact and has clear advantages over water‐coupled testing. The technology of air‐coupled ultrasound has gained maturity in recent years. Some systems have become commercially available and researchers are pursuing several different modalities of air‐coupled transduction. This paper reports our experience of applying air‐coupled ultrasound to the inspection of flaws, damage, and normal internal structures of composite parts. Through‐transmission C‐scans at 400 kHz using a focused receiver has resolution sufficient to image honeycomb cells in the sandwich core. With the transmitter and receiver on the same side of a laminate. Lamb waves were generated and used for the imaging of substructures. Air‐coupled scan results are presented for flaw detection a...