They are a couple of high sensitivity spherically focused air-coupled transducers, centre frequency 250 kHz, focal distance 65 mm, 6 dB focal spot of 4.5 mm and peak sensitivity of -22 dB, specially designed for the inspection of sandwich structural elements (CFRP / aluminum honeycomb /CFRP) used in the aeronautical industry. More details in transducers and NDT sections
Example of inspection of a sandwich panel mede of CFRP skin (with variable thickness) and a honeycomb core. Total thickness 40 mm. The honeycomb structure as well as several defects are clearly seen.