Ultrasonic testing is routinely employed for verification of the integrity of structural engineering components where it is used to detect the presence of defects within the volume of a structure. Ultrasound is a favoured technique in such non-destructive testing (with widely recognised and adopted standards) due to its ease of application, inherent low risks and lack of damage to the structure under test.

With increased pressures for sustainable aviation to meet 2050 net zero targets, and demand for civil aircraft production being at an all time high, there is an increasing interest in lightweight primary structures for commercial aviation. For example, Boeing’s 787 and Airbus A350 aircraft are 50% by weight manufactured from Carbon Fibre Reinforced Plastic (CFRP). This material brings challenges for ultrasonic inspection due to its inherent anisotropy, acoustic attenuation and scattering from multiple layers of carbon fibres. A further limitation is that conventional ultrasonic testing typically requires liquid couplant (usually water) to transfer acoustic energy into the structures being tested; this requirement can limit application in some CFRP structures that are not compatible with water (immersion or spray).

Recent advances in ultrasonic materials technology and signal processing have allowed new approaches in dry coupled ultrasound to be trialled whereby no liquid couplant is required. These advances open the way to new dry-coupled ultrasonic inspection for the next generation of advanced CFRP aerospace materials.