Engineers at Bristol University in the UK say they have developed new ultrasonic technology that can show hidden cracks in the wings of planes or bridges, which would previously have gone undetected.

This could mean increased safety as it provides an important tool for inspectors to replace materials before they get overused.

The way it works is that the system locates so-called acoustic nonlinearities, in other words places where multiple sound waves don’t add up as one might expect, which often reveal sites of cracks or extreme fatigue.

Anthony Croxford and his team use a technique called nonlinear ultrasonics to look inside the materials. Hundreds of sound signals are sent through the material, giving a picture of what is inside – and where even the tiniest cracks could be located.

“The way this works is that your energy essentially shakes that crack, it rattles it on the way in, and that leads to harmonics, so you put in one frequency and you get out other frequencies.