Tapping a non-cracked crystal glass a pure tone can be heard. If a crack is present in the glass it can clearly be heard that something is wrong. This can be carried out more sophisticated utilizing non-linear ultrasound.
Traditionally ultrasonic techniques find cracks in different objects. These often rely on that the transmitted wave is reflected from the crack. This means that the crack must be of a certain size if to be detected.
AcousticAgree AB use new sensitive methods, based on wave distortion when passing the cracked area, which is the case in the example with the crystal glass. The cracks can be small and the method works in most materials, for example steel, cast iron, rocks, titanium, rubber and sintered steel. The shape of the object is of minor importance – layered geometries or holes won’t cause problems.