Preparatory Notes for ASNT NDT Level III Examination - Ultrasonic Testing, UT

It is often desirable to eliminate the need for the water coupling and a number
of state-of-the-art UT scanning systems have done this. Laser ultrasonic
systems use laser beams to generate the ultrasound and collect the resulting
signals in an noncontact mode. Advances in transducer technology has lead
to the development of an inspection technique known as air-coupled
ultrasonic inspection. These systems are capable of sending ultrasonic
energy through air and getting enough energy into the part to have a useable
signal. These system typically use a through-transmission technique since
reflected energy from discontinuities are too weak to detect.