Abstract: Air-coupled ultrasonic non-destructive testing, possessing the characters of complete non-contact and non-destruction, can be used in some situations in which traditional ultrasonic testing is hardly applicable. The development of air-coupled ultrasonic non-destructive testing is summarized, and the main technical difficulties that restrict its progress are analyzed. Two methods to improve the efficiency of air-coupled ultrasonic transducers and corresponding research works are presented. Main detecting methods and corresponding application fields of air-coupled ultrasonic testing are introduced. It is concluded that air-coupled ultrasonic testing technique will be applied more widely in the future, however, the high efficiency transducer is a prerequisite for the successful application of the technology, and is also a focus of present research in this technical field.

Key words: Air-coupled, Non-destructive testing, Ultrasonic