Abstract: The basic principles of nonlinear acoustics and time reversal acoustics are briefly introduced and their applications in material NDT are reviewed and discussed. It is pointed out that nonlinear acoustic wave is sensitive to defects in solid media and sonic energy in solid media can be focused on any points by using time reversal acoustics. Identifying and locating defects precisely and accurately based on the defect sensitivity of nonlinear acoustic wave and self-focusing characteristics of time reversal acoustic wave has become a new trend in the research field of material NDT and will have a bright application prospect in industrial health monitoring, medical diagnosis, underwater communication and seismic analysis.

Key words: Defect identification, Nondestructive test, Non-linear acoustics, Time reversal