Surface and sub-surface flaws detection using Rayleigh wave time reversal mirrors

The time reversal process is used to detect surface and sub-surface flaws and leads to a self focusing process of Rayleigh waves. The surface waves are generated with an array of linear transducers coupled to a specimen surface with a Plexiglas wedge. The advantages of such a technique are demonstrated with the detection of surface and sub-surface holes of subwavelength dimensions. In a pulse-echo measurement, the signal to noise ratio is exponentially increased when the self focusing repetitive process is used Measurements are calibrated with an optical interferometer and results are compared with a surface focusing model to point out the sensitivity of such a detection method