Time recompression of dispersive Lamb waves using a time reversal mirror-application to flaw detection in thin plates

In this paper, the time reversal processing is applied to compensate for the effect of dispersive Lamb waves. A time reversal mirror, made of a 32 element transducer array is coupled to a Duralumin plate with a Plexiglas wedge. In the first experiment, a Nd-YAG laser is used to create a point source of Lamb waves. The transmitted pulse is then recorded and time-reversed by the array and both time recompression and spatial refocusing are observed at the source point. In the second part of this paper, flaw detection in plate is performed with a pulse echo time reversal technique and we show the effectiveness of this technique to enhance the signal to noise ratio.