Focusing aspects of delayed Time Reversal based Nonlinear Elastic Wave Spectroscopy methods

The focusing of ultrasound in the Non Destructive Testing of complex materials needs to be improved. Despite the considerable interest attracted by the Nonlinear Elastic Waves Spectroscopy (NEWS) and nonlinear Time Reversal (TR) techniques and the resulting advances in recent years, several aspects related to the use of modern signal processing tools remain to be addressed. We present here the concept of delayed TR-NEWS method aim at improving the focusing properties both in the spatial and the time domains. The concept uses the superposition principle which could be broken in the case of activation of nonclassical nonlinear effects coming from the aging of the complex medium.