Depth profile of a time-reversal focus in an elastic solid

• Out-of-plane motion is focused on the surface of an elastic solid with time reversal.
• The wave propagation in the bulk of the sample is studied with FEM.
• Experimental data is used to validate the FE model.
• The depth profile of the time reversal focus is characterized quantitatively.
• The size of the focus is linked to Lamb’s problem and the diffraction limit.

The out-of-plane velocity component is focused on the flat surface of an isotropic solid sample using the principle of time reversal. This experiment is often reproduced in the context of nondestructive testing for imaging features near the surface of the sample. However, it is not clear how deep the focus extends into the bulk of the sample and what its profile is. In this paper, this question is answered using both numerical simulations and experimental data. The profiles of the foci are expressed in terms of the wavelengths of the dominant waves, based on the interpretation of the Lamb’s problem and the use of the diffraction limit.