Time reversal of long coda waves: Experiments in the nonlinear regime.

A problem that arises when the time-reversal process is applied in a nonlinear regime is related to the generation of harmonics: conventional piezoelectric transducers cannot work properly at the frequency of the second harmonic. Then, the time-reversed wave cannot be completely emitted. Few works provide a solution to this issue.

Nonlinear wave propagation through multiple scattering media and virtual time reversal focusing.

In this work, the propagation of an ultrasonic nonlinear wave through a multiple scattering medium is experimentally studied. The interaction between multiple scattering and nonlinear phenomena is analyzed by the cross correlation of the scattered field. This approach corresponds to a virtual time reversal.