Acoustic time-reversal through high-order multiple scattering

The application of time-reversal mirrors (TRM) to media with very high-order multiple scattering is presented. Random sets of up to 2000 steel rods are considered. When a pulsed wave (typically a 1 μs pulse) traverses such a medium, it undergoes many scatterings before reaching,the TRM. The resulting pressure field spreads in time, up to 300 times the initial pulse duration; it is recorded, time-reversed and retransmitted through the same disordered medium. Surprisingly, the time-reversed waves are found to converge to their source and recover their original waveform and duration, unlike one could have expected given the high order of multiple scattering involved and the usual sensitivity to initial conditions of time-reversal processes. In addition to this, the observed resolution of the time-reversed waves was greatly increased, and found to be one sixth of the theoretical limit for the array´s aperture