Time reversal of elastic waves in soft solids

When a scalar far-field wave is time reversed, it starts to converge toward its initial point source location, then collapses and finally diverges. Without evanescent waves, the symmetric focus spot is limited by the Rayleigh criterion. We present an experimental observation of a time-reversal elastic wave in a soft solid cavity using the transient elastography technique. It is observed that the time-reversed far field wave collapses and gives birth to near fieldlike effects. Elastodynamic Green's functions computation confirms the experimental conclusions: the diffraction limit implies a direction dependant Rayleigh criterion.