Résumé:
We present time-reversal focusing experiments in an open multiple scattering medium undergoing a temperature change. Multiply scattered waves are recorded once to define a reference, then time-reversed and continuously backpropagated into the medium while the temperature decreases slowly. The temporal shift of the time-reversed peak enables to retrieve changes in temperature as small as 0.02° C, while the peak amplitude decays with temperature in a manner which is well predicted by a simple “shot noise” model. We also show that the sensitivity to a change of temperature increases with the scattering order (i.e. time), which cannot be accounted for by the shot-noise model, and is probably due to the elastic resonances of the scatterers, which result in a time-dependent phase variance in the scattered signals.

Mots-clés: time-reversal multiple scattering temperature DWS