Ultrasonic wave transport in resonant emulsions made of slow and fast droplets

International audienceThe key transport parameters of acoustic waves travelling in disordered media are studied through ultrasonic experiments on monodisperse resonant emulsions. Through accurate measurements of both ballistic and diffusive transport over a wide range of frequencies, we show that the group velocity of the ballistic component may differ significantly from the energy velocity of the diffusive waves, in particular in the vicinity of scattering resonances. Moreover, we evidence the crucial role played by the refractive acoustic index of the droplets relative to the surrounding media by studying emulsions made of ?slow" fluorinated oil droplets or ?fast" liquid metallic droplets dispersed in a water-based gel. Our observations are successfully confronted to theories based on independent scattering approximations relevant for these diluted media. Effects of droplets resonances in the diffusive regime are also discussed giving a complete study of the energy velocity of scalar waves in strongly scattering media. B. Tallon, T. Brunet, and J.H. Page, Physical Review Letters 119, 164301 (2017