Subwavelength focusing in bubbly media using broadband time reversal

Abstract

Thanks to a multiple-scattering theory algorithm, we present a way to focus energy at the deep subwavelength scale, from the far field, inside a cubic disordered bubble cloud by using broadband time reversal (TR). We show that the analytical calculation of an effective wavenumber performing the independant scattering approximation (ISA) matches the numerical results for the focal extension. Subwavelength focusings of $\ensuremath{\lambda}/100$ are reported for simulations with perfect bubbles (no loss). A more realistic case, with viscous and thermal losses, allows us to obtain a $\ensuremath{\lambda}/14$ focal spot, with a low volume fraction of scatterers $(\mathrm{\ensuremath{\Phi}}={10}^{\ensuremath{-}2})$. Bubbly materials could open a new perspective for acoustic actuation in the microfluidic context.