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A bubble metascreen is an exceptionally effective and low frequency resonator which can be optimized in order to exactly balance the energy provided by radiative process and lost under a viscous mechanism (critical coupling). Under this condition, one can absorb 99.9% of the energy carried by two phase-matched counter-propagating acoustic beams. This phenomenon, called coherent perfect absorption, is here observed with bubbles 75 times smaller than the incident wavelength and is shown to be remarkably broadband. Finally, tuning the relative phases of the two beams turns out to be an efficient way to control the absorption in the medium.
Lanoy et al. (Mon,) studied this question.