Hybrid resonance and the total absorption of low frequency acoustic waves

By creating two or more resonances on a structured thin membrane, it can be shown that a reflecting surface placed close by can cause the two neighboring resonances to hybridize at a frequency intermediate between the two. As the hybrid resonance's wave amplitude profile is necessarily the linear superposition of the two original resonant eigenfunctions, the two degrees of freedom can mean that the surface-averaged hybrid resonance amplitude, and its variance, may be separately tunable. It is shown that whereas the average amplitude can serve to match impedance with air, the variance component is “deaf” and serves to absorb the incoming wave energy. The result is a deeply subwavelength structure that can totally absorb the incident wave at tunable frequencies.