Perfect absorption is an interdisciplinary topic with a large number of applications, the challenge of which consists of broadening its inherently narrow frequency-band performance. We experimentally and analytically report perfect and broadband absorption for audible sound, by the mechanism of critical coupling, with a sub-wavelength multi-resonant scatterer (SMRS) made of a plate-resonator/closed waveguide structure. In order to introduce the role of the key parameters, we first present the case of a single resonant scatterer (SRS) made of a Helmholtz resonator/closed waveguide structure. In both cases the controlled balance between the energy leakage of the several resonances and the inherent losses of the system leads to perfect absorption peaks. In the case of the SMRS we show that systems with large inherent losses can be critically coupled using resonances with large leakage. In particular, we show that in the SMRS system, with a thickness of λ/12 and diameter of λ/7, several perfect absorption peaks overlap to produce absorption bigger than 93% for frequencies that extend over a factor of 2 in audible frequencies. The reported concepts and methodology provide guidelines for the design of broadband perfect absorbers which could contribute to solve the major issue of noise reduction.

We experimentally report perfect acoustic absorption through the interplay of the inherent losses and transparent modes with high Q factor. These modes are generated in a two-port, one-dimensional waveguide which is side-loaded by isolated resonators of moderate Q factor. In symmetric structures, we show that in the presence of small inherent losses, these modes lead to coherent perfect absorption associated with one-sided absorption slightly larger than 0.5. In asymmetric structures, near perfect one-sided absorption is possible (96 %) with a deep sub-wavelength sample (λ/28). The control of strong absorption by the proper tuning of few resonators with weak losses will open new possibilities in various wave-control devices. PACS numbers: 43.20.Mv, 43.20.Hq,43.20.Fn 1 arXiv:1509.01443v1 [physics.class-ph] 4 Sep 2015One of the most inspiring outcomes in the field of atom optics is the electromagneticallyinduced-transparency (EIT) which results from the coherent interferences between different excitation pathways of the excited states [1]. In the recent years, and after the theoretical revealing of the similarities between atoms driven by optical fields and resonators excited by incident waves, there has been an increasing interest in the implementations of classical analogues of EIT-like spectra. Thus, EIT-like behaviors have been theoretically studied and experimentally observed in plasmonic, photonic and acoustic resonator systems (see [2][3][4][5][6][7][8][9] and references therein). In the lossless case, these open system configurations show