Multiple selective absorption peaks of acoustic waves in a one-dimensional composite

We investigate a one-dimensional composite with a very low loss coefficient and find that multiple selective absorption peaks reach close to 100% absorption of incident acoustic waves when the acoustic waves propagate through this system. Especially, the unidirectional absorption is demonstrated when the propagation direction of acoustic waves is reversed. These high absorptions stem from the excitations of the strong resonances, which depend on not only the low loss in this composite but also the huge impedance mismatch at the outgoing interface. To further investigate those selective absorption, we construct an equivalent structural model, and our calculations show that these absorption peaks have the extraordinary response to the imaginary part of the effective mass density and bulk modulus. The results exhibit that the imaginary part of the effective mass density and bulk modulus at the frequencies of the absorption peaks abruptly appear, in the meanwhile the real part of those become zero. Based on these theoretical results, an unidirectional absorption device with multiple selection of frequencies can be designed. (c) 2019 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).