Exotic absorption peaks of acoustic waves in one-dimensional layered phononic crystal

In this article, we demonstrate the existence of exotic absorption peaks when acoustic wave propagates through a one-dimensional layered phononic crystal (PC) at frequencies within the band gap into a material of large acoustic impedance mismatch. By analyzing the displacement field distribution, it indicates that the absorption peaks are due to the excitation of the resonant interface states at boundary between the last layer of the PC and emergent material. The number of period and the thickness of last layer of the PC play the decisive role in determining the magnitude and frequency of absorption peaks. And the absorptivity can be nearly unity with a reasonable design of the structure. Specifically, these absorption peaks would almost disappear when the incident direction of acoustic waves is reversed. This property can be employed to design an acoustic wave unidirectional absorption device.