A thin multi-order Helmholtz metamaterial with perfect broadband acoustic absorption

We propose a multi-order Helmholtz metamaterial with deep-subwavelength thickness in which perfect continuous acoustic absorption is achieved within 400 Hz similar to 2800 Hz. The metamaterial is composed of multiple detuned cells, each of which is constructed by several perforated plates inserting into the cavity of a Helmholtz resonator (HR) and hence gains multiple individually-tuned high-order peaks besides the original HR peak. By precisely designing each peak of the cells, the extra-broadband perfect absorption can be obtained. This kind of metamaterials could possess broad applications in noise control engineering owing to the extraordinary absorption performance and high flexural stiffness. (C) 2019 The Japan Society of Applied Physics