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 ∼ 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.