Ultralow-frequency tunable acoustic metamaterials through tuning gauge pressure and gas temperature

Abstract Acoustic metamaterials possessing subwavelength characteristics can be used for low-frequency noise and vibration control. Acoustic metamaterials with adjustable dynamic properties can further enhance their possible applications. This paper designs a kind of tunable acoustic metamaterials consisting of the frame structure, airbag, and balancing weight. And their dynamic characteristics can be manipulated by tuning gauge pressure and gas temperature in the airbag. The calculation results indicate that the tunable acoustic metamaterials can effectively suppress the wave propagation and vibration in the ultralow-frequency band gap (about 13Hz ∼ 90Hz) during manipulation. The complete band gap is the overlapping frequency range of an out-of- and in-plane band gaps. Numerical analyses indicate that the formation of out-of-plane band gap is due to the coupling between the out-of-plane resonant mode of balancing weight and the anti-symmetric Lamb mode of the frame structure. In contrast, the formation of an in-plane band gap is due to the coupling between the in-plane resonant mode of balancing weight and the symmetric Lamb mode of the frame structure. Meanwhile, the manipulation mechanism of these band gaps stems from the fact that through tuning gauge pressure or gas temperature, the structural stiffness of the airbag (torsional stiffness, in-plane, and out-of-plane stiffness) and frame structure (in-plane and bending stiffness) can be significantly tuned so that the modes related to them can be manipulated. The tunable acoustic metamaterials can be used for active control of low-frequency vibration and noise. It is possible to provide guidelines for designing other acoustic metamaterials to suppress low-frequency vibration and noise.