Subwavelength Reconfigurable 3d Printed Acoustic Metamaterial

Abstract

In this study, we propose a new reconfigurable hexagonal Helmholtz resonator with a slit in each side. Numerical and experimental investigation of a single unit cell and the whole acoustic metamaterial chamber highlights the reliability and feasibility of the proposed metastructure. Highly efficient sound insertion loss can be captured with a simple and easily accessed resonator. By carefully designing rotation support in each unit cell and manufacturing a 3D printed base with periodic holes, the assembled resonators can be easily rotated, and the finite acoustic metamaterial chamber can be tuned to another configuration without the need of reprinting and redesigning the whole structure. The mechanisms of the system are systematically explained by numerical band structure, insertion loss and the corresponding experimental measurements. Specifically, the flat bands in the band structure reveal the weak coupling between the neighbouring resonators, and the highly trapped acoustic energy indicates that the bandgap originates from the local resonance mechanism. Thus, even one single unit in the system can efficiently attenuate the noise at subwavelength scale, and the effects become better when the number of resonators increases. These phenomena can also be explained by the sound pressure map in the waveguide analysis and the characteristics of the insertion loss. Interestingly, by changing the configuration of the full chamber, the device can keep the insertion loss at a high level, while exhibiting a better ventilation ability. Therefore, with the high degree of freedom of tuning, it is possible to actively control the whole system to simultaneously achieve efficient noise cancelling and free airflow. The reconfigurable, scalable, feasible and controllable system can be easily applied to several practical scenarios like the silent zone in the city center, the ventilated noise isolate device for the machines, and optically transparent ventilation sound-insulating structures.

Keywords: acoustic metamaterial, reconfigurability, Sound absorption, numerical computation, insertion loss measurement