Reconfigurable labyrinth structures as low frequency sound absorbers

Abstract

In this work, we designed a metamaterial labyrinth structure as sound absorber for low frequency. The labyrinth structure is made by stacking disks with holes or openings at its front and back surfaces, and these openings are linked by air channels within the disks. Five disks with different opening locations were designed and fabricated using 3D printing. The disks were stacked and rotated with respect to each other, connecting different inlets and outlets, to form various patterns of labyrinth. Using a two-microphone impedance tube, the absorption coefficient of these stacks, ranging from one to five disks, was measured. The results show that a stacked structure with more disks enhances the absorption at low frequencies. As each disk was designed with twelve possible rotational positions, a stack of three disks will give more than 8000 combinations. It is not practical to conduct experiments to measure the absorption coefficient of all possible combinations. Hence, a neural network was used to fit and predict the absorption. Using the fitted neural network model, we would be able to predict the combinations to give best absorption and target frequency band. [Work supported by Singapore MOE Tier 1 Grant A-0009119-00-00.]