Sound Transmission Performance of Plate-Type Acoustic Metamaterials for Quieter Aircraft Cabins

Abstract

Acoustic Metamaterials (AMMs) are man-made materials that consist of a regular pattern of sub-wavelength microstructures, referred to as ‘unit cells’ and are intended to control sound waves in a way that is distinct from that of traditional acoustic materials. The current research work primarily focuses on using plate-type acoustic metamaterials to attenuate the aircraft cabin noise, in order to provide a comfortable (quieter) atmosphere within the aircraft cabin for the passengers during their flight. Estimation of Sound Pressure Levels (SPL) are carried out in two stages; the first stage is performed at the coupon level, where the best design is chosen out of eight unit cell designs for the experiments, based on the structural design optimization at the coupon level; followed by finite element based vibroacoustic analysis is performed on the fuselage structure using the selected unit cell. The performances of the developed acoustic metamaterials in terms of Sound Transmission Loss (STL) are investigated experimentally using an impedance tube, and the use of 3D printed casing inside the impedance tube for holding the AMM specimen with airgap, is first of its kind. The study shows, for a constant thickness (t = 0.5 mm) of designed AMM, at various frequencies, the reductions of SPL is observed in the range of 15.3 dBA to 73.9 dBA. Considering the numerical analysis and experimental studies finding, it is observed that the implementation of this developed acoustic metamaterials into a aircraft fuselage construction has effectively reduced noise levels in the aircraft cabin.