Experimental validation of acoustic metamaterials noise attenuation performance for aircraft cabin applications

Over the past few decades, various low frequency noise control technology concepts incorporating acoustic metamaterials have been proposed in the literature. The proposed technologies showed promising performance, with a significant noise attenuation rate per thickness unit and are considered as an improved solution when compared to conventional sound insulation materials. Previously presented approaches with layered porous materials and embedded Helmholtz resonators (HR) exhibited considerable potential when tuned at tonal, multi-tonal or narrow frequency bands. In the present study, two noise control solutions were investigated numerically and their noise control performance was validated experimentally in single and double wall configurations when attached to a stiffened curved panel under diffuse field excitation in a sound transmission loss (STL) facility. The first solution comprised glass wool layers and a high flow resistivity micro-perforated screen for broad band noise attenuation. The second solution comprised glass wool layers with embedded HR designed to attenuate the effect of the ring frequency of the curved fuselage panel under diffuse field excitation. The paper discusses the main mechanisms involved in the STL performance of the two noise control solutions in single and double wall configurations.