Overview of concept designs and results of the New Acoustic Insulation Meta-Material for Aerospace (NAIMMTA) project

Reducing aircraft cabin noise to improve the comfort of passengers is an important and challenging issue in aeronautics. Relatively uncomfortable high noise levels of around 80 to 90 dBA with strong low frequency range components (below 500 Hz) and a tonal character, predominantly related to the engine fan during take-off and approach, are deemed critical. The conventional acoustic materials seem to have reached their physical limits in terms of sound proofing, and therefore non-conventional solutions, such as metamaterials, are sought for their promising performance such as, a significant noise attenuation rate (dB/m), and the capability to be tuned at tonal or narrow band frequencies. An international collaborative project was created to develop novel technologies aiming at improving the existing noise control systems by obtaining an additional 5 dB noise reduction in the low frequency range (100 to 400 Hz) without deteriorating the thermal insulation. Moreover, the proposed solutions were expected to be tunable with respect to tonal noise (bandwidth of 5 Hz) or narrowband noise (bandwidth of 40 Hz). A major design and integration constraint imposed that the metamaterial had to be embedded in the current existing insulation blanket and add a maximum of 20% additional mass in comparison to the conventional insulation. This paper presents an overview of the various solutions developed from numerical simulations and novel manufacturing procedures development and optimization to performance characterization and validations.