Enhancing low-frequency transmission loss in aircraft fuselage sidewalls with a flat array of covered Helmholtz resonators metamaterial

This paper explores the use of a flat array of covered Helmholtz resonators (CHRs) as a metamaterial for enhancing the acoustic transmission loss (TL) of aircraft fuselage sidewall. The benefits of CHRs are twofold: (i) decreasing the Helmholtz resonance frequency, thereby targeting lower frequencies, and (ii) providing precise control over the resonant frequency of the metamaterial when integrated into a fuselage sidewall. In this paper, we first examine the vibroacoustic behavior of a single CHR, observing a significant decrease in resonant frequency as the covering plate approaches the neck entrance. Subsequently, we evaluate arrays of CHRs, with different filling factors, and their impact on the TL of an aircraft fuselage sidewall. Placing the CHRs metamaterial in the dead space between stringers improves the TL by up to 10 dB at the panel's ring frequency, demonstrating their potential for low-frequency noise reduction in aircraft.