A novel gradient multi-Helmholtz cavities muffler for low-frequency broad band gaps

Abstract

Abstract With the development of local resonance theory, more and more researchers use Helmholtz cavity structures to reduce low-frequency noise. However, the absorption frequency is very narrow in the traditional structure. It is very inflexible in practical applications. To address this challenge, we first proposed a gradient multi-Helmholtz cavities muffler for low-frequency broad band gaps. By simplifying the structure into a neck-cavity model, we derived the resonance frequency of a single Helmholtz cavity. Next, we use COMSOL software to calculate the transmission loss (TL). The results of our analysis confirmed that the structure can reduce noise in its resonance frequency, and the range of absorption frequency is enlarged with the number of the cavities increases, almost 24.75 times that of one cavity. The transmission loss around the center frequency also increases from 45dB to near 100dB. In addition, the relationship between noise attenuation characteristics and the distance of the cavities is also studied. Results show that a deeper valley appears in the transmission loss curve with the increase of the distance, which greatly affects the sound absorption performance. The gradient multi-Helmholtz cavities designed in our paper enlarges the range of absorption frequency and improve the ability of noise reduction. Our findings can be widely applied to guide the design and optimization of metamaterial mufflers.