Design and analysis of acoustic metamaterial sound insulator for noise reduction at multiple frequencies

In this paper, a design of an acoustic metamaterial sound insulator based on porous material with embedded multiple Helmholtz resonators is proposed for noise reduction at multiple frequencies. The periodic unit cell of the metamaterial is made of the porous layer with embedded four, nine, and sixteen different Helmholtz resonators that are arranged in parallel. The cavities of the resonators have the same volume while the parameters of the necks are varied. The sound absorption coefficient and the transmission loss of the metamaterial obtained using finite element method show four, nine and sixteen resonant peaks that correspond respectively to the number of Helmholtz resonators within the unit cell. When the parameters of the necks and the cavities are identical resulting in identical resonators, the transmission loss and the sound absorption coefficient show only one resonant peak. The proposed metamaterial can attenuate the noise at four, nine, and sixteen different frequencies by choosing the number of resonators that constitute the unit cell and adjusting the parameters of the necks. It can be used in many engineering applications such as aerospace for noise attenuation at multiple frequencies.