A football-like acoustic metamaterial with near-zero refractive index and broadband ventilated sound insulation

Acoustic metamaterial with negative or near-zero refractive index exhibits extraordinary acoustic transmission characteristics, including acoustic total reflection, acoustic stealth and acoustic tunneling. Based on the coiled-up space structure, a football like near-zero refractive index acoustic metamaterial (FNZIM) was proposed. The result reveals the formation of two transmission peaks at 1270 Hz and 2300 Hz from the equivalent parameters by using the transfer matrix method. The first peak exhibits excellent air impedance matching, while the second peak arising from the metamaterial's near-zero refractive index. We then constructed an acoustic prism using 15 cells of FNZIM and calculated the dispersion curve, revealing that the near-zero refractive index supernormal transmission of metamaterials is attributable to multimode degeneracy. Furthermore, we find that the positions of the transmission peaks and transmission loss can be adjusted by appropriately altering the structural parameters. Finally, we tested two groups of samples by using impedance tube four-channel to verify the accuracy of the simulation and the validity of insulation performance of FNZIM. The broadband ventilation sound insulation coupled structure is constructed, and the average sound insulation performance of this structure is more than 25 dB in the range of 1140-2210 Hz.