Design of low-frequency and broadband acoustic metamaterials with I-shaped antichiral units

Controlling the propagation of low-frequency sound waves on the sub-wavelength scale is still a challenging problem. For the design of low frequency sound reduction materials, this paper introduces the I-shaped antichiral unit to the acoustic metamaterials with Mie resonance, which can manipulate the sub-wavelength acoustic waves and achieve effective low-frequency and broadband sound isolation. By adjusting the width of the ligament, the proportion of the omnidirectional bandgap is 65.6 % in the subwavelength range. Firstly, the designed acoustic metamaterials are constructed by rotating the I-shaped units with mutually orthogonal periodic distribution. The parametric geometric model of metamaterials is established, and the low-frequency and wide bandgap can be effectively realized by adjusting the ligament width. Then, the investigation of sound pressure and phase reveals that the bandgaps attribute to the Mie resonant mode. Furthermore, based on the transfer matrix method, the effective bulk modulus and effective mass density of acoustic metamaterials are derived. The results show that the frequency range of the negative effective parameters obtained is consistent with that of the band gap. Finally, experimental tests are carried out, the region where attenuation occurs is in good agreement with the bandgap range (1158–2500 Hz) predicted by eigenfrequency analysis. The experimental tests verify the effectiveness of the designed antichiral acoustic metamaterials for low frequency sound reduction. The introduction of the antichiral unit provides a broad space for the application of acoustic metamaterials in low-frequency sound reduction. The low-frequency and broadband can be effectively realized by adjusting the ligament width. The low-frequency can be effectively realized by adjusting the ligament width. The experimental tests verify the effectiveness of the designed antichiral unit.