Fig. 6: Ultra-open meta-barriers based on Helmholtz resonance.
From: Resonance-based acoustic ventilated metamaterials for sound insulation
a The ultra-open and omnidirectional meta-barrier and the unit, as well as the transmission coefficient for incident angle of 0°. Reproduced with permission from ref. 121. b The reconfigurable ultra-open meta-barrier and the absorption coefficient for the blades angle β = 10°. Reproduced with permission from ref. 60. c The unit cell consists of two symmetrical split-tube resonators, and the absorption coefficient spectra for the ultra-open meta-barrier. Reproduced with permission from ref. 118.
