Broadband sound reduction in space-coiling ventilation structures with microperforated shells

Ventilation structures supported by the Fano-like interference can act as high-performance sound silencers, yet the bandwidth gets limited eventually by coexisting resonant transmission. In this work, we focus on the space-coiling ventilation structure, and overcome the limitation by introducing a cylindrical shell made of microperforated panels (MPPs) in between the channel and ventilation pipe. The underlying mechanism is due to the resonance-induced field intensity enhancement within coiling channels, which can produce a significant pressure difference on both sides of the MPP to damp resonant acoustic transmission. Based on this behavior, broadband sound reduction with the bandwidth exceeding an octave can be achieved when two such structural elements are cascaded. Enhanced acoustic damping by MPPs and broadband sound reduction in bi-cell structures are numerically analyzed and validated experimentally.