Multi-order resonators for acoustic multiband asymmetric absorption and reflection

We propose a multiband asymmetric acoustic absorption and reflection system constructed from a waveguide and multi-order resonators with different radiant modes. Theoretical and experimental results confirm that the coupling of the dark and bright modes at each resonant frequency enables multiband high-efficiency absorption requiring only two functional units. More interestingly, we demonstrate a hybrid multiband asymmetric system based on customized multi-mode pairs. One side of the hybrid multiband system almost completely absorbs the lower frequency incident sound waves while reflecting the higher frequency ones; conversely, the other side effectively reflects the lower frequency ones and absorbs the higher frequency ones. Our design showcases the flexibility of customized multiband asymmetric absorption and also provides an approach for the design of bidirectional wave-manipulation devices.