Broadband Modulation Of Topological Interface States And Multiple Single-frequency Selective Absorption Peaks In One-dimensional Acoustic System

In recent years,by promoting the concepts of electronics and photonics,ancient acoustics revives again.In particular,the explorations and application of acoustic topological materials have become a hot field.The broadband modulation of the topological interface state in one-dimensional acoustic system is investigated in this thesis.The multiple single-frequency selective absorption peaks of sound waves in one-dimensional composites is also studied.Firstly,the acoustic analogy of topological insulator,the Su-Schrieffer-Heeger(SSH)model in one-dimensional acoustic systems,provides topological non-trivial phases.A “supermolecule” composed of two identical hollow cylinders with a side split is placed in a air matrix.The “supermolecules” is arranged in a line to form a SSH model,which has three band gaps including two(Brillouin)zone-folding-induced gaps and a local resonant gap in the subwavelength region.By analysing the eigenstates and Zak phases,we find that a topological phase transition takes place only in the zone-folding-induced gaps as the split-cylinders are rotated.Thus,a finite-size array,made of two sublattices with distinct topological properties,inevitably produces the topological interface states on an interface between two sublattices.Besides,we demonstrate that the topological interface states can be adjusted in a wide frequency range by rotating the cylinders that control the coupling strength between two split-cylinders in one supercell.These tunable topological interface states may have potential application prospects in wave filtering,wave detecting and so on.Secondly,we also study the multiple single-frequency selective absorption peaks of sound waves in one-dimensional composites.The composite with a very low loss coefficient shows that the multiple selective absorption peaks reach close to 100%absorption of incident acoustic waves when acoustic waves propagate through this system.Especially,the unidirectional absorption is demonstrated when the propagation direction of acoustic waves is reversed.These high absorptions stem from the excitations of the strong resonances,which depend on not only the low loss in this composite but also the huge impedance mismatch at the outgoing interface.Based onthese theoretical results,an unidirectional absorption device with multiple selection of single-frequency can be designed.