Research On Design Of Two-Dmensional Airborne Acoustic Topology Materials And Characteristics Of Their Edge State

Acoustic topological materials have become a research hotspot in the field of acoustics due to their wide range of potential applications in acoustic noise reduction,one-way acoustic transmission and acoustic communication.Based on k·p perturbation theory and finite element numerical simulation,this paper systematically studies the properties of acoustic topological materials and their associated field distributions,and experimentally verifies the robustness of acoustic topological materials.The main research contents and innovations are as follows:1.An acoustic topological insulator consisting of a honeycomb lattice sonic crystal based on direct or indirect band gap is proposed.It is found that band inversion and topological phase transition can be achieved by simply rotating the equilateral triangle scatterers in the sonic crystal.When the rotation angle is greater than 32.18°,the sonic crystal is converted from a direct band gap to an indirect band gap.Based on honeycomb lattice sonic crystals composed of equilateral triangular scatterers with rotation angles of 0°,30°and 60°respectively,two types of topological insulators are designed and implemented,including topological non-trivial sonic crystals with direct band gap（30°）and indirect band gap（60°）.The experimental results show that there are also pseudospin-dependent edge modes in the acoustic topological insulator based on the topological non-trivial sonic crystals with indirect band gap.These edge modes are almost immune to three different types of defects and are hardly affected by backscattering.2.A triangular sonic crystal based on gear-like scatterer is proposed,and an acoustic topological insulator with pseudospin-dependent edge mode is designed.The results show that the triangular lattice phononic crystal can realize the four-fold accidental degenerate Dirac point and the topological phase transition.On this basis,acoustic topological waveguides composed of two different sonic crystals with different topological phases are designed to realize pseudospin-dependent one-way acoustic transmission.The experimental results show that the one-way acoustic transmission in the topological waveguide is robust to lattice disorder and bend defects.3.A honeycomb sonic crystal based on gear-like scatterer is proposed,and an acoustic topological insulator with two working bands is designed.By adjusting the structural parameters of the gear-like scatterers in sonic crystals,the accidental degeneracy of double Dirac points can be realized at two different frequency bands simultaneously.On this basis,acoustic topological waveguides based on two honeycomb sonic crystals with different topological phases are designed.The robustness of pseudospin-dependent one-way acoustic transmission in acoustic topological waveguides is verified by experiments.4.A triangular sonic crystal(C_3v lattice symmetry)based on snowflake scatterers is proposed.An acoustic topological waveguide with two working bands is designed and implemented.The results show that when the rotation angle of the snowflake scatterer isθ=nπ/3（n is an integer）,at two different frequencies,the dispersion relationship of sonic crystals at K（K’）point form deterministic degenerate Dirac cones I and II.By rotating the scatterers clockwise and counterclockwise,the band inversion can be realized simultaneously around the two Dirac cones.Based on the sonic crystals composed of snowflake scatterers with rotational angles of-5°and+5°,the acoustic topological valley transport in two different working bands is systematically studied.The experimental results show that the edge modes of the acoustic topological waveguides support the acoustic topological valley transport in two different working bands.5.The triangular sonic crystals（C₃ lattice symmetry）based on windmill scatterers are proposed to design the acoustic topological waveguide structure.The results show that the Dirac point at K（K’）point of the band structure is no longer deterministic degenerate,but it can still be accidentally achieved by rotating windmill scatterers.When the rotation angle gradually changes from-60°to 60°,two valley Hall phase transitions occur in the low frequency region,while six valley Hall phase transitions occur in the high frequency region.In addition,acoustic topological valley transport is realized based on the acoustic topological waveguide composed of left-handed and right-handed windmill scatterers.The robustness of edge mode in acoustic topological valley transport in low frequency region is verified by experiments.