Study On Acoustic Metamaterials And One-dimensional Topological Acoustics

Acoustic metamaterials are a kind of artificial structures which possess some acoustic properties that are difficult to be realized by natural materials.In the early study of acoustic metamaterials,researchers realized zero negative refraction of sound waves by constructing acoustic metamaterials with effective mass and negative effective modulus.Subsequently,in the study of the construction of effective mass and negative effective modulus,acoustic stealth,acoustic ultra-transmission,acoustic ultra-absorption and other acoustic structures are gradually realized and closely combined with the practical application.Using these special properties of acoustic metamaterials can solve some difficult problems in medicine and industry,such as the processing of low-frequency noise and the interference of human bones on ultrasonic propagation.Therefore,the research and manufacture of new acoustic metamaterials have important academic value and industrial application prospect.At the same time,with the development of the theory of phononic crystals,researchers can realize the regulation of energy band structure in phononic crystals,so that many physical phenomena in photonic crystals can be realized in phononic crystals,which further expands the research field of acoustics.In recent years,with the development of electronic band theory and topology in the field of electromagnetic waves and photonic crystals,and because phononic crystals have waveguide and band properties similar to photonic crystals,the research scope of topology has also been extended to the field of acoustics,and topological acoustics has become a hot topic in the current acoustic research.This paper mainly introduces the research of low-frequency acoustic absorbing metamaterials and topological acoustics.In acoustic absorption,because the absorption of sound waves with the same amplitude is proportional to the square of the sound frequency,the high-frequency noise with long wave length is easy to be absorbed,while the noise with low frequency is not only difficult to be absorbed,but also has a low attenuation rate with distance.In order to solve the problem of low-frequency sound absorption,we designed a split-tube absorber for sub-wavelength size low-frequency sound waves(below 500Hz)based on the sound absorption principle of Helmholtz resonator.The absorber is composed of an oval tube with two openings inside and outside.By adjusting the geometric parameters of the absorber,it can change the frequency of absorbing sound waves,and still maintain the efficient absorption of corresponding frequency sound waves when changing the shape(the absorption rate is more than 90%).At the same time,we also study the effect of the obliquity Angle on the absorptivity when the sound wave is obliquely incident.Through the simulation calculation,we find that the sound absorption effect of the sound absorber is very good even at a large Angle in the case of oblique incidence.The absorber has the characteristics of simple structure and high stability,so it has potential application prospect in acoustic engineering.Second in the topology of acoustics,the famous Su-Schrieffer-Heeger(SSH)model,points out that if we keep in a periodic system symmetry,under the condition of continuous change its structure,can make the transition between units within the transition and the size of the change,which can make the band gap close and open again,that commonly occur in the process of topological transformation.Here,we construct a one-dimensional periodic acoustic system according to the basic principle of the SSH model.Its periodic element is composed of two resonators and two connecting tubes.In experiments and simulations,we proved that the size of intercell and intracell transitions could be changed by adjusting the radius of the connecting tube,so as to construct topological mediocre and topological non-mediocre structures,and verified that there is indeed a topological interface state in a system with both topological trivial and topological non-trivial structures.In addition,we demonstrate that topological non-trivial properties can support the realization of edge states in our acoustic systems,and those topological non-trivial properties are robust against local defects and perturbations.Because the sound is greatly enhanced at topological interface states and topological edge states,and topological interface states and edge states are a single frequency transmission peak in the bandgap,this structure may have potential applications in the manufacture of single frequency sound sources.