水下吸声超材料的质量集中效应

Mass Concentration Effect of Underwater Sound-Absorbing Metamaterials

为了降低水下吸声超材料的厚度,更加利于水下吸声的实际应用,提出了一种将质量集中效应引入水下薄板型声学超材料的设计思想。一般来说,对于经典的水下薄板型超材料,其单元胞结构是由一个四周固定的薄钢板及固定在薄钢板上方的振子构成,当平面波以一定频率垂直入射到单元胞表面时,会出现一个显著的由振子共振引起的声吸声峰。但是,在保持总质量不变的情况下,将原厚振子精确地划分为相邻的两个薄振子,可以获得类似的吸声性能,同时出现额外的吸声峰,具有多个模态,超材料的厚度会急剧下降,这种现象称为质量集中效应。为了更好地理解吸声的物理机理和优化吸声性能,运用阻抗匹配机理和有限元模拟方法,探讨了重要结构参数对吸声性能的影响。在此基础上,提出了一种多元胞结构,该结构在200~1000 Hz范围内具有良好的宽带吸声效果。该研究为水下低厚度超材料的设计提供了一种有效的方法。

To reduce the thickness of underwater sound absorbing metamaterials and facilitate their practical application of underwater sound absorption,a design idea of introducing mass concentration effect into underwater thin-plate acoustic metamaterials is proposed.Generally describing,for the classical underwater thin-plate metamaterial,the unit cell structure is composed of a thin steel plate fixed around and an oscillator fixed on the top of the thin steel plate.When a plane wave is vertically incident on the surface of the unit cell at a certain frequency,there is a significant sound absorption peak caused by oscillator resonance.However,in the case of keeping the total mass unchanged,if the original thick oscillator is accurately divided into two adjacent thin oscillators,similar sound absorption properties can be obtained,additional sound absorption peaks appear at the same time with multiple modes,and the thickness of the metamaterial decreases sharply.This phenomenon is called mass concentration effect.To reveal the physical mechanism of sound absorption and optimize sound absorption performance,the effects of important structural parameters on sound absorption performance are discussed by impedance matching mechanism and finite element simulation.Then a multi-cell structure is designed,which is endowed with good broadband sound absorption effect within the range of 200-1000 Hz.