Study On Material Properties Of Acoustic Artificial Structures

In recent years,the research of acoustic functional devices based on acoustic artificial structural materials has attracted extensive attention.The use of periodic arrangement or other special structural units to construct acoustic artificial structural materials can achieve the specific regulation of the transmission of sound waves,resulting in a variety of strange physical phenomena.In this paper,aiming at the singular phenomena of sound wave propagating in acoustic artificial structure materials,three structures,phononic crystal,acoustic black hole and elastic wave metasurface,are mainly studied.With the help of COMSOL Multiphysics,a commercial finite element software,the basic research work is completed by means of theoretical deduction and finite element simulation.Firstly,the bandgap characteristics of a novel two-dimensional non-convex hole singlephase phononic crystal are investigated by using the finite element method,and the effects of geometric parameters on the bandgap characteristics are discussed.By properly determining the geometrical parameters of the structure,the new phononic crystal can be used to generate relatively wide complete bandgap in the low frequency range.This work provides a theoretical basis for obtaining the bandgap structure of phononic crystals.Secondly,the structure of an acoustic black hole with arbitrary shape is studied.Based on the coordinate invariance of Helmholtz equation,the density tensor expression of materials in the transformation coordinate system is derived.However,this transformation method will lead to high anisotropy of material parameters.To overcome this disadvantage,a simplified design method of acoustic black holes with arbitrary shape is proposed by using proportional mapping transformation.The numerical simulation results verify the effectiveness of the absorbing properties of an arbitrary shape acoustic black hole.This work has important reference value for the research of acoustic energy absorption and noise control.Finally,a compact groove-structured metasurface structure is proposed in this paper.By using the grooves in the structure,the phase can be delayed at will,and the flexural Lamb wave can be completely controlled,resulting in abnormal refraction,focusing lens,self-accelerating sound beam,virtual source and other phenomena.Compared with previous designs,our design method can make the structure compact,achieve sub-wavelength thickness,and reduce the manufacturing complexity of metasurface structures.The results have potential application value for nondestructive testing,energy acquisition and high resolution lens applications.