Research On The Sound Properties Of Fractal Acoustic Metamaterials

Acoustic metamaterials are new acoustic functional materials based on phononic crystals.They are all artificial structural materials which could be used to manipulate acoustic wave propagation.The essence is its bandgap characteristics.There exist potential engineering application values such as sound insulation in low-frequency,filters,hyper lens.Scholars and research institutes all around the world are greatly concerned about its broad applications.Fractal theory is introduced to the microstructure design of acoustic metamaterials.Combinate both numerical simulation and theoretical analysis,sound properties of acoustic metamaterials are systematically studied and the main contents and results are as below:(1)Self-similar fractal theory is introduced into the structural design of acoustic metamaterials,considering the arrangement of different planar lattices(such as square lattices,central square lattices,triangular lattices,hexagonal lattices and Kagomé lattices)to study fractal acoustic metamaterial band structure and the influence of the Bravais lattice on the band structure.The results show that self-similar fractals and Bravais lattices have a significant effect on the band structure of labyrinth-type acoustic metamaterials.The of the self-similar fractal order increase,and both the path of the acoustic channel and the propagation time increase.By adjusting the Bravais lattice,there exist opportunities to produce excellent broadband and modulate band gaps.The studies of the influence of self-similar fractals and Bravais lattice on the band structure of labyrinth-type acoustic metamaterials provide guidance for a certain Bravais lattices with the desired band structure,which are beneficial to more practical engineering applications.(2)Combining self-similar fractals theory and acoustic metamaterials to construct self-similar fractal acoustic metamaterial,it could provide the possibility for acoustic filters in the infrasonic field.As the fractal order increases,the first band gap shifts to the lower frequency.The normalized frequency of the first bandgap of the third-order fractal space acoustic metamaterial is much less than 1 and the higher-order fractal spatial acoustic metamaterials are more easily used for sound insulation and noise reduction in the infrasonic field.By simply arraying coiled space acoustic metamaterial,it is easily to show that the band gap presenting in a single acoustic metamaterial will be divided into two or more isolated band gaps.As the number of fractal orders increases,the number of band gaps increases.Therefore,high-order fractal space acoustic metamaterials can effectively achieve sub-wavelength sound insulation and multi-band filtering.(3)The traditional acoustic performances are based on certain geometric,material and environmental factors to solve the sound properties of the sound field by numerical simulation analysis.There are a lot of uncertainties in the actual acoustic analysis.A certain number of samples are generated by random sampling to examine the acoustic transmission characteristics of third-order fractal acoustical metamaterials.The robust performance of the third-order fractal-wound space acoustic metamaterial designed in this paper is superior and provides a theoretical basis for similar acoustic metamaterial design.