The Design And Performance Analysis Of The Gradient Coiled Acoustic Metamaterial

In recent years,the emergence of acoustic metamaterials has opened a new door for the design of acoustic functional devices.Through artificial design,acoustic metamaterials can break through the limitations of natural materials and obtain many special properties that do not exist in natural materials.Among them,the coiled acoustic metamaterials obtains high refraction by curling the internal channel,and has rich acoustic properties.Moreover,the coiled acoustic metamaterials have a simple structure and are easy to prepare,and they have very important application prospects in the field of acoustic functional devices.The coiled acoustic metamaterials have the characteristics of extraordinary transmission,high refractive index,negative equivalent parameters and zero equivalent parameters,which can be used for the preparation of acoustic functional devices such as acoustic filtering,acoustic imaging,and acoustic cloaking.However,the extraordinary transmission characteristics of the coiled acoustic metamaterials have the problem of too narrow bandwidth,which greatly limits their application value.The acoustic horn and impedance matching layer structure proposed by the researchers can effectively broaden the extraordinary transmission bandwidth,but there will be a new problem,that is,the size of the metamaterials structure are too large,which are not conducive to the design of miniaturized acoustic functional devices.In order to overcome the problem of excessively narrow transmission bandwidth of the coiled acoustic metamaterial,while ensuring that the overall size of the metamaterial structure does not change,and to achieve the integration of multiple acoustic functions.In this paper,combining the structural characteristics of the coiled acoustic metamaterials and impedance matching theory,a gradient coiled acoustic metamaterial is designed,and the acoustic characteristics of the gradient coiled acoustic metamaterials are simulated and analyzed based on finite element software.The main contents of the thesis are as follows:(1)The design of the gradient coiled acoustic metamaterialBased on the structure and special performance of the coiled acoustic metamaterial,combined with the impedance matching theory,a gradient coiled acoustic metamaterial is designed by gradient distribution of the width of the coiled channel inside the coiled acoustic metamaterial;The gradient is established in the COMSOL Multiphysic finite element software Finite element simulation model of coiled acoustic metamaterials.(2)Analysis of the extraordinary transmission characteristic of the gradient coiled acoustic metamaterialBased on the equivalent medium theory and impedance method,the relationship between the acoustic transmission performance of the gradient coiled acoustic metamaterial and the gradient ratio q is derived;The law of the influence of the gradient ratio q on the extraordinary transmission characteristics and equivalent impedance of the gradient coiled acoustic metamaterial is explored;The optimal value of the gradient ratio q is selected to construct the model of the gradient coiled acoustic metamaterial,and broadband extraordinary transmission is realized through finite element simulation;The equivalent impedance of the gradient coiled acoustic metamaterial was calculated,and it is verified that the broadband extraordinary transmission characteristics of the gradient coiled acoustic metamaterial are based on the perfect equivalent impedance matching.(3)Zero equivalent parameter characteristic analysis of the gradient coiled acoustic metamaterialCalculated the band structure of the gradient coiled acoustic metamaterial tightly arranged in square unit cells with a certain lattice constant,and determined the frequency of the Dirac-like point;Calculated the equivalent parameters of the gradient coiled acoustic metamaterial,and verified that the gradient coiled acoustic metamaterial at the Dirac-like point has zero equivalent parameter characteristics;Based on the zero equivalent parameter characteristics of the gradient coiled acoustic metamaterial,the acoustic cloaking of regular and irregular obstacles,the cylindrical wave generated by the point sound source and the wavefront shaping of the chaotic sound wave generated after the plane wave passes through the rigid obstacle,and the sound channel function of 90°,180° right-angle transmission and arbitrary bending transmission of sound waves are realized.(4)Acoustic enhancement of the gradient coiled acoustic metamaterialCalculated the equivalent parameters of the gradient coiled acoustic metamaterial unit cell,and determined the frequency range corresponding to the negative equivalent bulk modulus;Based on the characteristic that the acoustic energy is concentrated at the center of the metamaterial in the frequency range of the negative equivalent bulk modulus,the acoustic enhancement effect of the gradient acoustic metamaterial unit cell in the gradient space is realized;Constructed the line defect and point defect structure of the gradient coiled acoustic metamaterial;Based on the defect state theory of acoustic metamaterials,the energy bands and acoustic enhancement coefficients of perfect gradient coiled acoustic metamaterial supercells and defect structure supercells are calculated,and the acoustic enhancement effect of gradient coiled acoustic metamaterial supercells is realized.The gradient coiled acoustic metamaterial designed in this paper achieves broadband extraordinary transmission,while the overall structure of the structure has not changed.In addition,based on the gradient coiled acoustic metamaterials,multiple acoustic functions such as acoustic cloaking,wavefront shaping,acoustic channel and acoustic enhancement are realized,which can be used to realize the development of various acoustic functional devices such as broadband bandpass filters,sound wave direction control,and signal amplification.It provides a new idea for the design of miniaturized and integrated multifunctional acoustic devices.