Research On Wave Steering Performance Of Acoustic Metasurface And Its Application In Sound Insulating

As an ever-expanding research area at present,the acoustic metasurface(AMS)combines the wave-field control theory of phased array with the extraordinary acoustic properties of metamaterial's subwavelength structures.The AMS can steer the wave front using the thinnest structure,and could be designed to obtain the functions such as arbitrary sound refraction angles,sound wave focusing and imaging,and high-efficiency coupling of surface wave.The study of AMS has generated some important concepts in the acoustic field,which beyond the traditional acoustic concepts.It provides new ideas and methods for better understanding of sonic theories and steering sound waves freely.As a recent emerged concept,the theories and methods to applicate the AMS to the acoustic control engineering still need further study.The noise reduction of pipeline based on the Helmholtz resonator is an important engineering problem in the vibration and noise control field,and a bottleneck of it is to insulate the low-frequency wave in smaller volume.We need to develop new method to increase the equivalent acoustic mass and acoustic compliance of the resonator in the limitation of the structure volume,to reduce the resonant frequency of the Helmholtz resonator.In response to the problem,this paper introduced the AMS to the design of Helmholtz insulator,and gives a feasible design that could remarkably decrease the frequency band of insulating,and discussed the influence factors,regulation and principle of the insulator.The main research contents and conclusions are as follows:1.Based on the generalized Snell's Law,we discussed the regulation of parameters distribution of AMS,and analyzed the influence regulation of input angles,phase gradients and the discretization of metasurface on the refraction angle of AMS.The results were verified by the theoretical model and the simulation of finite element model.2.Using the subwavelength Helmholtz resonator array as the unit cell,of which the effective parameters were obtained by the energy band analysis,we built the AMS structure in the air environment.The structure can give a good refraction under the low frequency of less than 1000 Hz.The effect of the impedance mismatch on the acoustic field was discovered under the condition that the equivalent velocity was much lower than the medium velocity.A reflective AMS was provided by analogy of transmission AMS.3.A new insulator was designed by using the AMS to the Helmholtz resonator.The influence of the AMS on the frequency of the transmission loss peak of Helmholtz resonator was then studied,and the formula of the AMS' influence was given.The best reflection angle of the AMS to realize the low-frequency insulating was given according to the regulation.As the simulation results show,the insulating frequency band of the device with the AMS was reduced by 60% compared to that without the AMS,and the sound transmission loss remained similar.