Study On Programmable Resonantor-Type Acoustic Metasurfaces

Acoustic metasurfaces have attracted extensive attention of researchers because of their subwavelength thicknesses and their abilities to achieve extraordinary acoustic manipulation functions such as acoustic focusing,acoustic refraction,acoustic lensing,and acoustic cloaking,etc.Traditional acoustic metasurfaces passively manipulate sound waves by using fixed structures,which have achieved many functions.However,the fixed structures of the traditional acoustic metasurfaces will cause poor reconfigurability,single functions and insufficient stability,which further limit the practical applications of the acoustic metasurfaces.Subsequently,the tunable metasurfaces with reconfigure abilities are proposed.Many researchers have designed a variety of tunable acoustic metasurfaces with different structures to achieve versatile,broadband and high-efficiency acoustic manipulations.However,the existing tunable acoustic metasurfaces still have some limitations in acoustic wave manipulations such as unstable adjustment methods,time-varying resonator volume,low focusing concentration,high inherent loss,failure to achieve multifocal acoustic focusing,difficulty in realizing more complex acoustic imaging,etc.Therefore,designing tunable acoustic metasurfaces with better acoustic performance is of great research significance for expanding the functions of acoustic metasurfaces and realizing continuous,stable and adjustable acoustic manipulations.Resonator-type acoustic metasurfaces have high transmittance in theory and practice because of their good impedance matching with the medium.However,there are few studies on the programmable tuning resonator-type acoustic metasurfaces.Therefore,in this study,two programmable resonator-type acoustic metasurfaces are designed based on two different arrangements of resonators and a narrow long straight acoustic channel,which have smaller thicknesses and can expand the acoustic manipulation functions.According to the acoustic performance of two kinds of acoustic metasurface units,unilaterally distributed and symmetrically distributed programmable resonantor-type acoustic metasurfaces are designed,respectively.In addition,a control system for programmable adjustment of the resonantor-type acoustic metasurfaces is designed based on both the hardware platform and the software platform.Finally,the finite element simulation and experimental methods are used to verify the acoustic manipulation functions of the two metasurfaces designed based on the theoretical method.The main work and conclusions of this paper are as follows:(1)A single-side distributed programmable resonator-type acoustic metasurface is designed based on acoustic theory.The performance of the metasurface unit are analyzed by finite element method and theoretical derivation method.It is found that the designed metasurface can achieve full phase control of-π ～ π in the range of slit width of 1.5 ～ 9mm,and has a high transmittance.In order to reduce the thickness of the acoustic metasurfaces and enhance acoustic focusing function.A symmetrical distributed programmable resonatortype acoustic metasurface unit composed of four symmetrically distributed resonantors and a narrow long straight acoustic channel is also designed.Using the aforementioned two analysis methods,it is found that the designed metasurface unit can achieve full phase control within a small variation range of 1.67～10 mm,and also has a high transmittance.(2)A unilaterally distributed programmable resonator-type acoustic metasurface composed of five unilaterally distributed resonantors and a narrow long straight acoustic channel is designed.The slit widths distributions of the designed metasurface are analyzed to realize the three kinds of functions including acoustic refraction and acoustic focusing from left to right and from top to bottom.Based on the maximum speed of the stepper motor,the slit widths distributions of metasurface for realizing the three functions is modified.In order to realize the programmable adjustment function,a control system composed of a hardware platform and a software platform for unilaterally distributed programmable resonator-type acoustic metasurface is designed.The experiments of the acoustic manipulations shows that the designed control system can continuously control the acoustic metasurfaces to modulate sound waves,and to realize the above three acoustic wave manipulation functions within a few tens of milliseconds.In addition,the influence of the designed motor motion algorithm for the entire system is between 0% and 1.1%,and the system runs relatively smoothly.(3)A symmetrical distributed programmable resonator-type acoustic metasurface is designed with a smaller thickness and can achieve better acoustic focusing function.This three-dimensional metasurface consists of twenty metasurface units,each unit contains four symmetrically distributed resonantors and a narrow long straight acoustic channel.The regulation of the sound field is achieved by adjusting the width of the acoustic channel of each metasurface unit to produce single focus point and double focus points.The slit width distributions of the designed acoustic metasurface for realizing single and double focus functions are analyzed based on the homogeneous medium theory.Experiments and simulations show that the designed metasurface can achieve high-intensity and high-focusing acoustic focusing functions.Benefit from the precise size design,the proposed metasurface wih a smaller thickness can realize better interconversion functions with single focus point and double focus points,respectively.