The Control Of Amplitude And Phase And Slow Sound Effect In Acoustic Metamaterials

The propagation of acoustic waves in materials is an important research area of physics,and it has many applications in people's life.Since there are many similarities between acoustic and optical wave,recently,people found that artificial microstructures could be a significant method to control sound waves.By means of acoustic metamaterials and acoustic metasurfaces,people have realized many novel phenomena such as sound negative refraction,subwavelength imaging,sonic focusing,acoustic cloaking,extraordinary transmission and so on.Based on this background,this paper studies the propagation of acoustic waves in several kinds of acoustic metamaterials and acoustic metasurfaces,and utilizes these structures to control the amplitude,phase and speed of sound.The specific content as follows:In the first part,we studied the transmission properties of acoustic waves through subwavelength acoustic gratings.We demonstrated the existence of full resonant transmission and realized manipulation of resonant modes by tuning the geometric parameters.In our research,we introduced "H" shaped grating and we found several high transmission peaks by calculation of transmission coefficient through rigorous coupled wave analysis.In the other hand,through finite element simulation method,we obtained the pressure distribution of the resonant modes.As a result,we concluded that the underlying mechanism is the coupling effect of the FP resonances in structure and the diffracted modes along the surface.Further,we demonstrated that we could tune the wavelength of the resonant transmission peaks by changing the geometrical shape of the grating.This research could provide some values for tunable subwavelength acoustic filters and other devices.In the second part,we designed an acoustic metasurface based on rectangular split ring structures,and we demonstrated the ability of phase control by realizing abnormal transmitted angles,plane focusing effect,negative refraction and the conversion of transmit waves into surface waves.For rectangular split ring structure,we indicated that it could be used to almost freely manipulate the transmitted wave's phase,by means of finite element simulations and effective electric model.Then we designed several kinds of phase distribution to realize some novel effects by numerical simulations,such as abnormal transmitted angle,plane focusing effect,negative refraction and so on.In addition,we fabricated samples for experiments by 3D printing,and we experimentally realized abnormal transmitted angle and negative refraction in the audible band.Our research may provide a new thought of the design of minor acoustic devices.In the third part,we demonstrated multi-mode acoustic transparency effect in the 1D waveguide based on Helmholtz resonators,and meanwhile we demonstrated the existence of slow sound effect.Through finite element simulation and analytical calculation,we obtained the transmission and phase curves of the acoustic wave in our dual-mode system.In this result,we found two transparent windows,and we extended it to multi-mode effect by increasing the HR numbers.Since the phase of transmitted wave varied very fast in the transparent window,we further studied the slow sound effect in the multi-mode transparent phenomenon.For example,we found that the group velocity could be significantly reduced and the group refraction index could be higher than 12 in the dual-mode system.These results could provide some new methods for the manipulation of acoustic waves in 1D waveguide.Above all,in this paper we mainly researched the propagation of acoustic waves in several acoustic metamaterials(including subwavelength acoustic grating and waveguide)and acoustic metasurfaces.We realized perfect resonant transmission in subwavelength grating by controlling acoustic wave's amplitude.And we significantly manipulate the phase of transmitted sound waves through acoustic metasurfaces based on split ring structures.As a result,we realized abnormal transmitted angles,plane focusing effect,negative refraction and so on.In addition,we demonstrated multi-mode acoustic transparency and slow sound effects in the 1D waveguide.These results could provide some unique thinking in the design of acoustic microdevices,including acoustic image,acoustic filter,acoustic sensing and so on.