Design And Experiment Of Sound-transparent Anisotropic Subwavelength Structure

Anisotropic acoustic subwavelength structures,often named as metafluids,allow special acoustic manipulations such as invisibility cloaking,waveguiding and beamshifting.This paper presents a design of anisotropic acoustically-transparent media that can eliminate the reflected wave in the bending path.The method to independently modulate the anisotropic effective acoustic parameters of metafluid is proposed.By analyzing the effective acoustic behavior of the proposed anisotropic structure in the quasistatic limit and adjusting the unit configurations in a specific order,the range of realizable effective parameters of such subwavelength structures is broaden.The sound-transparent effect of such anisotropic medium is experimentally demonstrated in a bending waveguide by periodically arranging the designed structure in its bending part,where the distorted acoustic field is restored as if the wave travel through a straight waveguide,and the transmitted acoustic signal is maintained nearly the same as the incident Gaussian pulse.In addition,we introduce underwater hollow structures for underwater acoustic field manipulations,and gives the theoretical derivation of equivalent parameters of such acoustic unit structures.The equivalent parameters and parametric anisotropy of underwater acoustic units composed of different materials with different configurations are numerically analyzed.By changing the shell thickness,volume ratio and other geometrical and physical configurations of the hollow structures,the method to modulate the equivalent acoustic parameters and broaden the parameter space of the underwater acoustic materials is demonstrated.The work in this paper provides a feasible method for the realization of acoustic units in strict accordance with the requirements of coordinate transformation,and a possibility for improving the performance of related acoustic devices.