The Design And Performance Analysis Of The Spiral-labyrinthine Acoustic Metamaterial By Coiling Up Space

With the development of the theoretic research and application of new artificial electromagnetic materials,more and more attention has been attracted on the application of acoustic metamaterials.The most typical feature of acoustical metamaterials is the subwavelength size and negative effective parameters.Thus,acoustic metamaterials exhibit strong abilities and extraordinary characteristics for manipulating sound wave from the range of acoustic cloaking,negative refraction to ultrasonic imaging.Distinguished with the traditional locally resonating acoustic metamaterials,the acoustic metamaterials based on coiling up space have many advantages such as considerable sound absorption and an isotropic response associated with its high symmetry.However,The ways of the coiling up space in the labyrinthine units presented above are mostly designed in a zigzag path.Here,we propose a spiral-labyrinthine acoustic metamaterial(SLAM)by coiling up space.Different from the zigzag path,the spiral-labyrinthine path will force the sound waves propagate alternatively along the path in a clockwise direction and an anticlockwise direction.Such a spiral-labyrinthine way can be employed to design the labyrinthine units with different shapes and easily extended to fabricate the acoustic metamaterial in three dimensions.Based on theoretical analysis and numerical simulation methods,this paper studies the design and performance analysis of the spiral-labyrinthine acoustic metamaterial.The main research work is as follows:(1)The Design of The Spiral-labyrinthine Acoustic Metamaterialcoiling up space and high refractive index are the two basic features of the labyrinthine acoustic metamaterial.Based on the above design principles,the existing labyrinthine acoustic metamaterials are mostly designed in the “zigzag” path method.However,the spiral-labyrinthine path of the SLAM will force the sound waves propagate alternatively along the path in a clockwise direction and an anticlockwise direction.Besides,the metamaterial exhibits the monopolar resonance and the dipolar resonance due to its high symmetry.Based on the retrieval method of effective properties,the negative effective parameters are proved to be generated by the resonance of the unit cell.The monopolar resonance can induce negative bulk modulus while the dipolar resonance can induce negative mass density.(2)The Analysis of The Sound Blocking Performance of The Spiral-labyrinthine Acoustic MetamaterialTwo trough frequencies are located at the transmission coefficient.The metamaterial exhibit extraordinary abilities and stabilities for sound absorption at the two trough frequencies in a subwavelength scale.Even in the extremely small filling ratio,the corresponding transmission loss for two trough frequencies are also up to95%.The reason is further explained by the resonant modes that the monopolar resonance and the dipolar resonance can remarkably concentrate the energy of sound wave.A much wider frequency range between the monopolar resonant frequency and the dipolar resonant frequency is obtained for sound blocking by increasing the number of metamaterials in waveguide.By the parameters analysis of the unit air thickness,frame thickness,rotation number,the frequency of sound blocking is reduced to [100Hz,1000Hz].In addition,the metamaterials has good robustness of the sound blocking against small displacements and angle changes.(3)The Analysis of The Density-near-zero Performance of The Spiral-labyrinthine Acoustic MetamaterialThe density-near-zero performance refers to the perfect transmission without amplitude and phase change of acoustic waves at the density-near-zero frequency.The SLAM can be applied to the acoustic cloaking and the sound supertunneling.We find that obstacle like a little fish shape is successfully cloaked by the SLAMs as if it doesn't exist.The SLAMs can be also applied to the sound supertunneling with little amplitude loss and little phase change in a complex bend waveguide.The metamaterial can also be applied to acoustic logic gates.The basic logic operations "or","and","xor",and "not" can all be realized by a fork type and T type device composed of SLAMs.Therefore,the labyrinthine acoustic metamaterial can be used to fabricate a high performance acoustic device.