Studies On The Design Of Functional Elements And Ordering Modes For Soft Acoustic Metamaterials

Acoustic metamaterials are artificial materials that use structural design to surpass natural acoustic materials.They can achieve extraordinary acoustic applications,including acoustic cloaking,sub-wavelength imaging,perfect sound absorption,acoustic hologram and so on.soft acoustic metamaterial is a great innovation of acoustic metamaterial.The introduction of soft materials can add tunable characteristics,realize low-cost and large-scale manufacturing of meta-devices,realize the conformal attachment of curved surfaces,and develop human friendly bio-acoustic interface.The development of soft acoustic metamaterials is still in its infancy.Meanwhile,the basic functional elements,ordering mode and related research methods are not abundant.This paper focuses on how to design new functional elements in flexible material system,how to improve the ordering mode of soft acoustic metamaterials and how to maintain their performance under deformation.Soft functional element,ordering mode in soft materials,and performance control of soft acoustic metammaterials under deformation are studied.These three aspects complement and promote soft acoustic metamaterials,and the research of each aspect expands new application scenarios.The main work of this paper is as follows:At First,a new soft acoustic functional element was prepared.We proposed a spring-mass resonator composed of soft fiber/rigid beads and fabricated ultrathin soft acoustic metasurface by electrospinning technology.The thickness of soft acoustic metasurface is about 30 ?m ?1 mm according to the specific working frequency,and the thinnest one is 1/680 of the controlled wavelength(the thickness required by the acoustic phase changing by 180 degrees),which is far thinner than the thickness of the present rigid acoustic metasurfaces.On the basis of the new soft acoustic metasurface,this paper proposes a scheme of cutting the metasurface by laser cutting technology in combination with the traditional Chinese paper-cut art,so as to arbitrarily control the wavefront of transmitted acoustic waves.Specifically,three patterns are designed to achieve acoustic focusing,acoustic vortex and acoustic superoscillation.Then,a new ordering mode design of soft acoustic metamaterials—disordered hyperuniform arrangement is introduced,and the disordered hyperuniform phonon structure is realized in soft materials.Furthermore,based on the fact that the boundary of the disordered hyperuniform phonon structure can be customized arbitrarily,a new soft disordered hyperuniform elastic metamaterials(DHEM)is designed by using the disordered hyperuniform distribution to construct the internal reflection interface to approximate the theoretical perfect acoustic black hole.DHEM has about 4000 times elastic wave enhancement effect in a wide frequency range.This soft DHEM has a more stable and tough structure,a top surface with arbitrary shape,lower material and processing costs,and lighter weight.In addition,soft DHEM can still maintain functionalities under small deformation.At last,a scheme to maintain the performance of soft acoustic metamaterials under deformation is proposed.Flexibility or softness can bring advantages such as conformal attachment to curved surfaces,but at the same time,structural changes may also make the original function invalid,which brings challenges to the design of metamaterials.This paper puts forward corresponding solutions to the two challenges.First of all,a significant challenge is that the design theory of planar metasurfces is no longer applicable when it fits to the curved surfaces.In order to solve this problem,this paper proposes the theory and design scheme of non-planar soft acoustic metasurface for focusing.Furthermore,based on the conic surface,an ‘umbrella model' is proposed to focus dynamically in real time.The second challenge is the large propagation loss of elastic waveguides under the condition of deformation.In this paper,a soft disordered hyperuniform elastic wave guide with low distortion loss is proposed.Under the conditions of stretching,compression,bending and other deformations,the average frequency bandwidth of the phononic crystal elastic waveguide decreases by about 50%,while the average bandwidth of the soft disordered hyperuniform elastic waveguide decreases by only about 20%.