Structural Design And Acoustic Wave Modulation Of Novel Phononic Crystals And Pentamode Metamaterials

Acoustic metamaterials are artificial periodic or nonperiodic structures with microstructurally ordered design at subwavelength dimensions,which can produce extraordinary acoustic or mechanical properties not possessed by conventional materials and provide a new theoretical basis for acoustic wave modulation.In recent years,the anisotropic elastic modulus of local resonant phononic crystals and pentamode metamaterials,which have important potential applications in acoustic wave modulation such as vibration and noise reduction and acoustic stealth,have received extensive attention from scholars at home and abroad.In this paper,we propose three new acoustic metamaterials starting from two important aspects of acoustic metamaterials: phononic crystals and pentamode metamaterials.First,for the need of suppressing elastic wave propagation,an innerconcave acoustic metamaterial with a central mass is proposed,and the energy band structure is calculated to show that the structure possesses multiple complete band gaps in the studied frequency range.The images of the transfer function are compared with the band gaps in the energy band structure,and the vibration isolation performance of the metamaterial is demonstrated.Secondly,the equivalent mass density and equivalent modulus are obtained based on the equivalent parametric analysis method of the pentamode metamaterial,and an octagonal pentamode microstructure with similar equivalent mass density and sound velocity as water is designed,and the simulation results demonstrate its fluid-like properties.The influence of the geometric parameters of the pentamode structure on the equivalent parameters is investigated,and anisotropic pentamode metamaterials are designed by adjusting the geometric parameters.Finally,the local resonance mechanism is introduced into the design of the pentamode metamaterial,and a diamond-shaped pentamode metamaterial is designed.This metamaterial has a band gap and a single-mode transmission region at the same time,which can realize low-frequency acoustic wave modulation.The three new structures proposed in this paper further enrich the structural forms of acoustic metamaterials.The research results of phononic crystals can provide theoretical references for vibration and noise reduction and seismic protection of building structures,while the research results of pentamode metamaterials can be used for hydroacoustic stealth and the design of new acoustic devices.