Research On The Propagation Of Low- And Medium-frequency Sound Waves Guided By Subwavelength-scale Acoustic Metamaterial

Acoustic metamaterials can manipulate sound waves according to human wishes and are mainly used in the design of acoustic functional devices,playing an important role in medical imaging,non-destructive testing,and other fields.However,in practical application scenarios,acoustic metamaterials mainly have the following problems:(1)lack of small size,simple and stable sound wave control structures that are easy to manufacture;(2)Not suitable for sound insulation and noise reduction in the air circulation scene;(3)When used for acoustic stealth,it is highly sensitive to the internal defect structure;(4)In the waveguide system containing slots,there are problems of low energy transmission and assembly.In order to solve these application problems,the following work has been done in this paper:1.Based on the fractal geometry model,a sub-wavelength scale acoustic metamaterial that does not depend on the structural vibration characteristics is designed,and there are multiple sound insulation forbidden bands in 0-1600 Hz;At near zero density frequency,strange physical phenomena such as acoustic tunneling and acoustic stealth are realized;Finally,the characteristics of sound propagation and energy loss in fractal metamaterials are evaluated through experimental tests.2.Based on the concept of integration and the concept of space curl,a Helmholtzlike acoustic metamaterial is proposed,which realizes the peculiar acoustic response through dipole and multipole vibration;A new acoustic stealth strategy is proposed,which is not affected by the boundary type of the object to be stealth;In terms of sound insulation and noise reduction,the structure produces an anti-resonance mode to realize the negative equivalent bulk modulus characteristics,and then produces an abnormal expansion effect,which produces a near-zero velocity region at the incident end of the sound wave,and produces high reflection while ensuring air circulation.3.A new way to enhance the sound transmission in the waveguide with a slot is proposed.Two near-zero density metamaterial plates are placed in the waveguide,and the efficient transmission of sound energy is realized by adjusting the plate spacing;By testing in the slot waveguide system with defects,it can be concluded that this mode is less affected by the waveguide shape and defects;Finally,the gain effect of Fabry-Perot(FP)vibration mode of metamaterial-slit system on acoustic energy transmission is further discussed.