Investigation On Acoustic Absorption And Acoustic Isolation Based On Acoustic Metamaterial

The absorption and isolation of sound energy,as an important issue in acoustic research,has always been concerned,and is of great significance in environmental noise control,architectural acoustics,noise reduction of electronic equipment and other occasions.Conventional methods include passive methods that rely on porous materials to absorb sound or use the law of mass to isolate sound and active methods that use secondary sound sources for active noise reduction.But the conventional methods have more or less inherent defects caused by the principle itself.Acoustic metamaterials generally refer to artificial materials with subwavelength dimensions.They possess special acoustic properties that are not possessed by natural materials,and by utilizing these peculiar acoustic properties,manual intervention and free regulation of acoustic wave propagation can be achieved.Therefore,more and more researchers have focused on this in recent years,hoping to design and prepare new acoustic artificial structures with better performance than traditional acoustic devices by using the characteristics of acoustic metamaterials.In this paper,the recent methods of acoustic absorption and isolation are studied,and then the high-efficiency sound absorption structure using genetic algorithm to optimize geometric parameters and ventilation sound insulation barrier based on Fano resonance mechanism is proposed.Finally the ultra-thin broadband sound absorption and sound insulation structure is realized.The content of this article is mainly divided into the following sections:In Chapter ?,the introduction mainly introduces the development of metamaterials and the research progress of sound absorption and sound insulation in recent years.In Chapter ?,the relevant theory of acoustic metamaterials such as the acoustic wave equation,the equivalent medium theory and the coiling up space theory are introduced.In Chapter ?,a sound absorbing structure design using genetic algorithm to optimize geometric parameters with broadband efficient absorption of acoustic energy is proposed.The design is composed of a plurality of labyrinth-folding resonant elements in parallel,and a significant acoustic energy loss is formed due to the influence of air viscous during resonance,thereby the absorber can achieve a high-efficiency sound absorption effect.And this chapter deduces the analytical formula for predicting the sound absorption coefficient quickly and accurately.Based on this formula,we use the genetic algorithm to design the relevant geometric parameters of the sound absorption structure,so that the sound absorption structure can obtain the maximum suction of acoustic energy within a certain thickness.Benefiting from the above mechanism,the sound absorbing structure designed in this paper has the advantages of ultra-thin thickness,wide-band and wide-angle sound absorption function of less than 1/25 working wavelength,and does not require additional sound absorbing materials and has great flexibility in material selection.In Chapter IV,the acoustic Fano resonance is realized by the coupling between the continuous state and the discrete state of the sound field.The design of the ventilation sound insulation barrier is proposed by using the space folding structure and the hollow pipe.Since the hollow pipe has no influence on the spatial continuity,the barrier proposed in this chapter allows the background fluid to pass freely while blocking the sound wave propagation.Compared with the traditional sound barrierbased on mass law,the structure designed in this chapter has no strict requirements on the materials(all materials with large acoustic impedances are feasible),and the thickness of the structure is much smaller than the wavelength.The structure has greater mechanical strength and better environmental tolerance compared with the film type metamaterial.Finally,Chapter V gives the main conclusions of this study and the outlook for the future.