An effective passive method to control noise is applying sound absorption materials and structures. Many works have been done to optimize parameters, structures and arrangements of the sound absorption materials to improve absorbing efficiency. In acoustics, metamaterials that possess extraordinary properties not found in nature have been of interest in recent years. It inspires that an acoustic metamaterial can be designed for effective noise reduction, making use of the extraordinary properties. In this thesis, acoustic metasurfaces as a category of the metamaterials are designed and studied for noise control. Firstly, an acoustic porous metasurface with periodic structures is proposed for concluding transmission regularities, which exert significant influences on sound isola...[ Read more ]

An effective passive method to control noise is applying sound absorption materials and structures. Many works have been done to optimize parameters, structures and arrangements of the sound absorption materials to improve absorbing efficiency. In acoustics, metamaterials that possess extraordinary properties not found in nature have been of interest in recent years. It inspires that an acoustic metamaterial can be designed for effective noise reduction, making use of the extraordinary properties. In this thesis, acoustic metasurfaces as a category of the metamaterials are designed and studied for noise control. Firstly, an acoustic porous metasurface with periodic structures is proposed for concluding transmission regularities, which exert significant influences on sound isolation. The factors affecting the transmission performance are studied to obtain the regularities of sound transmission through periodic structures. Based on the regularities, a porous metasurface with stair-stepping structures is proposed to manipulate reflected waves and refracted waves simultaneously. Through wave manipulations, the reflected and refracted waves can be prevented from radiating into the acoustic far field, making the proposed structure possess a potential for sound absorption performance. Then, a stair-stepping metasurface backed with a rigid plate is studied aiming at investigating sound absorption performance detailedly. Finally, a method to design a metaporous layer with a sub-wavelength thickness, which is a porous layer with engineered internal structures, is proposed to enhance sound absorption performance of the uniform porous layer. The cellular foam and fibrous material are applied to validate the applicability of the method. The works in this thesis open up a new way to design high-performance sound absorbers with huge possibilities for engineering applications. The studies also suggest a few research directions that could be followed for future research and provide some possibilities of interdisciplinary collaborations in future.