THESIS
2018
xxx, 146 pages : illustrations (some color) ; 30 cm
Abstract
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...[
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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.
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