Author: Chen, Siyu
Title: Ventilated helical structure acoustic metamaterials
Advisors: Choy, Yat Sze Tracy (ME)
Degree: M.Sc.
Year: 2021
Subject: Metamaterials
Metamaterials -- Design and construction
Acoustical materials
Hong Kong Polytechnic University -- Dissertations
Department: Department of Mechanical Engineering
Pages: ii, 96 pages : color illustrations
Language: English
Abstract: Ventilated acoustic metamaterials have attracted the attention of many researchers in terms of low-frequency sound filtering and fluid permeability. This research proposed a rotatable parallel helical acoustic metamaterial with broadband filtering and high-efficiency ventilation, which was designed based on the Fano resonance mechanism and coupling mechanism, to address the problem of unsatisfactory ventilation performance and bandwidth of existing helical metamaterials. A unit includes three helical channels and a cylindrical partition in the middle. It consists of two helical structures in parallel. The coupling between the parallel helical structures is realized based on the Fano resonance mechanism and generates the phenomenon of destructive interference of sound waves in the far-field area. Unlike the traditional single helical structure type metamaterial, the two resonant frequencies can be adjusted by adjusting the size parameters of the two helical structures, effectively blocking the sound wave energy of a specific frequency band. By coupling the two helical structures, sound insulation performance with wider broadband was obtained.
By optimizing the design and use of COMSOL software for finite element simulation, a structure composed of two dual-mode Fano resonance units can be designed. By coupling the two structures with different numbers of helical blades, this research obtained transmission loss of at least 13dB within the bandwidth of 840-1580Hz and achieved a high air circulation rate of 80%. The design structure samples were made by 3D printing, and then its ventilation performance was measured by the acoustics wind tunnel experiment. The method proposed in this research can be extended to the coupling of multi-Fano resonators to achieve ultra-wideband. The results of this research can also be expected to be beneficial in applications in sound filtering, tube noise reduction and sound control in limited volume.
Rights: All rights reserved
Access: restricted access

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