MPhil Thesis Presentation
This thesis investigates acoustic properties of porous acoustic metamaterials (AMs) including both planar and circular-interface types of AMs (PAMs and CAMs) and ultra-thin nano-fibrous membranes backed with melamine foams.
PAMs, including porous triangle-shaped AMs and porous labyrinthine type of AMs (LAMs), are studied analytically, by simulation and by laboratory tests. The triangle-shaped AMs significantly improve the sound absorption coefficient of the uniform melamine foams at the frequency of interest. Furthermore, the porous LAMs simultaneously demonstrate better sound absorption coefficient (more than 55%) and transmission loss property (more than 300%) from 1, 000 Hz to 3, 000 Hz than original melamine foams.
The sound absorptivity of ultra-thin nano-fibrous membranes backed with melamine foams is evaluated over a broad frequency range from 500 Hz to 6,400 Hz. The effects of the thickness of the nano-fibrous membrane, the nanofiber diameter and the melamine foam thickness are experimentally studied, which are also analysed by several analytical models. The proposed thin sound absorber possesses an excellent potential to improve sound absorption coefficients, especially for thin melamine foam samples.
Porous CAMs have been studied analytically, numerically and in a laboratory. An analytical expression of the sound refraction through the CAMs is derived based on the principle of the stationary phase. In the numerical and experimental study, porous LAMs are applied on circular interfaces. Results indicate that two parameters, which are the angular distance over a period of CAMs and the ratio between the radius of a circular interface and the incident wavelength, are determining factors in the excitation of high-order wave modes in the scattered sound pressure fields. This study provides an engineering method to apply CAMs in industrial applications.
(Supervisor: Prof. Kai Tang)