AbstractOver the last decade, the sound wave manipulation has become a focal point for many engineering applications, such as negative refraction, subwavelength imaging, cloaking and one-way transmittance. Only recently the sound wave manipulation has been deeply investigated to achieve full sound absorption because of the growing interest in noise mitigation and cancellation. However, the achieving of such challenging results is usually constrained by the general properties of naturally available materials, and this is the main reason for the emergence of engineered structures and metamaterials. In this thesis, the sound wave manipulation has been studied and applied in two main fields: material properties evaluation and perfect sound absorption. In the first case, a new approach based on the impedance tube test rig is proposed to evaluate not only the acoustic properties but also the elastic properties of the tested material. The proposed method results an innovative non-destructive approach to evaluate the out-of-plane elastic modulus for composite and porous materials.
Moreover the sound manipulation due to the sound wave and resonator structures interaction has been investigated with the main challenging purpose of low frequencies sound absorption using subwavelength structure. Therefore, in the following chapters of the thesis the developed new metamaterials are based respectively on Microperforated panel (MPP), elastic membrane, Graphene Oxide (GO) and Honeycomb structures. The sound absorption performances were studied through numerical and analytical models which helps to understand the absorption mechanism for each proposed metamaterial. Prototypes were manufactured for each of proposed metamaterial unit cells and their absorption performances experimental tested using an impedance tube test rig. The results demonstrated how the proposed metamaterials represents subwavelength and tuneable devices which allows almost perfect and broadband absorption at low frequencies.
|Date of Award||16 Sept 2020|
|Supervisor||Stephen Newman (Supervisor) & Michele Meo (Supervisor)|