Environmental noise impacts the everyday life of millions of people and it represents a growing concern for the health of the world's population. To mitigate this impact, noise reducing materials such as foam or barriers are employed extensively with effective results. However, the efficacy of such materials is limited by the inverse relationship between the frequency of the attenuated waves and materials characteristics like thickness and density, as described by the mass-law. In order to overcome this fundamental limitation, a new challenge in acoustic engineering has emerged to design and manufacture lightweight and subwavelength materials that can break the mass-law. A potential solution to this challenge is represented by a recently discovered family of materials, called acoustic metamaterials, which show properties typically not found in nature. These materials are made of resonant building blocks that are smaller than the wavelength of the attenuated acoustic wave. When these building blocks are combined to form a metamaterial, they lead to the formation of band gaps - near their resonance frequency - that deeply attenuate the incident sound. The manufacturing of noise reducing acoustic metamaterials could also largely benefit from recent advances in three-dimensional printing technologies, as they offer the possibility to fabricate abstract shapes and to carefully choose some properties of the printed materials. The work presented in this thesis describes the modelling, fabrication and measurement of noise reducing acoustic metamaterials based on Helmholtz resonators, thin plates and active piezoelectric plates. These materials have been produced through original and innovative three-dimensional printing techniques. The results of this thesis can be applied to noise control in audio applications such as headphones, hearing aids and smart speakers. Similarly, other fields like aerospace and automotive industry or architectural acoustics could also greatly benefit from lightweight subwavelength noise reduction.
|Date of Award||23 Aug 2021|
- University Of Strathclyde
|Sponsors||University of Strathclyde|
|Supervisor||Joseph Jackson (Supervisor) & James Windmill (Supervisor)|