Catapane, Giuseppe (2024) Acoustic Metamaterials: Design and Applications with Implications for Aeronautic Noise Control. [Tesi di dottorato]

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Abstract

In recent years, the reduction of aircraft noise has become a priority in the aerospace industry due to its environmental and health impacts, particularly in the context of increasingly stringent regulations imposed by international bodies such as the International Civil Aviation Organization (ICAO). This PhD thesis explores the development of advanced acoustic metamaterials to address the challenge of mitigating engine noise and improving cabin acoustics. The research focuses on passive noise reduction techniques through the design, modeling, and experimental validation of acoustic metamaterials. These innovative materials, which include locally resonant systems and periodic structures, are tailored to address the specific acoustic challenges in aerospace applications. Traditional materials such as glass wool and conventional acoustic liners have been widely used but are limited in their ability to mitigate low-frequency noise, which is a dominant factor in aircraft engine and cabin noise. A key innovation explored in this thesis is the use of coiled quarter-wavelength tubes (QWTs) embedded in honeycomb structures, which demonstrate superior noise attenuation across a wide frequency range compared to conventional liners. Additionally, micro-perforated panel absorbers and Helmholtz resonators are integrated with metamaterial designs to enhance their effectiveness at both high and low frequencies. In addition, several configurations of periodic inclusions embedded in porous materials are designed to achieve broadband noise reduction, demonstrating significant improvements in sound absorption. The experimental results, supported by finite element modeling and theory, confirm that these metamaterial structures provide enhanced sound attenuation compared to traditional acoustic treatments. For instance, the spiral resonators developed as part of this research exhibit excellent absorption characteristics under diffuse acoustic field (DAF) excitation, making them ideal for use in aircraft interiors. Beyond theoretical development, practical applications in aeronautics are also explored. The integration of metamaterial-based solutions into aircraft components, such as fan ducts and fuselage linings, presents promising avenues for further noise reduction without compromising performance or adding significant weight. This research contributes to the field of aerospace engineering by advancing the understanding and application of acoustic metamaterials. It provides a comprehensive analysis of their design, characterization, and practical implementation, laying the groundwork for future innovations in noise mitigation.

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