低頻段高效吸收的超透氣性聲學超表面之研究

Abstract

在日常生活中，存在許多噪音影響人們的生活，包括高架橋、高架鐵路、風力發電、各種施工等，都是急需改善的問題。談論多元噪音的產生許多是來自背景空氣的流動，如飛機引擎或風力發電等，故同時含括開口透氣面積與高效吸收噪音的工程需求亦是迫切不可或缺的，才能確保設備順利運行時亦能降低噪音的產生，因此優化降噪設備則為本文的重點摘要。 考量到微縮化與較佳的吸收效果，本研究所設計的聲學吸音結構以四分之一波長共振腔作為基礎，並將微波領域中提出的寬頻FSS吸收器的概念[1]運用的聲波中，可將相對頻寬增加，再透過有限元素法做分析。首先，從二維與三維的環境設計共振腔並將其縮小化，驗證其共振頻率與品質因子Q變化趨勢的正確性，將其設計為週期排列的聲波反射器，並保持開口透氣面積超過50 %以達到良好的透氣率，接著運用阻抗匹配設計聲波吸音器，再用電路中二級的概念將其吸收係數與相對頻寬最大化，最終設計出同時具有高效吸收(>90 %)與高透氣面積(>50 %)的聲波吸音器，模擬結果在二維與三維的環境下皆非常吻合。

關鍵字：四分之一波長共振腔、品質因子、聲波吸音器、吸收係數

ABSTRACT In daily life, the issue of noise affecting people's quality of life is ubiquitous. This includes noise generated by elevated railways, airport metros, and various construction activities, all of which require urgent improvement. Many sources of diverse noise arise from the flow of ambient air, such as airplane engines or wind power generation. Therefore, it is essential to simultaneously consider the engineering requirements of open ventilation areas and efficient noise absorption to ensure not only smooth equipment operation but also reduced noise generation. Consequently, optimizing noise reduction devices is the focal point of this thesis’ abstract. Considering miniaturization and improved absorption performance, the designed sound-absorbing structure in this thesis is based on a quarter-wavelength resonant cavity. Combining this concept with the frequency selective surface(FSS) circuit analogue absorber in the microwave domain, the fractional bandwidth can be increased and analyzed using finite element method (FEM). Firstly, two-dimensional and three-dimensional resonant cavity designs were created, and their miniaturization was validated, ensuring the correctness of the trend in resonance frequency and quality factor Q variations. The design was arranged in a periodic arrangement as a sound wave reflector while maintaining an open ventilation area of over 50% to achieve good air permeability. Next, impedance matching was applied to design the acoustic absorber, and the concept of two stages was used to maximize the absorption coefficient and relative bandwidth. Ultimately, an acoustic absorber was designed that simultaneously achieved high absorption (>90%) and a large open ventilation area (>50%). The simulation results were in excellent agreement in both the two-dimensional and three-dimensional environments. Keywords: Quarter-wave resonator, quality factor, acoustic absorber, absorption coefficient