以共振抑制實現超寬頻隔音之可透氣式聲波超材料

Abstract

在本文中，開發了一種由進階的並連雙管道結構（SAPDD）組成的可透氣式聲波超材料，。在實際應用上，這種超材料可以組成一個隔板在微型化的同時實現通風、寬頻隔音和擁有良好的隔音性能以隔離寬頻噪音，並且其薄度可以達到次波長。此超材料之單元是由一對SAPDD組成，其六角蜂窩狀的外型可以在阻隔噪音源時達到更好的包覆率，並且亦能減少彎管效應。此外SAPDD具有兩個兩端開口的管道，利於冷卻用流體散發熱量。由於隔音時最容易漏音的頻率是共振頻率，因此SAPDD利用額外的中間管道連接雙管道，設計能量損失和結點阻抗來達到共振抑制。在本文中，藉由分析聲波於任意截面形狀的管道中傳播，以創建涵蓋彎曲管道和熱黏性效應的精確傳輸線模型，此模型比有限元素分析（FEA）更有效率的優化幾何參數。此傳輸線模型和FEA的結果相當的吻合，並且亦與正向入射實驗在量測區間內的結果非常接近。最終的超材料可以同時實現微型尺寸、通風能力和超寬頻隔音，六角形單元的厚度和體積分別僅為0.06 和 〖6.24×10〗^(-5) λ^3，並具有27.02％ 的空氣通過率及-10 dB的工作頻寬涵蓋422 Hz至5886 Hz，相當於173.24％的分數帶寬。此聲波超材料未來有潛能應用於在有限空間內達到降噪並且需考慮散熱的情況。

In this thesis, a ventilated acoustic metamaterial composed of the structure of advanced parallel dual ducts (SAPDD) is developed to attain ventilation capability, broadband insulation, and insulation performance simultaneously in a miniature size. Practical applications have demonstrated that this metamaterial can constitute a panel to block broadband noises, and its thinness can reach subwavelength. A pair of the SAPDD composes a unit cell of the proposed metamaterial; the hexagonal honeycomb appearance can achieve better packing efficiency and reduce curved duct effects. Furthermore, the SAPDD has two ducts with open ends for coolant to dissipate the heat. Because the most critical frequencies for sound insulation are resonant frequencies, a SAPDD utilizes an additional middle duct connecting the dual ducts and successfully suppresses resonance with the appropriate design of energy losses and impedance at junctions. In this paper, the acoustic wave propagating in a duct of an arbitrary cross-sectional shape is analyzed in detail to create a precise transmission line model covering curved duct effects as well as thermoviscous effects and providing a method more efficient than finite element analysis (FEA) to optimize the geometric parameters. The results of the transmission line model and the FEA fit those of the normal incidence determination very well within the measured frequency range. The finalized metamaterial simultaneously achieves miniature size, ventilation capability, and ultra-broadband sound insulation. The thinness and the volume of the hexagonal unit cell are only 0.06 and 〖6.24×10〗^(-5) λ^3, respectively. Furthermore, the metamaterial has an air passage rate of 27.02 % and a -10 dB bandwidth ranging from 422 Hz to 5886 Hz, which equals a fractional bandwidth of 173.24 %. This metamaterial has great potential in the applications of sound insulation that require little space and are efficient in ventilation.