Pavan Golakoti, Singh Sneha
Department of Mechanical and Industrial Engineering, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand, 247667, India.
J Acoust Soc Am. 2024 Jan 1;155(1):496-510. doi: 10.1121/10.0023962.
Sound absorption below 1000 Hz has been extremely difficult through traditional barriers and absorbers, but it is required for noise control of appliances and machineries. Existing passive acoustic metamaterials attenuate low-frequency noise but with narrow bandwidths and bulky sizes. Hence, this paper proposes an acoustic metamaterial with enclosed symmetrical labyrinthine air channels and two micro-slits (configuration 1, identical slits; configuration 2, unequal length slits) at the end channels. Its theoretical model is established by acoustic impedance analysis using electro-acoustic analogy and validated numerically and experimentally. Sound absorption is found to happen as a result of impedance matching, Fabry-Perot-like labyrinthine resonances, and thermo-viscous losses in micro-slits. Parametric investigations reveal that increase in the number of channels, channel length, total height, and outer panel thickness shifts sound absorption peak to lower frequency but also decreases the magnitude and frequency range of absorption. Decreasing the channel width and slit width increases the sound absorption magnitude without changing absorption frequencies. Interestingly, unequal slit lengths perform better than equal slits by giving a lower frequency sound absorption with increased magnitude and frequency range, which is unlike that in existing labyrinthine metamaterials. Therefore, the proposed unequal slit metamaterial has enhanced low-frequency sound absorption and can be applied to appliances and machineries.
通过传统的隔音屏障和吸声器在1000赫兹以下实现吸声极其困难，但这对于电器和机械的噪声控制是必需的。现有的无源声学超材料能够衰减低频噪声，但其带宽较窄且尺寸庞大。因此，本文提出了一种声学超材料，它具有封闭的对称迷宫式空气通道，并且在末端通道处设有两个微狭缝（结构1，狭缝相同；结构2，狭缝长度不等）。通过电声类比法进行声阻抗分析建立了其理论模型，并通过数值模拟和实验进行了验证。发现吸声是由阻抗匹配、类似法布里 - 珀罗的迷宫式共振以及微狭缝中的热粘性损耗共同作用的结果。参数研究表明，通道数量、通道长度、总高度和外板厚度的增加会使吸声峰值向低频移动，但也会降低吸声的幅度和频率范围。减小通道宽度和狭缝宽度会增加吸声幅度而不改变吸收频率。有趣的是，不等长狭缝的性能优于等长狭缝，它能够在增加幅度和频率范围的情况下实现更低频率的吸声，这与现有的迷宫式超材料不同。因此，所提出的不等长狭缝超材料具有增强的低频吸声性能，可应用于电器和机械。
