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由于普通材料的固有耗散在低频区域的微弱性,长久以来,低频声波的衰减一直都是一个颇具挑战性的任务.为了能够在100—1000Hz范围内完全吸收某些频率的低频声波,文章作者设计了一种薄膜型的暗声学超材料样品:它是由在弹性薄膜上镶嵌有一些非对称性的硬质金属片而制成.实验表明,该样品在低频区域几乎能够百分之百地吸收声波,而在共振吸收频率处,空气中的声波波长要比薄膜的厚度大3个数量级以上.当共振发生时,硬质金属片的“拍动”导致很大的弹性曲率能量聚集在金属片的边界附近.由于薄膜的拍动模式与声波的辐射模式仅存在微弱的耦合作用,而弹性薄膜的整体能量密度又比入射声波的能量密度大2—3个数量级,该样品本质上是一个开放的共振腔,这也是它能够高效地吸收低频声波的原因所在.
The attenuation of low-frequency sound waves has long been a challenging task due to the inherent dissipation of common materials in the low-frequency region. In order to be able to fully absorb some frequencies of low-frequency sound waves in the 100-1000 Hz range, A kind of thin-film dark acoustic metamaterial sample is designed: it is made of a hard metal sheet with some asymmetric inlaid elastic films, and the experiment shows that the sample can absorb acoustic waves almost 100% in the low frequency region, At the resonant absorption frequency, the wavelength of the acoustic wave in the air is more than three orders of magnitude greater than the thickness of the film. When resonance occurs, the “flapping” of the hard metal sheet causes a large elastic curvature energy to accumulate in the metal sheet Near the boundary.As the flapping mode of the film has only weak coupling with the radiation mode of the acoustic wave and the overall energy density of the elastic film is in the order of 2-3 orders of magnitude greater than the energy density of the incident acoustic wave, Of the resonant cavity, which is why it can efficiently absorb low-frequency sound waves.