In this work, we propose a spiral metasurface for multi-order sound absorption in the low-frequency range (<1000 Hz). By dividing the long channel of the spiral metasurface into a series of tunable sub-cavities and employing recessed necks, the metasurface can quasi-perfectly (>0.95 in experiments) absorb airborne sound at multiple low-frequency orders without being limited by the number of equivalent cavities. Owing to the superior impedance manipulation provided by the spiral metasurface, each absorption order can be tuned flexibly with a constant external shape. By suitably modulating the sub-cavities and the recessed necks, we obtained multi-order high-absorption metasurfaces with dual-chamber, tri-chamber, and four-chamber designs. The ratio of the lowest resonant wavelength to the thickness is as high as 78. The samples, which are fabricated by three-dimensional printing technology, were measured to verify the theoretical results. We also investigate the relationship between the geometric parameters of the recessed necks and the sound absorption performance, which facilitates the more feasibly designed multi-order metasurfaces. The concept can be further applied to broadband absorption with ultra-thin thickness and has potential applications for noise reduction.

中文翻译：

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基于螺旋超表面的低频多阶吸声体

在这项工作中，我们提出了一种用于低频范围 (<1000 Hz) 多阶吸声的螺旋超表面。通过将螺旋超表面的长通道划分为一系列可调谐的子腔并采用凹陷的颈部，超表面可以准完美地（实验中>0.95）吸收多个低频阶的空气声，而不受数量的限制。等效腔。由于螺旋超表面提供了卓越的阻抗控制，每个吸收阶次都可以灵活调整，具有恒定的外部形状。通过适当调节子腔和凹颈，我们获得了具有双腔、三腔和四腔设计的多阶高吸收超表面。最低谐振波长与厚度之比高达78。样品，对采用三维打印技术制作的样品进行测量以验证理论结果。我们还研究了凹陷颈部的几何参数与吸声性能之间的关系，这有助于更可行地设计多阶超表面。该概念可以进一步应用于超薄厚度的宽带吸收，并具有降噪的潜在应用。