Acoustic impedance regulation of a neck embedded Helmholtz resonator is realized by introducing surface roughness to the neck so as to convert the initially non-perfect sound absorber to a perfect sound absorber. The proposed roughened-neck embedded Helmholtz resonator (R-NEHR) achieves perfect sound absorption ( α > 0.999) at 158 Hz across a deep subwavelength thickness of λ / 42. Theoretical predictions of the R-NEHR's performance are validated against experimental measurements. Physically, surface roughness triggers the periodic concentration effect of fluid vibration in the neck, thereby improving its acoustic mass and acoustic resistance and altering the resonant damping state of the absorber. As a result, the absorption peak position of the R-NEHR shifts by 16.0% to lower frequency, together with a peak value increase of 19.6%. This work provides an approach for perfect sound absorber design and impedance regulation of acoustic metamaterials.

中文翻译：

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亥姆霍兹谐振器的声阻抗调节通过粗糙的嵌入式颈部实现完美的吸声

颈部嵌入亥姆霍兹谐振器的声阻抗调节是通过在颈部引入表面粗糙度来实现的，从而将最初的非完美吸声体转换为完美的吸声体。建议的粗颈嵌入式亥姆霍兹谐振器 (R-NEHR) 在 158 Hz 下在 λ / 42 的深亚波长厚度下实现了完美的吸声 (α > 0.999)。 R-NEHR 性能的理论预测已根据实验测量得到验证。在物理上，表面粗糙度会触发颈部流体振动的周期性集中效应，从而提高其声质量和声阻，并改变吸声器的共振阻尼状态。结果，R-NEHR 的吸收峰位置向低频移动了 16.0%，峰值增加了 19.6%。