Double-layer micro-perforated panels (MPPs) have been studied extensively as sound absorption systems to increase the absorption performance of single-layer MPPs. However, existing proposed models indicate that there is still room for improvement regarding the frequency bands of absorption for the double-layer MPP. This study presents a double-layer MPP formed with two single MPPs with inhomogeneous perforation backed by multiple cavities of varying depths. The theoretical formulation is developed using the electrical equivalent circuit method to calculate the absorption coefficient under a normal incident sound. The simulation results show that the proposed model can produce absorption coefficient with wider absorption bandwidth compared with the conventional double- and even triple-layer MPPs. The bandwidth can be increased to higher frequency by decreasing the cavity depth behind a sub-MPP with small hole diameter and a high perforation ratio, and to lower frequency by increasing the cavity depth behind a sub-MPP with large hole diameter and a small perforation ratio. The experimental data, measured by impedance tube, are in good agreement with the predicted results.

中文翻译：

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具有多个腔深的双层不均匀微穿孔板的吸收系数

双层微孔板（MPP）已作为吸声系统进行了广泛的研究，以提高单层MPP的吸收性能。但是，现有的建议模型表明，双层MPP的吸收频带仍有改进的空间。这项研究提出了一个双层MPP，该MPP由两个具有不均匀穿孔的单个MPP组成，并由多个深度不同的腔体作为支撑。使用等效电路方法开发理论公式，以计算法向入射声下的吸收系数。仿真结果表明，与传统的双层甚至三层MPP相比，该模型可以产生具有更宽吸收带宽的吸收系数。可以通过减小孔径较小且穿孔率较高的子MPP后面的腔深度来将带宽增加到较高的频率，而通过增大孔径较大且穿孔率较小的MPP后面的腔体深度可以将带宽增加到较低的频率比。用阻抗管测得的实验数据与预测结果吻合良好。