High-stability sound transmission loss measurement method for acoustic metamaterials under grazing flow conditions

With the advancement of the practical application research of acoustic metamaterials, their performance under flow conditions becomes increasingly critical. However, the presence of flow field influences will greatly increase the complexity of predicting and evaluating acoustic metamaterial characteristics. Reliable results can be obtained through experimental methods, yet they face challenges in achieving high precision and stability under flow conditions. To overcome these challenges, this study proposes a High-stability Measurement Method (HSMM) for measuring sound transmission loss (STL) under grazing flow. The conventional scattering matrix describes the system performance of the sample and specific boundary rather than the inherent properties of the sample itself. In addition, the conventional transfer matrix is unaffected by the boundary conditions, but it has high requirements for the testing environment. Based on this, by introducing the self-spectrum and cross-spectrum signal processing methods into the transfer matrix method, we derive an adjusted transfer function H_ij for STL calculation. This study examines two acoustic structures through both numerical simulation and experimental validation using the HSMM. The results demonstrate that the proposed HSMM can significantly reduce the outliers and data fluctuations compared to the conventional transfer matrix method, demonstrating superior measurement stability. The experimental results are in good agreement with the numerical simulation results; validating STL in the range of 1–1600 Hz can be accurately measured under grazing flow conditions.