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Description
Microperforated plates are thin plates containing perforations in the submillimeter range. As the incident sound wave penetrates the material, energy is dissipated by friction in the perforations. In this study, the acoustic mechanisms in microperforated plates and foils are investigated. Due to different manufacturing techniques, the investigated materials exhibit different perforation geometries: circular and slitted perforations that form the microperforated absorber. To characterize the materials' absorption behavior, measurements in the impedance tube are performed. Using optimization techniques, the parameters of theoretical models, such as the Maa model, can be obtained. Here, a cost function is defined to optimize the absorption in a specified frequency range using the material parameters and the geometry as design variables. Since the investigations cover circular and slitted plates, the latter require a more in-depth analysis since the Maa model assumes a circular geometry. Here, numerical simulations using the finite element method are employed to accurately model the absorption via a unit cell of the microperforated plate. The numerical computations are based on the linearized compressible flow equations to investigate the viscous dissipation mechanism in depth. Comparisons with measurements suggest that the unit cell simulations can predict the absorption behavior of the microperforated plates well and efficiently, also for more complex slit geometries.