Absorption performance optimization of perforated plate using multiple-sized holes and a porous separating partition

This research proposes a new type of sound absorptive perforated plate with multiple-sized holes and a porous separating partition in an attempt to extend the sound absorption bandwidth. Separating different sized holes with a porous partition instead of a conventional rigid partition is an unprecedented idea. However, existence of a porous separating partition makes it hard to use theoretical surface impedance models to predict absorption performance. So we introduce appropriate finite element simulation method using the effective density of hole. To consider the end correction effects for hole length and viscosity length of a perforated plate, the effective density of the Johnson-Champoux-Allard model is modified and the end correction lengths of the modified effective density are corrected again in connection with finite element simulation. Material property of a porous separating partition is modeled by the Delany-Bazley material model. After constructing the finite element model, we analyzed the absorption coefficient graphs of perforated plates with two-sized holes and four-sized holes according to the separating partition types: no partition, rigid partition and porous partition. To enhance the wide-band absorption performance, flow resistivity value and thickness of a porous separating partition as well as hole sizes are optimized. From the analysis and design examples, we confirmed that the perforated plate using multiple-sized holes and a porous separating partition can make a continuous frequency range of high absorption coefficient compared to the perforated plate with a conventional rigid partition.