Effects of Geometric Parameters on Sound Absorption in Perforated Plates with Elliptical Holes

Perforated plates are fundamental components in sound absorption applications, often employed as resonant sound absorbers in various configurations. Typically, these configurations involve multilayer systems, where perforated plates form the initial layer. The simplest arrangement consists of a perforated plate and a backing air layer. The air mass within the holes acts as the inertial component of the resonant system, while the air backing layer serves as the restitutive force. The effective inertial mass of the perforations is subject to change based on the geometrical configuration of these systems. In contrast to conventional perforated plates with circular or square holes, elliptical perforations offer increased degrees of freedom in the geometrical configuration, with only limited systematic studies conducted to date. This study aims to systematically investigate the effects of geometrical parameters, such as form factor (eccentricity) and orientation angle, on the sound absorption characteristics of perforated plates with elliptic holes. A comprehensive experimental study was conducted using 3D-printed perforated plates. The sound absorption coefficient of the resonant system (comprising an air gap and an elliptic perforated plate) was measured in an impedance tube. Throughout the measurements, the air gap thickness was kept constant. For similar porosity and hole area, the effects of eccentricity on the sound absorption characteristics were relevant in increasing the absorption, whereas the impact of the orientation angle on the sound absorption coefficient was quite negligible with increasing the dimensions. This experimental campaign provides valuable insights into the influence of geometric parameters on the sound absorption properties of perforated plates with elliptical holes. The precise geometry of the hole pattern was identified as a crucial factor for tuning the frequency response of sound absorption systems. Future studies should expand on this research by exploring additional configurations and incorporating numerical simulations or analytical models for a more comprehensive understanding.