Computational viscothermal acoustic study of micro-electro-mechanical systems (MEMS) perforated plates

Abstract

Micro-perforated plates (MPP) are widely used as sound absorption materials in many noise control applications. Acoustic properties of the MPPs have been theoretically and experimentally studied for many years. The results of these studies are often used in the studies of MEMS devices with perforated plates. However, there exist differences in the physical dimensions of MPPs and MEMS perforated plates. The typical MPP perforation radius is in the range of 1 mm to 1 cm. For these dimensions and audio frequencies, the shear wave-number is much larger than 1. The dimensionless shear wave-number, which is an unsteady Reynolds number, is a measure for the ratio between inertial and viscous effects. Hence for typical MMPs, the inertial effects are dominant. However, the typical hole radius in the MEMS perforated plates is below 20 µm corresponding to subunit shear wave-numbers. Therefore, in MEMS perforated plates, the viscous effects are the dominant part of the impedance. In addition, typical MPPs have low porosities on the order of 1%, whereas typical MEMS perforated plates have high porosities in the range of 25% to 75%. In this work, viscous and thermal losses and also the end effects of the MEMS perforated plates are studied using the finite element method.Micro-perforated plates (MPP) are widely used as sound absorption materials in many noise control applications. Acoustic properties of the MPPs have been theoretically and experimentally studied for many years. The results of these studies are often used in the studies of MEMS devices with perforated plates. However, there exist differences in the physical dimensions of MPPs and MEMS perforated plates. The typical MPP perforation radius is in the range of 1 mm to 1 cm. For these dimensions and audio frequencies, the shear wave-number is much larger than 1. The dimensionless shear wave-number, which is an unsteady Reynolds number, is a measure for the ratio between inertial and viscous effects. Hence for typical MMPs, the inertial effects are dominant. However, the typical hole radius in the MEMS perforated plates is below 20 µm corresponding to subunit shear wave-numbers. Therefore, in MEMS perforated plates, the viscous effects are the dominant part of the impedance. In addition, typical MPPs have low po...