Micro-Grooved Elements - A Novel Solution for Noise Control

The goal of this paper is to present a novel type of advanced acoustic material - micro grooved element (MGE) - which is designed for noise control in a wide range of applications. MGEs have been proved to offer a respectable alternative for the existing micro-perforated elements (MPEs), while being cost effective and causing low pressure loss. These elements have been found to be suitable for substitution of fibrous materials, typically present in silencer units. Currently, the cost of the MPEs is relatively high due to the technological complexity of manufacturing process. On the other hand, cheaper solutions of MPEs, based on irregularly shaped micro-apertures, potentially cause higher pressure loss due to surface roughness. The key concept of the MGEs is the use of micro-grooves forming acoustic channels, instead of the micro-holes of MPEs, which the sound wave has to pass. This allows to replace the laser perforation process, used to manufacture the MPEs with circular cross section, with less time consuming and more cost effective alternatives. The acoustical performance of the MGEs has been modeled by adapting the theoretical models provided by Allard and Maa for rectangular ducts, circular duct and non-linearities. The transfer impedance and the absorption coefficient of a number of MGEs and of several types of MPEs have been experimentally measured and compared by using the classical two-port method. Additionally the non-linear behavior of such elements has been experimentally investigated by varying the excitation sound pressure level during the tests.