Extended investigations on micro-grooved elements - a novel solution for noise control

The goal of this paper is to provide a complete characterization of acoustic performance for a novel type of advanced acoustic material - micro grooved element (MGE). In a previous study, the MGEs have been proved to offer a respectable alternative for the existing and increasingly popular micro perforated elements (MPEs). The MGEs are multi-layer elements where the acoustic attenuation effect originates from viscous losses taking place in a number of sub-millimeter grooves forming acoustic micro-paths inside the material. This new configuration allows to replace the laser perforation process, used to manufacture the MPEs, with less time consuming and more cost effective technologies. Moreover, such elements preserve low weight and surface roughness. Experiments have demonstrated that the MGEs can be regarded as suitable solution for noise control in a wide range of applications. In this work, the transfer impedance and the absorption coefficient of a number of MGEs, composed of geometrically different apertures, have been investigated by using the classical two-port method. The effect of the main geometrical parameters controlling the acoustic performance has been analyzed and modeled. Also, the interaction between the micropaths has been studied. The non-linear behavior, observed in the presence of high excitation levels has been included in the model. The acoustic impedance of the micro-grooved elements has been derived from the experimentally obtained TL curve in the presence of grazing flow. Consequently, the model developed for MGEs has been further extended to the grazing flow conditions and compared to the well-known models proposed by Rice for micro-perforated elements.