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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.

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.

A rapid publicity growth has led to an extensive application of micro-perforated (MP) acoustic elements for broadband sound absorption in the exhaust systems of the internal combustion engine. Most typically, the MPs are exposed to grazing flow conditions, studied thoroughly by various authors in the past decades and represented by adequate acoustic models by now. However, in certain exhaust system designs implemented in the fibreless silencers of modern ground vehicles, an alternative layout for the tubular flow duct MP elements - the flow plug condition has been proven to be useful. In this type of MP’s application, the propagating gas flow is entirely guided through the micro-perforated sections upstream and downstream of the rigid plug, typically increasing the flow resistivity and the viscous damping of the sound in duct. Acoustic studies on such type of MP’s operating condition are scarce.

Micro-grooved elements (MGEs) represent a novel technology developed for noise control in automotive, aerospace and room acoustics. The key concept of the MGEs is based on the use of micro-grooved layers forming micro-paths where the energy dissipation of the acoustic waves is primarily originated by viscous friction. Composed of a multi-layer fiber-less material, the MGEs represent a potential alternative to the traditional fibrous material based solutions as well as to the increasingly popular micro-perforated elements (MPEs). MGEs are designed as cost effective elements, found to be suitable for substitution of fibrous materials, typically present in silencer units. In this paper, a design procedure for a fiber-less small engine silencer based on MGEs is presented and experimentally validated. Hereby, the acoustical performance of the MGEs has been modeled by adapting the theoretical models provided by Allard and Maa for rectangular and circular ducts.