The concept of microperforated noise control treatments was introduced by Maa 1975; in that theory, the transfer impedance of the microperforated layer was calculated based on oscillatory viscous flow within a small cylinder combined with resistive and reactive end corrections. Initially, microperforated materials were the subject of mostly academic study since practical implementations were rare owing to the cost of manufacturing the materials with acceptable accuracy. However, recently, new manufacturing procedures have dramatically lowered the cost of these materials, and perhaps as a result, there has been renewed interest in studying their properties. Since 1975, Maa’s original theory has been widely used to predict the performance of microperforated materials. However, in principal, that theory can only be used to describe cylindrical perforation, while in practice, perforations are rarely cylindrical. In addition, there have been questions about the dependence of end corrections on frequency, and on the effect of coupling between the motion of the fluid in the perforations and the solid sheet in which they are formed. Additionally, in his original paper, Maa drew a distinction between the dissipative properties of thermally conducting and adiabatic materials. The latter topic, in particular, has not been considered by any investigators since the idea was introduced. The purpose of our presentation is to introduce the numerical tools that can be used to address the open questions mentioned above, and to highlight important results obtained by using those tools.
microperforated panels, thermal dissipation, viscous dissipation, flexibility
Acoustics and Noise Control
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