This study seeks to improve the understanding of the acoustic characterisation of micro-perforate panels. It describes the development of a semi-empirical, single degree of freedom model, which predicts the impedance as a function of each of the panel effective geometric parameters, the installed flow, and the incident noise source conditions. The paper reports on both no flow normal impedance tube tests, and grazing flow in-situ impedance tests, performed on single layer micro-perforate liner configurations, sized for typical aircraft engine inlet applications, at high sound pressure levels (up to 155dB), and at high grazing flow Mach numbers (up to M0.7). The work shows that, in contrast to traditional perforates, the acoustic resistance of small hole diameter (＜ 300 microns) micro-perforate sheets has a significant linear component under zero grazing flow, which must be well captured in order to ensure accurate modelling of these panels. Test data also show the sheet inertance of a micro-perforate to be lower than that of a traditional perforate with the same open area. An improved prediction of the sheet mass reactance has also been established.
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