Multi-port techniques for acoustic characterisation of non-linear in-duct discontinuities

This paper discusses techniques for obtaining the acoustic properties of in-duct samples with non-linear acoustic characteristics such as perforates and other facing sheets used in aircraft engine liners and automotive mufflers. It is assumed that the non-linearity occurs locally at constrictions or sharp corners. Multi-port techniques using sinusoidal excitation for better characterization of samples with non-linear properties are developed and experimentally tested. These new techniques take non-linear energy transfer between sound field harmonics into account.

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