A technique for the in situ phase calibration of in-duct microphone arrays based on rotating sources

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Abstract
In acoustic testing for aircraft engines, duct-mounted microphone arrays are widely used for sound source localization, mode identification, and acoustic liner experiments. Phase calibration of arrays is considered equally critical as amplitude calibration; however, such calibration is often constrained by duct geometry and necessitates repeated disassembly, which poses a risk of mechanical damage. An in-situ microphone array calibration method based on a rotating sound source has been proposed in this paper. Because a rotating source enables frequency-shift of distinct azimuthal modes, the resulting mode-resolved sound fields can be used to distinguish positional phase differences from inter-channel phase errors in single-ring microphone arrays. By combining the proposed axial and single-ring phase calibration techniques, calibration of arrays with a large number of microphones is achieved and validated through Monte Carlo simulations and test rig experiments. Results demonstrate that the proposed method offers the advantages of in-situ calibration within acoustic ducts, compatibility with high-channel-count arrays, and robust, efficient operation.

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