Deconvolution of azimuthal mode detection measurements

• Published in: Journal of sound and vibration 2018-05, Vol.422, p.1-14
• Main Authors: Sijtsma, Pieter, Brouwer, Harry
• Format: Article
• Language: English
• Subjects: Acoustic beamforming; Acoustics; Algorithms; Azimuthal mode detection; Beamforming; Broadband; Deconvolution; Dynamic range; Noise; Non-equally spaced array; Point spread functions
• ISSN: 0022-460X; 1095-8568
• DOI: 10.1016/j.jsv.2018.02.029

Unequally spaced transducer rings make it possible to extend the range of detectable azimuthal modes. The disadvantage is that the response of the mode detection algorithm to a single mode is distributed over all detectable modes, similarly to the Point Spread Function of Conventional Beamforming with microphone arrays. With multiple modes the response patterns interfere, leading to a relatively high “noise floor” of spurious modes in the detected mode spectrum, in other words, to a low dynamic range. In this paper a deconvolution strategy is proposed for increasing this dynamic range. It starts with separating the measured sound into shaft tones and broadband noise. For broadband noise modes, a standard Non-Negative Least Squares solver appeared to be a perfect deconvolution tool. For shaft tones a Matching Pursuit approach is proposed, taking advantage of the sparsity of dominant modes. The deconvolution methods were applied to mode detection measurements in a fan rig. An increase in dynamic range of typically 10–15 dB was found.