The effect of sensor placement errors on cylindrical near-field acoustic holography

Abstract

This paper presents the results of a numerical investigation of the effects of sensor placement errors on the accuracy of cylindrical near-field acoustic holography (NAH). Results are presented using two data sets, one corresponding to numerically generated hologram plane pressures for a periodically ribbed cylindrical shell, and the other to measured hologram plane pressures for an identical small scale (1/50 scale) physical model. The numerically generated hologram plane pressures are valid in the range ka<4.0, while the experimental data are valid up to ka<20. The motivation for this investigation is to determine whether or not large scale implementation of NAH is feasible given the potentially increased sensor placement inaccuracies which are likely to be encountered at large scale. The effect of both random and systematic axial, circumferential, and radial sensor placement errors are assessed and compared. The majority of the results are presented as wave number comparisons of contaminated and uncontaminated surface pressure reconstructions. It is shown that, as is known to be the case for contamination by background noise, sensor placement errors also result in high wave number noise. Therefore, the success of implementing NAH at large scale when these sensor placement errors are present relies on the selection of a low-pass wave number filter suitable for removing these contaminating factors while preserving the cylinders actual wave number response.