Lee M., Bolton J.

The use of DFT-based near-field acoustical holography (NAH) for sound field visualization is attractive since it is efficient in terms of computation time; it also allows a sound field to be decomposed into wave number components, thus providing physically meaningful information about the sound field (by distinguishing between propagating and evanescent wave components, for example). However, the application of DFT-based NAH is sometimes limited due to the requirement that a sound field should be sampled with a uniform spacing on a surface of constant coordinate in a separable geometry and that the hologram be sufficiently large to avoid spurious effects resulting from the undue truncation of the sound field. To-date, various methods have been introduced to relieve the strictness of the second requirement. Of them, patch holography mitigates the finite measurement aperture effect by extending the sound field beyond the measurement aperture based on the use of an iterative algorithm. In the present work, the applications of the latter method in the context of DFT-based NAH were expanded. Specifically, a multi-patch holography procedure is described that allows a sound field to be reconstructed from hologram pressures measured over multiple, unconnected patches. A related approach also allows spatial resolution enhancement by interpolation between measured points, which helps to improve the reconstruction accuracy, particularly at high frequencies. The validity of the proposed approach is supported theoretically based on the concept of alternating orthogonal projections, and numerical simulation results obtained by using a synthetic sound field created by a point-driven, simply supported plate are presented.