Martin Gutierrez V.
Inst. of Acoust., Universidad Austral de Chile, Casilla 567, Valdivia, Chile
Since near-field acoustic holography (NAH) is a powerful tool to investigate the sound radiation of a wide range of sources immersed in a homogeneous medium, a corrective model for the presence of inhomogeneities in the near field, where the hologram is performed, is presented. Strong temperature gradients modify the propagation of the sound wave, because they modify the density of the medium and then the sound speed. Many models were developed to take into account this and other effects; most of them were proposed in the atmospheric sound propagation area. The actual model was developed to minimized the effect of temperature gradients in the near field. An early model, previously presented [M. Gutierrez and J. Arenas, J. Acoust. Soc. Am. 96, 3263(A) (1994)], based on the spatial transformation of sound fields technique, was modified in order to obtain a new mathematical expression based on a multilayered Green's function. Some theoretical sources were numerically tested with the new model, which supposed a disturbance during heat transmission to the free air by an ``omnidirectional'' heat source. The comparative results between NAH theory and the proposed model will be shown.