Abstract:

Near-field acoustical holography (NAH) provides a practical solution to a challenging inverse problem: Calculation of the normal velocity on the surface of a vibrator from the pressure field measured in the acoustic near field of the vibrating surface. Furthermore, NAH uses this same pressure measurement to compute the pressure field at the surface, and throughout the volume of interest. Thus structural vibration and acoustic radiation are reconstructed from a single pressure-array measurement. NAH has been used extensively throughout the years to study the vibration, radiation, and scattering applied to exterior problems, in particular, plates and cylinders. Recent applications, however, have been for interior problems in which the vibrations of the walls surrounding a cavity, as well as the pressure field throughout the cavity, are determined from a two-dimensional, conformal array interior pressure measurement. The aircraft fuselage is a good example of recent applications. Recent research is poised to solve the inverse problem for partially correlated noise sources. This research centers on a spherical measurement antenna for the interior problem, with the inversion relying on decomposition into spherical harmonics along with very fast numerical quadrature algorithms. Most current in this approach is the use of analytic continuation to translate the measured field to a different origin, without the need for further measurement.