Generalized holography for imaging elastic structures

Abstract

Generalized holography is a technique for determining the properties of acoustical sources or scatterers [R. P. Porter, Progress in Optics 27, 1989]. In its most general form, the radiating or scattered field and its normal derivative are measured on a recording surface of arbitrary shape. The resulting measurements can be forward propagated into the far field to calculate the radiation pattern. The field can also be backpropagated toward the original source location to generate an image. For the special case of a closed recording surface surrounding the source, the image is independent of the shape of the hologram. Moreover, the image will be independent of evanescent (subsonic) components of the field even when the measurements are made in the near field. This is an important consideration for locating sources of radiation on an object. In this talk, generalized holography is applied to simple elastic structures to determine the modes of vibration. Numerical results will be presented for spherical shells excited by localized surface pressure or by an incident pressure wave.