### ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

## 2aSA9. Generalized holography for imaging elastic structures.

**Robert P. Porter
**

**
Daniel Rouseff
**

**
**
*Appl. Phys. Lab., Univ. of Washington, Seattle, WA 98105
*

*
*
**David Bennink
**

**
**
*Appl. Measurement Systems, Bremerton, WA
*

*
*
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.