Interior holography.

Abstract

Interior spaces with vibrating walls embrace a broad set of structural acoustic problems (planes, trains and automobiles). In the hunt for efficient measurement schemes that provide details of both the acoustic and structural fields, inverse holographic methods are very promising. These methods use a surface of measured data and mathematically back-track the field in time and space filling in a 3-D volume around the array in the process and are particularly attractive since they can image the time averaged acoustic intensity vector, localizing and quantifying surface sources. There is a score of holographic back-propagation methods in use today. In almost all cases single measurement surfaces are not accurate due to reverberation and dual conformal surfaces are needed to separate sound fields coming from forward and backward directions. The spherical array (open or rigid) is a noticeable exception, an accurate mathematical approach is obtained with only one surface of data. This paper presents an overview of the inverse problem in interior spaces paying particular attention to the rigid spherical array, discussing improvements that extend the frequency range and volume of study, and simple regularization methods to stabilize the ill-posed nature of the volumetric reconstructions. [Work supported by ONR.]