Because its underlying principles are so fundamental, holography has been studied and applied in many areas of science. Recently, a technique has been developed which takes the maximum advantage of the fundamental principles and extracts much more information from a hologram than is customarily associated with such a measurement. In this paper the fundamental principles of holography are reviewed, and a sound radiation measurement system, called nearfield acoustic holography (NAH), which fully exploits the fundamental principles, is described.

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Transverse impact problems have recently been solved by several different methods including Timoshenko's integral equation method, the energy method, and the finite element method. This paper presents a lumped parameter method (LMP) for impact analysis, which is attractive for the solutions of impact of complex bodies. The advantages are in its simplification of mathematical formulation, computational efficiency, and improved understanding of the coupling effect of excited modes on the occurrence of multiple impacts. Experimentally obtained information of the dynamic characteristics of these impacting bodies permit easy extension to nonsimple body shapes.