Frequency-dependent, near-pole behavior of acoustic surface waves on a solid sphere

A laser vibrometer is used to measure waves generated by a piezoelectric transducer in a solid steel sphere. The spatial and temporal resolution make it possible to verify the theoretical dispersion relation of spherical surface waves. In particular, the area at the source antipode is investigated. The focusing of surface waves results in high-amplitude surface displacements in this area, which is therefore interesting in terms of seismic research and the understanding of the dynamic behavior of granular media. The influence of frequency on the diameter of the focal area is measured using windowed sine bursts as a source. As an example of the complex wave behavior near the poles, the interference of converging and diverging surface waves is demonstrated. (C) 2014 Elsevier Ltd. All rights reserved.