Refracto-vibrometry - a novel method for visualizing sound waves in transparent media

Abstract

For optimization of new sonic techniques, for development of acoustic sensors or for understanding of complex sonic phenomena it is often desirable to visualize the generation and distribution of the invisible sound waves. A novel method for measuring and visualizing the sound waves in transparent media was developed and tested by the authors. This non-contact method is based on a scanning laser-Doppler vibrometer. It can be used for measuring and visualizing sound fields in gases, fluids and even pellucid solid objects. The variation of the optical refractive index n of transparent media, caused by the sound waves is used as measuring effect. This justifies the denomination "refracto-vibrometry". The paper describes the theoretical fundamentals and the technical equipment required for the novel method. As examples, the generation and radiation of sound in air, water and transparent solid objects are presented. The animation of the results as videos is very impressive and instructive. In research, education and system design refracto-vibrometry has a large potential to make acoustics clearer and more feasible for application.