Refracto-vibrometry for visualizing ultrasound in small-sized channels, cavities and objects

A novel method for measuring and visualizing actually invisible ultrasound in transparent media was developed and tested by the authors. This non-contact method is based on a conventional Scanning Laser-Doppler Vibrometer (SLDV). As measuring effect the variation of the optical refractive index n of transparent media, caused by ultrasound, is used. This justifies the denomination ¿refracto-vibrometry¿. The method can be applied to measuring and visualizing ultrasound fields in gases, liquids or pellucid solid objects even in small-sized dimensions. The paper summarizes the theoretical fundamentals of the method and describes the technical equipment and the know-how required for effective measurements. As examples the propagation, reflection and absorption of ultrasound in narrow channels with perpendicularly arranged branch lines, in cavity resonators and in cm-sized Perspex objects are presented.