Full-field investigation of traveling acoustic waves with digital holography

In the domains of acoustics, vibro-acoustics, vibrations of structures or flow-induced vibrations, Laser Doppler Vibrometer is the most used for dynamics measurements. To get simultaneously a collection of data points at the surface of the inspected vibrating object, multipoint vibrometers were developed. Full-field evaluation can be obtained with coherent imaging based on digital holographic interferometry. Such an approach is well suited because of the high density of measuring points and the reduced measurement time. The use of time-averaging and quasi-time-averaging in digital Fresnel holography was proposed and discussed in the past. However, the stationary regime is a particular case for investigating the structure vibration behavior (propagation of travelling waves), and the characterization of structures under operational or real functioning conditions requires analysis in the time domain. Then, providing a real-time follow-up of the vibration amplitude, whatever the excitation condition is a challenge for full-field optical metrology. This paper aims at describing recent advances in high-speed coherent imaging based on digital holography; especially we will focus on the use of such an approach to investigate traveling acoustic waves in mechanical structures.