Interferometric hologram evaluation and real-time vibration analysis of diffuse objects

Vibration studies on some integral rib-stiffened plates

This paper describes a digital holographic setup based on in-line holography and a high-speed recording to get a multipoint vibrometer. The use of a high-speed sensor leads to specificities that enable the in-line configuration to be used. The case of transient vibrations is investigated through a full simulation of the holographic process. The simulation shows that the first instants are critical since distortion may occur, resulting in errors in the phase measurement. Experimental results are provided by exciting an aluminum beam with a transient signal. A comparison with the velocity measured by a pointwise vibrometer is provided. Frequency response functions are extracted and the experimental results confirm the ability of the method to provide full-field contactless measurements at the high-speed time scale evolution of the vibration.

Multi-point vibrometer based on high-speed digital in-line holography

Stroboscopic holographic interferometry: Application of digital techniques

This paper proposes a first attempt to visualize and analyze the vibrations induced by a bone-conduction device and propagating at the surface of the skin of a human face. The method is based on a new approach in a so-called quasi-time-averaging regime, resulting in the retrieval of the vibration amplitude and phase from a sequence of digital Fresnel holograms recorded with a high image rate. The design of the algorithm depends on the ratio between the exposure time and the vibration period. The results show the propagation of vibrations at the skin surface, and quantitative analysis is achieved by the proposed approach.

Evaluation of surface acoustic waves on the human skin using quasi-time-averaged digital Fresnel holograms

The application of time-averaged holography to the analysis of vibrating surfaces is now a widespread and very powerful experimental technique. However, the realtime method of exactly superimposing the reconstructed static image on the vibrating object and observing the resulting fringe patterns under stroboscopic illumination is becoming more common. In fact, by introducing an initial family of interference fringes by the rotation of the object (or image) before vibration begins, the advantages of both methods are combined.

S. D. Liem

Papers

Vibration analysis of plates by real-time stroboscopic holography