Full-field vibrometry with digital Fresnel holography

Abstract

A setup that permits full-field vibration amplitude and phase retrieval with digital Fresnel holography is presented. Full reconstruction of the vibration is achieved with a three-step stroboscopic holographic recording, and an extraction algorithm is proposed. The finite temporal width of the illuminating light is considered in an investigation of the distortion of the measured amplitude and phase. In particular, a theoretical analysis is proposed and compared with numerical simulations that show good agreement. Experimental results are presented for a loudspeaker under sinusoidal excitation; the mean quadratic velocity extracted from amplitude evaluation under two different measuring conditions is presented. Comparison with time averaging validates the full-field vibrometer.

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

“…Its influence has been described in [44,61,62]. The combined effect of amplitude and cyclic ratio was especially thoroughly discussed in [44]. In the present paper, we consider an intermediate recording regime that has not been discussed in literature: the quasi-time-averaging regime, for which the cyclic ratio can be qualified as moderate.…”

“…Its value is related to the possibility to reconstruct, without any error, the vibration from a synchronous hologram sequence. In 2005, Leval et al [44] demonstrated the possibility to reconstruct the sinusoidal mechanical vibration by recording a sequence including three digital holograms. To do so, the holograms must be synchronously phaseshifted with the vibration and the cyclic ratio must satisfy α < 1∕Δφ m .…”

“…A solution may lie in the use of stroboscopic [37,38] or pulsed light [39][40][41][42][43][44], which results in the direct measurement of the vibration amplitude. Such methods are quite useful for modal analysis and the determination of structural intensity [45,46], to measure 3D vibrations [47], surface acoustic wave [48], the high amplitude autooscillations of a clarinet reed [49] or 3D displacement on a cat's post-mortem tympanic membrane [50].…”

“…Its influence has been described in [44,61,62]. The combined effect of amplitude and cyclic ratio was especially thoroughly discussed in [44].…”

Investigation of dynamic of unconsolidated materials using two-color digital holography

“…The measurement principle leads to a 3-frame phase shifting algorithms, described in [9], which allows the determination of 3D amplitude and phase of the movement.…”