Tracking high amplitude auto-oscillations with digital Fresnel holograms

Abstract

Method for tracking vibrations with high amplitude of several hundreds of micrometers is presented. It is demonstrated that it is possible to reconstruct a synthetic high amplitude deformation of auto-oscillations encoded with digital Fresnel holograms. The setup is applied to the auto-oscillation of a clarinet reed in a synthetic mouth. Tracking of the vibration is performed by using the pressure signal delivered by the mouth. Experimental results show the four steps of the reed movement and especially emphasize the shocks of the reed on the mouthpiece.

Comparison between Digital Fresnel Holography and Digital Image-Plane Holography: The Role of the Imaging Aperture

“…This choice is justified as follows: recording a single hologram per instant is a powerful tool to study dynamic events and to carry out high speed acquisition. Examples demonstrating the potentiality of such an approach can be found in [17] for the DFH method and [18,19] for the DIPH one. As we aim at comparing objectively both methods, the same constraints must be applied.…”

Some figures of merit so as to compare digital Fresnel holography and speckle interferometry

“…This choice is justified as follows: recovering a single interferogram is a powerful tool to study dynamic events but also to carry out high speed acquisition and to process interferograms. Examples demonstrating the suitability of such an approach can be found in 30 for digital Fresnel holography and 31,32 for speckle interferometry. As we aim at comparing objectively both methods, the same constraints must be applied.…”

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

“…The parameter of interest is the cyclic ratio α T∕T 0 defined by the ratio between the exposure time T and the vibration period T 0 . Typically, if α ≪ 1, the recording regime is equivalent to a freezing of the object at the instant at which the recording is performed ("impulse regime") [44][45][46][47][48][49][50][51][52]. When, on the contrary, α ≫ 1, the regime is said to be "time-average."…”

“…In the past, the use of stroboscopic [41][42][43] or pulsed light [44][45][46][47][48] resulted in the direct measurement of the vibration amplitude. Such methods are quite useful for modal analysis and the determination of structural intensity [49,50], to measure 3D vibrations [40], surface acoustic wave [51], the high amplitude autooscillations of a clarinet reed [52], or 3D displacement on a cat's post-mortem tympanic membrane [53]. Hybrid techniques combining heterodyne holography with time-averaging or frequency shifting were also proposed recently [54][55][56].…”