For quite a number of years Electronic Specklepattern Interferometry (ESPI) has been an attractive alternative to Holographic Interferometry in industrial surroundings. As for conventional holographic interferometry, the information which is primarily obtained, is an image of the object superposed by a fringe pattern related to object motion. For harmonic loading integration over many periods leads to Besselfringes whereas subtraction mode used for deformation analysis leads to cosinefringes. In both cases a qualitative evaluation can be performed by visual inspection of the fringe pattern whereas quantitative analysis requires digital image processing, the latter becomning increasingly attractive with the access to more efficient PC's. A very prominent feature of ESPI is the possibility of aquiring one "hologram" per 1/25 sec. This makes it possible to obtain information of both vibrational amplitudes and phases within reasonable timeframes. This paper presents results of qualitative ESPI measurements on two transducers (an electretmicrophone and an accelerometer) identifying critical resonances. In both cases the measurements resulted in improved transducerdesign. Further presented are results of quantitative deformation analysis by phaseshifted ESPI followed by digital imageprocessing using a very simple phaseshift algorithm.
"ESPI Used Qualitatively For Vibration Analysis And Quantitatively For Deformation Analysis", Proc. SPIE 1183, Holography '89, (12 April 1990); doi: 10.1117/12.963838; https://doi.org/10.1117/12.963838