Identification of antinodes and zero-surface-strain contours of flexural vibration with time-averaged speckle pattern shearing interferometry

Abstract

A new time-averaged frame subtraction technique is introduced for vibration analysis by digital speckle shearing interferometry. The technique permits the enhancement of fringes by subtracting two Bessel fringe patterns at different forcing levels. Compared with the phase-shift method, this method is more efficient and easier to implement for qualitative vibration measurement, providing a means for fast inspection of plate vibration behavior. It is also capable of tracing contours of zero strain and locating antinodes on vibrating plates.

Prospects for speckle-pattern based vibration sensing in electromechanical equipment

“…Although originally introduced for the measurement of bending moments [74], ESSI is also applied to vibration measurement-an area which is currently attracting much interest [75][76][77][78][79][80][81][82][83][84]. ESSI uses single-beam illumination of the vibrating object, similarly to out-of-plane ESPI, but the reflected signal passes through a beam-splitting element so that two laterally displaced (or sheared) images are focused on to the CCD camera (figure 9).…”

“…In the technique of electronic speckle-pattern interferometry (ESPI) , the speckle distribution is combined usually with a smooth (spatially filtered) interferometric reference, providing a correlation interferogram (correlogram) of fringes representing the displacement profile of the surface. In a variation of ESPI known as electronic speckle-shearing interferometry (ESSI) [74][75][76][77][78][79][80][81][82][83][84], two sheared images of the surface interfere, so that the correlation fringes contour the spatial derivative of the displacement in the shear direction. Although ESSI is directly suited to strain monitoring, it is less sensitive to whole-body instability and turbulence than ESPI, making it an attractive alternative method of vibration measurement.…”