Vibration analysis of plate and shell by laser speckle interferometry

When an optically rough structure is illuminated by laser light, speckles are created throughout the space in front of the surface covered by the reflected wavelets. When the surface is under steady-state vibration these speckles also vibrate accordingly. By recording the speckles contained in a plane in front of the surface as a time average, the resulting speckle interferogram will yield a variety of information upon proper Fourier filtering. One can obtain a complete anti-nodal pattern, a partial antinodal pattern, and partial slope contours from which bending moments can be calculated. The method is applied to shell as well as plate vibration problems.