Absolute vibrational displacement measurements based on laser speckle method with burst resonator driving

A non-mechanical scanning method has been developed for mapping absolute vibrational patterns of piezoelectric devices based on a burst drive laser speckle method. By taking into account the statistical treatment for the distributions of the speckle intensity, the absolute vibrational shapes can be visualized. This method is based on a simple relation of coherent light interference on device surfaces and the linear relation of piezoelectricity. To derive the visibility, g, which is mandatory for determining absolute displacement, a polynomial approximation is applied to an expression of the surface interference. This is because g is not directly obtained from general interference equations when the device being tested is excited by the burst signal. Although the sensitivity of this method is lower than that of the synchronized laser speckle system that we proposed at 2005 FCS1, the simple measurement system and wide frequency range more than offset this disadvantage. The experimental results for AT-cut quartz resonators are presented