Nonscanning measurements for determining in-plane mode shapes in piezoelectric devices with polished surfaces

A nonmechanical scanning method has been developed for the visualization of the in-plane mode shapes of piezoelectric devices with polished surfaces. By taking into account the reflection versus laser-wavelength characteristics of the material of the electrodes, the in-plane motion can be measured even if the surface of the measurement plane is polished like a mirror. This method is based on laser speckle interference and two-dimensional correlation filtering that effectively enhance the mode-shape visualization for bulk and surface acoustic wave devices. Although this method cannot directly measure absolute displacement, the simple measurement system and high speed measurement more than offset this disadvantage. The experimental results for fundamental thickness-shear and nearby inharmonic modes in a bimesa-shaped rectangular AT-cut quartz resonator have been presented. The results of the experiments and the analyses obtained by the three-dimensional finite element analyses correlate well and show the advantages and validity of the proposed technique.