ELECTRICAL SURFACE PERTURBATION OF A PIEZOELECTRIC ACOUSTIC PLATE MODE BY A CONDUCTIVE LIQUID LOADING

Surface loading of a piezoelectric crystal supporting acoustic plate modes (APM) by a dilute conductive liquid is analyzed using a perturbation theory. The formulation of the problem is such that only the electrical loading is relevant and that mass loading and viscous entrainment caused by the solute are ignored. The perturbation in the propagation characteristics is then obtained relative to the solvent and is described in terms of the coupling coefficient, the capacitive loading and the conductivity of the liquid. The results are compared to measurements made on Z-cut X-propagating LiNbO3 APM device loaded with various conductive liquids of different concentrations. While an interpretation of the results can be given on the use of the APM device as a detector of the liquid properties, it is shown that a conductive liquid loading of the piezoelectric surface can be used as a means of assessing the electromechanical coupling coefficient of APM's.