Applications of lithium niobate acoustic plate mode as sensor for conductive liquids

Results on the use of Z-cut, X-propagating LiNbO₃ plate mode devices as detectors for dilute electrolyte or metal ion solutions are reported. It is shown that a relatively strong external electric field associated with the selected SH plate wave penetrates into an adjacent liquid and interacts with ions and dipoles. The resulting electrical loading leads to a measurable perturbation in the wave propagation characteristics, which can then be related to the liquid properties. Experiments were conducted with various aqueous and nonaqueous solutions, at various device frequencies. An increase in sensitivity and resolution of at least two orders of magnitude greater than that of previously reported acoustic plate mode sensors is observed. These promising results have also led to the investigation of the detection of aqueous metal ions (Fe³⁺, Mg²⁺, Cu²⁺, etc.) using solution conductivity changes rather than the commonly used mass sensitivity