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

Abstract

Results are reported on the use of ZX-LiNbOs plate mode devices as detectors for dilute electrolyte or metal ion solutions. 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 are 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 (APM) sensors is observed. These promising results have also led to the investigation of the detection of aqiieous metal ions (Fe3+, Mg'+, Cu2+, .... etc) using solution conductivity changes rather than the commonly used mass sensitivity. The method involves the bonding of metal ions in solution to a chemically modified silica support. The resulting change in conductivity, thus frequency and attmuation, can then be interpreted in terms of the concentration of the specific metal ions.