Quartz resonators as effective detectors for dilute conductive liquids

AT-cut quartz crystal resonators (QCR) have been recently investigated as mass and viscosity detectors in liquid environments. Some experiments have also suggested that the QCR can be used to detect electrical properties of liquids. It has been pointed out by others that the absence of a surface potential on a grounded electrode will prevent such interaction which can only be due to fringing fields. In the present work, it is shown that by modifying the geometry of the electroded surface in contact with the solution, the electrical field in the unelectroded region can be enhanced. This field can interact with an adjacent conductive solution which will result in relatively large changes in the parallel resonance conditions. Experiments conducted with such electrodes on AT-cut quartz show the use of QCRs as effective and reliable detectors in conductive liquid environments. The results are also discussed in terms of changes in a proposed electrical equivalent circuit