ANALYSIS OF ELECTRICAL EQUIVALENT-CIRCUIT OF QUARTZ-CRYSTAL RESONATORLOADED WITH VISCOUS CONDUCTIVE LIQUIDS

An electrical equivalent circuit of quartz crystal resonator (QCR), wi th modified electrodes, loaded with a viscous conductive liquid is pro posed. The electrode in contact with the liquid is modified so as to c reate an unmetallized crystal surface in contact with the liquid and t hus to introduce an acoustoelectric interaction at the crystal/liquid interface. The admittance-impedance characteristics of the equivalent circuit of the loaded QCR are analyzed to obtain expressions for the c hanges in the series and parallel resonant frequencies in terms of the liquid viscosity eta(L), density rho(L), dielectric constant epsilon( L), and conductivity sigma, as well as the quartz parameters and elect rode area geometry. Using a network analyzer, the S parameters of the equivalent circuit of various conductive liquid-loaded QCRs are measur ed and analyzed. It is shown that in addition to being a well-known de tector of mechanical properties of liquids, a QCR, when properly desig ned, can be used to monitor the electrical properties of dilute ionic solutions.