Evaluation of electromechanical coupling factor for a piezoelectric quartz crystal in liquid phase Original Research Article

Based on the Butterworth–Van Dyke (BVD) equivalent circuit model for a quartz crystal, the general equations upon the series resonant-frequency fs, and parallel resonant-frequency fp, were obtained by solving the quadratic equation of frequency at susceptance B=0. Consequently, the electromechanical coupling factor (K) in liquid was first evaluated by using fs and fp. In sucrose solutions, it was seen that K2 decreases as (ρη)1/2 increases, where ρ and η were the density and viscosity of the solution, respectively. It was also interesting to find that K2 linearly correlates with (ρη)1/2 of the media. The regression equation was K2=−1.216×10−6(ρη)1/2+5.204×10−6, correlation coefficient r2=0.9954. Regardless of unknown reason for this linear relationship, it was evident that the values of K2 showed apparent difference when a quartz crystal worked in different media.