Evaluation of electromechanical coupling factor for a piezoelectric quartzcrystal in liquid phase

Based on the Butterworth-Van Dyke (BVD) equivalent circuit model for a quar tz crystal, the general equations upon the series resonant-frequency f(s), and parallel resonant-frequency f(p), were obtained by solving the quadrati c equation of frequency at susceptance B=0. Consequently, the electromechan ical coupling factor (K) in liquid was first evaluated by using f(s) and f( p). In sucrose solutions, it was seen that K-2 decreases as (rho eta)(1/2) increases, where rho and eta were the density and viscosity of the solution , respectively. It was also interesting to find that K-2 linearly correlate s with (rho eta)(1/2) of the media. The regression equation was K-2=-1.216 x 10(-6)(rho eta)(1/2)+5.204 x 10(-6), correlation coefficient r(2)=0.9954. Regardless of unknown reason for this linear relationship, it was evident that the values of K-2 showed apparent difference when a quartz crystal wor ked in different media. (C) 2000 Elsevier Science B.V. All rights reserved.