Sensitivity of various critical frequencies of a QCR sensor in dilute electrolytes

For a quartz crystal resonator (QCR) loaded with a conductive solution, two groups of closely spaced resonance frequencies (f_m , f_s, f_r) and antiresonance frequencies (f _a, f_p, f_n) can be used to characterize the QCR sensor. The variation of all critical frequencies of the QCR sensor in terms of the electrical properties of dilute electrolytic solution is studied. Theoretical expressions, which include the QCR electrode geometrical factor, are obtained for the various frequencies. Experimentally, it is shown that by using a network analysis method, the impedance/admittance can be monitored to accurately track frequency variations in terms of liquid properties. The appropriate frequency of operation, hence the rate of change can then be selected to ensure highest sensitivity and reproducibility