Correlations of the impedance parameters and conductivity and permittivityof liquid and gel phases in a series piezoelectric quartz crystal sensor

The impedance characteristics of a series piezoelectric quartz crystal (SPQ C) sensor were investigated using a network/impedance analyzer. The correla tions between the impedance parameters, including the magnitude and phase o f the impedance and the resonant frequencies, and the conductivity and/or t he permittivity of the test solutions were derived theoretically and in goo d agreement with the experimental results. It was shown that the value of t he series frequency (f(s)) decreases with increasing conductivity and permi ttivity of the liquid. The parallel frequency (f(p)) is the constant. The v alues of the maximum impedance (/Z/(max)) and corresponding frequency (f(ma x)), are not related to the conductivity and permittivity of the liquid. Th e value of the minimum impedance (/Z/(min)) decreases with increasing permi ttivity and has a maximum in a solution of middle conductivity. The corresp onding frequency (f(min)) has the same value as the f(s). The maximum phase of the impedance (theta (max)) increases slightly with increasing permitti vity and has a minimum in electrolyte solution of middle conductivity. In t he impedance-frequency curves, there is an iso-impedance point for the SPQC in electrolyte solutions. The SPQC method was applied to monitor the proce ss of hydrogel formation. (C) 2001 Elsevier Science B.V. All rights reserve d.