Optimization of a liquid conductivity sensor using the lateral electric field excited resonator on a PZT ceramics

The influence of a conductive liquid on the characteristics of a lateral electric field resonator made of PZT-19 ceramic was experimentally studied with varying gap widths between the electrodes. At a fixed gap width, the frequency dependences of the real part of the electrical impedance were measured for different liquid conductivities for each of the three observed resonances. It turned out that as the liquid's conductivity increases, the resonant frequency initially does not practically change, then decreases in the range of 30 - 500 μS/cm and then remains constant. At that, the maximum value of the real part of the electrical impedance decreases in the conductivity range of 1-100 μS/cm and then remains practically unchanged. It has been shown that the growth of the gap width at a fixed liquid conductivity leads to an increase in the parallel resonance frequency and the maximum value of the real part of the electrical impedance. This leads to increasing the slope of the dependences of these parameters on the liquid conductivity and to the gain of the sensor's sensitivity to the changes in liquid conductivity. A comparison of the theoretical dependences of the resonant frequency and the maximum value of the real part of the electrical impedance on the conductivity of the liquid, obtained by the finite element method, showed their quantitative and qualitative agreement with the experiment. At that, the theoretical maximum value of the real part of the electrical impedance turned out to be somewhat higher than the experimental ones due to the influence of the liquid container, which was not taken into account in the theory.