A new liquid sensor based on a piezoelectric resonator with a radial electric field

The possibility of development a liquid sensor based on a piezoelectric resonator with radial concentric electrodes is shown. The specified resonator has a large number of resonance peaks corresponding to different vibrational modes. The influence of two types of liquid container with distilled water on the resonance characteristics of these vibrational modes is experimentally investigated. As a result, the optimal type of container and two vibrational modes with frequencies of 0.128 and 0.317 MHz were selected, which retain acceptable Q-factors in the presence of distilled water. The dependences of the resonance frequency and the maximum value of the real part of the electrical impedance of these resonance peaks on the conductivity of the liquid were measured. It has been found that with an increase in the conductivity of the liquid, the resonance frequency of the parallel resonance initially remains practically unchanged, but after reaching a certain value of the conductivity of water, it decreases for both resonances. In this case, the maximum value of the real part of the electrical impedance first decreases, reaches a minimum, and then increases in all cases. It is shown that using these dependences as calibration curves, one can unambiguously determine the conductivity of a liquid in the range of 45-5000 μS/cm.