Modelling and experiments on a quartz crystal resonator sensor for conductivity measurements of low-concentration ionic solutions

The monitoring and control of the electrical parameters of ionic solutions have different applications in industry and are particularly important in medical and biochemical studies, where ionic solutions are commonly used. This paper analyzes the effect of the conductivity of a low-concentration ionic solution on the resonant response of a Quartz Crystal Resonator (QCR) sensor with asymmetric electrodes put in contact with the solution. A model of the QCR sensor is presented, and experimental results obtained with a 6-MHz sensor exposed to low-concentration solutions of NaCl in water are reported. The model and experimental results are in very good agreement throughout the explored conductivity range between around 10 and 200 mS/m.