Optimization of a piezoelectric resonant sensor for liquids density measurement

Liquids density measurements are highly required in both research and industrial applications, from process control in petrochemical industry to product monitoring in food processing. Commercial devices are often expensive or unwieldy; therefore, in a previous work, a cheap and handy resonant sensor, based on a piezoelectric bimorph, was introduced. The operating principle is based on the variation of the device electrical impedance, due to the liquid mass. By fixing the liquid volume, the frequency variation can therefore be related to the liquid density. The maximum sensitivity of the device was obtained when the resonance frequency was higher. In this paper, two piezoelectric bimorphs with smaller diameter, and therefore resonating at higher frequencies, were considered as active elements and analyzed by means of a FEM commercial code, in order to maximize the device sensitivity, varying the liquid height. Finally, the sensitivity was computed, by using the height with the best sensitivity, and varying the liquid density. Best results were obtained by using the smallest diameter bimorph. First experimental measurements confirmed simulation results.