A resonant sensor for liquid density measurement based on a piezoelectric bimorph

Density is a characteristic property of a substance related to its mass and its volume. On-line density sensors play an important role in several industrial applications, for example in the monitoring of liquid products. In this work a resonant sensor to measure the density of liquids is proposed. The sensor active element is a piezoelectric bimorph, extensively used in buzzers and telephone receivers. The border of the bimorph is clamped into a steel structure, designed to realize the open chamber into which the liquid is poured. By fixing the volume of the chamber, the volume of the liquid is also fixed; thus, the variation of the resonance and anti-resonance frequencies of the bimorph, due to the mass of the liquid sample, can be related to its density. In the paper, the dimensions of the chamber are optimized by means of a Finite Element Analysis performed by ANSYS ® in order to maximize the device sensitivity.