Non-Contact Liquid Characterization Based on Electromechanical Impedance and Low-Cost Piezoelectric Transducers

Electromechanical impedance (EMI) has been widely applied as a non-destructive method for identifying damage in structures and various types of materials. Studies using this technique with low-cost piezoelectric transducers have shown good results in detecting burns in surface grinding processes and cracks in metallic structures. Therefore, this research investigates the feasibility of the EMI method for identifying and characterizing liquids without contact, varying properties such as viscosity and concentration, as well as the liquid level within the container. The feasibility analysis is performed by observing the electrical impedance curves of the transducer and the root mean square deviation (RMSD) and correlation coefficient deviation metric (CCDM) statistical indices of the respective curves, using different liquids such as mineralized water with different solutes, glycerin, distilled water, and motor oil. The results indicate excellent sensitivity of the piezoelectric diaphragm to small variations in the concentration of mixtures with water, particularly at higher frequencies, including the best sensitivity of the 27 mm diaphragm fixed to the circular container. Furthermore, a rightward shift of the impedance signatures is observed in liquids with higher viscosity and greater volume, demonstrating that the EMI technique has high potential for sensing, in a non-invasive and economical way, which ensures the non-contamination of liquids and the safety of the process, common in applications in the chemical and food industries.