Development of smart tongue devices for measurement of liquid properties

In this paper, we describe the design and characterization of shear horizontal surface acoustic wave devices for the analysis of liquid samples. Devices were fabricated on both 36° rotated Y-cut X-propagating LiTaO₃ and LiNbO₃ substrates. The design consists of a dual delay-line configuration where one delay line is metallized and shielded, while the other is left electrically active. Experiments to characterize the devices in terms of sensitivity, temperature dependence, and mass loading have been conducted and the results presented. Different liquid samples, i.e., water, orange juice, and milk, are 100% linearly separable using principal components analysis. In addition, it is possible to measure the fat content (±0.1%) as well as the freshness of full (whole) milk.