Fabrication and testing of smart tongue devices for liquid sensing

In this paper we describe the design and characterisation of shear horizontal surface acoustic wave (SH-SAW) 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 and the other is left electrically active. Experiments to characterise the devices in terms of sensitivity, temperature dependence and mass loading have been conducted and results presented. Discrimination between different liquid samples, i.e. water, orange juice and milk are 100%, using principal component analysis. In addition, experiments on the discrimination of milk samples with different fat content have also been performed as well as freshness of full (whole) milk. Finally the integration of electronic nose and smart tongue devices has been proposed.