Electronic tongues

The concept of a novel analytical sensing microsystem referred to here as an "electronic tongue" is presented; it is based upon a dual shear horizontal (SH) surface acoustic wave sensing device (SAW) that can discriminate between liquids of different basic tastes. 60 MHz SH-SAW dual delay-line sensors were micro-fabricated on 36° rotated Y-cut X-propagating LiTaO₃ and placed below a miniature housing containing the liquid under test. In this SAW sensor configuration, one delay-line is electrically shorted and the other is free. Theory relating to the electro-acoustic properties represented by the relative permittivity and conductivity of the sample liquid is presented and related to experimental results. Dilution tests have also been performed in order to determine the detection limit of this physical taste sensor and hence its potential application. Synthetic samples were analyzed with the four basic tastes of sour, salt, bitter, and sweet. The electronic tongue classified correctly all of the different basic tastes without a selective biological or chemical coating. The electronic tongue has also been employed to analysis the bacterial load in cow\´s milk. Finally, recent developments of high frequency, semi-wireless 433 MHz SAW sensors and associated fluidic micro-traps are given.