Design and experimental results of a surface acoustic wave (SAW) microsensor with polymer microfluidic cell for the sensing and identification of liquids is presented in this paper. This microsensor, which is a part of a smart tongue-nose system, uses a horizontally polarized SAW (SH-SAW) for the detection and identification of liquids. The SH-SAW microsensors are fabricated on 36 •-rotated Y-cut X-propagating LiTaO 3 (36Y X.LT) substrate. This design consists of a dual-delay-line configuration in which one line is free and other one is metallized and shielded. Polymer microfluidic cells were designed and fabricated on top of it using a microstereolithography system to avoid dielectric loading of the IDTs by liquid which leads to unwanted dielectric sensitivity to the sensor. Due to the high electromechanical coupling of the 36Y X.LT substrate, it could detect differences in electrical properties and hence distinguish different liquids. It is clear from these results that the microsensor based on 36Y X.LT is an effective liquid identification system for the electronic tongue application.
In this paper we present design, fabrication and integration of a micro fluidic cell for use with the electronic tongue. The cell was machined using microstereo lithography on a Hexanediol Diacrylate (HDDA) liquid monomer. The wet cell was designed to confine the liquid under test to the sensing area and insure complete isolation of the interdigital transducers (IDTs). The electronic tongue is a shear horizontal surface acoustic wave (SH-SAW) device. Shear horizontally polarized Love-waves are guided between transmitting and receiving IDTs, over a piezoelectric substrate, which creates an electronic oscillator effect. This device has a dual delay line configuration, which accounts for the measuring of both mechanical and electrical properties of a liquid, simultaneously, with the ability to eliminate environmental factors. The data collected is distinguished using principal components analysis in conjunction with preprocessing parameters. The experiments show that the micro fluidic cell for this electronic tongue does not affect the losses or phase of the device to any extent of concern. Experiments also show that liquids such as Strawberry Hi-C, Teriyaki Sauce, DI Water, Coca Cola, and Pepsi are distinguishable using these methods.
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