SH-SAW devices as effective identification system for liquids

This paper describes a liquid-identification system using shear horizontal surface acoustic wave (SH-SAW) sensors. The SH-SAW sensors are fabricated on 36°-rotated Y-cut X-propagating LiTaO₃. Since the piezoelectric crystal has a high electromechanical coupling coefficient, the SH-SAW sensor can detect electrical properties of the adjacent liquid with high sensitivity. For liquid identification, two methods by which the fine differences of the electrical properties between liquid samples can be discriminated are used. One method of identification is based on the conventional multivariate analysis that requires numerical calculation. The other method is new one which allows simultaneous representation of the sensor output signals on the permittivity-conductivity chart proposed by the present authors. In the experiment, many kinds of water samples, such as mineral and natural water, are examined and good identifications are obtained