IDENTIFICATION OF LIQUID SAMPLES USING SHEAR-HORIZONTAL SURFACE-ACOUSTIC-WAVE SENSORS

The shear-horizontal surface acoustic wave (SH-SAW) propagating on a p iezoelectric crystal is made of re strain wave coupled with a piezoele ctric potential due to the piezoelectric effect. Hence, the SH-SAW can detect not only the effect on the strain but also the phenomena affec ting the piezoelectric potential (acoustoelectric interaction). The SH -type surface acoustic wave on a 36 degrees rotated Y-cut X-propagatin g LiTaO3 is suitable for detection of the electrical properties (relat ive permittivity and conductivity) of liquid since its large electrome chanical coupling coefficient makes the acoustoelectric interaction st rong. In this paper, attention is directed to the frequency dependence of the sensor sensitivity for the acoustoelectric interaction. It is proposed to identify the liquid by means of the sensing system made of several SH-SAW devices with different frequencies. Specifically, elev en kinds of fruit juice and thirteen kinds of whiskey were identified. It is found that highly accurate distinction can be accomplished with out selective organic thin films.