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

The shear-horizontal surface acoustic wave (SH-SAW) propagating on a piezoelectric crystal is made of re strain wave coupled with a piezoelectric potential due to the piezoelectric effect. Hence, the SH-SAW can detect not only the effect on the strain but also the phenomena affecting the piezoelectric potential (acoustoelectric interaction). The SH-type surface acoustic wave on a 36 degrees rotated Y-cut X-propagating LiTaO3 is suitable for detection of the electrical properties (relative permittivity and conductivity) of liquid since its large electromechanical coupling coefficient makes the acoustoelectric interaction strong. 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, eleven kinds of fruit juice and thirteen kinds of whiskey were identified. It is found that highly accurate distinction can be accomplished without selective organic thin films.