ACOUSTIC-WAVE-BASED VOLTAGE SENSORS

Acoustic-wave-based voltage sensors utilizing surface acoustic wave (S AW) delay lines are reviewed. A SAW oscillator that consists of a SAW delay line and an amplifier connected between input and output interdi gital transducers (IDTs) can be used as a SAW-based voltage sensor, wh en a d.c. or a.c. voltage is applied on the SAW propagation path in th e piezoelectric substrate. The voltage sensors detect an applied volta ge as a fractional change of oscillation frequency. there are two elec trode configurations for applying a voltage to the substrates on which the SAW propagates. One is to apply a voltage perpendicular to the su rface of the substrate, and the other is to apply it parallel to the s urface of the substrate and perpendicular to the propagation direction of the SAW. The former configuration is used in a sensor having a ZnO thin film on Si and a sensor utilizing a Lamb wave, as well as in a s ensor utilizing a Rayleigh wave on LiNbO3 plates, whereas the latter i s used in a sensor with SAW waveguides.