ELECTROSTATIC VOLTAGE SENSOR USING SURFACE ACOUSTIC-WAVES DELAY-LINE OSCILLATOR

A surface acoustic wave (SAW) electrostatic voltage sensor was fabrica ted using an SAW oscillator. In the electrostatic voltage sensor, the electrodes to apply electrostatic voltage and produce strain by piezoe ffect are not located on the top and bottom surfaces of the substrate but rather on the propagation surface in parallel to the propagation p ath. Therefore, it is possible to reduce the gap spacing between the e lectrodes to apply an electrostatic voltage so that the sensitivity ca n be improved. When an electrostatic voltage is applied, the LiNbO3 si ngle crystal and PZT ceramic were used as substrates in this experimen t. The most sensitive crystal plane in a rotated Y-X plate rotating ab out the X axis was obtained for LiNbO3 single crystal. It was found th e result shows that the 90 degrees rotation Y-X plate is the best. In the experiment, a 131 degrees rotation Y-X plate with 20 x 25 x 1.0 mm (3) was used which is close to the derived angle and is obtained easil y. The interdigital transducer (IDT) electrodes and the electrodes for applying electrostatic voltage were fabricated by Al evaporation. The characteristics of the oscillation frequency versus electrostatic vol tage of the sensors were studied. The sensitivity was 0.133 Hz/V and 0 .03 Hz/V for the 131 degrees rotation Y-X plate and a Y-X plate in the case of LiNbO3. In the case of PZT ceramic, the sensitivity was 12 Hz /V. The dependence of the sensitivity on gap distance between the elec trodes for applying electrostatic voltage and on temperature was also studied.