ABSTRACT It is found that an acoustic wave which is nearly polarized in the shear horizontal (SH) direction can propagate along the X axis of a Z-cut lithium niobate plate if the ratio hλ, where h = plate thickness and λ acoustic wavelength, is less than about 0.5. Attractive properties of this quasi-SH wave include: 1) phase velocity nearly constant for all values of hλ 2) ability to propagate in contact with a liquid medium; and 3) electromechanical coupling coefficient as high as 0.15. These properties make the wave attractive for use in a variety of sensor and signal processing applications. An example of sensor applications is illustrated by using the wave to measure conductivity of liquids (aqueous KCl solution). The frequency of a 12-MHz quasi-SH mode oscillator fabricated on a 0.48 wavelength thick Z-X lithium niobate plate is found to vary by more than 80 kHz for variation in KCl concentration from 0 to 0.15%.
© 1996, by The Institute of Electrical and Electronics Engineers, Inc. All rights reserved.