Pure SH-SAW propagation, transduction and measurements on KNbO/sub 3/

Potassium niobate (KNbO/sub 3/) supports the electromechanically active pure shear horizontal surface acoustic wave (SH-SAW) mode along Z-axis cylinder orientations, Euler angles: (/spl phi/, 90/spl deg/, 0/spl deg/), in which two uncoupled wave solutions exist: a purely mechanical sagittal Rayleigh SAW and a piezoelectrically stiffened pure SH-SAW. Within this family of cuts, a maximum electromechanical coupling coefficient for the pure SH-SAW, K/sup 2/ = 53%, is observed along (0/spl deg/, 90/spl deg/, 0/spl deg/). This pure SH-SAW orientation also has the maximum value of electromechanical coupling observed along rotated Y-cut X propagation directions, Euler angles (0/spl deg/, /spl theta/, 0/spl deg/). The use of the pure SH-SAW mode is attractive for liquid-sensing applications because the SH-SAW is modestly attenuated by the adjacent liquid, unlike the generalized SAW (GSAW), which has particle displacement normal to the surface. This work investigates propagation and excitation properties of the SH-SAW and the shear horizontal bulk acoustic wave (SH-BAW) on single crystal KNbO/sub 3/, Euler angles (0/spl deg/, 90/spl deg/, 0/spl deg/). Interdigital transducer (IDT) arrays are analyzed using boundary element method (BEM) techniques, addressing IDT properties such as: power partitioning between the SH-SAW and SH-BAW, SH-BAW radiation as a function of wave vector direction and radiation angle, and overall IDT impedance. The percentage of SH-SAW power to total input power is above: 98% for IDTs containing 1.5 to 5.5 wavelengths of active electrodes with surrounding metalized regions. For nonmetalized regions outside the IDT, the ratio drops to between 1 and 2%, showing the importance of an energy trapping structure for efficient SH-SAW excitation and propagation along this orientation. Simulated and experimental IDT admittance results are compared, verifying the validity of the analysis performed. The reported measurements on the frequency variation with tempera- ure indicate that the orientation considered is temperature compensated at about 8/spl deg/C. The surface of the SH-SAW devices fabricated have been loaded with deionized water arid showed additional 1.6 dB transmission loss with respect to the unloaded surface, verifying the suitability of the pure SH-SAW mode on KNbO/sub 3/ for liquid sensor applications.