Characteristics of leaky SAW propagating along liquid/LiNbO/sub 3//sapphire structure and its application to liquid sensor

Liquid/LiNbO/sub 3//sapphire structure is proposed for high frequency liquid sensors, and the characteristics of leaky surface acoustic wave (leaky SAW) propagating along the layered-structure are examined by the numerical calculation based on the first-principle-equations. It is found that electromechanical coupling constant becomes maximum at Eulerian angles of (0,0,30+60n degree) (n: integer), whereas, shear horizontal component of the leaky SAW, which is coupled with the viscosity of the liquid, becomes large at other propagation directions. The maximum electromechanical coupling constant for glycerin/LiNbO/sub 3//(00.1) sapphire is about 1.3%, and the maximum leaky SAW velocity for water/LiNbO/sub 3/ (10 /spl mu/m)/(00.1) sapphire (30 MHz) is 5390 m/s. These results indicate that this layered-structure is useful for high frequency liquid sensors.