Orientation dependence of electromechanical coupling factors in KNbO/sub 3/

This paper is concerned with the electromechanical coupling factors for bulk waves in KNbO/sub 3/ crystal. The dependence of coupling factors on the orientation of vibrators for various types of vibration modes has been calculated. As a result, it has been found that most of these coupling factors are very large at certain orientations of vibrators. Especially, the maximum coupling factor of the thickness-extensional mode excited with a perpendicular field, k/sub t/, is as high as 69% for the rotated X-cut by an angle 49.5/spl deg/ about the Y-axis; that of the thickness-shear mode, k/sub s/, is 88% for the X-cut. To the best of our knowledge, these coupling factors are the highest among those of known piezoelectrics. It has also been found that the coupling factor of the width-extensional mode of a thin finite-width plate with electrodes on its edges, k/sub ww/´, is 82% for the rotated Z-cut by an angle 43.5/spl deg/ about the Y-axis. This vibrator would be promising as elements of phased array ultrasonic probes.