Measurement of leaky surface acoustic wave velocity using interdigital transducer in a layered structure composed of piezoelectric ceramic and fused quartz

Abstract

An ultrasonic system for measuring a leaky surface acoustic wave (SAW) velocity is described. A leaky SAW transducer consisting of a piezoelectric ceramic thin plate, an interdigital transducer (IDT), and a fused quartz plate is used in this system. A longitudinal wave which is reradiated from a test sample surface into a water layer is detected as electric signals having different delay times received at two different IDTs placed on a substrate surface. A phase difference between two delayed signals depends on the leaky SAW velocity. It is essential in this measurement method that an incident angle of an ultrasonic beam be nearly equal to the Rayleigh angle. The present method using a layered structure leaky SAW transducer has the advantage of a wider range of detecting SAW velocities, compared to a conventional single‐layer SAW one. Experimental results for a 128° rotated Y‐cut‐X propagation LiNbO3 plate and a glass plate are discussed. The layered structure leaky SAW transducer is useful for nondestructive evaluation of piezoelectric as well as nonpiezoelectric substrates.