Measurements of SAW velocity by using divergent-beam ultrasound transducers

A SAW (surface acoustic wave) velocity measurement system that uses a pair of divergent-beam ultrasound transducers positioned in parallel with a specimen in a liquid is presented. Of the divergent wave emitted by the transmitter, a specific angular-spectrum component that is incident on a specimen at the Rayleigh critical angle excites a leaky SAW on the specimen surface. Of various angular-spectrum components of the reflected wave, the receiver selectively detects the specularly reflected wave and the reradiation of the leaky SAW. These two components take the same path when the specimen is brought to a specific position. Since the two components are in opposite phase at the position, their interaction causes a so-called null zone in the reflected beam and a corresponding intensity minimum is detected by the receiver