Theoretical evaluation of SAW velocity measured by divergent-beam ultrasound transducers

A theoretical description for V(z) curves, which represents the output voltage (V) with the transducer specimen distance, is derived for the authors´ surface acoustic wave (SAW) velocity measurement system having divergent-beam ultrasound transducers. V(z) curves are calculated for stainless steel, and the SAW velocity obtained by detecting the minimum of the V(z) curve is evaluated for various transducer sizes and frequencies. The results are compared with the exactly calculated SAW velocity, and influence of the transducer geometry and frequency on the measurement accuracy of the system is examined theoretically. It is shown that there exists an optimal transducer geometry at each frequency of minimizing the measurement error. In the case of the optimal arrangement the incident field on the sample becomes a peak at the point of Rayleigh-angle incidence