Measurement and Mapping of Elastic Anisotropy of Solids Using a Leaky SAW Excited by an Interdigital Transducer

Abstmt-Methods of measuring the acoustic properties of solids using acoustic beams in a liquid generated by interdigital transducers (IDT) are described. An IDT can radiate acoustic waves into a liquid in oblique directions with respect to the substrate, and the wave fronts can be arbitrarily controlled by designing the IDT shape. When the acoustic beam is incident on the solid sample-water interface near the Rayleigh angle, the reflection field is equal to the superposed fields of the specular reflection and the reradiation from the leaky surface acoustic wave (SAW) excited on the sample. One normal IDT pair on a piezoelectric substrate is used to measure the acoustic properties of a solid sample. The velocity and the attenuation of the leaky SAW on the sample can be obtained by measuring the trailing field due to the reradiation. A new method for focusing the beam from an IDT and mapping a leaky SAW velocity on a solid sample surface is shown. An interdigital electrode is divided into several sections, each of which is positioned to form a one-dimensional Fresnelphase-plate interdigital transducer (FPP IDT) on a piezoelectric substrate. It has been found that the FPP IDT generates a converging beam onto a focal plane, and the present system is suitable for measuring the two-dimensional variation of the leaky SAW phase velocity on a sample surface. T