The Convergent Property of Surface Acoustic Waves Generated by Concave Transducers on Anisotropic Crystal Surfaces

艾嘉猷(Chia-Yu Ai) ； 鄒治璞(Chyr-Pwu Tzou) ； 王守益(Shou-Yih Wang) ； 黃大民(Dah-Min Hwang)

《Chinese Journal of Physics》 17卷1期 (1979/04) Pp. 12-21

並列摘要

The propagation characteristics of the surface acoustic waves (SAW) on anisotropic y-cut z-propagation LiNbO3 substrates were investigated. The SAW were excited by concave interdigital transducers with a radius of curvature of 8 mm and an aperture of 3.2 mm. The SAW energy distribution profiles were recorded by the laser optical probing technique. It was found that the SAW converged at a spot 17±1 mm from the transducer with the beam width narrowed down by a factor of 15 and the power density at least increased by a factor of 7. The diffraction patterns were calculated by the method of Sommerfeld diffraction integral with published phase velocity angular distribution curve as well as with the parabolic approximation. The experimental data do not agree with the results calculated exactly from the published curve; however, they agree with the results obtained from the parabolic approximation if the anisotropic parameter b was chosen to be -0.53. The values of b parameter cited in early works, which fall between -0.66 and -1.087, were obtained from the same phase velocity curve aforementioned which was calculated from elastic and piezoelectric constants. In our work, the b parameter was determined from the measured focal length which is a more direct way and we have more confidence in our b value.