The focusing of surface acoustic waves launched from a slanted chirped transducer. II. Anisotropic substrate

For pt.I see ibid., vol.UFFC-36, p.565-73 (1989). A characteristic feature of a slanted chirp transducer (SCT) with fingers only a few wavelengths long is that waves launched from it tend to a focus. Analytical expressions for key features of the radiation field are obtained for a linear chirp SCT on an anisotropic substrate and validated by comparison with experimental results obtained on Y-cut lithium niobate. It is found that anisotropy of velocity introduces cusps into the radiation field, giving the focal region properties comparable to those at the focus of a simple lens. Selection of the cuspoidal region combined with choice of finger length is shown to form the basis of a method of apodization.