1. C.C. Koch and D.S. Easton, Cryogenics 17, 391 (1977)
2. D.S. Easton, D.M. Droeger, W. Specking and C.C. Koch, J. Appl. Phys. 51, 2748 (1980)
3. J.W. Ekin, ch.7 in Superconductor Materials Science, Metallurgy, Fabrication and Applications, edited by S. Foner and B.B. Schwartz, ( Plenum, New York 1981 )
4. J.W. Ekin, IEEE Trans Mag, MAG-19, 900 (1983)
5. For a review see L.R. Testardi, Physical Acoustics, edited by W.P. Mason and R.N. Thurston (Academic, New York, 1973, 1977 ). Vol. X p. 193; Vol. XIII p. 29