1. G. A. Sofer and E. A. Hauser, J. Polym. Sci. 8, 6 (1952).
2. Mcdonnell-Douglas, St. Louis, Private Communication.
3. Norio Sato, Toshio Kurauchi and Osami Kamigaito, 31st Int. SAMPE Symp. 1986.
4. R. T. Harrold, U.S. Patent No. 4,590,803, May 27, 1986, “Acoustic Waveguide Monitoring”.
5. R. T. Harrold and Z. N. Sanjana, J. Polym. Sci. 26, 5 (1986).