1. A. K. Brovtsyn, Defektoskopiya, No. 5, 73 (1999).
2. O. I. Babikov, Ultrasonic Control Instruments (Mashinostroenie, Leningrad, 1985).
3. Ultrasound. A Small Encyclopedia, Ed. by I. P. Golyamina (Sovetskaya Éntsiklopediya, Moscow, 1979).
4. F. J. Berto, Oil Gas J., March 10, 63 (1997).
5. F. J. Berto, Oil Gas J., March 10, 68 (1997).