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2. 2) S. Higuchi, Z. Makihara, Y. Nonaka and N. Ooka: Key Eng. Mater. 270–273 (2004) 1316–1323.
3. 3) T. Kashiwa, S. Higuchi and N. Ooka: 12th APCNDT, Auckland, New Zealand, Nov., (2006) http://www.ndt.net/article/apcndt2006/papers/21.pdf
4. 4) ASME Code 2004 Sec. XI, Division I, Appendix VIII, Sup. 2 Performance Demonstrations for Ultrasonic Examination Systems.