In important small parts such as LSI, precise ultrasonic testings have been carried out. However, in the case of point focussing ultrasonic normal probes, no DGS diagram exists. Because of this it was difficult to evaluate the defect quantitatively. Therefore, there was a need to develop DGS diagrams for point focussing ultrasonic normal probes.

Using developed calculating procedures and the results of Torikai's research [3], DGS diagrams for point focussing normal probes were successfully obtained when the defect was on the sound axis. Experiments were carried out using several water immersion point focussing probes of 10 or 20 MHZ in frequency (311, 316 and 317, type A-S and V) made by Panametrics. Targets were the flat end surfaces of pins where diameters were 0.1, 0.2, 0.4 and 0.8 mm and a large flat surface. Probes were driven by the single pulse or sine burst wave.

In the case of sine burst wave, experimental results well agree with the theoretical results. Furthermore, in case of pulse, even when the band width of the echo exceeds 60 percent, experimental results agree fairly good with the theoretical results except on large flat targets. Therefore, DGS diagram will be effectively used in ultrasonic test using point focussing probes. REFERENCES

1. K. Kimura, "Calculation of AVG Diagram for Ultrasonic Normal Probe", Trans. National Research Institute for Metals, Vol. 22, No. 4, pp. 213-281, 1980
2. K. Kimura and S. Matsumoto, "DGS diagrams for angle probes", 3rd European Conference on NDT Florence, Vol. 3, pp. 93-102, 1984
3. Y. Torikai, "Ultrasonic fields and Lommel's functions", Report of the Institute of Industrial Science, University of Tokyo, Vol. 25, No. 4, 1976