3.　CONCEPT OF VERY LOW FREQUENCY SOURCES

　

3-1　Polygonal 30Hz source using giant magnetostrictive rods

The lower frequency transmission requires larger transmitting level of the source. It means larger displacement of a giant magnetositrictive material is required than that of the present 200Hz source. We are now planning two types of very low frequency sources. The one is an ordinary barrel type by the use of the several giant magnetostrictive rods which has larger diameter and larger prestress than the present source. Some theoretical results are shown.

Figure 12 shows a concept of 30Hz source using 16 driving units of giant magnetostrictive rods. Each rod has 40mm in diameter and 210mm in length. The diameter of the source is 2m, the height is 1.1m. The capacity of gas chamber is about 2.5m³ in the depth of 1000m. So, total height of the source is about 2m. The weight of the source is 5 toms in air and 3 tons in water. Figure 13 shows the calculated frequency characteristics of the transmiting sensitivity. The resonance frequency is 30Hz. Q factor is about 4. Transmitting current sensitivity is 192dB per A. The estimated maximum transmiting level is 195dB.

Fig. 12　Schematic giagram for a 30Hz glant magnetostrictive source.

Fig. 13　Estimated transmitting sensitivity for a 30Hz giant magnetostrictive source.

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