A 20Hz giant magnetostrictive source for monitoring of global ocean variability.
Toshiaki Nakamura1, Tomoyuki Kanaizumi1, Iwao Nakano1
Tomohiro Tsuboi2 and Takashi Yoshikawa2
1Japan Marine Science and Technology Center, 2-15 Natsushima-cho. Yokosuka 237 Japan
2Oki Electric Industry Co.. Ltd. 688 Ozuwa, Numazu 410 Japan
Abstract
This paper describes a concept of very low frequency (20Hz) source for monitoring of global ocean variability of 10Mm scale in long term observation of over ten years. A low frequency (200Hz) source has been developed for ocean acoustic tomography of 1000km scale by JAMSTEC. Our 200Hz source has an octagonal barrel shape, and consists of eight driving units by the use of giant magnetostrivtive rods. A giant magnetostrictive source has the advantage of small size, high transmitting level and long life span. We intend to apply the technology of this 200Hz source to very low frequency sources. We have already conducted a long term operation test of the driving units of the equivalent time to ten years, andproved its long life. However, lower frequency tronsmission requires lorger 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 20Hz sources. The one is on ordinary barrel type by the use of the several giant magnetostrictive rods which has larger diameter and lorger prestress than the present source. The other one is a bender bar type which made of giant magnetostrictive plates. The latter is expected to have a smaller size than the former because the displacement of bending plates can be larger than rods. Some theoretical results are shown for an extremely small 20Hz source within 1m diameter and 1m height.
