3-2 Bendar-bar 20Hz source using giant magnetostrictive plates
The other one is a bender bar type which made of giant magnetostrictive plates. This is expected to have a smaller size than the former because the displacement of bending plates can be larger than rods. To reduce the size of 20Hz source, we tried to introduce a bender-bar source. Ordinary bender bar is made of two ceramic stacks. The bar is fixed at upper and lower ends. When the one is compressed, the other is expanded. And the bar shows a bending motion. The advantage of this type has a very large complience by enlarging the length of the bar. It means to reduce the frequency of the soource.
We intend to apply a giant magnetostrictive material to a bender-bar. We design a concept os 20Hz bender-bar source using ten giant magnetostrictive bender-bars. Each bender-bar has the wodth of 0.25m and the height of 0.9m. The diameter of the source is 1m and height is 1m. The resonance frequency is 21Hz Q factor is about 3 . The maximum transmiting level is 197dB. But there are many ploblems to be solved. A giant magnetstrictive plate used in this source is not realized yet. We have to develop a giant nagnetostrictive plate. If we can get these plates in some way, we shall be able to construct a extremly small 20Hz source.
4. CONCLUSION
It was verified that characteristics of driving unit itself did not change in the use for 10 years by the present experiment. Finally, concepts of 20-30Hz sound source were shown This design example is, however, a result under the condition of the driving unit for 200Hz source tested this time. The examination in using giant magnetostrictive rod with the larger diameter and longer length is a future problem. And it is anticipated that the durability components such as rubber boot, o-ring etc. should become future test subjects for the use over 10 years. And if we can solve these problems, we shall be near the realization of an acoustic monitoring system of gloal ocean variability.
REFERENCES
1) Bruce Howe et.al., "Instrumentation for the Acoustic Thermometry of Ocean Climate (ATOC) Prototype Pacific Ocean Network", Proc. OCEANS'95, 1225-1231 (1995).
2) Toshiaki Nakamura et.al., "Development of 200Hz Transceiver System for Ocean Acoustic Tomography", Proc. 3rd ECUA '96, vol.II,797-802 (1996).
3) Walter Munk et.al., Ocean Acoustic Tomography, Cambridge University Press, New York 1995, Chap. 8.
4) Toshiaki Nakamura et.al., "Acceleration tests of long-term operation for giant magnetostrictive units of global ocean climate change.,"Proc. 4th ECUA '96, vol.II, (1998).
