source can be realized. We constructed a driving unit using a giant magnetostrictive rod as shown in Fig. 1. The diameter and the length of the rod are 20mm and 120mm respectively. The source with a pulsating barrel shape vibrates in the radial mode of octagonal radiating plates connected with eight driving units with giant magneto-strictive rods as shown in Fig. 2. Outer and inner sides of the cylindrical source are covered with rubber boots and filled with oil for pressure balance in deep sea use. The height of the source is 370mm and the diameters of outer and inner boots are 940mm and 560mm respectively. Inside of the inner boot, a cylindrical air cavity with 50mm thick is mounted for insulation of a backward radiation of sound and for reduction of the stiffness of the source. A pressure compensator is used to keep the volume of the air cavity constant for depth fluctuation of the source. The weight of the source is 410kg and the pressure compensator is 280kg.

Some experiments were conducted to measure the acoustic characteristics of the source at the depth around 1000m in the sea. The source and the measurement system which is a hydrophone and a recorder are suspended from the test ship at the depth between 800m to 1200m.

Fig. 2　Schematic diagram for the present 200Hz source using the giant magnetostrictive giving units

Fig. 3　The transmitting level for the 200Hz source measured at the depth of 800, 1000 and 1200m.

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