We describe the static and dynamic characteristics of a giant magnetostrictive material under high pre-stress, using the pre-stress given to the giant magnetostrictive material as a parameter, and also evaluate material constants. Seven evaluation units, each having an optimum magnetic bias applied to vary the pre-stress given to the material from 15 MPa to 54 MPa, were used to measure the static and dynamic characteristics. As a result, the trends of equivalent circuit constants such as stiffness, internal resistance, and force factor in response to the increase in pre-stress for enhancing the output, were clarified. Furthermore, considering the linearity to the input level, the necessity of examining the optimum pre-stress region, in addition to the simple increase in pre-stress, was suggested.

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A superior underwater projector having low frequency, high power, high efficiency, and broad bandwidth for the Ocean Acoustic Tomography (OAT) system has been developed. The OAT system is proposed to measure temperature and current distributions of a wide range of sea area with a diameter of about 1000 km on real time by using sound waves. The projector vibrates in the radial mode of octagonal radiating plates connected with eight driving units having giant magnetostrictive rods. The projector is able to emit sound of more than 190 dB [0 dB=1 μPa-m] at a low frequency of about 200 Hz under the operation depth of about 1000 m when it is excited by electric input power of about 900 W. The performance is enough to cover the range of 1000 km for the OAT system. Also, the derived values from measurements are in good agreement with the calculations based on the simple equivariant circuit model.

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