Advanced Magnetostrictive Materials for Sonar Applications

Piezoelectric or magnetostrictive materials can be utilised as active materials for electroacoustic underwater transducers. Piezoceramic materials gained edge over the conventional magnetostrictive materials during 1940s due to their unique electro-acoustic properties. At present, inspite of passive sonars there is a need of low-frequency high-power active sonars for the Navy. This led toresearch for new activematerials with competing characteristics to that of the existing piezo transducers. The discovery of a giant magnetostrictive material, commercially known as Terfenol-D, led to a breakthrough in the development of a new generation of sonar transducers. Now, the materials (including composites) as well as sensors are commercially available. A new generation of transducers have emerged in ocean-related areas like acoustic tomography, longrange underwater communication, geophysical exploration, oil well exploration, etc. Indian Institute of Technology Madras, Chennai, has also developed the basic material technology a few years back. At present, in India, National Institute of Ocean Technology, Chennai, is developing underwater transducers utilising giant magnetostrictive materials as well as piezoelectric materials for marine applications like sub-bottom profiling (seafloor mapping) and long-range underwater communications. A prototype of a portable, low-frequency medium power transmitter operating over a wide-frequency range has been developed. The main advantage of this transducer is its simplicity in design. In this paper, (he recent developments in material processes, importance of device-oriented material characterisation, and transducer design aspects have been emphasised. Some results on the underwater performance of a wide-band transducer have also been presented. These materials also have ultrasonic applications, capable of revolutionising the processing industry.