Application of high temperature superconducting wire to magnetostrictive transducers for underwater sonar

A low-frequency underwater acoustic transducer integrating high-temperature superconducting (HTS) coils and terbium-dysprosium (TbDy) magnetostrictive material was designed, fabricated and tested. This represents a novel application for high-temperature superconductivity and is a first example of an integrated system involving HTS coils cooled by a mechanical cryocooler. It also brings HTS technology together with a novel magnetic materials technology. The I-ITS coils were fabricated using react-and-wind BiSrCaCuO-2223 HTS wires. They produce a peak field of 0.1 Tesla at 50 K. A single-stage, Stirling-cycle cryocooler was used to cool the coils and the TbDy driver to cryogenic temperatures (50-65K). The coils provide an AC magnetic field superimposed on a DC bias field, which produces oscillatory strain within the magnetostrictive rod; this motion is transmitted through a cryostat to two head masses which project sound into the surrounding environment. High power acoustic output can be obtained by operating the transducer at its resonance frequencies of 520 Hz in air and 430 Hz underwater. This development demonstrates that, unlike low temperature superconductors, HTS wires can be considered for AC applications due to the low losses in these superconductors and the higher heat capacities of materials at temperatures above liquid helium.