SBIR-STTR Award

Current ASW missions require low frequency off-board sound sources that can operate monostatically or bistatically. Since these sources may or may not be recoverable, and may require a substantial number to cover the designated operating areas, the low frequency source transducers also need to be low cost. The team of Etrema Products and Applied Research Laboratory at The Pennsylvania State University (ARL Penn State) propose using magnetostrictive Galfenol, an iron-gallium alloy, in low frequency transducer devices to produce compact, high acoustic performance transducers at relatively low production costs. Galfenol is uniquely suited for use in low frequency transducers because of its formability, relatively high tensile strength, and relatively high magnetic permeability all of which allow the use of complex shapes to drive transducers. Two Galfenol spring transducer concepts will be investigated: a slotted cylinder transducer with a Gaflenol spring instead of a piezoceramic driver, and a simple double or four headed piston with Galfenol spring drivers. Both these concepts are potentially low-cost, high performance transducer that can reach source levels in excess of 210 dB, resonant frequency less than 1 kHz, and bandwidth greater than 200 Hz.

Benefit:
Anticipated benefits of the proposed research are efficient, broadband, low frequency transducer concepts that can be used to obtain the desired detection ranges against quiet threats in deep and littoral waters. These transducer concepts are targeted at frequency ranges below 1 kHz with source levels in excess of 210 dB and bandwidths greater than 200 Hz. Applications for these transducers include unmanned surface vehicles (USVs), unmanned underwater vehicles (UUVs), and sonobuoys. The transducer resulting from the proposed research is expected to be scalable and reconfigurable such that it can be adapted for both Navy and commercial applications. The oil and gas industry use compact, low frequency transducers for oil exploration and inspection of oil wells and would benefit from greater performance and reliability. Also, low cost, high power low frequency transducers may be useful as a deterrent to hostile swimmers/divers for harbor and ship defense.

Keywords:
magnetostriction, magnetostriction, low frequency transducer, slotted cylinder transducer, galfenol

In the Phase I effort a Galfenol-based slotted cylinder projector (SCP) device was conceived utilizing an existing PZT SCP design and analytical modeling to determine the geometry requirements necessary to achieve the performance specs: 210 dB source level, 750 Hz resonance frequency, 200 Hz bandwidth. The final form factor was a Galfenol SCP with overall dimensions of 7.75 0x9D diameter x 12 0x9D length utilizing a graphite composite shell material with Galfenol drivers comprising a rib-like structure within the shell. The technical objectives in Phase II will include design optimization through improved modeling efforts, the development of manufacturing processes capable of producing the Galfenol rib structures, and the construction and testing of one complete transducer system. Device test data will be compared to predicted performance results via the developed model. A design iteration will be completed on paper along with beginning investigations into reducing manufacturing costs.

Benefit:
An operational Galfenol SCP device would provide the Navy with an autonomous, low frequency active sonar ASW system that could be deployed by a variety of options including USV's. The cost of such a device is estimated to be 37% cheaper compared to existing technologies opening up the potential for expendable sources. The reliability and robustness of the Galfenol SCP will be superior due to fewer components, interfaces, and joints along with utilizing tougher active materials. Potential commercial applications for the Galfenol SCP would be for oil exploration and the inspection of oil wells.Transducers that provide low cost and greater performance would improve exploration and inspection capabilities. Also, low cost, high power low frequency transducers may be useful as a deterrent to hostile swimmers/divers for harbor and ship defense.

Keywords:
slotted cylinder projector, Sonar, transducer, galfenol, Magnetostrictive