Compact, Isolating Elastomeric Suspension for Vehicle Acoustic Vector Sensor Navy SBIR FY2006.2 Sol No.: Navy SBIR FY2006.2 Topic No.: N06-145 Topic Title: Compact, Isolating Elastomeric Suspension for Vehicle Acoustic Vector Sensor Proposal No.: N062-145-0814 Firm: KaZaK Composites Incorporated 10F GIll Street Woburn, Massachusetts 01801-1721 Contact: Rob Karnes Phone: (781) 932-5667 Web Site: kazakcomposites.com Abstract: The increasing use of small platforms such as unmanned underwater vehicles, which cannot support large hydrophone arrays, is driving the development of compact sensors which also work at lower signal-to-noise ratios. The acoustic vector sensor incorporates 3-axis accelerometers whose output can be integrated to give local fluid particle velocity information, so a single AVS can give unambiguous bearing information. Multiple vector sensors in arrays of moderate size can improve spatial resolution. For this sensor to respond with fidelity, it must be essentially adrift in the medium, hence mounting on a moving vehicle is necessarily a compromise. Also, there will always be a compromise between exposure of the sensor to the free field and its isolation from hydrodynamic loads. Finally, any type of mounting will be prone to transmitting some ownship noise into the sensor. KaZaK sees the problem in terms of vibration isolation and impedance matching, and proposes to address it by means of advanced materials: Reducing transmissibility of noise and accelerations with very soft "springs" embodied in an innovative 3-axis series shear mount, and surrounding the sensor with material of good impedance match to the medium and which lends itself to shaping for low drag and flow induced noise. Benefits: KaZaK sees an important opportunity with this topic to complement efforts such as the Office of Naval Research-sponsored slow-speed synthetic aperture sonar being developed for the Long Term Mine Reconnaissance System. The mount/surround design concept is compact, yet provides maximum exposure to the free field. Due to the series arrangement the mount provides effective noise isolation, but the particular configuration minimizes added mass effects under vibration regardless of orientation. The mount eliminates the issue of neutral buoyancy, although the materials we propose to employ have specific gravity near unity and therefore will place little bias force on the mount. The concept also enables easy hydrodynamic integration with the vehicle in both basic situations, bow and side, including a linear side array, with no need for a separate fairing and the complication it introduces of the tradeoff between structural and acoustical properties. For prototype work in the functioning materials, thermoset polyurethanes have the important advantage that they are reacted from liquid components and can be molded (cast) at moderate temperatures and atmospheric pressure in inexpensive, quickly produced tooling. Also, it is easy to mix in any desired liquid or particulate additives to tailor the physical properties. Commercial applications for a sensitively mounted AVS range across the oceanographic field, such as monitoring undersea seismic activity or oil exploration. More broadly, there is a limitless range of application for highly dissipating materials in acoustic isolation and antivibration mounts for machinery or vehicles. Return