No abstract

No abstract

No abstract

Data obtained from a vector-sensor line array (VSLA), while deployed vertically at Lake Pend Oreille during calibration, are examined in the context of propagation phenomena. Both broadband (FM sweep) and cw signals are analyzed. Only linear plane-wave beamforming is considered, based on well-established array processing techniques for vector sensors [Cray and Nuttall, J. Acoust. Soc. Am. 110, 324 (2001)]. Normalization is addressed, as is the determination of the vertical plane of propagation for proper steering of the vector components. Results show that the vector sensor array can be properly scaled and steered using a strong, single, cw source. Peak-to-sidelobe improvements of several dB were observed using vector beamforming rather than pressure-only beamforming. Arrival direction resolution using cardioid null is also presented. The vertical configuration allowed testing of predicted multipath interference behavior. As expected, arrival angle determinations with a single vector sensor is possible with the broadband signal. The difficulty of similarly resolving multipath arrival angles with one vector sensor and a single cw tone is shown. An array of vector sensors will resolve these angles. [Work completed with the support of Michael Traweek, Thomas Curtin, and Ellen Livingston, all from the Office of Naval Research, and by Daniel Deitz of NAVSEA-PMS403.]

The Naval Undersea Warfare Center in Newport, RI is developing an electro-active polymer-based sensing node for use in a persistent distributed underwater surveillance system. Persistence demands extreme energy conservation measures. The node will resemble a jellyfish in form, complete with tentacles housing a volumetric array of light-weight piezoelectric polyvinylidene fluoride trifluoroethylene (PVDF-TrFE) copolymer cylindrical hydrophones designed for an ultra-low power acoustic receiver. Each cylinder has conductive silver electrodes on the inside and outside surfaces, a length of 2.5 cm, an outside diameter of 11 mm, a 1 mm wall thickness, and a mass less than 2 g. Operating in the hydrostatic mode, the hydrophone sensitivity is typically -195 dB//1 V/μPa and is stable with both hydrostatic pressure (50 to 1000 psi) and temperature (-1 to 35°C). [Work supported by the Office of Naval Research.]