Parametric acoustic array development a the US Navy's New London, Connecticut laboratory

Abstract

A brief history of the development of parametric acoustic sources at the US Navy Underwater Sound Laboratory (USNUSL), and its successor, the Naval Underwater Systems Center. Inspired by Robert Mellen, the Parametric Sonar Group was formed to explore the practical implications of Westervelt's idea for underwater acoustics. Spanning more than two decades, this research pursued various potential applications exploiting the unique characteristics of parametric sources, including echo-ranging in reverberant environments, communications involving voice, data, music, and video signals, target-strength measurements, bottom bathymetry, high-resolution sub-bottom profiling, and measurements of scattering and reflection from surfaces. Parametric source design procedures were developed, and guidelines were established for diagnosing and avoiding undesirable effects, such as difference-frequency instability and spurious nonlinearities, such as direct radiation from the projector, cavitation, and receiver nonlinearity. Theoretical models extended the Westervelt theory to realistic primary fields. For planar projector arrays, parametric source design curves, valid for levels in the primary far field, enabled designers to predict performance without resorting to computer calculations. To obtain source-levels and beam-widths within the primary near field, where the secondary signal is generated, a computer program, called CONVOL5 in its present configuration, can be used to obtain more detailed performance predictions.