Frequency-sum beamforming in a random scattering environment

Abstract

In a uniform environment, sound propagation direction(s) or the location of a sound source may be determined from array-recorded signals by beamforming. However, the beamforming results may be degraded when there is random scattering between the source and the receivers. Such sensitivity to mild scattering may be altered through use of an unconventional beamforming technique that manufactures higher frequency information from lower-frequency signal components via a quadratic product of complex signal amplitudes. This presentation will describe frequency-sum beamforming, and then illustrate it with simulation results and near-field acoustic experiments. The simulations suggest that frequency-sum beamforming may be beneficial when there is one loud source and the environment provides one primary propagation path. The experiments were conducted in either a 1.0-m-deep 1.07-m-diameter cylindrical water tank using 50 kHz and 100 kHz signals broadcast from a single source to an array of 16 hydrophones when discrete scatterers are present and absent from the tank or in a tissue-mimicking phantom with a dominant scatterer embedded and insonified at 2 MHz and the scatter received by a 128-element array. The results from frequency-sum beamforming are compared to the output of conventional delay-and-sum beamforming and minimum variance beamforming. [Work supported by NAVSEA through the NEEC.]