Active impedance control within a cylindrical waveguide for generation of low-frequency, underwater plane traveling waves

Abstract

A cylindrical, water-filled acoustic waveguide with an active termination was used to generate constant-frequency, plane traveling waves. The waveguide was constructed of acrylic tubing with an underwater sound projector flanged to each end. One projector acted as the primary source and generated continuous harmonic waves. The active control system measured the transfer function between two hydrophones located inside the waveguide and used a pattern search algorithm to adjust the secondary source amplitude and phase in order to drive the measured transfer function to that for a plane traveling wave. The active control system was able to reduce the reflection coefficient to below 0.05 within the frequency range 12.5–400 Hz and adjust the acoustic pressure/particle velocity ratio to match that of a plane progressive wave.