5aAB4. Active impedance control in a water-filled waveguide for low-frequency bioacoustic testing.

Session: Friday Morning, December 5


Author: James J. Finneran
Location: Dept. of Mech. Eng., Ohio State Univ., Columbus, OH 43210
Author: Mardi C. Hastings
Location: Dept. of Mech. Eng., Ohio State Univ., Columbus, OH 43210

Abstract:

A challenging problem in studying low-frequency sound reception in aquatic animals is creating a suitable underwater acoustic testing environment. For studies of sound reception in fishes, a plane traveling wave is often a desirable stimulus because the relationship between acoustic pressure and particle velocity is well known. At low frequencies, the long acoustic wavelengths in water rule out obtaining traveling waves in rectangular aquaria. In this study, a cylindrical, water-filled acoustic waveguide, with an active termination was used to generate constant frequency, plane traveling waves in the 12--400-Hz frequency range. The waveguide was constructed of acrylic tubing with an NRL J-13 transducer flanged to each end. One J-13 was the primary source and generated continuous harmonic waves. The active control system measured the transfer function between two hydrophones located inside the tube 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 an unbounded wave. The active control system was able to reduce the terminating reflection coefficient to below 0.05 within the frequency range 12--400 Hz. [Work supported by ONR, Grant No. N00014-94-1-0337.]


ASA 134th Meeting - San Diego CA, December 1997