3aSPa8. Design of a plane rectangular near-field array with nearby reflective boundaries.

Session: Wednesday Morning, December 4

Time: 10:30

Author: James S. Martin
Location: Georgia Inst. of Technol., School of Mech. Eng., Atlanta, GA 30332-0405
Author: Peter H. Rogers
Location: Georgia Inst. of Technol., School of Mech. Eng., Atlanta, GA 30332-0405


The problem of designing an array for the generation of a spatially and temporally discrete region of plane-wave uniformity from 2 to 10 kHz is addressed. The problem is complicated by the fact that the array's dimensions are close to those of the tank containing it. The array lines are oriented horizontally to allow for phase steering in the vertical plane. Each line is comprised of 26 elements with identical real shading sets. The lines are irregularly spaced and loosely supported giving the array the appearance of a venetian blind. Time and frequency domain analysis are used with simple source assumptions to determine the drive signals for the 34 independently addressable lines in the array. The result is a set of frequency-dependent complex shading coefficients which constitute transfer functions analogous to localized wave solutions in radar and ultrasonics. The function of the peripheral elements of the array can be seen, from a time domain assembly of the transmit signal, to be active cancellation for the late energy from the center elements and the surface reflections. Nearby scatterers (tank walls, water surface, and neighboring array transducers) are modeled as image sources of the array. Drive signals are assembled digitally and applied via a system of simultaneously triggered buffers. Good agreement exists between experimental data and model predictions of array performance. [Work supported by ONR.]

ASA 132nd meeting - Hawaii, December 1996