Grating lobe reduction in 1‐D transducer arrays by driving a bar

Abstract

This presentation investigates the effect of placing a finite‐length bar between eight transducer elements and water in order to reduce undesirable grating lobes. The transducer elements are mounted to the bar, with a thin polyurethane layer between the elements and the bar, and force the bar to approximate the radiation of a continuous line source (i.e., no grating lobes). Reductions in the grating lobe with the insertion of a bar, compared to the unmodified array, have been found numerically and experimentally. In addition the transducer array can still be steered and amplitude shaded, and the bar geometry may be scaled according to the design frequency. Freely vibrating bending modes in the bar create undesirable additional radiation. The benefits and limitations of retrofitting existing array systems with a bar for grating lobe reduction, in frequency and steer angle, will be presented. The insertion of the bar provides a very inexpensive and easily implemented approach to reduce grating lobes without increasing the number of array elements. [Work sponsored by ONR Code 333, Dr. David Drumheller.]