Nondestructive evaluation of materials with A J 0 Bessel transducer : J-y. Lu and J. F. Greenleaf, Biodynamics Research Unit, Department of Physiology and Biophysics, Mayo Clinic and Foundation, Rochester, MN 55905

Abstract

In this paper, the two-dimensional planar array is designed to reduce the sidelobe levels without any extra processing for the feeding currents or changing the elements locations. The design will trim the elements at the four corners with a specific circular masking function which results in a redistribution of the sidelobes so that the two major planes of sidelobes at θ = 0 and 90 degrees are reduced at the cost of increasing other negligible sidelobes. The new masked two-dimensional array has the advantage of easier manufacturing over the concentric circular arrays while maintaining almost the same sidelobe levels and patterns. The analysis of the proposed array design shows that the sidelobe levels will be reduced by 4 dB at first sidelobe in the two major sidelobe planes and is more reduced by up to 10 dB at other sidelobes without any processing or change in the feeding currents. In addition, the sidelobe levels can be further reduced by applying amplitude window functions such as the Hamming window in conjunction with the masking which will reduce greatly the sidelobes level to greater than 30 dB below the main lobe level.