On the geometrical design of segmented annular arrays

Abstract

Segmented annular arrays (SAA) can be a good option to generate 3-D ultrasonic images. Design this kind of aperture involves a variety of geometrical parameters that are decisive for the quality of the image. For instance, it is possible to use regular or non-regular SAA configurations in which the number of annuli and the elements per annulus can be varied. The ob jective of this work is to analyze these configurations in order to define the most important design parameters. In this sense, our study is centered in several points: the alignment between rings, the array size and the element aspect ratio. The evaluation of these parameters is focused in obtaining the best trade-off between the number of elements and the image quality. The arrays under analysis are equivalent in the sense that their size, number of active elements and active areas are similar and they emit the same ultrasonic pulse. In order to achieve a clear analysis of the grating lobes, the array factor approach, which considers the array formed by vibrating points, is applied. Also a more accurate analysis, based on the computation of the spatial impulse response approach, is made to reinforce our conclusions in both excitation modes, continuous wave and wide band.