P3G-8 Random Thinning of Segmented Annular Arrays

Two-dimensional (2D) array designs based on a squared matrix (S-M) distribution of elements require half wavelength (lambda/2) pitch for reducing grating lobes. From this condition, a 2D array for ultrasonic imaging will typically contain several thousand of elements, which are much higher than the number of channels of present image systems. In contrast, segmented-annular (S-A) arrays have lower periodicity than squared patterns and allow increasing the inter-element distance surpassing one wavelength. Thus, the number of elements of the S-A array can be reduced by a factor of six with respect to the S-M array of equal size. However, for large apertures, this number is still a challenge for the existent technology, and thinning techniques are required. In this work, the results of applying the random thinning method to S-A arrays are analysed based on two different approaches: the array factor on the one hand, which considers omni-directional elements vibrating in continuous wave, and the real aperture in wide band on the other hand. Moreover, a comparison with the conventional S-M array of equivalent characteristics is also included. It is shown that the S-A array with pitch d = 1.2lambda, overcomes the equivalent S-M array, producing beams which can be acceptable for ultrasonic image