Patent ID: 6622562
Filing Date: 2003-09-23
Classification: B06B

Abstract:
An ultrasound annular array transducer for electronic steering of a symmetric focus Fz from a near focus, Fn to a far focus Ff by adding delays to array element signals, comprising:a plurality of annular array elements divided into groups of at least one of neighboring elements of the plural array elements, each group having a different fixed mechanical pre-focus, and the array elements within each group having substantially equal area, wherein a central group of the plural groups of array elements participates in an active aperture of said transducer for the whole focal range from Fn to Ff with a pre-focus F0 selected between Fn and Ff, wherein beyond a depth Fn1 at which a focal diameter of the central group expands past a selected limit, a next outer group of array elements is included in the active aperture from Fn1 to Ff, a fixed pre-focus F1 of the next outer group being selected between Fn1 and Ff, and wherein beyond each depth Fnm the focal diameter expands past selected limits and the next outer group of elements is included in the active aperture from Fnm to Ff, a fixed pre-focus Fm of the next outer group being selected between Fnm and Ff, so that the focal diameter of the array transducer is kept below selected limits within the whole region from Fn to Ff as the focus of the annular array is steered electronically.