Dynamic focus control for imaging with two-dimensional arrays

An efficient dynamic focus control scheme for a delay-and-sum based beamformer is proposed for two-dimensional arrays. The scheme simplifies dynamic focus control by exploiting the range dependent characteristics of the focusing delay. In addition, the aperture growth controlled by a constant f_{number/ is also utilized to devise a non-uniform quantization scheme for the focusing delay values. One design example shows that with the proposed dynamic focus control scheme, a 4096 element array only requires 227 independent controllers and 28 non-uniform quantization levels. Beam plots of a fully sampled array also show that sidelobes are slightly increased below the -30 dB level for imaging depths less than 3 cm. At deeper depths, there is no observable degradation}