256-element density-tapered spiral matrices for ultrasound phased imaging

The increasing interest in 3D ultrasound imaging is pushing the development of 2D probes with a challenging number (N) of active elements. The most popular approach in order to contain N is the sparse array technique. Here the design of the array layout requires complex optimization algorithms, which are typically constrained by a few steering conditions. Ungridded extensions of the sparse array technique offer improved performance by adding a further degree of freedom in the optimization process. In this paper, it is proposed to design the layout of large circular arrays with limited N according to Fermat's spiral seeds with spatial density modulation. This deterministic, aperiodic and balanced positioning procedure aims at guaranteeing uniform performance over a wide range of steering angles. The capabilities of the method is demonstrated by simulation comparing the performance of spiral and dense arrays.