Simulation, Design, and Characterization of a Large Divergent Element Sparse Array (LDESA) for 3-D Ultrasound Imaging

Sparse arrays address the complexity of manufacturing large 2-D arrays. However, they usually suffer from a low signal-to-noise ratio (SNR) due to their small element size. The large divergent element (LDE) technology overcomes this limitation by simultaneously having a large emitting area and a large angular aperture. The aim of this work is to demonstrate the feasibility of imaging in B-mode using the LDE sparse array (LDESA), that is, increasing the sparse array SNR without noteworthy impact on contrast. This article provides the simulation, the design, and an experimental characterization of a 1-MHz LDESA. Simulations are performed using the angular impulse response-based ultrasound simulation (AIRUS), providing coupled image-transducer optimizations of LDESA designs. Probe parameters, including probe diameter, layout, LDE size, and electroacoustic response, are optimized to maximize the contrast ratio (CR). The final layout is a 100-mm-diameter Fermat spiral covered by 256 LDEs. Each LDE is 3.5 mm wide in diameter and experimentally reaches an angular aperture of 75° at -6 dB in echo. The transmit focused beam is 1° wide and steerable up to 60° with an amplitude loss of only 10 dB. The array exhibits a 2.2-mm lateral resolution and a 1.8-mm axial resolution in a wire experiment.