Acoustic Lens Design Strategy for Increasing the Effective Field of View of Row-Column Transducers

Row-Column Addressed (RCA) transducers are promising for achieving high-resolution volumetric imaging. However, their clinical applicability is constrained by an inherently limited Field of View (FOV), which is restricted to the physical aperture of the transducer. A cost-effective and flexible solution to increase the FOV is to use a diverging lens. Yet, the geometry of the lens might introduce inhomogeneities in the transmit pressure field. This work investigates the impact of various sources of inhomogeneities and provides a framework for lens design and performance assessment. Three lenses are fabricated, investigating different strategies to optimize the FOV. The Spherical lens provided the most homogeneous pressure field but the smallest effective FOV (17°). The BiCylindrical lens provided a larger FOV (26°), due to a smaller curvature, but the incomplete coverage translated into hotspots in the pressure field. The BiQuadratic lens yielded the largest FOV (36°), due to its steep curvature, despite a rapid pressure drop at the edges of the transmit field. Ray-tracing simulations successfully captured the observed inhomogeneities, demonstrating their value for lens optimization. Finally, it was found that the effective FOV of lensed arrays, including those generating inhomogeneous pressure fields, is more robustly characterized using a 30 dB Signal to Noise Ratio (SNR) criterion rather than the conventional −6 dB isoline derived from the transmit pressure field. These findings provide a practical framework for optimizing acoustic lens design to achieve effective large-scale volumetric ultrasound imaging.