On the lateral resolution of focused ultrasonic fields from spherically curved transducers

Focused ultrasonic fields produced by spherically curved transducers occur in many areas, as, for example, in medical ultrasonics. Recently, transducers with a central hole have increasingly appeared in practice. The present paper theoretically investigates the lateral field distribution in the geometric focal plane, based on an approach with the Rayleigh integral. Results for the lateral width of the focal maximum in that plane are presented. It turns out that the appearance of a central hole leads to a reduction in the lateral width of the focal maximum, contrary to the behavior of the longitudinal width of that maximum shown earlier.