Effect of a curved dome on the effective foci of an annular array -numerical simulations and experimental measurements

A numerical method to estimate the effective focus and effective aperture changes when a geometrically pre-focused ultrasound annular array is placed inside a curved fluid filled dome is developed. The method is based on ray tracing. The effective element hypothesis and our numerical method to calculate it are verified by comparing simulated ultrasound fields for the following two cases: (1) the real elements in the inhomogeneous dome fluid/dome plastic/tissue medium; (2) the effective elements in a homogeneous medium. The ultrasonic fields both along the x- and z axes are found to be very similar within each array element´s active region. The focus moving effect prediction from the effective element model is verified by water tank ultrasound field hydrophone measurements of the on-axis z fields from elements of an array disposed in a fluid filled dome.