Design and characterization of a 10 cm annular array transducer for high intensity focused ultrasound (HIFU) applications

A large transducer to generate high intensity focused ultrasound (HIFU) for surgery via tissue ablation is described. Designed to address the need for therapeutic applications into deep tissue, the device operates at 1.25 MHz. In order to increase focus-to-entrance intensity ratios, the design was optimized to have a natural focal distance of 10 cm at f/1.0. Variable focus is achieved by phasing the array, and particular care was exercised to maximize the range of focal distances that can be achieved with a limited number of amplifiers and elements, using a constant-phase delay design. Design approach and tradeoffs are discussed, with emphasis on comparing theoretical calculations with test performance