Design of the radiation beam profile of an ultrasonic transducer using a shaded electrode and a multifocal acoustic lens

A new ultrasonic transducer structure is designed by incorporating both a shaded electrode and a multifocal lens to achieve an excellent beam profile radiating from the transducer's elevation. The beam profile of the transducer is investigated by the finite element method, and then the new structure is designed by simultaneously analyzing such performance parameters as focal range, beam width, and sidelobe level. The optimal structure is determined using the ratio of focal range to minimum beam width, focal range ratio, along the radiation axis as a new figure of merit. The resultant beam profile has a consistently narrower beam width over a longer distance from the transducer surface as compared to the initial profile. The focal-range ratio is increased by 19%, which results in the reduction of the minimum beam width by 59%. The design is validated by fabricating and characterizing a prototype transducer of the new structure and comparing its measured performance with that of a transducer of the initial basic structure.