Multi-point ultrasonic focusing by a binary phase plate

Multi-point ultrasonic focusing (MPUF) based on abruptly autofocusing beams (AAFBs) has been investigated theoretically, numerically, and experimentally. The AAFB can be generated by a binary phase plate (BPP), which consists of only two types of phase elements. By merging the AAFBs with different trajectories, the realization of MPUF becomes feasible. The design of the BPP for MPUF is accomplished through the application of the phase superposition method. Scaling factors are incorporated into the initial phase profile of the MPUF to regulate the intensity of each focal point. Various MPUF patterns, including three-point and four-point focusing, have been demonstrated. Furthermore, the BPP is fabricated using three-dimensional (3D) printing technology and experimentally verified to achieve the four-point ultrasonic focusing underwater. This work holds potential for applications in fields such as particle manipulation, non-destructive testing, and biomedical imaging.