Design and fabrication of an acoustic tweezer system for kidney stone manipulation

Acoustic radiation forces can surround and trap objects to manipulate them in three dimensions. It has been demonstrated that the radiation forces can maneuver solid heavy objects similar to kidney stones in live animals under safe acoustic exposure levels. However, initial experiments identified limitations on the steering range of objects because of the array design, and tissue aberrations. Here, we present a method to design an in-house 256 multi-element array to improve the steering range of 2–5 mm stones. We modeled the acoustic field for various geometrical parameters including the element size, transducer focusing, and F-number at a frequency range from 0.5 to 1 MHz. The parameters were then used to simulate the trapping radiation forces on stone models to finalize the design of the array. The array was fabricated with a center frequency of 950 kHz and a focal distance located at 120 mm and an F-number of 1.5. A holography scan was performed to characterize the transducer output. Various trapping beams were measured and compared to simulations. The resulting radiation forces produced were on the order of the weight of the trapped 2-5 mm stone models. [Work supported by NIH P01-DK043881, K25-132416, and Applied Physics Laboratory SEED fellowship.]