Calculated stress within an irregular 3D stone shape. The axial slice of pressure in the surrounding fluid and stress in the stone ((a) 2.6 mm) is shown zoomed in 3D in (c). The scales (b, d) related to both figures. Arrows indicate the direction of ultrasound propagation (350 kHz). The pressure applied is amplified in the stone, here approximately two times. Above a threshold frequency for a given stone size, amplification is greater than 5 [13
] (courtesy of Shunxiang Cao and Tim Colonius, Caltech).