Theoretical analysis of the radiation force dependence of an acoustic beam on a solid spherical scatterer on the ratio of the beam width to the diameter of the scatterer

In this work, the problem of increasing the efficiency of the method of remote displacement of small objects under the action of radiation force is theoretically solved by choosing optimal parameters of an ultrasonic beam. We consider a solid spherical scatterer located in the liquid, irradiated by a focused ultrasonic beam. One of the most important is the question of how the radiation force depends on the ratio between the beamwidth and the diameter of the scatterer. Calculations for a beam with a quasi-Gaussian transverse distribution have shown that the dependence has a clearly pronounced maximum when the transverse dimension of the beam and that of the scatterer are close. A similar result was obtained when using a focusing piston source that is more realistic to the practice. It was hypothesized that the physical cause of this effect is the resonance excitation of shear waves by an acoustic wave propagating along the surface of the stone in water. For verification, force calculations were carried out for two materials: calcium oxalate monohydrate (a material of one type of kidney stones) and gypsum cement U-30. In calculations, the velocity of the longitudinal wave was fixed, and the velocity of the transverse wave varied over a wide range. It turned out that the greatest radiation force was indeed achieved when the velocity of shear waves in the stone was close to the speed of sound in the liquid.