Method for measuring acoustic radiation force of a focused ultrasound beam acting on an elastic sphere

Acoustic radiation force (ARF) is a nonlinear phenomenon resulting from the wave momentum transfer to an absorbing or scattering target. ARF allows objects to be remotely manipulated, pushed, trapped, or pulled, which is used in medical applications such as kidney stone expulsion or acoustic tweezers. Such applications require development of methods for precision ARF measurements and calculations. The purpose of this paper is to present a method for direct measurement of the axial component of the ARF exerted by an ultrasound beam on its axis acting on a millimeter-sized spherical particle in a liquid. The method consists of weighing a rigid frame with a scatterer on electronic scales, similar to the radiation force balance method of measuring the total acoustic beam power. The capabilities of the method are demonstrated by applying it to spheres of different diameters (2-8 mm) and compositions (steel, glass). The additional objective is to provide experimental validation of the theoretical model of Sapozhnikov and Bailey [J. Acoust. Soc. Am. 133, (2013)], previously developed to calculate the ARF of an arbitrary acoustic beam on an elastic sphere in a liquid or gaseous medium based on the angular spectrum approach.