Experimental study of radiation force by a focused ultrasound beam on an elastic scatterer in a fluid.

The study aims to increase the accuracy of experimental methods for measuring acoustic radiation (AR) force acting on a millimeter-sized spherical scatterer in a liquid from a focused ultrasound beam[1], which was generated by a single-element, piezoceramic transducer positioned at the bottom of a water tank. The spherical scatterer was positioned on the vertically-oriented axis of the beam. The scatterer was fixed in a frame with 3-level trap of thin fishing lines. The measurement method is based on the balance between the AR, gravity, and buoyancy forces acting on the object, and initiation of its movement when the value of AR force crosses a certain threshold. The threshold power corresponded to the condition when the AR force was equal to the difference between the gravity and buoyancy forces. The AR force was calculated numerically using parameters of the scatterer and the known angular spectrum of the beam, which was determined from the acoustic hologram[2]. Experimental and theoretical results were in a good agreement in pre-focal and post-focal regions with an average error of 10%. If the beamwidth is smaller than the scatterer diameter, the most effective pushing occurred after the focus, where the beam was slightly wider than the scatterer. [ABSTRACT FROM AUTHOR]