Measurement of static and dynamic radiation force on spheres

The acoustic radiation force on a sphere insonified by two collimated ultrasound beams with slightly different frequency is measured. The radiation force has a static component and a dynamic component which is oscillating at the difference frequency of the two ultrasound beams. For a sphere suspended with very thin thread in water, the static radiation force is estimated from the deflection of the sphere, which is measured by an alignment laser moved on a micro-platform. The dynamic radiation force is estimated from the vibration speed of the sphere measured with a laser vibrometer. Experimental results on three steel spheres of different radius show that the dynamic and static radiation force have very similar magnitudes: with a difference less than 6%.