Acoustic radiation force on a sphere in an acoustic levitation device

This paper presents the numerical determination of the acoustic radiation force that acts on a sphere in an acoustic levitation device formed by a 25 kHz ultrasonic transducer and a concave reflector. The acoustic radiation force is determined by two numerical models based on the Finite Element Method. In the first model, the acoustic pressure and velocity distributions are calculated numerically without the presence of the sphere. Then these fields are used in the Gor'kov equation to obtain the radiation force on a sphere much smaller than the wavelength. The second numerical model takes into account the presence of the sphere and the acoustic radiation force is calculated by integrating an expression that depends on the pressure and velocity distributions in a closed surface encompassing the sphere. The comparison between the results provided by both models shows that, for small spheres, there is an excellent agreement between the acoustic radiation forces calculated by both models. However, when the sphere radius is increased, the force provided by the Gor'kov equation differs from that predicted by the second numerical model.