Acoustic radiation torque on a spheroidal droplet in standing Bessel beams

In the actual acoustic manipulation,a droplet often takes the shape of a spheroid due to the combined effects of the acoustic radiation force,surface tension and gravitational force,which can be rotated by the torque in helicoidal sound fields.Based on the theory of acoustic scattering,the scattering coefficients of a spheroidal droplet in standing Bessel beams are solved using the partial wave series expansion method,and the analytical expression of the acoustic radiation torque is also provided.On this basis,the results for spheroidal incompressible droplets and compressible droplets are both calculated numerically.The simulated results show that the acoustic radiation torque on incompressible droplets is more closely related to the half-cone angle of the beam,while compressible droplets are more dependent on specific frequencies.The growth of the beam order will increase the peaks of the acoustic radiation torque,but it is difficult to obtain an obvious radiation torque for compressible droplets at low and medium frequencies.The results of this study are expected to provide a theoretical guide for manipulating droplets using helicoidal acoustic beams.