Optimizing an ultrasonic levitator with two confronting emitters to levitate wavelength-scaled disks

Acoustic levitation is an important technique for contactless manipulation of solids and liquids and an effective space simulation approach for containerless environments, with expanding applications in physics, chemistry, and materials science. Here, we investigate the levitation dynamics of solid disks using an ultrasonic levitator with two confronting emitters. A three-dimensional acoustic model is established to calculate the acoustic radiation force by varying the emitters' surface curvature radius, cross section radius, and the levitated disks' inclination. The numerical results show the acoustic radiation force on the disk is mainly dominated by the bottom emitter, increasing abruptly from 0.01 N to 42.86 N by optimizing the levitator's geometric parameters, thus achieving enhanced levitation with two opposing ultrasonic waves. The dynamics of the levitated disk in the acoustic field is discussed, and a stable equilibrium levitation area is achieved. Once disturbed, the disks deviate from the central axis and tilt horizontally, reaching a new stable state. Further calculations reveal the distribution profiles of levitation force and torque on the disks, predicting the stable levitation region of wavelength-scaled solid disks at tilted angles. Manipulation of the levitated object is also proposed by modulating the phase parameters of the two confronting sound beams.