On the horizontal dynamic performance of standing wave-type near-field ultrasonic levitation

Near-field ultrasonic levitation (NFUL) technology is increasingly attracting attention for its advantages of non-contact nature, compactness, and environmental friendliness. Nevertheless, the development of NFUL is hindered by challenges such as carrying capacity and stability. To date, most studies have focused on the static stability of NFUL, primarily through analysis of the restoring force. However, there remains a significant gap in the literature regarding the motion prediction of levitated objects, which is the focus of this paper. A numerical model coupling the levitated object and the squeeze film is established, and then, the Reynolds equation considering the motion parameters of the levitator is derived. Since the misalignment and inclination of the levitator are concurrent cases, its inclination needs to be considered in the film thickness expression. Subsequently, due to the introduction of an imaginary levitator with a groove, the eight-point discrete method is applied to solve the discontinuous film thickness problem. Thereupon, the pressure profile is obtained by determining the inclination angle of the levitator using the spline interpolation. The motion trajectory and frequency of the levitator are estimated utilizing the time-marching method and corroborated through experimental measurements. Both numerical and experimental results indicate that the motion frequency initially increases sharply with rising the preset eccentricity, before gradually diminishing. Additionally, higher motion frequencies are observed at larger amplitudes of the vibrator and lower weights of the levitator. Comparatively, the motion frequency of a levitator under a flexible vibrator is also found to be higher than that under a rigid vibrator.