Stiffness model and object manipulation in near-field acoustic levitation

Near-field acoustic levitation (NFAL) is an emerging technique offering innovative solutions for non-contact manipulation of objects, with applications ranging from precision engineering to autonomous systems. Despite its potential, the theoretical framework of NFAL remains incomplete, particularly concerning its coupled dynamics and nonlinear behaviors. We propose a stiffness model of NFAL that describes the squeezed air film behaviors with effective stiffness coefficients that scale with the air film thickness. The model simplifies the PDE solution into explicit expressions to effectively describe the dynamic behaviors of NFAL systems. Furthermore, by accounting for the real-time vibration of the object, the model demonstrates that the stiffness-mass system resonates at a specific frequency, marked by a rapid phase shift between the two interacting surfaces. This framework provides explanations for several anomalous behaviors previously observed in NFAL systems. Additionally, leveraging insights from this stiffness-mass model, we explore NFAL applications, including the development of a self-running NFAL actuator, an NFAL motor, and a wireless floating robot.