Model based, nonlinear control of near-field acoustically levitated objects

The near-field acoustic levitation phenomenon uses ultrasonic vibrations of a driving surface, to elevate the average pressure in the thin gas layer trapped between this surface, and a freely suspended planar object. This is done, exploiting the compressibility and the viscosity of the entrapped gas. Due to the pressure elevation, the planar object can be manipulated vertically between dozens and hundreds of microns, without any mechanical contact. This paper introduces a novel, simplified model, describing the governing, slow dynamics of near-field acoustically levitated objects. This model replaces the commonly used Reynolds equation based model, with a second order, ordinary differential equation, where the stiffness and damping terms are given explicitly. Due to the simplicity of the model presented here, it sets a convenient foundation for model based control algorithms. Indeed, based on this model, a continuous gain scheduling controller is designed and implemented experimentally, showing good performance.