A three-axis Nanopositioner based on Near-Field Acoustic Levitation and Electromagnetic Actuation
Near-field acoustic levitation (NFAL) enables nanometer-scale positioning resolution and bandwidth exceeding several hundred hertz specifically along the vertical (Z) direction, owing to its high acoustic stiffness and squeeze film damping. However, its application to horizontal (XY) positioning is limited by significantly lower acoustic stiffness and insufficient damping in horizontal directions, resulting in reduced resolution and bandwidth. Moreover, NFAL-based positioning systems typically lack multi-axis actuation capabilities due to challenges in generating multi-directional acoustic forces. This work presents a hybrid positioning approach that overcomes the mentioned limitations by integrating NFAL with electromagnetic actuation. A planar magnetic platform is acoustically levitated, while a coplanar current-carrying coil provides horizontal trapping stiffness more than three orders of magnitude higher than that achievable with acoustic forces alone. Additionally, the coil generates three-dimensional electromagnetic forces, enabling multi-axis positioning capability. Eddy currents induced in a thin copper sheet integrated with the coil enhance horizontal damping by 52 times. We experimentally demonstrate precise 3-axis linear motion with a root mean square (RMS) positioning resolution better than 20 nm along all axes. The system achieves an in-plane motion range of 1.42 mm with a bandwidth of 16 Hz and a Z-axis motion range of 40 micrometers with a positioning bandwidth of 171 Hz.