Aerodynamic Fluid Bearings for Translational and Rotating Capacitors in Noncontact Capacitive Power Transfer Systems

Wireless power transfer (WPT) is commonly accomplished with magnetic (inductive) techniques for a wide range of applications. Electrostatic or capacitive power transfer (CPT) approaches to WPT have had limited exposure primarily due to lower achievable power density when compared to inductive WPT techniques. Recently, high-frequency (in kilohertz to megahertz) power electronics have reintroduced capacitive techniques as an option for WPT over short distances (< 2 mm) for applications such as slip ring replacement. To further the practicality of CPT, capacitive coupling must be maximized in an effective manner, i.e., the volumetric capacitance density of rotating/translational capacitors must be significantly increased. This paper proposes the use of aerodynamic fluid bearings to maximize capacitive coupling between stationary and moving surfaces, by minimizing their separation distance, allowing for greater surface area per unit volume. The technique allows micrometers of separation distance between moving surfaces while maintaining manufacturability and mechanical robustness. Coupling capacitance is increased up to 100 times greater than rigid plate rotating and translational CPT systems. Additional benefits include the estimation of mechanical system parameters such as speed. Operational characteristics and design highlights are presented and corroborated with experimental results for general slip ring replacement applications.