Structural analysis and design of radial magnetic bearing rotor considering skin effect

This paper investigates the structural design of solid rotors, which are commonly used in small-sized radial magnetic bearings, focusing on the eddy current-induced skin effect as a means for optimization. Unlike laminated silicon steel rotors where eddy currents are suppressed, the performance of solid rotors is significantly influenced by this effect, rendering this study particularly relevant. The primary objective is to reduce the rotor's volume and weight for high-speed applications without significantly compromising its load-bearing capacity. The methodology integrates theoretical analysis, Finite Element Method (FEM) simulations, and experimental validation. A custom test platform was built to measure the dynamic electromagnetic force on various rotor specimens. The simulation and experimental results consistently demonstrate that for a solid rotor, the electromagnetic force decays as speed increases due to the skin effect, which concentrates the magnetic flux near the rotor surface. A key finding from the experiments is that at a high speed of 12000 rpm, a thin-walled solid rotor exhibits a load capacity nearly identical to that of a much thicker one. This result provides strong evidence that the inner material of a solid rotor becomes less effective for force generation at high speeds. In conclusion, this study validates the feasibility of designing thinner, lighter solid rotors for high-speed magnetic bearings by leveraging the skin effect, offering a practical approach to developing more compact and efficient small-sized rotating machinery supported by magnetic bearings.