A Comprehensive Review of Concentric Magnetic Gears

Due to the contactless feature and low noise and vibration, magnetic gears (MGs) have been unprecedently developed in recent years, and many new structures have been proposed. Through integrating flux-modulating effect into the design, concentric MGs (CMGs) are able to involve all their permanent magnets (PMs) into the torque transmission, which significantly increases their torque density. This paper aims to give a comprehensive review on the state-of-the-art CMG topologies, which are categorized into three groups, namely rotor-PM CMGs, reluctance CMGs, and emerging CMGs, according to their PM arrangements and working principles. The main design considerations and their effects on the CMGs' performance are systematically studied, and the potential industrial applications of CMGs are discussed in detail. In the end, a comprehensive comparison among the reviewed CMGs in terms of volumetric torque density (VTD), gear ratio, number of pole pairs, and the manufacturing complexity is conducted.