## 5 Application Areas
For example, in a proposed MG structure, the input and output shafts were, respectively, defined through the inner rotor and carrier rotor. A fixed outer rotor and an SMC-based core structure facilitated 3D flux flow and enabled low eddy current losses. This system achieved power transmission at 6.7 kW and a 3.33:1 gear ratio with 84.73% efficiency [110]. In order to visualize the concentration of research efforts in magnetic gear applications, the references reviewed in this study were classified into five application domains. As shown in Figure 17, electric vehicles dominate the scientific focus with 47 related references, followed by renewable energy, aerospace, and others. Renewable energy systems are among the most prominent application areas of this technology. In particular, the use of magnetic gears for power transmission between the rotor and the generator in wind turbines reduces mechanical losses and improves overall system efficiency. In this context, the triple-rotor triple-speed coaxial magnetic gear (TSCMG) system has been shown to meet high power requirements effectively [111]. On the other hand, when examining fault statistics in wind turbines, the gearbox is identified as the component with the greatest impact on system downtime. This supports the potential of contactless magnetic gears to reduce failure rates [112]. Additionally, dual-input coaxial magnetic gear transmission (CMGT) systems developed to enhance efficiency at low wind speeds have been designed using equivalent magnetic circuit modeling, contributing significantly to improved energy capture [113]. More recently, flux modulation magnetic gears with axial flux structures have gained attention due to their reduced axial dimensions and ease of assembly. However, in such designs, integer gear ratios often lead to cogging torque issues, resulting in undesirable effects such as vibration and noise. To address this problem, new pole piece geometries have been proposed and alternative design strategies developed to mitigate cogging effects [114]. Similarly, magnetic gears are increasingly finding application in the drivetrain systems of electric vehicles. Studies have shown that outer rotor magnetic gears integrated with permanent magnet brushless DC motors achieve both high power density and meet direct-drive requirements [115]. In PM magnetic gear systems with sequential pole dual-rotor configurations, magnetic flux control has been achieved through DC windings placed along the axis, effectively extending the constant power range. This innovative design also  
Figure 17: Distribution of scientific publications on magnetic gear systems across different application areas, based on the categorization of references reviewed in this study. offers advantages in terms of flux variation processes and is supported by results validated through finite-element analysis [116]. In another system developed for power distribution in electric vehicles, a coaxial magnetic gear has been combined with an electromagnetic clutch and locking mechanism, enabling dynamic control of four different driving modes. This integrated architecture optimizes both the power flow and control strategies [117]. Applications for magnetic gears in the maritime sector are particularly noteworthy, due to their low maintenance requirements and silent operation. Research shows that integrating magnetic gears into marine energy converters provides more economical and reliable solutions compared to traditional mechanical transmission systems. In this context, magnetic gears have been applied to four different marine energy converter types, testing the adaptability of the technology [118]. Additionally, in a design proposed for wave-powered linear motion generators, a linear magnetic gear and a permanent magnet generator were integrated on the same shaft to harvest high-voltage energy from reciprocating wave motion. Finite-element analysis indicates that this method offers greater efficiency than conventional systems [119].