## 6 Discussion  
This review study has examined the literature on magnetic gear systems from the past thirty years by classifying it based on topological diversity, core material usage, torque density, loss analysis, and application areas. The findings indicate that coaxial magnetic gear (CMG) structures, in particular, stand out in current research due to their high torque density and efficiency advantages. CMG configurations, with their compact size, contactless operating principle, and low maintenance requirements, are increasingly being used in a wide range of applications from electric drive systems to renewable energy technologies. Despite their high performance, these structures face technical limitations, such as manufacturing complexity, optimization of modulator segments, air-gap control,and torque ripple resulting from magnet configurations. On the other hand, axial flux-oriented systems, harmonic and cycloidal designs offer different advantages in torque transmission, yet challenges such as structural asymmetry, low torque stability, and limited scalability are highlighted in the literature.  
For future research directions, topics such as increasing volumetric torque density, reducing core and eddy current losses, integrating next-generation magnetic materials (e.g., Somaloy 700 HR, Vacodur 50A), and optimizing thermal performance are becoming increasingly important. Meaningful performance improvements may be achieved through modifications in carrier geometry, reconfiguration of Halbach arrays, and optimization of the air gap between rotors. Additionally, understanding how losses differ based on material properties in high-frequency applications is a critical research subject that should be experimentally validated in future work.  
Magnetic gears have a wide range of application potential, and depending on gear ratio and design parameters, they can be readily integrated into sectors such as energy, automotive, defense, aerospace, and robotics. This demonstrates that next-generation systems developed through interdisciplinary approaches may potentially replace conventional mechanical gear mechanisms.  
Beyond magnetic performance metrics, this study has also presented a detailed manufacturability assessment for each core material, considering both prototyping and mass production scenarios. The findings indicate that, while M400-50A offers the most balanced manufacturing compatibility, Somaloy 700 HR 5P demonstrates superior feasibility in high-volume powder metallurgy, and Vacodur 50A excels in magnetic performance but presents considerable production challenges.  
These results emphasize that early-stage design processes should incorporate not only electromagnetic and thermal criteria, but also practical production feasibility. Material-process-volume alignment is a critical factor in determining the commercial viability of magnetic gear technologies, particularly as these systems transition from laboratory prototypes to industrial deployment.  
Moreover, hybrid design strategies such as combining high-saturation cobalt alloys for rotor segments with powder-pressed SMCs for modulators may help achieve optimal trade-offs between performance and manufacturability in next-generation magnetic gear architectures.