## 3 Topological Diversity and Structural Design in Magnetic Gear Systems
### Design Parameters of Magnetic Gears
It is well-known that, with an increasing rotational speed, both eddy current and core losses intensify, leading to elevated temperatures and reduced system efficiency [61; 62; 67]. To mitigate eddy current formation in magnets, design strategies such as axial and circumferential segmentation are commonly employed. Additionally, core losses are another important factor affecting system efficiency. In a study using the modified Steinmetz equation, core losses were analyzed considering the influence of harmonics, and high accuracy was achieved when compared to FEM results [68]. Lastly, in a study investigating different modulator structures with solid and laminated outer rotor materials, the impact of structural configurations on magnetic torque and efficiency was explored. The circumferentially laminated modulator design showed the lowest efficiency but was reported to offer simpler manufacturing advantages [69]. Recent studies have highlighted that eddy current losses increase nonlinearly with rotational speed and that magnet segmentation plays a critical role in mitigating these losses. Particularly in systems utilizing solid magnets, it has been analytically and experimentally demonstrated that eddy current losses rise proportionally to the square of the rotational speed (Pe \(\propto\omega^{2}\)). For instance, [PERSON] et al. [70] reported that increasing the rotational speed from 1000 rpm to 4000 rpm under constant magnetic flux density leads to more than a sixfold increase in eddy current losses. This dramatic increase in speed is clearly illustrated in Figure 9, which shows the trend of eddy current loss as a function of rotational speed in unsegmented magnet configurations [71]. To mitigate such losses, a widely adopted strategy involves segmenting permanent magnets into electrically insulated pieces along the direction of motion. [PERSON] and [PERSON] [72] demonstrated that dividing a solid magnet ring into six or more segments can reduce eddy current losses by up to 70%, especially at high speeds. In their work, the loss behaviors of segmented and non-segmented magnet structures under different speeds and frequencies were presented graphically, clearly demonstrating the effectiveness of segmentation. This strategy also positively influences thermal performance by limiting localized temperature rise. Furthermore, advanced design approaches beyond linear segmentation have been proposed. Techniques such as axial and circumferential magnet segmentation offer additional benefits by physically interrupting eddy current paths, thereby further reducing losses [72; 73; 74; 75; 76]. In this context, Figures 10-12 presented in study [77] provide a  
Figure 9: PM eddy current loss versus speed by using FEM and analytical method [71]. detailed illustration of the impact of segmentation on magnetic losses from both a design and electromagnetic analysis perspective. Figure 10 presents a comparative illustration of magnet geometries with segmented and axially segmented configurations. Figure 11 highlights the intensity and distribution of eddy current paths within a solid magnet segment. In Figure 12, it is demonstrated through finite-element (FE) simulation results that the eddy current losses are significantly reduced in a structure segmented axially, owing to the disruption of current paths. These findings demonstrate that magnetic gear systems must be optimized not only in terms of torque density and efficiency but also in terms of thermal management. This ensures enhanced performance, as well as long-term operational reliability. Figure 11: The eddy current path for a single magnet segment from FE simulation [77]. Figure 12: The eddy current path in a magnet with partial axial segmentation from FE simulations [77]. Figure 10: Segmented magnet design (**left-side** magnet) and single segment with partial axial segments (**right-side** magnet) for IPM motors [77].