Permeability-Gradient Nanocrystalline Toroidal Core with Uniform Magnetic Flux Density Distribution

Inductors play a crucial role in electronic devices and are widely utilized. However, the uneven distribution of magnetic flux density (MFDD) within the toroidal core can lead to premature saturation on the inner side, ultimately decreasing material utilization. To address the issue of non-uniform MFDD, a nanocrystalline toroidal core with a permeability gradient (PG) along its radius has been proposed and manufactured. The permeability of the nanocrystalline flake ribbon (NFR) can be easily configured and controlled through a physical crushing process. A magnetic reluctance model is developed using a differential approach to explain this phenomenon. Then, the influence of the sub-layer number and permeability gradient are simulated using finite element analysis software. Following this, four NFR cores are fabricated for experimental testing, and the temperature rise is measured to indirectly assess the MFDD within the core. For the core with a single relative permeability (μ = 1500), the temperature rise is 92.2 °C on the inner side and 82.86 °C on the outer side, resulting in a maximum temperature difference of 9.34 °C. In contrast, the core with a permeability gradient (μ = 1600-2200) shows a much smaller temperature difference of only 2.51 °C. The simulation and experimental results align closely, indicating that the proposed PG-NFR core demonstrates a more uniform magnetic flux density distribution.