Thermal Enhancement of Permeability-Gradient Nanocrystalline Toroidal Core With Uniform Magnetic Flux Density Distribution

Inductors are the essential components in electronic devices, but the nonuniform magnetic flux density distribution (MFDD) in toroidal cores will lead to premature saturation and reduced material utilization. To address this problem, we propose a nanocrystalline toroidal core with a permeability gradient (PG) along the radius direction. The permeability of the nanocrystalline flake ribbon (NFR) can be easily adjusted through a physical crushing process, providing the fabrication condition for the PG-NFR core. The influence of the sublayer number and the PG are simulated and investigated by finite-element analysis. In the experiment, four NFR cores are fabricated, and temperature rises are measured and compared. For a core with uniform permeability (μ = 1500), the inner temperature rises to 92.2 °C, while the outer side reaches 82.86 °C, resulting in a maximum difference of 9.34 °C. In contrast, the core with a PG (μ = 1600–2200) shows only a 2.51 °C discrepancy. Simulation and experimental results are in high agreement, indicating that the PG-NFR core achieves a more uniform MFDD.

I. Introduction

As the indispensable components in electronic equipment, the inductor has a decisive influence on minimizing the devices’ volume and improving the power density [1], [2]. Typically, ferrite materials, such as MnZn and NiZn, have been widely used to make magnetic cores in high-power and high-frequency applications due to their low-cost and mature manufacturing process [3], [4].