Substantial Reduction of Solenoidal Ferrite Rod Coil Losses Through Winding Geometry Modification

Ferrite rod coils are prevalent in applications where a concentrated or sensed external magnetic field is needed. However, their ac losses rapidly increase with frequency due to the proximity effect significantly enhanced by the presence of the open core. This article proposes an efficient method using finite element method (FEM) simulations to reduce the major part of these losses. The method optimizes the winding geometry based on the simulated magnetic field distribution near the long rod core. Results are presented for both a simulated and a fabricated coil design. Compared to the original design, the optimized configuration exhibits a significant reduction in losses. At 400 kHz, the fabricated coil achieved 57% lower losses, with a corresponding increase in coil volume by a factor of 2.4. This substantial loss reduction supports the use of open-core ferrite rod coils in high-frequency applications or scenarios demanding improved efficiency.